Characteristics Of Leaf-litter-soil Carbon And Nitrogen Isotopes And Their Nutrients In Cunninghamia Lanceolata Plantations Across An Altitudes Gradient

In order to to assess the impact of global climate change on plant functional traits in forest ecosystems,the Cunninghamia lanceolata plantation forests across an altitude gradient?first-generation forests:750 m,850 m,1000 m,1150 m;second-generation forests 850 m,1000m,1150 m?were selected in Mazongling Forest Farm in Jinzhai County,Anhui Province.The leaf-litter-soil carbon and nitrogen isotopes,nutrient contents,and their physical and chemical properties of Cunninghamia lanceolata stands were measured,and the controlling effects of leaf-litter-soil factors on the distribution of different forms of carbon and nitrogen isotopes were analysed.The results obtained are as follows.?1?Carbon and nitrogen isotopes in leaves(?¹³C,?¹⁵N)The change of altitude significantly affected the?¹³C content of leaves?P<0.05?.The response of the leaves of the first-generation forest to the altitude is more obvious.As the altitude increased,the?¹³C of the leaves showed a wave-like downward trend.Among the leaf-litter-soil stand factors,the regression analysis screening out chlorophyll b?Chl_b?was the main controlling factor affecting foliar?¹³C.The response of the 1-year-old leaves of the second-generation forest to altitude is more obvious.As the altitude increases,the foliar?¹³C first increased and then decreased,reaching a maximum at 1000 m,and the leaf thickness?LT?was the main control of the foliar?¹³C in the second-generation forest.The change in altitude significantly changed the foliar?¹⁵N content in the first-generation forest?P<0.05?.With the increase of the altitude,the?¹⁵N first decreased,then increased,and reached the lowest value at 850 m.The regression analysis showed that the soil moisture was the main controlling factor.There is no significant difference in the foliar?¹⁵N in the second-generation forest over the altitude gradient?P>0.05?.?2?Other factors of leavesIn the first-generation forest,only foliar total phosphorus?TP?,total nitrogen/total phosphorus?TN/TP?,and leaf dry matter content?LDMC?had significant differences across the altitude gradient?P<0.05?,and other factors were not significantly different.The principal component analysis?PCA?showed that the main difference in leaf factor was between 850 m and 1150 m.In the second-generation forest,changes in altitude mainly altered the foliar total nitrogen?TN?contents,total carbon/total nitrogen?TC/TN?,and total nitrogen/total phosphorus?TN/TP??P<0.05?.PCA analysis indicated that the difference in leaf factors in the second-generation stands was mainly between altitude at 1000 m and 1150 m.?3?Carbon and nitrogen isotopes of litterAltitude changes did not significantly change the carbon and nitrogen isotopes of litter?P>0.05?,but regression analysis identified that total carbon?TC?and soil p H were the main factors influencing?¹³C in the litter of the first-generation forests,and the main effect of?¹³C content in the litter in the second-generation forests were litter?¹⁵N and foliar TN;while the foliar TP was the main factor influencing litter?¹⁵N for the first-generation forests,and total leaf chlorophyll content(Chl_a+b)was the main factor influencing litter?¹⁵N in the second-generation forests.?4?Other factors of litterThe litter TN and TP were significantly different over the altitudes in the first-generation forests,while there were no significant differences in the second-generation forests.According to the PCA analysis,the difference between the first-generation forests was mainly between750 m and the other three altitudes,and the main differences in the litter nutrients in the second-generation forests were between altitudes at 1000 m and 850 m.?5?Soil carbon and nitrogen isotopesAltitude had a significant effect on soil carbon and nitrogen isotopes?P<0.05?.In first-generation of forests,as the altitude increased,soil carbon and nitrogen isotopes showed decrease first and then increase,the lowest value was appeared at 850 m.The regression analysis identified that the main factors affecting soil?¹³C were leaf LDMC and soil temperature,and the main factor affecting soil?¹⁵N was soil TN/TP.In the second-generation forests,carbon and nitrogen isotopes showed all increase with increasing altitude.The main factor affecting soil?¹³C was soil temperature,and the main factor affecting soil?¹⁵N was soil moisture.?6?Other soil factorsAltitude changes significantly altered soil nutrients and soil physicochemical properties?P<0.05?.Through PCA,the differences between soil factors in the first-generation forests were mainly between the two altitudes at 850 m and 1150 m.The difference in altitudes was mainly between 850 m and 1150 m in second-generation forests.