Response of Soil Nematode Communities to Zero-Tillage Weed Control Practices

The combined effects of warming and increased nitrogen (N) deposition in various ecosystems have become global issues. We used high‐throughput sequencing in an 8‐year field experiment to evaluate the impacts of the interactions between warming and nitrogen addition on soil nematode communities in a desert steppe. The soil nematode community presented with a certain degree of tolerance to warming. Warming mainly altered soil nematode diversity and community stability in deep soils whereas nitrogen addition primarily affected the nematode community in surface soils. Moreover, warming interacted with nitrogen addition exacerbated its negative effects on nematode richness and diversity. A Mantel analysis showed that soil pH was significantly negatively correlated with soil NH4+ and NO3− content. All three soil physicochemical (pH, NH4+ and NO3−) parameters were significantly correlated with desert steppe soil nematode community structure. Based on network and relative abundance analyses, we determined that Paratylenchus, Cervidellus, and Acrobeloides were the major hub soil nematode genera responding to soil warming and nitrogen addition in a desert steppe. The present study comprehensively analyzed the responses of desert steppe soil nematode communities to warming and nitrogen addition and provided an exemplar for studying the impact of environmental factors on soil nematodes communities worldwide.

Environmental variables such as soil moisture and phosphorus (P) might influence above- and below-ground biodiversity. In this study, we investigated the rarely reported individual and interactive multifactor effects of soil moisture and phosphorus addition with the type of above-ground tree species (biological interactions) on the soil nematode community structure. We established a completely randomized experimental design with two plant types (N2-fixer and non-nitrogen fixer) and different combinations of water treatments and P additions (i.e., water with P addition, water only, drought with P addition, and drought only) in a greenhouse and investigated their effects on the soil chemical properties and nematode community. Soil samples were collected at the end of the experiment and were analyzed for soil moisture content (SM), available phosphorus (aP), nitrate nitrogen (NO3−–N), ammonium nitrogen (NH4+–N), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and nematode community. The following trophic groups were assigned to the nematodes: bacterivores (Ba), fungivores (Fu), omnivores–predators (Op), and plant parasites (PP). The channel index (CI), enrichment index (EI), maturity index (MI), genus richness (GR), and Simpson dominance (Ig) were adopted to indicate the indices of the nematode food web. Phosphorus addition and its interaction with water treatments had no statistically significant effects on the soil nematode community, but there were significant decreasing (p < 0.05) effects of P addition on the total density of nematodes of the N2-fixing tree under optimum water treatment. There were no significant interactive effects of P addition and water treatments on all the trophic groups, but plant type, water treatments, and their interactions significantly affected the density of most nematode trophic groups. The total nematode abundances of bacterivores, plant parasitic, omnivores, and enrichment index were significantly higher in the N2-fixers than in the non-nitrogen-fixing tree. Soil nematode abundance and community composition were more affected by the plant type than by the P addition and its interaction with water treatments. Drought exerted adverse effects on the total density of soil nematodes, the dominant genera, and the trophic groups. This study demonstrated that the rate of drought impact hinges more on the type of tree and that N2-fixing tree could still maintain the soil food web structure irrespective of the environmental changes.

Intercropping Persian walnut (Juglans regia L.) and wheat (Triticum aestivum L.) have been widely applied in the Xinjiang Uygur Autonomous Region in Northwest China as a means of reducing soil and water losses and improving both land-use efficiency and economic returns. To understand how changes in soil conditions and nematode community structure can contribute to the evaluation of wheat–walnut intercropping systems from the view of soil fauna, we studied the soil nematode community in wheat rhizosphere soil under both monoculture and intercropping systems for 2 years. The results showed that the pH and total nitrogen and organic matter contents in intercropping systems with walnut trees were decreased compared with those of system with wheat alone. The nematode communities differed significantly between intercropping and monoculture plots, e.g., Rhabditis and Dorylaimus were dominant only in monocultures, whereas Tylenchus was dominant only in intercropping systems. Moreover, intercropping systems resulted in decreased nematode abundance, increased proportions of plant-feeding nematodes, and decreased omnivores/predators, particularly in the second year (2012). The decrease in diversity indices (H′) and ecological indices (WI, EI, and SI) of the nematode communities indicated high disturbance and low soil fertility in intercropping systems. Overall, wheat intercropping with walnut had a significant negative effect on wheat rhizosphere soil conditions.

