Shifts In Plant Communities Research Articles

Cascading effects of fire retardant on plant-microbe interactions, community composition, and invasion.

Climate change, historical fire suppression, and a rise in human movements in urban-forest boundaries have resulted in an increased use of long-term fire retardant (LTFR). While LTFR is an effective fire-fighting tool, it contains high concentrations of nitrogen and phosphorus, and little is known about how this nutrient pulse affects terrestrial ecosystems. We used field surveys and greenhouse experiments to quantify effects of LTFR on plant productivity, community composition, and plant interactions with the ubiquitous root symbiont arbuscular mycorrhizal fungi (AMF). In the field, LTFR applications were associated with persistent shifts in plant communities toward exotic annuals with little or no dependency of AMF. Plants exposed to LTFR were less colonized by AMF, both in field surveys and in the greenhouse, and this was most likely due to the substantial and persistent increase in soil available phosphorus. All plants grew bigger with LTFR in the greenhouse, but the invasive annual cheatgrass (Bromus tectorum) benefitted most. While LTFR can control fires, it may cause long-term changes in soil nutrient availabilities, disrupt plant interactions with beneficial soil microbes, and exasperate invasion by some exotic plants.

Drained coastal peatlands: A potential nitrogen source to marine ecosystems under prolonged drought and heavy storm events—A microcosm experiment

Over the past several decades there has been a massive increase in coastal eutrophication, which is often caused by increased runoff input of nitrogen from landscape alterations. Peatlands, covering 3% of land area, have stored about 12–21% of global soil organic nitrogen (12–20Pg N) around rivers, lakes and coasts over millennia and are now often drained and farmed. Their huge nitrogen pools may be released by intensified climate driven hydrologic events—prolonged droughts followed by heavy storms—and later transported to marine ecosystems. In this study, we collected peat monoliths from drained, natural, and restored coastal peatlands in the Southeastern U.S., and conducted a microcosm experiment simulating coupled prolonged-drought and storm events to (1) test whether storms could trigger a pulse of nitrogen export from drought-stressed peatlands and (2) assess how differentially hydrologic managements through shifting plant communities affect nitrogen export by combining an experiment of nitrogen release from litter.During the drought phase, we observed a significant temporal variation in net nitrogen mineralization rate (NMR). NMR spiked in the third month and then decreased rapidly. This pattern indicates that drought duration significantly affects nitrogen mineralization in peat. NMR in the drained site reached up to 490±110kgha−1year−1, about 5 times higher than in the restored site. After the 14-month drought phase, we simulated a heavy storm by bringing peat monoliths to saturation. In the discharge waters, concentrations of total dissolved nitrogen in the monoliths from the drained site (72.7±16.3mgL−1) was about ten times as high as from the restored site. Our results indicate that previously drained peatlands under prolonged drought are a potent source of nitrogen export. Moreover, drought-induced plant community shifts to herbaceous plants substantially raise nitrogen release with lasting effects by altering litter quality in peatlands.

Beyond plant–soil feedbacks: mechanisms driving plant community shifts due to land‐use legacies in post‐agricultural forests

Summary Although biotic legacies of past agricultural practices are widespread and increasing in contemporary ecosystems, our understanding of the mechanisms driving such legacies is still poor. Forest understories on former agricultural land show low frequencies and abundance of typical woodland species when compared with ancient forests. These community shifts have been ascribed to the effects of dispersal limitation. A rarely considered mechanism is that post‐dispersal processes driven by plant‐associated communities determine the poor performance and recruitment of woodland indicators. Given the strong alterations in soil conditions due to former agricultural practices, we hypothesized that (abiotic) plant–soil feedbacks could be a major factor in community shifts. We addressed this hypothesis by comparing plant‐associated communities in the soil and above the ground in ancient and post‐agricultural alluvial forests; then, we experimentally tested whether the changes in biotic and abiotic soil properties could affect above‐ground herbivore abundance and pressure and plant performance. Ancient and post‐agricultural communities clearly differed in composition at different levels of the food web. Besides the plant community, we also observed the differences in the microbial and nematode community with increased abundance of root‐feeding nematodes in post‐agricultural soils. The composition of the above‐ground invertebrate community did not differ in ancient and post‐agricultural forest parcels; however, plants growing in post‐agricultural sites showed higher abundance of invertebrate herbivores and suffered more herbivory. Nutrient analyses of soil and plants showed that increased levels of phosphorus (and to a lesser extent, nitrogen) made plants more nutritious for insect herbivores. Laboratory experiments further pointed to this mechanism as an explanation of the poorer performance of woodland indicators in post‐agricultural woodlands. Our results point to biotic and abiotic plant–soil feedbacks coupled with herbivory as a new mechanism to explain the legacy effects in temperate forests. The modification of the below‐ground community and soil abiotic characteristics by previous agricultural activity affects not only the plant growth but also the plant nutrient content in the compared understorey species, making them more susceptible to above‐ground herbivory. Our results provide one of the first examples of integrating plant–soil feedback and above‐ and below‐ground interactions to explain land‐use legacies.

