Satellite data indicate significant advancement in alpine spring phenology over decades of climate warming, but corresponding field evidence is scarce. It is also unknown whether this advancement ...results from an earlier shift of phenological events, or enhancement of plant growth under unchanged phenological pattern. By analyzing a 35‐year dataset of seasonal biomass dynamics of a Tibetan alpine grassland, we show that climate change promoted both earlier phenology and faster growth, without changing annual biomass production. Biomass production increased in spring due to a warming‐induced earlier onset of plant growth, but decreased in autumn due mainly to increased water stress. Plants grew faster but the fast‐growing period shortened during the mid‐growing season. These findings provide the first in situ evidence of long‐term changes in growth patterns in alpine grassland plant communities, and suggest that earlier phenology and faster growth will jointly contribute to plant growth in a warming climate.
Climate change reshapes plant growth patterns by shifting phenology earlier, enhancing growth rate, and shortening growth period in a Tibetan alpine grassland over 35 years. The changes in growth patterns alters seasonal, but not annual, biomass production.
Climatic change is altering ecosystem structure and function, especially in the southwestern United States where trees are near their physiological water stress threshold. In piñon‐juniper (Pinus ...edulis‐Juniperus monosperma; PJ) woodlands, increased drought is causing differential mortality of piñon resulting in an ecosystem that is becoming juniper dominated. Using a precipitation manipulation, we assessed how both increased and decreased precipitation altered ecosystem function beneath piñon and juniper. We predicted that changes in precipitation would alter nitrogen (N) availability and mineralization at the site. Further, we predicted that these responses would differ beneath piñon and juniper crowns due to plant‐level differences in transpiration and N uptake in response to drought. We found minimal interactions between tree species and the precipitation treatments on N cycling. However, across all years measured, soil nitrate decreased with increasing soil volumetric water content; a pattern that is likely due to reduced turnover in dry plots. In contrast, potential soil net‐nitrogen mineralization was reduced in water removal plots relative to water addition plots indicating that nitrogen cycling rates were slower under drought. Tree type also influenced nitrogen dynamics in this woodland. Across all 4 years, soil N availability and potential soil net‐mineralization rates were higher in soils beneath piñon relative to juniper across all treatments. Interestingly, the observed shifts in N cycling were not reflected in the abundance of N in microbial biomass or in ammonia‐oxidizing bacteria, which are responsible for nitrification. The observed patterns may be due to increased N leaching from the soil during periods of increased rainfall or due to decreased microbial activity or plant N uptake when conditions are dry. The effect of precipitation change on N cycling may have long‐term consequences on the plant community in this semi‐arid ecosystem. Nitrogen concentrations are highest in the soil when water availability is low, thus when N concentrations are high, plants and microbes are relatively inactive and unable to use this resource.
Recent vegetation changes in arctic-alpine tundra ecosystems may affect several ecosystem processes that regulate microbe and soil functions. Such changes can alter ecosystem carbon (C) cycling with ...positive feedback to the atmosphere if plant C uptake is less than the amount of soil C released. Here, we examine how differences in plant functional traits, microbial activity, and soil processes within and across Salix-dominated shrub, dwarf shrub-dominated heath, and herb- and cryptogam-dominated meadow communities influence C cycling. We develop a hypothesized framework based on a priori model selection of variation in daytime growing season gross ecosystem photosynthesis (GEP) and above- and belowground respiration. The fluxes were standardized to light and temperature.
Gross ecosystem photosynthesis was primarily related to soil moisture and secondarily to plant functional traits and aboveground biomass, and belowground respiration was dependent on the community weighted mean of specific leaf area (SLA
CWM
). Similarly, microbial activity was linked with SLA
CWM
and was highest in meadows, and carbon-degrading microbial activity decreased with vegetation woodiness. These results suggest that shrub expansion may influence summer C cycling differently depending on plant community, as belowground respiration might increase in the heath and decrease in the meadow communities.
Soils contain more carbon than plants or the atmosphere, and sensitivities of soil organic carbon (SOC) stocks to changing climate and plant productivity are a major uncertainty in global carbon ...cycle projections. Despite a consensus that microbial degradation and mineral stabilization processes control SOC cycling, no systematic synthesis of long-term warming and litter addition experiments has been used to test process-based microbe-mineral SOC models. We explored SOC responses to warming and increased carbon inputs using a synthesis of 147 field manipulation experiments and five SOC models with different representations of microbial and mineral processes. Model projections diverged but encompassed a similar range of variability as the experimental results. Experimental measurements were insufficient to eliminate or validate individual model outcomes. While all models projected that CO₂ efflux would increase and SOC stocks would decline under warming, nearly onethird of experiments observed decreases in CO₂ flux and nearly half of experiments observed increases in SOC stocks under warming. Long-term measurements of C inputs to soil and their changes under warming are needed to reconcile modeled and observed patterns. Measurements separating the responses of mineral-protected and unprotected SOC fractions in manipulation experiments are needed to address key uncertainties in microbial degradation and mineral stabilization mechanisms. Integrating models with experimental design will allow targeting of these uncertainties and help to reconcile divergence among models to produce more confident projections of SOC responses to global changes.
