- Research
- Open access
- Published:
Leaf ecological stoichiometry and anatomical structural adaptation mechanisms of Quercus sect. Heterobalanus in southeastern Qinghai–Tibet Plateau
BMC Plant Biology volume 24, Article number: 325 (2024)
Abstract
Background
With the dramatic uplift of the Qinghai–Tibet Plateau (QTP) and the increase in altitude in the Pliocene, the environment became dry and cold, thermophilous plants that originally inhabited ancient subtropical forest essentially disappeared. However, Quercus sect. Heterobalanus (QSH) have gradually become dominant or constructive species distributed on harsh sites in the Hengduan Mountains range in southeastern QTP, Southwest China. Ecological stoichiometry reveals the survival strategies plants adopt to adapt to changing environment by quantifying the proportions and relationships of elements in plants. Simultaneously, as the most sensitive organs of plants to their environment, the structure of leaves reflects of the long-term adaptability of plants to their surrounding environments. Therefore, ecological adaptation mechanisms related to ecological stoichiometry and leaf anatomical structure of QSH were explored. In this study, stoichiometric characteristics were determined by measuring leaf carbon (C), nitrogen (N), and phosphorus (P) contents, and morphological adaptations were determined by examining leaf anatomical traits with microscopy.
Results
Different QSH life forms and species had different nutrient allocation strategies. Leaves of QSH plants had higher C and P and lower N contents and higher N and lower P utilization efficiencies. According to an N: P ratio threshold, the growth of QSH species was limited by N, except that of Q. aquifolioides and Q. longispica, which was limited by both N and P. Although stoichiometric homeostasis of C, N, and P and C: N, C: P, and N: P ratios differed slightly across life forms and species, the overall degree of homeostasis was strong, with strictly homeostatic, homeostatic, and weakly homeostatic regulation. In addition, QSH leaves had compound epidermis, thick cuticle, developed palisade tissue and spongy tissue. However, leaves were relatively thin overall, possibly due to leaf leathering and lignification, which is strategy to resist stress from UV radiation, drought, and frost. Furthermore, contents of C, N, and P and stoichiometric ratios were significantly correlated with leaf anatomical traits.
Conclusions
QSH adapt to the plateau environment by adjusting the content and utilization efficiencies of C, N, and P elements. Strong stoichiometric homeostasis of QSH was likely a strategy to mitigate nutrient limitation. The unique leaf structure of the compound epidermis, thick cuticle, well-developed palisade tissue and spongy tissue is another adaptive mechanism for QSH to survive in the plateau environment. The anatomical adaptations and nutrient utilization strategies of QSH may have coevolved during long-term succession over millions of years.
Background
The uplift of the Qinghai–Tibetan Plateau (QTP) was an important geological event of the Cenozoic [1,2,3]. After two uplifts and two deplanations in the Eocene and late Oligocene up to early Miocene [4,5,6], most of the plateau remained at low elevation and had a warm and humid tropical/subtropical climate [7, 8]. Vegetation was evergreen-deciduous broad-leaved forests, with Magnoliaceae, Theaceae, Lauraceae, and Fagaceae as the main components of the paleoforest [9]. In the late Pliocene up to early Quaternary, the southeastern QTP was dramatically uplifted nearly 3,500 m, resulting in global climate reshaping, with cooling and drying of the environment and wide changes in vegetation [10,11,12]. Certainly, the inhospitable conditions of the plateau environment are unfavorable for the development and survival of plants, and thus, the majority species that originally inhabited the ancient subtropical evergreen-deciduous broad-leaved forests essentially disappeared [12]. However, the Quercus sect. Heterobalanus (QSH) of the genus Quercus in the family Fagaceae have shown remarkable adaptability to the challenging plateau environment, with nine species of QSH: Q. spinosa, Q. pannosa, Q. semecarpifolia, Q. aquifolioides, Q. longispica, Q. fimbriata, Q. senescens, Q. monimotricha, and Q. rehderiana [13]. As altitude increased in the Pliocene, some of the QSH species changed from being companion species in mixed forests to dominant or constructive species in many areas of the Hengduan Mountains region [10, 14]. The QSH species are ecologically important, because the plants are “umbrella plants” to other plants, animals, and microorganisms on the plateau. However, little is known about the mechanisms that QSH species employ adapt to the harsh environment. Ecological stoichiometry can be used to understand how plants adapt to different environments by adjusting the composition and proportion of chemical elements within their bodies [15, 16]. Meanwhile, as the largest exposed vegetative organ of plants, leaves are highly responsive to the environment, and their anatomical structure directly reflects the plant’s adaptive strategies to specific environments [17]. Consequently, the field research has focus on elucidating the adaptive mechanisms of QSH survival in plateau environments by studying of ecological stoichiometry and leaf anatomical traits.
Ecological stoichiometry in terrestrial ecosystems is used to examine relations between carbon (C), nitrogen (N), and phosphorus (P) in plants [18, 19]. Analyzing patterns of elemental interactions and constraints within plants, elemental balances, and ecological interactions can help to understand allocation and cycling of plant nutrients and to assess the degree of nutrient scarcity or limitation [20,21,22]. Carbon is a structural element that is also a substrate and energy source for plant physiological and biochemical processes and growth [23, 24]. Nitrogen and P are the main nutrients for plant growth and in most cases, are also factors limiting plant adaptation and survival [20, 25]. Stoichiometric homeostasis is the theoretical foundation of ecological stoichiometry [26], and the H-value is used to represent the ability to maintain homeostasis in individual plants [27, 28], with higher H-values indicating higher homeostasis and more stable nutrient contents in plants [29]. Strong stoichiometric homeostasis and conservative nutrient use may be essential for species to survive in arid and barren environments [28, 30], and the degree of homeostasis may be highly correlated with species adaptation and ecological strategy [31, 32]. Thus, stoichiometric homeostasis can be used as a predictive tool for plant adaptation to the external environment [18].
Leaves are the plant part most exposed and sensitive to the environment and as a result, have relatively high plasticity and variability. Leaves are the main assimilation organs and physiological activities include photosynthesis, respiration, and transpiration [33,34,35]. The main anatomical features of leaves are epidermis, mesophyll, and vascular system [36], and differences in those structures can indicate adaptations to specific environments [37, 38]. For example, changes in epidermis thickness can protect leaf tissues against adverse factors and also adjust leaf moisture level and preserve heat [39]. Palisade tissue is the main site of photosynthesis and regulates leaf photosynthetic efficiency by changes in porosity [40]. Spongy tissues with large intercellular spaces can increase gas change. Differences in palisade and sponge tissues can indirectly reflect environmental water status, and thus, the ratio of palisade tissue thickness to sponge tissue thickness (P/S) can reflect leaf resource-use strategies in different habitats [39]. Generally, the higher the P/S ratio reflects the higher the photosynthetic utilization efficiency, which may be one important reason why plants can resist drought stress. Leaves tend to develop morphological structures that are adapted to specific environments [34, 41]. For example, in response to high altitude, evergreen broad leaves usually have relatively thick leaves and palisade and spongy tissues and additional palisade mesophyll layers [33]. Because leaf structure is closely associated with various functions and can reflect long-term adaptability to the environment, it is important to study leaf anatomical characteristics to explore how plants adapt to the environment.
