Role Of Soil Biota Research Articles

Native Plant Diversity Generates Microbial Legacies That Either Promote or Suppress Non-Natives, Depending on Drought History.

Diverse native plant communities resist non-native plants more than species-poor communities, in part through resource competition. The role of soil biota in diversity-invasibility relationships is poorly understood, although non-native plants interact with soil biota during invasions. We tested the responses of non-native plants to soil biota generated by different native plant diversities. We applied well-watered and drought treatments in both conditioning and response phases to explore the effects of 'historical' and 'contemporary' environmental stresses. When generated in well-watered soils, the microbial legacies from higher native diversity inhibited non-native growth in well-watered conditions. In contrast, when generated in drought-treated soils, the microbial legacies from higher native diversity facilitated non-native growth in well-watered conditions. Contemporary drought eliminated microbial legacy effects on non-native growth. We provide a new understanding of mechanisms behind diversity-invasibility relationships and demonstrate that temporal variation in environmental stress shapes relationships among native plant diversity, soil biota and non-native plants.

Soil biotic associations play a key role in subsoil C mineralization: Evidence from long-term tillage trial in the black soil of Northeast China

Quantifying the potential of soil carbon (C) mineralization improves our understanding of changes in soil health in agricultural ecosystems. Previous studies rarely linked the trait of interactions inherent in soil communities to soil C mineralization rate (Cmin). This study provides field-based evidence of tillage-driven changes in biological associations and their impacts on soil Cmin. Data obtained from a long-term (15 years) conservation tillage field experiment in Northeast China, and showed that the soil Cmin (per unit soil mass) and specific Cmin (per unit soil C) were 79% and 33% higher in topsoil (0–5 cm) and 27% and 24% lower in subsoil (5–20 cm) under no tillage with residue (NT) compared to conventional tillage with residue removal (CT). Meanwhile, in topsoil, NT strengthened biotic associations in June and August; in subsoil, a more complex network was found in CT. In topsoil, soil Cmin was not related to soil biotic associations, but was positively (P < 0.05) correlated with soil organic C (SOC) and certain biotic properties (e.g., MBC (microbial biomass carbon), microbial phospholipid fatty acid (PLFA) biomass and the relative abundance of AMF (arbuscular mycorrhizal fungi) and PP (plant-parasites)). Among them, the increases in SOC under NT exerted a positive effect on soil Cmin directly or indirectly through mediating biotic biomass properties (MBC, the PLFA biomass of all microbial groups and BF biomass). In contrast, in subsoil, soil Cmin was positively (P < 0.05) correlated with soil biotic associations, SOC and the relative abundance of PP. Notably, the increase in soil Cmin value was mainly achieved by strengthening biological associations. These findings provide novel insights into the role of soil biota in C mineralization, highlighting the diverse mechanisms underlying soil Cmin in response to tillage systems at different soil depths.

Differences in leaf and root litter decomposition in tropical montane rainforests are mediated by soil microorganisms not by decomposer microarthropods.

Plant litter decomposition is a key process in carbon and nutrient cycling. Among the factors determining litter decomposition rates, the role of soil biota in the decomposition of different plant litter types and its modification by variations in climatic conditions is not well understood. In this study, we used litterbags with different mesh sizes (45 µm, 1 mm and 4 mm) to investigate the effect of microorganisms and decomposer microarthropods on leaf and root litter decomposition along an altitudinal gradient of tropical montane rainforests in Ecuador. We examined decomposition rates, litter C and N concentrations, microbial biomass and activity, as well as decomposer microarthropod abundance over one year of exposure at three different altitudes (1,000, 2,000 and 3,000 m). Leaf litter mass loss did not differ between the 1,000 and 2,000 m sites, while root litter mass loss decreased with increasing altitude. Changes in microbial biomass and activity paralleled the changes in litter decomposition rates. Access of microarthropods to litterbags only increased root litter mass loss significantly at 3,000 m. The results suggest that the impacts of climatic conditions differentially affect the decomposition of leaf and root litter, and these modifications are modulated by the quality of the local litter material. The findings also highlight litter quality as the dominant force structuring detritivore communities. Overall, the results support the view that microorganisms mostly drive decomposition processes in tropical montane rainforests with soil microarthropods playing a more important role in decomposing low-quality litter material.