Linking intraspecific variation in plant traits to ecosystem carbon uptake may allow us to better predict how shift in populations shape ecosystem function. We investigated whether plant populations ...of a dominant old‐field plant species (Solidago altissima) differed in carbon dynamics and if variation in plant traits among genotypes and between populations predicted carbon dynamics. We established a common garden experiment with 35 genotypes from three populations of S. altissima from either Tennessee (southern populations) or Connecticut (northern populations) to ask whether: (1) southern and northern Solidago populations will differ in aboveground productivity, leaf area, flowering time and duration, and whole ecosystem carbon uptake, (2) intraspecific trait variation (growth and reproduction) will be related to intraspecific variation in gross ecosystem CO2 exchange (GEE) and net ecosystem CO2 exchange (NEE) within and between northern and southern populations. GEE and NEE were 4.8× and 2× greater in southern relative to northern populations. Moreover, southern populations produced 13× more aboveground biomass and 1.4× more inflorescence mass than did northern populations. Flowering dynamics (first‐ and last‐day flowering and flowering duration) varied significantly among genotypes in both the southern and northern populations, but plant performance and ecosystem function did not. Both productivity and inflorescence mass predicted NEE and GEE between S. altissima southern and northern populations. Taken together, our data demonstrate that variation between S. altissima populations in performance and flowering traits are strong predictors of ecosystem function in a dominant old‐field species and suggest that populations of the same species might differ substantially in their response to environmental perturbations.
Our work is the first to measure intra‐specific variation in performance traits and physiological traits within an ecologically relevant plant species elucidating potential implications towards ecosystem‐level carbon dynamics in both northern and southern geographic ranges. We also link intra‐specific variation in performance traits to better explain ecosystem‐level carbon dynamics.
Predators can disproportionately impact the structure and function of ecosystems relative to their biomass. These effects may be exacerbated under warming in ecosystems like the Arctic, where the ...number and diversity of predators are low and small shifts in community interactions can alter carbon cycle feedbacks. Here, we show that warming alters the effects of wolf spiders, a dominant tundra predator, on belowground litter decomposition. Specifically, while high densities of wolf spiders result in faster litter decomposition under ambient temperatures, they result, instead, in slower decomposition under warming. Higher spider densities are also associated with elevated levels of available soil nitrogen, potentially benefiting plant production. Changes in decomposition rates under increased wolf spider densities are accompanied by trends toward fewer fungivorous Collembola under ambient temperatures and more Collembola under warming, suggesting that Collembola mediate the indirect effects of wolf spiders on decomposition. The unexpected reversal of wolf spider effects on Collembola and decomposition suggest that in some cases, warming does not simply alter the strength of top-down effects but, instead, induces a different trophic cascade altogether. Our results indicate that climate change-induced effects on predators can cascade through other trophic levels, alter critical ecosystem functions, and potentially lead to climate feedbacks with important global implications. Moreover, given the expected increase in wolf spider densities with climate change, our findings suggest that the observed cascading effects of this common predator on detrital processes could potentially buffer concurrent changes in decomposition rates.
While numerous studies focus on the ecosystem effects of invasive mammals, few explore the causal mechanisms of such effects. Wild boar is one of the most widely introduced invasive mammal species in ...the world. By overturning extensive areas of vegetation and soil to feed on belowground resources, wild boar alter the soil food web and thus many microbial-mediated soil processes. Here, we take advantage of a long-term, 8-year, wild boar exclosure experiment across three plant community types in Patagonia, Argentina to explore how wild boar impact soil communities and their potential function. Previous work in this experimental system found that wild boar significantly impacted litter decomposition in the field, but it remained unclear if this effect was mediated through changes in abiotic or biotic soil properties. To explore both the abiotic and biotic drivers of decomposition, we measured soil moisture, soil temperature, soil bulk density, and soil respiration as well as soil micro-arthropod richness and abundance, earthworm abundance, and microbial biomass inside and outside of 10 exclosures in each of three plant community types. To assess potential microbial activity, we measured potential decomposition rates, substrate-induced respiration, and soil microbial enzyme activity. Rooting decreased soil moisture by 18% across plant communities, and soil respiration by 30% in
Nothofagus
and
Austrocedrus
forests. Additionally, rooting decreased soil micro-arthropod richness and abundance by ~ 80% in shrublands. However, rooting had no effect on soil potential microbial activity. Together, our results suggest that changes in both abiotic and biotic soil factors likely mediate observed wild boar impact on decomposition rates. Overall, we show that wild boar rooting alters soil functioning, but the pathway of impact varies by plant community, suggesting that wild boar impacts on native ecosystems can be difficult to predict.