With the rise of the QTP to high altitude, plants suffered from nutrient limitations and a low-moisture environment and leaves were exposed to high radiation. Whereas many plants might have disappeared because they did not develop specific adaptation mechanisms, QSH plants may have developed comprehensive adaptation strategies to survive and occupy vacated sites. Hence, this article aims to address the following: (1) Do QSH have unique ecological stoichiometric characteristics? (2) Are there any particular anatomical features exhibited by QSH leaves? (3) Is there a correlation between the ecological stoichiometry and leaf anatomical structure of QSH? This paper attempts to understand the QSH nutrient-use strategies that developed in response to the cold, dry, and high-radiation environment of the modern QTP through the ecological stoichiometry and anatomical structures of QSH leaves.
Results
Leaf nutrient contents and C: N:P ratios of QSH life forms
Leaf C, N, and P contents differed slightly among life forms (Fig. 1a and Supplementary Table S1). Mean contents of C and N in leaves of trees were 657.15 g/kg and 12.71 g/kg, respectively, and those in leaves of shrubs were 653.96 g/kg and 12.32 g/kg respectively. Mean P content in leaves of trees (1.84 g/kg) was significantly higher than that in leaves of shrubs (1.45 g/kg), an increase of 26.90% (P < 0.05).
In trees leaves, mean nutrient ratios were C: N = 54.30, C: P = 468.11, and N: P = 8.72, whereas in shrubs leaves, mean nutrient ratios were C: N = 56.53, C: P = 470.34, and N: P = 8.81 (Fig. 1b and Supplementary Table S1).
Leaf C, N, and P contents and stoichiometric ratios of six QSH species
Leaf C, N, and P contents and C: N, C: P, and N: P ratios were significantly different among the six QSH species (Fig. 2). Leaf C content in the six species ranged from 614.03 to 671.63 g/kg (Fig. 2a), with a mean of 650.51 g/kg and a coefficient of variation of 2.97%. Leaf C content was in the order Q. monimotricha > Q. spinosa > Q. semicarpifolia > Q. pannosa > Q. longispica > Q. aquifolioides. Leaf N content in the six species ranged from 9.74 to 15.59 g/kg (Fig. 2b), with a mean of 12.25 g/kg and a coefficient of variation of 20.41%. Leaf N content of Q. aquifolioides, Q. monimotricha, and Q. semicarpifolia was significantly lower than that in the other three species (P < 0.05). Leaf P content in the six species ranged from 0.61 to 2.33 g/kg (Fig. 2c), with a mean of 1.44 g/kg and a coefficient of variation of 38.99%. Quercus spinosa had the highest P content, and there were significant differences among the six species (P < 0.05).
Leaf stoichiometric ratios were significantly different among the six QSH species (P < 0.05; Fig. 2). The mean C: N ratio was 56.18, with ratios varying from 41.84 to 70.84 (Fig. 2d) and a coefficient of variation of 20.99%. The C: N ratios of Q. monimotricha was significantly higher (P < 0.05) than those of the other species, and Q. longispica had the lowest C: N ratio. The mean C: P ratio was 540.80, with ratios varying from 300.55 to 1,003.35 (Fig. 2e) and a coefficient of variation of 45.61%. Quercus aquifolioides and Q. spinosa had the highest and lowest C: P ratios, respectively. The mean N: P ratio was 9.98, with ratios ranging from 6.21 to 17.66 (Fig. 2f) and a coefficient of variation of 41.83%. The highest N: P ratio was in Q. aquifolioides, whereas the N: P ratios of Q. monimotricha was significantly lower than those of the other five species (P < 0.05).
Stoichiometric homeostasis regulation coefficient of QSH plants
The homeostasis regulation coefficient of C (1/HC) was less than 0.25 (P < 0.1; Table 1), indicating the samples were homeostatic. The value of 1/HN varied from − 0.1 to 0.28, indicating strictly homeostatic (P > 0.10) and homeostatic and weakly homeostatic (P < 0.10) regulation. The value of 1/HP ranged from − 8.97 to 4.80, with higher variation than that of N and indicating strictly homeostatic (P > 0.10) regulation. Values of 1/HC: N and 1/HC: P consistently indicated homeostatic regulation (P < 0.10). The value of 1/HN: P varied from 0.02 to 1.22. There was greater variability in values of 1/HN: P than in those of 1/HC: N and 1/HC: P, and the values indicated strictly homeostatic (P > 0.10) and weakly homeostatic (P < 0.10) regulation. In conclusion, strong stoichiometric homeostasis characterized the leaves of QSH plants, suggesting good adaptability to environmental changes.
Leaf anatomical structural characteristics of six QSH species
The QSH plants had complex epidermal structure, with tightly arranged epidermal cells, most of which were irregularly shaped, and the leaves were covered with dense epidermal hairs (Fig. 3). Leaf anatomical structure of QSH plants differed significantly among life forms and species (P < 0.05; Table 2).
Thickness of upper epidermal cuticle (CU), upper epidermis (TE), palisade tissue (TP), spongy tissue (TS), lower epidermis (LE), and blade thickness (LT) were significantly greater in trees than in shrubs (P < 0.05), whereas thickness of palisade tissue to thickness of sponge tissue ratio (P/S ratio) and organizational tightness (CTR) were significantly greater in shrubs than in trees (P < 0.05). The coefficient of variation of the different anatomical structures was small and ranged from 1.48 to 10.54%.
Among QSH species, CU ranged from 4.23 to 6.81 μm, with a mean of 5.97 μm and a coefficient of variation of 15.28%. The TE ranged from 27.16 to 40.75 μm, with a mean of 31.71 μm and a coefficient of variation of 16.57%. The TP ranged from 107.49 to 153.28 μm, with a mean of 130.39 μm and a coefficient of variation of 12.12%. The TS ranged from 89.53 to 114.01 μm, with a mean of 101.58 μm and a coefficient of variation of 8.24%. The LE ranged from 6.63 to 9.52 μm, with a mean of 7.80 μm and a coefficient of variation of 15.12%. The LT ranged from 236.79 to 319.55 μm, with a mean of 276.11 μm and a coefficient of variation of 10.20%. The P/S ratio ranged from 1.21 to 1.46, with a mean of 1.29 and a coefficient of variation of 7.49%. The CTR ranged from 43.53 to 52.74%, with a mean of 47.39% and a coefficient of variation of 7.65%.
