Belowground Biodiversity Research Articles

Divergent patterns of microbial community composition shift under two fertilization regimes revealed by responding species

Using patterns of belowground biodiversity to predict ecological functions and to manage productivity has been a longstanding objective for agronomists and ecologists. However, inconsistent associations between microbial diversity and fertilization have been found in frequency, which can be partly due to the dilution effect of immense silent species in microbial communities. Therefore, we studied the responding pool of the microbial communities, which was determined by filtering out taxa that did not vary significantly between fertilization treatments and the control. With responding species, we hypothesized that the difference of microbial response to different fertilization regimes and between bacterial and fungal response to treatments can be enlarged. In this study, bacterial and fungal community compositions and networks were characterized from soils with chemical fertilization (F), the combined application of chemical fertilizers and organic residues (MRF) and without fertilization (Control) in a 7-year experiment located at the Fengqiu Agroecological Experimental Station. As a result, >90% of the phyla, 75% of the genera and 92% of the OTUs were silent microbes. When filtering out these species, 9 phyla, 88 genera and 185 OTUs of bacteria responded significantly to the MRF treatment compared with those of the Control with an average abundance variation of 0.06% in responding OTUs. In contrast, only 2 phyla, 9 genera and 30 OTUs of bacteria significantly responded to the F treatment with an average amplitude of 0.11%. The higher connectedness and the lower average geodesic distance under the MRF treatment showed a more connective and closer bacterial network compared with the F treatment. Similar but stronger responses were detected in the fungal community composition and networks. To conclude, combined fertilization exerted a moderate impact on many microbial taxa (MM pattern), and chemical fertilization showed a substantial effect on a small amount of taxa (SS pattern). It was further inferred that a variation of the “MM” pattern can result in a more stable, harmonious and efficient ecosystem via maintenance of microbial diversity, stimulation of beneficial species, and exhibition of a more efficient microbial network. Our study showed explicit patterns of microbial communities under fertilization regimes revealed by responding species and highlighted the advantages of combined fertilization with organic matter in agroecosystems.

Omics applications: towards a sustainable protection of tomato.

Transcriptome data and gene expression analysis have a huge potential in the study of multiple relationships involving plants, pathogens, and pests, including the interactions with beneficial microorganisms such as endophytes or other functional groups. Next-generation sequencing (NGS) and other recent long-read-based sequencing approaches (i.e., nanopore and others) provide unprecedented tools allowing the fast identification of plant information processing systems, in situ and in real time, fundamental for crop management and pest regulation. Other -omics approaches such as metagenomics and metatranscriptomics allow high-resolution insights on the rhizosphere ecology. They may highlight key factors affecting belowground biodiversity or processes, modulating the expression of stress-responsive pathways. The application of miRNAs and other small RNAs is a relatively new field of application, with enormous potential for the selective activation of defense pathways. However, limitations concerning the stability of the RNA molecules and their effective delivery must be overcome.

Responses of plant diversity and soil microorganism diversity to water and nitrogen additions in the Qinghai-Tibetan Plateau

The Qinghai-Tibetan Plateau is experiencing significant nitrogen (N) deposition and increased precipitation. Although changes in N deposition and precipitation may cause changes in the composition and diversity of plants, the relationships between plant diversity and soil microbial diversity still has not been fully researched. Thus, we conducted a field simulation experiment in an alpine meadow that included three N and two water (W) addition levels, as well as their interactions. The abbreviations of all treatments are shown below: CK, control; W, added water; N5, added 5 g N m−2 yr−1; N10, added 10 g N m−2 yr−1; N5W, added N5 and W; N10W, added N10 and W. The dominant plant species belong to the Gramineae family and include Elymus dahuricus, Stipa capillata, Poa pratensis and Agropyron cristatum. One year later after N and water addition, the results indicated that soil pH decreased with N addition, and with a combination of N and W addition together. High rate of N addition significantly lowered plant diversity. For different plant functional groups, the relative abundance of grasses significantly increased, while the relative abundance of forbs significantly decreased under N10, N5W and N10W treatments. Under N10W treatment, the relative abundance of legumes was significantly reduced, while the relative abundance of cyperaceae was significantly increased. W and N interactions significantly decreased soil bacterial and fungal diversity. N addition showed an indirect effect on the fungal diversity by directly affecting plant productivity. Water addition showed an indirect effect on bacterial diversity by directly affecting plant diversity. Soil bacterial diversity showed a positive correlation with plant diversity, while soil fungal diversity had no significant correlation with plant diversity, but had a negative correlation with plant productivity. It also indicates that the strength of feedbacks between aboveground and belowground biodiversity will vary depending on which groups of soil biota are considered.

