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Legume trees form an abundant and functionally important component of tropical forests worldwide with N₂-fixing symbioses linked to enhanced growth and recruitment in early secondary succession. However, it remains unclear how N₂-fixers meet the high demands for inorganic nutrients imposed by rapid biomass accumulation on nutrient-poor tropical soils. Here, we show that N₂-fixing trees in secondary Neotropical forests triggered twofold higher in situ weathering of fresh primary silicates compared to non-N₂–fixing trees and induced locally enhanced nutrient cycling by the soil microbiome community. Shotgun metagenomic data from weathered minerals support the role of enhanced nitrogen and carbon cycling in increasing acidity and weathering. Metagenomic and marker gene analyses further revealed increased microbial potential beneath N₂-fixers for anaerobic iron reduction, a process regulating the pool of phosphorus bound to iron-bearing soil minerals. We find that the Fe(III)-reducing gene pool in soil is dominated by acidophilic Acidobacteria, including a highly abundant genus of previously undescribed bacteria, Candidatus Acidoferrum, genus novus. The resulting dependence of the Fe-cycling gene pool to pH determines the high iron-reducing potential encoded in the metagenome of the more acidic soils of N₂-fixers and their nonfixing neighbors. We infer that by promoting the activities of a specialized local microbiome through changes in soil pH and C:N ratios, N₂-fixing trees can influence the wider biogeochemical functioning of tropical forest ecosystems in a manner that enhances their ability to assimilate and store atmospheric carbon.

1. Despite urbanization being a major driver of land-use change globally, there have been few attempts to quantify and map ecosystem service provision at a city-wide scale. One service that is an increasingly important feature of climate change mitigation policies, and with other potential benefits, is biological carbon storage. 2. We examine the quantities and spatial patterns of above-ground carbon stored in a typical British city, Leicester, by surveying vegetation across the entire urban area. We also consider how carbon density differs in domestic gardens, indicative of bottom-up management of private green spaces by householders, and public land, representing top-down landscape policies by local authorities. Finally, we compare a national ecosystem service map with the estimated quantity and distribution of above-ground carbon within our study city. 3. An estimated 231 521 tonnes of carbon is stored within the above-ground vegetation of Leicester, equating to 3.16 kg C m⁻² of urban area, with 97.3% of this carbon pool being associated with trees rather than herbaceous and woody vegetation. 4. Domestic gardens store just 0.76 kg C m⁻², which is not significantly different from herbaceous vegetation landcover (0.14 kg C m⁻²). The greatest above-ground carbon density is 28.86 kg C m⁻², which is associated with areas of tree cover on publicly owned/managed sites. 5. Current national estimates of this ecosystem service undervalue Leicester's contribution by an order of magnitude. 6. Synthesis and applications. The UK government has recently set a target of an 80% reduction in greenhouse gas emissions, from 1990 levels, by 2050. Local authorities are central to national efforts to cut carbon emissions, although the reductions required at city-wide scales are yet to be set. This has led to a need for reliable data to help establish and underpin realistic carbon emission targets and reduction trajectories, along with acceptable and robust policies for meeting these goals. Here, we illustrate the potential benefits of accounting for, mapping and appropriately managing aboveground vegetation carbon stores, even within a typical densely urbanized European city.

Background Soil phosphorus availability declines during long-term ecosystem development on stable land surfaces due to a gradual loss of phosphorus in runoff and transformation of primary mineral phosphate into secondary minerals and organic compounds. These changes have been linked to a reduction in plant biomass as ecosystems age, but the implications for belowground organisms remain unknown. Methods We constructed a phosphorus budget for the well-studied 120,000 year temperate rainforest chronosequence at Franz Josef, New Zealand. The budget included the amounts of phosphorus in plant biomass, soil microbial biomass, and other soil pools. Results Soil microbes contained 68-78 % of the total biomass phosphorus (i.e. plant plus microbial) for the majority of the 120,000 year chronosequence. In contrast, plant phosphorus was a relatively small pool that occurred predominantly in wood. This points to the central role of the microbial biomass in determining phosphorus availability as ecosystems mature, yet also indicates the likelihood of strong competition between plants and saprotrophic microbes for soil phosphorus. Conclusions This novel perspective on terrestrial biogeochemistry challenges our understanding of phosphorus cycling by identifying soil microbes as the major biological phosphorus pool during long-term ecosystem development.