Correlations between leaf C, N, and P contents and stoichiometric ratios and anatomical traits of QSH plants
Pearson correlations between C, N, and P contents and C: N, C: P, and N: P ratios and leaf anatomical structures were significant (P < 0.05, P < 0.01; Fig. 4). Nitrogen was significantly positively correlated with CU, TE, TS, LE, and LT, and the N: P ratio was significantly positively correlated with CU, TP, LE, and LT. Nitrogen was significantly negatively correlated with CTR, and the C: N ratio was significantly negatively correlated with CU, TE, TS, and LT. Notably, the correlations between N, LT, and TS were highly significantly positive (P < 0.01), with correlation coefficients of 0.631 and 0.627, respectively.
Discussion
Research on plant adaptations to the environment has received increasing attention because they are crucial to ecosystem conservation [42]. In terrestrial ecosystems, ecological stoichiometry focuses on organismal energy flow and the balance of multiple chemical elements, which is essential information for exploring plant responses to environmental change, ecological strategies, and use of nutrients that limit plant growth [20, 23, 28, 30]. In addition, because leaf structure is the basis for leaf function, leaves can develop appropriate morphological structures to optimize functions with long-term exposure to the environment. Thus, leaf anatomical traits are also key factors in understanding plant adaptation to the environment [34, 41, 43].
Leaf nutrient contents of QSH plants
Ecological stoichiometry of C, N, and P is an important indicator of C, N, and P status of ecosystems that can be used to understand nutrient characteristics of organisms and to provide important information about N and P limitation [20, 44].
In this study, leaf C contents of trees and shrubs were 41.63% and 40.94% higher, respectively, than the mean global terrestrial leaf C content [45] and 34.86% and 34.20% higher, respectively, than that for Q. variabilis in China [46]. Leaf N contents of trees and shrubs were 36.77% and 38.71% lower, respectively, than the global mean value for terrestrial plants [45] and 37.08% and 39.01% lower, respectively, than that for Chinese terrestrial plants [47], and 33.11% and 35.16 lower, respectively, than that for Q. variabilis in China [46]. There was a significant difference (P < 0.05) in leaf P content between life forms, with P content in tree leaves 26.90% higher than that in shrub leaves (Fig. 1a). The leaf P content of both trees and shrubs was 52.07% and 19.83% higher, respectively, than the mean for Chinese terrestrial plants [47], and 78.64% and 40.78 higher, respectively, than that for Q. variabilis in China [46]. The results indicated that the growth rate of trees was faster compared to shrubs, and thus, trees required more P to support their rapid growth, resulting in a higher P content in tree leaves [45, 48, 49].
Leaf C content in the six QSH species ranged from 614.03 to 671.63 g/kg, which was 32.33–44.75% higher than the mean global terrestrial leaf C content [45], and 26.01–37.83% higher than the mean for Q. variabilis in China [46], and the highest C content was in Q. monimotricha (Fig. 2a). Leaf N content ranged from 9.74 to 15.59 g/kg (Fig. 2b), which was 22.44–51.54% lower than the global mean for terrestrial plants [45] and 22.82–51.78% lower than the Chinese mean for terrestrial plants [47], and 17.95–48.74% lower than the mean for Q. variabilis in China [46]. The lowest leaf N content was in Q. semicarpifolia and Q. monimotricha. Leaf P content ranged from 0.61 to 2.33 g/kg (Fig. 2c), with P contents 92.56% higher in Q. spinosa, 31.40% higher in Q. monimotricha, 26.45% higher in Q. pannosa, and 16.53% higher in Q. longispica than the mean P content of Chinese terrestrial plants [45]. However, leaf P content of Q. semicarpifolia and Q. aquifolioides was 2.48% and 49.59% lower, respectively, than the mean in Chinese terrestrial plants [47]. Compared to the average P content of Q. variabilis in China [46], with P contents 126.21% higher in Q. spinosa, 54.37% higher in Q. monimotricha, 48.54% higher in Q. pannosa, 14.56% higher in Q. semicarpifolia, and 36.89% higher in Q. longispica. Conversely, the P content of Q. aquifolioides was 40.78% lower than the average for Q. variabilis in China [46].
Leaf C content of QSH plants was significantly higher than the global mean of terrestrial plants [45] and the mean of Q. variabilis in China [46], indicating high C storage capacity. Because of the importance of leaves as assimilation organs, leaf C content can increase to develop defenses against cold and drought and increase overall stress resistance to external environmental factors [50]. Leaf N content in QSH plants was lower than global and Chinese means terrestrial plants [45, 47], and also lower than the mean for Q. variabilis in China [46], which suggested that N was relatively scarce in the study area. Leaf P content was divided into two categories: (1) a few samples with leaf P content lower than that in Chinese terrestrial plants [47] and lower than the average for Q. variabilis in China [46], and (2) most samples with leaf P content higher than the means for Chinese terrestrial plants [47] and Q. variabilis in China [46]. The results indicated there was selective absorption of P and thus differences in the nutrient allocation strategies of QSH plants in adapting to different habitats. The results in this study are consistent with those of Lin et al. [51], who found that Larix gmelinii adopts different nutrient allocation strategies to increase adaptability to different environments. Results also indicated that low temperature leads to an imbalance in the metabolic sink of plants, slowing down plant metabolism [52]. In response, QSH plants regulate the metabolic balance by storing P to increase the ability to resist stress. Furthermore, the coefficient of variation of leaf N content was smaller than that of leaf P content (Figs. 1 and 2), which is a result consistent with that of Vitousek [53], who proposed that N content is more stable than P content in leaves. In addition, the results of this study support the proposal of Reich and Oleksyn [54] that N is the major limiting nutrient in relatively young temperate and high-latitude ecosystems.
Leaf nutrient utilization in QSH plants
Leaf C: N and C: P ratios are typically used to indicate nutrient use efficiency, which reflects the ability of plants to use N and P to assimilate C, and the leaf N: P ratio is used to provide key information about nutrient limitations in plants [45, 48, 55]. However, there are different opinions on the N: P ratio threshold. According to Koerselman and Meuleman [56], an N: P ratio < 14 indicates N restriction, an N: P ratio > 16 indicates P limitation, and the N: P ratio between 14 and 16 indicates plant growth is limited by both N and P. In contrast, according to Güsewell [57], a leaf N: P ratio < 10 indicates N limitation, an N: P > 20 indicates P limitation, and an N: P ratio between 10 and 20 indicates both N and P limitation. The limiting nutrients in QSH plants in this study were identified according to the N: P ratio threshold.
