Plant Nutrient Acquisition Strategies Research Articles

Effects of plant nutrient acquisition strategies on biomass allocation patterns in wetlands along successional sequences in the semi-arid upper Yellow River basin.

The ecological environment of wetlands in semi-arid regions has deteriorated, and vegetation succession has accelerated due to climate warming-induced aridification and human interference. The nutrient acquisition strategies and biomass allocation patterns reflect plant growth strategies in response to environmental changes. However, the impact of nutrient acquisition strategies on biomass allocation in successional vegetation remains unclear. We investigated 87 plant communities from 13 wetland sites in the semi-arid upper Yellow River basin. These communities were divided into three successional sequences: the herbaceous community (HC), the herbaceous-shrub mixed community (HSC), and the shrub community (SC). The nutrient composition of stems and leaves, as well as the biomass distribution above and belowground, were investigated. Results revealed that aboveground biomass increased with succession while belowground biomass decreased. Specifically, SC exhibited the highest stem biomass of 1,194.53 g m-2, while HC had the highest belowground biomass of 2,054.37 g m-2. Additionally, significant positive correlations were observed between leaf and stem biomasses in both HC and SC. The nitrogen (N) and phosphorus (P) contents within aboveground parts displayed an evident upward trend along the succession sequence. The highest N and P contents were found in SC, followed by HSC, and the lowest in HC. Stem N was negatively correlated with stem, leaf, and belowground biomass but positively correlated with root-shoot ratio. Leaf P displayed positive correlations with aboveground biomass while showing negative correlations with belowground biomass and root-shoot ratio. The ratios of C:N, C:P, and N:P in stem and leaf exhibited positive correlations with belowground biomass. The random forest model further demonstrated that stem N and leaf P exerted significant effects on aboveground biomass, while leaf P, stem N and P, and leaf C:P ratio had significant effects on belowground components. Additionally, the root-shoot ratio was significantly influenced by leaf P, leaf C:P ratio, and stem N, P, and C:P ratio. Therefore, the aboveground and belowground biomasses exhibited asynchronism across successional sequences, while plant nutrient acquisition strategies, involving nutrient levels and stoichiometric ratios, determined the biomass allocation pattern. This study offers valuable insights for assessing vegetation adaptability and formulating restoration plans in the semi-arid upper Yellow River basin.

Below‐ground root nutrient‐acquisition strategies are more sensitive to long‐term grazing than above‐ground leaf traits across a soil nutrient gradient

Abstract Understanding how plant nutrient acquisition strategies respond to grazing at the community level is critical understanding ecosystem structure and functioning in grasslands. However, few studies have simultaneously compared the difference in above‐ground (leaf) and below‐ground (root) nutrient‐acquisition strategies in response to long‐term grazing, especially at the regional scale. Here, we measured a set of leaf and fine‐root traits that correspond to the fast‐slow economic spectrum at the community level in 10 experimental sites from paired grazed and ungrazed grasslands across a soil nutrient gradient covering three major types of grasslands in northern China. We found that patterns of variations of leaf and fine‐root traits were consistent with both a leaf and root economic spectrum at the community level for both grazed and non‐grazed plots. Grazing had minor effect on community‐level leaf nutrient‐acquisition strategies but strongly influenced community‐level root nutrient‐acquisition strategies. Specifically, root nutrient‐acquisition strategies were shifted to more exploitative resource use in grazed communities. Moreover, soil nutrient contributed to the changes in both leaf and root nutrient‐acquisition strategies, which tended towards a more resource acquisition strategy with increasing soil nutrient levels. Grazing significantly interacted with soil nutrient to affect root nutrient‐acquisition strategies, and grazing contributed more to root nutrient‐acquisition strategies than soil nutrient. Synthesis. Our results demonstrated completely inconsistent responses of community‐level above‐ and below‐ground resource acquisition strategies to long‐term grazing, and below‐ground acquisition strategies were more sensitive to long‐term grazing. Our findings also suggest that high intensity anthropogenic activities such as grazing may strongly modify below‐ground resource acquisition strategies. Read the free Plain Language Summary for this article on the Journal blog.

