黄土丘陵区典型退耕恢复植被土壤生态化学计量特征

Characteristics of soil ecological stoichiometry in typical fallow-restored vegetation in the loess hilly areas

为探究不同植被土壤碳(C)、氮(N)、磷(P)化学计量特征及其影响因素,以黄土丘陵区油松、刺槐、沙棘和草地4种典型退耕恢复植被0~100 cm土壤为研究对象,分析不同植被土壤有机碳(SOC)、全氮(STN)、全磷(STP)含量及其化学计量特征。结果表明:(1)不同恢复植被对土壤养分含量有显著影响,刺槐的SOC、STN最高,油松的SOC、STN最低,STP表现为草地>刺槐>油松>沙棘。(2)不同恢复植被土壤养分具有“表聚性”,随土层深度增加,SOC和STN含量呈下降趋势,而STP的变异性较弱。特别是刺槐的SOC和STN在60~100 cm呈增加趋势。(3)不同恢复植被土壤SOC:STN(C:N)、SOC:STP(C:P)差异不显著(P>0.05),刺槐的土壤STN:STP(N:P)显著高于其他植被类型(P<0.05),土壤C:N、C:P、N:P均低于全球及全国平均水平,研究区有机质的分解速率较快,P的有效性高,植被生长主要受N元素限制。(4)研究区土壤C:N、C:P和N:P主要受SOC和STN影响;土壤养分与土壤含水量(SWC)和土壤容重(BD)呈负相关,与土壤粉粒(slit)和黏粒(clay)含量呈正相关,STP对土壤细颗粒的响应强度大于SOC和STN。研究区土壤化学计量在不同退耕恢复植被间差异显著,其中刺槐的土壤养分含量较其他植被类型更好,可为该地区植被恢复工作进一步开展提供参考。

The hilly and gully areas of China’s Loess Plateau are an arid and semi-arid region characterized by fragile ecosystems and harsh climates.A series of implemented ecological restoration projects,such as the“Grain for Green Project”,have greatly improved the local environments.To understand local nutrient cycling following vegetation restoration,it is important to study the content and ecological stoichiometry of soil carbon(C),nitrogen(N),and phosphorus(P)in different vegetation types and determine their driving factors.In our study,soil samples were collected in 0-100 cm layers from Pinus tabulaeformis,Robinia pseudoacacia,Hippophae rhamnoides,and grassland.The content and ecological stoichiometry of soil organic carbon(SOC),total nitrogen(STN),and total phosphorus(STP)were analyzed.The effects of soil water content(SWC),soil bulk density(BD),and soil texture on the stoichiometric characteristics were also analyzed.The results showed that:(1)Vegetation types had significant effects on the variations in soil nutrient contents.More specifically,Robinia pseudoacacia had the highest SOC and STN contents,whereas Pinus tabulaeformis had the lowest SOC and STN contents.STP content levels can be arranged in the following order:grassland>Robinia pseudoacacia>Pinus tabulaeformis>Hippophae rhamnoides.(2)Substantial soil nutrients accumulated on the soil surface among different vegetation types.With increasing soil depth,SOC and STN showed similar downward trends,whereas the variability of STP was comparatively weak.In particular,SOC and STN in Robinia pseudoacacia showed increases from 60-100 cm.(3)The variations in soil C:N and C:P among different vegetation types were not significant.Robinia pseudoacacia had significantly higher N:P than Pinus tabulaeformis,Hippophae rhamnoides,and grassland.In our study area,C:N,C:P and N:P were lower than global and national average levels,which indicated that the decomposition rate of organic matter in the soil was slow;the effectiveness of phosphorus was high,and vegetation growth was primarily limited by soil nitrogen.(4)C:N was mainly affected by SOC,whereas C:P and N:P were mainly affected by SOC and STN.Overall,soil nutrients were negatively correlated with SWC and BD but positively correlated with soil silt and clay content.The response of STP to soil fine particles was greater than that of SOC and STN.In our study,significant differences in soil stoichiometry characteristics were detected in the 0-100 cm soil layers among different fallow-restored vegetation types.Most notably,Robinia pseudoacacia had higher soil nutrients than other vegetation types.The results of the study can provide guidance for further revegetation restoration work in loess hilly areas.