In our study, leaf C: N ratios of trees (54.30) and shrubs (56.53) were 46.36% and 52.37% higher, respectively, than those in plants of a global forest ecosystem [25] and 90.53% and 98.35% higher, respectively, than those in plants of Chinese forest ecosystems [25], and 111.72% and 120.41%, respectively, higher than that of Q. variabilis in China [46]. Leaf C: P ratios of trees (468.11) and shrubs (470.34) were 8.75% and 8.32% lower, respectively, than those in plants of Chinese forest ecosystems [19], and 1.06% and 0.58% lower, respectively, than Q. variabilis in China [46]. The results suggested that QSH trees and shrubs had relatively high N and low P utilization efficiencies, which resulted in an increase in storage of P and a decrease in leaf C: P ratio. Therefore, QSH plants might have relatively fast growth rates, especially trees, even in a deteriorated environment [21, 58]. Furthermore, N:P ratios of trees (8.72) and shrubs (8.81) were less than 10, indicating that growth of them was limited by N [56, 57].
Leaf C: N ratios were high among QSH species (41.84–70.84), with ratios 12.78–90.94% higher than those in plants of a global forest ecosystem [25] and 46.81–148.56% higher than those in Chinese forest ecosystems [25], and 63.14–176.21% higher than Q. variabilis in China [46]. The highest C: N ratio was in Q. monimotricha (Fig. 2d). The result indicated that QSH plants had high N use efficiency as a strategy to successfully compete in barren environments. Additionally, C:P ratios of Q. aquifolioides and Q. semicarpifolia were higher than those in plants of Chinese forest ecosystems [19] by 95.58% and 17.72%, respectively, and C: P ratios of Q. aquifolioides, Q. semicarpifolia and Q. longispica were all higher than those of Q. variabilis in China [46], which might be the result of relatively high C and low P content in leaves. However, the C: P ratios of the other four species (Q. monimotricha, Q. spinosa, Q. pannosa, and Q. longispica) were 7.19–41.41% lower than those in plants of Chinese forest ecosystems [19], and C: P ratios of Q. monimotricha, Q. spinosa and Q. pannosa were all lower than those of Q. variabilis in China [46], indicating they had relatively low P utilization efficiency, which were findings consistent with those of life forms. Within Chinese forest ecosystems, Q. aquifolioides (N: P = 17.66) and Q. longispica (N: P = 11.32) (Fig. 2f) were co-limited by N and P, whereas the other species were restricted by N [57]. However, according to Koerselman and Meuleman [56], only Q. aquifolioides (N: P = 17.66) was primarily limited by P, whereas the other species were primarily limited by N. Together with the results of previous studies, in this paper, the framework of Güsewell was considered more accurate [57].
Leaf stoichiometric homeostasis in QSH plants
Stoichiometric homeostasis is a key parameter in ecological stoichiometry [18], and homeostasis regulation reflects potential physiological and biochemical allocation of an organism in response to its surroundings [54, 59]. When external environmental changes lead to nutrient limitations on plant growth, plant can use various physiological mechanisms to improve nutrient availability and use efficiency and maintain stable levels and related functions of nutrients [23]. Plants with strong stoichiometric homeostasis are relatively conservative in nutrient use, whereas those with relatively weak homeostasis can flexibly use nutrients when abundant [28, 60]. Thus, the level of stoichiometric homeostasis can reveal plant ecological adaptation mechanisms [18, 32, 59]. In this study, 1/H was used as a quantitative index to determine the level of homeostasis, and stoichiometric homeostasis of QSH leaves was classified as strictly homeostatic, homeostatic, and weakly homeostatic (Table 1). However, 1/HP and 1/HN: P values of some species were not within the range to evaluate homeostasis. The most likely explanation for those results might be that a constant C that close to the true value was not identified or that the dependent variable Y was less than or equal to the constant C, resulting in P < 0.10 and 1/H > 1. Furthermore, in this study, there were differences in absorption, storage, and utilization of N and P among different life forms and species. The differences might be driven by the life history or specific habitats of plants. The homeostasis level of trees was weaker than that of shrubs, and the high homeostasis of Q. aquifolioides might be one of the important factors for its wide distribution in the Hengduan Mountains region (author observation). The stoichiometric characteristics and homeostasis of C, N, and P contents and stoichiometric ratios in leaves led to the conclusion that QSH plants had strong stoichiometric homeostasis and were conservative in use of nutrients [28, 59]. In addition, the species with the highest stoichiometric homeostasis had the most constant response to environmental changes [27, 28, 59]. The high degree of stoichiometric homeostasis might help explain how QSH plants adapted to the arid, cold, and nutrient-poor environment of the plateau.
Leaf anatomical structures in QSH plants
In response to the environment, leaves are the most sensitive and plastic organs during plant growth and development, and because leaf morphological structure is the foundation of leaf functions, leaf structural characteristics are good indicators of plant adaptability to the environment [38, 41, 61, 62]. In the Hengduan Mountains, with perennial low temperatures, drought, and intense light environment, the leaves of QSH plants should form structures compatible with that environment. In this study, the differences in anatomical traits among different life forms and species of QSH plants reflected different survival strategies in specific growth environments. However, in general, leaves of QSH plants had dense epidermal hairs and thick cuticle and upper epidermis (Table 2; Fig. 3), which can effectively reduce water evaporation, mitigate UV radiation, and resist pathogen invasion [33, 34]. Thus, leaf structure was an important manifestation of QSH plant adaptation to harsh environments. The compound epidermal structure of QSH plants is unique in the Quercus genus, and it benefited QSH plants and allowed them to become winners in the plateau competition [63]. Moreover, the coefficients of variation of different anatomical structures of QSH leaves were relatively small (Table 2). One explanation might be that the ecological adaptability of QSH plants to the environment was manifested in a relatively stable morphological structure, which may also be a systematic evolutionary trait. Leaf traits can be interpreted as one reason why only QSH plants survived after the severe uplift of the QTP in late Pliocene up to early Quaternary. Additionally, the activity of photosynthesis-related enzymes is restricted under low temperatures, which results in a decrease in photosynthetic rate [52, 61]. Palisade tissue is the main site of photosynthesis, and large cellular spaces in sponge tissue increase gas exchange [34, 36]. In this study, the QSH plants had well-developed palisade tissue and sponge tissue, which increased the number of chloroplasts and CO2 diffusion rate, compensating for the short photosynthesis period on the plateau [39, 52, 64]. The P/S ratio was greater than one and indicated that QSH plants were typical drought-resistant plants. The CTR can be used to evaluate plant cold resistance [52]. Thus, the high CTR and increases in palisade tissue in leaves among different life forms and species of QSH plants suggested reductions in damage caused by low temperatures, drought, and UV radiation in the Hengduan Mountains. The P/S ratio and CTR of shrubs were higher than those of trees, and Q. aquifolioides had the highest values among the six species (Table 2), which was consistent with the results of stoichiometric homeostasis. This result was considered to be the outcome of coevolution between anatomical traits and nutrient use in developing plant adaptation strategies.
