Research On Several Crops Net Photosynthetic Rate In Light, Soil Moisture And CO₂Response

In order to explore the combined effects of light intensity and soil moisture on net photo synthetic rate of crops, and to construct the mathematical model of net photosynthetic rate and related environmental factors, a gradient of soil moisture content at an interval of10%within the range of30%-80%was installed for Zea mays, Morus alba, Glycine max and Helianthus annuus in a pot culture experiment, with the light response parameters, the CO2response parameters, net photosynthetic rate and several other parameters measured. The experimental results showed that:1. The net photosynthetic rates of Zea mays, Morus alba, Glycine max and Helianthus annuus had significant correlation with light intensity and CO2concentration under the suitable soil moisture (SRWC). Both PAR and SRWC had impacts on Pn, and the affecting magnitude varied with soil moisture content.2. In response to light intensity,the net photosynthetic rates(Pn), apparent quantum yield(AQY) and light saturation point(LSP) of Zea mays and Helianthus annuus declined with SRWC decreasing, but the light compensation point(LCP) increased. Meanwhile, the net photosynthetic rates(Pn) and light saturation point(LSP) of Morus alba and Glycine max decreased and there was no significant change on AQY.3. In response to CO2concentration,the net photosynthetic rates(Pn), Carboxylation efficiency(CE) and CO2saturation point(CSP) of Zea mays and Helianthus annuus declined with SRWC decreasing, but the CO2compensation point(CCP) increased.4. Meanwhile, the net photosynthetic rates(Pn) and CO2saturation point(CSP) of Morus alba and Glycine max increased firstly then decreased when attained a certain value, but the CO2compensation point(CCP) increased. There was no significant change on CE. Under the condition of drought stress or high water, improving CC appropriately will reduce photosynthesis inhibition phenomena as far as C3crops Morus alba and Glycine max are considered. The same will happen on C4crops Zea mays and Morus alba just under drought stress condition.5. We found that the comprehensive impacts from PAR and SRWC to Pn could be expressed by Pn=PAR*Exp(bl-b2/SRWC)+SRWC*Exp(b3-SRWC/b2)+b4, and the threshold of appropriate soil moisture content of the four crops can be calculated directly by the mathematical model. The threshold of appropriate soil moisture content for Zea mays, Morus alba, Glycine max and Helianthus annuus respectively were62.15%,51.17%,63.19%and59.25%.