Relationships between root exudation and root morphological and architectural traits vary with growing season.

Plants allocate a substantial amount of C belowground for root exudates and for the construction and adjustment of root morphological and architectural traits. What relationships exist between root exudates and other root traits and these relationships change with growing season, however, remain unclear. We quantified the root exudation rate and root morphological traits, including total root length (RL), total root surface area (RS), root diameter (RD), specific root length (SRL), specific root area (SRA) and root tissue density (RTD), and architectural traits, such as branching intensity (BI), and investigated their associations during the rapidly growing season (April and August) and the slowly growing season (December) of three common native tree species, Liquidambar formosana, Michelia maudiae and Schima superba, in subtropical China. We found that the linkages of RD, SRL, SRA, RTD and BI did not change with the growing season, reflecting their highly conservative relationships. The root exudation rate varied significantly with growing season (P<0.05) and produced various associations with other root traits at different growing seasons. During the rapidly growing season (i.e., April), the exudation rate was the highest and was positively correlated with RL. The exudation rate was the lowest during the slowly growing season (i.e., December) and was negatively associated with RL, RS and RTD. Our findings demonstrate the seasonality of the linkages of root exudation rate with other root traits, which highlights the highly plastic and complex associations of belowground root traits. These findings help to deepen our understanding of plant nutrient acquisition strategies.

Restoration on magnetite mine waste substrates using Western Australian native plants only marginally benefited from a commercial inoculant

Post-mining landscapes often lack self-sustaining plant communities and functional belowground microbial communities. Inappropriate management of soil can hinder ecological restoration of mine sites. However, the potential role of microbial inoculants and plant nutrient-acquisition strategies in improving mined substrates and facilitating mine-site restoration remains relatively unexplored. An eight-month glasshouse experiment was conducted to test: (1) whether a commercially-available microbial inoculant was effective in restoring biological properties of mined substrates, and (2) the effect of plant nutrient-acquisition strategies on improving the chemical properties of mined substrates for the growth of native plants. There was no significant improvement in plant growth by adding a commercially-sourced microbial inoculant. Soil microbial biomass carbon and phosphorus increased significantly after plant growth (main effect of species * substrates * inoculation interaction). The non-mycorrhizal disturbance-specialist plant species Maireana georgei was effective in improving hostile conditions of the mine waste. Our results highlight that re-vegetating stockpiled topsoil using local keystone species is a desirable practice that can improve soil biological properties and benefit mine-site restoration. Commercially-available agricultural-based microbial inoculants may not be compatible for mine-site restoration using native plants, but future research using indigenous soil microbes is warranted.

Plant-soil feedback regulates the trade-off between phosphorus acquisition pathways in Pinus elliottii.

Plant-soil feedback (PSF) is conventionally characterized by plant biomass growth, yet it remains unclear how PSF affects plant nutrient acquisition strategies (e.g., nutrient absorption and nutrient resorption) associated with plant growth, particularly under changing soil environments. A greenhouse experiment was performed with seedlings of Pinus elliottii Englem and conditioned soils of monoculture plantations (P. elliottii and Cunninghamia lanceolata Hook). Soil sterilization was designed to test plant phosphorus (P) acquisition strategy with and without native soil fungal communities. Soils from P. elliottii and C. lanceolata plantations were used to explore the specific soil legacy effects on two different P acquisition pathways (absorption and resorption). Phosphorus addition was also applied to examine the separate and combined effects of soil abiotic factors and soil fungal factors on P acquisition pathways. Due to diminished mycorrhizal symbiosis, PSF prompted plants to increasingly rely on P resorption under soil sterilization. In contrast, P absorption was employed preferentially in the heterospecific soil, where species-specific pathogenic fungi could not affect P absorption. Higher soil P availability diluted the effects of soil fungal factors on the trade-off between the two P acquisition pathways in terms of the absolute PSF. Moreover, P addition plays a limited role in terms of the relative PSF and does not affect the direction and strength of relative PSF. Our results reveal the role of PSF in regulating plant P acquisition pathways and highlight the interaction between mycorrhizal and pathogenic fungi as the underlying mechanism of PSF.

