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Tropical forest soils represent some of Earth's largest stores of soil carbon. Humid and warm conditions promote high primary productivity offsetting high ecosystem respiration rates, and this balance has resulted in significant carbon accumulation in plant biomass and soils. These vast carbon stocks can be destabilized under a changing climate, and model projections predict tropical and subtropical regions will experience disturbance to the hydrological cycle, with an increased likelihood of more frequent and prolonged droughts interspersed with periods of intense precipitation. Herein, we examine the functional response of belowground communities to a reduction in throughfall across a 1 m precipitation gradient (2350 to 3400 mm) spanning three sites from the Caribbean coast to the interior of Panama. At each site, 4 throughfall exclusion plots (10 x 10 m) were established to reduce precipitation, and exacerbate the natural variability in seasonal hydrological cycles. In January 2020, approximately 18 months since the inception of throughfall exclusion, each plot was sampled at six locations and two depths (0-10 and 10-20 cm). To identify the traits and mechanisms involved in responding to drought perturbation, we sequenced the microbiomes of the soil samples from the throughfall exclusion and corresponding controls at each site, and measured metabolite accumulation within the soils. Here we report on the accumulation of distinct metabolites along the precipitation gradient and under throughfall exclusion. We note that constitutive production of compatible solutes increases from the wettest to the driest site, indicative of trait selection due to climate history. However, under throughfall exclusion the gradient end members show a more muted metabolic response than the intermediate site. We discuss these responses with respect specific pathways invoked under drying stress, and soil carbon dynamics.

Tropical forests contain some of the largest soil carbon (C) stocks on Earth, making them broadly relevant to terrestrial-climate feedbacks, yet our understanding of how their soil organic C (SOC) fractions vary over space and time is limited. We studied effects of season, fertility, and mean annual precipitation (MAP) on the C contents of soil fractions across 14 lowland forests in Panama. We measured free-debris, occluded-debris, and mineral-associated SOC fractions, as well as soluble C associated with each fraction. We hypothesized that mineral-associated SOC would be greatest in infertile, strongly weathered soils with large reactive mineral contents. We also hypothesized that the debris SOC fractions would accumulate during the dry season, reflecting seasonal increases in litterfall. To address this, we compared soil fractions in wet and dry seasons from fertile and infertile soils across a range of 1809–2864 mm MAP. The C content (mg C/g soil) of all soil fractions varied with fertility and MAP: specifically, free-debris SOC was greatest in wet, high-fertility soils, and occluded-debris SOC was greater in high-fertility than low-fertility soils. The mineral-associated SOC fraction, which contained the majority of bulk soil C, showed increasing C content with greater MAP in infertile sites, presumably driving similar spatial patterns in the bulk soil. Only the free-debris SOC fraction showed strong seasonal variation, increasing in mass during the dry season. Nitrogen behaved similarly to C. In summary, soil C contents increased with MAP in infertile sites but not fertile sites, driven by the mineral-associated SOC fraction. The dry season had greater free-debris SOC, but this seasonal trend was not apparent in bulk soil C, likely because of the small size of the free-debris SOC fraction. Thus, changes in the quantity and seasonality of precipitation, which are projected for tropical forests, might shift spatial and temporal patterns of soil C storage, which would in turn influence forest-climate feedbacks for this C-rich biome.

