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Tropical vegetation dynamics and ecosystem carbon (C) stocks typically vary with local topography and forest disturbance history. Yet, neither remote sensing nor vegetation modeling captures the underlying mechanistic processes determining ecosystem functioning and therefore the resulting estimates often do not match field observations of vegetation C stocks, especially so in hyperdiverse tropical forest ecosystems. This mismatch is further aggravated by the fact that multiple interacting factors, such as climatic drivers (i.e., temperature, precipitation, climate seasonality), edaphic factors (i.e., soil fertility, topographic diversity) and diversity-related parameters (i.e., species composition and associated plant functional traits) in concert determine ecosystem functioning and therefore affect tropical forest C sink-strength. Here, we propose a novel framework designed for integrating in-situ observations of local plant species diversity with remotely sensed estimates of plant functional traits, with the goal to deduce parameters for a recently developed trait- and size-structured demographic vegetation model. Plant-FATE (Plant Functional Acclimation and Trait Evolution) captures the acclimation of plastic traits within individual plants in response to the local environment and simulates shifts in species composition through demographic changes between coexisting species, in association with differences in their life-history strategies. Our framework may be used to project the functional response of tropical forest ecosystems under present and future climate change scenarios and thus should have crucial implications for assisted restoration and management of tropical plant species threatened by extinction.

In early stages of forest succession plants have a high nutrient demand, but it is still a matter of debate if regrowth success of pioneer species is related to plant functional traits favoring fast soil colonization and nutrient acquisition. In general, we would expect trade-offs between plant growth performance and fine root morphological properties in association with different plant life-history strategies. Hence, we hypothesized that fast growing plants should have a more efficient root system that allows them to outcompete slow-growing neighbors in a resource-limited environment. To test our hypothesis we monitored plant successional growth dynamics in a tropical lowland rainforest reforestation experiment conducted in southwest Costa Rica. We collected absorptive roots (<2mm diameter) from plant individuals (comprising 20 tree species and 11 plant families) with different growth dynamics (as indicated by measurements of stem diameter and height). For these samples we assessed a suite of fine root morphological traits, such as legume nodulation status, and furthermore quantified fine root nutrient concentration and phosphatase activities, as well as microbial biomass and phosphatase activity in soils in the close vicinity of fine roots. We found stark differences in fine root characteristics between the tree species investigated in this study, such that fast growing species exhibited relatively larger specific root length and higher turnover, whereas slow growing species tend to rely on mechanical resistance by increasing root tissue density and root life span. Our results suggest that the identified differences in the root trait spectrum between fast and slow growing species reflect plant functional adaptions to resource limitation, edaphic properties and soil microbial symbioses. Our findings further highlight the crucial need to foster our understanding of belowground root morphological and physiological traits during forest succession, especially so when a

Soil fertility and plant productivity are globally constrained by N availability. Proteins are the largest N reservoir in soils and the cleavage of proteins into small peptides and amino acids has been shown to be the rate limiting step in the terrestrial N cycle. However, we are still lacking a profound understanding of the environmental controls of this process. Here we show that integrated effects of climate and soil geochemistry drive protein cleavage across large scales. We measured gross protein depolymerization rates in mineral and organic soils sampled across a 4000-km-long European transect covering a wide range of climates, geologies and land uses. Based on structural equation models we identified that soil organic N cycling was strongly controlled by substrate availability e.g. by soil protein content. Soil geochemistry was a secondary predictor by controlling protein stabilization mechanisms and protein availability. Precipitation was identified as the main climatic control on protein depolymerization by affecting soil weathering and soil organic matter accumulation. In contrast, land use was a poor predictor of protein depolymerization. Our results highlight the need to consider geology and precipitation effects on soil geochemistry when estimating and predicting soil N cycling at large scales.

Nitrous acid (HONO) photolysis produces hydroxyl radicals—a key atmospheric oxidant. Soils are strong HONO emitters, yet HONO production pathways in soils and their relative contributions are poorly constrained. Here, we conduct ¹⁵N tracer experiments and isotope pool dilution assays on two types of agricultural soils in Finland to determine HONO emission fluxes and pathways. We show that microbial processes are more important than abiotic processes for HONO emissions. Microbial nitrate reduction (denitrification) considerably exceeded ammonium oxidation as a source of nitrite—a central nitrogen pool connected with HONO emissions. Denitrification contributed 97% and 62% of total HONO fluxes in low and high organic matter soil, respectively. Microbial ammonium oxidation only produced HONO in high organic matter soil (10%). Our findings indicate that microbial nitrate reduction is an important HONO production pathway in aerobic soils, suggesting that terrestrial ecosystems favouring it could be HONO emission hotspots, thereby influencing atmospheric chemistry.

