抛荒土地不同处理及利用方式对喀斯特地区土壤微生物的影响

土壤微生物特性是土壤养分的储存库，土壤养分也影响土壤微生物活性，了解两者的相互作用机制对土地利用与管理提供理论依据，而喀斯特地区不同土地利用方式相关研究较少。基于喀斯特峰丛洼地火烧、刈割、刈割除根、封育、种植玉米、种植桂牧1号杂交象草6种坡面典型的土地利用方式的动态监测样地建设与调查，该文分析了不同土地利用方式下土壤微生物特性，揭示其与土壤养分相互作用机制。结果表明，不同土地利用方式对土壤养分的影响不同，土壤有机质（soil organic matter，SOM）、全氮（total nitrogen，TN）、全磷（total phosphorus，TP）、碱解氮（available nitrogen，AN）等沿封育、火烧、刈割、刈割除根、种植桂牧1号、种植玉米等土地利用方式的转变而减少；不同土地利用方式土壤微生物生物量各不同，土壤微生物量碳（microbial biomass carbon, MBC）：244.98～1 246.89 mg/kg、土壤微生物量氮（microbial biomass nitrogen，MBN）：35.44～274.69 mg/kg、土壤微生物量磷（microbial biomass phosphorus，MBP）：30.88～64.72 mg/kg，其中，种植玉米土壤微生物生物量均最低，其土壤质量退化现象严重；不同土地利用方式土壤微生物种群数量及组成影响不同，种植玉米和桂牧1号杂交象草细菌占绝对优势，而火烧、刈割、刈割除根及封育均以放线菌占绝对优势，真菌的比例很少；不同土地利用方式土壤微生物特性与土壤养分之间相互作用关系不同：火烧的土壤TP和MBP、全钾（total potassium，TK）与MBC、TN与放线菌作用最强且均呈正相关，刈割的土壤TN与MBC呈正相关，刈割除根的速效磷（available phosphorus，AP）与MBN正相关，封育的pH值与MBC、真菌负相关，种植玉米的TN、TK与MBP负相关，种植桂牧1号杂交象草的pH值与真菌负相关、与放线菌正相关；聚类分析可以将喀斯特峰丛洼地6种土地利用方式划分为4类，其中封育和火烧最好。

Effects of different treatment and utilization types after land leaving unused on soil microbial properties in Karst region

Abstract: Soil microbial properties are the reserve for soil nutrients, while soil nutrients would in reverse influence soil microbial activities. Therefore, gaining some knowledge of the interaction between them is urgent to help with land utilization and management. Depression between Karst hills is a typical landscape, which is located in the slope of the Karst region in southwest China, with a small environmental capacity resulting in a low ability in recovery. However, the related research studies under different land use types in the depression between Karst hills are rare. Based on the dynamic monitoring and investigation of six common land use types (i.e., burning, cutting, cutting plus with root removal, enclosure, maize plantation, and pasture of Guimu No. 1 (Pennisetum purpureum cv. Guimu-1) plantation) on a slope in a Karst region, this paper analyzed soil microbial properties, as well as the interactions between microbial properties and soil nutrients. The results showed that the status of soil nutrients differed among six land use types, and contents of soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and available nitrogen (AN) reduced along the conversion from enclosure, burning, cutting, cutting plus with root removal, pasture plantation, to maize plantation. Soil microbial biomass varied in the six land use types, microbial biomass carbon (MBC) ranging from 244.98 to 1 246.89 mg/kg, microbial biomass nitrogen (MBN) from 35.44 to 274.69 mg/kg, and microbial biomass phosphorus (MBP) from 30.88 to 64.72 mg/kg. Among them, soil microbial biomass was lowest under maize plantation and when it was indicated that the soil was in a severe degradation status. Soil microbial population and composition varied in the six land use types: bacterium were predominant under planting maize and pasture of Guimu No. 1, which may be due to fertilization making some improvement in soil physical properties and microbial zone; actinomycetes were predominant under burning, cutting, cutting plus with root removal, and enclosure, which suggests that under these four land use types, actinomycetes had stronger fertility, competition, and consumption over soil nutrients other than microbial populations; while fungi accounted for a small proportion in all the six land use types. The interaction between soil microorganisms and soil nutrients diversified in the different land use types. The interactions between soil TP and MBP, total potassium (TK) and MBC, TN and actinomycetes under burning, TN and MBC under cutting, available phosphorus (AP) and MBN under cutting plus with root removal, pH values and actinomycetes under pasture plantation were positively strongest. While the interaction between pH values and MBC and fungus under enclosure, TN, TK, and MBP under maize plantation, pH values and fungi under planting pasture of Guimu No.1 were negatively strongest. The six land use types in the Karst region could be clustered into four categories, and enclosure and burning were best. This would provide some basis for land utilization and management in the depression between Karst hills and even for the whole Karst region in the southwest of China.