Rising to meet global, interconnected challenges, such as food security and ecosystem resilience to global change, requires insights from across the Earth. This is especially true for belowground terrestrial ecological processes. Soil ecologists have answered this call: like mushrooms, large global datasets and databases on soil physics, chemistry and ecology are sprouting up everywhere (e.g. Fine‐Root Ecology Database (Iversen et al., 2018), FunFun (Zanne et al., 2020), GlobalFungi (Větrovský et al., 2020), COntinuous SOil REspiration (Jian et al., 2020), Global distribution of earthworm diversity (Philips et al., 2019) etc.). It is now time to leverage synergies among these datasets to link the continuum of belowground processes to ecosystem functions (e.g. decomposition, nutrient cycling and soil respiration). Built on interdisciplinary and international collaborations, data synthesis that leads to a holistic understanding is one of the best ways of predicting the future of terrestrial ecosystems and for preserving ecosystem services under global change. In 2020, global interconnectedness was on display as we saw a pandemic sweep across the world in weeks. The pandemic allowed the Ecological Society of America (ESA) to enter a new digital era by holding a fully virtual conference. While technology cannot yet replicate all aspects of an in‐person conference, the virtual platform increased accessibility and reduced the climate impact of the annual conference. It also provided an opportunity for early‐career plant and microbial ecologists from five ESA Organized Oral Sessions and one Inspire Session to organize Ecology Underground, a two‐day program of live virtual talks and open discussions on integrative belowground ecology on 4 and 5 August 2020. Ecology Underground was sponsored by New Phytologist, the ESA Soil Ecology Section, the US Department of Energy, Biological and Environmental Research program and the Oak Ridge Institute for Science and Education (ORISE), and gathered 453 participants over two days. The online platform allowed for participation across the globe (37 countries were represented; Fig. 1) and was an opportunity to think creatively about how scientific discussions and global collaborations can take place, now and in the future. Open in a separate window Fig. 1 The online platform of Ecology Underground allowed for participation across the globe.

Humid tropical forests contain some of the largest soil carbon (C) stocks on Earth, yet there is uncertainty about how carbon dioxide (CO2) fluxes will respond to climate change in this biome. The magnitude of change in soil respiration over seasonal wetting and drying cycles can provide insight to how CO2 fluxes might respond to precipitation changes. We measured soil respiration in 15 distinct forests across rainfall and soil fertility gradients in lowland Panama to assess spatial variation in seasonal patterns. We predicted that seasonal changes in soil respiration would be related to soil moisture, and that the ratio of wet to dry season CO2 fluxes across landscape gradients would be regulated by soil organic C and nutrient availability. We found that soil respiration during the dry season was relatively stable across the rainfall gradient, averaging 4.3 ± 0.3 µmol CO2 m−2 s−1. In contrast, wet season respiration varied markedly, ranging among sites from a decline of 19% to an increase of 360% in comparison to dry season values. Soil moisture, air temperature, and rainfall were the best predictors of instantaneous soil respiration (R2 = 0.18). Meanwhile, ratios of wet to dry season CO2 fluxes were best predicted by site-scale resin-extractable phosphorus (P; R2 = 0.48). That is, soil respiration in P-rich sites increased more during the wet season relative to respiration in P-poor sites. Also, sites with Wet:Dry season CO2 flux ratios

Model projections predict that climate change impacts on the tropics will include an increased frequency of drought and precipitation cycles. Such environmental fluctuations at the soil pore-scale play an important role in shaping microbial adaptive capacity, and trait composition of a community, which feeds back on to the breakdown and formation of soil organic matter (SOM). Understanding the factors controlling the carbon balance of humid tropical forest soils remains a social imperative. Microbial feedback to SOM pools is critical. Herein, we examine the microbial response to drought perturbations across 3 different, but complementary scales. At the largest scale, we explored the impacts of drought across a 1 m precipitation gradient spanning four sites from the Caribbean coast to the interior of Panama. At each site 4, throughfall exclusion plots (10 x 10 m) were established to reduce precipitation by 50 %. In addition, 4 corresponding control plots were also constructed. At the meso-scale, we incubated intact soil cores from one of these sites (P12) under 3 different hydrological treatments (control, drought, rewetting-drying cycles) for over a 5-month period. For the field and meso-scale experiments, we evaluated changes imparted by hydrological perturbations using multi-omic approaches, and physico-chemical measurements. In order to identify the traits involved in response to drought at the field and meso-scale, we isolated a range of bacteria to subject to stress at the scale of the single-cell and simple communities. Cell extracts were subjected to osmotic or matric stress and the short-term physiological responses determined using non-destructive synchrotron radiation-based Fourier Transform-Infrared spectromicroscopy. Through this approach, we identified changes in metabolic allocation within different cells, in particular to the secondary metabolome of the different bacteria. Our contribution will discuss the outcomes of these multi-scale experiments. Specifically focusing on how shifts in the microbial community and physiological changes may influence tropical soil carbon stability under future scenarios of altered drought and precipitation cycles.