Tropical rainforests harbor exceptionally high biodiversity and store large amounts of carbon in vegetation biomass. However, regional variation in plant species richness and vegetation carbon stock can be substantial, and may be related to the heterogeneity of topoedaphic properties. Therefore, aboveground vegetation carbon storage typically differs between geographic forest regions in association with the locally dominant plant functional group. A better understanding of the underlying factors controlling tropical forest diversity and vegetation carbon storage could be critical for predicting tropical carbon sink strength in response to projected climate change. Based on regionally replicated 1-ha forest inventory plots established in a region of high geomorphological heterogeneity we investigated how climatic and edaphic factors affect tropical forest diversity and vegetation carbon storage. Plant species richness (of all living stems >10 cm in diameter) ranged from 69 to 127 ha−1 and vegetation carbon storage ranged from 114 to 200 t ha−1. While plant species richness was controlled by climate and soil water availability, vegetation carbon storage was strongly related to wood density and soil phosphorus availability. Results suggest that local heterogeneity in resource availability and plant functional composition should be considered to improve projections of tropical forest ecosystem functioning under future scenarios.

Species-rich plant communities have been shown to be more productive and to exhibit increased long-term soil organic carbon (SOC) storage. Soil microorganisms are central to the conversion of plant organic matter into SOC, yet the relationship between plant diversity, soil microbial growth, turnover as well as carbon use efficiency (CUE) and SOC accumulation is unknown. As heterotrophic soil microbes are primarily carbon limited, it is important to understand how they respond to increased plant-derived carbon inputs at higher plant species richness (PSR). We used the long-term grassland biodiversity experiment in Jena, Germany, to examine how microbial physiology responds to changes in plant diversity and how this affects SOC content. The Jena Experiment considers different numbers of species (1-60), functional groups (1-4) as well as functional identity (small herbs, tall herbs, grasses and legumes). We found that plant species richness (PSR) accelerated microbial growth and turnover and increased microbial biomass and necromass. Plant species richness also accelerated microbial respiration, but this effect was less strong than for microbial growth. In contrast, PSR did not affect microbial CUE or biomass-specific respiration. Structural equation models (SEMs) revealed that PSR had direct positive effects on root biomass, and thereby on microbial growth and microbial biomass carbon. Finally, PSR increased SOC content via its positive influence on microbial biomass carbon. We suggest that PSR favors faster rates of microbial growth and turnover, likely due to greater plant productivity, resulting in higher amounts of microbial biomass and necromass that translate into the observed increase in SOC. We thus identify the microbial mechanism linking species-rich plant communities to a carbon cycle process of importance to Earth’s climate system.

Nitrification is a fundamental process in terrestrial nitrogen cycling. However, detailed information on how climate change affects the structure of nitrifier communities is lacking, specifically from experiments in which multiple climate change factors are manipulated simultaneously. Consequently, our ability to predict how soil nitrogen (N) cycling will change in a future climate is limited. We conducted a field experiment in a managed grassland and simultaneously tested the effects of elevated atmospheric CO2, temperature, and drought on the abundance of active ammonia-oxidizing bacteria (AOB) and archaea (AOA), comammox (CMX) Nitrospira, and nitrite-oxidizing bacteria (NOB), and on gross mineralization and nitrification rates. We found that N transformation processes, as well as gene and transcript abundances, and nitrifier community composition were remarkably resistant to individual and interactive effects of elevated CO2 and temperature. During drought however, process rates were increased or at least maintained. At the same time, the abundance of active AOB increased probably due to higher NH4+ availability. Both, AOA and comammox Nitrospira decreased in response to drought and the active community composition of AOA and NOB was also significantly affected. In summary, our findings suggest that warming and elevated CO2 have only minor effects on nitrifier communities and soil biogeochemical variables in managed grasslands, whereas drought favors AOB and increases nitrification rates. This highlights the overriding importance of drought as a global change driver impacting on soil microbial community structure and its consequences for N cycling.