Correlations between leaf stoichiometric and anatomical traits in QSH plants
Correlations between leaf stoichiometric and anatomical structural traits of QSH plants at 16 plots in the Hengduan Mountains were analyzed, and N content and C: N and C: P ratios were significantly correlated with anatomical structures (P < 0.05, P < 0.01; Fig. 4). In the previous section, it was concluded that leaf N content in QSH (Figs. 1 and 2) life forms and species was lower than the mean N levels of terrestrial plants globally and in China [45, 47], which indicated that N was scarce in the study area. Leaf N content was highly positively correlated (P < 0.01) with blade thickness (r = 0.631) and sponge tissue (r = 0.627) (Fig. 4). The low N content indicated that QSH leaves were relatively thin overall, which might be the result of high leathering and lignification of leaves. The conclusion in this study differs from that in previous studies in which high light intensity led to an increase in blade thickness [65, 66]. Thinning leaves is beneficial for plants, because dry matter of the same quality can be used to increase leaf area, thereby increasing solar energy capture capacity and carbon accumulation [38] and ultimately causing high C: N ratios and strengthened leaf fibers. Consistent with that conclusion, in this study, Q. monimotricha leaves were the thinnest (236.79 μm; P < 0.05) but had the highest C content and C: N ratio, which indicated leaf leathering and lignification increased to improve plant resistance. Simultaneously, the thin spongy tissue, which corresponded to low leaf N content, suggested that the leaves had well-developed palisade tissue and high organizational tightness, which reduced the damage caused by strong light and UV radiation and helped QSH plants adapt to cold, arid, and nutrient-poor habitats. Correlation analysis further indicated the potential coevolution of nutrient use and leaf anatomical traits in adaptation strategies of QSH plants to the plateau environment.
Conclusion
In this study, leaf nutrient contents, stoichiometric ratios, and anatomical traits of QSH plants were examined in the Hengduan Mountains, southeastern QTP, Southwest China. Stoichiometric characteristics of different QSH life forms and species were different and therefore indicated unique strategies to adapt to the plateau environment. Increases in leaf C content caused high C: N ratios and increases in leaf P content caused low C: P ratios. Growth of QSH plants was primarily limited by N, except in Q. aquifolioides and Q. longispica, which were limited by both N and P. Although stoichiometric homeostasis of trees was weaker than that of shrubs and there were some differences among species, the stoichiometric homeostasis of QSH plants was very strong overall, indicating a strategy to address the nutrient limitations to some extent. In addition, leaf anatomical traits were different among different life forms and species of QSH plants. Generally, the morphological structure of QSH plant leaves was adapted to the plateau environment, with thick cuticle, compound epidermal layer, dense epidermal hairs, and developed palisade tissue reducing water transpiration and damage from UV radiation. More importantly, QSH plants increased leathering and lignification by thinning leaves. Furthermore, leaf ecological stoichiometric and anatomical structural traits were significantly correlated, suggesting that QSH plants jointly regulated the different functional traits in response to the unfavorable environmental conditions in the Hengduan Mountains.
Methods
Study area
The study was conducted in the Hengduan Mountains in southeastern QTP, Southwest China (26°08′54″–30°42′49″N, 99°09′28″–101°29′15″E), which are a world-renowned biodiversity hotspot [67]. The Hengduan Mountains are mainly influenced by the confluence of air currents of southeast Pacific monsoon, southwest Indian Ocean monsoon, and south branch rapids of the high-altitude westerly circulation of the Tibetan Plateau, which result in an overall pattern of dry winters and rainy summers. Average elevation is greater than 3,500 to 4,000 m, annual average temperature is 14 ℃ to 16 ℃, over 85% of total precipitation occurs between June and August, and the soil is shallow, barren, and with high gravel ratio and low water retention ability. The vertical spectrum of the climate is obvious, and the vegetation zones from bottom to top of a mountain are successively composed of trees, shrubs, and meadows, with the primary species including Larix gmelinii, Pinus densata, Picea asperata, Abies fabri, Quercus sp., Juniperus recurva, Rhododendron simsii, Spiraea salicifolia, Lonicera japonica, and Rhodiola rosea. The QSH plants are constructive or dominant species on the sunny slopes of many parts in the Hengduan Mountains region.
Sampling and measurements
Samples of QSH plants were collected from southwest China in August 2022 (Fig. 5). Voucher specimens have been deposited in the herbarium of the Southwest Forestry University. The experiment involved 16 sample plots, including a total of six species of QSH: Q. pannosa, Q. aquifolioides, Q. spinosa, Q. semecarpifolia, Q. longispica, and Q. monimotricha. These species include two life forms: trees and shrubs (Table 3). Sample sites were distant from anthropogenic disturbances and had pure forests of QSH plants and sunny slopes. Three uniform trees of the same species were randomly selected in each plot, and fully exposed and mature leaves were collected in the outer parts of the same canopy of each tree in east, south, west, and north directions using a branch shear. Soil samples (depth: 1–10 cm) were collected from each sample tree along the directions of east, south, west, and north. The leaves were mixed separately into a composite sample for each plot and then placed in labeled, sealed bags and taken to the laboratory. In the lab, leaf samples were boiled at 105 °C for 30 min and then dried at 65 °C to constant weight and ground into powder and passed through a 100-mesh sieve for chemical analysis. Carbon content was measured by a potassium dichromate external heating method [68], and N and P contents were measured with an automatic Kjeldahl apparatus method (NY/T2419-2013) and a vanadium molybdate blue colorimetric method (NY/T2421-2013), respectively. Soil C contents was measured by an elemental analyzer method [69], and soil N and P contents determined using the Kjeldahl method (HJ717-2014) and the forest soil phosphorus determination method (LY/T1232-2015-3), respectively. Three replicates were set for every measurement.