Warming Alters Expressions of Microbial Functional Genes Important to Ecosystem Functioning.

Soil microbial communities play critical roles in ecosystem functioning and are likely altered by climate warming. However, so far, little is known about effects of warming on microbial functional gene expressions. Here, we applied functional gene array (GeoChip 3.0) to analyze cDNA reversely transcribed from total RNA to assess expressed functional genes in active soil microbial communities after nine years of experimental warming in a tallgrass prairie. Our results showed that warming significantly altered the community wide gene expressions. Specifically, expressed genes for degrading more recalcitrant carbon were stimulated by warming, likely linked to the plant community shift toward more C4 species under warming and to decrease the long-term soil carbon stability. In addition, warming changed expressed genes in labile C degradation and N cycling in different directions (increase and decrease), possibly reflecting the dynamics of labile C and available N pools during sampling. However, the average abundances of expressed genes in phosphorus and sulfur cycling were all increased by warming, implying a stable trend of accelerated P and S processes which might be a mechanism to sustain higher plant growth. Furthermore, the expressed gene composition was closely related to both dynamic (e.g., soil moisture) and stable environmental attributes (e.g., C4 leaf C or N content), indicating that RNA analyses could also capture certain stable trends in the long-term treatment. Overall, this study revealed the importance of elucidating functional gene expressions of soil microbial community in enhancing our understanding of ecosystem responses to warming.

Burn Severity Dominates Understory Plant Community Response to Fire in Xeric Jack Pine Forests

Fire is the most common disturbance in northern boreal forests, and large fires are often associated with highly variable burn severities across the burnt area. We studied the understory plant community response to a range of burn severities and pre-fire stand age four growing seasons after the 2011 Richardson Fire in xeric jack pine forests of northern Alberta, Canada. Burn severity had the greatest impact on post-fire plant communities, while pre-fire stand age did not have a significant impact. Total plant species richness and cover decreased with disturbance severity, such that the greatest richness was in low severity burns (average 28 species per 1-m2 quadrat) and plant cover was lowest in the high severity burns (average 16%). However, the response of individual plant groups differed. Lichens and bryophytes were most common in low severity burns and were effectively eliminated from the regenerating plant community at higher burn severities. In contrast, graminoid cover and richness were positively related to burn severity, while forbs did not respond significantly to burn severity, but were impacted by changes in soil chemistry with increased cover at pH >4.9. Our results indicate the importance of non-vascular plants to the overall plant community in this harsh environment and that the plant community is environmentally limited rather than recruitment or competition limited, as is often the case in more mesic forest types. If fire frequency and severity increase as predicted, we may see a shift in plant communities from stress-tolerant species, such as lichens and ericaceous shrubs, to more colonizing species, such as certain graminoids.

Does ecosystem sensitivity to precipitation at the site‐level conform to regional‐scale predictions?

Central to understanding global C cycle dynamics is the functional relationship between precipitation and net primary production (NPP). At large spatial (regional) scales, the responsiveness of aboveground NPP (ANPP) to interannual variation in annual precipitation (AP; ANPPsens) is inversely related to site-level ANPP, coinciding with turnover of plant communities along precipitation gradients. Within ecosystems experiencing chronic alterations in water availability, plant community change will also occur with unknown consequences for ANPPsens. To examine the role plant community shifts may play in determining alterations in site-level ANPPPsens, we experimentally increased precipitation by approximately 35% for two decades in a native Central U.S. grassland. Consistent with regional models, ANPPsens decreased initially as water availability and ANPP increased. However, ANPPsens shifted back to ambient levels when mesic species increased in abundance in the plant community. Similarly, in grassland sites with distinct mesic and xeric plant communities and corresponding 50% differences in ANPP, ANPPsens did not differ over almost three decades. We conclude that responses in ANPPsens to chronic alterations in water availability within an ecosystem may not conform to regional AP-ANPP patterns, despite expected changes in ANPP and plant communities. The result is unanticipated functional resistance to climate change at the site scale.

