Dominant Plant Functional Groups Research Articles

Rising plant demand strengthens nitrogen limitation in tidal marsh.

Nitrogen (N) is a limiting nutrient for primary productivity in most terrestrial ecosystems, but whether N limitation is strengthening or weakening remains controversial because both N sources and sinks are increasing in magnitude globally. Temperate marshes are exposed to greater amounts of external N inputs than most terrestrial ecosystems and more than in preindustrial times owing to their position downstream of major sources of human-derived N runoff along river mouths and estuaries. Simultaneously, ecosystem N demand may also be increasing owing to other global changes such as rising atmospheric [CO2]. Here, we used interannual variability in external drivers and variables related to exogenous supply of N, along with detailed assessments of plant growth and porewater biogeochemistry, to assess the severity of N-limitation, and to determine its causes, in a 14-year N-addition × elevated CO2 experiment. We found substantial interannual variability in porewater [N], plant growth, and experimental N effects on plant growth, but the magnitude of N pools through time varied independently of the strength of N limitation. Sea level, and secondarily salinity, related closely to interannual variability in growth of the dominant plant functional groups which drove patterns in N limitation and in porewater [N]. Experimental exposure of plants to elevated CO2 and years with high flooding strengthened N limitation for the sedge. Abiotic variables controlled plant growth, which determined the strength of N limitation for each plant species and for ecosystem productivity as a whole. We conclude that in this ecosystem, which has an open N cycle and where N inputs are likely greater than in preindustrial times, plant N demand has increased more than supply.

Precipitation seasonality and soil texture interact to shape dryland recovery from severe disturbance

Abstract Disturbances drive large changes in plant composition and ecosystem functioning in drylands, but current understanding of how recovery following disturbance depends on the environment is limited due to challenges in analysing effects of disparate disturbances across abiotic gradients. We combined remote sensing and field observations across 5600+ km of natural gas pipeline corridors and adjacent undisturbed vegetation to investigate how recovery from a uniform, severe disturbance varied with factors that influence water availability in drylands. We found that recovery of net primary production (NPP) often remains incomplete, with only 42% of our sites projected to fully recover within 100 years. NPP recovery was quicker and more complete in regions that receive most of their annual precipitation at low temperatures and have fine‐textured soil; recovery of total shrub cover (median timing of 81 years) was faster on fine‐textured soils in locations that receive most of their annual precipitation at high temperatures. Locations with quick recovery of shrub cover were linked with a shift in dominant shrub species and incomplete NPP recovery. Synthesis. Recovery of NPP and shrub cover in drylands were driven by different environmental factors. For both NPP and shrub cover, locations with high pre‐disturbance values required more time to recover to adjacent undisturbed levels than locations with low pre‐disturbance values. Quick recovery of shrub cover or productivity was generally linked with a shift in dominant plant species or functional group.

Effects of plant taxonomic position on soil nematode communities in Antarctica.

Antarctica terrestrial ecosystems are facing the most threats from global climate change, which is altering plant composition greatly. These transformations may cause major reshuffling of soil community composition, including functional traits and diversity, and therefore affect ecosystem processes in Antarctica. We used high-throughput sequencing analysis to investigate soil nematodes under 3 dominant plant functional groups (lichens, mosses, and vascular plants) and bare ground in the Antarctic region. We calculated functional diversity of nematodes based on their diet, life histories, and body mass with kernel density n-dimensional hypervolumes. We also calculated taxonomic and functional beta diversity of the nematode communities based on Jaccard dissimilarity. The presence of plants had no significant effect on the taxonomic richness of nematodes but significantly increased nematode functional richness. The presence of plants also significantly decreased taxonomic beta diversity (homogenization). Only mosses and vascular plants decreased nematode functional beta diversity, which was mostly due to a decreased effect of the richness difference component. The presence of plants also increased the effect of deterministic processes potentially because environmental filtering created conditions favorable to nematodes at low trophic levels with short life histories and small body size. Increasing plant cover in the Antarctic due to climate change may lead to increased diversity of nematode species that can use the scarce resources and nematode taxonomic and functional homogenization. In a future under climate change, community restructuring in the region is possible.