Sympatric soil biota mitigate a warmer-drier climate for Bouteloua gracilis.

Climate change is altering temperature and precipitation, resulting in widespread plant mortality and shifts in plant distributions. Plants growing in soil types with low water holding capacity may experience intensified effects of reduced water availability as a result of climate change. Furthermore, complex biotic interactions between plants and soil organisms may mitigate or exacerbate the effects of climate change. This 3-year field experiment observed the performance of Bouteloua gracilis ecotypes that were transplanted across an environmental gradient with either sympatric soil from the seed source location or allopatric soil from the location that plants were transplanted into. We also inoculated plants with either sympatric or allopatric soil biotic communities to test: (1) how changes in climate alone influence plant growth, (2) how soil types interact with climate to influence plant growth, and (3) the role of soil biota in mitigating plant migration to novel environments. As expected, plants moved to cooler-wetter sites exhibited enhanced growth; however, plants moved to warmer-drier sites responded variably depending on the provenance of their soil and inoculum. Soil and inoculum provenance had little influence on the performance of plants moved to cooler-wetter sites, but at warmer-drier sites they were important predictors of plant biomass, seed set, and specific leaf area. Specifically, transplants inoculated with their sympatric soil biota and grown in their sympatric soil were as large as or larger than reference plants grown at the seed source locations; however, individuals inoculated with allopatric soil biota were smaller than reference site individuals at warmer, drier sites. These findings demonstrate complicated plant responses to various aspects of environmental novelty where communities of soil organisms may help ameliorate stress. The belowground microbiome of plants should be considered to predict the responses of vegetation more accurately to climate change.

Role of soil biota in grassland restorations in high nutrient soils

Soil biota are abundant in grasslands; however, disturbances such as invasions or conversion to agriculture may alter soil communities in ways that reduce the success of native species and/or increase the competitiveness of invasive plants. Predicting the magnitude and direction of these effects on plant growth remains challenging, particularly in high nutrient soils, which can impact plant‐microbe and plant–plant interactions in different ways. In greenhouse experiments, invasive and native Palouse prairie plants were grown individually and in a community with soil from a Palouse prairie remnant, soil invaded by Bromus tectorum, a nutrient release treatment, or no treatment. We tested (1) whether arbuscular mycorrhizal fungal infectivity and function of soil biota differ in invaded versus remnant prairie soil; (2) if growth responses to soil biota are related to plant nutrient demands; (3) if individual plant responses to soil biota predict competitive outcomes; and (4) if successional status predicts plant growth response to soil biota in high nutrient soils. We found no difference in mycorrhizal inoculation potential or function in invaded versus remnant prairie soil. We show a continuum of plant growth responses to soil biota, which correlate with nutrient responses, even under the high baseline soil nutrient conditions. We found that growth response to soil biota may increase with native plant successional stage. Understanding how different plant species respond to soil biota and assessing functionality of soil biota at a site will help managers plan restorations in high nutrient soils, and inform whether inoculations may be beneficial at a particular site.

Globally, plant-soil feedbacks are weak predictors of plant abundance.

Plant‐soil feedbacks (PSFs) have been shown to strongly affect plant performance under controlled conditions, and PSFs are thought to have far reaching consequences for plant population dynamics and the structuring of plant communities. However, thus far the relationship between PSF and plant species abundance in the field is not consistent. Here, we synthesize PSF experiments from tropical forests to semiarid grasslands, and test for a positive relationship between plant abundance in the field and PSFs estimated from controlled bioassays. We meta‐analyzed results from 22 PSF experiments and found an overall positive correlation (0.12 ≤ r¯ ≤ 0.32) between plant abundance in the field and PSFs across plant functional types (herbaceous and woody plants) but also variation by plant functional type. Thus, our analysis provides quantitative support that plant abundance has a general albeit weak positive relationship with PSFs across ecosystems. Overall, our results suggest that harmful soil biota tend to accumulate around and disproportionately impact species that are rare. However, data for the herbaceous species, which are most common in the literature, had no significant abundance‐PSFs relationship. Therefore, we conclude that further work is needed within and across biomes, succession stages and plant types, both under controlled and field conditions, while separating PSF effects from other drivers (e.g., herbivory, competition, disturbance) of plant abundance to tease apart the role of soil biota in causing patterns of plant rarity versus commonness.