Aboveground soil supports high levels of biological activity in oil palm plantations

Oil palm plantations are expanding rapidly throughout Southeast Asia due to increasing global food demand, thereby putting greater pressure on local ecosystems. These plantations usually replace rainforests, resulting in major losses of soil structure and fertility, and belowground biodiversity. However, despite causing soil degradation, oil palms may provide a novel microhabitat for soil biota in suspended soil that accumulates in the axils of cut palm fronds attached to the trunks of these trees. We examined soil communities belowground and in frond axils in a 16‐year‐old oil palm plantation in Sumatra, Indonesia. Community metabolism of small arthropods, nematodes, and testate amoebae (protists) per gram of soil was much higher in axils (suspended soil) than in belowground soil, and accounted for approximately 28% of total soil fauna metabolism at the plantation scale (considering the top 5 cm of soil). Preserving these aboveground microhabitats of suspended soil as hotspots of biological activity during plantation management may therefore partly offset the detrimental impacts of oil palm plantations on soil‐borne processes and biodiversity.

Land use as a driver for protist community structure in soils under agricultural use across Europe

Soil biodiversity is threatened by intensification of land use. The consequences of different land use on belowground biodiversity remain insufficiently explored for soil protists. Alongside being abundant and extremely diverse in soil, protists provide many ecosystem services: key players in the microbial loop, turnover of organic matter and stimulation of plant growth-promoting rhizobacteria. However, we lack knowledge of effects of site, land use intensity and management on diversity of soil protists. Here we assessed protist communities in four European arable sites with contrasting land use intensities at each site: Lusignan, France; Moskanjci, Slovenia; Castro Verde, Portugal and Scheyern, Germany as well as two grassland sites: Hainich, Germany and Lancaster, UK. Each site has consistent agricultural management history of low and high land use intensities quantified in terms of land use index (LUI). We employed high-throughput sequencing of environmental DNA, targeting the V4 region of the 18S rRNA gene. By assigning the protist composition to trophic groups, we inspected for effects of management, and other biotic and abiotic variables. While overall protist richness was unaffected by LUI within sites, specific trophic groups such as plant pathogens and saprotrophs were affected. Effects on protist biome across land uses and sites were also observed. LUI sensitive taxa were taxonomically diverse in each plot, and their trophic groups responded in specific patterns to specific practices. The most abundant trophic group was phagotrophs (73%), followed by photoautotrophs (16%), plant pathogens (4%), animal parasites (2%) and saprotrophs (1%). Community compositions and factors affecting the structure of individual trophic groups differed between land uses and management systems. The agricultural management selected for distinct protist populations as well as specific functional traits, and the protist community and diversity were indeed affected by site, LUI and management, which indicates the ecological significance of protists in the soil food web.

