黄土丘陵沟壑区典型人工林植物-凋落物-土壤化学计量特征及互作关系

Plant-litter-soil stoichiometric characteristics of typical plantation forests and their interaction in loess hilly and gully region

人工造林是黄土丘陵沟壑区治理水土流失和恢复退化土地的重要措施,而人工林植物-凋落物-土壤化学计量特征是影响植被重建的关键限制因素。以山西省静乐县退耕还林示范区油松纯林、油松+柠条锦鸡儿混交林、华北落叶松纯林和华北落叶松+柠条锦鸡儿混交林为研究对象,分析乔木层各器官(叶、枝、干、根)、凋落物和土壤(土层深度0~30 cm)碳(C)、氮(N)、磷(P)化学计量特征及其相互关系,为黄土高原植被重建模式提供科学支撑。结果表明:1)4种人工林乔木C、N、P质量分数变化均呈叶>枝>干>根,华北落叶松+柠条锦鸡儿混交林叶片N质量分数显著增加3.18 g/kg,叶片C∶N和C∶P降低,且区域乔木生长表现出P限制。2)华北落叶松+柠条锦鸡儿混交林凋落物N质量分数显著增加1.35 g/kg,同时凋落物C∶N降低,油松+柠条锦鸡儿混交林凋落物化学计量无显著变化。3)4种人工林土壤C、P质量分数随土层深度增加而减少,其中0~10 cm土层C、P质量分数显著高于其他土层,分别是8.92和0.31 g/kg。华北落叶松+柠条锦鸡儿各土层C质量分数升高,其中0~10 cm土层增加最明显,显著增加49.15%。4)Pearson分析和结构方程模型表明,凋落物层N质量分数直接对土壤层C∶N产生影响,进而影响乔木层养分特征,而乔木层C∶N又正向影响凋落物层。混交可有效改善研究区人工林养分状况,且华北落叶松+柠条锦鸡儿混交林最优,研究结果可为该区植被恢复提供理论依据。

[Background]The ecological environment of the Loess Plateau is fragile and its soil fertility is quite low,the“Grain for Green Project”is a key measure for soil and water conservation and restoration of degraded land in this region.The study of the plant-litter-soil stoichiometric characteristics of typical plantation forests and their interrelationships may reveal the limiting elements of vegetation growth.Comparing differences in ecological stoichiometric characteristics between pure and mixed forests can help to find out which of the two silvicultural modes is the better choice in the process of vegetation restoration in the region and provide scientific support for the reconstruction mode of vegetation on the Loess Plateau.[Methods]We selected four types of plantation forests(pure Pinus tabuliformis forest,P.tabuliformis+Caragana korshinskii mixed forest,pure Larix principis-rupprechtii forest,and L.principis-rupprechtii+C.korshinskii mixed forest)in Jingle county,Shanxi province,and set up 3 sampling sites in each forest.We collected tree layer organs(leaves,branches,stems and roots),litter,and soil(0-30 cm)samples and determined the C,N and P content using potassium dichromate oxidative heating and AA3 continuous flow analyzer.We used ANOVA,correlation analysis and structure equation modelling to analyze the ecological stoichiometric characteristics and their interactions among tree layer organs(leaves,branches,stems and roots),litter,and soil(0-30 cm).[Results]1)The changes of C,N and P contents of trees in 4 plantation forests were in the form of leaf>branch>stem>root.Only L.principis-rupprechtii leaf N content significantly increased by 3.18 g/kg after mixing,leaf C∶N and C∶P decreased,and regional tree growth showed P limitation.2)Only L.principis-rupprechtii litter N content increased significantly by 1.35 g/kg after mixing,while litter C∶N was reduced,and there were no significant changes in litter of P.tabuliformis forests.3)The C and P contents of plantation forest soil both decreased with increasing soil depth,in which the C and P contents of 0-10 cm soil layer were significantly higher than those of other soil layers,which were 8.92 and 0.31 g/kg,respectively.Mixing increased the C contents of each soil layer of L.principis-rupprechtii,in which the 0-10 cm soil layer increased the most significantly,with a significant increase of 49.15%.4)Pearson and SEM analyses showed that the N contents of the litter layer directly influenced the soil layer C∶N,which in turn influenced the nutrient pattern of the arbor layer,which in turn positively influenced the litter layer.[Conclusions]Mixing can effectively improve the nutrient status of plantation forests.However,the introduction of the same hybrid shrubs varied significantly among tree species,while the L.principis-rupprechtii+C.korshinskii mixed forest is optimal.In the future,mixed afforestation should be preferred for vegetation restoration in loess hilly and gully region.