August 2024
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341 Reads
Nature Ecology & Evolution
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August 2024
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341 Reads
Nature Ecology & Evolution
August 2024
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576 Reads
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4 Citations
Nature Ecology & Evolution
Global change is associated with variable shifts in the annual production of aboveground plant biomass, suggesting localized sensitivities with unclear causal origins. Combining remotely sensed normalized difference vegetation index data since the 1980s with contemporary field data from 84 grasslands on 6 continents, we show a widening divergence in site-level biomass ranging from +51% to −34% globally. Biomass generally increased in warmer, wetter and species-rich sites with longer growing seasons and declined in species-poor arid areas. Phenological changes were widespread, revealing substantive transitions in grassland seasonal cycling. Grazing, nitrogen deposition and plant invasion were prevalent in some regions but did not predict overall trends. Grasslands are undergoing sizable changes in production, with implications for food security, biodiversity and carbon storage especially in arid regions where declines are accelerating.
July 2024
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350 Reads
Forbs (“wildflowers”) are important contributors to grassland biodiversity and services, but they are vulnerable to environmental changes that affect their coexistence with grasses. In a factorial experiment at 94 sites on 6 continents, we tested the global generality of several broad predictions arising from previous studies: (1) Forb cover and richness decline under nutrient enrichment, particularly nitrogen enrichment, which benefits grasses at the expense of forbs. (2) Forb cover and richness increase under herbivory by large mammals, especially when nutrients are enriched. (3) Forb richness and cover are less affected by nutrient enrichment and herbivory in more arid climates, because water limitation reduces the impacts of competition with grasses. We found strong evidence for the first, partial support for the second, and no support for the third prediction. Forb richness and cover are reduced by nutrient addition, with nitrogen having the greatest effect; forb cover is enhanced by large mammal herbivory, although only under conditions of nutrient enrichment and high herbivore intensity; and forb richness is lower in more arid sites, but is not affected by consistent climate-nutrient or climate-herbivory interactions. We also found that nitrogen enrichment disproportionately affects forbs in certain families (Asteraceae, Fabaceae). Our results underscore that anthropogenic nitrogen addition is a major threat to grassland forbs and the ecosystem services they support, but grazing under high herbivore intensity can offset these nutrient effects.
December 2023
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574 Reads
Communications Biology
Covering approximately 40% of land surfaces, grasslands provide critical ecosystem services that rely on soil organisms. However, the global determinants of soil biodiversity and functioning remain underexplored. In this study, we investigate the drivers of soil microbial and detritivore activity in grasslands across a wide range of climatic conditions on five continents. We apply standardized treatments of nutrient addition and herbivore reduction, allowing us to disentangle the regional and local drivers of soil organism activity. We use structural equation modeling to assess the direct and indirect effects of local and regional drivers on soil biological activities. Microbial and detritivore activities are positively correlated across global grasslands. These correlations are shaped more by global climatic factors than by local treatments, with annual precipitation and soil water content explaining the majority of the variation. Nutrient addition tends to reduce microbial activity by enhancing plant growth, while herbivore reduction typically increases microbial and detritivore activity through increased soil moisture. Our findings emphasize soil moisture as a key driver of soil biological activity, highlighting the potential impacts of climate change, altered grazing pressure, and eutrophication on nutrient cycling and decomposition within grassland ecosystems.
October 2023
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1,495 Reads
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54 Citations
Little is currently known about how climate modulates the relationship between plant diversity and soil organic carbon and the mechanisms involved. Yet, this knowledge is of crucial importance in times of climate change and biodiversity loss. Here, we show that plant diversity is positively correlated with soil carbon content and soil carbon-to-nitrogen ratio across 84 grasslands on six continents that span wide climate gradients. The relationships between plant diversity and soil carbon as well as plant diversity and soil organic matter quality (carbon-to-nitrogen ratio) are particularly strong in warm and arid climates. While plant biomass is positively correlated with soil carbon, plant biomass is not significantly correlated with plant diversity. Our results indicate that plant diversity influences soil carbon storage not via the quantity of organic matter (plant biomass) inputs to soil, but through the quality of organic matter. The study implies that ecosystem management that restores plant diversity likely enhances soil carbon sequestration, particularly in warm and arid climates.
