Early decomposer assemblages of soil organisms in litterbags with vetch and rye roots

The assemblages of microbial (bacteria and fungi), microfaunal (protozoa and nematodes) and mesofaunal (microarthropods) populations were studied in decomposing root residues from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) in a litterbag field experiment. Litterbags containing vetch or rye root residues were buried in soil at the same day as either vetch or rye winter catch crops were incorporated into the field soil from which the materials were gathered. The litterbags were sampled after 6 weeks in the field. In vetch, bacterial and fungal biomasses were similar whereas fungi dominated microbial biomass in rye. The biomass of the bacterial consuming fauna dominated by nematodes and microarthropods was similar to the biomass of bacteria in vetch as opposed to in rye where bacterivore biomass was lower than bacterial biomass. This suggests a much higher bacterial production in vetch compared to rye. Furthermore, in vetch dauer larvae of bacteria feeding nematodes prevailed, which is also a sign of high bacterial production followed by food shortage for the bacterivores. Bacterivorous and predatory nematodes with capability of consuming protozoa showed an inverse relationship to flagellated protozoa. This suggests that these nematodes controlled the protozoan biomass constituting a lower fraction of the bacterivore biomass in vetch compared to in rye. Such intraguild predator-prey relationship is therefore indicated for microbivorous organisms among bacterivorous and predatory nematodes (the intraguild predator) protozoa (the intraguild prey) and bacteria (the common prey). The much higher fungal biomass in rye than in vetch litterbags was not reflected in the biomass of the fungal feeders. Due to the generally lower intrinsic rate of increase of the fungivores, as well as of the omnivores and predators, in comparison with the bacterial feeders, they were not able to generate dense populations at this early stage of decomposition.     

Crop resistance traits modify the effects of an aboveground herbivore,brown planthopper,on soil microbial biomass and nematode community via changes to plant performance

Plant-mediated effects of aboveground herbivory on the belowground ecosystem are well documented, but less attention has been paid to agro-ecosystems and in particular how crop cultivars with different traits (i.e. resistance to pests) shape such interactions. A fully factorial experiment was conducted using four rice cultivars with different insect-resistance, with and without the aboveground herbivore Nilaparvata lugens (brown planthopper), and to test two hypotheses (1) aboveground herbivory affects the soil microbial biomass and nematode community by altering plant performance and soil resource availability and (2) herbivory effects will depend on cultivar resistance traits. Our results suggested that cultivar resistance mediated both herbivory intensity and herbivore effects on plant performance. N. lugens decreased the availability of soil resources (soluble sugars, amino acids, organic acids, dissolved organic carbon and nitrogen), microbial biomass and percentages of bacterivores when feeding on a susceptible cultivar but increased them in a resistant cultivar. However, total nematode abundance and the percentage of plant-parasitic nematodes responded in the opposite way, increasing under a susceptible cultivar and decreasing under a resistant cultivar. The development of plant-parasites under resistant cultivars before aboveground herbivory might contribute to their resistance traits. Our findings provide evidence that N. lugens significantly reversed the pattern of soil resource availability, microbial biomass and nematode community structure (abundance and trophic composition) across cultivars with distinct resistance. In the presence of aboveground pests, the agronomic use of resistant rice cultivars could also control populations of plant-parasites and promote soil resource availability, further extended to higher trophic level of soil food web.     

Effects of crumb rubber waste as a soil conditioner on the nematode assemblage in a turfgrass soil