Currently applied dynamic vegetation models do not realistically represent forest ecosystem processes and thus are not able to reproduce in-situ observations of forest ecosystem responses to drought. This is due to the fact that models typically rely on plant functional types to forecast the functional response of vegetation to climate change and to anthropogenic disturbance. However, recent observations of divergent ecosystem responses between topographic forest sites, differing in the availability of water and nutrients, indicate that we should no longer rely on this outdated concept but rather should explore new avenues of representing vegetation dynamics and associated climate change response in next-generation approaches. Global climate change scenarios forecast increasing severity of climate extremes in association with El Niño–Southern Oscillation (ENSO). Such climate anomalies have been shown to affect forest ecosystem processes such as net primary productivity, which is determined by climate (precipitation, temperature, and light) and soil fertility (geology and topography). However, more recently it has been suggested that the impact of such climate fluctuations on forest productivity was strongly related to local site characteristics, which determined the sensitivity of forest ecosystem processes to climate anomalies. We propose a novel approach integrating in-situ observations with remotely sensed estimates of forest aboveground productivity for parameterization of next-generation vegetation models capable of forecasting realistic forest ecosystem responses under future scenarios. Our approach considers local site characteristics associated with topography and disturbance history, both of which determine the sensitivity of forest aboveground productivity to projected climate anomalies. Our results therefore should have crucial implications for management and restoration of forest ecosystems and could be used to refine estimates of forest C sink-strength

Forest biomass is an essential indicator for monitoring the Earth’s ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25ha scale from field measurements made in permanent research plots across the world's forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities. Live, most up-to-date dataset is available at https://forest-observation-system.net

Forest biomass is an essential indicator for monitoring the Earth’s ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world’s forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities.

Recent studies have reported a consistent pattern of strong dominance of a small subset of tree species in neotropical forests. These species have been called “hyperdominant” at large geographical scales and “oligarchs” at regional‐landscape scales when being abundant and frequent. Forest community assembly is shaped by environmental factors and stochastic processes, but so far the contribution of oligarchic species to the variation of community composition (i.e., beta diversity) remains poorly known. To that end, we established 20.1‐ha plots, that is, five sites with four forest types (ridge, slope and ravine primary forest, and secondary forest) per site, in humid lowland tropical forests of southwestern Costa Rica to (a) investigate how community composition responds to differences in topography, successional stage, and distance among plots for different groups of species (all, oligarch, common and rare/very rare species) and (b) identify oligarch species characterizing changes in community composition among forest types. From a total of 485 species of trees, lianas and palms recorded in this study only 27 species (i.e., 6%) were nominated as oligarch species. Oligarch species accounted for 37% of all recorded individuals and were present in at least half of the plots. Plant community composition significantly differed among forest types, thus contributing to beta diversity at the landscape scale. Oligarch species was the component best explained by geographical and topographic variables, allowing a confident characterization of the beta diversity among tropical lowland forest stands.

In fluvial ecosystems mineral erosion, carbon (C), and nitrogen (N) fluxes are linked via organomineral complexation, where dissolved organic molecules bind to mineral surfaces. Biofilms and suspended aggregates represent major aquatic microbial lifestyles whose relative importance changes predictably through fluvial networks. We tested how organomineral sorption affects aquatic microbial metabolism, using organomineral particles containing a mix of 13C, 15N-labeled amino acids. We traced 13C and 15N retention within biofilm and suspended aggregate biomass and its mineralization. Organomineral complexation restricted C and N retention within biofilms and aggregates and also their mineralization. This reduced the efficiency with which biofilms mineralize C and N by 30% and 6%. By contrast, organominerals reduced the C and N mineralization efficiency of suspended aggregates by 41% and 93%. Our findings show how organomineral complexation affects microbial C:N stoichiometry, potentially altering the biogeochemical fate of C and N within fluvial ecosystems.