The homeostasis coefficient 1/H was used to indicate the strength of plant stoichiometric homeostasis [48] and was calculated as follows:
where Y is the C, N, or P content or C: N, C: P, or N: P ratio in leaves; X is the C, N, or P content or C: N, C: P, or N: P ratio in soil (Supplementary Table S2); and C is a constant. Values for H and C are obtained according to the regression between Y and X, and 1/H is the regression slope between log X and log Y, with an absolute value of 0.00 to 1.00. According to one-tailed tests with α = 0.10, when a regression relation was not significant (P > 0.10), the plant was defined as “strictly homeostatic”, whereas when the regression relation was significant (P < 0.10), stoichiometric homeostasis was divided into homeostatic (0 < 1/H < 0.25), weakly homeostatic (0.25 < 1/H < 0.5), weakly plastic (0.5 < 1/H < 0.75), and plastic (1/H > 0.75) [60].
Collected fresh leaf samples were cut into 1 cm × 1 cm pieces and immediately put into FAA solution (100 mL of FAA = 90 mL of 70% ethanol + 5 mL of 37% formaldehyde + 5 mL of 99.5% glacial acetic acid). Fixed materials were dehydrated in ethanol, made transparent in xylene, embedded in paraffin, and then sliced using a microtome (Leica RM 2016, Shanghai, China) to a section thickness of 8–10 μm. Safranine O-fast green staining [70] was performed after specimens were dried, and then, specimens were sealed using neutral resin and photographed with an optical microscope (Leica DM750, Weztlar, Germany). Data were obtained by CaseViewer 2.4 (Budapest, Hungary). Ten measurements were performed per leaf, and the mean was obtained. The measured parameters were thickness of upper epidermal cuticle (CU), thickness of upper epidermis (TE), thickness of palisade tissue (TP), thickness of spongy tissue (TS), blade thickness (LT), and thickness of lower epidermis (LE). The P/S ratio (P/S = TP/TS) and organizational tightness (CTR = TP/LT × 100) were obtained by calculation.
Statistical analyses
SPSS software (v20.0, IBM, Armonk, NY, USA) was used to process and analyze data, and figures were made using Origin (v2023b, OriginLab Corporation, Hampton, USA). Significant differences in leaf C, N, and P contents and C: N, C: P, and N: P ratios and in leaf anatomical structures among life forms and species were analyzed by one-way ANOVA and t-test, respectively. The significance level was set at 5%. Pearson correlation analysis was performed to analyze the relationship between leaf stoichiometric and anatomical traits. There were three replicates in each measurement. Data are represented as mean ± standard deviation.
Data availability
The data sets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Abbreviations
- QTP:
-
Qinghai–Tibet Plateau
- QSH :
-
Quercus sect. Heterobalanus
- C:
-
carbon
- N:
-
nitrogen
- P:
-
phosphorus
- C:
-
N carbon to nitrogen ratio
- C:
-
P carbon to phosphorus ratio
- N:
-
P nitrogen to phosphorus ratio
- CV:
-
the coefficient of variation
- 1/H :
-
homeostasis coefficient
- 1/H C :
-
homeostasis regulation coefficient of carbon
- 1/H N :
-
homeostasis regulation coefficient of nitrogen
- 1/H N :
-
homeostasis regulation coefficient of phosphorus
- 1/H C :
-
N homeostasis regulation coefficient of carbon to nitrogen ratio
- 1/H C :
-
P homeostasis regulation coefficient of carbon to phosphorus ratio
- 1/H N :
-
P homeostasis regulation coefficient of nitrogen to phosphorus ratio
- CU:
-
thickness of upper epidermal cuticle
- TE:
-
thickness of upper epidermis
- TP:
-
thickness of palisade tissue
- TS:
-
thickness of spongy tissue
- LE:
-
thickness of lower epidermis
- LT:
-
blade thickness
- P/S:
-
thickness of palisade tissue to thickness of sponge tissue ratio
- CTR:
-
organizational tightness
- Cu:
-
cuticle
- Ue:
-
upper epidermis
- Pa:
-
palisade tissue
- Sp:
-
spongy tissue
- Le:
-
lower epidermis
- Eh:
-
epidermal hair
References
Rowley DB. Age of initiation of collision between India and Asia: a review of stratigraphic data. Earth Planet Sci Lett. 1996;145:1–13.
Xu H, Su T, Zhang ST, Deng M, Zhou ZK. The first fossil record of ring-cupped oak (Quercus L. Subgenus Cyclobalanopsis (Oersted) Schneider) in Tibet and its paleoenvironmental implications. Palaeogeogr Palaeoclimatol Palaeoecol. 2016;442:61–71.
Tang H, Micheels A, Eronen JT, Ahrens B, Fortelius M. Asynchronous responses of east Asian and Indian summer monsoons to mountain uplift shown by regional climate modelling experiments. Clim Dyn. 2013;40:1531–49.
Rowley DB, Currie BS. Palaeo-altimetry of the late Eocene to Miocene Lunpola basin, central Tibet. Nature. 2006;439:677–81.
Tapponnier P, Zhiqin X, Roger F, Meyer B, Arnaud N, Wittlinger G, Jingsui Y. Oblique stepwise rise and growth of the Tibet Plateau. Science. 2001;294:1671–77.
Royden LH, Burchfiel BC, Van Der Hilst RD. The geological evolution of the Tibetan Plateau. Science. 2008;321:1054–58.
Knorr G, Butzin M, Micheels A, Lohmann G. A warm Miocene climate at low atmospheric CO2 levels. Geophys Res Lett. 2011;38:1–5.
Yao YF, Bruch AA, Mosbrugger V, Li C, Li CS. Quantitative reconstruction of Miocene climate patterns and evolution in Southern China based on plant fossils. Palaeogeogr Palaeoclimatol Palaeoecol. 2011;304:291–307.
Jacques FMB, Su T, Spicer RA, Xing YW, Huang YJ, Zhou ZK. Late miocene southwestern Chinese floristic diversity shaped by the southeastern uplift of the Tibetan Plateau. Palaeogeogr Palaeoclimatol Palaeoecol. 2014;411:208–15.
Zhou ZK, Yang QS, Xia K. Fossils of Quercus sect. Heterobalanus can help explain the uplift of the Himalayas. Chin Sci Bull. 2007;52:238–47.
Molnar P, Boos WR, Battisti DS. Orographic controls on climate and paleoclimate of Asia: thermal and mechanical roles for the tibetan plateau. Annu Rev Earth Planet Sci. 2010;38:77–102.
Du FK, Hou M, Wang W, Mao K, Hampe A. Phylogeography of Quercus aquifolioides provides novel insights into the Neogene history of a major global hotspot of plant diversity in south-west China. J Biogeogr. 2017;44:294–307.
Zhang SB, Zhou ZK, Hu H, Xu K, Yan N, Li SY. Photosynthetic performances of Quercus pannosa vary with altitude in the Hengduan Mountains, Southwest China. Ecol Manage. 2005;212:291–301.
