Variation and Dynamics of Soil Nematode Communities in Greenhouses with Different Continuous Cropping Periods

Continuous cropping in greenhouses can result in root-knot nematode outbreaks resulting from imbalances in the soil nematode community.However,the changes in soil nematode communities in greenhouses with continuous crop production are unclear.We compared soil nematode communities in greenhouses after 2 years(2-yr)and 10 years(10-yr)of continuous crop production by 18S rDNA high-throughput sequencing.Compared with the 2-yr greenhouse,soil in the 10-yr greenhouse showed acidification,nutrient accumulation and salinization.Bacterial-feeding nematodes(BF)were dominant in the 2-yr greenhouse over the whole growing season,but plant-parasitic nematodes(PP)were the dominant group in the 10-yr greenhouse during the late growing season.Meloidogyne gradually became the dominant group and had a relative abundance of 70.9%(maximum)in the 10-yr greenhouse.Rhabditidae,with relative abundance ranging from 99.8%to 26.8%,was the predominant group in the 2-year greenhouse.Forβ-diversity,hierarchical clustering analysis,unweighted UniFrac principal component analysis(PCA)and principal co-ordinates analysis(PCoA)all revealed that soil nematode communities in the two types of greenhouses were significantly different.Redundancy analysis(RDA)showed that soil nematode communities in the 10-yr greenhouse were related to high soil organic material,total nitrogen,electrical conductivity and disease index of root-knot nematodes.Fisher’s exact test and Pearson’s correlation coefficients revealed that Meloidogyne contributed to themain differences in soil nematode communities between the two types of greenhouses.Population dynamics of Meloidogyne were divided into dormant phase,low-level increasing phase and exponential phase during the whole season.The soil nematode communities within the 2-yr and 10-yr greenhouses had significant variation and different dynamics.This work contributes to a deeper understanding of changes in the soil nematode community in greenhouses with different continuous cropping duration.

Precipitation regulated soil nematode community and footprint in cropland ecosystems

●Nematode abundance and footprint show unimodal patterns with precipitation levels.●MAP governed nematode diversity along the precipitation gradient of agroecosystem.●Soil pH determined nematode abundance and footprint in low precipitation levels.Precipitation plays a crucial role in global biodiversity change across terrestrial ecosystems.Precipitation is proven to affect soil organism diversity in natural ecosystems.However,how precipitation change affects the function of the soil nematode community remains unclear in cropland ecosystems.Here,we tested soil nematode communities from different precipitation sites(300 mm to 900 mm)of the agricultural ecosystem.The abundance of total nematodes,fungivores,and plant parasites,together with the footprint of fungivores was significantly affected by mean annual precipitation(MAP)in cropland ecosystem.Plant parasites diversity and footprint showed negative relationships with MAP.The random forest suggested plant parasite footprint was the most responsive to MAP.The structural equation model revealed that MAP affected nematode abundance and footprint indirectly via soil pH;nematode diversity was affected by MAP directly.We conclude that precipitation could act as the main selection stress for nematode diversity among the large gradient of agricultural ecosystems.However,the soil pH may act as a stress factor in determining nematode community and carbon flow in the soil food web.Our study emphasized that using nematode value by trophic group would provide a deep understanding of nematode response to precipitation in cropland ecosystems.

Effect of grassland degradation on soil quality and soil biotic community in a semi-arid temperate steppe

Grasslands provide a number of ecosystem services for human society.Degradation of grasslands results in the loss of biodiversity and leads to the deterioration of ecosystem functions.In order to accurately assess the influence of grassland degradation on belowground ecosystems,we conducted experiments on a temperate steppe with different levels of degradation and investigated the influence of degradation on soil quality and soil biotic communities.Our results showed that grassland degradation significantly decreased soil quality,with lower values of soil quality index(SQI)observed in the degraded grassland than the meadow steppe and the grassland from the forest-steppe ecotone.Changes in the SQI along the grassland degradation gradient were positively correlated with soil carbon stock and the aboveground biomass,and negatively correlated with the root shoot ratio.Nematode trophic diversity and the ratio of fungal to bacterial PLFA were lower in the degraded grassland than the grassland from the forest-steppe ecotone.The dissimilarities in soil microbial and nematode community composition increased with the changes in soil quality index.Our results indicate that soil quality index based on the minimum data sets could effectively assess the influence of grassland degradation on soil biodiversity and ecosystem function.In order to effectively restore degraded grasslands,the key contributors to the soil quality,such as soil carbon,should be taken on priority basis for revitalizing the soil biodiversity and ecosystem function.