Photosynthetic Response to Soil Water Contents of an Annual Pioneer C<sub>4</sub> Grass (Agriophyllum squarrosum) in Hunshandak Sandland, China

Abstract

Net photosynthetic rate (P N), transpiration rate (E), stomatal conductance (g s), and leaf water potential (Ψl) of an annual pioneer C4 grass (Agriophyllum squarrosum) were compared under different simulated precipitation events in a field of Hunshandak Sandland, China. The increase of soil water content (SWC) had significant effect on these physiological traits (p<0.001). In the vegetative stage, the values of P N, E, and g s went up sharply when SWC increased at the beginning, while they went down with continuous increase of SWC. P N, E, and g s increased 1.4, 1.7, and 1.7 fold, respectively, with SWC range from 6.7 to 11.6 %. In the reproductive stage, similar trends were found, except for the climate with a higher SWC. This indicated that A. squarrosum was very sensitive to the small increment of SWC which might have a large photosynthetic potential. Ψl increased by about 8 % as the SWC changed from 6.7 to 8.8 %, and then maintained a steady level when the SWC was higher than 8.8 %, while the values of P N, E, and g s kept increasing even after this SWC. This might indicate that the adjustment of Ψl response to the changes of SWC lagged that of the photosynthetic parameters.