Nematode Faunal Response to Grassland Degradation in Horqin Sandy Land

doi:10.1016/S1002-0160(07)60072-1

Pedosphere

Volume 17, Issue 5, October 2007, Pages 611-618

https://doi.org/10.1016/S1002-0160(07)60072-1 Get rights and content

Abstract

The responses of soil nematode communities to grassland degradation were studied under undegraded grassland (UG), degraded grassland (DG), and improved grassland (IG), in Horqin Sandy Land, Inner Mongolia, Northeast China. Soil samples were collected at depths of 0–10, 10–20, and 20–30 cm. Total organic carbon (TOC) and total nitrogen (TN) exhibited positive effects on the total number of nematodes and trophic groups. Significant treatment effects were found in the total number of nematodes, plant parasites, and omnivores-predators. Measures taken in the improved grassland could improve the number of omnivore-predators, especially in the deeper soil layers. Nematode richness was lower in the DG treatment than in the IG and UG treatments. The food web structure index (SI) was Significantly higher in the UG and IG treatments than in the DG treatment. A higher SI suggested a food web with more trophic linkages and relatively healthy ecosystems.

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Greater nematode abundance in soils collected from 0 to 15 cm, as compared to 15–30 cm, was observed in all three grasslands and across all management practices. These observations agree with previous studies that found soil fauna tends to gather on soil surfaces (Valocka and Sabova, 1997; Liang et al., 2007). Soil physical and chemical properties, as well as plant community composition, likely play an important role in the diversity and structure of nematode communities (Hu et al., 2015).
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Second, lower plant diversity and species asynchrony contributed to lower ecosystem stability of the severely degraded grassland (Zhou et al., 2020), leading to weak resistance of soil nematodes to DF. Third, some soil nematodes such as Aphelenchus and Mesodorylaimus in the severely degraded grassland showed strong adaptability to the altered precipitation (Liang et al., 2007) (Table S3), contributing to their higher dominance, which decreased evenness and diversity of nematode accordingly. This showed that in the severely degraded grassland, soil nematode diversity was not only affected by soil moisture fluctuations, but also due to the existence of the developed dominant species further affected the soil nematode diversity.
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However, few studies explored the relationship between soil nematodes and DOM in forest ecosystems. DOC and DON had a positive impact on the abundance and diversity of soil nematodes by regulating the content of soluble nutrients in grassland ecosystems (Liang et al., 2007). Huang et al. (2020) found that DOM quality was the most important driving factor to explain soil fungal diversity and community composition.
Soil nematode is an essential component of the soil micro-food web and plays an important role in soil nutrient cycling. The biogeographic distribution pattern of the soil nematode community and its main driving factors have attained greater attention in the last few decades. However, previous studies mainly focused on low and middle latitudes, and few studies were conducted in cold and temperate regions at high latitudes. The structure and diversity of soil nematodes along the altitudinal gradient are still unclear, which prevents understanding and comparing the diversity of soil nematodes at different spatial scales. In this study, six altitudes (750, 830, 950, 1100, 1300, and 1420 m) were set in the Oakley Mountain in the cold-temperate zone in China, and Illumina MiSeq sequencing method was used to explore the community composition and structural characteristics of soil nematodes in 0- to 10-cm soil. The diversity of soil nematode community in a high-latitude cold-temperate zone showed a decreasing pattern of monotonicity along the altitudinal gradient. One phylum, 3 classes, 11 orders, and 43 genera were identified; plant–parasites were the dominant trophic groups at each altitude. Altitude was the main factor affecting the diversity of soil nematodes at higher latitudes. Sobs, Chao1, Shannon index, and Faith's phylogenetic diversity all showed a downward trend with the increase in altitude. Soil bulk density, soil temperature, pH, soluble organic carbon, and soluble organic nitrogen were significant factors affecting the altitude distribution of soil nematodes. Soil pH and soluble organic nitrogen were the key factors to explain the changes in the community composition of nematodes.
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An evaluation of changes in nematode populations in response to management was performed using a field scale experiment along a gradient of land-use intensity in the context of management intensive grazing. Four levels of decreasing intensity were measured over three growing seasons. The treatments included: 1) intensive grazing management where cows were allowed to graze for each grazing cycle, followed by routine clipping and harrowing; 2) semi-intensive grazing where cows were allowed to graze for each grazing cycle, with only one clipping event per year; 3) extensive grazing where cows were allowed to graze during every 2nd grazing cycle and no clipping or harrowing was performed; 4) stockpiling treatment where cows were permitted to graze only during the final grazing cycle, followed by clipping at the end of the season. Most indices (MI, PPI, ∑MI, and ∑MI25) resulted in significant seasonal differences; however, only familial diversity (H′) and the total number of families showed significant season by treatment interaction. Bacterivores comprised most of the nematode population with Cephalobidae being the most common family. Abundance of plant feeders was affected by season and soil moisture, whereas bacterivore abundance was associated with total organic N and soil pH. Nematode body length increased slightly in most families through time, and was associated with season, bulk density, soil moisture, and total N and C. Although omnivore numbers were highest in the extensive and semi-intensive treatments, there was a significant increase in dorylaimid body length observed in the intensive treatment through time. Increases in body length were also observed in Monhysteridae and Cephalobidae in all treatments.
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Citation Excerpt :
The numbers of bacterivores and fungivores were higher in soils treated with organic manure than in those treated with chemical fertilizer [10]. Omnivores-predators are most sensitive to environmental disturbances resulting from changes in land use, they were higher in a natural land than in an disturbed agricultural land [6,20,28]. The population of plant parasites was usually higher in agricultural fields than in natural forest or fallow fields [25,38].
The impact of long-term application of fertilizers in soybean fields on soil nematode community structure was studied. The long-term application model of fertilizers lasted 13 years in a soybean–wheat–corn rotation, and included three treatments: no fertilizer (NF), chemical fertilizer (urea and ammonium phosphate, CF), and pig manure combined with chemical fertilizer (MCF). The soil nematode community structures and ecological indices were determined from soil samples taken at five soybean growth stages from May to October in the soybean phase of the rotation. Fertilizer application had significant effects on abundance of plant parasites, bacterivores and fungivores (P < 0.05), but had no significant effects on total nematodes and omnivores-predators. Abundance of plant parasites was higher in NF than in MCF and CF, and abundance of bacterivores was highest in MCF. Fertilizer application significantly affected Plant-parasitic Nematode Maturity Index (PPI) and Nematode Channel Ratio (NCR) ecological indices (P < 0.05). Shannon–Weaver Index (H′) and Species Richness (SR) indices were higher in MCF than in either NF or CF. The abundances of total nematode and plant parasites showed increasing trend with soybean growth in all three treatments. This is probably due to soil environment being more suitable for soil nematode survival with more food available for plant parasites as the soybean grows. Soybean growth stage significantly affected the H′, Free Living Nematode Maturity Index (MI) and PPI. Bacterivores significantly correlated with soil nutrient status suggesting that they could be used as a potential indicator of soil fertility.

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: Project supported by the National Key Technologies R & D Program of China (No. 2005BA517A-8).

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Nematode Faunal Response to Grassland Degradation in Horqin Sandy Land

Abstract

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