Gas Exchange and Chlorophyll Fluorescence Response to Simulated Rainfall in Hedysarum fruticosum var. mongolicum

The response of gas exchange and chlorophyll fluorescence along with changes in simulated rainfall were studied in water stressed plants Hedysarum fruticosum var. mongolicum (H.f.m.). Net photosynthetic rate (P_N), stomatal conductance (gs), leaf water potential (_leaf), and apparent carboxylation efficiency (P_N/C_i) were significantly increased with the increase of rainfall. However, they did not change synchronously. The complete recovery of both P_N and P_N/C_i appeared 3 d after watering while g_s and _leaf were recovered 1 d after treatment. Gas exchange characters increased sharply from 5 to 15 mm rainfall and then maintained steady state with increasing rainfall. During the initial phase of water recovery, photosystem 2 (PS2) activity was not affected and its complete recovery occurred also 3 d after rainfall. Hence the recovery of P_N was attributed to both opening of stomata and increase in carboxylation efficiency. Furthermore, PS2 activity was really impaired by water stress and could recover to the normal status when the water stress disappeared.