不同退化程度人工梭梭林对土壤理化性质与生物学特性的影响

根据植被数据将民勤荒漠绿洲过渡带12个退化人工梭梭林样点采用聚类分析的方法划分为4个退化程度,研究了不同退化程度人工梭梭林对土壤理化性质与生物学特性的影响,结果表明,1)人工梭梭林退化对土壤容重、全盐含量与阳离子代换量影响不显著,对有机质与pH影响显著;随着土层深度增加以及退化程度加剧,有机质含量降低,pH值变化复杂。2)三类微生物数量与微生物总数总体随着土层深度增加而降低,0~5 cm土层中细菌数量占极大优势,其他土层上细菌数量与放线菌数量相当,各土层中真菌数量极少。随着退化程度的加剧,真菌数量无明显变化;0~5 cm与5~10 cm土层的细菌数量、放线菌数量与微生物总数均显著减少,10~20 cm土层无显著变化;0~5 cm土层细菌和放线菌比例变化复杂,而其他土层无显著变化。3)4种酶的活性总体上随土层加深而降低,0~5 cm土层酶活性随退化程度加剧而降低,而5~10 cm与10~20 cm土层无显著变化。人工梭梭林退化对土壤过氧化氢酶、脲酶与蛋白酶活性的影响大于对蔗糖酶活性的影响,过氧化氢酶、脲酶与蛋白酶的敏感性强于蔗糖酶。4)土壤理化性质、微生物数量以及酶活性间相关性总体较强,但理化性质间相关性较弱,容重、放线菌数量同其他指标相关性较弱。退化人工梭梭林的土壤肥力、生物学性质等已经发生衰减,其恢复需要土壤的综合改良。

Physicochemical and biological properties of soil in Haloxylon ammodendron plantations with different states of degradation

Haloxylon ammodendron was introduced to the Minqin region from Xinjiang province in the 1960s.It became the primary species for windbreak and sand stabilization planting.The area in H.ammodendron plantation forest in Minqin County is about 3.5 × 104 ha,51.5％ of the total plantation forest area.Degradation H.am modendron forest had been observed since the 1970s,seriously threatening the survival and development of the Minqin Oasis.The aim of this study was to investigate the physicochemical and biological properties of soil under H.ammodendron forests with different degradation states in the Minqin oasis-desert ecotone,Gansu.12 plots were selected in the degradation gradient;soil samples were collected from 0-5 cm,5-10 cm,10-20 cm depths from a representative area in each plot.Each plot was assigned (using vegetation indices) to one of four degradation grades (no degradation,light degradation,moderate degradation and severe degradation) using hierarchical cluster analysis.The soil physicochemical properties,microbial number,and enzyme activities were analysed.The effect of degradation of H.ammodendron forest on soil bulk density,total salt content,cation exchange capacity was not obvious,but soil organic gradually decreased and pH changed complexly with increasing degradation and increasing of soil depth.The total number of microbes and microbe species decreased with increasing soil depth;numbers of bacteria were much higher than actinomycetes in 0-5 cm soil depth,but they were similar in deeper soil layers.Fungi were not prevalent in any soil layers.Increased degradation was not associated with changes in the number of fungi observed.Enzyme activity decreased with increasing soil depth with increased degradation.The impact of degradation of H.ammodendron forest on protease activity,catalase activity,urease activity was greater than for invertase activity,the former showed greater sensitivity to changes in resources and environment.There were strong correlations among soil physicochemical properties,number of soil microbes and soil enzyme activities,but the correlation among soil physicochemical indicators,between soil bulk density,number of actinomycetes and other indicators were not significant.Soil fertility and biological properties in degraded H.ammodendron plantations have declined;restoration of the soil is necessary for restoration of these forests.