The impacts of waste crumb rubber soil amendment on nematode abundance, community structure and soil characteristics were studied in pot grown Lolium perenne L. Three treatments, no crumb rubber (CK), 10% and 15% crumb rubber (CR), were arranged in a randomized complete design. After 3 months’ turfgrass growth, soil nematodes were extracted and identified to genus level, and populations of total, bacterivorous, fungivorous, omnivorous, predatory and plant parasite nematodes were counted. Genus diversity, richness, evenness, plant parasite index (PPI) and maturity index (MI) were calculated to compare nematode community structure. Thirteen genera of soil nematodes in all treatments were identified, of which Helicotylenchus was dominant. Crumb rubber incorporation significantly decreased plant parasite and omnivorous nematode populations, but increased the abundance of predatory nematodes. However, fungivorous and bacterivorous nematode populations were not significantly affected by crumb rubber amendment. Pots treated with 15% CR had the lowest number of plant parasite, omnivorous nematodes and the highest number of fungivorous, predatory nematodes. Shannon's diversity index (H′), evenness (J′), PPI and PPI/MI reduced in pots receiving crumb rubber, whereas dominace (λ) and maturity index (MI) increased in crumb rubber treatments. In addition, CR application decreased soil bulk density and pH value, but increased soil moisture.     

Nematode migration and nutrient diffusion between vetch and barley material in soil

This paper deals with migration of nematodes along nutrient gradients in soil. Portions of barley straw and green vetch leaves were mixed with soil and buried at 6, 12, 18, and 50 mm distance from each other in soil. During the following 12 weeks respiration activity, microbial (SIR) biomass, nitrogen limitation of respiration activity in soil slurries all indicated that nitrogen was transferred in the soil from the nutrient rich vetch to the nutrient poor barley at least during the first 3 weeks of the experiment. Twelve out of 39 taxonomic groups of nematodes showed different growth in the two plant material-soil mixtures. Only one of these taxonomic groups (long rhabditid larvae) suggested that migration could have contributed to population development; for three other groups (short rhabditid larvae, Aphelenchoides, and Bursilla) nutrient transport through the soil was the likely mechanism for a distance-dependant population development. We suggest that for most microbivorous nematodes, except larvae of fast growing bacterivores, migration over distances exceeding one centimetre does not contribute markedly to population development even when cues such as nutrient gradients to stimulate the activity exist.     

放牧管理对青藏高原东缘高寒草甸土壤线虫的影响及作用机制

不同强度、季节的放牧是草地生态系统中主要的放牧管理措施,在生物多样性维持以及生态过程发挥中起着重要的作用,然而,关于青藏高原东缘高寒草甸地区放牧对土壤线虫群落的研究甚少。本文调查了放牧（轻度、中度和重度）对植物群落、土壤理化性质和线虫群落的影响。结果表明：植物群落、土壤理化性质和线虫群落受到放牧、时间以及放牧和时间共同作用的影响;食细菌线虫、植物凋落物生物量、根生物量、土壤含水量、土壤有机碳含量在轻度放牧草地内最高（p＜0.05）;杂类草生物量在中度放牧草地内最高;杂食线虫数量在重度放牧地内最低（p＜0.05）。植物群落和土壤特性与土壤线虫群落有明显的相关关系（p＜0.05）。结构方程模型显示食草动物主要通过植物群落影响植食和食细菌线虫,进一步的研究应针对植物群落多样性以及个体特征对线虫群落的影响。     

Effects of four organic amendments on banana parasitic nematodes and soil nematode communities

Plant–parasitic nematodes are injurious crop pests that have been managed mainly by chemical nematicides. However, safe and alternative methods such as those based on organic materials need to be developed. Our study has evaluated (i) the effects of four organic amendments with different biochemical compositions that are abundantly produced in the study area (Guadeloupe, French West Indies) on soil nematode communities and (ii) some of the suppression mechanisms of banana parasitic nematodes, especially those involving the soil food web. This study is based on a microcosm experiment comparing sugarcane bagasse, sugarcane sludge, plant residues and sewage sludge. All amendments except sewage sludge decreased the root abundances of plant–parasitic nematodes, by 96% in the case of sugarcane bagasse. For this treatment, soil densities of carnivorous nematodes were six times higher than the treatments without organic amendment. Plant residues and bagasse were mainly composed of materials that are difficult to decompose, namely cellulose and lignins. These organic materials favored a fungal decomposition pathway and permitted development of carnivorous nematode populations and increased the Channel Index (CI). Pratylenchus coffeae control after sugarcane refinery sludge application remains unexplained. Lastly, sewage sludge, composed mainly of easily degradable compounds, did not permit nematode control, and only bacterivorous nematode populations were enhanced by this treatment.     

