Growth And Physiological Responses Of Cunninghamia Lanceolate Saplings To Soil Warming And Nitrogen Deposition

Global warming and nitrogen deposition are the two main characteristics of global climate change,both of which would substantially affect tree growth and development and thereby affect the function,productivity and biodiversity of terrestrial ecosystems.However,due to the lack of field research,the underlying ecophysiological mechanisms of tree responding to warming and nitrogen deposition remain unclear,which greatly limits our ability on accurate predicting of forest response to climate change.Cunninghamia lanceolata is an endemic fast-growing coniferous tree species to China,which has been widely in the subtropical China,with substantial values in both economy and ecosystems.In this study,3-year-old C.lanceolata saplings were selected for a manipulated field soil warming and nitrogen deposition experiment conducted in a state-owned forest farm in Chenda,Sanming.Four treatments were set to study the effects of soil warming and nitrogen deposition on growth and physiology of C.lanceolata saplings,which included the control treatment,the soil warming treatment（ambient+5°C）,the nitrogen addition treatment(ambient+40kg hm^-2a^-1),and the soil warming plus nitrogen addition treatment.Results indicated that:（1）The effects of soil warming on leaf gas exchange and non-structural carbohydrates（NSC）of C.lanceolata saplings were seasonally different.Soil warming promoted the gas exchange rates(A_sat+60.95%,g_s+37.34%;P<0.05)during the non-growing season（January）.Soil warming also regulated the aboveground growth by affecting the photosynthesis/respiration of C.lanceolata saplings and the NSC contents in conifers.It significantly promoted the growth in the fast growing season（May,October）and the non-growing season（January）（the growth rate of volume+27.49%-60.30%;P<0.05）,and without affecting or even inhibiting the growth in the slow growing season（July）.（2）Nitrogen deposition had no significant effect on gas exchange processes,NSC contents or nutrient contents of C.lanceolata saplings.However,the growth indexes of C.lanceolata saplings were significantly affected,and there were seasonal differences:in October,it showed a significant inhibitory effect（the growth rate of ground diameter-59.70%,the growth rate of volume-29.42%;P<0.05）.In other seasons,it produced a promoting effect（the growth rate of volume+19.05%-256.17%;P<0.05）.（3）The interaction of warming and nitrogen deposition significantly promoted the gas exchange processes of C.lanceolata saplings in non-growing season(A_sat+68.79%,A_max+56.77%,g_s+44.54%,E+40.90%;P<0.05).However,there were no significant differences in the growth and physiology if compared with the single factor effect.This effect may be only the cumulative effect of the two single factors.Overall,warming is the main factor.（4）The growth rate and physiological indexes of C.lanceolata saplings have seasonal changes.The growth and physiology were affected by warming in different seasons.In the low temperature seasons（May,October,January）,there was no effect or even inhibition in the high temperature summer（July）.The effect of nitrogen deposition on the growth of C.lanceolata saplings showed seasonal variation,which was inhibited in October and promoted in other seasons.However,there was no significant difference in the effects of the interaction between warming and nitrogen deposition on the growth of C.lanceolata saplings under different seasons.