Precipitation effects on nematode diversity and carbon footprint across grasslands

Climate-induced range expansion of cushion plants promotes functional homogenization of soil nematode communities

Global climate change is causing plants and other organisms to naturally expand their ranges to higher latitudes or altitudes. This expansion is leading to a strong reshuffling of biotic interactions with consequent ecosystem functions in the new ranges. We report here that soil fauna communities respond strongly to the cushion plants in a large-scale latitudinal gradient in the Qinghai-Tibet Plateau. Local taxonomic, functional, and phylogenetic diversity of soil nematodes increased with the presence of cushion plants independently of the latitudinal gradient, but communities became more functionally similar in the presence of cushion plants and with increasing latitude. This functional homogenization was driven by deterministic processes through which the presence of cushion plants favored some functional traits (i.e., nematode trophic groups: herbivores and bacterivores). Our study reveals functional homogenizations of soil fauna communities in response to climate warming-induced plant range expansion. Given that soil nematodes represent the most abundant and functionally diverse animal communities in terrestrial ecosystems, these findings indicate important changes in the functional dimension of biodiversity and in the delivery of ecosystem functions under climate change.

Changes in Plant Biomass Are Driven by Persisting Plant Species, but Species Gains Drive Nematode Carbon Dynamics

Global change drivers, such as shrub encroachment, alter above- and belowground communities, and the consequences of these changes for ecosystem functioning are largely unknown. We used the modified Price equation to quantify how the presence of shrubs alters the richness, composition, and abundance of plant and nematode communities and the resulting effects on ecosystem functioning (i.e., plant biomass and nematode carbon [C] metabolism) on the Qinghai-Tibet Plateau. Plots with shrubs had increased plant biomass (mostly due to persisting plant species producing more biomass) and nematode C metabolism (mostly due to increases in nematode species richness). The strength of the species richness effect on plant biomass was positively associated with the strength of the species richness on nematode C metabolism. Increases in the biomass of persisting species and species gains promote plant biomass and nematode C metabolism, respectively, which may accelerate decomposition and C turnover on the Qinghai-Tibet Plateau.

Distribution pattern of soil nematode communities along an elevational gradient in arid and semi-arid mountains of Northwest China

Soil nematodes are the most abundant soil metazoans, occupying multiple trophic levels in the soil food web and playing an important role in soil function. Research on the biogeographic distribution patterns of soil nematode communities and their drivers has received greater attention. However, the distribution characteristics of soil nematode communities along the elevational gradient in the arid and semi-arid regions of Northwest China remain unclear. In this study, four elevational gradients (1750-1900, 1900-2100, 2100-2350 and 2350-2560 m) were established on Luoshan Mountain, Ningxia, an arid and semi-arid region in Northwest China, and soil nematodes in the soil layers of 0-10, 10-20 and 20-40 cm were investigated using the improved Baermann funnel method. The results revealed a monotonically decreasing trend in the total number of soil nematodes along the elevational gradient and soil layer depth, decreasing by 63.32% to 79.94% and 73.59% to 86.90%, respectively, while the interactions were not obvious. A total of 1487 soil nematodes belonging to 27 families and 32 genera were identified across the elevational gradient, with Helicotylenchus as the dominant genus, accounting for 10.43% of the total number of nematodes, and bacterivore nematodes as the main trophic groups, accounting for 32.39% to 52.55% of the relative abundance at each elevation, which increased with increasing elevation. Soil nematode community diversity, richness and maturity indices were relatively low at high elevation and decreased by 44.62%, 48% and 54.74%, respectively, with increasing soil layer depth at high elevations. Compared to low elevations, high-elevation soils experienced greater disturbance, reduced structural complexity and nutrient enrichment of the soil food web, and a shift in soil organic matter decomposition from bacterial to fungal pathways as elevation increased. Finally, redundancy analysis showed that soil pH, bulk density, soil moisture, soil organic carbon, available nitrogen, available phosphorus and available potassium were the main soil factors affecting the composition of soil nematode communities, which well explained the differences in nematode communities at different elevations and soil depths. This study can be used as basic information for further research on soil biota in this mountainous region, expanding our further understanding of the spatial ecology of soil nematodes in the arid and semi-arid mountain ecosystems.

The Life-History Traits of Soil-Dwelling Nematode (Acrobeloides sp.) Exhibit More Resilience to Water Restriction Than Caenorhabditis elegans

In the context of climate warming, the intensity and frequency of drought occurrences are progressively increasing. However, current research on the impacts of drought on the life-history traits and physiological activities of animals rarely encompasses soil animals that play crucial roles within soil ecosystems. Therefore, this study focused on a soil nematode species (Acrobeloides sp.) and a model nematode (Caenorhabditis elegans) to investigate whether nematodes adjust the trade-off of their life-history traits to confront arid environments, utilizing a Petri dish experiment. Subsequently, we assessed the resilience of the two nematode species to moisture variations by comparing the extent of changes in various indicators (i.e., life-history traits, physiological traits, and oxidative stress) of nematodes before and after drought and rehydration. The results revealed that both nematode species are capable of adapting to arid environments by altering the trade-off between life-history traits. Specifically, they reduce reproductive investment and body mass while maintaining life span, thus responding to drought conditions. Follow-up rehydration experiments post-drought stress highlighted that the soil-dwelling nematode exhibits a superior recovery capacity in response to moisture fluctuations in comparison to the model nematode. To the best of our knowledge, this is the first investigation into life history of drought adaptation within soil-dwelling nematodes. Moreover, the findings hold significant implications for the exploration of drought adaptation and its mechanisms in soil-dwelling animals.