Extreme environmental conditions prevail on the Antarctic continent and limit plant diversity to cryptogamic communities, dominated by bryophytes and lichens. Even small abiotic shifts, associated with climate change, are likely to have pronounced impacts on these communities that currently exist at their physiological limit of survival. Changes to moisture availability, due to precipitation shifts or alterations to permanent snow reserves, will most likely cause greatest impact. In order to establish a baseline for determining the effect of climate change on continental Antarctic terrestrial communities and to better understand bryophyte species distributions in relation to moisture in a floristically important Antarctic region, this study surveyed finescale bryophyte patterns and turf water and nutrient contents along community gradients in the Windmill Islands, East Antarctica. The survey found that the Antarctic endemic, Schistidium antarctici, dominated the wettest habitats, Bryum pseudotriquetrum distribution spanned the gradient, whilst Ceratodon purpureus and Cephaloziella varians were restricted to the driest habitats. These patterns, along with knowledge of these species relative physiology, suggest the endemic Schistidium antarctici will be negatively impacted under a drying trend. This study provides a model for quantitative finescale analysis of bryophyte distributions in cryptogamic communities and forms an important reference site for monitoring impacts of climate change in Antarctica.

Microbes are major players in leaf litter decomposition and therefore advances in the understanding of their control on element cycling are of paramount importance. Our aim was to investigate the influence of leaf litter stoichiometry in terms of carbon (C) : nitrogen (N) : phosphorus (P) ratios on the decomposition processes and to track changes in microbial community structures and functions in response to temperature stress treatments. To elucidate how the stoichiometry of beech leaf litter (Fagus sylvatica L.) and stress treatments interactively affect the microbial decomposition processes, a terrestrial microcosm experiment was conducted. Beech litter from different Austrian sites covering C:N ratios from 39 to 61 and C:P ratios from 666 to 1729 were incubated at 15 °C and 60% moisture for six months. Part of the microcosms were then subjected to severe changes in temperature (+30 °C and −15 °C) to monitor the influence of temperature stress. Extracellular enzyme activities were assayed and respiratory activities measured. A semi-quantitative metaproteomics approach (1D-SDS PAGE combined with liquid chromatography and tandem mass spectrometry; unique spectral counting) was employed to investigate the impact of the applied stress treatments in dependency of litter stoichiometry on structure and function of the decomposing community. In litter with narrow C:nutrient (C:N, C:P) ratios, microbial decomposers were most abundant. Cellulase, chitinase, phosphatase and protease activity decreased after heat and freezing treatments. Decomposer communities and specific functions varied with site, i.e. stoichiometry. The applied stress combined with the respective time of sampling evoked changes of enzyme activities and litter pH. Freezing treatments resulted in a decline in residual plant litter material and increased fungal abundance, indicating slightly accelerated decomposition. Overall, a strong effect of litter stoichiometry on microbial community structures and fun

Agricultural systems that receive high amounts of inorganic nitrogen (N) fertilizer in the form of either ammonium (NH4+), nitrate (NO3-) or a combination thereof are expected to differ in soil N transformation rates and fates of NH4+ and NO3-. Using 15N tracer techniques this study examines how crop plants and soil microbes vary in their ability to take up and compete for fertilizer N on a short time scale (hours to days). Single plants of barley (Hordeum vulgare L. cv. Morex) were grown on two agricultural soils in microcosms which received either NH4+, NO3- or NH4NO3. Within each fertilizer treatment traces of 15NH4+ and 15NO3- were added separately. During 8 days of fertilization the fate of fertilizer 15N into plants, microbial biomass and inorganic soil N pools as well as changes in gross N transformation rates were investigated. One week after fertilization 45-80% of initially applied 15N was recovered in crop plants compared to only 1-10% in soil microbes, proving that plants were the strongest competitors for fertilizer N. In terms of N uptake soil microbes out-competed plants only during the first 4 h of N application independent of soil and fertilizer N form. Within one day microbial N uptake declined substantially, probably due to carbon limitation. In both soils, plants and soil microbes took up more NO3- than NH4+ independent of initially applied N form. Surprisingly, no inhibitory effect of NH4+ on the uptake and assimilation of nitrate in both, plants and microbes, was observed, probably because fast nitrification rates led to a swift depletion of the ammonium pool. Compared to plant and microbial NH4+ uptake rates, gross nitrification rates were 3-75-fold higher, indicating that nitrifiers were the strongest competitors for NH4+ in both soils. The rapid conversion of NH4+ to NO3- and preferential use of NO3- by soil microbes suggest that in agricultural systems with high inorganic N fertilizer inputs the soil microbial community could adapt to high