Long-term agricultural management maximizing hay production can significantly reduce belowground C storage

Liming and fertilization of grasslands have been used for centuries to sustain hay production. Besides improving hay yields, these practices induce compositional shifts in plant and soil microbial communities, including symbiotic arbuscular mycorrhizal (AM) fungi. However, in spite of increasing interest in soil carbon (C) sequestration to offset anthropogenic CO2 emissions, little is known about the long-term effects of these agronomic interventions on soil C stocks. We examined how plants, AM fungi, and soil C respond to more than seven decades of annual applications of lime, mineral nitrogen (N), and mineral phosphorus (P) to test the hypotheses that (1) management practices increasing aboveground plant production decrease C allocation to roots, AM fungi and the soil; and (2) the relative availability of N and P predicts belowground C allocation in a consistent manner. Our study was conducted at the Rengen Grassland Experiment, established in 1941. Lime combined with N increased hay yields and promoted development of AM fungal hyphae in soil, while reducing relative C allocation to roots. Simultaneous enrichment of soil with lime, N, and P further boosted hay production, promoted grasses and suppressed other plant functional groups. This treatment also decreased soil organic C and strongly suppressed AM fungi in the soil, although the response to P varied among different AM fungal taxa. Our results indicate that agricultural management practices aimed at maximization of hay production may, in the long run, significantly (−20%) reduce belowground C storage. This is a great concern with respect to the intended use of grasslands as anthropogenic CO2 sinks because the fertilization-induced decrease in soil C stocks can partly or fully negate the C sequestration potential of the grassland ecosystems as a whole.

Plant community shifts caused by feral swine rooting devalue Florida rangeland

Invasive species threaten agriculture by changing agroecosystem structure and function, reducing habitat value, decreasing biodiversity and ecosystem services and increasing management costs. Grazing lands in south central Florida are a mosaic of sown pastures, native grasslands, wetlands and woodlands that provide a variety of ecosystem services. Disturbance of these pastures and native grasslands by invasive feral swine (Sus scrofa) can have negative consequences for both economic productivity and biodiversity. In this study, we show that the effect of rooting on plant diversity depends on ecosystem type and initial levels of plant species diversity. For example, in native grassland pasture, rooting was initially associated with declines in plant species richness, while in sown pastures, rooting was associated with more sustained increases in plant species richness. In both sown pastures and native grasslands, swine rooting altered plant community composition reducing agricultural productivity. Forage grasses were primarily associated with unrooted areas, whereas low quality forage species or nuisance species were found in rooted areas. We provide an example of monetary losses that cattle ranches can incur when feral swine are abundant on the landscape and control is minimal. Ranch managers and government agencies are encouraged to consider implementing more stringent feral swine management programs to minimize negative effects of feral swine rooting on ecological and economic value of grazing lands.

