Photosynthetic gas exchange and chlorophyll a fluorescence of three wild soybean species in response to NaCl treatments

Responses of photosynthetic gas exchange and chlorophyll (Chl) a fluorescence of three wild soybeans, Glycine soja, G. tomentella, and G. tabacina occurring in different habitats of Taiwan, to four NaCl treatments, OS, LS, MS, and HS (i.e. 0, 17, 5 1, and 85 mM NaCl) were compared. In G. soja following exposure to NaCl treatment for one month, the photon saturated photosynthetic rate (P-N), the ratio of variable to maximum fluorescence (F-v/F-m), the quantum yield of photosystem 2 (Phi(PS2)), and the electron transport rate (ETR) decreased dramatically. These reductions increased with increasing concentration of NaCl treatment. Plants of MS and HS treatments did not survive after extending the treatment to two months. Reductions in P-N, Phi(PS2), and ETR (but not in F-v/F-m) were found in G. tabacina after two months of exposure to MS and HS treatments, but the reduction was not as severe as that in G. soja. In G. tomentella, significant reductions in P-N and g(s) were found only in HS plants after two months of treatment, but no significant differences in F-v/F-m, Phi(PS2), and ETR were found among plants of the four treatments. Thus the three wild soybeans in Taiwan have differentiated in their photosynthetic susceptibility to salinity, G. tomentella being the least susceptible, G. soja the most sensitive, and G. tabacina the inter-mediate. Different mechanisms are attributed to the inhibition effect of salinity on photosynthesis of the three species.