Biodiversity and trophic structure of soil nematode communities are altered following woody plant invasion of grassland

Woody plant encroachment is an important land cover change in dryland ecosystems throughout the world, and frequently alters above and belowground primary productivity, hydrology, and soil microbial biomass and activity. However, there is little known regarding the impact of this geographically widespread vegetation change on the biodiversity and trophic structure of soil fauna. Nematodes represent a major component of the soil microfauna whose community composition and trophic structure could be strongly influenced by the changes in ecosystem structure and function that accompany woody encroachment. Our purpose was to characterize nematode community composition and trophic structure along a grassland to woodland chronosequence in the Rio Grande Plains of southern Texas. Research was conducted at the La Copita Research Area where woody encroachment has been documented previously. Soil cores (0–10 cm) were collected in fall 2006 and spring 2007 from remnant grasslands and woody plant stands ranging in age from 15 to 86 years, and nematodes were extracted by sugar centrifugation. Neither nematode densities (3200–13,800 individuals kg⁻¹ soil) nor family richness (15–19 families 100 g⁻¹ soil) were altered by woody encroachment. However, family evenness decreased dramatically in woody stands >30 years old. This change in evenness corresponded to modifications in the trophic structure of nematode communities following grassland to woodland conversion. Although root biomass was 2–5× greater in wooded areas, root-parasitic nematodes decreased from 40% of all nematodes in grasslands to <10% in the older wooded areas, suggesting the quality (C:N or biochemical defenses) of woody plant root tissue could be limiting root-parasites. In contrast, bacterivores increased from 30% of nematodes in grasslands to 70–80% in older woody patches. This large increase in bacterivores may be a response to the 1.5–2.5× increase in soil microbial biomass (bacteria + fungi) following woody encroachment. Therefore, while energy flow through grassland nematode communities appears to be distributed nearly equally among herbivory, fungivory and bacterivory, the energy flow through nematode communities in wooded areas appears to be based primarily on bacterivory. We speculate that these shifts in nematode community composition and trophic structure could have important implications for ecosystem patterns and processes. First, the low abundance of root-parasitic nematodes (and presumably root herbivory) under woody plants may be one mechanism by which woody plants are able to establish and compete effectively with grasses during succession from grassland to woodland. Second, the large increase in bacterivores following woody encroachment likely accelerates microbial turnover and the mineralization of N, thereby providing a feedback that enables the persistence of N-rich woody plant communities.     

不同农业管理措施对土壤线虫的影响

研究了不同农业管理措施对土壤线虫的影响,结果表明:日光温室中土壤线虫的优势种群为食细菌的小杆线虫(Rhabditis),常规农田中优势种群为食细菌的小杆线虫和植食性的螺旋线虫(Helicotylenchus),休闲地中优势种群为植食性线虫,包括螺旋线虫、盘旋线虫(Rotylenchus)和丝尾垫刃线虫(Filenchus);线虫的多样性、丰富度、ΣMI、EI、SI指数表明日光温室所受到土壤线虫的扰动最强,常规农田次之,休闲地所受干扰最小;PPI/MI、WI、BI、CI指数表明日光温室土壤营养丰富,常规农田和休闲地营养贫瘠.     