October 2023
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51 Reads
Evansia
September 2023
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421 Reads
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4 Citations
Dominance often indicates one or a few species being best suited for resource capture and retention in a given environment. Press perturbations that change availability of limiting resources can restructure competitive hierarchies, allowing new species to capture or retain resources and leaving once dominant species fated to decline. However, dominant species may maintain high abundances even when their new environments no longer favour them due to stochastic processes associated with their high abundance, impeding deterministic processes that would otherwise diminish them. Here, we quantify the persistence of dominance by tracking the rate of decline in dominant species at 90 globally distributed grassland sites under experimentally elevated soil nutrient supply and reduced vertebrate consumer pressure. We found that chronic experimental nutrient addition and vertebrate exclusion caused certain subsets of species to lose dominance more quickly than in control plots. In control plots, perennial species and species with high initial cover maintained dominance for longer than annual species and those with low initial cover respectively. In fertilized plots, species with high initial cover maintained dominance at similar rates to control plots, while those with lower initial cover lost dominance even faster than similar species in controls. High initial cover increased the estimated time to dominance loss more strongly in plots with vertebrate exclosures than in controls. Vertebrate exclosures caused a slight decrease in the persistence of dominance for perennials, while fertilization brought perennials' rate of dominance loss in line with those of annuals. Annual species lost dominance at similar rates regardless of treatments. Synthesis. Collectively, these results point to a strong role of a species' historical abundance in maintaining dominance following environmental perturbations. Because dominant species play an outsized role in driving ecosystem processes, their ability to remain dominant—regardless of environmental conditions—is critical to anticipating expected rates of change in the structure and function of grasslands. Species that maintain dominance while no longer competitively favoured following press perturbations due to their historical abundances may result in community compositions that do not maximize resource capture, a key process of system responses to global change.
June 2023
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493 Reads
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5 Citations
Human activities are altering ecological communities around the globe. Understanding the implications of these changes requires that we consider the composition of those communities. However, composition can be summarized by many metrics which in turn are influenced by different ecological processes. For example, incidence-based metrics strongly reflect species gains or losses, while abundance-based metrics are minimally affected by changes in the abundance of small or uncommon species. Furthermore, metrics might be correlated with different predictors. We used a globally distributed experiment to examine variation in species composition within 60 grasslands on six continents. Each site had an identical experimental and sampling design: 24 plots × 4 years. We For affiliations refer to page 13. expressed compositional variation within each site-not across sites-using abundance-and incidence-based metrics of the magnitude of dissimilarity (Bray-Curtis and Sorensen, respectively), abundance-and incidence-based measures of the relative importance of replacement (balanced variation and species turnover, respectively), and species richness at two scales (per plot-year [alpha] and per site [gamma]). Average compositional variation among all plot-years at a site was high and similar to spatial variation among plots in the pretreatment year, but lower among years in untreated plots. For both types of metrics, most variation was due to replacement rather than nestedness. Differences among sites in overall within-site compositional variation were related to several predictors. Environmental heterogeneity (expressed as the CV of total aboveground plant biomass in unfertilized plots of the site) was an important predictor for most met-rics. Biomass production was a predictor of species turnover and of alpha diversity but not of other metrics. Continentality (measured as annual temperature range) was a strong predictor of Sorensen dissimilarity. Metrics of compositional variation are moderately correlated: knowing the magnitude of dissimilarity at a site provides little insight into whether the variation is driven by replacement processes. Overall, our understanding of compositional variation at a site is enhanced by considering multiple metrics simultaneously. Monitoring programs that explicitly incorporate these implications, both when designing sampling strategies and analyzing data, will have a stronger ability to understand the com-positional variation of systems and to quantify the impacts of human activities.
