Effects of Soil Water Stress on Photosynthetic Characteristics in Five Provenances of Chinese Pine(Pinus tabulaeformis Carr.)

Seedlings of five provenances of Chinese pine(Pinus tabulaeformis Carr.),including Zhongtiao(ZT) Mountains,Lvliang(LL) Mountains,Taihang(TH) Mountains,Luonan(LN) county and Huangling(HL) county in Shanxi,were transplanted in pots in a greenhouse and treated with progressive soil drought.The net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),intercellular CO2 concentration(Ci) and water use efficiency(WUE) of them were measured with LI-6400 Portable Photosynthesis System.The quantitative relationships between their Pn and soil water content(SWC) were analyzed.The results showed that Pn,Tr and Gs of them firstly increased,then decreased with increased soil drought.The provenance of TH had the maximum Pn,Tr and Gs,while HL and HN had lower values than others.On the 4th day of treatment(SWC was 15~25%),Pn,Tr and Gs of five provenances reached the maximum values during the period of 13 days.On the 7th day of treatment(SWC was 7~9%),significant differences were observed in Pn,Tr,Gs and WUE among these provenances(P0.01),and an order of ZTTHLLHLLN was found in Pn,Tr,Gs and WUE.After the 10th day of treatment(SWC was under 5%),only respiration was observed for LL,TH,LN and HL.According to SWC values at Pn=0 in the quadratic equations(R2=0.980~0.997) of Pn with SWC,drought resistance was reduced with an order of THZTLLHLLN.There were distinctive differences among five provenances in their responses to progressive soil drought.