Low Soil Nutrient Availability Research Articles

Regional emissions of soil greenhouse gases across Tibetan alpine grasslands

Soil greenhouse gas (GHG) emissions play an important role in regional climate feedback on the Qinghai-Tibetan Plateau (QTP). Previous studies have focused on soil GHGs based on observations within a limited space on the QTP, however, the regional GHG emissions remain unclear. Analyzing soil samples from 25 sites along a 2,700 km transect across QTP, we showed significantly higher soil CO2 and N2O emission rates in alpine meadows than other upland grassland types, but similar soil CH4 uptake rates across all grassland types. The spatial variations of total soil GHG balance were dominated by CO2 emission. We found that CO2 emission was primarily constrained by high soil pH, low soil moisture and nutrient availability, and fungal abundance, N2O emission was inhibited by high soil pH, while CH4 uptake was dominated by methanotrophic abundance. Furthermore, we estimated a current regional total soil GHG balance of 144.4 Tg CO2-eq yr−1 for surface soil across Tibetan alpine grasslands, which increased by 17.6%, 24.8%, and 38.9% under warming scenarios of 1.5℃, 2℃ and 3℃, respectively. Our results provide a baseline for regional soil GHG emissions responding to climate warming on the QTP.

First-Year Mortality of Four Early-Successional Species on Severely Degraded Sites in Eastern Canada as Influenced by a Factorial of Site Preparation Treatments

Barren, severely disturbed sites lacking soil, such as mine sites and waste deposit sites, present severe challenges to ecological service restoration because of high temperatures, solar radiation, and wind speeds; extreme temperature changes; and low soil moisture and nutrient availability. An ecological restoration experiment using three site preparation treatments was conducted. Straw (S), Meri-Crusher (MC), and coarse woody debris (CWD) were assessed in a site, no site preparation 2 × 2 × 2 factorial, including a control treatment, on sites barren for 25 years. In addition, four early-successional species: white birch (WB, Betula papyrifera Marsh), gray birch (GB, Betula populifolia Marsh), green alder (GA, Alnus viridis Vill. ssp. crispa Ait) and speckled alder (SA, Alnus incana L. ssp. rugosa Du Roi), were examined for mortality. Mortality was measured after three time periods, summer-related 2021, winter-related, and frost heave mortality (spring 2022). Summer-related mortality was predominantly influenced by S treatments (reduced mortality) and their interactions. Straw’s ability to retain moisture strongly suggests it mitigated summer-related drought mortality. S interactions were not rank changes but magnitude effects. The species × straw interaction showed that SA had the greatest magnitude difference, with 25% and 3.6% summer-related mortality for NS and S treatments, respectively. SA, a hydrophilic species, accounted for nearly half the total summer-related mortality, and there were strong species effects and species interactions. The full combination of site preparation treatments had the lowest summer-related mortality, at 1%. Winter-related mortality only affected 1.9% of the total sample size, and there were no species effects or interactions, but contrary to other results, S was the leading cause of mortality due to fungal presence found on expired seedlings. For frost heave mortality, it was clear that the S treatment was effective, with 1.2% and 20.7% overall mortality for S and NS, respectively. MC alone had the greatest negative effect, with 46.9% frost heave mortality; however, when interacting with S or CWD, the mortality decreased substantially. Frost heave had no species interactions and only a species effect, with SA having the greatest mortality. Over the first full year, MC alone and control had the greatest mortality, with 60% and 38%, respectively, after one year. Overall, one-year mortality showed S reduced mortality by 27% and CWD by 19%, while MC increased mortality by approximately 4%. When treatments were combined in any way, mortality dropped significantly, showing an additive effect, with the three-combination treatment resulting in the lowest one-year mortality, of only 3.1%. Straw provided the strongest effect, both as an effective barrier to moisture evaporation, providing up to 10% more soil moisture under dry conditions and provided an effective thermal barrier that substantially reduced the frost heave mortality. Even early-successional species such as WB, GB, GA, and SA need site preparation treatments to establish and survive the first year on long-term barren lands.