Global warming and drying are important environmental issues. Our study aimed to investigate how warming and precipitation changes affect soil nematode communities in an Inner Mongolian desert steppe for 10 years. Soil nematodes were extracted by the Baermann funnel method. Changes in the nematode communities under artificial warming and precipitation conditions were assayed by analyzing their abundance and ecological indices. Soil nematode abundance decreased significantly by 37.47% under artificial warming; however, there was no significant effect of warming on the nematode community diversity. As for precipitation experiment, the decreased precipitation eliminated some of non-dominant nematode genera, such as Pratylenchus, Helicotylenchus, and Aphelenchus. It caused not only a significant decrease (37.65%) in soil nematode abundance but also a more structured food web and shorter food chain. However, nematode faunal analysis indicated that the soil nematode community was more resistant to drought. Both soil nematode abundance and community diversity increased significantly as increase of precipitation. In particular, the abundance of plant parasitic nematodes increased by 46.69%, which may due to the increase in total nitrogen content in soil. Nematode faunal analysis showed that increased precipitation improved soil environment for the nematodes, and increased food web connectivity and food chain length. However, bacterivorous nematode abundance decreased by 74.39%, and the decomposition pathway of the nematode community had switched from the bacterial channel to the fungal channel. In the Inner Mongolian steppe, both climate drying and warming had negative impacts on soil nematode abundance; however, only drying affected nematode community diversity and food web structure and slowly changed nematode ecological functions. Increased precipitation may aid soil nematode community recovery.

Effects of wild boar grubbing on the soil nematode community subject to seasonal variation in a broad-leaved Korean pine forest in Northeast China

Climatic warming is known to impact terrestrial ecosystem structure and functioning. The response of belowground fauna such as soil nematodes to climatic warming has received little attention, yet the fauna plays crucial roles in the nutrient decomposition and cycling processes. An in situ factorial experiment was conducted to examine the effects of warming on the soil nematode community in a desert steppe. Both moderate-long and severe-short warming treatments were established using a thermal infrared heating facility, along with an unheated control, from 2011 to 2015. The main results were as follows: (i) climatic warming significantly decreased the abundances of total nematodes, plant parasites, fungal-feeding nematodes, and nematodes with high values on the colonizer-persister scale, such as predators and omnivores; (ii) warming significantly decreased the generic richness, maturity index, plant-parasite index, modified maturity index, and structural index, while increased the basal index of the nematode community; (iii) the soil nutrition status was significantly associated with the changes in the composition of the nematode community; and (iv) the responses of the soil nematode community to climatic warming and the consequent drought depended on soil layers and growing seasons. These results indicate a promotion of a more acquisitive resource-use strategy, one in which soil nematodes and soil microbes together impose an adaptive coordination to accelerate soil nutrient cycling by influencing carbon and nitrogen decomposition under climatic change in the desert grassland. The findings suggest that climatic warming could alter ecosystem functioning by altering the soil nematode community in arid areas.

Effects of long-term turfgrass management practices on soil nematode community and nutrient pools

The community characteristics of soil nematodes are an important basis for evaluating and indicating soil health. In this study, cotton fields with different continuous monocropping years (5, 10, 15, 20, and 25 years) were selected. High-throughput sequencing technology was used to explore the responses of soil properties and nematode communities to long-term continuous monocropping in cotton fields. The results showed that after 10-15 years, soil pH and soil conductivity increased significantly, and the contents of soil organic carbon, total nitrogen, available phosphorus (AP), available potassium, nitrate and soil microbial biomass carbon (MBC) decreased significantly. A total of 25 genera, 18 families, 7 orders and 3 classes of soil nematodes were identified. Among them, Helicotylenchus was the dominant genus. Parasitic nematodes were the dominant trophic groups, showing a trend of first decreasing and then increasing. Compared with other continuous monocropping years, plant parasitic nematodes increased by 9.1%-208.6% and Helicotylenchus increased by 392.0% under continuous monocropping for 25 years. With the increases of continuous monocropping duration, plant parasitic nematodes such as Tylenchorhynchus, Ditylenchus, Discopersicus, Mesocriconema, and Criconemoides were detected. After continuous monocropping for 15 years, soil nematode richness index and maturity index of free-living nematodes (MI) decreased significantly, PPI/MI increased significantly, and diversity index (Shannon) and Wasilewska index were the lowest. Soil AP and MBC were the main environmental factors affecting the changes of soil nematode communities. Our results suggested that, after 10-15 years continuous monocropping, soil nutrients were unbalanced, the diversity of soil nematodes was reduced, the stability of soil food network was deteriorated, and the parasitic nematodes were increased, which resulted in continuous monocropping obstacles in cotton.