High ecosystem multifunctionality under moderate grazing is associated with high plant but low bacterial diversity in a semi-arid steppe grassland

Current studies on the relationship between biodiversity and ecosystem functioning have mostly focused on plant communities. Less is known about the individual and combined effects of biodiversity components above-and-below-ground on ecosystem multifunctionality. The aim of this study was to explore how different management regimes influence multifunctionality via modification of both plant and soil microbial (bacterial and fungal) diversity. We used a 6-year experiment in Inner Mongolian grassland to compare multifunctionality and separate functions related to the C, N, P cycles and plant productivity under four management regimes and examine relationships between these functions and different components of biodiversity, both above- and belowground. Ecosystem multifunctionality and the rates of nutrient cycling and plant productivity, were greatest under moderate grazing intensity, and lowest under no grazing. Further, across all management regimes, multifunctionality was positively related to plant diversity, and plant and soil microbial diversity combined explained a much greater (62.5%) proportion of variance in multifunctionality than that did either component alone. Different components of biodiversity showed contrasting relationships with individual functions: plant diversity was positively related to C and N cycling, whereas bacterial diversity was negatively related to P cycling and plant productivity. Moderate grazing has better outcomes for biodiversity conservation and ecosystem multifunctionality than mowing and cessation of grazing. Sustainable grazing management is a viable strategy to conserve both above- and belowground biodiversity and enhance the delivery of multiple ecosystem functions.

Climatic factors have unexpectedly strong impacts on soil bacterial β-diversity in 12 forest ecosystems

It is critical to identify the community assembly patterns (i.e., deterministic or stochastic processes) of soil microbes and the potential driving factors to better predict the belowground biodiversity and functioning in forest ecosystems. Here, a combined approach of neutral model and multivariate analysis was employed to examine the soil bacterial communities in 12 undisturbed forests in China, spanning a wide latitudinal range from 21.6°N to 50.8°N. A clear divergent pattern was found for community composition, indicating that deterministic processes dominated the community assembly of soil bacteria. The α-diversity (richness) nonlinearly changed from tropical to cold temperate zones, with the lowest and highest values detected in subtropical and temperate zones, respectively. Although no latitudinal pattern was observed for β-diversity (community variation), there were clear climate zone patterns. Unlike the minor effects of mean annual precipitation (MAP) and temperature (MAT) on bacterial α-diversity, MAP and MAT were important factors affecting soil bacterial β-diversity. Soil pH was a strong driver of α- and β-diversity, but plant factors had only minor effects. Altogether, this study highlights the unexpected importance of climatic factors in shaping bacterial β-diversity in forest soils. Our findings have implications for future investigations of bacterial community dynamics in forest ecosystems, particularly the responses of community composition to global climate change scenarios across large geographical scales.

Research in Forest Biology in the Era of Climate Change and Rapid Urbanization

Green plants provide the foundation for the structure, function, and interactions among organisms in both tropical and temperate zones. To date, many investigations have revealed patterns and mechanisms that generate plant diversity at various scales and from diverse ecological perspectives. However, in the era of climate change, anthropogenic disturbance, and rapid urbanization, new insights are needed to understand how plant species in these forest habitats are changing and adapting. Here, we recognize four themes that link studies from Asia and Europe presented in this Special Issue: (1) genetic analyses of diverse plant species; (2) above- and below-ground forest biodiversity; (3) trait expression and biological mechanisms; and (4) interactions of woody plants within a changing environment. These investigations enlarge our understanding of the origins of diversity, trait variation and heritability, and plant–environment interactions from diverse perspectives.

Using a meta-analysis approach to understand complexity in soil biodiversity and phosphorus acquisition in plants