Modern agriculture, in seeking to maximize yields to meet growing global food demand, has caused loss of soil organic carbon (SOC) and compaction, impairing critical regulating and supporting ecosystem services upon which humans also depend. Own‐growing makes an important contribution to food security in urban areas globally, but its effects on soil qualities that underpin ecosystem service provision are currently unknown. We compared the main indicators of soil quality; SOC storage, total nitrogen (TN), C : N ratio and bulk density (BD) in urban allotments to soils from the surrounding agricultural region, and between the allotments and other urban greenspaces in a typical UK city. A questionnaire was used to investigate allotment management practices that influence soil properties. Allotment soils had 32% higher SOC concentrations and 36% higher C : N ratios than pastures and arable fields and 25% higher TN and 10% lower BD than arable soils. There was no significant difference between SOC concentration in allotments and urban non‐domestic greenspaces, but it was higher in domestic gardens beneath woody vegetation. Allotment soil C : N ratio exceeded that in non‐domestic greenspaces, but was lower than that in garden soil. Three‐quarters of surveyed allotment plot holders added manure, 95% composted biomass on‐site, and many added organic‐based fertilizers and commercial composts. This may explain the maintenance of SOC, C : N ratios, TN and low BD, which are positively associated with soil functioning. Synthesis and applications. Maintenance and protection of the quality of our soil resource is essential for sustainable food production and for regulating and supporting ecosystem services upon which we depend. Our study establishes, for the first time, that small‐scale urban food production can occur without the penalty of soil degradation seen in conventional agriculture, and maintains the high soil quality seen in urban greenspaces. Given the involvement of over 800 million people in urban agriculture globally, and its important contribution to food security, our findings suggest that to better protect soil functions, local, national and international urban planning and policy making should promote more urban own‐growing in preference to further intensification of conventional agriculture to meet increasing food demand.

Rising atmospheric CO2 has stimulated plant productivity, with terrestrial ecosystems currently absorbing nearly one-third of anthropogenic CO2 emissions. Increases in photosynthesis can subsequently lead to increased carbon (C) storage in plants and soil. However, there is growing evidence that nitrogen (N) availability constrains elevated CO2 (eCO2) responses, yet we know much less about the role of phosphorus (P) limitation on productivity under eCO2. This is important because P-limited ecosystems are globally widespread, and the biogeochemical cycles of N and P differ fundamentally. In the Peak District National Park of northern England, we conducted a free-air CO2 enrichment (FACE) experiment for three years on two contrasting P-limited grasslands under long-term nutrient manipulation. Here we show that competition between plants and microbes for P can determine plant productivity responses to eCO2. In a limestone grassland, aboveground productivity increased (16%) and microbial biomass P remained unchanged, whereas in an acidic grassland, aboveground productivity and P uptake declined (11% and 20%, respectively), but P immobilization into microbial biomass increased (36%). Our results demonstrate that strong competition with microbes can cause plant P uptake to decline under eCO2, with implications for the future productivity of P-limited ecosystems in response to climate change.The competition between grassland vegetation and microbes for phosphorus controls how plant productivity responds to elevated CO2, according to free-air CO2 enrichment experiments on phosphorus-limited grasslands.

The discovery that Mucoromycotina, an ancient and partially saprotrophic fungal lineage, associates with the basal liverwort lineage Haplomitriopsida casts doubt on the widely held view that Glomeromycota formed the sole ancestral plant–fungus symbiosis. Whether this association is mutualistic, and how its functioning was affected by the fall in atmospheric CO₂concentration that followed plant terrestrialization in the Palaeozoic, remains unknown. We measured carbon‐for‐nutrient exchanges between Haplomitriopsida liverworts and Mucoromycotina fungi under simulated mid‐Palaeozoic (1500 ppm) and near‐contemporary (440 ppm) CO₂concentrations using isotope tracers, and analysed cytological differences in plant–fungal interactions. Concomitantly, we cultured both partners axenically, resynthesized the associations in vitro, and characterized their cytology. We demonstrate that liverwort–Mucoromycotina symbiosis is mutualistic and mycorrhiza‐like, but differs from liverwort–Glomeromycota symbiosis in maintaining functional efficiency of carbon‐for‐nutrient exchange between partners across CO₂concentrations. Inoculation of axenic plants with Mucoromycotina caused major cytological changes affecting the anatomy of plant tissues, similar to that observed in wild‐collected plants colonized by Mucoromycotina fungi. By demonstrating reciprocal exchange of carbon for nutrients between partners, our results provide support for Mucoromycotina establishing the earliest mutualistic symbiosis with land plants. As symbiotic functional efficiency was not compromised by reduced CO₂, we suggest that other factors led to the modern predominance of the Glomeromycota symbiosis.