Effects of light on the short term competition for organic and inorganic nitrogen between maize and rhizosphere microorganisms were investigated using a mixture of amino acid, ammonium and nitrate under controlled conditions. The amount and forms of N added in the three treatments was identical, but only one of the three N forms was labeled with 15N. Glycine was additionally labeled with 14C to prove its uptake by maize and incorporation into microbial biomass in an intact form. Maize out-competed microorganisms for 15 \textNO3- 15NO3− during the whole experiment under low and high light intensity. Microbial uptake of 15N and 14C was not directly influenced by the light intensity, but was indirectly related to the impact the light intensity had on the plant. More 15 \textNH4+ 15NH4+ was recovered in microbial biomass than in plants in the initial 4 h under the two light intensities, although more 15N-glycine was incorporated into microbial biomass than in plants in the initial 4 h under low light intensity. Light had a significant effect on 15 \textNO3- 15NO3− uptake by maize, but no significant effects on the uptake of 15 \textNH4+ 15NH4+ or 15N-glycine. High light intensity significantly increased plant uptake of 15 \textNO3- 15NO3− and glycine 14C. Based on 14C to 15N recovery ratios of plants, intact glycine contributed at least 13% to glycine-derived nitrogen 4 h after tracer additions, but it contributed only 0.5% to total nitrogen uptake. These findings suggest that light intensity alters the competitive relationship between maize roots and rhizosphere microorganisms and that C4 cereals such as maize are able to access small amounts of intact glycine. We conclude that roots were stronger competitor than microorganisms for inorganic N, but microorganisms out competed plants during a short period for organic N, which was mineralized into inorganic N within a few hours of application to the soil and was th

Natural N-15 abundance measurements of ecosystem nitrogen (N) pools and N-15 pool dilution assays of gross N transformation rates were applied to investigate the potential of delta N-15 signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil delta N-15 values of both forest sites increased with depth to 50 cm, but then decreased below this zone. delta N-15 values of microbial biomass (mixed stand: 4.7 +/- 0.8 parts per thousand, spruce stand: 5.9 +/- 0.9 parts per thousand) and of dissolved organic N (DON; mixed stand: 5.3 +/- 1.7 parts per thousand, spruce stand: 2.6 +/- 3.3 parts per thousand) were not significantly different; these pools were most enriched in N-15 of all soil N pools. Denitrification represented the main N2O-producing process in the mixed forest stand as we detected a significant N-15 enrichment of its substrate NO3- (3.6 +/- 4.5 parts per thousand) compared to NH4+ (-4.6 +/- 2.6 parts per thousand) and its product N2O (-11.8 +/- 3.2 parts per thousand). In a N-15-labelling experiment in the spruce stand, nitrification contributed more to N2O production than denitrification. Moreover, in natural abundance measurements the NH4- pool was slightly N-15-enriched (-0.4 +/- 2.0 parts per thousand) compared to NO3- (-3.0 +/- 0.6 parts per thousand) and N2O (-2.1 +/- 1.1 parts per thousand) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N2O. The more positive delta N-15 values of N2O in the spruce stand than in the mixed stand point to extensive microbial N2O reduction in the spruce stand. Combining natural N-15 abundance and N-15 tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately.

In contrast to terrestrial plants, epiphytic tank bromeliads take up nutrients mainly over their tank leaf surface. The form in which nutrients are available in the tanks is determined by the source and the complex interplay between tank microbes, which transform them and the epiphytes that take them up. To elucidate the importance of different nitrogenous compounds for the nitrogen (N) nutrition of Vriesea gigantea from the Atlantic Rainforest, Brazil, N transformation processes in tank water as well as foliar uptake rates were estimated by N-15 labelling techniques. Microorganisms actively transformed N compounds in the tank. Specifically, organic N compounds were rapidly mineralized to NH4+, while nitrification was negligible. Plants took up both organic and inorganic N forms, with a clear preference for NH4+. NH4+ comprised the largest and, because of fast mineralization rates, the most constant dissolved N pool in the tank water. Excretion of ureases by the plants together with an unusual uptake kinetic for urea also suggests that urea may be potentially important as an N source.