Current soil phosphorus (P) management is neither environmentally nor economically sustainable. Soil biodiversity has been offered as a solution to unsustainable land management and to promote ecosystem service provision. We know soil biology is instrumental in plant access to soil P, but specific effects of biological complexity, (used here to describe the number of links between different organisms), under different P levels on plant productivity are not well understood. We conducted a meta-analysis on relevant literature, which reported the response of terrestrial plants of economic and anthropogenic importance to P conditions, and controlled for biological treatments across different land-uses (arable, grassland and woodland). We hypothesised that: 1) in arable systems increased biological complexity will enhance plant productivity; 2) in perennial systems such as grassland and woodlands, increasing biological complexity will have no effect; 3) increasing the fertility of the system by addition of P fertiliser will reduce any benefits of biological complexity. We found that soil organisms are not always beneficial to plant shoot biomass, but that the effects of - and interaction among - bacteria, protozoa, nematodes, mycorrhizae, collembola and earthworms differ in their impact on plant biomass (positive or negative) dependent on the presence of other community members, P-level status and time. These findings bring into question existing frameworks that link below-ground biodiversity with above-ground plant productivity. We recommend further experimental work be conducted, which controls for land-use, P status, and soil biological composition and complexity. Such work should be followed by future systematic reviews, which could pragmatically inform more tailored biological management for plant P requirements, land-use and ecosystem service provision. To enable further meta-analyses of this type we recommend habitual inclusion of sufficient experimental detail and data, as a prerequisite for publication and a useful way to utilise increased online publication space.

Agriculture erases climate constraints on soil nematode communities across large spatial scales.

Anthropogenic conversion of natural to agricultural land reduces aboveground biodiversity. Yet, the overall consequences of land-use changes on belowground biodiversity at large scales remain insufficiently explored. Furthermore, the effects of conversion on different organism groups are usually determined at the taxonomic level, while an integrated investigation that includes functional and phylogenetic levels is rare and absent for belowground organisms. Here, we studied the Earth's most abundant metazoa-nematodes-to examine the effects of conversion from natural to agricultural habitats on soil biodiversity across a large spatial scale. To this aim, we investigated the diversity and composition of nematode communities at the taxonomic, functional, and phylogenetic level in 16 assemblage pairs (32 sites in total with 16 in each habitat type) in mainland China. While the overall alpha and beta diversity did not differ between natural and agricultural systems, all three alpha diversity facets decreased with latitude in natural habitats. Both alpha and beta diversity levels were driven by climatic differences in natural habitats, while none of the diversity levels changed in agricultural systems. This indicates that land conversion affects soil biodiversity in a geographically dependent manner and that agriculture could erase climatic constraints on soil biodiversity at such a scale. Additionally, the functional composition of nematode communities was more dissimilar in agricultural than in natural habitats, while the phylogenetic composition was more similar, indicating that changes among different biodiversity facets are asynchronous. Our study deepens the understanding of land-use effects on soil nematode diversity across large spatial scales. Moreover, the detected asynchrony of taxonomic, functional, and phylogenetic diversity highlights the necessity to monitor multiple facets of soil biodiversity in ecological studies such as those investigating environmental changes.

Responses of ground-active arthropods to black locust (Robinia pseudoacacia L.) afforestation in the Loess Plateau of China

Afforestation is one of the most common management approaches for preventing soil erosion. Robinia pseudoacacia (RP), a pioneer and nitrogen-fixing tree, have been widely used for afforestation in the highly eroded regions of the Loess Plateau. While its effects on soil properties are well known, there have been few studies on the biodiversity, especially the belowground biodiversity. Here, we investigated vegetation communities, soil properties, and ground-active arthropod diversity in areas where RP was planted 16, 19, and 31 years (Y) ago and natural control areas without RP plantation in the Loess Plateau. We recorded 2335 individuals that belonged to 23 taxonomic groups in the study site. At the community level, the overall ground-active arthropod abundance and Simpson index (except 16-Y plots) did not significantly vary between the control and afforested RP plots, whereas richness and Shannon index were higher in the RP plots (except 16-Y plots) compared with the control plots. At the functional group level, the abundance and richness of predator did not significantly vary between the control and afforested RP plots, but the phytophage richness was significantly higher in the afforested RP plots (except 16-Y plots). We also found that the richness and/or diversity of ground-active arthropods at both levels generally increased with increasing plantation age. Additionally, the community composition differed among the four habitats, and these differences were primarily attributed to differences in soil temperature and pH, most likely in response to the RP plantation. The results demonstrated that functional groups had differing responses to RP plantation; in particular, RP plantation and plantation age had positive effects on ground-active arthropod diversity. These findings indicated that RP plantation can produce positive conservation outcomes for ground-active arthropods in the Loess Plateau, except at their early age.