Familiar soil conditions help Pinus ponderosa seedlings cope with warming and drying climate

Changes in temperature and moisture as a result of climate forcing can impact performance of planted trees. Tree performance may also be sensitive to new soil conditions, for example, brought about by seeds germinating in soils different from those colonized by ancestral populations. Such “edaphic constraint” may occur with natural migration or human‐assisted movement. Pinus ponderosa seedlings, sourced from one location (“home” site), were grown across a field environmental gradient in either their original home soil or in soils from two different “away” sites. Seedlings were inoculated with site‐specific soil organisms by germinating seeds in living soil. After 6 months, the inoculated seedlings were transplanted into sterilized soils from the home or away sites. This experimental design allowed us to uncouple the importance of abiotic and biotic soil properties and test (1) how biotic and abiotic soil properties interact with climate to influence plant growth and stress tolerance, and (2) the role of soil biota in facilitating growth in novel environments. Seedlings grew least in hotter and drier away sites with away soil biota. Home soil biota ameliorated negative impacts on growth of hotter and drier away sites. Measurements of photosynthetic rate, stomatal conductance, and chlorophyll florescence (Fv/Fm) suggest that edaphic constraint reduced growth by increasing tree water stress. Results suggest that success of Ponderosa pine plantings into warming environments will be enhanced by pre‐inoculation with native soil biota of the seed source.

The interplay between abiotic factors and below-ground biological interactions regulates carbon exports from peatlands

Climate change projections indicate increases in CO2 emissions and DOC release from peatlands, thereby potentially transforming them from sinks to carbon sources. The individual effects of abiotic and biotic factors on peatland carbon exports and the interactions among all these factors are still poorly understood. Therefore, we conducted a field study over two years in a peatland complex by selecting four habitats differing in their dominant vegetation (shrub, grass, sedge and moss) in order to assess the links between abiotic and biotic factors and carbon release at each habitat. Accounting for the wide variability across habitats allowed us to examine the direct and indirect effects of abiotic and biotic factors on carbon cycling at the ecosystem level (i.e. the whole peatland complex). Results showed that the habitats dominated by vascular plants had the highest microbial and above-ground plant biomass, as well as the highest values of Acari and Collembola biomass, whereas Enchytraeidae biomass was dominant in the moss habitat. Furthermore, at ecosystem level, the SEM explained 75% of the total soil respiration variation and 33% of the DOC variation. Accordingly, soil respiration was directly linked to enchytraeid biomass, with these invertebrates being positively related to soil moisture. In contrast, both soil temperature and soil moisture had direct effects on microbial and Acari biomass, and the interaction between Acari biomass and below-ground plant biomass was responsible for DOC release. These findings provide new insights into the role of soil biota in carbon dynamics in peatlands, by showing that the direct effects of abiotic factors on biotic communities (both plants and soil organisms) determine how much carbon is lost from these systems (either as CO2 e or DOC).

Subsoil Arbuscular Mycorrhizal Fungi for Sustainability and Climate-Smart Agriculture: A Solution Right Under Our Feet?

With growing populations and climate change, assuring food and nutrition security is an increasingly challenging task. Climate-smart and sustainable agriculture, that is, conceiving agriculture to be resistant and resilient to a changing climate while keeping it viable in the long term, is probably the best solution. The role of soil biota and particularly arbuscular mycorrhizal (AM) fungi in this new agriculture is believed to be of paramount importance. However, the large nutrient pools and the microbiota of subsoils are rarely considered in the equation. Here we explore the potential contributions of subsoil AM fungi to a reduced and more efficient fertilization, carbon sequestration, and reduction of greenhouse gas emissions in agriculture. We discuss the use of crop rotations and cover cropping with deep rooting mycorrhizal plants, and low-disturbance management, as means of fostering subsoil AM communities. Finally, we suggest future research goals that would allow us to maximize these benefits.

