荒漠区食细菌线虫对生物土壤结皮下土壤微生物量的影响

为探明荒漠区土壤食细菌线虫与生物土壤结皮下土壤微生物量的关系,以腾格里沙漠东南缘的人工植被固沙区生物土壤结皮覆盖的沙丘土壤为研究对象,采集藻-地衣结皮和藓类结皮下0—10 cm土样,并以每克土壤15、30、45、60、90、120、150条的食细菌线虫密度接种,以未接种线虫的土样为对照,经一段时间的培养后测定接种和未接种食细菌线虫土壤的微生物量碳和氮。结果表明:无论藻-地衣结皮还是藓类结皮下的土壤,每克土壤90条以内的土壤食细菌线虫均可显著提高土壤微生物量碳和氮(P<0.05),但随着土壤食细菌线虫的繁殖或过量接种,其与土壤微生物量之间呈现出由正相关性向负相关性的转变;此外,结皮类型也显著影响土壤微生物量碳和氮的含量(P<0.05),发育晚期的藓类结皮下土壤微生物量碳和氮均高于发育早期的藻-地衣结皮。因此,在腾格里沙漠人工植被固沙区藻-地衣结皮和藓类结皮下,一定密度的土壤食细菌线虫能显著提高土壤微生物量,指示适当密度的土壤食细菌线虫可促进荒漠区土壤修复和改良。

荒漠区食细菌线虫对生物土壤结皮下土壤酶活性的影响

作为土壤的重要生物组分,食细菌线虫影响土壤的能量流动和物质循环,但它在荒漠生态系统的作用仍不清楚。为探明土壤食细菌线虫对荒漠区土壤的影响,以腾格里沙漠东南缘人工植被固沙区生物土壤结皮覆盖的沙丘土壤为研究对象,分别采集藻-地衣和藓类结皮及结皮下0—10 cm土样,按每克土壤10、30、60、90、120、150条的密度接种食细菌线虫,以未接种线虫的土壤为对照,测定接种食细菌线虫后土壤脲酶、蔗糖酶、脱氢酶和碱性磷酸酶活性的变化,明确食细菌线虫对荒漠区土壤质量的影响。结果表明:土壤食细菌线虫可提高生物土壤结皮下土壤脲酶、蔗糖酶、脱氢酶和碱性磷酸酶活性,且土壤酶活性随土壤食细菌线虫接种密度的增加呈现先升后降的规律,指示土壤食细菌线虫与微生物存在互利共生关系;此外,接种土壤食细菌线虫背景下,结皮类型也显著影响土壤酶的活性,藓类结皮下土壤酶的活性显著高于藻-地衣结皮(P<0.05),指示结皮发育有利于土壤食细菌线虫与微生物的互长模式。因此,在腾格里沙漠人工植被固沙区土壤食细菌线虫可提高生物土壤结皮下土壤酶的活性,指示土壤食细菌线虫可促进荒漠区土壤的修复进程,有利于荒漠生态系统的改良。

Effect of Different Bacterial-Feeding Nematode Species on Soil Bacterial Numbers,Activity,and Community Composition

The effects of bacterial-feeding nematodes on bacterial number, activity, and community composition were studied through a microcosm experiment using sterilized soil inoculated with soil bacteria （soil suspension） and with bacteria and three species of bacterial-feeding nematodes （ Cephalobus persegnis, Protorhabditis filiformis, and Caenorhabditis elegans）. Catalyzed reporter deposition-fluorescence in situ hybridization, CO2 evolution, and denaturing gradient gel electrophoresis （DGGE） of PCR ampli- fied 16S rRNA gene fragments were used to investigate bacterial numbers, antivity, and community composition, respectively. Our results showed that bacterial numbers and activity significantly increased in the presence of bacterial-feeding nematodes, which indicated that bacterial-feeding nematodes had a significant positive effect on soil bacteria. The different nematode species had different effects on bacterial numbers and activity. C. persegnis and P. filiformis, isolated from native soil, increased the bacterial number and activity more than C. elegans. The DGGE analysis results showed that dominant bacterial species significantly differed among the treatments, which suggested that bacterial-feeding nematode species modified the bacterial community composition in soil. Further gene sequence analysis results showed that the dominant bacterial species in this study were gram-negative bacteria. Given the completely same conditions except nematode species, the varied selective feeding behavior of different nematode species was the most likely reason for the altered bacterial community composition. Overall, the alteration of bacterial numbers, activity and community composition resulting from the bacterial-feeding nematodes may ult!mately affect soil ecological functioning and processes.