Apr 2021, Volume 3 Issue 2

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  • Nematodes are widely distributed, small-bodied soil metazoans that account for more than 80% of the abundance of animals on Earth . Their global species richness is tentatively predicted to exceed 1 million. They occur in all ecosystems, with various feeding types in food webs and functional diversity. They also act as important bio-indicators, with key roles in mediating ecosystem processes. Although nematodes are so important, we still do not fully understand their communit [Detail] ...

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    Weixin Zhang, Shenglei Fu
    Xinyu Zhu, Yunchuan Hu, Zhiguo Li, Donghui Wu

    •Ÿ Earthworms increased soil macroaggregate (>2 mm and 0.25–2 mm) formation

    •Ÿ Maize roots and earthworms interact to produce soil macroaggregate

    •Ÿ Earthworms were effective in transferring rhizodeposit carbon into macroaggregate, especially in soil derived from a long-term no-till system

    •Ÿ Rhizodeposits were protected during soil aggregation

    As soil ecosystem engineers, earthworms are the main promoters of soil aggregation, a process that drives the production of ecosystem services by soils. A crucial factor in the ecosystem service of carbon sequestration is rhizodeposit carbon, which is the main energy source of soil food webs. The effects of earthworms on the distribution of rhizodeposit-carbon in soil aggregates remain unclear. Here, we conducted a 13CO2 labeling experiment to determine the effects of earthworms on maize rhizodeposit carbon in soil aggregates after 14 years (2002–2016), in both conventional tillage (CT) and conservation tillage (no tillage, NT) soils. Four treatments were established in total: NTE (no tillage soil with earthworms), CTE (conventional tillage soil with earthworms), NTC (control, no tillage soil without earthworms), and CTC (control, conventional tillage soil without earthworms). Earthworms significantly enhanced the abundance of soil macroaggregates (>2000 μm and 250–2000 μm) on day 30 compared with day 2 (after labeling), especially in the NT soils. On day 30, in the presence of earthworms, the amounts of rhizodeposit carbon in the>2000 μm and 250–2000 μm soil aggregates in the NT soils were significantly higher than in those in the CT soils (P<0.05), and higher d13C signatures in the same size aggregates were observed in the NT soils than in the CT soils (P<0.05). These findings indicated that compared with the CT soils, with the involvement of earthworm activity, the NT soils promoted more rhizodeposit carbon transformation to the soil macroaggregates. Our results clearly indicate that soil macroaggregates formed in different tillage soils in the presence of 2 different engineers (earthworms and roots) significantly differ from those formed in the presence of only one organism (roots) in the long term.

    Mingda Xie, Xinwei Wu, Shucun Sun

    •Ÿ A one-sided negative relationship existed between tunneling beetles and earthworms.

    •Ÿ Beetles and earthworms interactively increased dung removal.

    •Ÿ Beetles and earthworms additively facilitated plant growth.

    Interspecific interactions between two spatiotemporally co-occurred species sharing a single resource are considered to be either competitive or facilitative. This study examined the possible interspecific interactions between a dung-tunneling beetle species (Onthophagus yubarinus) and an earthworm species (Aporrectodea nocturna), two major detritivores responsible for dung removal in a Tibetan alpine meadow. We conducted a two-way, factorial field experiment using replicated chambers, and measured the performances of beetles and earthworms, as well as yak dung removal, soil properties and aboveground plant biomass over two months. Earthworm presence significantly decreased the body size of beetle larvae and the weight of tunnel dung that beetle larvae live on. In contrast, beetle presence did not affect the performance of earthworms. Beetles, earthworms and their interaction significantly increased dung removal and soil organic carbon concentration at the end of the experiment. Beetles alone significantly increased soil total N and P, soluble N and P concentrations, but earthworms alone had nonsignificant effects on these nutrient variables. Beetles and earthworms additively enhanced soluble N and P concentrations, and aboveground plant biomass at the end of the experiment. These results indicate 1) there was a one-sided negative relationship between dung-tunneling beetles and earthworms, resulting from the consumption of earthworms on food resource of beetle larvae; and 2) the coexistence of beetles and earthworms facilitated dung removal interactively and plant growth additively by increasing nutrient availability.

    Meixiang Gao, Yuxi Guo, Jie Liu, Jinwen Liu, Sina Adl, Donghui Wu, Tingyu Lu

    • Ground arthropods distribution was compared at the local and regional scales.