Soil properties and root traits are important factors driving rhizosphere soil bacterial and fungal community variations in alpine Rhododendron nitidulum shrub ecosystems along an altitudinal gradient

Both soil properties and plant root traits are pivotal factors affecting microbial communities. However, there is still limited information about their importance in shaping rhizosphere soil microbial communities, particularly in less-studied alpine shrub ecosystems. To investigate the effects of altitude (3300, 3600, 3900, and 4200 m) on the diversity and composition of rhizosphere soil bacterial and fungal communities, as well as the factors shaping rhizosphere soil microbial communities, we conducted this study in alpine Rhododendron nitidulum shrub ecosystems from the Zheduo mountain of the eastern Tibetan Plateau. Results demonstrated that bacterial community diversity and richness decreased to the lowest value at 3600 m and then increased at higher altitudes compared with 3300 m; whereas fungal richness at 3300 m was much lower than at other altitudes, and was closely related to soil properties and root traits. The composition of rhizosphere soil bacterial and fungal communities at the low altitude (3300 m) was different from that at high altitudes. Permutational multivariate analysis of variance and redundancy analysis indicated that soil properties (soil water content, pH, NO3−-N, and available phosphorus) and root traits (surface area, and maximum depth) were the major factors explaining the variations of rhizosphere soil bacterial and fungal communities. Specific bacterial and fungal taxa along altitudes were identified. The bacterial taxa Planctomycetota was dominant at 3300 and 3600 m with low soil nutrient availability and high root surface area, whereas the fungal taxa Mortierellomycota was abundant at 3900 and 4200 m with high soil nutrient availability and low root surface area. These results suggested that different soil microbes can respond differently to altitude. This study provides a novel insight into factors driving rhizosphere soil bacterial and fungal community variations, which could improve our understanding of microbial ecology in alpine R. nitidulum shrub ecosystems along altitude.

Contrasting distribution of enzyme activities in the rhizosphere of European beech and Norway spruce.

Recent policies and silvicultural management call for forest regeneration that involve the selection of tree species able to cope with low soil nutrient availability in forest ecosystems. Understanding the impact of different tree species on the rhizosphere processes (e.g., enzyme activities) involved in nutrient mobilisation is critical in selecting suitable species to adapt forests to environmental change. Here, we visualised and investigated the rhizosphere distribution of enzyme activities (cellobiohydrolase, leucine-aminopeptidase, and acid phosphomonoesterase) using zymography. We related the distribution of enzyme activities to the seedling root morphological traits of European beech (Fagus sylvatica) and Norway spruce (Picea abies), the two most cultivated temperate tree species that employ contrasting strategies in soil nutrient acquisition. We found that spruce showed a higher morphological heterogeneity along the roots than beech, resulting in a more robust relationship between rhizoplane-associated enzyme activities and the longitudinal distance from the root apex. The rhizoplane enzyme activities decreased in spruce and increased in beech with the distance from the root apex over a power-law equation. Spruce revealed broader rhizosphere extents of all three enzymes, but only acid phosphomonoesterase activity was higher compared with beech. This latter result was determined by a larger root system found in beech compared with spruce that enhanced cellobiohydrolase and leucine-aminopeptidase activities. The root hair zone and hair lengths were significant variables determining the distribution of enzyme activities in the rhizosphere. Our findings indicate that spruce has a more substantial influence on rhizosphere enzyme production and diffusion than beech, enabling spruce to better mobilise nutrients from organic sources in heterogeneous forest soils.

Genotypic variability for tolerance to low soil phosphorus availability in faba bean (Vicia faba L.)

The capacity of legumes to fix atmospheric dinitrogen in partnership with rhizobia provides an input-saving and resource-conserving alternative, thereby reducing the need for chemical fertilizers while enhancing overall crop productivity. However, low soil nutrient availability, notably phosphorus (P), is among the most nutrient limitations for legumes, since legume nodules responsible for N2 fixation have a high P requirement. In order to explore the genetic variability for P uptake and use efficiency in low-P availability in soils, three faba bean genotypes namely Sidi Aich, Castel and Diva were studied in two field sites (S1 and S2) over two growing seasons 2018 and 2019. At flowering stage, plants were harvested and analyzed for their nodulation, growth, P content and yield. Results indicate that low-P availability in the soil of S1 significantly limited plant growth, nodulation, and grain yield for all genotypes though with highest extent for Diva and Castel. We found a significant correlation between nodule growth of all genotypes and Olsen-P content in the rhizosphere soil during two growing seasons. It is concluded that the genotypes selected for their P uptake and use efficiency had a higher yield and could best adapt to low-P availability under field conditions.