Exploring patterns of Camellia seed cake application in relation to plant growth,soil nematodes and microbial biomass

ABSTRACT

The suppression of plant-parasitic nematodes is crucial for maintaining the worldwide development of the banana industry. In this study, different application patterns of Camellia seed cake previously reported to suppress root-knot nematode were conducted to manage pests and promote banana seedling growth. The results demonstrated seven days delay before transplanting was necessary after Camellia seed cake application. The dose 5 g/kg soil resulted in best plant growth promotion performance, which increased banana seedling height, stem diameter, shoot, and root fresh weight by upto 29%, 27%, 47%, and 21%, respectively. Plastic film mulching was beneficial when high amount (2%) of Camellia seed cake was added. The application of Camellia seed cake increased nutrient potassium amounts; the abundance of soil free-living nematodes, especially bacterivores; and the abundance of soil microbes and the soil catalase activity, while reduced plant-parasitic nematodes amounts. Further correlation analysis between the soil nematodes and microbial abundance showed that plant-parasite numbers had significant negative correlations with the bacterial biomass and a portion of the fungal biomass; bacterivores had significant positive correlations with the bacterial biomass; and omnivores had significant correlations with the bacterial biomass and fungal biomass. A fundamental challenge of root-knot nematode control is to sustain ecological services without losing biodiversity. This study provided an environmentally friendly strategy based on Camellia seed cake to regulate the soil health and quality.     

Recovery of soil nematode populations from cropping stress by natural secondary succession to meadow land

The spectrum and densities of soil nematode species were studied in an extensively managed sub-thermophilous meadow and in conventionally managed and abandoned fallow fields left to natural succession. In the meadow, 115 species and 71 genera of soil nematodes were found and the total mean nematode abundance was 1019×10³ individuals/m². The dominant feeding groups were root-fungal feeders (31%, mainly Filenchus), bacterivores (26%; variety of genera, mainly Panagrolaimus, Rhabditis, Acrobeloides, Bursilla, Plectus, Anaplectus, and Eucephalobus), and fungivores (16%, Aphelenchoides). The cultivated field had 66 species and 41 genera of nematodes and a mean nematode abundance of 546×10³ individuals/m². The eudominant trophic group was bacterivores (53%; mainly Panagrolaimus and Acrobeloides) accompanied by fungivores (28%, Aphelenchoides). During 2 years of natural succession in an abandoned field, the total mean nematode abundance rose to 938×10³ individuals/m², and the number of species and genera increased to 73 and 46, respectively. Omnivores (25%, Aporcelaimellus and Eudorylaimus), fungivores (24%, Aphelenchus) and bacterivores (21%, Eucephalobus and Panagrolaimus) became the leading trophic groups, and the values of the Shannon Index of diversity and the Maturity Index increased. The development of soil nematode populations in the early successional stages of abandoned cambisol fields in Central Europe is discussed.     

Secondary succession of nematodes in power plant ash dumps reclaimed by covering with turf

An analysis of successive changes in nematode assemblages in reclaimed waste area offers information about the sensitivity of species or groups of nematodes to specific conditions and ability to colonise new habitats. The study was carried in ash dumps being a by-product of the combustion of hard coal and reclaimed by covering with mineral turf (light loam warp soil) or organic turf (alder peat). In the first 3 years of reclamation diversity of nematodes was low, especially in the dump covered with mineral turf—Shannon diversity index below 3. Later on the value of Shannon index increased and did not differ from those recorded for meadows in Poland. In the ash dump reclaimed for a longer time period (8–11 years) the contribution of K strategist species was higher than in the dumps reclaimed for a shorter time period (2–5 years). At the earlier stages of succession bacterivores Acrobeloides, and two fungivores Aphelenchoides and Aphelenchus, predominated. In the ash dump reclaimed longer the dominance of these three genera decreased and some plant feeders achieved high contribution (> 30%). The composition of nematode communities depended significantly on the period of reclamation, but did not depend either on the soil moisture and pH or on season.     