Arbuscular mycorrhiza: a viable strategy for soil nutrient loss reduction.

Arbuscular mycorrhiza fungi's (AMF) role in plant nutrition and stress management is well known, but very few researches and studies have been conducted so far on the fungal ability to reduce different nutrient losses (runoff, leaching and volatilization) from the soil system. This important ecosystem service of AMF had been neglected largely. From the recent findings, it has been confirmed that mycorrhizal symbiosis has potential to check the losses of applied nutrients. The role of soil biota in nutrient cycling is indispensable and determines the nutrient availability to plants. Among these biota, AMF's association with plants is the most prevalent, but the exact mechanisms followed by AMF in nutrient cycling, transformation and reducing nutrient loss ability are still inconclusive. In this review, we will try to unlock this particular aspect of AMF which is important to achieve global food demand in a sustainable way.

Role and influence of soil microbial communities on plant invasion

It is known that plant invasions are of major concern as they result in loss of biodiversity and alterations in ecosystem processes and functions. Although numerous mechanisms have been postulated to find out the reasons behind plant invasiveness, the actual and precise mechanism is still obscure. Soil microbes are considered as one of the important determinants of plant growth and establishment. Plant invasion leads to changes in the composition and structure of soil microorganisms. Most of the earlier studies have focused on the aboveground mechanisms of plant invasion. Recently the belowground mechanisms for plant invasion are being investigated. In this review, we focus on the various hypotheses related to soil microbes in either enhancing or suppressing plant invasions. The interactions between soil microbes with native and non-native plant species, the role of the plant-soil feedback system in the invasion and its impact, the function of mycorrhizal and bacterial symbiosis in plant species invasion and the role of soil biota and changes brought about in soil nutrient cycling and soil enzymes due to plant invasion are also discussed.

Roles of Arbuscular Mycorrhizal Fungi and Soil Abiotic Conditions in the Establishment of a Dry Grassland Community.

BackgroundThe importance of soil biota in the composition of mature plant communities is commonly acknowledged. In contrast, the role of soil biota in the early establishment of new plant communities and their relative importance for soil abiotic conditions are still poorly understood.Aims and MethodsThe aim of this study was to understand the effects of soil origin and soil fungal communities on the composition of a newly established dry grassland plant community. We used soil from two different origins (dry grassland and abandoned field) with different pH and nutrient and mineral content. Grassland microcosms were established by sowing seeds of 54 species of dry grassland plants into the studied soils. To suppress soil fungi, half of the pots were regularly treated with fungicide. In this way, we studied the independent and combined effects of soil origin and soil community on the establishment of dry grassland communities.Key ResultsThe effect of suppressing the soil fungal community on the richness and composition of the plant communities was much stronger than the effect of soil origin. Contrary to our expectations, the effects of these two factors were largely additive, indicating the same degree of importance of soil fungal communities in the establishment of species-rich plant communities in the soils from both origins. The negative effect of suppressing soil fungi on species richness, however, occurred later in the soil from the abandoned field than in the soil from the grassland. This result likely occurred because the negative effects of the suppression of fungi in the field soil were caused mainly by changes in plant community composition and increased competition. In contrast, in the grassland soil, the absence of soil fungi was limiting for plants already at the early stages of their establishment, i.e., in the phases of germination and early recruitment. While fungicide affects not only arbuscular mycorrhizal fungi but also other biota, our data indicate that changes in the AMF communities are the most likely drivers of the observed changes. The effects of other soil biota, however, cannot be fully excluded.ConclusionsThese results suggest that the availability of soil fungi may not be the most important limiting factor for the establishment of grassland species in abandoned fields if we manage to reduce the intensity of competition at these sites e.g., by mowing or grazing.