Long-term nitrogen addition changes soil microbial community and litter decomposition rate in a subtropical forest

Large amounts of nitrogen (N) are loaded in tropical and subtropical regions due to anthropogenic activities. However, the long-term effect of this deposition on soil biodiversity and its ecological functions remains poorly understood. In this study, we established a 10-year-long field experiment examining the effect of simulated N deposition on soil bacterial diversity and litter decomposition processes in a subtropical Chinese fir forest. The N levels were 0 (control), 6, 12, and 24 g m−2 yr−1. Soil bacterial diversity was measured by high throughput sequencing analysis, while litter decomposition was investigated by a microcosm experiment with a reciprocal soil and litter design. Our long-term experimental results demonstrated that N addition significantly changed soil pH, NH4+-N, available P and soil moisture; reduced soil bacterial diversity; and changed soil microbial community composition at the phyla and class levels. Meanwhile, the rate of litter decomposition decreased in treatments with high doses of N addition. The decreased soil pH and changes in understory plants were significantly correlated with the altered soil microbial diversity and community composition according to the structure equation model analysis. Our results showed that changes in soil microbial community composition (but not soil microbial diversity) mainly contributed to the decline in litter decomposition in higher doses of N addition. Our findings conclude that global change phenomena such as N deposition would depress both above- and below-ground biodiversity and would strongly affect ecosystem functions and processes in subtropical forests.

Cover crop species have contrasting influence upon soil structural genesis and microbial community phenotype

Cover crops (plants grown in an agricultural rotation between cash crops) can significantly improve soil quality via sequestering carbon, retaining nutrients, decreasing soil erosion, and maintaining belowground biodiversity. However, little is known about the effects of such plants upon soil structure. The aim of the study was to assess the impact of four species typically used as cover crops and which have contrasting root architecture (viz. clover, black oat, phacelia, tillage radish) on soil structural genesis and the associated modification of microbial community structure in a clay soil. The four plant species were grown in a replicated pot experiment with sieved soil (<2 mm), with unplanted soil as control for 8 weeks. X-ray Computed Tomography was used to quantify the formation of pore networks in 3D and phospholipid fatty acid analysis was performed to characterise the microbial community phenotype. Black oats developed a greater soil-pore connectivity than the other species throughout the growth period, whereas phacelia decreased both the porosity and pore-connectivity. The microbial community phenotype under phacelia was notably different from the other species, with a greater proportion of fungal markers. Thus, different plant species have differential effects upon soil structural genesis and microbial community phenotype, which provides evidence that certain species may be more suitable as cover crops in terms of soil structural conditioning depending upon specific contexts.

Tropical forest conversion to rubber plantation affects soil micro- & mesofaunal community & diversity

Tropical rainforests play important roles in carbon sequestration and are hot spots for biodiversity. Tropical forests are being replaced by rubber (Hevea brasiliensis) plantations, causing widespread concern of a crash in biodiversity. Such changes in aboveground vegetation might have stronger impacts on belowground biodiversity. We studied tropical rainforest fragments and derived rubber plantations at a network of sites in Xishuangbanna, China, hypothesizing a major decrease in diversity with conversion to plantations. We used metabarcoding of the 18S rRNA gene and recovered 2313 OTUs, with a total of 449 OTUs shared between the two land-use types. The most abundant phyla detected were Annelida (66.4% reads) followed by arthropods (15.5% reads) and nematodes (8.9% reads). Of these, only annelids were significantly more abundant in rubber plantation. Taken together, α- and β-diversity were significantly higher in forest than rubber plantation. Soil pH and spatial distance explained a significant portion of the variability in phylogenetic community structure for both land-use types. Community assembly was primarily influenced by stochastic processes. Overall it appears that forest replacement by rubber plantation results in an overall loss and extensive replacement of soil micro- and mesofaunal biodiversity, which should be regarded as an additional aspect of the impact of forest conversion.