Synergy of saprotrophs with mycorrhiza for litter decomposition and hotspot formation depends on nutrient availability in the rhizosphere

Plants acquire and recycle nutrients from soil organic matter, and these dynamics depend on a highly diverse array of microorganisms in the rhizosphere. Although functions of many microbial groups have been identified, how different groups interact to affect biogeochemical processes is still poorly understood. We investigated the interactive effects of saprotrophs and arbuscular mycorrhizal fungi (AMF) on Medicago sativa litter decomposition and spatial distribution of enzyme activity in the rhizosphere in nutrient poor and rich soils, using compartmented microcosms designed for zymography. In nutrient poor soils, co-inoculation of saprotrophic bacteria (Alcaligenes faecalis) or fungi (Phanerochaete chrysosporium) with AMF (Rhizophagus irregularis) resulted in faster litter decomposition and greater hotspot areas of enzymes in the rhizosphere compared to mono-inoculations. These positive effects were stronger in the interaction of AMF with saprotrophic bacteria than that with saprotrophic fungi. The synergy of saprotrophic bacteria with AMF for litter decomposition and enzymatic hotspot formation was weaker in nutrient rich soils than that in nutrient poor soils. In contrast, in nutrient rich soils, co-inoculation of saprotrophic fungi with AMF reduced litter decomposition. A partial least squares path modeling (PLS-PM) analysis indicated that faster litter decomposition and larger enzymatic hotspots increased overall plant growth. These findings suggest the existence of important synergistic relationships between these two microbial guilds for plant growth in nutrient poor soils. Specifically, AMF accelerated litter mineralization by increasing saprotrophic biomass and enzyme activities (i.e., nitrate reductase, urease and cellulase). At the same time, saprotrophs increased AMF colonization rate, which increased the hotspot areas of enzyme activities. These hotspots, in turn, broadened the nutrient mobilization zone around the roots - in the rhizosphere. Consequently, the synergistic interactions between saprotrophs and AMF for litter decomposition and the formation of enzymatic hotspots may be an important mechanism for promoting plant fitness under low soil nutrient availability.

Low soil nutrient availability does not decrease post-drought recovery of Brachiaria Mavuno

Low soil nutrient availability does not decrease post-drought recovery of Brachiaria Mavuno

Contrasting responses of saproxylic beetles and plants to non-native tree invasion reveal feedback mechanisms between trophic levels

Invasive, alien trees threaten native biodiversity, but detailed information about the patterns and mechanisms of diversity loss remain unknown. We explored the impact of an invasive tree on vascular plants and saproxylic beetles. We compared their species richness, community composition, and selected biological characteristics between stands of invasive black locust (Robinia pseudoacacia), a nitrogen-fixing clonal tree, and native oak-dominated, broadleaf forests in the SE Czech Republic and W Slovakia.Compared to native forests, R. pseudoacia stands were characterised by low canopy cover, high light and soil nutrient availability, and similar deadwood volumes. R. pseudoacacia had species-poor, dense understorey vegetation composed of tall, nitrophilous herbs. Saproxylic beetles, on the other hand, were similarly diverse and abundant in both R. pseudoacacia stands and native forests. Their communities were mainly shaped by forest structure, as overall beetle diversity and guilds exploiting more decayed wood benefited from the open canopies and high deadwood volumes. Richness and abundance of threatened plants and beetles requiring fresh wood, together with total richness of threatened beetles were, however, substantially lower in R. pseudoacacia stands.The adverse impacts of R. pseudoacacia on plants partly contrasted with its much less pronounced effects on saproxylic beetles. In intensively exploited landscapes, R. pseudoacacia stands can offer refuge to saproxylic beetles. However their lower diversity and lower incidence of threatened species show that R. pseudoacacia contributes to homogenization and impoverishment of plant and insect assemblages. Robinia stands thus should be eliminated from protected areas and minimalised wherever biodiversity conservation is of concern.