Meng HH, Su T, Gao XY, Li J, Jiang XL, Sun H, Zhou ZK. Warm–cold colonization: response of oaks to uplift of the Himalaya–Hengduan Mountains. Mol Ecol. 2017;26:3276–94.
Meunier CL, Boersma M, El-Sabaawi R, Halvorson HM, Herstoff EM, Van de Waal DB, et al. From elements to function: toward unifying ecological stoichiometry and trait-based ecology. Front Environ Sci. 2017;5:1–10.
Rivas-Ubach A, Sardans J, Pérez-Trujillo M, Estiarte M, Peñuelas J. Strong relationship between elemental stoichiometry and metabolome in plants. Proc. Natl. Acad. Sci. 2012;109:4181–6.
Simioni PF, Eisenlohr PV, Pessoa MJG, Silva IV. da. Elucidating adaptive strategies from leaf anatomy: do Amazonian savannas present xeromorphic characteristics? Flora. 2017;226:38–46.
Wei Y, Dang X, Wang J, Gao J, Gao Y. Response of C:N:P in the plant-soil system and stoichiometric homeostasis of Nitraria tangutorum leaves in the oasis-desert ecotone, Northwest China. J Arid Land. 2021;13:934–46.
Sun J, Gao P, Li C, Wang R, Niu X, Wang B. Ecological stoichiometry characteristics of the leaf–litter–soil continuum of Quercus acutissima Carr. And Pinus densiflora Sieb. In Northern China. Environ Earth Sci. 2019;78:1–13.
Tao Y, Wu G, Zhang Y, Zhou X. Leaf N and P stoichiometry of 57 plant species in the Karamori Mountain Ungulate Nature Reserve, Xinjiang, China. J Arid Land. 2016;8:935–47.
Elser JJ, Dobberfuhl DR, Mackay NA, Schampel JH. Organism size, life history, and N: P stoichiometry: toward a unified view of cellular and ecosystem processes. Bioscience. 1996;46:674–84.
Zhao Y, Li T, Liu J, Sun J, Zhang P. Ecological stoichiometry, salt ions and homeostasis characteristics of different types of halophytes and soils. Front Plant Sci. 2022;13:990246.
Hessen DO, Ågren GI, Anderson TR, Elser JJ, De Ruiter PC. Carbon sequestration in ecosystems: the role of stoichiometry. Ecology. 2004;85:1179–92.
Schade JD, Kyle M, Hobbie SE, Fagan WF, Elser JJ. Stoichiometric tracking of soil nutrients by a desert insect herbivore. Ecol Lett. 2003;6:96–101.
Mcgroddy ME, Daufresne T, Hedin LO. Scaling of C:N:P stoichiometry in forests worldwide: implications of terrestrial Redfield-type ratios. Ecology. 2004;85:2390–401.
Sun P, Li X, Gong X, Liu Y, Zhang X, Wang L. Carbon, nitrogen and phosphorus ecological stoichiometry of Lateolabrax macultus and Acanthogobius Ommaturus in the estuary of Yangtze River, China. Acta Ecol Sin. 2014;34:196–203.
Gu Q, Zamin TJ, Grogan P. Stoichiometric homeostasis: a test to predict tundra vascular plant species and community-level responses to climate change. Arct Sci. 2017;3:320–33.
Yu Q, Chen Q, Elser JJ, He N, Wu H, Zhang G, et al. Linking stoichiometric homoeostasis with ecosystem structure, functioning and stability. Ecol Lett. 2010;13:1390–99.
Peng H, Chen Y, Yan Z, Han W. Stage-dependent stoichiometric homeostasis and responses of nutrient resorption in Amaranthus mangostanus to nitrogen and phosphorus addition. Sci Rep. 2016;6:37219.
Yu Q, Elser JJ, He N, Wu H, Chen Q, Zhang G, Han X. Stoichiometric homeostasis of vascular plants in the Inner Mongolia grassland. Oecologia. 2011;166:1–10.
Frost PC, Evans-White MA, Finkel ZV, Jensen TC, Matzek V. Are you what you eat? Physiological constraints on organismal stoichiometry in an elementally imbalanced world. Oikos. 2005;109:18–28.
Jeyasingh PD, Weider LJ, Sterner RW. Genetically-based trade-offs in response to stoichiometric food quality influence competition in a keystone aquatic herbivore. Ecol Lett. 2009;12:1229–37.
Kröber W, Heklau H, Bruelheide H. Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits. Plant Biol. 2015;17:373–83.
Kuster VC, Barbosa De Castro SA, Vale FHA. Photosynthetic and anatomical responses of three plant species at two altitudinal levels in the neotropical savannah. Aust J Bot. 2016;64:696–703.
de la Riva EG, Villar R, Pérez-Ramos IM, Quero JL, Matías L, Poorter L, Marañón T. Relationships between leaf mass per area and nutrient concentrations in 98 Mediterranean Woody species are determined by phylogeny, habitat and leaf habit. Trees. 2018;32:497–510.
Oguchi R, Onoda Y, Terashima I, Tholen D. Leaf anatomy and function. In: Adams III, Terashima W, I, editors. The leaf: a platform for performing photosynthesis. Advances in photosynthesis and respiration. Volume 44. Cham: Springer; 2018.
Bosabalidis AM, Kofidis G. Comparative effects of drought stress on leaf anatomy of two olive cultivars. Plant Sci. 2002;163:375–79.
Tian M, Yu G, He N, Hou J. Leaf morphological and anatomical traits from tropical to temperate coniferous forests: mechanisms and influencing factors. Sci Rep. 2016;6:19703.
Liu X, Chen H, Sun T, Li D, Wang X, Mo W, et al. Variation in woody leaf anatomical traits along the altitudinal gradient in Taibai Mountain, China. Glob Ecol Conserv. 2021;26:e01523.
Kumar V, Kodandaramaiah J, Rajan MV. Leaf and anatomical traits in relation to physiological characteristics in mulberry (Morus sp.) cultivars. Turk J Bot. 2012;36:683–9.
Ahmad KS, Hameed M, Fatima S, Ashraf M, Ahmad F, Naseer M, Akhtar N. Morpho-anatomical and physiological adaptations to high altitude in some Aveneae grasses from Neelum Valley, Western Himalayan Kashmir. Acta Physiol Plant. 2016;38:1–14.
Mediavilla S, Gallardo-López V, González-Zurdo P, Escudero A. Patterns of leaf morphology and leaf N content in relation to winter temperatures in three evergreen tree species. Int J Biometeorol. 2012;56:915–26.
Dunbar-Co S, Sporck MJ, Sack L. Leaf trait diversification and design in seven rare taxa of the hawaiian Plantago radiation. Int J Plant Sci. 2009;170:61–75.