Birch invasion of heather moorland increases nematode diversity and trophic complexity

To determine whether successional changes in plant communities may influence belowground community structure, we quantified nematode abundance, trophic structure and diversity along two separate chronosequences from heather moorland to birch woodland in the Scottish uplands. Tree invasion markedly altered plant community composition, and hence litter inputs, both directly, and indirectly through changes in understorey species. In turn, these changes in detrital inputs were reflected in consistent changes in nematode community structure. Nematode abundance increased from moorland to birch woodland, with moorland soils being dominated by a few taxa, notably root-hair and fungal feeders, compared to the more diverse composition of the birch woodland soils. Trophic structure was altered through an increase in the abundance of bacterial feeding relative to fungal-feeding nematodes, and an increase in the abundance of predatory nematodes. The increase in predators during the succession from moorland to woodland was associated with an increase in soil pH, highlighting that not only changes in the plant community, but also changes in soil properties associated with tree invasion may influence soil nematodes. Nematode diversity increased from moorland to birch woodland, with nematode richness being positively related to both plant species richness and soil pH. These results suggest that trees may control soil community structure through the manipulation of resources and the soil physico-chemical environment, promoting greater nematode diversity and trophic complexity.     

Soil feedback effects to the foredune grass Ammophila arenaria by endoparasitic root-feeding nematodes and whole soil communities

In coastal foredunes, the grass Ammophila arenaria develops a soil community that contributes to die-back and replacement by later successional plant species. Root-feeding nematodes and pathogenic soil microorganisms are involved in this negative feedback. Regular burial by wind-blown beach sand results in vigorous growth of A. arenaria, probably because of enabling a temporary escape from negative soil feedback. Here, we examine the role of root-feeding nematodes as compared to the whole soil community in causing negative feedback to A. arenaria. We performed a 3-year sand burial experiment in the field and every year we determined the feedback of different soil communities to plant growth in growth chamber bioassays.In the field, we established A. arenaria in tubes with beach sand, added three endoparasitic root-feeding nematode species (Meloidogyne maritima, Heterodera arenaria and Pratylenchus penetrans) or root zone soil to the plants, and created series of ceased and continued sand burial. During three subsequent years, plant biomass was measured and numbers of nematodes were counted. Every year, bioassays were performed with the field soils and biomass of seed-grown A. arenaria plants was measured to determine the strength of feedback of the established soil communities to the plant.In the field, addition of root zone soil had a negative effect on biomass of buried plants. In the bioassays, addition of root zone soil also reduced the biomass of newly planted seedlings, however, only in the case when the field plants had not been buried with beach sand. Addition of the three endoparasitic root-feeding nematodes did not influence plant biomass in the field and in the bioassays. Our results strongly suggest that the negative feedback to A. arenaria is not due to the combination of the three endoparasitic nematodes, but to other components in the soil community, or their interactions with the nematodes.     

Short-term effects of different tillage in a sustainable farming system on nematode community structure

This study investigated the effects of different tillage practices on the nematode community structure. The different tillage systems were: untilled control, conventional deep plough, two-layer plough and cultivator. Sampling was carried out in a field experiment at Wörrstadt-Rommersheim (Rhineland-Palatinate, Germany) in order to study the effects of these tillage systems in a sustainable farming system. Soil samples were taken every 3?months from June 1994 to March 1995 and divided into two depths of 0–10 and 10–20?cm in order to study the vertical distribution of nematode density and community structure. Nematode density was significantly reduced after the first tillage. The second tillage had no effect on the nematode density, whereas the nematode community structure was strongly influenced on both structural (taxonomic) and functional (trophic group, life strategy) level. After tillage, the density of plant parasitic nematodes decreased and the density and dominance of bacterivorous nematodes increased. In the tilled plots, and especially in the cultivator and the two-layer plough plot, the nematode community was dominated by bacterial feeders, whereas, in the untilled control, plant feeders were more dominant. Our results showed that the nematode Maturity Index and Plant Parasite Index are suitable for indicating immediate tillage effects on the nematode community.     

