Fig. 1
The changes in photosynthetic characteristics of the two soybean genotypes under CK and LN stress. (a) young leaves net photosynthetic rate (PN); (b) young leaves stomatal conductance (gs); (c) young leaves transpiration rate (E); (d) young leaves ratio of sub-stomatal to atmospheric CO2 concentrations (Ci/Ca); (e) young leaves chlorophyll a (Chl a); (f) young leaves chlorophyll b (Chl b); (g) young leaves chlorophyll a + chlorophyll b (Chl (a + b)); (h) young leaves carotenoid (Car); (i) old leaves net photosynthetic rate (PN); (g) old leaves stomatal conductance (gs); (k) old leaves transpiration rate (E); (l) old leaves ratio of sub-stomatal to atmospheric CO2 concentrations (Ci/Ca); (m) old leaves chlorophyll a (Chl a); (n) old leaves chlorophyll b (Chl b); (o) old leaves chlorophyll a + chlorophyll b (Chl (a + b)); (p) old leaves carotenoid (Car); C, cultivar soybean; W, wild soybean. CK, control treatment; LN, low-nitrogen stress; Error bars indicate the standard error (n = 4); * and ** indicate significant (P < 0.05) and highly significant (P < 0.01) differences, respectively