不同悉生培养条件下食细菌线虫对细菌种群的影响

1 引言 线虫是地球上物种多样性和功能类群最丰富的生物种之一,土壤自生线虫(Free-living Nematodes)约占线虫总数的52%,而其中大部分属于食细菌线虫[3,4,8,9].来自田间和土培试验的研究表明,食细菌线虫在土壤生态系统有机物分解、养分矿化等生态过程中起着重要作用[1,3-7]但由于土壤的高度异质性和环境的复杂性,迄今对食细菌线虫与细菌在种群水平上的相互作用尚缺乏深入的了解,限制了对该类土壤动物功能及作用机理的认识[6].

The effects of prescribed fire on soil nematodes in an arid juniper savanna

Prescribed fire produced a landscape with two types of severely burned patches: charred shrub patches and charred patches with tree trunks at the center. Soil nematodes were more abundant in burned and unburned juniper (Juniperus monosperma) tree patches than in yucca-shrub patches. There were no differences in nematode abundance between burned and unburned patches during the late spring and summer samples. Nematode abundance was significantly (p < 0.05) higher in unburned patches than in burned patches in the early spring samples, reflecting large differences in soil moisture between unburned and burned patches. There were no differences in soil nematode abundance between burned and unburned patches at oneyear post-burn and three-year post-burn sites. When all samples were pooled, taxonomic diversity, ecological indices, and abundance of trophic groups (bacteria-feeders, fungi-feeders, and omnivore-predators) were higher in unburned than burned patches. These results suggest that the long-term (up to three years post-burn) effects of fire on soil nematodes are indirect, i.e., by loss of tree canopies, litter accumulation, and shrub foliage, which affects soil temperatures and water redistribution.

Responses of soil nematode community to monoculture or mixed culture of a grass and a legume forage species in China

Mixed cultivation of fast-growing grasses and nitrogen(N)-fixing legumes for forage production is widely considered effective for obtaining sustained high forage yields without depleting soil N levels.However,the effects of monoculture and mixed culture of these species on soil food webs are poorly understood.In this study,soil nematode communities were examined as indicators of the soil food web structure of monoculture and mixed culture of grass and legume at three N levels,i.e.,338(low),450(moderate),and 675(high)kg N ha-1 year-1,across 2 years in wet and dry seasons,using the grass Paspalum wetsfeteini and the legume Medicago sativa(alfalfa),both commonly cultivated worldwide.Repeated-measures analysis of covariance showed that compared with grass monoculture,legume monoculture and grass-legume mixture increased abundances of herbivorous,bacterivorous,and fungivorous nematodes in the soil food web under the low and moderate N fertilization levels.Principal response curve results showed that the abundance of Helicotylenchus,a plant parasite,was significantly higher under legume monoculture than other planting systems at the low N fertilization level.Structural equation model analysis indicated that the legume increased bacterivore abundance,while increasing N fertilization decreased omnivore abundance.The legume might increase the quantity and quality of food resources for soil biota,resulting in the bottom-up control of soil nematode communities.Our results indicate that targeted control of a soilborne pathogen,Helicotylenchus,is required in alfalfa-based planting systems.In addition,high inorganic N application,which is detrimental to legume-rhizobia symbiosis,nullified the otherwise positive effects of legumes on soil nematodes.

Contribution of bacterivorous nematodes to soil resistance and resilience under copper or heat stress

The functional performance of soil ecosystems following disturbance determines ecosystem stability,and although contributions of bacterivorous nematodes to soil ecosystems are recognized,their roles in functional stability have received little attention.The objective of this study was to evaluate the roles of bacterivorous nematodes in functional stability following stress.In a factorial laboratory experiment,soil microcosms were prepared with two levels of nematode abundance,either an enriched abundance of bacterivores(Nema soil)or background abundance of nematodes(CK soil),and three levels of stress,copper,heat,or an unstressed control.The resistance and resilience of nematode abundance,as well as soil microbial function by determining decomposition of plant residues and microbial substrate utilization pattern using a BIOLOG microplate,were followed post stress.The relative changes of two dominant bacterivores,Acrobeloides and Protorhabditis,responded differently to stresses.The resistance and resilience of Protorhabditis were greater than that of Acrobeloides to copper stress during the whole incubation period,while both bacterivores only showed higher resilience under heat stress at the end of incubation.The enrichment of bacterivores had no significant effects on the soil microbial resistance but significantly increased its resilience to copper stress.Under heat stress,the positive effect of bacterivores on soil resilience was only evident from 28 days to the end of incubation.The differences in the responses of soil function to stress with or without bacterivores suggested that soil nematodes could be conducive to ecosystem stability,highlighting the soil fauna should be taken into account in soil sustainable management.