喀斯特峰丛洼地不同退耕还林还草模式的土壤微生物特性

以坡耕地为对照,研究了喀斯特峰丛洼地任豆、香椿、板栗、柑橘、任豆+桂牧1号、桂牧1号和撂荒7种常见退耕还林还草模式下土壤微生物种群数量、微生物量碳氮磷及其分形特征和主要土壤酶活性特征。结果表明,不同退耕还林还草模式土壤微生物种群数量组成不同,除任豆模式外其他退耕还林还草模式均能提高土壤微生物总数量;不同退耕还林还草模式(除任豆模式外)土壤微生物量碳(MB_C)含量极显著增加,撂荒地最高,土壤微生物量氮(MB_N)含量变化范围不大,呈下降趋势,土壤微生物量磷(MB_P)含量的变异很大,香椿、板栗、撂荒和桂牧1号模式显著或极显著高于坡耕地;土壤MB_C与细菌数量的关系最相关(D=-4.07,R=0.81,P<0.01),其次为MB_C与放线菌数量(D=3.82,R=0.44,P<0.05),再次为MB_N与真菌数量(D=0.58,R=0.61,P<0.01),MB_C与真菌数量、MB_N与细菌、放线菌数量以及MB_P与细菌、真菌、放线菌数量之间不存在分形关系;不同退耕还林还草模式(除桂牧1号模式外)均显著或极显著增加了土壤蔗糖酶、脲酶和磷酸酶活性。总之,不同退耕还林还草模式均改善了土壤微生物特性,为喀斯特峰丛洼地脆弱生态系统恢复与重建提供了重要依据。

Soil microbial properties under different grain-for-green patterns in depressions between karst hills

Soil microbial life in vivo is a major component of soils throughout the whole process of soil development.The living environment for soil microorganisms is a very sensitive early-warning indicator of change in soil ecosystems.Using slope cropland as a contrast,we investigated the main soil microbial populations,microbial biomass carbon(MBC),nitrogen(MBN),and phosphorus(MBP) and their fractal characteristic model,as well as soil enzyme activities under seven grain-for-green patterns(cultivation of Zenia insignis,Toona sinensis,Castanea mollissima,Citrus reticulate,Zenia insignis + Guimu No.1 forage,Guimu No.1 forage,and abandoned cropland) in depressions between karst hills.The main soil microbial populations differed under different grain-for-green patterns.Actinomycetes were 71.28% to 96.44% of the microbial population in the slope cropland,Zenia insignis + Guimu No.1,Guimu No.1,and abandoned cropland.Differences in their populations covered up to three orders of magnitude.Bacteria dominated in the other four soils,being 55.24% to 71.79% of the microbial population,but fungi were less than 1%.Bacteria were highest under Guimu No.1 and abandoned cropland,and were lowest in the slope cropland.Fungi populations were in the order: abandoned cropland > Zenia insignis > Guimu No.1 > Citrus reticulate > Castanea mollissima > slope cropland > Toona sinensis > Zenia insignis + Guimu No.1,with significant differences between them.All the grain-for-green patterns except Zenia insignis increased total soil microbial populations.The differences between Guimu No.1,abandoned cropland,and Zenia insignis + Guimu No.1 were significant(P<0.05),and were significantly higher than the others.Microbial biomass carbon(MBC) in the all grain-for-green patterns except Zenia insignis was significantly higher than in the slope cropland,and was highest in the abandoned cropland.Microbial biomass nitrogen(MBN) varied within a small range,showing a downward trend.Differences in MBN between cultivation of Zenia insignis + Guimu,Citrus reticulata,Zenia insignis and slope cropland were significant(P<0.05).Microbial biomass phosphorus(MBP) varied widely in Toona sinensis,Castanea mollissima,abandoned cropland and Guimu No.1 but was significantly higher than in slope cropland.MBC was well correlated with bacteria(D=-4.07,R=0.81,P<0.01),followed by the correlation between MBC and actinomycetes(D=3.82,R=0.44,P<0.05) and that between MBN and fungi(D=0.58,R=0.61,P<0.01).However,there was no fractal relationship between the other microbial biomass and microbial populations.Compared with the slope cropland,all the grain-for-green patterns except Guimu No.1 forage significantly increased the activities of soil sucrase,urease and phosphatase,suggesting an increase in carbon and nitrogen cycling.Under different grain-for-green patterns,the activity of soil sucrase was highest under Toona sinensis,reaching(29.10±7.73) mg g-1 d-1,while the activity of soil urease was highest in the abandoned cropland,reaching(540.7±34.77) μg g-1 d-1,and the activity of soil phosphatase was highest under Castanea mollissima,reaching(991.1±76.28) μg g-1 d-1.All the grain-for-green patterns improved soil microbial properties,suggesting important benefits arising from fragile ecosystem restoration and reconstruction in depressions between karst hills.