| The climate warming and nitrogen deposition have been also increasing with the continuous development of economic globalization, and become the important environmental problems that human have already been faced with in the21st century. The subtropical evergreen broad-leaved forest as the main forest community plays an important regulatory role in the atmospheric environmental change. Therefore, the paper taked Castanopsis fargesii, Castanopsis sclerophylla and Cyclobalanopsis glauca seedings as the study object, that the dominant species of evergreen broad-leaved forest in the mid-subtropical zone, set air temperature warming and different nitrogen fertilizer addition level (CK,0kg N. hm-2. a-1; N1,60kgN. hm-2. a-1; N2,120kg N. hm-2. a-1) by MSR-2420infrared radiation warming devices and nitrogen fertilizer application to study the effects of the warming(W), nitrogen fertilizer addition(N1and N2) and their interaction(WN1and WN2) on leaf photosynthetic physiological indexes and leaf functional traits. That can give an insight into the changes of plant physioecology and leaf functional traits at the leaf level under the context of global warming and the increasing nitrogen deposition in the future. The main results are as follows:(1) Warming made the average air temperature increased by1.22℃and the average relative air humidity increased by7.07%in warming area. The average soil temperature increased by1.05℃and0,65℃respectively, the average soil volumetric water content was reduced by7.02%and5.52%respectively at5cm and20cm. That warming contributes to the increase of air temperature and soil temperature, but the decrease of air relative humidity and soil volumetric water content.(2) Warming had no significant effect on soil pH, soil organic carbon and total nitrogen content at0～10cm,10～30cm, and30～50cm, while nitrogen (N1and N2) and the joint action of warming and nitrogen (WN1and WN2) made soil organic carbon and total nitrogen content increased significantly, but pH was significantly reduced at each of soil layer and led to soil acidification obviously. (3) Warming had no significant effect on the maximum net photosynthetic rate(Amax), apparent quantum efficiency (AQE), mesophyll cell conductance (gm), maximum electron transfer rate (Jmax), maximum carboxylation rate (Vcmax), maximum triose phosphate utilization (TPU) and CO2apparent carboxylation efficiency (CCE) of the leaves of Castanopsis fargesii, Castanopsis sclerophylla and Cyclobalanopsis glauca basically. Under the condition of low nitrogen (N1), Amax, AQE, gm, Jmax, Vcmax, TPU and CCE of three kinds of plant leaves basically were significantly increased compared with control. Under the condition of high nitrogen (N2), the reaction is different compared with control to different plants. Gm, Jmax, Vcmax, TPU and CCE of Castanopsis fargesii leaves is reduced, but the Amax and AQE increased. All gas exchange indexes of Castanopsis sclerophylla and Cyclobalanopsis glauca were significantly increased, and the effect of N1is greater than N2to Castanopsis sclerophylla. In the joint action of warming and nitrogen (WN1and WN2), the response results of gas exchange indexes of three kinds of plant leaves were basically consistent with separate nitrogen compared with the control, and the effect of WN2is greater than WN1to Cyclobalanopsis glauca.(4) Warming caused a decreased trend of photochemical quenching (qP), non-photochemical quenching (NPQ) and electron transport rate (ETR) of Castanopsis fargesii, Castanopsis sclerophylla and Cyclobalanopsis glauca, and maximum photochemical efficiency (Fv/Fm) of Castanopsis fargesii and Castanopsis sclerophylla was reduced, but it is increased to Cyclobalanopsis glauca. Nitrogen (N1and N2) and the joint action of warming and nitrogen (WN1and WN2) can make Fv/Fm, qP and ETR of three kinds of plant leaves increased, but NPQ were decreaced, and the effect of N1is greater than the N2to Fv/Fm.(5) Warming caused the decrease of Chl a, Ch b, Ch1a+Chl b, soluble protein and soluble sugar content while the Ch1a/Chl b and the content of starch were increased. Under the condition of nitrogen addition(Nl and N2), the increase of Ch1a, Ch1b, Ch1a+Chl b content and the decrease of soluble sugar and starch content were significant. The soluble protein content of Castanopsis fargesii and Castanopsis sclerophylla seedling leaves increased while Cyclobalanopsis glauca seedling leaves showed the reverse changing trend. The interactive effects of warming and nitrogen addition(WN1and WN2) on photosynthetic physiological indexes of three seedlings were consistent with nitrogen fertilizer addition. There were somewhat differences between WN1and WN2among different tree species.(6) In the condition of warming, the LDMC was higher than that of the control area while the SLA and Nmass were opposite. The nitrogen addition led to the increase of Nmass, Narea and LDMC and the decrease of SLA. The SLA, Nmass, Narea and LDMC responses of Castanopsis fargesii, Castanopsis sclerophylla and Cyclobalanopsis glauca to warming and nitrogen interaction were different. The independent effect of warming and nitrogen on the SLA of Castanopsis fargesii was lower than that of their interactions, and the interactions on the SLA of Castanopsis sclerophylla were similar to the independent nitrogen, but there was no significant effects on the SLA of Cyclobalanopsis glauca. The response of three seedlings Nmass to the interaction of warming and nitrogen was basically consistent with separate nitrogen. The independent and interactive effects of warming and nitrogen to the Narea of Castanopsis sclerophylla were similar. The effects of warming and nitrogen interaction to Narea of Castanopsis fargesii was higher than that of the independent nitrogen, and the effect of WNl was lower than WN2. The effects of warming and nitrogen interaction to Narea of Cyclobalanopsis glauca was lower than that of the independent nitrogen, and the effect of WN1was lower than WN2. The interaction of warming and nitrogen(WN1and WN2) caused the LDMC increment of three seedling leaves.(7) Warming, nitrogen and combination of both can all caused the decrease of photosynthetic nitrogen use efficiency (PNUE) of three kinds of plant leaves significantly, and the effect of N2is greater than the Nl to separate nitrogen. |
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