Changes in belowground biodiversity during ecosystem 1 development

Changes in belowground biodiversity during ecosystem 1 development

Earthworms modulate the effects of climate warming on the taxon richness of soil meso- and macrofauna in an agricultural system

Anthropogenic climate change is altering the functioning of terrestrial ecosystems. Agricultural systems are particularly vulnerable to climate change as they are frequently disturbed by intensified management practices. This also threatens belowground organisms that are responsible for providing crucial ecosystem functions and services, such as nutrient cycling and plant disease suppression. Amongst these organisms, earthworms are of particular importance as they can modulate the effects of climate change on soil organisms by modifying the biotic and abiotic soil conditions. However, they are also known to decline under intensified management, justifying their use as key biotic indicators of intensified agriculture. Yet, our knowledge of the responses of belowground species to the interacting effects of warming and land-use intensification (simulated by earthworm reduction in the experimental setup) remains limited. Here, we tested the interactive effects of soil warming and reduced earthworm densities on soil protists, nematodes, meso- and macrofauna, and their diversity in a common barley system in the Hohenheim Climate Change Experiment. We found that belowground species richness was lowest at elevated temperature and reduced earthworm densities, indicating that earthworms can buffer warming effects on belowground biodiversity. Furthermore, warming increased the densities of plant-feeding nematodes, and herbivorous macrofauna benefitted from reduced earthworm densities. Our results indicate that warming and reduced earthworm densities may simultaneously modify the functioning and service provisioning of soils via shifts in diversity and density of soil biota that would likely lead to simplified belowground food webs. These findings thus highlight the importance of maintaining greater densities of ecosystem engineers like earthworms that may help buffering the detrimental effects of climate warming in agricultural systems.

Belowground Biodiversity Relates Positively to Ecosystem Services of European Forests

Biodiversity of ecosystems is an important driver for the supply of ecosystem services to people. Soils often have a larger biodiversity per unit surface area than what can be observed aboveground. Here, we present what is to our knowledge, the most extensive literature-based key-word assessment of the existing information about the relationships between belowground biodiversity and ecosystem services in European forests. The belowground diversity of plant roots, fungi, prokaryota, soil fauna, and protists was evaluated in relation to the supply of Provisioning, Regulating, Cultural, and Supporting Services. The soil biota were divided into 14 subgroups and the ecosystem services into 37 separate services. Out of the 518 possible combinations of biotic groups and ecosystem services, no published study was found for 374 combinations (72%). Of the remaining 144 combinations (28%) where relationships were found, the large majority (87%) showed a positive relationship between biodiversity of a belowground biotic group and an associated ecosystem service. However, for the majority of the combinations (102) there were only three or fewer studies. The percentage of cases for which a relationship was detected varied strongly between ecosystem service categories with 23% for Provisioning, 8% for Regulating, 40% for Cultural, and 48% for Supporting Services. We conclude that (1) soil biodiversity is generally positively related to ecosystem services in European forests; (2) the links between soil biodiversity and Cultural or Supporting services are better documented than those relating to Provisioning and Regulating services; (3) there is a huge knowledge gap for most possible combinations of soil biota and ecosystem services regarding how a more biodiverse soil biota is associated with a given ecosystem service. Given the drastically increasing societal demand for knowledge of the role of biodiversity in the functioning of ecosystems and the supply of ecosystem services, we strongly encourage the scientific community to conduct well-designed studies incorporating the belowground diversity and the functions and services associated with this diversity.

