European Journal of Soil Biology最新文献

Species interactions exert important influences on biodiversity and ecosystem stability. In complex natural communities, species interactions have gone beyond pairwise mechanisms, as interactions between two species can be regulated by one or more other species (higher-order species interactions). However, few studies consider higher-order interactions among organisms that are indirectly contacted, particularly under high soil nutrient conditions. Here, we performed a common garden experiment to investigate how natural herbivory (aboveground weevil) and simulated herbivory (leaf clipping) affect plant (Triadica sebifera) interactions with soil antagonists (root-knot nematodes) and mutualists (arbuscular mycorrhizal fungi; AMF) under nitrogen and phosphorus addition. We also tested the effects of nitrogen, phosphorus, and herbivory-stimuli on T. sebifera leaf extrafloral nectary (EFN) production. We found that T. sebifera can compensate for biomass loss caused by clipping or weevil feeding, moreover, high nitrogen availability caused plant biomass to outpace herbivory-stimuli. Plant–antagonist (root-knot nematodes) interactions were not affected by clipping or weevil feeding under ambient nitrogen condition but were reduced by clipping or weevil feeding under high nitrogen supply, however, we did not find the same pattern under phosphorus addition. Aboveground herbivory-stimuli did not affect plant–mutualist (AMF) interactions, whether fertilized or not. In addition, nitrogen addition stimulated plants to secrete more EFN against clipping but did not increase EFN production against weevil feeding. Clipping and weevil feeding exhibited consistent effects on both plant–antagonist (root-knot nematodes) interactions and plant–mutualist (AMF) interactions. These results suggest that aboveground antagonists mainly mitigate belowground plant–antagonist interactions but not affect plant–mutualist interactions, and higher-order species interactions depend on nitrogen addition but not phosphorus addition.

Alley cropping is the combination of tree rows and crop alleys. The tree row is covered by an understory vegetation strip (UVS), providing a beneficial habitat for many soil fauna, which could disperse through spillover to the crop alleys. However, such movements have never been directly studied. Our experiment investigated earthworm fluxes in the tree row vicinity using a trap technique, in a Mediterranean agroforestry alley cropping field cultivated with peas and planted with walnut trees. We assessed earthworm density at different distances from the UVS (0 m, 0.3 m, 1 m and 6 m) by hand sorting soil monoliths (25*25*30 cm) in spring 2019, at the start and the end of a two-month experiment. During this period, we detected earthworm fluxes by placing directional traps at 30 cm from the UVS border. Traps consisted of three glued plastic walls placed vertically in the soil. They delimited a soil block of 25*25 cm by 20 cm depth and were open on one side. More epigeic earthworms were found in the UVS and up to 30 cm from the UVS border than in the middle of the crop alley. By contrast, the earthworm Allolobophora chlorotica presented a homogeneous distribution in the plot. Trapped earthworms were mostly of the All. chlorotica species, and 1.6 times more earthworms were found in traps open towards the crop alley than in traps open towards the UVS. These results suggest that in spring, earthworms are moving more from the crop alley towards the UVS than in the other direction, probably using the tree row and its vicinity as a refuge against adverse summer conditions in the crop alley.

Microbial necromass carbon (C) is a crucial soil organic carbon (SOC) component. In the context of alpine grassland degradation on the Qinghai-Tibet Plateau, the establishment of artificial grasslands is an effective restoration method; however, the accumulation of microbial necromass C and its contribution to SOC in these ecosystems, especially for the different plant species composition, remain unclear. We collected surface soil (0-10 cm) from artificial grasslands of four different types in 2022, including annual unicast Triticale and annual grass-legume mixed artificial grasslands sown last time in 2022, and perennial Elymus nutans and perennial Poa pratensis artificial grasslands sown in 2019. By measuring soil moisture and pH value, contents of amino sugars, and microbial biomass (MB) characteristics, we aimed to investigate the variations in microbial necromass C and its contribution to SOC and identify the factors influencing these processes. The content of microbial necromass C followed the order: perennial Elymus nutans > perennial Poa pratensis > annual grass-legume mixed > annual unicast Triticale. This was mainly because belowground biomass indirectly affected microbial necromass C by altering soil properties. The ratio of MB C/N and soil moisture were identified as the primary factors influencing the contribution of microbial necromass C to SOC. The contribution of microbial necromass C to SOC was more favorable under perennial grasslands with a low MBC/MBN ratio and high SWC than under annual grasslands. Thus, from the perspective of microbial necromass accumulation, perennial grasslands were the most suitable vegetation type for sustainable soil restoration.

