| In order to study the impact of root and litter treatments on the plant physiology, two common broadleaved forests, Cinnamomum camphora and Liquidambar formosana, in subtropical region were chosen. the relation between soil carbon input and nitrogen mineralization, we executed4kinds of treatments to the forests investigated including litter exclusion, litter addition and trenching:â‘ litter exclusion to control aboveground carbon input,â‘¡litter addition to control aboveground carbon input,â‘¢trenching and litter exclusion to control above-and below-ground carbon input,â‘£trenching and litter addition to control above-and below-ground carbon input. Meanwhile,2kinds of treatments to the forest including the trenching and the nature were as the controls. The dynamic change of maximum net photosynthetic rate, leaf water potential and the content of K, Mg, N, P four kinds of mineral elements in leaves under the change of carbon input in these two kinds of stand were studied from July2010to October2011. The main results are as follow:1. There is a dynamic change of net photosynthetic rate of the camphor trees and Liquidambar trees. As the season change, the net photosynthetic rate of camphor and sweet gum gradually increases followed by decreases. There is still increase of maximum net photosynthetic rate in both double litter and removal of the root and extra litter compared to the control treatment under the camphor tree and Liquidambar, however, the treatment of removal of litter and removal of the root and litter are decrease. Compared with the control treatment, the maximum net photosynthetic rate of double litter of liquidambar and removal of the root and extra litter increased by an average of2.32%and3.87%respectively; but the plots that removal of the litter, removal of the root and litter and removal of the root decreased by7.72%,7.47%and3.05%.respectively. In the camphor tree stand, compared with the control treatment, the maximum net photosynthetic rate of double litter and removal of the root and extra litter increased by an average of5.03%and10.31%respectively; But the plots that removal of the litter, removal of the root and litter and removal of the root decreased by6.81%,3.48%and8.03%.Compared with the control treatment, the difference of the other five treatment is significant (P<0.05).2. The leaf water potential in both camphor and sweet gum stand of six kinds treatment also presents significant seasonal change, but the trend is just the opposite to maximum net photosynthetic rate. With the increase of maximum net photosynthetic rate, the leaf water potential decreases obviously, he annual average of the leaf water potential of six kinds treatment of Camphor:removal of the root> removal of the root and extra litter>removal of the root and litter>removal of litter>control treatment> double litter; however, In the camphor tree stand, The annual average of the leaf water potential of six kinds treatment:removal of the root and litter> removal of litter>removal of the root>control treatment>removal of the root and extra litter>double litter.3. Under six kinds of treatment of the camphor tree and sweet gum, the content of leaf elements N, P, K and Mg has changed seasonally. The change of sweet gum K element showing inverted "single peak" curve. The mean value of element K under six treatments of the sweet gum trees come to the high peak in April, and the minimum mean value of sweet gum trees are in July. The maximum mean value is the treatment of removal of the root and extra litter and the minimum mean value is removal of litter and removal of the root and litter among six kinds of treatment. While the camphor K elements is gradually decreased, The mean value of element K under six treatments of camphor trees come to the high peak in April and the minimum mean value of camphor trees are in July. The maximum mean value is the treatment of removal of the root and extra litter and the minimum mean value is removal of litter and removal of the root and litter among six kinds of treatment. The dynamic Variation of leaf element Mg in the camphor tree is relatively small, but in sweet gum leaf, it changes significantly as season, showing a inverted "single peak" curve. The maximum mean value of Mg is the treatment of removal of the root and extra litter, and the minimum mean value is removal of litter and removal of the root and litter among six kinds of treatment. Annual average of the elements N content of camphor leaf:removal of the root and extra litter>double litter>control treatment> removal of litter>removal of the root>removal of the root and litter, and annual average of the elements N content of sweet gum leaf:removal of the root and extra litter>double litter>removal of the root>control treatment>removal of litter> removal of the root and litter; annual average of the elements P content of camphor leaf:removal of the root and extra litter>removal of the root>double litter>control treatment>removal of litter>removal of the root and litter, and annual average of the elements P content of sweet gum leaf: removal of the root and extra litter>double litter>removal of the root>control treatment>removal of the root and litter> removal of litter. The leaf N, P content in camphor tree is more than the sweet gum, however, the sweet gum leaf N/P ratio is larger than camphor trees.This study shows that the way to change the root and litter treatments had a significant effect on the physiological and ecological characteristics of the stand. Compared with the control treatment, change of maximum net photosynthetic rate, leaf water potential and the content of leaf K, Mg, N and P four kinds of mineral elements of camphor and sweet gum, the difference of the other five treatment is significant (P<0.05), and there was a negative correlation between Maximum net photosynthetic rate and leaf water potential, Maximum net photosynthetic rate was positively correlated with the blade element. To apply the principal factor analysis to maximum net photosynthetic rate and leaf water potential and leaf element indicators under the six kinds of treatment of the two forests, the result shows, the cumulative contribution rate of the camphor tree of the four elements and leaf water potential maximum net photosynthetic rate changes to97.951%, and the first principal component is the four elements of K, Mg, N and P, variance contribution rate is68.364%, the second main component is the leaf water potential, variance contribution rate is29.587%. The cumulative contribution rate of the sweet gum tree of the four elements and leaf water potential maximum net photosynthetic rate changes to97.951%, and the first principal component is K, Mg and P elements, variance contribution rate is71.643%, the second main component is the leaf water potential and N element in the leaves, variance contribution rate is23.459%. |
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