Changes in belowground biodiversity during ecosystem development

Belowground organisms play critical roles in maintaining multiple ecosystem processes, including plant productivity, decomposition, and nutrient cycling. Despite their importance, however, we have a limited understanding of how and why belowground biodiversity (bacteria, fungi, protists, and invertebrates) may change as soils develop over centuries to millennia (pedogenesis). Moreover, it is unclear whether belowground biodiversity changes during pedogenesis are similar to the patterns observed for aboveground plant diversity. Here we evaluated the roles of resource availability, nutrient stoichiometry, and soil abiotic factors in driving belowground biodiversity across 16 soil chronosequences (from centuries to millennia) spanning a wide range of globally distributed ecosystem types. Changes in belowground biodiversity during pedogenesis followed two main patterns. In lower-productivity ecosystems (i.e., drier and colder), increases in belowground biodiversity tracked increases in plant cover. In more productive ecosystems (i.e., wetter and warmer), increased acidification during pedogenesis was associated with declines in belowground biodiversity. Changes in the diversity of bacteria, fungi, protists, and invertebrates with pedogenesis were strongly and positively correlated worldwide, highlighting that belowground biodiversity shares similar ecological drivers as soils and ecosystems develop. In general, temporal changes in aboveground plant diversity and belowground biodiversity were not correlated, challenging the common perception that belowground biodiversity should follow similar patterns to those of plant diversity during ecosystem development. Taken together, our findings provide evidence that ecological patterns in belowground biodiversity are predictable across major globally distributed ecosystem types and suggest that shifts in plant cover and soil acidification during ecosystem development are associated with changes in belowground biodiversity over centuries to millennia.

Divergent national-scale trends of microbial and animal biodiversity revealed across diverse temperate soil ecosystems

Soil biota accounts for ~25% of global biodiversity and is vital to nutrient cycling and primary production. There is growing momentum to study total belowground biodiversity across large ecological scales to understand how habitat and soil properties shape belowground communities. Microbial and animal components of belowground communities follow divergent responses to soil properties and land use intensification; however, it is unclear whether this extends across heterogeneous ecosystems. Here, a national-scale metabarcoding analysis of 436 locations across 7 different temperate ecosystems shows that belowground animal and microbial (bacteria, archaea, fungi, and protists) richness follow divergent trends, whereas β-diversity does not. Animal richness is governed by intensive land use and unaffected by soil properties, while microbial richness was driven by environmental properties across land uses. Our findings demonstrate that established divergent patterns of belowground microbial and animal diversity are consistent across heterogeneous land uses and are detectable using a standardised metabarcoding approach.

Plant evenness modulates the effect of plant richness on soil bacterial diversity

Understanding the relationships between aboveground and belowground biodiversity will help to expand our knowledge on how ecological communities and processes are interactively determined, and thus provide new perspectives for the conservation of biodiversity. Despite the theoretical analyses generally predicting a positive relationship between plant richness and soil microbial diversity, the results from empirical studies have been mixed, probably due to the effect of plant evenness. To investigate this relationship, we conducted field experiments in two geographically distinct sites (Linhai and Shenmu, >1400km apart), by simultaneously manipulating plant richness (2, 4, and 8 species) and evenness (homogeneous versus non-homogeneous). After one year, the bacterial response to plant richness with different plant evenness levels was evaluated using terminal restriction fragment length polymorphism (T-RFLP) analysis. Our results showed that plant evenness modulated plant richness effects on bacterial community, as reflected by the more pronounced positive correlations between bacterial richness and plant richness in homogeneous plant community than in the non-homogeneous treatment. Additionally, plant community structure significantly affected bacterial communities only in the homogeneous treatment in Shenmu, but not in the non-homogeneous treatments. Our results demonstrate that plant evenness could regulate plant richness effects on bacterial alpha- and beta-diversity and thus provide valuable insights into the association between aboveground and belowground biodiversity.