Ecological Stoichiometric Characteristics of Carbon,Nitrogen and Phosphorus in Leaf-Litter-Soil System of Picea Crassifolia Forest in the Qilian Mountains
Ecological stoichiometric ratios of C,N and P are important indices characterizing process and functions of a forest ecosystem. Picea crassifolia is an important constructive or dominant species of the subalpine mountain forest vegetation in the Qilian Mountains,and its forest is a typical kind of water conservancy forest. Based on field survey and laboratory analysis,the objective of this study with the Picea crassifolia forest in the Pailugou watershed of the Qilian Mountains selected as subject,the leaf、litters and soil at different elevation gradient(2 900~3 300 m)were selected to measure their organic carbon (C),total nitrogen(N)and total phosphorous(P)contents,carried out on ecological stoichiometric characteristics of carbon,nitrogen and phosphate in the leaf-litters-soil systems of the Picea crassifolia forest different in elevation gradient and their correlations using the principles and methodology of ecological stoichiometry. Results show that carbon,nitrogen and phosphorus ecological stoichiometric ratios of Picea crassifolia forest in elevation gradient indicate that different variation laws and significance of difference with altitude increasing. Among them,C∶N ratio in leaf and soil of Picea crassifolia forest increased gradually, C∶N ratio in litter increased gradually with the increase of altitude and then decreased at 3 300 m. C∶P ratio in leaf first increase and then decrease,at an altitude of 2 900 m was significantly lower than other altitude C∶P(p < 0.05). C∶P ratio in litter has no obvious change. C∶P ratio in soil first increases and then decreases,only at an altitude of 2 900 m was significantly lower than other altitude C∶P(p < 0.05). N∶P ratio in leaf and soil first increases and then decreases,the N∶P ratio of the low altitude(2 900~3 100 m) was significantly higher than that of the high altitude(3 200~3 300 m)(p < 0.05). In this systems along the elevation gradient,C∶N ratio in leaf,litters and soil varied in the range of 22.95~36.72,21.41~41.61 and 12.41~20.70,respectively,and in terms of average of the ratios,the three components of the system followed an order of litters > leaf > soil;C∶P ratio did in the range of 510.2~739.8,398.6~698.1 and 134.1~219.7,respectively,and N∶P ratio did in the range of 18.13~26.86,6.71~26.28 and 7.96~16.56,respectively,and in terms of average of either N∶P or C∶N ratio,the three followed an order of leaf > litters > soil. All the ratios in all the three components varied sharply with rising altitude,except for soil C:N ratio,which did not as much(p>0.05). Three components were significantly positively related(p>0.05)to each other in C∶N ratio,while both leaf and soil were negatively related to litters in C∶P ratio(p>0.05). And the relationships of leaf with soil C∶P ratio and with litters and soil in N∶P ratio were not obvious(p>0.05). The findings of the study help further understand interactions between carbon,nitrogen and phosphorus in the three components of the Picea crassifolia forest system and their laws and mechanisms.
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