Understorey plant community assemblage of AustralianEucalyptuswoodlands under elevated CO2 is modulated by water and phosphorus availability

AbstractAimsGiven the key functional role of understorey plant communities and the substantial extent of forest cover at the global scale, investigating understorey community responses to elevated CO2 (eCO2) concentrations, and the role of soil resources in these responses, is important for understanding the ecosystem-level consequences of rising CO2 concentrations for forest ecosystems. Here, we evaluated how experimentally manipulating the availabilities of the two most limiting resources in an extremely phosphorus-limited eucalypt woodland in eastern Australia (i.e. water and phosphorus) can modulate the response of the understorey community to eCO2 in terms of germination, phenology, cover, community composition and leaf traits.MethodsWe collected soil containing native soil seed bank to grow experimental understorey plant communities under glasshouse conditions.Important FindingsPhosphorus addition increased total plant cover, particularly during the first 4 weeks of growth and under high water conditions, a response driven by the graminoid component of the plant community. However, the treatment differences diminished as the experiment progressed, with all treatments converging at ~80% plant cover after ~11 weeks. In contrast, plant cover was not affected by eCO2. Multivariate analyses reflected temporal changes in the composition of plant communities, from pots where bare soil was dominant to high-cover pots dominated by a diverse community. However, both phosphorus addition and the interaction between water availability and CO2 affected the temporal trajectory of the plant community during the experiment. eCO2 also increased community-level specific leaf area, suggesting that functional adaptation of plant communities to eCO2 may precede the onset of compositional responses. Given that the response of our seed bank-derived understorey community to eCO2 developed over time and was mediated by interactions with phosphorus and water availability, our results suggest a limited role of eCO2 in shaping plant communities in water-limited systems, particularly where low soil nutrient availability constrains productivity responses.

Biogeographic patterns and co-occurrence networks of diazotrophic and arbuscular mycorrhizal fungal communities in the acidic soil ecosystem of southern China

Low soil nutrient availability severely constrains plant growth and productivity in acidic soil ecosystems. Diazotrophs and arbuscular mycorrhizal fungi (AMF) are the important microbial groups that improve the bioavailability of soil nitrogen (N) and phosphorus (P), respectively. Therefore, the objective was to investigate the biogeographic patterns and co-occurrence networks of the diazotrophic and AMF communities in the acidic soil ecosystem. We collected 52 soil samples from four long-term field observation stations with spatial distances of 961.3 km in the acidic soil region of southern China, and analyzed the community composition and biogeographic distributions of the diazotrophs and AMF using high-throughput sequencing of the functional gene amplicons. The variation partition analysis indicated that soil physicochemical factors provided more contributions than geographic distance, sampling stations and land-use types in the assembly of the diazotrophic and AMF community communities. Distance-decay relationships and Mantel tests showed that soil physicochemical factors had remarkable effects on both microbial community structures, whereas geographic distance only significantly affected the diazotrophic community variations. Co-occurrence network analysis revealed that AMF network was more complex and stable than the diazotrophic network. Furthermore, the dominant genera Bradyrhizbium and Glomus might be the more important keystone taxa in the diazotrophic and AMF networks, respectively. These findings suggest that the diazotrophic and AMF communities exhibit different assembly mechanisms and co-occurrence ecological networks in the acidic soil region of southern China, and both community assemblies were mainly driven by soil physicochemical factors.

Assessment of inland valley soils for sugarcane (Saccharum officinarum L.) production in some floodplains in central Nigeria

Abstract Sugarcane is an energy crop with great economic potentials. Information on soil evaluation for sugarcane in central Nigeria is very scanty. This study was carried out to evaluate the suitability of some soils of the floodplains in central Nigeria for sugarcane cultivation. A semi-detailed soil survey was carried out on 18,500 hectares of land straddling the floodplains of Rivers Niger and Benue in Korton-Karfe Local Government Area of Kogi State. Land resource survey was carried out using a 500 m×500 m grid pattern. Identified soil types were further examined with standard soil profiles. Samples were collected from the soil genetic horizons as well as surface (0–30 cm) soils at selected sampling points for fertility analysis. Parametric and non-parametric suitability evaluation methods were used to relate land qualities with land use requirements for commercial sugarcane cultivation. Relationships between evaluation methods were assessed using Spearman’s rank correlation coefficients. Nine soil mapping units were identified in the study areas which were mainly Inceptisols (55.4%) and Alfisols (22.5%) which correlates with Fluvisols (40.4%), Cambisols (15.1%) and Lixisols (22.5%) in the World Reference Base (WRB) classification system. The evaluation methods used revealed that 0%, 4.95%, 49.48%, 23.55% of the soils were highly suitable (S1), moderately suitable (S2), marginally suitable (S3) and not suitable (N) for sugarcane cultivation, respectively. Potentially, 0%, 9.52%, 44.91% and 23.55% of the soils were found to be highly suitable (S1), moderately suitable (S2), marginally suitable (S3) and not suitable (N) for sugarcane cultivation, respectively. The soils were strongly limited by low soil nutrient availability, soil acidity and flood hazard. Soil management practices such as application of organic manures, fertiliser and liming could be adopted to ameliorate the soil acidity and supply deficient nutrients while land development strategies such as drainage, flood control and possibly sub-soiling would mitigate other major limitations to sugarcane cultivation.

