Why mixed-nitrogen nutrition increases drought tolerance in rice: from plant growth, to mesophyll conductance and photochemical efficiency

Fig. 1 Rice xylem sap amount (A), root secretion rate (B) and water use efficiency (WUE) (C) of rice plants subjected to different N forms and water regimens. N, NP, A, AP, NA and NAP represent the nitrate (NO3-), NO3-+PEG 6000, ammonium (NH4+), NH4++PEG 6000, mixture of NO3- and NH4+ (NO3-+NH4+) and NO3-+NH4++PEG 6000 treatments, respectively. The same occurs below.

Fig. 2 Rice leaf Chl (A), total N (B) and Rubisco (C) contents of rice plants subjected to different N forms and water regimens.

Fig. 3 Concentrations of soluble sugars and starch in the leaves and roots of rice seedlings subjected to different N forms and water regimens.

Fig. 4 The CO2 response curves of rice plants subjected to different N forms and water regimens.

Fig. 5 Leaf photosynthetic rate (Pn), stomatal CO2 diffusion conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) of rice plants subjected to different N forms and water regimens under the 400 µmol mol-1 CO2 concentration.

Fig. 6 The relationships of net photosynthesis A) and water use efficiency (WUE) to the mesophyll diffusion conductance (gm), stomatal CO2 diffusion conductance (gs) and the ratio of gm to gs in rice leaves.