The LPJ-GUESS dynamic vegetation model uniquely combines an individual- and patch-based representation of vegetation dynamics with ecosystem biogeochemical cycling from regional to global scales. We ...present an updated version that includes plant and soil N dynamics, analysing the implications of accounting for C–N interactions on predictions and performance of the model. Stand structural dynamics and allometric scaling of tree growth suggested by global databases of forest stand structure and development were well reproduced by the model in comparison to an earlier multi-model study. Accounting for N cycle dynamics improved the goodness of fit for broadleaved forests. N limitation associated with low N-mineralisation rates reduces productivity of cold-climate and dry-climate ecosystems relative to mesic temperate and tropical ecosystems. In a model experiment emulating free-air CO2 enrichment (FACE) treatment for forests globally, N limitation associated with low N-mineralisation rates of colder soils reduces CO2 enhancement of net primary production (NPP) for boreal forests, while some temperate and tropical forests exhibit increased NPP enhancement. Under a business-as-usual future climate and emissions scenario, ecosystem C storage globally was projected to increase by ca. 10%; additional N requirements to match this increasing ecosystem C were within the high N supply limit estimated on stoichiometric grounds in an earlier study. Our results highlight the importance of accounting for C–N interactions in studies of global terrestrial N cycling, and as a basis for understanding mechanisms on local scales and in different regional contexts.
New biological models are incorporating the realistic processes underlying biological responses to climate change and other human-caused disturbances. However, these more realistic models require ...detailed information, which is lacking for most species on Earth. Current monitoring efforts mainly document changes in biodiversity, rather than collecting the mechanistic data needed to predict future changes. We describe and prioritize the biological information needed to inform more realistic projections of species' responses to climate change. We also highlight how trait-based approaches and adaptive modeling can leverage sparse data to make broader predictions. We outline a global effort to collect the data necessary to better understand, anticipate, and reduce the damaging effects of climate change on biodiversity.
Earth's biodiversity and human societies face pollution, overconsumption of natural resources, urbanization, demographic shifts, social and economic inequalities, and habitat loss, many of which are ...exacerbated by climate change. Here, we review links among climate, biodiversity, and society and develop a roadmap toward sustainability. These include limiting warming to 1.5°C and effectively conserving and restoring functional ecosystems on 30 to 50% of land, freshwater, and ocean "scapes." We envision a mosaic of interconnected protected and shared spaces, including intensively used spaces, to strengthen self-sustaining biodiversity, the capacity of people and nature to adapt to and mitigate climate change, and nature's contributions to people. Fostering interlinked human, ecosystem, and planetary health for a livable future urgently requires bold implementation of transformative policy interventions through interconnected institutions, governance, and social systems from local to global levels.
Interactive effects of reductions in plant species diversity and increases in atmospheric CO₂ were investigated in a long-term study in nutrient-poor calcareous grassland. Throughout the experiment, ...soil nitrate was persistently increased at low plant species diversity, and CO₂ enrichment reduced soil NO₃- at all levels of plant species diversity. In our study, soil NO₃- was unrelated to root length density, microbial biomass N, community legume contents, and experimental plant communities differed only little in total N pools. However, potential nitrification revealed exactly the same treatment effects as soil NO₃-, providing circumstantial evidence that nitrification rates drove the observed changes in NO₃-. One possible explanation for plant diversity effects on nitrification lies in spatial and temporal interspecific differences in plant N uptake, which would more often allow accumulation of NH₄+ in part of the soil profile at low diversity than in more species-rich plant communities. Consequently, nitrification rates and soil NO₃- would increase. Elevated CO₂ increased soil water contents, which may have improved NO₃- diffusion to the root surface thereby reducing soil NO₃-. Higher soil moisture at elevated CO₂ might also reduce nitrification rates due to less aerobic conditions. The accordance of the diversity effect on soil NO₃- with previous experiments suggests that increased soil NO₃- at low species diversity is a fairly general phenomenon, although the mechanisms causing high NO₃- may vary. In contrast, experimental evidence for of CO₂ enrichment on soil NO₃- is ambiguous, and the antagonistic interaction of plant species reductions and elevated CO₂ we have observed is thus probably less universal.
1. The effects of global change on below-ground processes of the nitrogen (N) cycle have repercussions for plant communities, productivity and trace gas effluxes. However, the interacting effects of ...different components of global change on nitrification or denitrification have rarely been studied in situ. 2. We measured responses of nitrifying enzyme activity (NEA) and denitrifying enzyme activity (DEA) to over 4 years of exposure to several components of global change and their interaction (increased atmospheric CO2concentration, temperature, precipitation and N addition) at peak biomass period in an annual grassland ecosystem. In order to provide insight into the mechanisms controlling the response of NEA and DEA to global change, we examined the relationships between these activities and soil moisture, microbial biomass C and N, and soil extractable N. 3. Across all treatment combinations, NEA was decreased by elevated CO2and increased by N addition. While elevated CO2had no effect on NEA when not combined with other treatments, it suppressed the positive effect of N addition on NEA in all the treatments that included N addition. We found a significant$CO_2-N$interaction for DEA, with a positive effect of elevated CO2on DEA only in the treatments that included N addition, suggesting that N limitation of denitrifiers may have occurred in our system. Soil water content, extractable N concentrations and their interaction explained 74% of the variation in DEA. 4. Our results show that the potentially large and interacting effects of different components of global change should be considered in predicting below-ground N responses of Mediterranean grasslands to future climate changes.