Soil water conditions together with plant nitrogen acquisition strategies control vegetation dynamics in semi-arid wetlands undergoing land management changes

Land management changes can significantly alter wetland soil environment, vegetation, and their interactions. Although the relationships between plant communities and environmental factors have been widely studied, the intrinsic driving mechanisms of vegetation dynamics are poorly understood because nutrient acquisition strategies play an important role in plant community assembly. This study compared the plant community characteristics of wetlands under different land management practices in the semi-arid western Songnen Plain, Northeast China, and investigated soil properties and plant community nutrient contents. Results showed compared with those in natural wetlands, the values of growth characteristics of plant communities were generally lower, whereas species diversity was higher in grazed or mowed wetlands. Furthermore, soil carbon (C), nitrogen (N), phosphorus (P) contents, their stoichiometric ratios, and soil water content were lower, and N contents in leaves and stems, soil bulk density, and pH were higher compared with those in natural wetlands. The plant community characteristics were significantly correlated with soil properties and plant nutrient contents. A redundancy analysis showed that soil water content, bulk density, and organic carbon, accounted for 59.3%, 15.6%, and 2.9%, respectively, the N in leaves, stems, and roots accounted for 62.8%, and the P in leaves and roots accounted for 12.2% of the variation in the plant community. Variation partitioning analysis further demonstrated that soil properties, plant nutrient contents, and their interactions explained 19.1 %, 11.8%, and 59.4% of the variation in the plant community, respectively. Therefore, the wetland vegetation dynamics are combinedly controlled by soil properties (especially soil water conditions) and plant nutrient acquisition strategies (especially plant nitrogen acquisition) under different land management practices. This study provides the theoretical basis for maintaining the stability of wetland ecosystems by designing plant resources-related managements in semi-arid regions.

Fungi in ant-plant interactions: a key to enhancing plant nutrient-acquisition strategies.

This article is a Commentary on Gegenbauer et al. (2023), 238: 2210–2223.

Effects of long-term nitrogen addition on the δ15N and δ13C of Larix gmelinii and soil in a boreal forest

BackgroundNatural abundance of carbon (C) and nitrogen (N) stable isotope ratios (δ13C and δ15N) has been used to indicate the state and cycle of ecosystem C and N. However, it is still unclear how C and N cycle of boreal forests respond to the N deposition.ResultsWe conducted an 8-year continuous N addition field experiment in a Larix gmelinii forest in Greater Khingan Mountains, Northeast China. Four N treatments (0, 25, 50, 75 kg N ha−1 year−1) were built. The effects of N addition on the δ13C and δ15N of needle, branch, bark, and fine root of Larix gmelinii and soil were studied. The result of the balance between the N input and output flux showed that N addition significantly increased the δ15N in each organ of Larix gmelinii, but did not change the δ15N of soil. We also found that the N absorption by needles of Larix gmelinii could increase the needle photosynthesis rate and δ13C by increasing carboxylation, but N addition had no significant effect on the δ13C of soil and other organs. In addition, both the soil δ15N and δ13C increased with the soil depth.ConclusionsLong-term N addition may lead to more open C and N cycles and further affect plant nutrient acquisition strategies in boreal forest ecosystems.

Effects of Long-Term Fertilization and Stand Age on Root Nutrient Acquisition and Leaf Nutrient Resorption of Metasequoia glyptostroboides.

