黄土丘陵区退耕撂荒地土壤微生物量演变过程

 【目的】土壤微生物量是表征土壤生态系统中物质和能量流动的重要参数，研究黄土丘陵区坡耕地撂荒后微生物量及其活性的变化过程对认识该地区生态恢复过程中土壤质量的演变及其效果评价具有重要意义。【方法】采用时空互代法，以典型侵蚀环境纸坊沟流域生态恢复过程中不同年限的撂荒地为研究对象，选取坡耕地和天然侧柏林为参照，通过室内测试分析，并运用统计和相关分析等方法，研究坡耕地撂荒后土壤微生物量、呼吸强度、代谢商（qCO2）及土壤理化性质的演变特征。【结果】侵蚀环境下的坡耕地土壤微生物量含量偏低，土壤理化性质较差，撂荒后理化性质得到显著改善，微生物量碳（Cmic）在撂荒1 a后显著增大，前7 a较为剧烈，增幅较大，随后呈波动式上升，50 a达到最大值;微生物量氮（Nmic）在撂荒初期增长缓慢，40 a时才达到显著水平，微生物量磷（Pmic）在撂荒初期显著降低，５～7ａ达到最低值，随后逐渐上升，20～25 a时和坡耕地没有显著差异，50 a时达到最大值。撂荒50 a时土壤Cmic、Nmic和Pmic分别较坡耕地增加166%、146%和52%，但仅为侧柏林的43.42%、45.06%和51.47%。呼吸强度在撂荒初期迅速增加，随后趋于稳定，与侧柏林差异不显著。qCO2在撂荒初期显著升高，随后波动式降低，50 a后达到最低值，仍显著高于天然侧柏林。相关性分析显示，微生物量碳、氮、磷、qCO2与土壤养分显著相关，Cmic、Nmic、Pmic、有机碳、全氮、碱解氮和速效钾随撂荒年限呈一次线性增长。【结论】侵蚀环境下的黄土丘陵区坡耕地撂荒后可在一定程度上通过生物的自肥作用恢复土壤肥力和增加微生物量，但恢复到破坏前该地区顶级群落时的土壤微生物量和理化指标的过程相对于林地开垦后的土壤肥力退化要漫长的多。

Dynamics of Soil Microbial Biomass on the Abandoned Cropland in Loess Hilly Area

【Objective】 Soil microbial biomass is an important parameter representing material cycle and energy flow in soil ecosystem. Study on dynamics of soil microbial biomass in the abandoned cropland in loess hilly area so as to understand the change and effect evaluation during process of ecological restoration is of great importance. 【Method】 The research was carried out in Zhifanggou small watershed of typical erosive environment, the croplands abandoned in different times were selected as objects, interchangeablely spece-time method was adopted and slope croplands and the plots with Platycladus orientailis were used as contrasts. Several indexes were analyzed such as soil microbial biomass, respiration and metabolic quotient (qCO2) and involvement characteristics of physical and chemical properties. 【Result】 The research indicates that the content of microbial biomass and physical and chemical properties under erosive slope cropland was low. However, there was a significant improvement on physical and chemical properties after abandoning. Soil microbial biomass C increased dramatically one year abandoned later, rose sharply in the first 7 years of abandonment, then took on wavelike rising and reached maximum 50 years later. Soil microbial biomass N increased slowly at early stage and reached significant level after 40 years. Soil microbial biomass P dropped significantly at early abandoned stage, reached minimum 5-7 years later and then rose gradually, after 20-25 years, there was no significant difference compared with the slope cropland but reached maximum 50 years later. After abandoning 50 years, soil microbial biomass C, N and P increased by 166%, 146%, and 52%, respectively, compared with slope cropland, which were only 43.42%, 45.06%, and 51.47% of that in soil with Platycladus orientailis. Respiration increased sharply at early abandoned stage and tended to be stable, which did not differ significantly compared with Platycladus orientailis. Metabolic quotient (qCO2) increased drastically at early abandoned stage, then took on wavelike dropping and dropped to minimum which was also higher greatly than that of Platycladus orientailis. Correlation analysis showed that there was a significant relationship between soil microbial biomass C, N, P and soil nutrition. Soil microbial biomass C, N, P, organic C, total N, available N and available K presented a linear growth. 【Conclusion】 The results suggest that it is impossible to recovery soil fertility and soil microbial biomass by natural vegetation recovery under erosive slope cropland in the loess hilly area, but much longer time, compared with degradation of soil fertility after deforestation, is required to reach to the climax before vegetation destruction.