喀斯特土壤微生物和活性有机碳对生态恢复的快速响应

喀斯特地区普遍面临生态退化的问题，退耕还林作为其重要的生态恢复措施之一而备受关注。土壤活性有机碳通常较总有机碳对环境变化和干扰更加敏感，此外土壤微生物对环境变化和干扰亦十分敏感。然而，关于喀斯特不同时间尺度退耕还林土壤活性有机碳和微生物的系统研究尚少见报导。为了揭示土壤活性有机碳和微生物对喀斯特生态恢复的快速指示作用，为喀斯特生态恢复评价和生态环境治理提供科学依据，以广西古周村典型喀斯特景观为代表，采用空间代替时间的方法，选取不同年限（2 a、4 a、8 a、12 a）退耕还林地和玉米耕地对照样地，研究了表层土壤微生物指标和活性有机碳指标随退耕还林的变化特征。研究结果显示，较耕地对照相比，退耕还林8 a后，土壤总有机碳（TOC）质量分数才发生显著变化，提升24%；而还林2 a后，土壤水溶性有机碳（WSOC）、颗粒有机碳（POC）和易氧化有机碳（KMnO4-C）的绝对含量便分别显著提高62%、36%和38%，相对含量分别显著提升60%、34%和36%，且随还林年限的延长呈升高趋势；退耕还林2 a后，土壤微生物生物量碳（MBC）、基础呼吸（BR）和微生物商（MBC︰TOC）分别显著增加56%、27%和54%，并随还林年限的延长呈逐渐升高趋势；土壤微生物代谢熵（qCO2）在退耕还林2 a后显著降低19%，之后随还林年限延长呈下降趋势。本研究表明，土壤活性有机碳及土壤微生物指标可以作为喀斯特生态恢复的早期指示者。

Rapid Responses of Soil Microbes and Active Organic Carbon to Eco-restoration in Karst Region

Eco-degradation problem generally occurs in karst region, and reforestation as an eco-restoration practice has been received more and more attention. Soil active organic carbon fractions generally show more sensitive response to environmental change and disturbance than soil total organic carbon, and also responses of soil microorganisms are sensitive. However, no information is available on soil active organic carbon and microbes following reforestation in time scales in karst region. Guzhou village representative for karst landscape was selected to conduct this study. We selected four reforestation sampling areas with a chronosequence of 2, 4, 8 and 12 years and one arable sampling area as control. As compared to the arable system, soil total organic carbon content did not change under 2-yr, or 4-yr reforestation, but significantly increased by 24% under 8-yr reforestation. Soil water soluble organic carbon, particulate organic carbon and labile organic carbon contents were significantly higher 62%, 36%and 38%, respectively under 2-yr reforestation than the arable system, and showed an increasing trend with reforestation ages. Relative contents of these carbon indicators also showed similar patterns. Consistently, soil microbial biomass carbon content, basal respiration and microbial quotient were significantly higher 56%, 27%and 54%, respectively under 2-yr reforestation than the arable system, and showed an increasing trend with reforestation ages. Microbial metabolic quotient showed opposite pattern. Our results indicate that these active organic carbon and microbial indicators can provide early indication for karst eco-restoration.