The plant nutrient acquisition strategies are diverse, such as root nutrient acquisition and leaf nutrient resorption, playing important roles in driving soil processes, vegetation performance as well as ecosystem nutrient cycling. However, it is still in a debate whether there is a synergy or tradeoff between above- and below-ground nutrient acquisition strategy under nitrogen (N) and phosphorus (P) addition, or with stand age. Herein, this study investigated the responses of root-soil accumulation factor (RSAF) and leaf nutrient resorption efficiency (NuRE) to long-term N and P fertilization, and further explored the trade-off between them in Metasequoia glyptostroboides plantations with different stand age. Results showed that under N fertilization in young plantations, leaf N resorption efficiency (NRE) increased, and root-soil accumulation factor for P (RSAF-P) decreased. For young forests under P fertilization, the NRE increased whereas RSAF-P decreased. For middle-aged forests under P fertilization, the NRE and leaf P resorption efficiency (PRE) increased and the RSAF-P decreased. Under P fertilization in young and middle-aged plantations, PRE had a significant positive correlation with RSAF-P. Under N fertilization in young plantations, NRE was significantly positive correlated with root-soil accumulation factor for N (RSAF-N). The covariance-based structural equation modeling (CB-SEM) analysis indicated that stand age had positive effects on PRE whether under N or P fertilization, as well as on RSAF-P under N fertilization, whereas had no effects on the NRE or RSAF-N. Overall, our results can shed light on the nutrient acquisition strategies of M. glyptostroboides plantations under future environmental changes and the results could be applied to the nutrient management practices.

Plant carbon investment in fine roots and arbuscular mycorrhizal fungi: A cross-biome study on nutrient acquisition strategies

Comparing the belowground allocation of assimilated carbon (C) to roots and mycorrhizal fungi across biomes can reveal specific plant nutrient acquisition strategies in ecosystems and allows to predict consequences of environmental changes. Three natural ecosystems (arid shrubland, coastal matorral, humid-temperate forest) distinct in annual precipitation and vegetation cover and compositions were selected to conduct a 13CO2 pulse labeling of natural woody vegetation to chase the allocation of assimilated C to arbuscular mycorrhizal (AM) fungi and fine roots. Further, nitrogen (N) and phosphorus (P) availability, root traits, root colonization, and the extraradical AM fungal mycelium (PLFA and NLFA 16:1ω5c) were analyzed to evaluate the efficiency of nutrient acquisition strategies. AM fungal colonization decreased with increasing aridity by up to 55% intraradical and by up to 90% extraradical. High root tissue densities – indicating longevity of roots – and low specific root lengths – indicating a low nutrient uptake capacity – pointed to a slow and resource conservative acquisition strategy of plants in the arid shrubland. Plants in the matorral, on the contrary, had lower root tissue densities but higher specific root lengths and higher root N contents, pointing to a fast nutrient acquisition strategy. The expression of abundant acquisitive fine roots of plants in the matorral, however, comes at the cost of larger C investment, shown by high 13C incorporation into root tissue. High root tissue densities and greater root diameter indicated that plants in the humid-temperate forest followed a resource-conservative strategy and outsource their nutrient acquisition to AM fungi. This outsourcing provides an efficient pathway to compensate a low uptake capacity of thick and dense roots. These ecosystem-specific acquisition strategies and distinct mutualism with AM fungi across the biomes will likely affect the sensitivity of plants to abiotic and biotic stressors and, thus, ecosystem responses to future climatic and environmental changes.

Response of root nutrient resorption strategies to rhizosphere soil microbial nutrient utilization along Robinia pseudoacacia plantation chronosequence