Self‐stabilizing maintenance process in plant communities of alpine meadows under different grazing intensities

AbstractBackgroundsGrazing prohibition and reduced grazing intensity, as two important “vegetation close‐to‐nature recovery” methods, have been suggested as economical and effective technologies for enhancing forage production. However, numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows, but not in others. To reveal the mechanism behind this phenomenon, we proposed a series of experiments.MethodsWe monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai‐Tibet Plateau for 6 years. We estimated the relationships between the plant community and soil nutrients and obtained the following results.ResultsAll measured variables were positively correlated with each other. The plant community structure had higher path coefficients to aboveground biomass, soil organic matter, total nitrogen, and nitrate nitrogen than to other factors. The plant community structure played an important role in response to grazing intensity. Different plant functional groups (PFGs) had different responses to grazing intensity, which led to plant community re‐establishment or re‐organization under different grazing intensities. Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs, and the ratio of Kobresia biomass (including Kobresia humilis and Kobresia pygmaea) to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities. With Kobresia pygmaea as the dominant species, the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass. If Poaceae is the dominant PFG, grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.ConclusionsTherefore, the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.

Variation characteristics of different plant functional groups in alpine desert steppe of the Altun Mountains, northern Qinghai-Tibet Plateau.

In grassland ecosystems, the plant functional group (PFG) is an important bridge connecting individual plants to the community system. The grassland ecosystem is the main ecosystem type on the Qinghai-Tibet Plateau. Altun Mountain is located in the key grassland transcontinental belt of the northern Qinghai-Tibet Plateau. The composition and changes in the PFG in this ecosystem reflect the community characteristics in the arid and semi-arid extreme climate regions of the Plateau. The main PFGs were forbs and grasses, and the importance values (IVs) accounted for more than 50%. Plant species diversity of the community was influenced by the IV of the legumes, and the increase in legumes would promote the increase in plant community diversity. The C, N, and P contents of plant communities were mainly influenced by forbs and grasses, and the relationship between forbs and C, N, and P was opposite to that of grasses. However, under the influence of different hydrothermal conditions, forbs and grasses as dominant functional groups had a stronger correlation with community and soil nutrients. This indicates that the dominant PFGs (forbs and grasses) can dominate the C, N, and P contents of the community and soil, and legumes affect community composition and succession. In this study, we analyzed the changing characteristics of functional groups in dry and cold extreme environments and the difference in their impacts on community development compared with other grassland ecosystem functional groups.

Changes and Relationships between Components in the Plant-Soil System and the Dominant Plant Functional Groups in Alpine Kobresia Meadows Due to Overgrazing