Global change is altering species distributions and thus interactions among organisms. Organisms live in concert with thousands of other species, some beneficial, some pathogenic, some which have ...little to no effect in complex communities. Since natural communities are composed of organisms with very different life history traits and dispersal ability it is unlikely they will all respond to climatic change in a similar way. Disjuncts in plant-pollinator and plant-herbivore interactions under global change have been relatively well described, but plant-soil microorganism and soil microbe-microbe relationships have received less attention. Since soil microorganisms regulate nutrient transformations, provide plants with nutrients, allow co-existence among neighbors, and control plant populations, changes in soil microorganism-plant interactions could have significant ramifications for plant community composition and ecosystem function. In this paper we explore how climatic change affects soil microbes and soil microbe-plant interactions directly and indirectly, discuss what we see as emerging and exciting questions and areas for future research, and discuss what ramifications changes in these interactions may have on the composition and function of ecosystems.
The decline of
Tsuga canadensis
(eastern hemlock)-a foundation tree species-due to infestation by
Adelges tsugae
(hemlock woolly adelgid) or its complete removal from a stand by salvage logging ...dramatically affects associated faunal assemblages. Among these assemblages, species composition (richness and abundance) of ants increases rapidly as
T. canadensis
is lost from the stands. Because ants live and forage at the litter-soil interface, we hypothesized that environmental changes caused by hemlock loss (e.g., increased light and warmth at the forest floor, increased soil pH) and shifts in ant species composition would interact to alter soil ecosystem variables. In the Harvard Forest Hemlock Removal Experiment (HF-HeRE), established in 2003,
T. canadensis
in large plots were killed in place or logged and removed to mimic adelgid infestation or salvage harvesting, respectively. In 2006, we built ant exclosure subplots within all of the canopy manipulation plots to examine direct and interactive effects of canopy change and ant assemblage composition on soil and litter variables. Throughout HF-HeRE,
T. canadensis
was colonized by the adelgid in 2009, and the infested trees are now declining. The experimental removal of
T. canadensis
from the canopy was associated with an increase in the rate of cellulose decomposition by >50%, and exclosure of ants from subplots directly reduced their soil nitrate availability by 56%. Partial least squares path models revealed sequential interactive effects prior to adelgid infestation: canopy change (as a proxy for associated environmental changes) altered both decomposition and ant assemblage structure; changes in ant assemblage structure and decomposition rates altered nitrogen availability. The results illustrate that biotic changes directly associated with decline of
T. canadensis
can have cascading effects on ecosystem nutrient availability and cycling.
Extreme drought is increasing in frequency and intensity in many regions globally, with uncertain consequences for the resistance and resilience of ecosystem functions, including primary production. ...Primary production resistance, the capacity to withstand change during extreme drought, and resilience, the degree to which production recovers, vary among and within ecosystem types, obscuring generalized patterns of ecological stability. Theory and many observations suggest forest production is more resistant but less resilient than grassland production to extreme drought; however, studies of production sensitivity to precipitation variability indicate that the processes controlling resistance and resilience may be influenced more by mean annual precipitation (MAP) than ecosystem type. Here, we conducted a global meta-analysis to investigate primary production resistance and resilience to extreme drought in 64 forests and grasslands across a broad MAP gradient. We found resistance to extreme drought was predicted by MAP; however, grasslands (positive) and forests (negative) exhibited opposing resilience relationships with MAP. Our findings indicate that common plant physiological mechanisms may determine grassland and forest resistance to extreme drought, whereas differences among plant residents in turnover time, plant architecture, and drought adaptive strategies likely underlie divergent resilience patterns. The low resistance and resilience of dry grasslands suggests that these ecosystems are the most vulnerable to extreme drought – a vulnerability that is expected to compound as extreme drought frequency increases in the future.
Display omitted
•Whether forests and grasslands respond similarly to extreme drought is unknown.•Meta-analysis compared forest and grassland production resistance and resilience.•Resistance followed a common continuum of mean annual precipitation (MAP).•Grassland resilience increased, forest resilience decreased, with increasing MAP.•Dry grasslands are most vulnerable; dry forest response requires more research.
PDF