Diversity of root-associated culturable fungi of Cephalanthera rubra (Orchidaceae) in relation to soil characteristics.

Cephalanthera rubra (L.) Rich., Red Helleborine, is a widespread orchid in Europe but known only from three very small populations in England. These populations are in decline with no natural seed setting for more than a decade. The species may become extinct in the UK soon unless viable strategies are in place for ex situ conservation, especially the use of symbiotic propagation. Because of the fragile nature of the populations in England mycorrhizal fungal diversity study is not feasible. Therefore, to understand the factors needed for healthy Red Helleborine populations, soil characteristics and diversity of culturable root-derived fungi of the populations from a small area in the Loire Valley in France were studied. The main objectives of the study were: (1) Which culturable mycorrhizal fungi associated with C. rubra roots and (2) To what extent is variation in fungal communities related to variation in soil characteristics? Here, we report a significant difference in diversity of culturable mycorrhizal and non-mycorrhizal fungi depending on soil pH and phosphorus content. Mycorrhizal associations were favoured by plants in locations with low soil nutrient availability and comparatively higher pH. Our study shows that mycorrhizal fungi, both ecto and endo, can be cultured from roots of plants at different maturity stages.

Isotopic constraints on plant nitrogen acquisition strategies during ecosystem retrogression.

Plant root associations with microbes such as mycorrhizal fungi or N-fixing bacteria enable ecosystems to tap pools of nitrogen (N) that might otherwise be inaccessible, including atmospheric N or N in large soil organic molecules. Such microbially assisted N-foraging strategies may be particularly important in late-successional retrogressive ecosystems where productivity is low and soil nutrients are scarce. Here, we use natural N-stable isotopic composition to constrain pathways of N supplies to different plant functional groups across a well-studied natural soil fertility gradient that includes a highly retrogressive stage. We demonstrate that ectomycorrhizal fungi, ericoid mycorrhizal fungi, and N-fixing bacteria support forest N supplies at all stages of ecosystem succession, from relatively young, N-rich/phosphorus (P)-rich sites, to ancient sites (ca. 500 ky) where both N supplies and P supplies are exceedingly low. Microbially mediated N sources are most important in older ecosystems with very low soil nutrient availability, accounting for 75-96% of foliar N at the oldest, least fertile sites. These isotopically ground findings point to the key role of plant-microbe associations in shaping ecosystem processes and functioning, particularly in retrogressive-phase forest ecosystems.

An Ammoniated Straw Incorporation Increased Biomass Production and Water Use Efficiency in an Annual Wheat-Maize Rotation System in Semi-Arid China

Water shortage and excessive chemical fertilizers application result in low soil water and nutrient availability and limit crop production in the Loess Plateau of Northwest China. Ammoniated straw incorporation with N fertilization may be an efficient strategy to maintain agricultural sustainability. However, the interactive effects of straw incorporation and N fertilizer on the biomass water use efficiency (WUE) in the winter wheat–summer maize rotation system remain unclear. A 3-year field experiment was conducted to evaluate the effects of combining ammoniated straw incorporation and N fertilizer on soil water, biomass yield and biomass water use efficiency (WUE) in an annual summer maize (Zea mays L.)—Winter wheat (Triticum aestivum L.) rotation system. There were three treatments: (i) long straw (5 cm) mulching with N fertilizer (CK), (ii) long straw with N fertilizer plowed into the soil (LP), and (iii) ammoniated long straw with N fertilizer plowed into the soil (ALP). Compared with the CK treatment, LP and ALP led to a similar soil water storage capacity. ALP improved summer maize biomass yield and winter wheat biomass yield at the jointing-maturity stage. ALP improved summer maize WUE at the ten-leaf collar-tasseling stage and winter wheat WUE from the tillering stage to the maturity stage. Also, the ALP treatment increased the total water use efficiency (TWUE) of winter wheat by 4.1–22.0%. Overall, ammoniated straw incorporation produced the most favorable biomass yield and WUE in the summer maize—Winter wheat rotation system in the Loess Plateau of China.