Nematodes: an overlooked tiny engineer of plant health

Nematodes are a crucial component of rhizosphere biodiversity, affecting plant health as the most abundant and functionally diverse soil animals. Plant-parasitic nematodes are generally considered harmful, which may overlook their potential benefits to plants when coexisting with free-living nematodes in soil. We provide new insights into nematodes as vital plant partners. Plant root damage by plant-parasitic nematodes creates opportunities for pathogens and beneficial microbiota to colonize the rhizosphere. Free-living nematodes coordinate microbiota to suppress plant diseases, but they are susceptible to mortality from plant pathogens, potentially favoring pathogen release in the root zone. We conclude that the nematode's role in regulating plant pathogens represents a missing link, constraining our ability to predict and control soil-borne diseases in healthy plants.

Soil nematode assemblages respond to interacting environmental changes

Multi-factor experiments suggest that interactions among environmental changes commonly influence biodiversity and community composition. However, most field experiments manipulate only single factors. Soil food webs are critical to ecosystem health and may be particularly sensitive to interactions among environmental changes that include soil warming, eutrophication, and altered precipitation. Here, we asked how environmental changes interacted to alter soil nematode communities in a northern Chihuahuan Desert grassland. Factorial manipulations of nitrogen, winter rainfall, and nighttime warming matched predictions for regional environmental change. Warming reduced nematode diversity by 25% and genus-level richness by 32%, but declines dissipated with additional winter rain, suggesting that warming effects occurred via drying. Interactions between precipitation and nitrogen also altered nematode community composition, but only weakly affected total nematode abundance, indicating that most change involved reordering of species abundances. Specifically, under ambient precipitation, nitrogen fertilizer reduced bacterivores by 68% and herbivores by 73%, but did not affect fungivores. In contrast, under winter rain addition, nitrogen fertilization increased bacterivores by 95%, did not affect herbivores, and doubled fungivore abundance. Rain can reduce soil nitrogen availability and increase turnover in the microbial loop, potentially promoting the recovery of nematode populations overwhelmed by nitrogen eutrophication. Nematode communities were not tightly coupled to plant community composition and may instead track microbes, including biocrusts or decomposers. Our results highlight the importance of interactions among environmental change stressors for shaping the composition and function of soil food webs in drylands.

Shrub and precipitation interactions shape functional diversity of nematode communities on the Qinghai-Tibet Plateau

Land use and climate change alter biodiversity patterns and ecosystem functioning worldwide. Land abandonment with consequent shrub encroachment and changes in precipitation gradients are known factors in global change. Yet, the consequences of interactions between these factors on the functional diversity of belowground communities remain insufficiently explored. Here, we investigated the dominant shrub effects on the functional diversity of soil nematode communities along a precipitation gradient on the Qinghai-Tibet Plateau. We collected three functional traits (life-history C-P value, body mass, and diet) and calculated the functional alpha and beta diversity of nematode communities using kernel density n-dimensional hypervolumes. We found that shrubs did not significantly alter the functional richness and dispersion, but significantly decreased the functional beta diversity of nematode communities in a pattern of functional homogenization. Shrubs benefited nematodes with longer life-history, larger body mass, and higher trophic levels. Moreover, the shrub effects on the functional diversity of nematodes depended strongly on precipitation. Increasing precipitation reversed the effects shrubs have on the functional richness and dispersion from negative to positive but amplified the negative effects shrubs have on functional beta diversity of nematodes. Benefactor shrubs had stronger effects on the functional alpha and beta diversity of nematodes than allelopathic shrubs along a precipitation gradient. A piecewise structural equation model showed that shrubs and its interactions with precipitation indirectly increased the functional richness and dispersion through plant biomass and soil total nitrogen, whereas it directly decreased the functional beta diversity. Our study reveals the expected changes in soil nematode functional diversity following shrub encroachment and precipitation, advancing our understanding of global climate change on nematode communities on the Qinghai-Tibet Plateau.

Soil biota diversity and plant diversity both contributed to ecosystem stability in grasslands

Understanding the effects of diversity on ecosystem stability in the context of global change has become an important goal of recent ecological research. However, the effects of diversity at multiple scales and trophic levels on ecosystem stability across environmental gradients remain unclear. Here, we conducted a field survey of α-, β-, and γ-diversity of plants and soil biota (bacteria, fungi, and nematodes) and estimated the temporal ecosystem stability of normalized difference vegetation index (NDVI) in 132 plots on the Mongolian Plateau. After climate and soil environmental variables were controlled for, both the α- and β-diversity of plants and soil biota (mainly via nematodes) together with precipitation explained most variation in ecosystem stability. These findings evidence that the diversity of both soil biota and plants contributes to ecosystem stability. Model predictions of the future effects of global changes on terrestrial ecosystem stability will require field observations of diversity of both plants and soil biota.

Calling for comprehensive explorations between soil invertebrates and arbuscular mycorrhizas

Arbuscular mycorrhizal (AM) fungi and soil invertebrates represent a large proportion of total soil biomass and biodiversity and are vital for plant performance, soil structure, and biogeochemical cycling. However, the role of soil invertebrates in AM fungi development remains elusive. In this opinion article, we summarize the ecological importance of AM fungi and soil invertebrates in the plant-soil continuum and highlight the effects of soil invertebrates on AM fungal hyphae development and functioning. In a context of global change, we envision that better mechanistic understanding of the complex feedback via chemical signaling pathways across the interactions between soil invertebrates and AM fungi is critical to predict their ecological consequences and will open new avenues for promoting ecosystem resilience and sustainability.