Phtotsynthetic physiological Response of Larrea tridentata due to the increase of CO_2 concentration and drought

Li-6400 portable photosynthesis system was used to measure the photosynthetic physiological responses of larrea triden-tata to the increase of CO2 concentration and drought.The results showed that: Water stress had little influence on the leaf’s actinic process.Photosynthetic apparatus were not harmed by drought when the soil water potential was above-0.884 5 MPa.The light satu-ration point,the photosynthetic rate and the apparent photon utilization efficiency increased as the CO2 concentration increased.The positive effect of CO2 concentration increased is bigger than the negative effect from the drought,so the drought resistance ability of L.tridentata was raised to a certain extent by the CO2 concentration increase.The CO2 concentration saturation point(CSP) increased with the PARs and CO2 concentration increase.This indicated that the CO2 utilization efficiency increased.The stomatal conductance and transpiration decreased while WUE increased with the increase in CO2 concentration.The CO2 concentration which saturated leaf RubisCO while cause stoma closed was 700-800 μmol.mol-1.The current CO2 concentration has not saturated the RubisCO of L.tridentata.The CO2 concentration increased in the future will promote the photosynthesis of L.tridentata,and may increase the drought resistance ability of L.tridentata.