藏北高原草地群落的数量分类与排序

PDF HTML阅读 XML下载 导出引用 引用提醒 藏北高原草地群落的数量分类与排序 DOI: 10.5846/stxb201504240848 作者: 作者单位: 中国科学院地理科学与资源研究所,中国人民大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家科技支撑课题资助项目（2011BAC09B03）；科技部973课题资助项目（2013CB956300）；国家自然科学基金资助项目（41271067） Quantitative classification and ordination of grassland communities on the Northern Tibetan Plateau Author: Affiliation: Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,Renmin University of China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用TWINSPAN数量分类和DCA、CCA排序的方法，对藏北高原草地29个样点进行统计分析。结果显示：（1）TWINSPAN数量分类将藏北高寒草地群落划分成10种类型。（2）样点DCA排序第一轴基本反映了水分环境梯度，第二轴基本反映了热量梯度。（3）TWINSPAN分类所划分的各群落在DCA排序图上都有各自的分布范围和界限，说明DCA排序能较好的反应各优势群落与其环境资源之间的关系。（4）样点CCA排序表明，影响群落分布的首要环境因子是水分因子（年均降水量）和空间因子（经度），其次是热量因子（年均温度），CCA排序进一步阐明了群落分布决定于水分和温度等环境因子，并间接验证了TWINSPAN的分类结果。（5）物种CCA排序和TWINSPAN分类结果表明：植物群落中物种的分布格局与植物群落类型的分布格局存在一定的相似性。 Abstract:The relationship between vegetation and the environment is one of the fundamental questions in understanding plant species composition and community distribution along an environmental gradient. Understanding vegetation-environment correlations may help predict possible shifts in plant communities in response to climate and land use changes. There are 48 million hm2 of natural grasslands on the Northern Tibetan Plateau, accounting for 59% of the total grassland area in the Tibet Autonomous Region. However, these alpine grasslands are threatened by global climate change and intense human activities in recent decades, and are now widely degraded. Quantitative classification and ordination are important methods in examining the internal classification of plant communities, characteristics of their associations, and in revealing the ecological relationships between vegetation and the environment. TWINSPAN classification and DCA,CCA ordination were used to conduct a classification and ordination of the plant communities of 29 plots in the northern Tibetan grassland. Our results indicate that: (1) Northern Tibetan alpine meadows are classified into 10 associations: Stipa purpurea+Festuca nitidula+Carex ivanovae; Stipa purpurea+Carex ivanovae; Stipa purpurea+Leontopodium nanum; Kobresia pygmaea; Kobresia pygmaea+Stipapur purea; Stipa purpurea; Stipa purpurea+Blysmus sinocompressus+Oxytropis; Stipa purpurea+Heteropappus semiprostratus+Astragalus puivinalis; Carex moorcroftii+Stipa purpurea+Rhodiola smithii; and Stipa glareosa+Stipa purpurea+Ajania khartensis; (2) The first axis of DCA basically reflected a moisture gradient, and the second axis indicated a thermal gradient; (3) Each community divided by TWINSPAN classification had its specific distribution and boundaries on the DCA ordination diagram, which indicated that DCA ordination can explain the relationships between the plots and environment; (4) CCA plots indicated that the primary environmental factors controlling the distribution of communities were rainfall (average annual rainfall) along longitude, followed by temperature (average annual temperature); CCA sorting further elaborated the relationship between plant community distribution and the environment, and indirectly supported the results of the TWINSPAN classification; (5) Quantitative analysis of 74 species by CCA indicated that the distribution pattern of species and plots in DCA was similar. The first axis of species CCA reflected water conditions of species distribution. Taken together, we conclude that the distribution patterns of plant species communities closely mirror each other. In general, the present study provides an ecological interpretation of the distribution of plant species communities along an environmental gradient on the Northern Tibetan Plateau. 参考文献 相似文献 引证文献

Plant community composition as a driver of decomposition dynamics in riparian wetlands

Riparian wetlands are well known for providing the important ecosystem service of carbon storage. However, changes in land-use regimes surrounding riparian wetlands have been shown to result in alterations to the wetland plant community. These plant community changes have the potential to alter litter quality, decomposition rates, and ultimately the capacity of riparian wetlands to store carbon. To determine the effects of plant community shifts associated with disturbance on decomposition and carbon inputs, we performed a yearlong decomposition experiment using in situ herbaceous material, leaf litter, and control litter and examined biomass inputs in six headwater riparian wetlands in central Pennsylvania. Two sites were classified as Hemlock-Mixed Hardwood Palustrine Forest, two were classified as Broadleaf Palustrine Forest, and two were classified as Reed Canary Grass-Floodplain Grassland (Zimmerman et al. 2012). Plant matter with greater initial percent C, percent lignin, and lignin:N ratios decomposed more slowly while plant matter with greater initial cellulose decomposed more quickly. However, no significant differences were found between plant community types in decomposition rate or amount of carbon remaining at the end of the experiment, indicating that the differences in plant community type did not have a large impact on decomposition in riparian wetlands. This work has important implications for studies that examine the decomposition dynamics of a few select species, as they may not capture the decomposition dynamics of the plant community and thus extrapolating results from these studies to the larger ecosystem may be inappropriate.