Understanding root nutrient resorption strategies and their drivers is essential to explore plant nutrient acquisition strategies in restored ecosystems. However, the interaction between root nutrient resorption and the nutrient utilization of rhizosphere soil microorganisms in restored ecosystems has yet to be determined. In this study, we investigated plant fine roots and rhizosphere soils in Robinia pseudoacacia plantations at four stages of forest succession (14, 20, 30, and 45 years of age) on the Loess Plateau in China. We studied the characteristics of root nitrogen and phosphorus resorption efficiencies (NRE and PRE) at different recovery stages and analyzed the relationships among nutrient resorption and rhizosphere soil variables (nutrients and microbial communities). We detected a tendency of an initial reduction and subsequent increase in root NRE and PRE with stand age (the lowest value at 30-y sites), whereas the nutrient contents of rhizosphere soil increased with stand age, and soil available nutrients initially increased and then declined. The diversity of rhizosphere soil microorganisms also showed an initial increase and subsequent decline. Proteobacteria were considered to be at an advantage during the nutrient-rich stage of restoration (30-y sites), whereas Acidobacteria were found to be dominant during the low-nutrient restoration stage (14-y sites). Furthermore, the microbial nutrient utilization ratios of soil microbial biomass carbon: soil organic carbon, microbial biomass nitrogen: soil total nitrogen, and microbial biomass phosphorus: soil total phosphorus also showed an initial increase and then decreased (with peaks at the 30-y sites). Redundancy analysis indicated that the nutrient contents of rhizosphere soil were significantly related to microbial communities and correlation analysis revealed that microbial nutrient-use efficiencies were significantly related to rhizosphere soil nutrient contents and the dominant microbial communities. We also detected a significant negative correlation between root nutrient resorption and microbial nutrient utilization. Partial least squares path modeling revealed that forest restoration influences the contents of nutrients in rhizosphere soil and the composition of microbial communities, whereas microbial biomass and nutrient utilization efficiency were shown to have a negative effect on root resorption efficiency. Based on our findings, we propose that the highly conservative nutrient utilization strategies of the rhizosphere soil microbial community may negatively drive root nutrient resorption strategies during the succession of R. pseudoacacia.

Temporal trends of plant nutrient-acquisition strategies with soil age and their ecological significance

Temporal trends of plant nutrient-acquisition strategies with soil age and their ecological significance

Biotic interactions with mycorrhizal systems as extended nutrient acquisition strategies shaping forest soil communities and functions

Plant nutrient acquisition strategies involving ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) associations, are key plant functional traits leading to distinct carbon (C) and nutrient dynamics in forests. Yet, little is known about how these strategies influence the structure and functioning of soil communities, and if such mycorrhizal effects may be more or less pronounced depending on the type of forest and various abiotic factors. Here we explore the potential interactions occurring between plant-EcM and plant-AM systems with the diverse soil organisms occurring in forest soils, and in the process draw attention to major issues that are worthy for future research directions. Based on these potential interactions, we suggest that EcM systems, especially those involving gymnosperms in colder climates, may select for a soil community with a narrow set of functions. These EcM systems may exhibit low functional redundancy, dominated by symbiotic interactions, where EcM fungi maintain low pH and high C/N conditions in order to tightly control nutrient cycling and maintain the dominance of EcM trees. By contrast, AM systems, particularly those involving deciduous angiosperm trees in mild and warmer climates, may facilitate a functionally more diverse and redundant soil community tending towards the dominance of competitive and antagonistic interactions, but also with a range of symbiotic interactions that together maintain diverse plant communities. We propose that the contrasting belowground interactions in AM and EcM systems act as extended nutrient acquisition traits that contribute greatly to the prevailing nutrient and C dynamics occurring in these systems.

Variations in the natural 13C and 15N abundance of plants and soils under long-term N addition and precipitation reduction: interpretation of C and N dynamics

BackgroundThe nitrogen isotope natural abundance (δ15N) provides integrated information on ecosystem N dynamics, and carbon isotope natural abundance (δ13C) has been used to infer how water-using processes of plants change in terrestrial ecosystems. However, how δ13C and δ15N abundances in plant life and soils respond to N addition and water availability change is still unclear. Thus, δ13C and δ15N abundances in plant life and soils were used to investigate the effects of long-time (10 years) N addition (+ 50 kg N·ha− 1·yr− 1) and precipitation reduction (− 30% of throughfall) in forest C and N cycling traits in a temperate forest in northern China.ResultsWe analyzed the δ13C and δ15N values of dominant plant foliage, litterfall, fungal sporophores, roots, and soils in the study. The results showed that δ15N values of foliage, litterfall, and surface soil layer’s (0–10 cm) total N were significantly increased by N addition, while δ15N values of fine roots and coarse roots were considerably decreased. Nitrogen addition also significantly increased the δ13C value of fine roots and total N concentration of the surface soil layer compared with the control. The C concentration, δ13C, and δ15N values of foliage and δ15N values of fine roots were significantly increased by precipitation reduction, while N concentration of foliage and litterfall significantly decreased. The combined effects of N addition and precipitation reduction significantly increased the δ13C and δ15N values of foliage as well as the δ15N values of fine roots and δ13C values of litterfall. Furthermore, foliar δ15N values were significantly correlated with foliage δ13C values, surface soil δ15N values, surface soil C concentration, and N concentrations. Nitrogen concentrations and δ13C values of foliage were significantly correlated with δ15N values and N concentrations of fine roots.ConclusionsThis indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15N under precipitation reduction, suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.