Inhibitory effects of soil biota are ameliorated by high plant diversity

The idea that plant communities with high species diversity are more stable, productive, and resistant to invasion at small spatial scales has become an important ecological paradigm. Recently, the role of soil biota has emerged as a major driver of this relationship between plant species diversity and ecosystem function. In greenhouse experiments, we found that soil collected from experimentally constructed species-rich plant assemblages (that originally contained between 10 and 16 species) promoted the growth of 4 native target plant species more than soil from species-poor communities (that originally contained between 2 and 5 species). Sterilization of soils from species-poor communities improved the growth of these target species more than sterilization of soils from species-rich plant communities, indicative that inhibitory soil biota had greater negative impacts on plant growth in low versus high diversity soils. These results suggest that strong soil biota effects in soils do not simply accrue in experimental monocultures, but can occur in low diversity assemblages that are more realistic of what occurs in nature. Our findings suggest a mechanistic explanation for the diversity-productivity relationship, and further support the importance of inhibitory soil biota as significant contributors to spatial and temporal patterns of abundance in natural plant communities through negative plant-soil feedback.

Enhancement of late successional plants on ex-arable land by soil inoculations.

Restoration of species-rich grasslands on ex-arable land can help the conservation of biodiversity but faces three big challenges: absence of target plant propagules, high residual soil fertility and restoration of soil communities. Seed additions and top soil removal can solve some of these constraints, but restoring beneficial biotic soil conditions remains a challenge. Here we test the hypotheses that inoculation of soil from late secondary succession grasslands in arable receptor soil enhances performance of late successional plants, especially after top soil removal but pending on the added dose. To test this we grew mixtures of late successional plants in arable top (organic) soil or in underlying mineral soil mixed with donor soil in small or large proportions. Donor soils were collected from different grasslands that had been under restoration for 5 to 41 years, or from semi-natural grassland that has not been used intensively. Donor soil addition, especially when collected from older restoration sites, increased plant community biomass without altering its evenness. In contrast, addition of soil from semi-natural grassland promoted plant community evenness, and hence its diversity, but reduced community biomass. Effects of donor soil additions were stronger in mineral than in organic soil and larger with bigger proportions added. The variation in plant community composition was explained best by the abundances of nematodes, ergosterol concentration and soil pH. We show that in controlled conditions inoculation of soil from secondary succession grassland into ex-arable land can strongly promote target plant species, and that the role of soil biota in promoting target plant species is greatest when added after top soil removal. Together our results point out that transplantation of later secondary succession soil can promote grassland restoration on ex-arable land.

The role of soil biota in the weathering of minerals: A review of literature

Two methodological approaches used in the study of the mineral weathering in soils under the effect of biota were analyzed. According to one approach, which is based on the concepts of coordination chemistry, the dissolution of minerals is considered at the ion-molecule level and can be described using the terms and notions of classical thermodynamics. According to the other approach, the weathering of minerals in the supergenesis zone is considered at the ion-electron level within the framework of the corrosion model of supergenesis on the basis of anode-cathode processes, when the mineral in the electrolyte environment serves as an anode and is oxidized being an electron donor. Microorganisms act as a cathodic associate of minerals, i.e., an electron acceptor. The kinetic parameters related to the rate of the biological processes and the diffusion come out on top in this case. The review deals with the mechanisms of the direct and indirect effect of biota on the weathering of minerals in soils; the features of the soil in the rhizosphere and the ectomycorrhizosphere; the impact of fungi, bacteria, and higher plants on the minerals; and the generated synergistic effect.

Lack of belowground mutualisms hinders Pinaceae invasions

Why particular invasions succeed and others fail is not well understood. The role of soil biota has been proposed as important. However, the role of mutualists has received much less attention than that of pathogens. Here we report that lack of adequate ectomycorrhizal fungi hinders invasion by exotic Pinaceae on Isla Victoria, Argentina, by reducing both the probability of establishment and growth of invading individuals. More than one hundred exotic tree species were introduced to this island ca. 80 years ago, but invasive trees are found in high densities only in areas adjacent to plantations. With a series of greenhouse and field experiments we found lower mycorrhizal colonization levels and few fungal species far from original plantings, and key fungal mutualists are confined to areas near plantations, probably owing to dispersal limitations. Low inoculum levels far from the plantations are retarding the invasion. Our experiments indicate that positive interactions belowground can play a key but underappreciated role in invasion dynamics.