Synergistic impacts of co‐occurring invasive grasses cause persistent effects in the soil‐plant system after selective removal

Abstract Human influence on the environment is so extensive that virtually all ecosystems on the planet are now affected by biological invasions. And, often, ecosystems are invaded by multiple co‐occurring non‐native species. Hence, it is important to understand the impacts these invasions are producing on biodiversity and ecosystem processes. Here, we present results of a 2‐year long field experiment where we tested the effects of co‐occurring invasive C4 African grasses in a Cerrado area in central Brazil. We compared plant and arthropod communities, plant biomass, and soil nitrogen dynamics and soil chemical characteristics across five experimental treatments: Urochloa decumbens removal; Melinis minutiflora removal; both U. decumbens and M. minutiflora removal; U. decumbens and M. minutiflora invaded plots; and uninvaded Cerrado. We hypothesized that selective removal of invasive grasses would have distinct effects on the native ecosystem structure and functioning. We expected that each invasive grass would produce a different type of impact on the native ecosystem and that their impacts would be synergistic when co‐occurring. Removal of M. minutiflora doubled native plant diversity and biomass when compared to invaded plots, whereas removal of U. decumbens did not alter these parameters. Cerrado plots had four times more plant species than plots cleared of invasives. Removal of invasive grasses did not affect the species richness or community composition of soil epigeal fauna. Cerrado soils had lower fertility, organic matter content and pH than invaded soils. The effects were generally higher when both invasive grasses were removed, suggesting impacts were synergistic, but M. minutiflora had greater effects on plants and soils than U. decumbens. Both invasive species produced negative impacts, but a single species was the main driver. We also detected persistent effects of the invasive grass species on the ecosystem after 2 years of removal. We conclude that invasive species of the same functional group have similar types of effects in native ecosystems, but the magnitude of impact was largely dependent on invasive species biomass and cover. Where multiple invasive species are present, research and management of invaded ecosystems should tackle the interacting effects of co‐occurring invaders.

Thistle crops in marginal lands after compost addition: Plant biomass and effect on soil physical, chemical and biological properties

AbstractThe growing interest in bioenergy crops that do not compete with food production for land use has promoted the implementation of low‐input crops on marginal lands. However, these crops can be highly limited by the low soil nutrient and water availability in these lands. In this work, biosolid compost (BC) was applied to improve the quality of a degraded, C‐poor soil under Mediterranean conditions. We evaluated the effects of BC addition on soil physical, chemical and biochemical properties in a field experiment with two native species with potential as bioenergy crops (Cynara cardunculus and Silybum marianum). The addition of BC significantly increased soil C content from <0.9% to >1%, and produced a two‐fold increase in soil P availability. Respiration rates and microbial activity were only slightly improved by BC, while significant increases in the PLFA molar content assigned to general classes of bacteria were recorded. The beneficial effects of BC triggered the percentage of seed germination in S. marianum (from 64% in control plots to 85% in the compost treatment) as well as the production of biomass in both species (two‐fold increase in the second year). Application of BC led to increases in energy yield of 58% for C. cardunculus and of 71% for S. marianum. Considering the low economic cost of BC, its application on marginal soils in combination with C. cardunculus crops, producing much larger biomass than S. marianum, could be considered as an option for degraded Mediterranean soils.

Nutrient scarcity strengthens soil fauna control over leaf litter decomposition in tropical rainforests.