Plant nutrient-acquisition strategies drive topsoil microbiome structure and function.

Plant nutrient-acquisition strategies drive soil processes and vegetation performance, but their effect on the soil microbiome remains poorly understood. This knowledge is important to predict the shifts in microbial diversity and functions due to increasing changes in vegetation traits under global change. Here we documented the topsoil microbiomes of 145 boreal and temperate terrestrial sites in the Baltic region that broadly differed in vegetation type and nutritional traits, such as mycorrhizal types and symbiotic nitrogen-fixation. We found that sites dominated by arbuscular mycorrhizal (AM) vegetation harbor relatively more AM fungi, bacteria, fungal saprotrophs, and pathogens in the topsoil compared with sites dominated by ectomycorrhizal (EM) plants. These differences in microbiome composition reflect the rapid nutrient cycling and negative plant-soil feedback in AM soils. Lower fungal diversity and bacteria:fungi ratios in EM-dominated habitats are driven by monodominance of woody vegetation as well as soil acidification by EM fungi, which are associated with greater diversity and relative abundance of carbohydrate-active enzymes. Our study suggests that shifts in vegetation related to global change and land use may strongly alter the topsoil microbiome structure and function.

Root Exudation of Primary Metabolites: Mechanisms and Their Roles in Plant Responses to Environmental Stimuli.

Root exudation is an important process determining plant interactions with the soil environment. Many studies have linked this process to soil nutrient mobilization. Yet, it remains unresolved how exudation is controlled and how exactly and under what circumstances plants benefit from exudation. The majority of root exudates including primary metabolites (sugars, amino acids, and organic acids) are believed to be passively lost from the root and used by rhizosphere-dwelling microbes. In this review, we synthetize recent advances in ecology and plant biology to explain and propose mechanisms by which root exudation of primary metabolites is controlled, and what role their exudation plays in plant nutrient acquisition strategies. Specifically, we propose a novel conceptual framework for root exudates. This framework is built upon two main concepts: (1) root exudation of primary metabolites is driven by diffusion, with plants and microbes both modulating concentration gradients and therefore diffusion rates to soil depending on their nutritional status; (2) exuded metabolite concentrations can be sensed at the root tip and signals are translated to modify root architecture. The flux of primary metabolites through root exudation is mostly located at the root tip, where the lack of cell differentiation favors diffusion of metabolites to the soil. We show examples of how the root tip senses concentration changes of exuded metabolites and translates that into signals to modify root growth. Plants can modify the concentration of metabolites either by controlling source/sink processes or by expressing and regulating efflux carriers, therefore challenging the idea of root exudation as a purely unregulated passive process. Through root exudate flux, plants can locally enhance concentrations of many common metabolites, which can serve as sensors and integrators of the plant nutritional status and of the nutrient availability in the surrounding environment. Plant-associated micro-organisms also constitute a strong sink for plant carbon, thereby increasing concentration gradients of metabolites and affecting root exudation. Understanding the mechanisms of and the effects that environmental stimuli have on the magnitude and type of root exudation will ultimately improve our knowledge of processes determining soil CO2 emissions, ecosystem functioning, and how to improve the sustainability of agricultural production.

Strong linkage between plant and soil fungal communities along a successional coastal dune system.