November 2022
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494 Reads
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9 Citations
Declines in grassland diversity in response to nutrient addition are a general consequence of global change. This decline in species richness may be driven by multiple underlying processes operating at different time‐scales. Nutrient addition can reduce diversity by enhancing the rate of local extinction via competitive exclusion, or by reducing the rate of colonization by constraining the pool of species able to colonize under new conditions. Partitioning net change into extinction and colonization rates will better delineate the long‐term effect of global change in grasslands. We synthesized changes in richness in response to experimental fertilization with nitrogen, phosphorus and potassium with micronutrients across 30 grasslands. We quantified changes in local richness, colonization, and extinction over 8–10 years of nutrient addition, and compared these rates against control conditions to isolate the effect of nutrient addition from background dynamics. Total richness at steady state in the control plots was the sum of equal, relatively high rates of local colonization and extinction. On aggregate, 30%–35% of initial species were lost and the same proportion of new species were gained at least once over a decade. Absolute turnover increased with site‐level richness but was proportionately greater at lower‐richness sites relative to starting richness. Loss of total richness with nutrient addition, especially N in combination with P or K, was driven by enhanced rates of extinction with a smaller contribution from reduced colonization. Enhanced extinction and reduced colonization were disproportionately among native species, perennials, and forbs. Reduced colonization plateaued after the first few (<5) years after nutrient addition, while enhanced extinction continued throughout the first decade. Synthesis. Our results indicate a high rate of colonizations and extinctions underlying the richness of ambient communities and that nutrient enhancement drives overall declines in diversity primarily by exclusion of previously established species. Moreover, enhanced extinction continues over long time‐scales, suggesting continuous, long‐term community responses and a need for long‐term study to fully realize the extinction impact of increased nutrients on grassland composition.
November 2022
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286 Reads
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23 Citations
Soil Biology and Biochemistry
Anthropogenic nitrogen (N) input is known to alter the soil microbiome, but how N enrichment influences the abundance, alpha-diversity and community structure of N-cycling functional microbial communities in grasslands remains poorly understood. Here, we collected soils from plant communities subjected to up to 9 years of annual N-addition (10 g N m⁻² per year using urea as a N-source) and from unfertilized plots (control) in 30 grasslands worldwide spanning a large range of climatic and soil conditions. We focused on three key microbial groups responsible for two essential processes of the global N cycle: N2 fixation (soil diazotrophs) and nitrification (AOA: ammonia-oxidizing archaea and AOB: ammonia-oxidizing bacteria). We targeted soil diazotrophs, AOA and AOB using Illumina MiSeq sequencing and measured the abundance (gene copy numbers) using quantitative PCR. N-addition shifted the structure of the diazotrophic communities, although their alpha-diversity and abundance were not affected. AOA and AOB responded differently to N-addition. The abundance and alpha-diversity of AOB increased, and their community structure shifted with N-addition. In contrast, AOA were not affected by N-addition. AOA abundance outnumbered AOB in control plots under conditions of low N availability, whereas N-addition favoured copiotrophic AOB. Overall, N-addition showed a low impact on soil diazotrophs and AOA while effects for AOB communities were considerable. These results reveal that long-term N-addition has important ecological implications for key microbial groups involved in two critical soil N-cycling processes. Increased AOB abundance and community shifts following N-addition may change soil N-cycling, as larger population sizes may promote higher rates of ammonia oxidation and subsequently increase N loss via gaseous and soil N-leaching. These findings bring us a step closer to predicting the responses and feedbacks of microbial-mediated N-cycling processes to long-term anthropogenic N-addition in grasslands.
... We first constructed phenological indicators based on the Google Earth Engine (GEE) platform, including Normalized Difference Vegetation Index (NDVI)、 Normalized Difference Water Index (NDWI). NDVI is often used to reflect surface vegetation characteristics 23 , evaluate crop growth status, and is one of the important indicators for identifying crops 24 . NDWI is a key indicator for distinguishing between water and land, often used to identify rice planting areas 25,26 . ...
August 2024
Nature Ecology & Evolution
... Meanwhile, microorganisms had high C utilization efficiency (low qCO 2 ), resulting in less SOC loss during microbial decomposition. This is beneficial for increasing soil C storage (Spohn et al. 2023), contributing to the high SOC content in NS (Table 1). Indeed, we found that qCO 2 was significantly negatively correlated with SOC content (Table S1). ...