Stand development affects soil properties, nitrogen (N) dynamics, and soil microbial community composition, but the question remains whether differences in N mineralization rates are mirrored by the abundance of relevant functional genes. In this study, we used the ¹⁵N pool-dilution method to estimate N mineralization (i.e., ammonification and nitrification) rates across a Chinese fir (Cunninghamia lanceolata) chronosequence, with stands aged 7, 16, 29, 36, and >80 years. Gene copy numbers of bacteria (16S rRNA), fungi (ITS), ammonia-oxidizing archaea (AOA) and bacteria (AOB) (amoA), denitrifiers (nirS, nirK), N₂ fixers (nifH) and organic N decomposers (chiA) were quantified by qPCR. Gross ammonification and nitrification rates increased linearly with stand age in the topsoil (0–5 cm depth) and were strongly positively correlated with the abundance of the bacterial 16S rRNA gene and AOA amoA, respectively. Higher net nitrification but lower NO₃⁻ immobilization rates in older stands (32 and > 80 years) drove higher N availability for vegetation than in young stands (7 years). Older stands also had higher rates of NH₄⁺ consumption than younger stands due to the increased fungal ITS abundance and higher microbial biomass N (MBN), and AOA amoA was more abundant and active than AOB amoA due to the more acid conditions characteristic of mature forests. Redundancy analysis showed that functional gene abundance was strongly affected by soil properties such as pH, NH₄⁺-N content, and MBN. We also found that microbial N storage potential was lower, and the NO₃⁻-N leaching and gaseous N loss potential were higher in older stands than in younger stands. Collectively, stand developmental stage gave rise to the observed spatial gradient of gross ammonification and nitrification rates by altering the abundance of microbial functional genes, which affected plantation productivity via its modulation of the supply of bioavailable N.

The restoration of soil fauna on a spoil heap is a strong indicator of successful reclamation. The studies were conducted on two types of materials: bare rock (BR) and BR with topsoil (TS) which were applied during coal spoil reclamation and three vegetation types. Four variants investigated included natural forest succession on BR (Succession_BR) and TS (Succession_TS), afforestation (Reclamation_TS) and afforestation with Robinia pseudoacacia (Robinia_TS). Soil pH, soil organic carbon (SOC) and total nitrogen (TN) content, and soil texture were measured in 0–10 cm layers. Earthworms were collected using hand sorting method, and enchytraeids were collected using wet extraction with the heating method.

The investigated soil had varying pH values from 5.3 in a BR to 7.2 in Robinia_TS. The highest content of SOC and TN were in Successinon_BR, and the lowest was in Succession_TS. Enchytraeids density was in the following increasing order: 275, 2982, 3001 and 4548 ind m⁻² for Succession_BR, Robinia_TS, Succession_TS and Reclamation_TS, respectively. Earthworm density ranged from 0 ind. m⁻² in the Succession_BR through 116 ind m⁻² and 120 ind m⁻² in Reclamation_TS and Succession_TS, respectively up to 162 ind m⁻² in the Robinia_TS.

The reclamation treatment was a major driver for soil fauna development while vegetation type was of secondary importance. Investigated soil fauna was positively related to pH value and clay content. The most stimulating variant for the development of earthworms and enchytraeids was the application of reclamation with various tree species and the planting of Robinia pseudoacacia on the topsoil.

Earthworm activity and plant residues in the soil can strongly influence soil organic carbon (SOC) dynamics. However, studies on how earthworms, especially epigeic and endogeic species alone or together, affect the main soil greenhouse gas (GHG) emissions (CO₂ and N₂O) and SOC under the long-term no-till (NT) and conventional tillage (CT) in Mollisols in Northeast China are unclear. The effects of two different species of earthworms (epigeic, Eisenia nordenskioldi; endogeic, Metaphire tschiliensis) on the soil GHG emissions and the SOC content were studied in NT and CT soils in a 337-day mesocosm experiment. The presence of earthworms enhanced the soil cumulative CO₂ and N₂O emissions in both NT and CT soils, and the soil GHG emissions (expressed in terms of the global warming potential, GWP) were increased by 20.43 %–42.99 % in NT soil and by 0–55.62 % in CT soil, respectively. Compared to E. nordenskioldi, the presence of M. tschiliensis (endogeic species) significantly increased soil GHG emissions. Earthworms in NT soil induced less soil GHG emissions than those in CT soil. The presence of earthworms did not increase the SOC content in CT soil but significantly increased the SOC content in NT soil. Our study suggests that earthworms in the long-term no-till soil can contribute to the reduction of soil GHG emissions. This research helps to understand the effects of different ecological categories of earthworms on soil GHG emissions and SOC dynamics under different tillage systems and to mitigate soil GHG emissions.