Complex interactions between plants and soil microorganisms drive key ecosystem and community properties such as productivity and diversity. In nutrient-poor systems such as sand dunes, plant traits and fungal symbioses related to nutrient acquisition can strongly influence vegetation dynamics. We investigated plant and fungal communities in a relic foredune plain located on an archipelago in Québec, Canada. We detected distinct communities across the edaphic and successional gradient. Our results showed a clear increase in plant species richness, as well as in the diversity of nutrient-acquisition strategies. We also found a strong correlation between aboveground vegetation and soil fungal communities, and both responded similarly to soil physicochemical properties. Soil pH influenced the composition of plant and fungal communities, and could act as an important environmental filter along this relic foredune plain. The increasing functional diversity in plant nutrient-acquisition strategies across the gradient might favor resource partitioning and facilitation among co-occurring plant species. The coordinated changes in soil microbial and plant communities highlight the importance of aboveground-belowground linkages and positive biotic interactions during ecological succession in nutrient-poor environments.

Additive effects of dung amendment and plant species identity on soil processes and soil inorganic nitrogen in grass monocultures

Plant species can exert a strong influence on soil processes. The aim of this field study was to examine the interactive effects of plant species identity and dung amendment on key soil properties related to carbon (C) and nitrogen (N) cycling. Monocultures of three co-occurring grass species (Dactylis glomerata, Lolium perenne, Festuca rubra) with contrasting nutrient acquisition strategies were examined. Soil CO2 fluxes, leaf litter decomposition, C and N storage in soil and soil microbes were measured in plots with and without dung addition. Four months after dung addition, soil sampled from plots was used in a greenhouse bioassay experiment to assess soil fertility. Dung addition increased CO2 fluxes from soil irrespective of plant species; increased leaf litter mass loss and C and N stocks in soil and microbial biomass were also observed. Bioassay results confirmed dung-induced increases in soil fertility. Significant plant species’ effects were found for soil CO2 fluxes, soil inorganic N content, leaf litter mass loss and bioassay seedling root: shoot ratio. Nevertheless, dung effects showed no significant interactions with plant species identity on any of the soil variables examined. Soil responses to dung show additive effects with grass species identity, but are not clearly linked to plant nutrient acquisition strategy in this temperate study system. High nutrient inputs may buffer plant-soil interactions against variation in plant nutrient acquisition strategies.

Diversity of plant nutrient-acquisition strategies increases during long-term ecosystem development

Plant species diversity increases as soil phosphorus availability declines during long-term ecosystem development1,2. The increase in plant species diversity is associated with a decline in above-ground functional diversity, because leaf traits converge on a high phosphorus-use efficiency strategy on old and infertile soils3,4. In contrast, the response of below-ground traits that directly influence nutrient acquisition remains poorly understood3,5; yet it might be key to understanding how soil fertility drives patterns of plant species diversity1. Here we show a marked increase in the richness and diversity of plant nutrient-acquisition strategies with declining soil phosphorus availability during long-term ecosystem development in a global biodiversity hotspot. Almost all nutrient-acquisition strategies currently known were found in plants from the most infertile soils, despite these being some of the most phosphorus-impoverished soils on Earth. Mycorrhizal plants declined in relative abundance by >30%, although the decline was compensated by an increase in non-mycorrhizal, carboxylate-exuding species that ‘mine’ phosphorus from the soil using different strategies. Plant species richness within individual nutrient-acquisition strategies also increased dramatically, with the species richness of many strategies more than doubling between the youngest and oldest soils. These results reveal increasing functional diversity of below-ground traits related to nutrient acquisition during ecosystem development, suggesting that no single combination of traits, including those related to nutrient-acquisition strategies, is superior to all others at extremely low soil fertility. Furthermore, the increasing diversity of nutrient-acquisition strategies with declining soil fertility, despite functional convergence of above-ground traits4,6, suggests that fundamentally different plant community assembly processes operate above- and below-ground. Studies of plants on a series of Australian sand dunes show that leaves and roots have different approaches to coping with phosphorus limitation. While leaves concentrate on using phosphorus efficiently, roots take on rich and diverse nutrient-acquisition strategies.