Many efforts to restore disturbed landscapes seek to meet ecological goals over timescales from decades to centuries. It is thus crucial to know how different actions available to restoration practitioners may affect ecosystems in the long term, yet few such data exist. Here, we test the effects of seed and compost applications on plant community composition 9 years after their application, by taking advantage of a well-controlled restoration experiment on a mountainside severely degraded by over 80 years of zinc smelting emissions. We asked whether plots have converged on similar plant communities regardless of initial seed and compost treatments, or if these initial treatments have given rise to lasting differences in whole plant communities or in the richness and abundance of native, exotic, and planted species. We found that compost types significantly affected plant communities 9 years later, but seed mix species composition did not. Observed differences in species richness and vegetative cover were negatively correlated, and both were related to the differences in plant communities associated with different compost types. These observed differences are due primarily to the number and abundance of species not in original seed mixes, of which notably many are native. Our results underscore the importance of soils in shaping the aboveground composition of ecosystems. Differences in soil characteristics can affect plant diversity and cover, which are both common restoration targets. Even in highly polluted and devegetated sites, compost and seed application can reinstate high vegetative cover and allow continued colonization of native species.

© 2018 Elsevier Ltd Climate change and rising atmospheric carbon dioxide (CO2) concentrations are likely to alter tropical forest net primary productivity (NPP), potentially affecting soil C storage. We examined biochemical and physical changes in soil C fractions in a humid tropical forest where experimental litter manipulation changed total soil C stocks. We hypothesized that: (1.) low-density soil organic C (SOC) fractions are more responsive to altered litter inputs than mineral-associated SOC, because they cycle relatively rapidly. (2.) Any accumulation of mineral-associated SOC with litter addition is relatively stable (i.e. low leaching potential). (3.) Certain biomolecules, such as waxes (alkyl) and proteins (N-alkyl), form more stable mineral-associations than other biomolecules in strongly weathered soils. A decade of litter addition and removal affected bulk soil C content in the upper 5 cm by +32% and −31%, respectively. Most notably, C concentration in the mineral-associated SOC fraction was greater in litter addition plots relative to controls by 18% and 28% in the dry and wet seasons, respectively, accounting for the majority of greater bulk soil C stock. Radiocarbon and leaching analyses demonstrated that the greater mineral-associated SOC in litter addition plots consisted of new and relatively stable C, with only 3% of mineral-associated SOC leachable in salt solution. Solid-state13C NMR spectroscopy indicated that waxes (alkyl C) and microbial biomass compounds (O-alkyl and N-alkyl C) in mineral-associated SOC are relatively stable, whereas plant-derived compounds (aromatic and phenolic C) are lost from mineral associations on decadal timescales. We conclude that changes in tropical forest NPP will alter the quantity, biochemistry, and stability of C stored in strongly weathered tropical soils.

Background and aimsElemental uptake in serpentine floras in eastern North America is largely unknown. The objective of this study was to determine major and trace element concentrations in soil and leaves of three native pseudo-metallophyte C4 grasses in situ at five sites with three very different soil types, including three serpentine sites, in eastern USA.MethodsPseudo-total and extractible concentrations of 15 elements were measured and correlated from the soils and leaves of three species at the five sites.ResultsElement concentrations in soils of pseudo-metallophytes varied up to five orders of magnitude. Soils from metalliferous sites exhibited higher concentrations of their characteristic elements than non-metalliferous. In metallicolous populations, elemental concentrations depended on the element. Concentrations of major elements (Ca, Mg, K) in leaves were lower than typical toxicity thresholds, whereas concentrations of Zn were higher.ConclusionsIn grasses, species can maintain relatively low metal concentrations in their leaves even when soil concentrations are richer. However, in highly Zn-contaminated soil, we found evidence of a threshold concentration above which Zn uptake increases drastically. Finally, absence of main characteristics of serpentine soil at one site indicated the importance of soil survey and restoration to maintain serpentinophytes communities and avoid soil encroachment.

