不同恢复年限刺槐林土壤碳、氮、磷含量及其生态化学计量特征

地处西秦岭山地的甘肃天水吕二沟小流域土壤侵蚀问题严重,上世纪五六十年代开始,当地政府在研究区实施了多年的生态恢复措施以保持水土,但目前尚未有植被恢复对土壤生态计量特征的系统调查。分析不同林龄人工林土壤碳、氮、磷含量及其生态化学计量特征可在一定程度上揭示土壤养分的限制情况。选取黄土丘陵沟壑区不同生长年限(5、20、40、56 a)的人工刺槐林(Robinia pseudoacacia L.)为研究对象,以荒地为对照,探讨不同恢复年限人工刺槐林0-100 cm土壤碳、氮、磷含量及其生态化学计量特征。结果表明,5年恢复期后,随林龄的增加,土壤有机碳、全氮、C:P比和N:P比均显著增加(P<0.05),平均值分别为5.09 g·kg^-1、0.66 g·kg^-1、9.02、1.18,均低于中国土壤生态计量平均水平;土壤含水率下降,土壤干化明显;土壤容重和C:N比的变化不大(P>0.05);全磷无明显变化规律,均值为0.56 g·kg^-1,接近中国土壤的平均值。长期的植被恢复有利于增加土壤有机碳和全氮含量,但仍需要更长期的人工刺槐林种植来提高土壤肥力。研究区人工恢复水保林水分亏空是限制刺槐生长的重要因素,氮是流域土壤的主要限制性营养元素。本研究有助于当地政府调整植树造林措施、保持土壤质量稳步提升、预防人工林地退化,为人工林管理提供参考。

Soil Carbon,Nitrogen,Phosphorus Content and Their Ecological Stoichiometric Characteristics in Different Plantation Ages

Soil erosion is a serious problem in Lvergou watershed of Tianshui city,Gansu province.Since 1950 s,government has implemented ecological restoration measures to preserve soil and water.However,there is several investigations on soil ecological stoichiometric characteristics during vegetation restoration,which reveal the soil nutrient limitation.So the research object is the artificial Robinia Pseudoacacia forests for different growth year(5 years,20 years,40 years and 56 years)and wasteland as a control,to discuss soil carbon,nitrogen,phosphorus and its ecological stoichiometric characteristics in 0-100 cm soil.The results showed that SOC,TN,C:P ratio and N:P ratio increased significantly with the increase of forest age(P<0.05).The mean values were 5.09 g·kg^-1,0.66 g·kg^-1,9.02 and 1.18,which were lower than Chinese average level of SOC,TN,C:P ratio and N:P ratio,respectively.Soil water content decreased significantly and soil bulk density and C:N ratio changed moderatly(P>0.05).The mean value of total phosphorus content is 0.56 g·kg^-1,which is equal to Chinese average value.Long-term vegetation restoration is beneficial to increase SOC and TN content,but it is still needed to improve soil fertility.The soil water content is an important factor limiting the growth of Robinia Pseudoacacia and nitrogen is the main limiting nutrient element in the study area.This study is helpful for governments to adjust afforestation measures,keep soil quality improving,prevent degradation of artificial forestland,and provide reference for plantation management.