    • Beta-diversity finds distinct communities at the regional but not local scales.

    • Turnover contributed more than nestedness of all arthropods at multiple scales.

    • Spatial variables were important regulators at the local scale.

    • Spatially structured environmental factors contributed most at regional scale.

    Understanding the factors determining the formation of each community and metacommunity across a landscape is one of the most important ideas in soil animal ecology. However, the variables and parameters that shape soil arthropod communities in agroecosystems have not been resolved. These arthropods can serve as important bioindicators of field management and its sustainability. We sampled five corn plantations in each of three locations across a region spanning 600 km to come up with these determinants of the community structure of ground-dwelling spiders (Erigoninae: Araneae), carabids (Coleoptera: Carabidae), and ants (Hymenoptera: Formicidae). The analysis of the five fields within each of the three locations represent our local-scale samples, while the comparisons of the 15 sites across all three locations represent the regional scale samples. We tested the hypothesis that in the models we sampled, environmental/soil variables would drive community assembly locally (within location comparisons), but at the regional scale (between location comparisons), climatic and spatial variables would drive metacommunity assembly. The outcomes of our study showed distinct communities at each of the three locations when compared across regions but locally, fields were similar in species composition, as expected. Locally, spatial variables were important but not soil variables, regulated species richness and abundance. Turnover contributed more than nestedness to explain the biodiversity of spiders, carabids, and ants at both the local and regional scales. Neither purely climate variables, nor purely soil or spatial variables were significant enough explanations for the regional scale arthropod community composition. However, spatially structured environmental factors contributed most to explain the patterns supporting our hypothesis. We conclude that biodiversity in this agroecosystem area can be promoted by a mosaic of land uses being encouraged to increase landscape complexity at the regional scale.

    Haifeng Xiao, Wenting Wang, Shangwen Xia, Zhipeng Li, Jianmin Gan, Xiaodong Yang

    •Relationships between environmental factors and nematode distributions at different spatial scales are assessed.

    •Nematode diversity peaked in tropical forest ecosystem.

    •Nematode diversity showed contrary patterns compared with their abundance.

    •Factors most strongly affecting nematode communities changed across spatial scales.

    Understanding biodiversity and biogeographic distribution of soil fauna is an important topic in ecology. While nematode communities have been compared among ecosystems, knowledge remains limited about how environmental factors and nematode distributions are linked at different spatial scales. Here, we employed high-throughput sequencing to compare nematode communities in tropical (Xishuangbanna), subtropical (Ailaoshan), and cold temperate spruce-fir (Lijiang) forest ecosystems with identical spatial sampling. Relationships between nematode communities and environmental factors were analyzed using redundancy analysis (RDA). Our results showed that nematode richness and diversity peaked in Xishuangbanna; however, no significant differences were observed in other two forest ecosystems. Bacterial feeders and Omnivores / Carnivores (Om & Ca) had the lowest relative abundance, but the highest diversity, in Xishuangbanna, with the opposite pattern being detected for fungal and plant feeders. Our data also demonstrated that, for forest ecosystems, climate factors drive nematode communities distributions at the regional scale, while terrain and soil characteristics (including pH and nutrients) drive nematode communities distributions at local scales. This study improves our current understanding of key factors (environmental parameters) responsible for the biogeographical distribution of forest nematode communities at different spatial scales.

    Yingbin Li, Siwei Liang, Xiaofang Du, Xinchang Kou, Xiaotao Lv, Qi Li

    Soil nematodes are the most numerous components of the soil fauna in terrestrial ecosystems. The occurrence and abundance of nematode trophic groups determine the structure and function of soil food webs. However, little is known about how nitrogen deposition and land-use practice (e.g. mowing) affect soil nematode communities. We investigated the main and interactive effects of nitrogen addition and mowing on soil nematode diversity and biomass carbon in nematode trophic groups in a temperate steppe in northern China. Nitrogen addition and mowing significantly decreased the abundance of soil nematodes and trophic diversity but had no effects on nematode richness and the Shannon-Wiener diversity. Nitrogen addition influenced soil nematode communities through decreasing soil pH. Mowing influenced soil nematode communities through decreasing soil moisture. Nitrogen addition enhanced the bacterial energy channel but mowing promoted fungal energy channel in the soil micro-food web. Our study emphasizes that ecosystem function supported by soil organisms can be greatly influenced by nitrogen deposition, and mowing cannot mitigate the negative effects of nitrogen deposition on soil food webs.