Earthworms are known to improve plant growth in a soil-dependent way, notably via modifications of the rhizosphere microbiota and its functions. We tested the hypothesis that earthworms influence the abundance of microbial genes involved in N cycle according to the type of soil. In three soils with contrasting texture, we quantified five N-cycling genes in different microsites (bulk, rhizosphere or earthworm casts) of microcosms containing (i) neither plants nor eathworms, (ii) plants, (iii) earthworms, (iv) both plant and earthworms. In the presence of earthworms, rhizophere was enriched in nifH (N₂ fixation) and depressed in nosZ or narG (denitrification) in sandy soil, suggesting a shift in N balance towards immobilization; rhizosphere was enriched in nifH but also nosZ and narG in loamy soil; no effect was detected in clayey soil. The pattern of gene abundance across the different soils and microsites suggests that earthworms could favor microorganisms with a potential beneficial effect on plants specifically in sandy soils.

Integration of perennial peanuts into warm-season grasslands offers a potential solution to reduce nitrogen (N) fertilizer input and enhance N cycling through soil microbial activities. There is limited information on the changes in soil microbial diversity and communities following the short-term integration of rhizoma perennial peanut (RPP; Arachis glabrata Benth.) into warm-season perennial bahiagrass (Paspalum notatum Flüggé) as well as its impact on N cycling processes. This study investigated changes in N cycling populations and soil microbial communities in bahiagrass-RPP mixtures compared to their monocultures at <2 years after RPP establishment in Spring (March) and Fall (October) seasons. Real-time qPCR was used to quantity N functional groups in the soil involved in nitrification, denitrification, and N₂ fixation. DNA amplicon sequencing was employed to examine co-occurrence networks of soil microbes, while activities of soil enzymes [N-Acetyl-β-d-glucosaminidase (NAG) and leucine aminopeptidase (LAP)] involved in N mineralization were also measured. Bahiagrass-RPP mixtures had no effect on N cycling genes. Ammonia oxidizing archaea were the major ammonia oxidizing prokaryotes compared to ammonia oxidizing bacteria in bahiagrass-RPP systems. We found that bahiagrass-RPP mixtures exhibited greater prokaryotic alpha diversity and NAG activities than RPP monoculture. Meanwhile, RPP influenced soil fungal community composition (beta diversity) and enhanced the relative abundance of dominant soil fungal genera (Fusarium, Gibberella, and Humicola). The presence of RPP in bahiagrass systems led to increased negative microbial interactions in microbial occurrence networks. Greater complexities in microbial networks were linked to forage growth season, which was related to enrichment of the relative abundance of Basidiomycota. Our findings showed that RPP has the potential to influence N cycling process in bahiagrass system by altering the abundance of certain N cycling microbes, especially fungal taxa, within 2 years of RPP establishment.

As global climate change progresses, Artic permafrost melts. Deeper layers of permafrost contain organic matter which can migrate into deeper soil by a process called cryoturbation. While this organic matter does not decompose in frozen soils, it decomposes rapidly in melting permafrost. Warming soils may experience increased litter input and earthworm colonization. The effects of litter addition and earthworm colonization on the decomposition and condition of permafrost remain unclear. This study used laboratory experiments to compare effects of willow litter (Salix caprea) addition and earthworm activity (Aporectodea caliginosa) on cryogenic organic matterfrom permafrost soils mixed in mineral soil and mineral soil itself. Respiration and stability of organic matter was monitored over two years with new litter added three times once litter in the soil with earthworms had disappeared from the soil surface. After a two-year period, treatments with litter addition and with earthworms alone showed increased system respiration, but effects were non-cumulative. The soil samples receiving earthworms showed higher proportions of organic matter stabilized in the mineral fraction by the end of the experiment. These preliminary lab results suggest that litter supply and earthworm colonization may both stabilize and speed up mineralization of organic matter released from melting permafrost.