Delayed response to ring nematode (Mesocriconema xenoplax) feeding on grape roots linked to vine carbohydrate reserves and nematode feeding pressure

The chronic impact of ring nematode (Mesocriconema xenoplax) feeding on grapevine (Vitis vinifera) was studied under controlled conditions. ‘Pinot noir’ grapevines were exposed to ring nematode or kept nematode-free for three growing seasons and vines were either grown in full sunlight, 15% of full sun, or partially defoliated to manipulate vine carbohydrate status. Whole plants were destructively sampled to assess the impact of ring nematode on whole plant biomass, carbohydrate, and mineral nutrient accumulation. Vine shoot growth and total biomass was unaffected by ring nematode in the first growing season, although reserves of nonstructural carbohydrates (NSC), P, K, and Ca in the roots and wood were reduced in all canopy management treatments. Vine shoot growth and total biomass were reduced by ring nematode in Year 2, and greater declines in reserve NSC and most mineral nutrients had occurred. Reserves of NSC were affected more than biomass or nutrients during the second year. During the third year of exposure to ring nematode, vines in the 15% sun treatment were dying (prompting an earlier destructive harvest), even though these vines had similar biomass and NSC reserves as the partially defoliated vines at the end of the second year. The demise of the 15% sun vines was associated with higher ring nematodes per unit of root mass, as compared to either full sun or defoliated vines. Therefore, predicting plant response to this nematode requires an understanding of nematode density per quantity of roots, not nematodes per unit of soil which is how plant parasitic nematodes are currently enumerated.     

设施菜地长期施肥对土壤线虫群落结构和多样性的影响

基于设施菜田肥料定位试验地,研究了长期施用化肥对土壤线虫群落结构及多样性的影响,为设施蔬菜的合理施肥和可持续生产提供理论依据。研究期间,共鉴定土壤线虫38个属,其中假海矛属(Pseudhalenchus)、短体属(Pratylenchus)和真滑刃属(Aphelenchus)为优势属。长期施用化肥显著增加各研究土层的线虫总数,并改变线虫的群落结构。长期施化肥对0～10 cm土层线虫各生态指数的影响不显著。在10～20 cm和20～40 cm土层,长期施用化肥显著提高食真菌与食细菌线虫比例(F/B)而降低线虫通路比值(NCR),表明其促进以食真菌为主的腐屑食物网分解通道;其显著提高优势度指数(λ)而降低香农指数(H)'、均匀度指数(J)和丰富度指数(SR),表明长期施用化肥导致土壤线虫多样性降低。土壤线虫可以作为评价施肥对土壤质量影响的生物指标。     

Cattle grazing increases microbial biomass and alters soil nematode communities in subtropical pastures

This study focused on examining the impacts of cattle grazing on belowground communities and soil processes in humid grasslands. Multiple components in the soil communities were examined in heavily grazed and ungrazed areas of unimproved and improved bahiagrass (Paspalum notatum Flugge) pastures in south-central Florida. By using small (1-m×1-m) sampling plots, we were able to detect critical differences in nematode communities, microbial biomass, and mineralized C and N, resulting from the patchy grazing pattern of cattle. Soil samples were collected on three occasions between June 2002 and June 2003. Microbial C and N were greater (P?0.01) in grazed than in ungrazed plots on all sampling dates. Effects of grazing varied among nematode genera. Most genera of colonizer bacterivores were decreased (P?0.10) by grazing, but more persistent bacterivores such as Euteratocephalus and Prismatolaimus were increased, as were omnivores and predators. Higher numbers of persisters indicated that grazing resulted in a more structured nematode community. Some herbivores, particularly Criconematidae, were decreased by grazing. Abundance of omnivores, predators, and especially fungivores were strongly associated with C mineralization potential. Strong correlation of microbial C and N with nematode canonical variables composed of five trophic groups illustrates important links between nematode community structure and soil microbial resources. Including the analysis of nematode trophic groups with soil microbial responses reveals detection of grazing impact deeper into the hierarchy of the decomposition process in soil, and illustrates the complexity of responses to grazing in the soil foodweb. Although highly sensitive to grazing impacts, small-scale sampling could not be used to generalize the overall impact of cattle grazing in large-scale pastures, which might be determined by the intensity and grazing patterns of various stocking densities at the whole pasture level.     