Soil fauna is a key control of the decomposition rate of leaf litter, yet its interactions with litter quality and the soil environment remain elusive. We conducted a litter decomposition experiment across different topographic levels within the landscape replicated in two rainforest sites providing natural gradients in soil fertility to test the hypothesis that low nutrient availability in litter and soil increases the strength of fauna control over litter decomposition. We crossed these data with a large dataset of 44 variables characterizing the biotic and abiotic microenvironment of each sampling point and found that microbe-driven carbon (C) and nitrogen (N) losses from leaf litter were 10.1 and 17.9% lower, respectively, in the nutrient-poorest site, but this among-site difference was equalized when meso- and macrofauna had access to the litterbags. Further, on average, soil fauna enhanced the rate of litter decomposition by 22.6%, and this contribution consistently increased as nutrient availability in the microenvironment declined. Our results indicate that nutrient scarcity increases the importance of soil fauna on C and N cycling in tropical rainforests. Further, soil fauna is able to equalize differences in microbial decomposition potential, thus buffering to a remarkable extent nutrient shortages at an ecosystem level.

Root nutrient concentration and biomass allocation are more plastic than morphological traits in response to nutrient limitation

Understanding the magnitude of phenotypic plasticity within a species is important, particularly when comparing species from diverse habitats or when using traits from global databases. Our objective was to quantify the magnitude of intraspecific variability of fine root, stem, and leaf traits in response to nutrient availability. We measured growth rates and traits from fine roots, stems, and leaves on replicate seedlings of four species grown in two treatments: low and high soil nutrient availability. We used ANOVA to test for effects of fertilizer, species, and their interaction on trait expression, and ranked intraspecific trait variation using the coefficient of variation. Root nutrient concentration, relative growth rate, and biomass allocation exhibited the most plastic responses to nutrient availability. Specific root length, specific leaf area, root diameter, and wood density were the least variable traits within species. Nutrient limitation only induced greater root branching in the non-mycorrhizal Proteaceae species that produced more cluster roots. Woody plants respond to nutrient limitation by increasing root mass fraction, rather than by adjusting root morphology or structure. We urge caution when using root tissue chemistry traits obtained from global databases in local studies, as this is one of the most plastic traits in response to nutrient availability.

Nutrient-cycling mechanisms other than the direct absorption from soil may control forest structure and dynamics in poor Amazonian soils

Tropical forests store large amounts of biomass despite they generally grow in nutrient-poor soils, suggesting that the role of soil characteristics in the structure and dynamics of tropical forests is complex. We used data for >34 000 trees from several permanent plots in French Guiana to investigate if soil characteristics could predict the structure (tree diameter, density and aboveground biomass), and dynamics (growth, mortality, aboveground wood productivity) of nutrient-poor tropical forests. Most variables did not covary with site-level changes in soil nutrient content, indicating that nutrient-cycling mechanisms other than the direct absorption from soil (e.g. the nutrient uptake from litter, the resorption, or the storage of nutrients in the biomass), may strongly control forest structure and dynamics. Ecosystem-level adaptations to low soil nutrient availability and long-term low levels of disturbance may help to account for the lower productivity and higher accumulation of biomass in nutrient-poor forests compared to nutrient-richer forests.

Plant, soil and microbial controls on grassland diversity restoration: a long‐term, multi‐site mesocosm experiment

Summary The success of grassland biodiversity restoration schemes is determined by many factors; as such their outcomes can be unpredictable. There is a need for improved understanding of the relative importance of below‐ground factors to restoration success, such as contrasting soil type and management intensities, as well as plant community composition and order of assembly. We carried out an 8‐year mesocosm experiment across three locations in the UK to explore the relative and interactive roles of various above‐ground and below‐ground factors in the establishment of target species, to determine general constraints on grassland restoration. Each location had a series of mesocosms with contrasting soil types and management status, which were initially sown with six grasses typical of species‐poor grasslands targeted for restoration. Over 5 years, sets of plant species were added, to test how different vegetation treatments, including early‐coloniser species and the hemiparasite Rhinanthus minor, and soil type and management, influenced the establishment of target plant species and community diversity. The addition of early‐coloniser species to model grasslands suppressed the establishment of target species, indicating a strong priority effect. Soil type was also an important factor, but effects varied considerably across locations. In the absence of early‐coloniser species, low soil nutrient availability improved establishment of target species across locations, although R. minor had no beneficial effect. Synthesis and applications. Our long‐term, multi‐site study indicates that successful restoration of species‐rich grassland is dependent primarily on priority effects, especially in the form of early‐coloniser species that suppress establishment of slow‐growing target species. We also show that priority effects vary with soil conditions, being stronger in clay than sandy soils, and on soils of high nutrient availability. As such, our work emphasises the importance of considering priority effects and local soil conditions in developing management strategies for restoring plant species diversity in grassland.