Habitat changes and changing predatory habits in North American fossil canids

The spread of open grassy habitats and the evolution of long-legged herbivorous mammals with high-crowned cheek teeth have been viewed as an example of coevolution. Previous studies indicate that specialized predatory techniques in carnivores do not correlate with the spread of open habitats in North America. Here we analyse new data on elbow-joint shape for North American canids over the past ∼37 million years and show that incipiently specialized species first appeared along with the initial spread of open habitats in the late Oligocene. Elbow-joint morphologies indicative of the behavior of modern pounce-pursuit predators emerged by the late Miocene coincident with a shift in plant communities from C3 to C4 grasses. Finally, pursuit canids first emerged during the Pleistocene. Our results indicate that climate change and its impact on vegetation and habitat structure can be critical for the emergence of ecological innovations and can alter the direction of lineage evolution.

Biotic community shifts explain the contrasting responses of microbial and root respiration to experimental soil acidification

Soil respiration is comprised primarily of root and microbial respiration, and accounts for nearly half of the total CO2 efflux from terrestrial ecosystems. Soil acidification resulting from acid deposition significantly affects soil respiration. Yet, the mechanisms that underlie the effects of acidification on soil respiration and its two components remain unclear. We collected data on sources of soil CO2 efflux (microbial and root respiration), above- and belowground biotic communities, and soil properties in a 4-year field experiment with seven levels of acid in a semi-arid Inner Mongolian grassland. Here, we show that soil acidification has contrasting effects on root and microbial respiration in a typical steppe grassland. Soil acidification increases root respiration mainly by an increase in root biomass and a shift to plant species with greater specific root respiration rates. The shift of plant community from perennial bunchgrasses to perennial rhizome grasses was in turn regulated by the decreases in soil base cations and N status. In contrast, soil acidification suppresses microbial respiration by reducing total microbial biomass and enzymatic activities, which appear to result from increases in soil H+ ions and decreases in soil base cations. Our results suggest that shifts in both plant and microbial communities dominate the responses of soil respiration and its components to soil acidification. These results also indicate that carbon cycling models concerned with future climate change should consider soil acidification as well as shifts in biotic communities.

Evidence for long‐term shift in plant community composition under decadal experimental warming

Summary Long‐term, slow ecological processes such as changes in plant community structure and composition strongly regulate ecosystem responses to climate change. Shifts in plant community are expected in chronically altered environments under warming. However, experimental evidence for long‐term shifts and the associated mechanisms is still scarce in temperate grasslands. Here, we explore the long‐term responses of a prairie plant community to 14‐year (2000–2013) manipulations of climate warming and clipping in Oklahoma, USA. Infrared heaters were used to elevate soil temperature by about 2 °C all year round, and annual clipping was applied to mimic hay harvest. Community composition was resistant to experimental warming in the first seven years, but started to show responses starting from the eighth year; clipping consistently affected community composition over the years. Compositional change under long‐term warming was mainly due to one invasive species and three dominant species. The negative correlations in relative abundance between the invasive species and the dominant species suggest interspecific competition. Community structure (i.e. richness, evenness and diversity) had no overall response to experimental warming. However, in 2007, the extreme wet year, warming reduced species richness by 30%. Clipping promoted species richness by 10% on average over the 14 years but decreased community evenness. Warming did not interact with clipping in influencing the plant community variables. Synthesis. Our study provides experimental evidence for long‐term shifts in plant community composition due to warming and revealed novel mechanisms (i.e. species invasion and associated biotic interactions) underlying the long‐term shift. The results also suggest that climate extremes may elicit or advance community responses to climate warming. The findings highlight that long‐term climate change experiments are essential to reveal potential shifts in community composition.

