The Study On Ecological Threshold Of Water Of Pinus Sylvestris Var. Mongolica

Pinus sylvestris var. mongolica aged 16 were studied on their ecophysiological characteristics such as the net and total photosynthesis rate, the transpiration rate as well as their annual life cycle under different water deficit in Huhhot suburb of semi-drought areas. The research indicated: (1) With the water deficit increasing, the resaturated relative water content (RSWSD), the net and total photosynthesis rate, the transpiration rate declined. (2) When the water deficit fell to turgor initial loss point, net photosynthesis rate was zero, bulk osmotic potential at turgor initial loss point was regarded as the critical value of the growth water potential (CGWP) of P sylvestris var. mongolica and the value from the water potential in morning to CGWP was defined as the growth water potential threshold (GWPT) .The annual life cycle of the CGWP and GWPT of P sylvestris var. mongolica showed that CGWP of P sylvestris var. mongolica on May and June was the lowest (the absolutive value) and GWPT on May and June was the narrowest in the whole year course. (3) Comparing of relationship between the water potential of the transpiration rate being zero, the total photosynthesis being zero and the water saturation deficit corresponding to the content of mechanical water, the result showed while the total photosynthesis rate was zero, the water potential was regard as the critical value of life water potential (CFWP) of P sylvestris var. mongolica and the value from CGWP and the CDWP was defined as the life water potential threshold (FWPT) of P sylvestris var. mongolica. The annual life cycle of CFWP and FWPT of P sylvestris var. mongolica showed that CFWP on July was the highest (the absolutive value) and FWPT on July was the widest in the whole year course, which defined the ecological adaptability of P sylvestris var. mongolica to water content in the environment was good. So it was considered that the change of the critical value of water potential and the water potential threshold of P sylvestris var. mongolica was characteristics of adaptability to habitat.