Effects Of Continuous Cropping On Photosynthesis In Leaves Of Populus × Euramericana Cv. ‘Neva’

Continuous cropping obstacle is the common problems in practice,which restricts the agricultural production and the sustainable development of plantation seriously. Continuous cropping obstacle caused the decline in lower yields and quality is a global problem. At present there are continuous cropping phenomenon in many plants in China.The planting area is wide, and continuous cropping obstacle problem is very serious in some plants.In this paper determines the change regularity and chlorophyll fluorescence parameters of light response and CO2 response of the two generation of poplar planting trees in the planting increased gradually in the process algebra of each gas exchange parameters the continuous cropping of poplar, explores the impact of productivity in view of the long-term continuous planting of poplar which takes I-107 poplar clones as test sample in Ning yang Gaoqiao Forest Farm of Taian. Through the research on the two generation of poplar tree light response and CO2 response process, for understanding under the conditions of continuous cropping trees photosynthesis ability and physiological ecology, provides certain theory basis for the guidance of poplar species configuration, reasonable culture and system construction. The results showed that:(1) with the increase of continuous cropping poplar algebra, photosynthetic primary productivity decreases. The performance is, the net photosynthetic rate(Pn) generation of poplar leaves > two generation of poplar leaf net photosynthetic rate(Pn); a generation of poplar leaf transpiration rate(Tr) < two generation of poplar leaf transpiration rate(Tr); a generation of poplar leaves the maximum WUE value > two generation of Poplar leaves WUE. This study shows that, the first and second generation of poplar light saturation point had little difference。The LSP of poplar is at about 1000~2200μmol?m-2?s-1 because of different position of canopy. The light compensation point of the first and second generation of poplar have great difference, and the first generation LCP was significantly less than two rotation,the LCP of them is at about 16and31 μmol?m-2?s-1.That shows poplar has typical photosynthetic characteristics of Positive plants. But resistance to negative is poor. In the condition of continuous cropping, the photosynthetic physiological parameters of poplar leaf shows that the second generation is lower than the first one,which means poplar continuous cropping restrains photosynthesis.(2) Primary productivity of leaves in different canopy position is different, the overall performance shows that the photosynthetic capacity of upper leaves is stronger. The LCP, LSP and other Gas exchange parameters are also bigger in the upper canopy.(3) With the increase of continuous cropping algebra, the CO2 assimilation capacity of Poplar decreases.Which manifested as,low concentration of CO2 of CE carboxylation efficiency increased with continuous cropping algebra,the CCP rises and the maximum net photosynthetic rate decreased.The light respiration rate increased, the assimilation ability decreased approach. While the ability of alienation improves, this is bound to reduce the accumulation of assimilation, thus reducing the primary productivity.(4) The primary productivity in different leaves canopy position is different, The overall performance of it is that the photosynthetic capacity is stronger in upper leaves. The lower blade for long time to adapt to the weak light environment, so its assimilation capacity decrease. The performance for the carboxylation efficiency, CO2 saturation point CSP, light respiration rate and net photosynthetic rate decreased, while the CO2 compensation point(CCP) increased.