| The stoichiometry characteristics of plant ecology have an important indicative effect on the health of forest ecosystems,and the study of ecostoichiometry characteristics is conducive to exploring the cycling and equilibrium mechanism of C,N,P and other elements in plants.In mountain forest ecosystems,environmental heterogeneity in temperature,humidity,and soil fertility caused by elevation gradients can affect differences in tree survival strategies.Uncertainty also exists in the trade-offs of resource allocation based on ecological stoichiometry of carbon(C),nitrogen(N)and phosphorus(P)in different organs of trees under the elevation gradient,and their drivers need to be further investigated.In this paper,a typical coniferous species sensitive to climate of Picea crassifolia(Qinghai spruce)in Qilian Mountains was selected as the research object,and three sampling gradients were set at low(2600m),middle(2900m)and high(3200m)elevations.The ecological stoichiometric characteristics of Qinghai spruce whole plants,leaves,branches,trunks,thick and fine roots at different elevations and their environmental drivers were analyzed by applying relative importance analysis,redundancy analysis and variance partitioning analysis.The aim is to analyze the ecological stoichiometric patterns of Qinghai spruce and its resource allocation trade-offs under different elevation gradients from the perspective of changes in plant nutrient distribution in whole plants and organs,and to provide basic data and important references for the scientific management of dominant coniferous forests in Qilian Mountains.The main results of the study are as follows:(1)Soil water content and soil N:P showed a significant increase trend(P<0.05)from low,middle to high elevation,while soil bulk density,soil pH and soil P content showed a gradual decreasing trend.Soil stoichiometric characteristics were closely related to soil environmental factors,and showed variability at different elevations.At low elevation,soil C and C:P were positively correlated with soil pH(P<0.05).At middle elevation,soil C content was positively correlated with soil water content(P<0.05)but it was negatively correlated with soil pH(P<0.05),and soil N:P was positively correlated with soil pH(P<0.05).At high elevation,soil C:P and N:P showed a significant negative correlation with soil water content(P<0.05),soil P content was negatively correlated with soil bulk density(P<0.05),but soil C:P and N:P were positively correlated with soil bulk density(P<0.05).Soil P content and C:P positively correlated with soil pH(P<0.05).(2)Qinghai spruce can adapt to heterogeneous environment by changing resource allocation strategies.From low to high elevation,the whole plant N content,C:P,and N:P of Qinghai spruce increased significantly(P<0.05),while C content and P content showed a trend of decreasing and then increasing.At the same time,Qinghai spruce adapted to the stressful environment by changing the nutrient partitioning pattern among different organs,with N and P invested mainly in leaves and branches(low elevation:39%,36%,middle elevation: 35%,31%,high elevation: 36%,31%)and C invested mainly in the trunks(low elevation: 21%,middle elevation: 21%,high elevation: 21%)at each elevation.(3)There was a significant correlation between the C,N,and P contents and their ratios in the whole plant and each organ of Qinghai spruce in the three elevations.The C:N,C:P and N:P of different organs of Qinghai spruce showed strong correlations at all elevations.However,the correlations were different at different elevations,specifically,at low elevation,the N content and C:N of Qinghai spruce whole plants and organs showed significant negative correlations with P content and C:P(P<0.05).At middle elevation,there was a significant positive correlation(P<0.05)between N and P for the whole plant and all organs of Qinghai spruce.At high elevation,there was a significant positive correlation between C and N in the whole plant of Qinghai spruce and in all organs except branches(P<0.05).(4)The results showed that soil nutrients,water content,pH and bulk density were the main drivers for the distribution of ecological stoichiometric characteristics in the whole plant and organs of Qinghai spruce.At low and middle elevations,soil water content and soil pH were the most important factors affecting the variation of stoichiometric characteristics of the whole plant and different organs of Qinghai spruce.At high elevations,soil pH,soil N content and bulk density were the most important environmental driving forces for the spatial variation of the stoichiometric characteristics of Qinghai spruce whole plant and different organs,respectively.At the whole elevation scale,the interaction of climatic and soil factors was the main driver of ecological stoichiometry changes in Qinghai spruce whole plants and organs,with contributions of 56.79%(whole plants),42.17%(leaves),24.63%(branches),66.83%(trunks),43.52%(thick roots),and 52.60%(fine roots),respectively. |
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