Response Of Carbon Storage And Distribution In Pinus Koraiensis And Fraxinus Mandshurica To Water Stress And Nitrogen Addition

Nitrogen deposition and warming-drying are the main ecological issues in Northeast China.How it will affect forest ecosystems has always been one of the cores of ecological research.In this study,Pinus koraiensis and Fraxinus mandshurica,two domain and key tree species in temperate broad-leaved Korean pine forest in Northeast China,were chosen as the research objects.And the dynamic changes of leaf,stem,root biomass of those seedlings under nitrogen(N)addition and water stress treatments were analyzed to explore the response of two trees species to climate warming-drying.Additionally,the storage and consumption of non-structural carbohydrates(NSC)in organs of the seedlings were also detected.The main conclusions are as follows:(1)The responses of seedlings growth of P.koraiensis and F.mandshurica to nitrogen addition and water stress were significantly different.Comparatively,P.koraiensis is more sensitive to water stress.In the early stage(in 10 weeks)of water stress treatment,the biomass of leaves of P.koraiensis significantly decreased while the root biomass increased.N addition only significantly reduced the root and total biomass of P.koraiensis when water stress occurred.While the response of F.mandshurica was more sensitive to N addition.N addition rapidly increased the stem,root and total biomass of F.mandshurica.Only sustained water stress could significantly affect the stem,root and total biomass of F.mandshurica.This study also found that under the circumstances of continuous water stress and N addition,the biomass proportions of leaves and roots to whole seedling,and the ratio of aboveground to underground biomass of both tree species tended to maintain a constant value,which might indicate that both of them had strong self-regulation ability.The results suggest that when drought occurred in the future,P.koraiensis will adopt a "positive" adjustment strategy,while F.mandshurica will adopt a "passive" response,therefore that the survival and adaptability of P.koraiensis will be stronger.But F.mandshurica will benefit more than P.koraiensis when N deposition occurred.(2)P.koraiensis and F.mandshurica both tend to maintain a stable biomass ratio of leaves and roots and aboveground and underground biomass ratio under continuous water stress and N addition treatment,indicating that both species have strong self-regulation ability.The above results show that under the future drought conditions,of P.koraiensis adopts as an " active" adjustment strategy,while F.mandshurica adopts as a "passive" response,thus P.koraiensis may have stronger survival and adaptability compared with others.However,F.mandshurica will benefit more in the environment where N deposition increases.(3)The response strategies of NSC in different organs of P.koraiensis and F.mandshurica to water stress were different.P.koraiensis responded to stress by converting starch concentration from organs to soluble sugar concentration during the wintering period(S3).At this stage,starch concentration in all organs of P.koraiensis decreased significantly,soluble sugar concentration increased significantly,and total NSC concentration did not change much.During the growing season,water stress significantly reduced NSCs of P.koraiensis,and high nitrogen addition reduced starch and NSC concentrations of leaves,and increased NSC concentrations of roots.F.mandshurica responded to stress by consuming starch from stems and roots during overwintering.During the wintering period,the starch concentration of stems and roots decreased significantly,while the total concentration of soluble sugar and NSC did not change much.During the growing season,the total concentration of soluble sugar and NSC in leaves decreased under water stress.The concentration of NSCs in different organs was significantly decreased by high nitrogen addition.