Wang Z, Zheng F. Ecological stoichiometry of plant leaves, litter and soils in a secondary forest on China’s Loess Plateau. PeerJ. 2020;8:e10084.
Elser JJ, Fagan WF, Denno RF, Dobberfuhl DR, Folarin A, Huberty A, et al. Nutritional constraints in terrestrial and freshwater food webs. Nature. 2000;8:578–80.
Sun X, Kang H, Kattge J, Gao Y, Liu C. Biogeographic patterns of multi-element stoichiometry of Quercus variabilis leaves across China. Can J for Res. 2015;45:1827–34.
Han W, Fang J, Guo D, Zhang Y. Leaf nitrogen and phosphorus stoichiometry across 753 terrestrial plant species in China. New Phytol. 2005;168:377–85.
Sterner RW, Elser JJ. Ecological stoichiometry: the biology of elements from molecules to the biosphere. Princeton: Princeton University Press; 2003.
Li W, Li Y, Zhong J, Fu H, Tu J, Fan H. Submerged macrophytes exhibit different phosphorus stoichiometric homeostasis. Front Plant Sci. 2018;9:1207.
Rong Q, Liu J, Cai Y, Lu Z, Zhao Z, Yue W, Xia J. Leaf carbon, nitrogen and phosphorus stoichiometry of Tamarix chinensis Lour. In the Laizhou Bay coastal wetland, China. Ecol Eng. 2015;76:57–65.
Lin Y, Lai Y, Tang S, Qin Z, Liu J, Kang F, Kuang Y. Climatic and edaphic variables determine leaf C, N, P stoichiometry of deciduous Quercus species. Plant Soil. 2022;474:383–94.
Zhang F, Lu K, Gu Y, Zhang L, Li W, Li Z. Effects of low-temperature stress and brassinolide application on the photosynthesis and leaf structure of Tung tree seedlings. Front Plant Sci. 2020;10:1767.
Vitousek PM. Foliar and litter nutrients, nutrient resorption, and decomposition in hawaiian Metrosideros polymorpha. Ecosystems. 1998;1:401–7.
Reich PB, Oleksyn J. Global patterns of plant leaf N and P in relation to temperature and latitude. Proc Natl Acad Sci U S A. 2004;101:11001–6.
Schreeg LA, Santiago LS, Wright SJ, Turner BL. Stem, root, and older leaf N:P ratios are more responsive indicators of soil nutrient availability than new foliage. Ecology. 2014;95:2062–68.
Koerselman W, Meuleman AF. The vegetation N:P ratio: a new tool to detect the nature of nutrient limitation. J Appl Ecol. 1996;1441–50.
Güsewell S. N:P ratios in terrestrial plants: variation and functional significance. New Phytol. 2004;164:243–66.
Makino W, Cotner JB, Sterner RW, Elser JJ. Are bacteria more like plants or animals? Growth rate and resource dependence of bacterial C:N:P stoichiometry. Funct Ecol. 2003;17:121–30.
Wang J, Wang J, Guo W, Li Y, Wang GG, Wu T. Stoichiometric homeostasis, physiology, and growth responses of three tree species to nitrogen and phosphorus addition. Trees. 2018;32:1377–86.
Persson J, Fink P, Goto A, Hood JM, Jonas J, Kato S. To be or not to be what you eat: regulation of stoichiometric homeostasis among autotrophs and heterotrophs. Oikos. 2010;119:741–51.
Zhang FJ, Zhang KK, Du CZ, Li J, Xing YX, Yang LT, Li YR. Effect of drought stress on anatomical structure and chloroplast ultrastructure in leaves of sugarcane. Sugar Tech. 2015;17:41–8.
Hajnajari H, Akbari H, Abdossi V. Genesis of ultra-specialized histology with stable traits in mesophyll of drought tolerant apple cultivars. Sci Hortic. 2019;249:168–76.
Zhekun Z, Wilkinson H, Zhengyi W. Taxonomical and evolutionary implications of the leaf anatomy and architecture of Quercus L. Subgenus Quercus from China. Cathaya. 1995;7:1–34.
Terashima I, Hanba YT, Tholen D, Niinemets Ü. Leaf functional anatomy in relation to photosynthesis. Plant Physiol. 2011;155:108–16.
Murchie EH, Hubbart S, Peng S, Horton P. Acclimation of photosynthesis to high irradiance in rice: gene expression and interactions with leaf development. J Exp Bot. 2005;56:449–60.
Jinwen L, Jingping Y, Pinpin F, Junlan S, Dongsheng L, Changshui G, Wenyue C. Responses of rice leaf thickness, SPAD readings and chlorophyll a/b ratios to different nitrogen supply rates in paddy field. Field Crops Res. 2009;114:426–32.
López-Pujol J, Zhang FM, Sun HQ, Ying TS, Ge S. Centres of plant endemism in China: places for survival or for speciation? J Biogeogr. 2011;38:1267–80.
Zhang Y, Zhou C, Lv W, Dai L, Tang J, Zhou S, et al. Comparative study of the stoichiometric characteristics of karst and non-karst forests in Guizhou, China. J Res. 2019;30:799–806.
Sato JH, de Figueiredo CC, Marchão RL, Madari BE, Benedito LEC, Busato JG, et al. Methods of soil organic carbon determination in Brazilian savannah soils. Sci Agric. 2014;71:302–8.
Hu Y, Yang L, Gao C, Liao D, Long L, Qiu J, et al. A comparative study on the leaf anatomical structure of Camellia Oleifera in a low-hot valley area in Guizhou Province, China. PLoS ONE. 2022;17:e0262509.
Acknowledgements
Not applicable.
Funding
This research was supported by the National Natural Science Foundation of China (Nos. 31860208, 31560207) and the Scientific Research Fund of Yunnan Provincial Department of Education (No. 2023Y0736).
Author information
Authors and Affiliations
Contributions
A.Z. performed the experiments and wrote the manuscript, Bairuixue G., S.C. and D.K. participated in the experiments, J.W. made helpful comments on the manuscript, Y.Z. and H.M. conceived, designed the research, revised the manuscript and supervised the project. All authors had read and approved the final manuscript.
Corresponding authors
Ethics declarations
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Additional information
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Electronic supplementary material
Below is the link to the electronic supplementary material.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
About this article
Cite this article
Zhou, A., Ge, B., Chen, S. et al. Leaf ecological stoichiometry and anatomical structural adaptation mechanisms of Quercus sect. Heterobalanus in southeastern Qinghai–Tibet Plateau. BMC Plant Biol 24, 325 (2024). https://doi.org/10.1186/s12870-024-05010-x
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/s12870-024-05010-x