Photo-physiological Responses Of Typical Crops To Different Soil Moisture Conditions In The Northern China Plain

Photosynthesis is the key factor that influences of water use efficient. The objective of thispaper is to study photosynthetic characteristics under different soil water condition to increaseefficiency of solar radition and water use efficiency (WUE).The experiment was conducted in the Northern China Plain. Photosynthetic physiologicalcharacteristics under different soil moisture were measured using LI-6400portable photosyntheticsystem and eddy covariance system in a typical winter wheat-maize rotation from October2010toOctober2011. Results showed that:1. Diurnal variation of stomatol conductence (Cond), photosynthesis rate (Pn), transpirationrate (Tr) water use efficientfluctuated during the whole growth stage. The peak values were around10:00and14:00in general. After jointing stage, water stress had different effects on photosyntheticcharacteristics. Appropriate degree of water stress could regulate stoma movement and decreasetranspiration to increase water use efficiency.2. Correlation between Pnand WUE and soil moisture decreased as SWC decreases.Photosynthesis rate and WUE had positive response to soil water content. The critical value of soilmoisture for high Pnand WUE were about19%~25%and21%~28%. Under water stress conditions,soil moisture plays an important role on photosynthetic characteristics.3. With the combition method of Farquhar model and rectangle hyperbolae model,photosynthetic response of flag leaf to light intensity and CO2concentration were measured underdifferent irrigation treatments in filling stage. Results showed that the values of Vcmax、Jmax、Pnmaxand CE in T1were31.81%,32.56%,30.27%and25.77%, respectively, higher than those in T3.Stomatal conductance and transpiration both decreased as CO2concentration increased and thechanges were more sensitive under T1than T3. However, no significant difference was detectedbetween two treatments. Water use efficiency under T1was slightly higher than that of T3,indicating that moderate water stress did not make much effect on physiological mechanism ofwinter wheat.4. The diurnal variation of Pnand Trof maize’s leaves demonstrated a single peak curve andthe peak value were around12:00. With the decrease of soil moisture, light restrain was taken placein the middle and lower layers of maize canopy, and the Apparent Quantum Efficiency (AQE) wasdecreased by20%.5. The critical value of soil moisture for high Pnand WUE for maize were about19%~25%and21%~28%.