In the last several decades, overgrazing has led to various changes in the plant communities, soil nutrients and soil microbial communities in alpine Kobresia meadows, which contain various plant communities coexisting on the Qinghai–Tibet Plateau. Investigating the variations in the biomass and concentration of nutrients in the plant–soil system in these communities may improve understanding of the biochemical responses and adaptation strategies they use to resist disturbances due to overgrazing. We therefore assessed 12 factors across four grazing intensities in alpine Kobresia meadows to explore the following three questions. (1) What the responses are in alpine Kobresia meadows to overgrazing. (2) How they affect plant–soil systems in alpine Kobresia meadows under overgrazing. (3) What factors can be used to evaluate the effects of overgrazing on the ecosystem health status of alpine Kobresia meadows. The results gave the following answers to the above questions. (1) Overgrazing caused the total aboveground biomass to decrease from 333.2 ± 17.4 g/m2 to 217.4 ± 30.2 g/m2, the coverage of plant functional groups of Gramineae and Cyperaceae to decrease from 74.2 ± 3% to 22.5 ± 1.9%, and the total belowground biomass to increase from 4028.5 ± 7.3 g/m2 to 6325.6 ± 24.8 g/m2. (2) Overgrazing resulted in variations in plant–soil systems at three levels. The concentrations of carbon (C) in soil nutrients and plant communities, explained 50.9% of the variation of biomass in plant functional groups; the concentration of soil available nutrients, explained 22.2% of the variation; and the ratio of C and N in shoots and soil total N, explained 11.0% of the variation. (3) The variations in C/N stoichiometry in total soil nutrients and soil microorganisms were 3.4–8.4% and 2.0–3.0%, respectively, and the load of (ammonium-nitrogen (NH4+-N) + nitrate-nitrogen (NO3–-N)) to growth of roots tissue increased from 84.1 ± 5.0 g/m2/(mg/kg) via 99.0 ± 1.3 g/m2/(mg/kg) to 86.1 ± 2.1 g/m2/(mg/kg) at 0 to 40 cm soil in an alpine meadow with grazing intensities rising. Overgrazing would thus increase the deficit of those two kinds of inorganic N on roots growing by 11.4%, 17.7% and 2.4% as grazing rates increased by 93.3%, 126.7% and 213.3%, respectively, compared to a meadow grazed at the lowest rate in the research. We concluded that the alpine meadow changed its distribution of biomass in the plant community, which increased the limiting nutrient deficit on production and altered the concentration and ratio of C and N. This destroyed the original balance to enable the plant community to resist overgrazing. Plot “KH”—a pasture with a grazing intensity next to the lowest one—was the key state in which persistent overgrazing could increase the limiting nutrient load on plant community production, change the dominant position of functional plant groups and species, and lead to plant community degradation. Using ratio of Gramineae to Cyperaceae or Kobresia humilis to K. pygmaea to monitor plant community succession could indirectly estimate these limiting nutrients deficit and balance, and their strategy for incorporating matter into roots and shoots. However how to use those outward characteristics to assess the ecosystem health requires further studies.

Dominant Plant Functional Group Determine the Response of the Temporal Stability of Plant Community Biomass to 9-Year Warming on the Qinghai–Tibetan Plateau

Ecosystem stability characterizes ecosystem responses to natural and anthropogenic disturbance and affects the feedback between ecosystem and climate. A 9-year warming experiment (2010–2018) was conducted to examine how climatic warming and its interaction with the soil moisture condition impact the temporal stability of plant community aboveground biomass (AGB) of an alpine meadow in the central Qinghai-Tibetan Plateau (QTP). Under a warming environment, the AGB percentage of grasses and forbs significantly increased but that of sedges decreased regardless of the soil water availability in the experimental plots. The warming effects on plant AGB varied with annual precipitation. In the dry condition, the AGB showed no significant change under warming in the normal and relatively wet years, but it significantly decreased in relatively drought years (16% in 2013 and 12% in 2015). In the wet condition, the AGB showed no significant change under warming in the normal and relatively drought years, while it significantly increased in relatively wet years (12% in 2018). Warming significantly decreased the temporal stability of AGB of plant community and sedges. Species richness remained stable even under the warming treatment in both the dry and wet conditions. The temporal stability of AGB of sedges (dominant plant functional group) explained 66.69% variance of the temporal stability of plant community AGB. Our findings highlight that the temporal stability of plant community AGB is largely regulated by the dominant plant functional group of alpine meadow that has a relatively low species diversity.

Nitrogen addition amplified water effects on species composition shift and productivity increase

Abstract Aims Water and nitrogen (N) are two key resources in dryland ecosystems, but they may have complex interactive effects on the community structure and ecosystem functions. How future precipitation (rainfall vs snowfall) change will impact aboveground net primary production (ANPP) is far from clear, especially when combined with increasing N availability. Methods In this study, we investigated changes in community productivity, abundance and aboveground biomass of two dominant plant functional groups (PFGs), i.e. perennial rhizome grasses (PR) and perennial bunchgrasses (PB) under the impacts of increased precipitation (rainfall vs snowfall) combined with N addition in a semiarid temperate steppe. Important Findings Summer rainfall augmentation marginally increased community ANPP, whereas it significantly increased the abundance and aboveground biomass of PR, but not those of PB. Summer rainfall addition increased the fraction of PR biomass (fPR) while decreased that of PB (fPB). Spring snow addition had no effect on aboveground biomass of either compositional PFG although it marginally increased community ANPP. Nitrogen addition significantly increased community ANPP with greater increase in PR under summer rainfall addition, indicating strong interactive effects on community ANPP largely by enhancing PR biomass. We also found a nonlinear increase in the positive effect of nitrogen addition on productivity with the increased precipitation amount. These findings indicate an amplified impact of precipitation increase on grassland productivity under the accelerated atmospheric N deposition in the future.