    Lina Zhao, Binbin Yu, Mengmeng Wang, Jie Zhang, Zhifeng Shen, Yang Cui, Junyong Li, Ji Ye, Weizhong Zu, Xiaojing Liu, Zongji Fan, Shenglei Fu, Yuanhu Shao

    • We experimentally reduced litter and root inputs in forests at different latitudes.

    • Litter reduction at high and mid latitudes and root removal at low latitudes reduced nematode richness but did not alter nematode abundance.

    • The effects of plant resource inputs on nematode energy flux are affected by climate and plant resource type.

    The relative abundance of different components of the soil food web can vary tremendously in response to plant resource inputs. However, little is known about the mechanisms that plant resource regulate the energy fluxes and soil community composition. Here, we experimentally reduced litter and root inputs for two years in China at low-, mid-, and high-latitude forests to explore the effects of plant-derived resource inputs on the nematode energy flux and community composition. Litter reduction at high and mid latitudes and root removal at low latitudes reduced nematode richness but did not alter nematode abundance. Besides, Litter reduction reduced energy fluxes of bacterial-feeding nematodes at mid latitudes and energy fluxes of plant-feeding, bacterial-feeding and omnivorous-predatory nematodes at low latitudes, thus reducing the energy fluxes of total nematodes in mid- and low-latitude forests. By contrast, root removal reduced energy fluxes and relative energy flux of plant-feeding nematodes in high- and low-latitude forests. In most cases, nematode diversity in different trophic groups increased with increasing energy flux to nematodes. Taken together, our results suggest that the effects of plant resource inputs on nematode energy flux are affected by climate and plant resource type, which improves our understanding of plant-soil interactions.

    Cancan Zhao, Yin Li, Chenlu Zhang, Yuan Miao, Mengzhou Liu, Wanlin Zhuang, Yuanhu Shao, Weixin Zhang, Shenglei Fu

    • Nematodes was investigated in a young Acacia crassicapa plantation in southern China

    • Both litter addition and root presence enhanced soil nematode abundance

    • Litter addition significantly altered soil nematode community composition

    • Root presence had a limited impact on nematode trophic group composition

    Aboveground litter inputs and root exudates provide basal resources for soil communities, however, their relative contributions to soil food web are still not well understood. Here, we conducted a field manipulative experiment to differentiate the effects of litter inputs and living root on nematode community composition of surface and subsoils in a young Acacia crassicapa plantation in southern China. Our results showed that both litter addition and root presence significantly enhanced soil nematode abundance by 17.3% and 35.3%, respectively. Litter addition altered nematode trophic group composition, decreased fungivore to bacterivore ratio, and enhanced maturity index and structure index, which led to a bacterial-based energy channel and a more complex food web structure. However, root presence had a limited impact on the nematode community composition and ecological indices. Despite nematodes surface assembly, soil depth did not affect nematode trophic group composition or ecological index. Our findings highlight the importance of litter inputs in shaping soil nematode community structure and regulating soil energy channel.

    Simin Wang, Xiaoyun Chen, Debao Li, Jianping Wu

    • Three typical forest soils and three soil organisms were collected.

    Ÿ• Interactions among soils and organisms were examined by incubation experiment.

    • Biotic factors mainly affect microbial CUE by changing biomass.

    • Temperature regulates microbial CUE by affecting microbial respiration.

    Microbial carbon use efficiency (CUE) affects the soil C cycle to a great extent, but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood. In the current study, microcosms were used to investigate how microbial respiration, biomass, and CUE responded to biotic and abiotic factors in natural tropical, subtropical, and temperate forests. Soil samples from the forests were collected, sterilized, and populated with one or a combination of three types of soil organisms (the fungus Botrytis cinerea, the bacterium Escherichia coli, and the nematode Caenorhabditis elegans). The microcosms were then kept at the mean soil temperatures of the corresponding forests. Microbial respiration, biomass, and CUE were measured over one-month incubation period. The results showed that microbial biomass and CUE were significantly higher, but microbial respiration lower in the subtropical and temperate forest soils than in tropical forest soil. Biotic factors mainly affected CUE by their effect on microbial biomass, while temperature affected CUE by altering respiration. Our results indicate that temperature regulates the interactive effects of soil organisms on microbial biomass, respiration, and CUE, which would provide a basis for understanding the soil C cycle in forest ecosystems.