October 2023
... However, since ecosystem functioning depends heavily on the traits of the most abundant species (Grime 1998;Smith et al. 2020), if dominant species change in a way that is different from the responses of other species with lower abundance in the system (Collins et al. 2022), changes in community weighted means can diverge from how traits influence species-specific responses to global change (Lepš and de Bello 2023). For example, it is possible that dominant species may maintain dominance even if they do not have the functional trait values that are favoured by a particular global change factor if other competing species are kept in check by biotic interactions such as herbivory or pathogens (Wilfahrt et al. 2023). In this case, community-weighted trait shifts would be limited despite changes in the responses of some individual species. ...
September 2023
... No protected species were sampled. Those specimens were later identified at the University of Washington Herbarium in Seattle, WA using the contemporary regional flora manual [27]. With herbarium specimens available for comparison and experts in the regional flora on the field teams, taxa were identified with unique accuracy both in the field and in the herbarium. ...
June 2023
... several species of Vochysiaceae) (Haridasan 1982), while others release carboxylates to exclude Al (de Castro et al. 2022). However, nutrient imbalances or increased nutrient availability can favor fast-growing or invasive species, negatively impacting community assembly and diversity (Lannes et al. 2016;Muehleisen et al. 2023). ...
November 2022
... Moreover, a large amount of N input disrupted the original nutrient distribution pattern and caused a priming effect, leading to a lower C/N ratio in the soil, resulting in changes in life history strategies [68][69][70]. Furthermore, the N addition could enhance the function of microbial taxa that specifically decompose organic compounds, facilitating material transformation and nutrient availability [71,72]. Therefore, further exploration of the effects of key functional species on nutrient turnover under different fertilization treatments is necessary. ...
November 2022
Soil Biology and Biochemistry
... Furthermore, nutrients addition seems to be intrinsically associated with reduced temporal stability of primary production ( Zhang et al. 2016 ;Zhou et al. 2020 ;Seabloom et al. 2021 ). More broadly, deleterious effects of nutrient enrichment on species diversity have been associated with increased instability of (agro) ecosystem functions ( Zhang et al. 2018 ;Carroll et al. 2021 ;Su et al. 2022 ;. Temporal stability of primary productivity is the key to stable provisioning of ecosystem services to human beings ( Su et al. 2022 ). ...
December 2021
Ecology Letters
... This research enhances our understanding of the complex tripartite interactions among plants, pathogens and AMF, highlighting the importance of these biotic factors in sustaining healthy plant populations, agricultural productivity and overall ecosystem functions. Given the increasing prevalence of pathogen damage and the cumulative loss of species, our findings underscore the critical role of these interactions in ecological resilience [34,69,70]. ...
October 2021
... After 20 years of land use, when the amounts of available phosphorus and potassium decreased to 60-80 mg kg −1 , the biomass yield in the MGunf plot decreased significantly (p < 0.05) compared to MGf and did not differ from the biomass yield at the AL site (p > 0.05). According to [46], nitrogen and phosphorus deficiencies limit grassland biomass production, as well as the efficiency of micronutrients. Mineral fertilizers have a more positive effect on biomass yield than combined nitrogen, phosphorus, and potassium fertilizers, while the pH indicator has a weakly pronounced positive effect [47]. ...
October 2021
Ecology Letters
... For example, livestock at stocking rates much higher than natural densities (Fløjgaard et al., 2022) or high (selective) mesoherbivore densities in simplified faunal assemblages or islands (Chollet et al., 2016) can have negative effects on diversity (Coggan et al., 2018). Recent longer term studies have improved our understanding of temporal diversity dynamics, providing important insights into the understanding of local species extirpations and the effect of dominance shifts on species richness (Koerner et al., 2018;Wilfahrt et al., 2021). Understanding the relative influence of such complexities and how different parameters result in more positive, neutral or negative responses of diversity (including trait-based functional diversity) is a major outstanding challenge. ...
August 2021