A mixture of grass and clover combines the positive effects of both plant species on selected soil biota

The introduction of N₂-fixing white clover (Trifolium repens) in grassland is a management measure that may contribute to sustainable grassland systems by making them less dependent on inorganic fertilizers. However, little is known about the impact of this measure on soil biota and ecosystem services. We investigated earthworms, nematodes, bacteria and fungi in an experiment in which white clover-only and a mixture of grass and white clover without fertilization were compared with grass-only with and without fertilization.In comparison with grass-only, white clover-only had a lower total root biomass and a lower C/N-ratio in the above- and below-ground plant biomass. These plant characteristics resulted in a lower bacterial biomass, a lower fungal biomass, a higher proportion of bacterivorous nematode dauerlarvae, a lesser proportion of herbivorous nematodes and a greater abundance of earthworms in clover-only.The quantity and quality (C/N-ratio) of the above- and below-ground plant biomass in the mixture of grass and white clover (20–30% clover in the DM) was comparable with grass fertilized with 150 kg N ha⁻¹ of inorganic fertilizer. Differences between these treatments might show specific clover effects in the grass–clover mixture on soil biota other than quantity and C/N-ratio of the litter. However, the only differences were a higher proportion of bacterivorous nematode dauerlarvae and a different nematode community composition in grass–clover.The soil structure in white clover-only showed a higher proportion of angular blocky elements, a lower penetration resistance, a higher number of earthworm burrows, a higher potential N-mineralization and respiration than the soil in grass-only. This suggests that clover stimulates the ecosystem services of water infiltration and supply of nutrients, but is less conducive to soil structure maintenance. The grass–clover mixture differed from grass-only in a higher respiration and from clover-only in a higher percentage of soil crumbs. We suggest that when clover is introduced in grassland to reduce the reliance on inorganic fertilizer, the mixture of grass and clover maintains the positive impact of grass roots on soil structure and increases the supply of nutrients via the soil food web. Thus, a grass–clover mixture combines the agronomic benefits of the two plant types.     

Cover crops alter the soil nematode food web in banana agroecosystems

Cover crops are increasingly being used in agriculture, primarily for weed or erosion management. The addition of cover crops increases the primary productivity of the system and diversifies basal resources for higher trophic levels. How increases in the quality and quantity of basal resources affect bottom-up and top-down control remains a key question in soil food web ecology. We evaluated the response of the nematode community to the introduction of cover crops between rows of a banana plantation. We measured changes in nematode food web structure and inferred the prevalence of bottom-up and top-down effects on the abundance of phytophagous nematodes (i.e., plant-feeding and root-hair-feeding species) 1.5 years after plots with cover crops (Poaceae or Fabaceae species) or bare soil were established. The addition of a cover crop greatly affected the structure and the abundance of the soil nematode community 1.5 years after planting. The abundance of all trophic groups except for plant-feeding nematodes tended to increase with the addition of cover crops. The Shannon–Weaver diversity index and the enrichment index increased with the addition of cover crops, indicating that opportunistic, bacterivorous and fungivorous nematodes benefited from the added resources. Plant-feeding nematodes were least abundant in plots with Poaceae cover crops, while bacterivorous, omnivorous, and root-hair-feeding nematodes were more abundant with Fabaceae cover crops than with bare soil, indicating that cover crop identity or quality greatly affected soil food web structure. Bottom-up effects on all trophic groups other than plant-feeding nematodes were evident with Poaceae cover crops, suggesting an top-down control of plant-feeding nematodes by omnivorous nematodes. Conversely, plant-feeding nematodes were evidently not suppressed in Fabaceae cover crops, perhaps because bottom-up effects on omnivorous nematodes were weaker (hence, top-down control by omnivorous nematodes was weaker), and because Fabaceae cover crops probably served as good hosts for some plant-feeding nematodes.