Effects Of Soil Water On Light Response Process Of Photosynthesis Of Three Tree Species

In order to investigate light response characteristics of photosynthetic efficiency and the quantitative relationships between the effciency and soil water in three tree species in Loss Hilly Region, and provide a thoretical and technical reference for plant introduction and selection, stand retional allocation and community structure disposition in vegetation rehabilitation in vulnerable ecosystem, this paper measured light responses of different tree species under different soil water conditions and stimulated the light response processes by rectangular hyperbola model, non-rectangular hyperbola model, index model and modified model based on rectangular hyperbola model, materialed by potted and field plantlet of Prunus sibirica L., Hippophae rhamnoides L. and Pinus tabulaeformis Carr. Therefore, we made clear response regularities of photosynthetic efficiency to light intensity and soil water of three trees, determined soil water range of keeping high photosynthetic rate and water use efficiency and discussed the applicability of different light response models sitimulating different trees'photosynthetic rate-light response processes and parameters in different soil water.The main results and conclusions are as follows:1,Response characteristics of photosynthetic efficiency to light intensity and soil water of three tree species were clarified.(1) Soil water stress, together with strong light stress, led to serious photoinhibition of three tree species; three tree species all had high light use ability to strong light in appropriate moisture conditions.When the relative soil water content(RWC) was respectively at the range of 56.3%～80.9%,41.48%～74.8%,42.9%～82.86%,51.5%～65.5%,36.7%～92.6%,35.04%～95.89%, potted Prunus sibirica L., field Prunus sibirica L., potted Hippophae rhamnoides L., field Hippophae rhamnoides L., potted Pinus tabulaeformis Carr. and field Pinus tabulaeformis Carr. could keep high photosynthetic level and didn't have obvious photoinhibition in strong light. However, when the RWC exceeded these water ranges, each plant had obvious photoinhibition in strong light, which showed that the photosynthetic rate(P_n) signally dropped and the light saturation point(LSP) clear decreased as the photosynthetical active radiation(PAR) increased. (2) Leaf gas exchange parameters of three tree species had clear threshold response to soil water.The photosynthetic rate(P_n),water use efficiency(WUE),light use efficiency(LUE),maximum photosynthetic rate(P_nmax),apparent quantum yield(Φ),light saturation point(LSP),light compensation point(LCP),dark respiratory rate(R_d) of both the potted and the field plants of three tree species all showed clear threshold response to relative soil water content(RWC). As the RWC increased, P_n,WUE,LUE,P_nmax,Φ,LSP and R_d increased first and then decreased. When the RWC respectively was about 68.2%,41.48%,71.69%,59.14%,63.98%,54.07%, the above parameters of potted Prunus sibirica L., field Prunus sibirica L., potted Hippophae rhamnoides L., field Hippophae rhamnoides L., potted Pinus tabulaeformis Carr. and field Pinus tabulaeformis Carr. were highest. Change trends of different tree species'Φto RWC were different. As the RWC increased, the LCP of Hippophae rhamnoides L. and Pinus tabulaeformis Carr. increased first and then decreased while the LCP of Prunus sibirica L. decreased first and then increased.(3) Prunus sibirica L., Hippophae rhamnoides L. and Pinus tabulaeformis Carr. all had higher drought resistance capability and larger range of soil water keeping higher photosynthetic level; field plants had higher resistance capability than potted ones.Potted Prunus sibirica L., field Prunus sibirica L., potted Hippophae rhamnoides L., field Hippophae rhamnoides L., potted Pinus tabulaeformis Carr. and field Pinus tabulaeformis Carr. had higher P_n,LSP and WUE when the RWC was repectively at the range of 45.71～81.2%,42～90.23%,46.8～88.16%,48.9～74.2%,38.85～92.6%,50.05～88.4% and had higherΦwhen the RWC was repectively at the range of 44.7%～68.2%,35%～63.6%,55.7%～82.86%,41.1%～74.2%,36.7%～92.6%,30%～81.46%. When the RWC was at about 44.7%～81.2%,35%～90.23%,46.8%～88.16%,41.1%～70%,36.7%～92.6%,30%～88.4%, the above plants could keep higher photosynthesis level and When the RWC was at about 68.2%,41.48%,71.69%,59.14%,63.98%,54.07%, the above plants had the highest photosynthesis level. It showed that Prunus sibirica L., Hippophae rhamnoides L. and Pinus tabulaeformis Carr. all had higher drought resistance capability and larger range of soil water keeping higher photosynthetic level; field plants had higher resistance capability than potted ones.2,simulations of light response process of photosynthetic efficiency and light respone parameters of three tree species in different soil water were discussed. Soil water largely affected the effects of four models fitting different plants'light response process of photosynthetic efficiency and light respone parameters of three tree species. As the three tree species didn't have clear photoinhibition when the RWC was respectively in the range of 56.3%～80.9%,41.48%～74.8%,42.9%～82.86%,51.5%～65.5%,36.7%～92.6%,35.04%～95.89%, four models better simulated the the photosynthesis light response curves (R²>0.9)and light response parameters—Φ,LCP and Rd. Among the four models, the non-rectangular hyperbola model fitted the data best; the rectangular hyperbola model fitted the data worst. When the RWC exceeded the optimal range, obvious photoinhibition and significant decrease in photosynthesis were observed in leaves of three tree species under strong light, Under this circumstance, only the modified rectangular hyperbola model could well fit light response of photosynthesis and the main parameters. The modified rectangular hyperbola model could well fit light response curves of photosynthesis and the main parameters under all the different soil water conditions. The rectangular hyperbola model, index model and non-rectangular hyperbola model could only be used to fit light response curves of photosynthesis and the main parameters under the optimal soil water conditions.