生物土壤结皮对荒漠土壤线虫群落的影响

在干旱的沙漠生态系统中,生物土壤结皮对于沙丘的固定和土壤生物的维持起着相当重要的作用.土壤线虫能敏感的指示土壤的恢复程度,是衡量沙区生态恢复与健康的重要生物学属性,而目前关于生物土壤结皮与土壤线虫的关系研究很少.为探明生物土壤结皮对土壤线虫的影响,以腾格里沙漠东南缘的人工植被固沙区藻结皮和藓类结皮覆盖的沙丘土壤为研究对象,根据固沙年限的不同将样地分为4个不同的区进行采样(1956、1964、1981和1991年固沙区),以流沙区作为对照；同时,在不同季度(4、7、9和12月)分别采集腾格里沙漠东南缘的人工植被固沙区藻结皮和藓类结皮覆盖下不同土层(0-10、10-20和20-30 cm)的沙丘土壤,以沙坡头地区的红卫天然植被区为对照,分析生物土壤结皮下土壤线虫的时空变化.采用改良的Baermann漏斗法进行分离线虫,用光学显微镜鉴定并统计.研究表明:1956、1964、1981和1991年人工植被固沙区的藻结皮和藓类结皮均可显著提高其下土壤线虫多度、属的丰富度、Shannon-Weaver多样性指数、富集指数和结构指数(P＜0.05),这可能是因为生物土壤结皮的存在为土壤线虫提供了重要的食物来源和适宜的生存环境；固沙年限与结皮下土壤线虫多度、属的丰富度、Shannon-Weaver多样性指数、富集指数和结构指数存在显著的正相关关系(P＜0.05),这说明固沙年限越久,越有利于土壤线虫的生存和繁衍；结皮类型显著影响土壤线虫群落,相对于藻结皮而言,藓类结皮下土壤线虫多度与属的丰富度更高(P＜0.05),这说明演替后期的藓类结皮比演替早期的藻结皮更有利于土壤线虫的生存和繁衍.此外,藻结皮和藓类结皮均可显著增加其下0-10、10-20和20-30 cm土层线虫多度和属的丰富度(P＜0.05),但随着土壤深度的增加,这种影响逐渐减弱,表明生物土壤结皮更有利于表层土壤线虫的生存；而且,随着季节的变化,藻结皮和藓类结皮下土壤线虫多度基本表现为秋季＞夏季＞春季＞冬季,这些反映了生物土壤结皮的生物量、盖度和种类组成随着季节变化而变化.因此,腾格里沙漠东南缘的人工植被固沙区生物土壤结皮的存在与演替有利于土壤线虫的生存和繁衍,增加了线虫数量、种类和多样性,这指示了生物土壤结皮有利于该区土壤及其相应生态系统的恢复.

Effects of biological soil crusts on desert soil nematode communities

Biological soil crusts (BSCs) play an important role in dune fixation and maintaining soil biota in arid desert ecosystems. Soil nematodes can be used as significant bio-indicators to reflect soil recovery regimes and important biological properties in studies of the restoration and health of sandy ecological areas. However, the relationship between BSCs and nematodes is currently poorly understood. To understand how BSCs affect soil nematodes, sand dune soils under algal and moss crusts were investigated in an artificially revegetated desert area at the southeastern edge of the Tengger Desert, China. Sample plots were selected in four areas that had undergone different periods of sand-fixing (the sand dunes were stabilized in 1956, 1964, 1981 and 1991, respectively). Mobile sand dunes were used as the control. Soil samples from different soil layers (0-10, 10-20 and 20-30 cm, respectively) under algal and moss crusts were collected in different months (4, 7, 9 and 12, respectively) to analyze the temporal and spatial variation of soil nematodes in the artificially revegetated desert areas at the southeastern edge of the Tengger Desert. Natural vegetation areas at Hongwei in the Shapotou area were used as the control. Soil nematodes were separated using the improved Baermann funnel method and were identified and counted by an optical microscope. Our results showed that algal and moss crusts could significantly enhance nematode abundances, generic richness, Shannon-Weaver index, enrichment index and structure index in the sand dunes, artificially stabilized in 1956, 1964, 1981 and 1991, respectively (P<0.05). This can be attributed to the presence of BSCs providing an essential food source and the creation of suitable habitats for soil nematodes. The time of sand dune fixation was positively correlated with soil nematode abundances, generic richness, Shannon-Weaver index, enrichment index and structure index under crusts(P<0.05). This result suggested that long periods of sand dune fixation were more beneficial to the survival and reproduction of soil nematodes than short periods of sand dune fixation. Crust type significantly affected soil nematode communities, with moss crusts having higher nematode abundances and generic richness than those of algal crusts. This result suggested that the late-successional moss crusts were more beneficial to the survival and reproduction of soil nematodes than the early-successional algal crusts. In addition, algal and moss crusts significantly increased soil nematode abundances and generic richness in the 0-10, 10-20 and 20-30 cm soil layers. However, the effect gradually decreased with increasing soil depth, which demonstrated that BSCs were more beneficial to the survival of soil nematodes in topsoil than in subsoil. There were also seasonal changes of nematode abundances under algal and moss crusts, in the following order: autumn > summer > spring > winter. Seasonal changes could reflect changes in the biomass, cover and species composition of BSCs with season changes. Therefore, the presence and succession of BSCs were beneficial to the survival and reproduction of soil nematodes, which increased their amount, species and diversity. The results indicate that BSCs could improve the recovery of soil and corresponding ecological systems in the artificially revegetated desert areas at the southeastern edge of the Tengger Desert.