Soil‐carbon preservation through habitat constraints and biological limitations on decomposer activity

AbstractWe review recent experimental results on the role of soil biota in stabilizing or destabilizing soil organic matter (SOM). Specifically, we analyze how the differential substrate utilization of the various decomposer organisms contributes to a decorrelation of chemical stability, residence time, and carbon (C) age of organic substrates.Along soil depth profiles, a mismatch of C allocation and abundance of decomposer organisms is consistently observed, revealing that a relevant proportion of soil C is not subjected to efficient decomposition. Results from recent field and laboratory experiments suggest that (1) bacterial utilization of labile carbon compounds is limited by short‐distance transport processes and, therefore, can take place deep in the soil under conditions of effective local diffusion or convection. In contrast, (2) fungal utilization of phenolic substrates, including lignin, appears to be restricted to the upper soil layer due to the requirement for oxygen of the enzymatic reaction involved. (3) Carbon of any age is utilized by soil microorganisms, and microbial C is recycled in the microbial food web. Due to stoichiometric requirements of their metabolism, (4) soil animals tend to reduce the C concentration of SOM disproportionally, until it reaches a threshold level.The reviewed investigations provide new and quantitative evidence that different soil C pools underlie divergent biological constraints of decomposition. The specialization of decomposers towards different substrates and microhabitats leads to a relatively longer persistence of virtually all kinds of organic substrates in the nonpreferred soil spaces. We therefore propose to direct future research explicitly towards such biologically nonpreferred areas where decomposition rates are slow, or where decomposition is frequently interrupted, in order to assess the potential for long‐term preservation of C in the soil.

Abstracts of Papers Presented to The ANPC National Forum: What Lies Beneath? The Role of Soil Biota in the Health and Rehabilitation of Native Vegetation Canberra, 17-19 April 2007

Abstracts of Papers Presented to The ANPC National Forum: What Lies Beneath? The Role of Soil Biota in the Health and Rehabilitation of Native Vegetation Canberra, 17-19 April 2007

The role of soil fauna in ecosystems: A historical review

Summary The research development in this review is divided into successive periods: (1) “From Darwin to Satchell”, covering the “pre-experimental” decades dealing with the functions of earthworms, (2) “Litterbag Studies”, characterized by field experiments on the faunal influence on litter decomposition, (3) “The Time of IBP”, concentrating on community energetics, (4) “The Microcosm Era”, laboratory studies that started with simple systems, followed by increasing complexity of experimental setup and community of organisms, including living plants, and ending to laboratory-scale “ecosystems”, (5) the recent “Biodiversity Boom”, analysing the relations between soil biodiversity and ecosystem functions, and (6) the current “Holistic View” that tends to link the diversity and functions of aboveground and belowground communities. These “periods” started roughly in this order, but are largely overlapping, since the early techniques are in continuing use together with the modern ones. The current knowledge on the role of soil biota, their diversity and various components has accumulated mainly during the last 30 years, resulting in the modern view of soil fauna as a part of the ecosystem.

Soil biota and invasive plants

Interactions between plants and soil biota resist invasion by some nonnative plants and facilitate others. In this review, we organize research and ideas about the role of soil biota as drivers of invasion by nonnative plants and how soil biota may fit into hypotheses proposed for invasive success. For example, some invasive species benefit from being introduced into regions of the world where they encounter fewer soil-borne enemies than in their native ranges. Other invasives encounter novel but strong soil mutualists which enhance their invasive success. Leaving below-ground natural enemies behind or encountering strong mutualists can enhance invasions, but indigenous enemies in soils or the absence of key soil mutualists can help native communities resist invasions. Furthermore, inhibitory and beneficial effects of soil biota on plants can accelerate or decelerate over time depending on the net effect of accumulating pathogenic and mutualistic soil organisms. These 'feedback' relationships may alter plant-soil biota interactions in ways that may facilitate invasion and inhibit re-establishment by native species. Although soil biota affect nonnative plant invasions in many different ways, research on the topic is broadening our understanding of why invasive plants can be so astoundingly successful and expanding our perspectives on the drivers of natural community organization.