• Liverworts, which are amongst the earliest divergent plant lineages and important ecosystem pioneers, often form nutritional mutualisms with arbuscular mycorrhiza-forming Glomeromycotina and fine-root endophytic Mucoromycotina fungi, both of which coevolved with early land plants. Some liverworts, in common with many later divergent plants, harbour both fungal groups, suggesting these fungi may complementarily improve plant access to different soil nutrients. • We tested this hypothesis by growing liverworts in single and dual fungal partnerships under a modern atmosphere and under 1500 ppm [CO₂], as experienced by early land plants. Access to soil nutrients via fungal partners was investigated with 15N-labelled algal necromass and 33P orthophosphate. Photosynthate allocation to fungi was traced using 14CO₂. • Only Mucoromycotina fungal partners provided liverworts with substantial access to algal 15N, irrespective of atmospheric CO₂ concentration. Both symbionts increased 33P uptake, but Glomeromycotina were often more effective. Dual partnerships showed complementarity of nutrient pool use and greatest photosynthate allocation to symbiotic fungi. • We show there are important functional differences between the plant–fungal symbioses tested, providing new insights into the functional biology of Glomeromycotina and Mucoromycotina fungal groups that form symbioses with plants. This may explain the persistence of the two fungal lineages in symbioses across the evolution of land plants.

The magnitude of future climate change could be moderated by immediately reducing the amount of CO 2 entering the atmosphere as a result of energy generation and by adopting strategies that actively remove CO 2 from it. Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO 2 -removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure. Managed croplands worldwide are already equipped for frequent rock dust additions to soils, making rapid adoption at scale feasible, and the potential benefits could generate financial incentives for widespread adoption in the agricultural sector. However, there are still obstacles to be surmounted. Audited field-scale assessments of the efficacy of CO 2 capture are urgently required together with detailed environmental monitoring. A cost-effective way to meet the rock requirements for CO 2 removal must be found, possibly involving the recycling of silicate waste materials. Finally, issues of public perception, trust and acceptance must also be addressed. To reduce climate warming we must stop adding CO 2 to the atmopshere, and develop approaches for removing it. Adding crushed, fast-reacting silicate rocks to croplands could improve productivity, restore soil quality and reduce atmospheric CO 2 .

Urban trees sequester carbon into biomass and provide many ecosystem service benefits aboveground leading to worldwide tree planting schemes. Since soils hold ∼75% of ecosystem organic carbon, understanding the effect of urban trees on soil organic carbon (SOC) and soil properties that underpin belowground ecosystem services is vital. We use an observational study to investigate effects of three important tree genera and mixed-species woodlands on soil properties (to 1 m depth) compared to adjacent urban grasslands. Aboveground biomass and belowground ecosystem service provision by urban trees are found not to be directly coupled. Indeed, SOC enhancement relative to urban grasslands is genus-specific being highest under Fraxinus excelsior and Acer spp., but similar to grasslands under Quercus robur and mixed woodland. Tree cover type does not influence soil bulk density or C∶N ratio, properties which indicate the ability of soils to provide regulating ecosystem services such as nutrient cycling and flood mitigation. The trends observed in this study suggest that genus selection is important to maximise long-term SOC storage under urban trees, but emerging threats from genus-specific pathogens must also be considered.

Urbanization is widely presumed to degrade ecosystem services, but empirical evidence is now challenging these assumptions. We report the first city-wide organic carbon (OC) budget for vegetation and soils, including under impervious surfaces. Urban soil OC storage was significantly greater than in regional agricultural land at equivalent soil depths, however there was no significant difference in storage between soils sampled beneath urban greenspaces and impervious surfaces, at equivalent depths. For a typical U.K. city, total OC storage was 17.6 kg m −2 across the entire urban area (assuming 0 kg m −2 under 15% of land covered by buildings). The majority of OC (82%) was held in soils, with 13% found under impervious surfaces and 18% stored in vegetation. We reveal that assumptions underpinning current national estimates of ecosystem OC stocks, as required by Kyoto Protocol signatories, are not robust and are likely to have seriously underestimated the contributions of urban areas.