Effects Of Forest Thinning On The Photosynthesis Characteristic Of Quercus Aliena Var.Acuteserrata And Pinus Tabulaeformis Forests On South Slope Of Qinling Mountains

Quercus aliena var. acuteserrata and Pinus tabulaeformis forests are main forest tree species and arewidely distributed in Qinling mountains. Studying on the influence of different thinning intensities on thephotosynthesis characteristic of Quercus aliena var. acuteserrata and Pinus tabulaeformis forests can notonly be instructive to the study on the relationship between forest thinning and carbon sequestration, butalso provide theoretical basis for the forest thinning of Quercus aliena var. acuteserrata forests at thesouthern Qinling Mountains. Photosynthetic characteristics of Quercus aliena var. acuteserrata and Pinustabulaeformis forest with different thinning intensities were monitored and the data were statisticallyanalysed. The result shown that the photosynthesis characteristic of trees in both forests altered afterthinning.In Quercus aliena var. acuteserrata forests, the environmental conditions of forests changed afterthinning, the daily variance of environmental factors was in single-peak type, the peak value of PAR was at12:00, while the peak value of Ta, Ca and RH were at14:00; by variance analysis, PAR, Ta, Ca increasedsignificantly but RH decreased significantly at the15%and20%thinning intensity(P<0.01); forest thinningalso altered photosynthetic parameters, the daily change curve of Pn at thinned forests was in single-peaktype, but bimodal type in Ck, the dynamic of Ci was similar to Gs, which was higher at morning andevening but lower at noon, the dynamic of Ls, Tr was on contrary, the trend was lower at morning andevening but higher at noon, the dynamic of WUE was bimodal type, by variance analysis, Pn was higherafter thinning, it was significantly increased at thinning intensity of10%(P<0.05), while it was moresignificantly increased at thinning intensity of15%and20%(P<0.01); By photosynthetic light curveanalysis, Pmax was higher after thinning, but it was significantly increased at thinning intensity of15%and20%(P<0.01), LCP was no significant difference in different thinning intensity forests, LSP wassignificantly increased at thinning intensity of5%and20%(P<0.05), in the thinning intensity of15%and20%forests, AQE was significantly decreased but Rd was significantly increased(P<0.05); By usinghypothesis analysis, significant regression relationships were observed among Pn and environmentalfactors (P<0.05); There were significant positive correlations (P<0.01) among Pn, PAR and Ta and therewere significant negative correlations among Pn, Gs and Ci (P<0.01); By hypothesis test, the regressiverelationship between Pn and environmental factors was significant(P<0.05); The amounts of accumulativephotosynthesis was increased in the thinned forests, and it was higher at the15%thinning intensity. Thus the thinning intensities of15%was more suitable for the Quercus aliena var. acuteserrata forests on SouthSlope in Qinling Mountains.In Pinus tabulaeformis forests, the environmental conditions of forests changed after thinning, thedaily variance of environmental factors was in single-peak type, the peak value was at14:00, by varianceanalysis, PAR, Ta, Ca increased significantly but RH decreased significantly at the20%and25%thinningintensity(P<0.01); forest thinning also altered photosynthetic parameters, the daily change curve of Pn ateach forests was in single-peak type, the peak value was at12:00, the dynamic of Ci was similar to Gs,which was higher at morning and evening but lower at noon, the dynamic of Ls, Tr was on contrary, thetrend was lower at morning and evening but higher at noon, the dynamic of WUE was single type, the peakvalue was at12:00, then decreased quickly; by variance analysis, Pn was higher after thinning, it wassignificantly increased at thinning intensity of5%,10%and15%(P<0.05), while it was more significantlyincreased at thinning intensity of20%and25%(P<0.01); By photosynthetic light curve analysis, Pmaxand Rd were higher after thinning, but there were significantly increased at thinning intensity of20%and25%(P<0.01), LCP was no significant difference in different thinning intensity forests, LSP wassignificantly increased at thinning intensity of20%and25%(P<0.05). In the thinning intensity of15%,20%and25%forests, AQE was significantly decreased (P<0.05), but there was no difference in otherforests; By using hypothesis analysis, significant regression relationships were observed among Pn andenvironmental factors (P<0.05); There were significant positive correlations (P<0.01) among Pn, PAR andTa and there were significant negative correlations among Pn, Gs and Ci (P<0.01); By hypothesis test, theregressive relationship between Pn and environmental factors was significant(P<0.05); The amounts ofaccumulative photosynthesis was increased in the thinned forests, and it was higher at the thinning intensityof15%and20%. Thus the thinning intensities of15%to20%was more suitable for the Pinustabulaeformis forests on South Slope in Qinling Mountains.