Field experiments were conducted at Ashland Bottoms in northeastern Kansas and at Hays in western Kansas in 2001, 2002, and 2003 to determine the response of soil microbial and nematode communities to different herbicides and tillage practices under a glyphosate-resistant cropping system. Conventional herbicide treatments were a tank mixture of cloransulam plusS-metolachlor plus sulfentrazone for soybean and a commercially available mixture of acetochlor and atrazine for corn. Glyphosate was applied at 1.12 kg ai ha−1when weeds were 10 or 20 cm tall in both corn and soybean. Soil samples were collected monthly at Ashland Bottoms during the growing period for soil microbial biomass (SMB) carbon determination. In addition, substrate-induced respiration (SIR) and BIOLOG substrate utilization were determined at the end of the growing season each year at Ashland Bottoms, and nematode populations were determined at the beginning and the end of the growing season at both sites. Direct effects of glyphosate rates on soil microbial and nematode communities were also studied in a controlled environment. Values for SMB carbon, SIR, and BIOLOG substrate utilization were not altered by glyphosate. Nematode community response to the glyphosate treatment was similar under both conventional tillage and no-till environments. Total nematode densities were similar with the glyphosate and conventional herbicide treatments. SMB carbon and BIOLOG substrate utilization did not differ between tillage treatments. Nematode densities were greater under conventional tillage than in the no-till system. This study showed that soil health when glyphosate was applied in a glyphosate-resistant cropping system was similar to that of cropping systems that used conventional herbicides.

Excessive pig manure application probably degrades arable soil quality in some intensive pig farming areas. The responses of the nematode community to dosages of pig manure were investigated in Ferric Acrisols under 3-season peanut monoculture. Varying dosages of manure (1.75, 3.5, 7, 14 and 28 t·ha−1·yr−1) in combination with chemical fertilizer were applied to field plots, and chemical fertilizer alone was also applied as a control. With increasing manure application, the abundance of bacterivores and omnivores-predators increased, the abundance of plant parasites decreased, and fungivores abundance exhibited hump-shaped variation. Simpson diversity index and plant parasite index/maturity index of the nematode communities increased to a maximum level at a manure application rate of 3.5 t·ha−1·yr−1 and then sharply decreased. The changes in the soil nematode community were further determined to be correlated with chemical properties; available phosphorus had the strongest quadratic correlation with the two indices, implying that available phosphorus had a better indicative effect than other soil properties to nematode community. Available phosphorus in soil was deduced from 49 to 64 mg·kg−1 with the best nematode communities. Our results emphasized the importance of regular applications of manure in agriculture field to balance nematode diversity and build healthy agro-ecosystems.

In order to elucidate the distribution of soil nematodes in coastal wetlands and the effect of different distance from the sea line on soil nematode communities, we investigated the community structure of soil nematodes in one wetland perpendicularly oriented from Bohai sea coastline. In June 2006, soil samples were collected from the Yellow River Delta wetlands, in Dongying city of Shandong Province, China. Soil nematode communities were analyzed at the depths of 0–10 and 10–20 cm. The results showed that plant parasite nematodes were the most abundant trophic groups in both depths and at four sites. The average relative abundance was 91.33% of the nematode community. Several ecological indices which reflected soil nematode community structure, diversity, maturity and plant parasitism were compared in these four sites. The results indicated that the maturity index (MI) and plant parasitism index (PPI) were more sensitive than the other indices for assessing the response of soil nematode communities to soil of coastal wetland.

Land use and temperature shape the beta diversity of soil nematodes across the Mollisol zone in northeast China

Impacts of Nighttime Warming on the Soil Nematode Community in a Winter Wheat Field of Yangtze Delta Plain, China

Response of soil aggregate-associated microbial and nematode communities to tea plantation age

Global climate change is characterized by enhanced atmospheric carbon dioxide concentration ([CO2]) and temperature, with unknown consequences for soil nematode communities. Soil nematode in response to elevated [CO2], warming and their interaction in paddy field remain largely unknown. Here we aimed to understand how factorial combinations of elevated [CO2] and canopy warming affect soil nematode in a rice paddy field. A rice paddy field was consistently treated with elevated [CO2] (500 ppm), canopy warming (+2 °C) or their combinations. Soil samples after a two-year treatment were collected during the rice growing season and nematode communities were extracted with a modified Baermann funnel extraction to examine the changes in nematode abundance and composition under climate change. Soil nematode communities were altered by elevated [CO2] and warming, but these responses were dependent on rice growing stages. When averaged over the four stages, total nematode abundances were increased by 31.5% under elevated [CO2], and by 25.7% under warming. Elevated [CO2] had no effect on nematode diversity, but slightly altered the composition of different trophic groups. In contrast, warming decreased nematode diversity, but increased plant parasite index, which was negative correlated with crop production. This was attributed to increases in the relative abundance of herbivores under simulated climate change conditions. Elevated [CO2] and warming had a positive effect on nematode abundance, but potentially reduced nematode diversity and soil health. These results suggest that multi-factors interactively affect the responses of soil nematode communities, which is important for food productivity under climate change.