Mixture of plant functional groups inhibits the release of multiple metallic elements during litter decomposition in alpine timberline ecotone

Mixed litter decomposition is a common phenomenon in nature and is very important for the circulation of material through an ecosystem. Different plant functional groups (PFGs) are likely to interact during decomposition. It is unclear how mixed decomposition influences the release of multiple metallic elements, and the biogeochemical circulation mechanism in the alpine ecosystem remains elusive. In this study, a two-year experiment on decomposition of mixed litter from six dominant PFGs was conducted at two elevations in an alpine timberline ecotone using the litterbag method. First, the results suggested that PFG identity had greater impacts on the release of all metallic elements than elevation. The release rates of potassium (K), calcium (Ca), magnesium (Mg) and copper (Cu) in graminoid, deciduous shrub and forb litter were significantly higher than those in evergreen conifer, evergreen shrub and mixed litter. Second, the release of metallic elements showed non-additive effects during mixed litter decomposition. K, Ca, Mg, sodium (Na), Cu, and aluminium (Al) exhibited antagonistic effects, while Fe exhibited a synergistic effect. The antagonistic effects on Na, K, Ca and Cu release increased with increasing elevation, while the antagonistic effects on Mg, Al and Mn release decreased with increasing elevation. Third, Al and Fe showed high levels of accumulation. The K release rate decreased while Al and Fe accumulation increased with plant litter upward shift. In conclusion, mixtures of PFGs inhibits the release of multiple metallic elements during litter decomposition in the alpine timberline ecotone. We speculate that an upward shift in PFGs in response to climate warming will slow the release of K and accelerate the enrichment of Fe and Al in alpine timberline ecotones.

Mowing alters nitrogen effects on the community-level plant stoichiometry through shifting plant functional groups in a semi-arid grassland

Land-use practices such as mowing and nitrogen (N) fertilization can have significant impacts on plant stoichiometry. However, the interactive effects of mowing and N fertilization on the community-level plant stoichiometry and the underlying processes are not well understood. We examined the impacts of mowing (once a year) and N fertilization (12 g N m−2 yr−1) on the community-level plant stoichiometry in a semi-arid grassland on the Loess Plateau. Results obtained showed that mowing alone had no effect on the community-level plant N or phosphorus (P) concentration. N fertilization alone significantly reduced the community-level plant P concentration, but did not affect the community-level plant N concentration, leading to an enhancement of plant N:P ratio. However, mowing altered the effects of N fertilization, leading to a higher plant N (and P) concentration than the fertilization-only plots. Also, mowing significantly reduced soil nitrate (NO3−), but increased soil temperature, photosynthetic active radiation, plant diversity, richness and gross ecosystem productivity. In addition, mowing and N fertilization significantly affected plant community composition through shifting dominant plant functional groups (PFGs) (e.g. asteraceae, forbs and grass). Further, our structural equation modeling analysis showed that shifts in PFGs played an important role in regulating plant stoichiometry under mowing and N fertilization. Together, these results illustrate that effective management of mowing and N fertilization may induce changes in soil limiting nutrients and shifts in plant community composition, potentially altering plant N:P stoichiometry at the community level.

Climatic and edaphic controls over tropical forest diversity and vegetation carbon storage

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.