Potential Shift in Plant Communities with Climate Change: Outcome on Litter Decomposition and Nutrient Release in a Mediterranean Oak Forest

The ongoing decline in biodiversity has fuelled concerns about its impact on ecosystem functioning. Mediterranean oak forests may prove very sensitive to global change, which could strongly influence the species composition of plant communities and thereby affect ecosystem processes. To determine the potential outcome of shifts in species composition on litter decomposition dynamics, we conducted a full-factorial decomposition experiment over a gradient of litter species diversity in a Mediterranean Downy oak (Quercus pubescens Willd.) forest. We used litter from the three dominant tree species naturally present in the Downy oak forest and litter from Aleppo pine (Pinus halepensis Mill.) in anticipation of its possible spread in the future with global change. Litter water holding capacity and N/P ratio were the most important and positive drivers of decomposition process. In contrast to other ecosystems where synergistic non-additive effects are prevalent, we observed 54% of additive and 46% of non-additive effects on litter mass loss in our Mediterranean ecosystem. These results could indicate less complementarity among decomposers for decomposition of diverse plant material in such a stressful climate. Moreover, dominant tree species are of key importance for nutrient availability, and the arrival of Aleppo pine would strongly reduce the N release during the decomposition process. Based on calculations of an annual partial nutrient budget at the ecosystem level, we showed that a shift in plant communities could affect nutrient release, ranging from 5 to 36% for N and 63 to 83% for P depending on the co-occurring tree species in the Downy oak forest.

Forest disturbance accelerates thermophilization of understory plant communities

Summary Climate change is likely to shift plant communities towards species from warmer regions, a process termed ‘thermophilization’. In forests, canopy disturbances such as fire may hasten this process by increasing temperature and moisture stress in the understory, yet little is known about the mechanisms that might drive such shifts, or the consequences of these processes for plant diversity. We sampled understory vegetation across a gradient of disturbance severity from a large‐scale natural experiment created by the factorial combination of forest thinning and wildfire in California. Using information on evolutionary history and functional traits, we tested the hypothesis that disturbance severity should increase community dominance by species with southern‐xeric biogeographic affinities. We also analysed how climatic productivity mediates the effect of disturbance severity, and quantified the functional trait response to disturbance, to investigate potential mechanisms behind thermophilization. The proportion of north‐temperate flora decreased, while the proportion of southern‐xeric flora increased, with greater disturbance severity and less canopy closure. Disturbance caused a greater reduction of north‐temperate flora in productive (wetter) forests, while functional trait analyses suggested that species colonizing after severe disturbance may be adapted to increased water stress. Forests with intermediate disturbance severity, where abundances of northern and southern species were most equitable, had the highest stand‐scale understory diversity. Synthesis. Canopy disturbance is likely to accelerate plant community shifts towards species from warmer regions, via its effects on understory microclimate at small scales. Understory diversity can be enhanced by intermediate disturbance regimes that promote the coexistence of species with different biogeographic affinities.

Fire Recurrence and the Dynamics of the Enhanced Vegetation Index in a Mediterranean Ecosystem

This study area is located in the eastern littoral of the Iberian Peninsula; its importance resides in its Mediterranean ecosystem, complex topography, extensive land use changes, and intensive forest fires history. The study is done at the landscape level, covering a wide area for an extended period of time. This work uses Geographic Information Systems (GIS) and Satellite Remote Sensing (SRS) techniques to evaluate the impact of spatio-temporal parameters on shaping Mediterranean landscapes. Interacting ecological parameters are analysed and correlated to post-fire vegetation regeneration in an attempt to understand its dynamics. The results provide evidence that the number of fires separated by short time intervals influence vegetation growth negatively measured as Enhanced Vegetation Index (EVI). During this period, micro-climatic effects (soil and environmental humidity) are major factors influencing EVI-measured vegetation regeneration. The conclusions expect shifts in Mediterranean plant communities in heavily burned ecosystems stressing the importance of their correct short and long term post-fire management.

Watershed hydrology and dissolved organic matter export across time scales: minute to millennium

Ecological theory emphasizes headwater streams and wetlands as hotspots for metabolism of terrestrially derived organic matter and biogeochemical transformations. Growing evidence indicates that freshwater ecosystems may be as important as terrestrial and marine environments in the annual flux of CO2 to the atmosphere. The National Ecological Observatory Network (NEON) and the Stream Ecological Observatory Network (STREON) offer the opportunity to collect and analyze data related to these processes at spatial scales ranging from local to continental and at temporal scales from minutes to millennia. These data can be used to understand how global climate change and subsequent shifts in terrestrial plant communities and precipitation regimes will influence the export and composition of dissolved organic matter (DOM) to headwater streams, downstream freshwater ecosystems, and coastal environments. Moreover, temporal scaling of DOM export among watersheds is an underexploited frontier research area throughout the earth sciences. Long-term, high-frequency fluorometry and discharge data sets collected at NEON and STREON observatories could be linked to evaluate, quantify, and forecast DOM export among watersheds and across time scales ranging from individual hydrologic events to decadal changes in precipitation regimes.

