Photosynthetic Physiology For Pinus Massoniana In Jin Yun Mountain

Soil moisture may influence physiological mechanism of plant (photosynthetic rate、transpiration rate and water use efficiency,etc). Suitable soil moisture ensures physiological process and the accumulation of organic matter of plant to be normal. Chongqing was polluted seriously by acid rain, which cause the the damage and apoptosis of plants. In this study daily variation、seasonal variation、 the influence soil moisture and acid rain for Pinus massoniana were meamured with LI-6400in Jin Yun Mountain during2011to2012.It explored photosynthetic characteristics、the resistance drought and acid rain,and provide the scientific theoretical basis about cultivaton and management for people.Results showed that:Diurnal and seasonal changes in net photosynthetic rate and transpiration rate were obvious.In spring, they exhibited single peak, and the maximum were6.69μmol·m-2s-1and1.59mmol·m-2s-1. In summer, they exhibited two peaks, and the maximum were7.65μmol·m-2s-1and2.75mmol·m-2s-1. Photosynthetic-light response curve in spring and summer was a certain difference, and maximum net photosynthetic rate and light saturation point were higher than spring. Light compensation points and light saturation point were high for Pinus massoniana, which may adapt to the strong light, and belong to the sun plant.With normal stress (70%～80%), mild stress(50%～60%), curves of net photosynthetic rate of Pinus massoniana had an obvious diurnal change and exhibited two peaks that limited by stomatal factors.With moderate stress (35%～45%) and severe stress (20%～30%), net photosynthetic rate and transpiration rate were low down significantly, especially severe stress, reaching up to5.36μmol·m-2s-1and2.85mmol·m-2s-1.Under the conditions of normal, mild and moderate stress, the diurnal changes of stomatal conductance and net photosynthetic rate of Pinus massoniana had the same treend; with severe stress, the stomatal conductance declined gradually, and the trend was not obvious.With normal, mild and moderate stress, the differences of water use efficiency of Pinus massoniana were not obvious (p>0.05), that with mild and moderate stress were higher, that with severe stress was lower than other three treatments, that with mild stress had a best effect.Net photosynthetic rate, transpiration rate and stomata conductance were slightly affected by the acid rain ranged from pH3.5to pH5.6, while decreased rapidly when pH values varies between2.5and3.0, wichi is toreduce as much as2.51μmol·mˇ2s-1、0.66mmol·m-2s-1and0.04mol·m-2s-1. On contrary, water use efficiency was scarcely influenced by acid rain stress. Meanwhile, the maximum net photosynthetic rate, the light saturation point and the light composition point hold almost constant values under the acid condition of pH4.0to pH5.6, but started to dramatically decline when the pH reduced below to3.5, even more, they cannot be simulated when the pH reached2.0. Overall, the critical range that the acid rain acted an important role on Pinus massoniana is between3.5and4.0.