We examined the effects of decreasing plant diversity and functional group identity on root biomass, soil bulk density, soil nitrate and ammonium concentrations, microbial basal respiration, density ...of predaceous and non-predaceous nematodes, earthworm biomass and density and Shannon–Wiener indices of earthworm diversity in a temperate grassland. Plant species and functional group diversity did not have significant effects on any of these measured variables. However, functional group identity of the plants did significantly affect root biomass and soil abiotic factors. In addition, root biomass, Shannon–Wiener indices of earthworm diversity and density of epigeic earthworms were significantly higher in the presence of legumes, while we found no correlation between functional group identity and other groups of soil biota. We also found several significant relationships among root biomass density, soil microbial basal respiration, nematodes and earthworms.
Thus, how can the lack of correlation between soil variables and plant diversity manipulation be explained? Firstly, plant litter input and historical land use have long-term effects on soil properties, which suggests effects of plant diversity manipulation might only be manifested over the long-term. However, we found significant relationships between root biomass density and soil biota suggesting that changes in root biomass density with declining plant diversity could lead to changes in soil biota that might be detectable despite large temporal lags in the soil system. Secondly, we did not find significant effects of plant diversity on root biomass but we found that it was significantly related to the identity of functional groups. Thirdly, we observed complex interactions among trophic levels of soil organisms, which may counteract and buffer effects of changes in plant diversity on soil biota. Fourth, our results suggest that belowground properties might be much more influenced by the identity (and litter quality) of plant functional groups than plant species diversity per se.
Responses of soil nitrogen (N) cycling to simultaneous and potentially interacting global environmental changes are uncertain. Here, we investigated the combined effects of elevated CO
2
, warming, ...increased precipitation and enhanced N supply on soil N cycling in an annual grassland ecosystem as part of the Jasper Ridge Global Change Experiment (CA, USA). This field experiment included four treatments-CO
2
, temperature, precipitation, nitrogen-with two levels per treatment (ambient and elevated), and all their factorial combinations replicated six times. We collected soil samples after 7 and 8 years of treatments, and measured gross rates of N mineralization, N immobilization and nitrification, along with potential rates of ammonia oxidation, nitrite oxidation and denitrification. We also determined the main drivers of these microbial activities (soil ammonium and nitrate concentrations, soil moisture, soil temperature, soil pH, and soil CO
2
efflux, as an indicator of soil heterotrophic activity). We found that gross N mineralization responded to the interactive effects of the CO
2
, precipitation and N treatments: N addition increased gross N mineralization when CO
2
and precipitation were either both at ambient or both at elevated levels. However, we found limited evidence for interactions among elevated CO
2
, warming, increased precipitation, and enhanced N supply on the other N cycling processes examined: statistically significant interactions, when found, tended not to persist across multiple dates. Soil N cycling responded mainly to single-factor effects: long-term N addition increased gross N immobilization, potential ammonia oxidation and potential denitrification, while increased precipitation depressed potential nitrite oxidation and increased potential ammonia oxidation and potential denitrification. In contrast, elevated CO
2
and modest warming did not significantly affect any of these microbial N transformations. These findings suggest that global change effects on soil N cycling are primarily additive, and therefore generally predictable from single factor studies.
Soil and nutrient properties, via their influence on nutrient diffusion rates in the soil, may play a key role in determining the outcome of plant competition for nutrients. We used two models to ...explore the potential contributions of nutrient uptake kinetics, root density, soil properties, and nutrient type to interspecific plant competition for soil nutrients. The first model uses well-known nutrient diffusion and absorption relationships to generate soil nutrient concentration maps and nutrient uptake at the scale of individual roots (PARIS-M). A second model (PARIS-E) was developed based on a fit of the Hill equation to the output of PARIS-M. The PARIS-E model provides an accurate and simple means of determining the relative contributions of sink strength (root surface area x uptake kinetics) vs. space occupation (number of roots per unit area) to competition at equilibrium as modeled by PARIS-M. An analysis based on these two models suggests the following: (1)Diffusive supply (soil nutrient buffer capacity x effective diffusion coefficient) determines the relative importance of space occupation vs. sink strength for nutrient competition. (2) At the low range of reported values of diffusive supply, competition depends on space occupation and, therefore, the species with the most roots per unit area is the most competitive. Sink strength gains in importance as diffusive supply increases and dominates competitive interactions at the high end of the range of reported diffusive supplies. (3) The relative importance of space occupation vs. sink strength depends primarily on soil water content and soil texture, because diffusive supply is sensitive to these factors. Diffusive supply is relatively insensitive to nutrient type. This analysis suggests that nutrient competition models should include the effects of soil properties as a determinant of the relative contributions of sink strength vs. space occupation.
Interactive effects of increases in atmospheric CO2 and reductions in plant species diversity were investigated in planted calcareous grassland communities in northwestern Switzerland. The ...experimental communities were composed of 5, 12 and 31 species assembled from the native species pool.
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