The factors affecting plant uptake of heavy metals from metalliferous soils are deeply important to the remediation of polluted areas. Arbuscular mycorrhizal fungi (AMF), soil-dwelling fungi that engage in an intimate exchange of nutrients with plant roots, are thought to be involved in plant metal uptake as well. Here, we used a novel field-based approach to investigate the effects of AMF on plant metal uptake from soils in Palmerton, PA, USA contaminated with heavy metals from a nearby zinc smelter. Previous studies often focus on one or two plant species or metals, tend to use highly artificial growing conditions and metal applications, and rarely consider metals’ effects on plants and AMF together. In contrast, we examined both direct and AMF-mediated effects of soil concentrations on plant concentrations of 8-13 metals in five wild plant species sampled across a field site with continuous variation in Zn, Pb, Cd, and Cu contamination. Plant and soil metal concentration profiles were closely matched despite high variability in soil metal concentrations even at small spatial scales. However, we observed few effects of soil metals on AMF colonization, and no effects of AMF colonization on plant metal uptake. Manipulating soil chemistry or plant community composition directly may control landscape-level plant metal uptake more effectively than altering AMF communities. Plant species identities may serve as highly local indicators of soil chemical characteristics. This article is protected by copyright. All rights reserved.

One of the many ways that climate change may affect human health is by altering the nutrient content of food crops. However, previous attempts to study the effects of increased atmospheric CO2 on crop nutrition have been limited by small sample sizes and/or artificial growing conditions. Here we present data from a meta-analysis of the nutritional contents of the edible portions of 41 cultivars of six major crop species grown using free-air CO2 enrichment (FACE) technology to expose crops to ambient and elevated CO2 concentrations in otherwise normal field cultivation conditions. This data, collected across three continents, represents over ten times more data on the nutrient content of crops grown in FACE experiments than was previously available. We expect it to be deeply useful to future studies, such as efforts to understand the impacts of elevated atmospheric CO2 on crop macro- and micronutrient concentrations, or attempts to alleviate harmful effects of these changes for the billions of people who depend on these crops for essential nutrients.

One of the many ways that climate change may affect human health is by altering the nutrient content of food crops. However, previous attempts to study the effects of increased atmospheric CO2 on crop nutrition have been limited by small sample sizes and/or artificial growing conditions. Here we present data from a meta-analysis of the nutritional contents of the edible portions of 41 cultivars of six major crop species grown using free-air CO2 enrichment (FACE) technology to expose crops to ambient and elevated CO2 concentrations in otherwise normal field cultivation conditions. This data, collected across three continents, represents over ten times more data on the nutrient content of crops grown in FACE experiments than was previously available. We expect it to be deeply useful to future studies, such as efforts to understand the impacts of elevated atmospheric CO2 on crop macro- and micronutrient concentrations, or attempts to alleviate harmful effects of these changes for the billions of people who depend on these crops for essential nutrients.

experiments contribute more than tenfold more data regarding both the zinc and iron content of the edible portions of crops grown under FACE conditions than is currently available in the literature. Consistent with earlier meta-analyses of other aspects of plant function under FACE conditions 14,15 , we considered the response comparisons observed from different species, cultivars and stress treatments and from different years to be independent. The natural logarithm of the mean response ratio (r5 response in elevated [CO2]/response in ambient [CO2]) was used as the metric for all analyses. Meta-analysis was used to estimate the overall effect of elevated [CO2] on the concentration of each nutrient in a particular crop and to determine the significance of this effect (see Methods). We found that elevated [CO2] was associated with significant decreases in the concentrations of zinc and iron in all C3 grasses and legumes (Fig. 1 and Extended Data Table 1). For example, wheat grains grown at elevated [CO2] had 9.3% lower zinc (95% confidence interval (CI)212.7% to25.9%) and 5.1% lower iron (95% CI26.5% to23.7%) than those grown at ambient [CO2]. We also found that elevated [CO2] was associated with lower protein content in C3 grasses, with a 6.3% decrease (95% CI27.5% to25.2%) in wheat grains and a 7.8% decrease (95% CI 28.9% to26.8%) in rice grains. Elevated [CO2] was associated with a small decrease in protein in field peas, and there was no significant