Plant functional group effects on peat carbon cycling in a boreal rich fen

Dominant plant functional groups (PFGs) found in boreal rich fens include sedges, grasses, horsetails, and cinquefoils (obligate wetland shrubs). Precipitation regime shift and permafrost thaw due to climate change will likely trigger changes in fen plant community structure through shifts in these PFGs, and it is thus crucial to understand how these PFGs will impact carbon cycling and greenhouse gas dynamics to predict and model peatland-climate feedbacks. In this study, we detail the above and belowground effects of these PFGs on aspects of carbon cycling using a mesocosm approach. We hypothesized that PFGs capable of aerating the rhizosphere (sedges, horsetails, and grasses) would oxidize the belowground environment supporting higher redox potentials, a favorable environment for decomposition, and higher CO2:CH4 in pore water and gas efflux measurements than PFGs lacking aerenchyma (cinquefoil, unplanted control). Overall, sedges, horsetail and grasses had an oxidizing effect on rhizosphere pore water chemistry, producing an environment more favorable for methanotrophy during the growing season, as supported by an approximate isotopic enrichment of pore water methane (δ13CH4) by 5‰, and isotopic depletion in pore water carbon dioxide (δ13CO2) by 10‰, relative to cinquefoil treatments. Cinquefoil and unplanted control treatments fostered a reducing environment more favorable for methanogenesis. In addition, cinquefoil appeared to slow decomposition in comparison with the other PFGs. These findings, paired with PFG effects on oxidation–reduction potential and CO2 and CH4 production, point to the ability of rich fen plant communities to moderate biogeochemistry, specifically carbon cycling, in response to changing climatic conditions.

Arbuscular mycorrhizal fungi shape the adaptive strategy of plants by mediating nutrient acquisition in a shrub-dominated community in the Mu Us Desert

Whether Arbuscular mycorrhizal fungi (AMF) influence community composition by changing plant adaptation to resource limitation remains unclear. This study examined how AMF affect the biodiversity and functional traits of plant functional groups in a shrub-dominated community in Mu Us Desert. In a field experiment, mycorrhizae were suppressed via benomyl to address how AMF alter the adaptive strategy of plants and community structure in a shrub-dominated community. The relationship between nutrient acquisition and proxies of growth and reproduction of dominant plant functional groups (shrubs and perennial grasses) were determined using a structure equation model. The diversity and aboveground biomass of plant functional groups were not affected by benomyl treatment. Shrubs’ vegetative biomass responded negatively to AMF owing to the nitrogen (N) limitation induced by phosphorous (P) increase, whereas a positive response in reproduction was related to foliar carbon (C) accumulation for drought tolerance. The abundance and height of perennial grasses varied with AMF, and it was correlated with foliar P and N contents. Different local adaptive strategies of shrubs and perennial grasses were associated with AMF through the regulation of plant nutrient acquisition. The link between AMF and plant adaptation highlights a potential mechanism underlying plant community dynamics in the resource-limited desert ecosystem.

Grazing buffers the effect of climate change on the species diversity of seedlings in an alpine meadow on the Tibetan Plateau.

Climate change predominated by warming over the past decades has affected plant biodiversity, distribution, and ecosystem functioning in alpine grasslands. Yet, little is known about the interactive effect of climate change and grazing on biodiversity and ecosystem functioning. Here, we conducted a vegetation translocation experiment (ten soil‐vegetation blocks were translocated from high‐altitudinal site 3,245 m to low‐altitudinal site 3,045 m) combined with grazing treatment in an alpine meadow on the Tibetan Plateau. The results showed that (a) translocation induced effect of climate change from harsh, high‐altitudinal site to benign, low‐altitudinal site significantly promoted species richness, and density of asexual and sexual seedling, with an increase in the proportion of asexual recruitment to sexual recruitment; (b) grazing decreased the proportion of asexual seedling to sexual recruitment within community, led to a shift in the dominant plant functional groups from graminoids and legumes to forbs; and (c) grazing partly offset the increased species richness of seedling, but not seedling density, induced by climate change. These findings suggest that moderate grazing may buffer the effect of climate change on the plant community composition, and thus, functional role in alpine meadows. Further understanding the influence of climate change on grassland ecosystems needs to consider the non‐additive effect of grazing and climate change to sustainability of grassland services.