European Semiarid Mediterranean Ecosystems are Sensitive to Nitrogen Deposition: Impacts on Plant Communities and Root Phosphatase Activity

Nitrogen (N) deposition is predicted to impact on the structure and functioning of Mediterranean ecosystems. In this study, we measured plant species composition, production and root phosphatase activity in a field experiment in which N (0, 10, 20 and 50 kg N ha−1 year−1) was added since October 2007 to a semiarid shrubland in central Spain. The characteristically dominant annual forb element responded negatively to N after ~2.5 and ~3.5 years. In contrast, the nitrophilous element (mainly crucifers) increased with N after ~2.5 and ~5.5 years, a response controlled by between-year variations in rainfall and the heterogeneous distribution of P availability. We also described a hierarchy of factors driving the structure and composition of the plant community: soil fertility was the most important driver, whereas calcareousness/acidity of soils and shrub cover played a secondary role; finally, N deposition contributed to explain a smaller fraction of the total variance, and its effects were predominantly negative, which was attributed to ammonium toxicity. Root phosphatase activity of three species was not responsive to N after ~2.5 years but there was a negative relationship with soil P in two of them. We conclude that increased N deposition in semiarid Mediterranean ecosystems of Europe can contribute to cause a shift in plant communities associated with an increase in the nitrophilous element and with a decline in abundance of various forb species adapted to the local conditions.

Long-term experimental warming alters community composition of ascomycetes in Alaskan moist and dry arctic tundra.

Arctic tundra regions have been responding to global warming with visible changes in plant community composition, including expansion of shrubs and declines in lichens and bryophytes. Even though it is well known that the majority of arctic plants are associated with their symbiotic fungi, how fungal community composition will be different with climate warming remains largely unknown. In this study, we addressed the effects of long-term (18years) experimental warming on the community composition and taxonomic richness of soil ascomycetes in dry and moist tundra types. Using deep Ion Torrent sequencing, we quantified how OTU assemblage and richness of different orders of Ascomycota changed in response to summer warming. Experimental warming significantly altered ascomycete communities with stronger responses observed in the moist tundra compared with dry tundra. The proportion of several lichenized and moss-associated fungi decreased with warming, while the proportion of several plant and insect pathogens and saprotrophic species was higher in the warming treatment. The observed alterations in both taxonomic and ecological groups of ascomycetes are discussed in relation to previously reported warming-induced shifts in arctic plant communities, including decline in lichens and bryophytes and increase in coverage and biomass of shrubs.

Long-term regional shifts in plant community composition are largely explained by local deer impact experiments.

The fact that herbivores and predators exert top-down effects to alter community composition and dynamics at lower trophic levels is no longer controversial, yet we still lack evidence of the full nature, extent, and longer-term effects of these impacts. Here, we use results from a set of replicated experiments on the local impacts of white-tailed deer to evaluate the extent to which such impacts could account for half-century shifts in forest plant communities across the upper Midwest, USA. We measured species' responses to deer at four sites using 10–20 year-old deer exclosures. Among common species, eight were more abundant outside the exclosures, seven were commoner inside, and 16 had similar abundances in- and outside. Deer herbivory greatly increased the abundance of ferns and graminoids and doubled the abundance of exotic plants. In contrast, deer greatly reduced tree regeneration, shrub cover (100–200 fold in two species), plant height, plant reproduction, and the abundance of forbs. None of 36 focal species increased in reproduction or grew taller in the presence of deer, contrary to expectations. We compared these results to data on 50-year regional shifts in species abundances across 62 sites. The effects of herbivory by white-tailed deer accurately account for many of the long-term regional shifts observed in species' abundances (R2 = 0.41). These results support the conjecture that deer impacts have driven many of the regional shifts in forest understory cover and composition observed in recent decades. Our ability to link results from shorter-term, local experiments to regional long-term studies of ecological change strengthens the inferences we can draw from both approaches.