喀斯特峰丛洼地土壤剖面微生物特性对植被和坡位的响应

选取广西环江县喀斯特峰丛洼地:草丛(T)、灌丛(S)、原生林(PF)(中坡位)不同植被类型,原生林上、中、下不同坡位,按土壤发生层采集淋溶层(A层,0-10 cm)、过渡层(AB层,20-30 cm,草丛和灌丛；30-50 cm,原生林)、淀积层(B层,70-100cm)样品,研究土壤微生物量碳、氮(Soil microbial biomass carbon (SMBC)、soil microbial biomass nitrogen (SMBN))、微生物碳熵、氮熵(ratio of SMBC to soil organic carbon (qMBC)、ratio of SMBN to soil total nitrogen (qMBN))、土壤基础呼吸(soil basic respiration (SBR))以及代谢熵(microbial metabolic quotient(qCO2))的剖面分异特征及其影响因素.结果表明,植被、土层深度显著影响土壤微生物量及基础呼吸,随植被恢复,SMBC、SMBN、SBR由草丛、灌丛、原生林依次上升,并随土壤发生层位的加深逐渐减少,qCO2在3种植被类型间差异显著:T＞PF＞S；原生林A层SMBC,SMBN在各坡位间均显著高于AB层、B层,SBR在A层由下坡位至上坡位递减,而在AB和B层的上、下坡位间无显著差异,qCO2坡位间无显著差异(P＞0.05)；SMBC与SMBN之间存在显著正相关(r=0.825,P＜0.01,n=45),且SMBC、SMBN、SBR分别与有机碳、全氮、碱解氮均呈显著正相关.因此,随植被恢复,土壤质量明显改善,且坡位对A层土壤的影响较AB层和B层更显著,对于维持土壤微生物调节的土壤养分循环功能,调控土壤氮素营养与土壤有机质同等重要,这为合理制订喀斯特生态恢复措施提供了理论依据.

Responses of soil microbial properties in soil profile to typical vegetation pattern and slope in karst-cluster depression area

Closed-forest type land coverage is an important measure for the restoration of degraded karst ecosystems, and soil microorganisms are one of the most useful indicators of soil quality; however, little is known about the effects of the vegetation pattern and slope on microbial characteristics within the soil profile. In this study, soil samples derived from three different genetic layers along the profile-leaching layer (A, 0-10 cm); transition layer (AB, 20-30 cm, tussock (T) and shrub (S); 30-50 cm, primary forest (PF)); and deposited layer (B, 70-100 cm)-were collected from the middle slope position of three ecosystems-tussock (T), shrub (S), and primary forest (PF)and in addition, from the upper and lower slope positions of primary forest (PF). The study determined soil microbial biomass carbon (SMBC), nitrogen (SMBN), ratio of SMBC to soil organic carbon (qMBC), ratio of SMBN to soil total nitrogen (qMBN), basic respiration (SBR), microbial metabolic quotient (qCO₂) and certain physico-chemical characteristics in order to identify changes in the microbial characteristics along the soil profile in response to the typical vegetation pattern and slope position, and the relationships between the soil microbial- and physico-chemical characteristics. Our results showed that the vegetation pattern and the type of soil genetic layer significantly affected soil microbial biomass and basic respiration, whereas no consistent effect on the slope position was observed. The values of soil microorganism biomass carbon along the soil profile from tussock (T) and shrub (S) ecosystems were 56.7-367 and 161-640 mg/kg, respectively, which were significantly lower than the 532-1217 mg/kg value for the primary forest (PF) ecosystem. The same trend (TPF>S) was observed for the microbial metabolic quotient. SMBC, SMBN, qMBC, and SBR declined for each progressive soil genetic layer, and the effect of slope position on these indicators was more significant within the leaching layer (A) than in the transition (AB) and deposited layers (B). In contrast, for SBR, two-way ANOVA showed that the slope position had no significant influence on qCO₂. A significant positive correlation was observed between SMBC and SMBN (r=0.825, P < 0.01, n=45). Further, there were significant differences in soil nutrients (TN, SOM, AN) along the profile between different vegetation patterns and slope positions; and SMBC, SMBN, and SBR were also correlated with organic carbon, total nitrogen, and available nitrogen. As a result, vegetation restoration had positive effects on the physico-chemical and microbial characteristics, and these changes were more prominent in surface soil than in deep soil. Soil nitrogen nutrition and soil organic matter were equally important for the maintenance of the soil microbial community and its ecological function. These findings should help facilitate preservation and revegetation activities in karst regions.