DEGRADATION ISSUES OF FESCUE-FORBS RANGELAND IN MOUNTAIN STEPPE

The total area of Fescue-forbs rangeland in Mongolia is 10 million hectares, in account of 8.5% of total rangeland area. Fescue-forbs rangeland is the main type of rangeland in mountain steppe. The Mongolian rangeland has degraded for the last decades mainly due to overgrazing and climate change. The main objective of this study is to determine the change of plant community and reduction of abundance and productivity of dominant species Festuca lenensis in different degradation levels. The dominant species and main plant functional groups were completely changed in Fescue-forbs rangeland in compared with three degradation levels. The cover of Festuca lenensis was decreased by 98.6-99.5% and biomass percentage was decreased by 95.3-100% in three different degradation levels compared with no degraded pasture. Regarding the results of species composition, the highest number of species reached in moderately degraded pasture, lowest number of species reached in heavily degraded pasture. The species similarity coefficient=0.45 between slightly and moderately degraded pastures. Heavily degraded pasture was different from other two pastures. Quantity of individual species increased in moderately and heavily degraded pastures compared with slightly degraded site. It has depended on increaser and tolerant plant species, these are Arenaria capillaris, Potentilla acaulis, Artemisia frigida, A.commutata, Chamaerodos erecta and Carex duriuscula. Our study to reveal a degradation process of Fescue-forbs rangeland in mountain steppe of Mongolia.

Overdispersed Spatial Patterning of Dominant Bunchgrasses in Southeastern Pine Savannas.

Spatial patterning is a key natural history attribute of sessile organisms that frequently emerges from and dictates potential for interactions among organisms. We tested whether bunchgrasses, the dominant plant functional group in longleaf pine savanna groundcover communities, are nonrandomly patterned by characterizing the spatial dispersion of three bunchgrass species across six sites in Louisiana and Florida. We mapped bunchgrass tussocks of >5.0 cm basal diameter in three [Formula: see text] plots at each site. We modeled tussocks as two-dimensional objects to analyze their spatial relationships while preserving sizes and shapes of individual tussocks. Tussocks were overdispersed (more regularly spaced than random) for all species and sites at the local interaction scale (<0.3 m). This general pattern likely arises from a tussock-centered, distance-dependent mechanism, for example, intertussock competition. Nonrandom spatial patterns of dominant species have implications for community assembly and ecosystem function in tussock-dominated grasslands and savannas, including those characterized by extreme biodiversity.

Nitrogen fixation ability explains leaf chemistry and arbuscular mycorrhizal responses to fertilization

Atmospheric nitrogen (N) and phosphorus (P) deposition rates are predicted to drastically increase in the coming decades. The ecosystem level consequences of these increases will depend on how plant tissue nutrient concentrations, stoichiometry and investment in nutrient uptake mechanisms such as arbuscular mycorrhizal fungi (AMF) change in response to increased nutrient availability, and how responses differ between plant functional types. Using a factorial nutrient addition experiment with seedlings of multiple N-fixing and non-N-fixing tree species, we examined whether leaf chemistry and AMF responses differ between these dominant woody plant functional groups of tropical savanna and dry forest ecosystems. We found that N-fixers have remarkably stable foliar chemistry that stays constant with external input of nutrients. Non-N-fixers responded to N and N + P addition by increasing both concentrations and total amounts of foliar N, but showed a corresponding decrease in P concentrations while total amounts of foliar P stayed constant, suggesting a ‘dilution’ of tissue P with increased N availability. Non-N-fixers also showed an increase in N:P ratios with N and N + P addition, probably driven by both an increase in N and a decrease in P concentrations. AMF colonization decreased with N + P addition in non-N-fixers and increased with N and N + P addition in N-fixers, suggesting differences in their nutrient acquisition roles in the two plant functional groups. Our results suggest that N-fixers and non-N-fixers can differ significantly in their responses to N and P deposition, with potential consequences for future nutrient and carbon cycling in savanna and dry forest ecosystems.

Biome stability in South America over the last 30 kyr: Inferences from long‐term vegetation dynamics and habitat modelling

AbstractAimThe aim was to examine the links between past biome stability, vegetation dynamics and biodiversity patterns.LocationSouth America.Time periodLast 30,000 years.Major taxa studiedPlants.MethodsWe classified South America into major biomes according to their dominant plant functional groups (grasses, trees and shrubs) and ran a random forest (RF) classification with data on current climate. We then fitted the algorithm to predict biome distributions for every 1,000 years back to 21,000 yr BP and estimated biome stability by counting how many times a change in climate was predicted to shift a grid cell from one biome to another. We compared our model‐based stability map with empirical estimates from selected pollen records covering the past 30 kyr in terms of vegetation shifts, changes in species composition and time‐lag of vegetation responses.ResultsWe found a strong correlation between our habitat stability map and regional vegetation dynamics. Four scenarios emerged according to the way forest distribution shifted during a climate change. Each scenario related to specific regional features of biome stability and diversity, allowing us to formulate specific predictions on how taxonomic, genetic and functional components of biodiversity might be impacted by modern climate change.Main conclusionsOur validated map of biome stability provides important baseline information for studying the impacts of past climate on biodiversity in South America. By focusing exclusively on climatic changes of manifested relevance (i.e., those resulting in significant habitat changes), it provides a novel perspective that complements previous datasets and allows scientists to explore new questions and hypotheses at the local, regional and continental scales.

Biomass responses in a temperate European grassland through 17years of elevated CO2.

Future increase in atmospheric CO2 concentrations will potentially enhance grassland biomass production and shift the functional group composition with consequences for ecosystem functioning. In the "GiFACE" experiment (Giessen Free Air Carbon dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2 (eCO2 ) year-round during daylight hours since 1998, at a level of +20% relative to ambient concentrations (in 1998, aCO2 was 364ppm and eCO2 399ppm; in 2014, aCO2 was 397ppm and eCO2 518ppm). Harvests were conducted twice annually through 23years including 17years with eCO2 (1998 to 2014). Biomass consisted of C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass (TAB) was significantly increased under eCO2 (p=.045 and .025, at first and second harvest). The dominant plant functional group grasses responded positively at the start, but for forbs, the effect of eCO2 started out as a negative response. The increase in TAB in response to eCO2 was approximately 15% during the period from 2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time, tentatively a consequence of the fertilization management. Biomass and soil moisture responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested in the latter years was associated with a positive biomass response of both functional groups. The direction of the biomass response of the functional group forbs changed over the experimental duration, intensified by extreme weather conditions, pointing to the need of long-term field studies for obtaining reliable responses of perennial ecosystems to eCO2 and as a basis for model development.

Effects of functional diversity loss on ecosystem functions are influenced by compensation.

Understanding the impacts of biodiversity loss on ecosystem functioning and services has been a central issue in ecology. Experiments in synthetic communities suggest that biodiversity loss may erode a set of ecosystem functions, but studies in natural communities indicate that the effects of biodiversity loss are usually weak and that multiple functions can be sustained by relatively few species. Yet, the mechanisms by which natural ecosystems are able to maintain multiple functions in the face of diversity loss remain poorly understood. With a long-term and large-scale removal experiment in the Inner Mongolian grassland, here we showed that losses of plant functional groups (PFGs) can reduce multiple ecosystem functions, including biomass production, soil NO3 -N use, net ecosystem carbon exchange, gross ecosystem productivity, and ecosystem respiration, but the magnitudes of these effects depended largely on which PFGs were removed. Removing the two dominant PFGs (perennial rhizomatous grasses and perennial bunchgrasses) simultaneously resulted in dramatic declines in all examined functions, but such declines were circumvented when either dominant PFG was present. We identify the major mechanism for this as a compensation effect by which each dominant PFG can mitigate the losses of others. This study provides evidence that compensation ensuing from PFG losses can mitigate their negative consequence, and thus natural communities may be more resilient to biodiversity loss than currently thought if the remaining PFGs have strong compensation capabilities. On the other hand, ecosystems without well-developed compensatory functional diversity may be much more vulnerable to biodiversity loss.