Affect Plant Community Research Articles

Nontarget effects of pre‐emergent herbicides and a bioherbicide on soil resources, processes, and communities

Community‐type conversions, such as replacement of perennials by exotic annual grasses in semiarid desert communities, are occurring due to plant invasions that often create positive plant–soil feedbacks, which favor invaders and make restoration of native perennials difficult. Exotic annual grass control measures, such as pre‐emergent herbicides, can also alter soil ecosystems directly or indirectly (i.e. via the plant community), yet there are few studies on the topic in natural, non‐cropped landscapes. We asked how spray treatments applied to soil post‐fire with the intention of inhibiting invasive annual grasses (such as Bromus tectorum L.) and releasing existing native perennial grasses affected soil resources, a microbial process, and invertebrates in three climatically varied sagebrush steppe sites. Spray treatments included chemical herbicides (imazapic and rimsulfuron) that strongly affected plant communities and a bioherbicide (Pseudomonas fluorescens strain D7) that did not. Chemical herbicides increased soil mineral nitrogen in proportion to their negative effects on plant cover for 2 years after treatments in all sites and increased soil water and net N mineralization (measured at one site) but did not affect total carbon, nitrogen, or organic matter. Invertebrate responses to herbicides varied by site, and invertebrates increased with chemical herbicides at the highest, wettest site. We show that herbicide treatments can exacerbate pulses of mineral nutrients, which previous studies have shown can weaken ecosystem resistance to invasion. Thus, restoration strategies that increase the likelihood that desired plants can capture mineralized nutrients after herbicide application will likely be more successful.

Effects of short- and long-term plant functional group loss on alpine meadow community structure and soil nutrients.

The rapid loss of global biodiversity can greatly affect the normal functioning of ecosystems. However, how biodiversity losses affect plant community structure and soil nutrients is unclear. We conducted a field experiment to examine the short- and long-term effects of removing plant functional groups (Gramineae, Cyperaceae, legumes, and forbs) on the interrelationships among the species diversity, productivity, community structure, and soil nutrients in an alpine meadow ecosystem at Menyuan County, Qinghai Province. The variations in the species richness, above- and belowground biomass of the community gradually decreased over time. Species richness and productivity were positively correlated, and this correlation tended to be increasingly significant over time. Removal of the Cyperaceae, legumes, and other forbs resulted in fewer Gramineae species in the community. Soil total nitrogen, phosphorus, organic matter, and moisture contents increased significantly in the legume removal treatment. The removal of other forbs led to the lowest negative cohesion values, suggesting that this community may have difficulty recovering its previous equilibrium state within a short time. The effects of species removal on the ecosystem were likely influenced by the species structure and composition within the community. Changes in the number of Gramineae species indicated that they were more sensitive and less resistant to plant functional group removal. Legume removal may also indirectly cause distinct community responses through starvation and compensation effects. In summary, species loss at the community level led to extensive species niche shifts, which caused community resource redistribution and significant changes in community structure.

The interplay between historical land‐use and the distribution of Helichrysum shrubs in an African‐protected grassland

AbstractHuman land use can have lasting impacts on landscape characteristic, yet there remains a lack of information on how former land use affects plant communities in protected African grasslands. In this study, we investigated how land uses prior to the creation of Kitulo National Park, Tanzania, shaped the presence and abundance of the native shrub, Helichrysum species. We evaluated both plant species composition and soil properties across the park by dividing our sample into three different zones of historical land use based on participatory mapping. We divided the park into three former land uses: (1) livestock grazed and cultivated; (2) grazed only and (3) wild grazing with limited human impact. We observed that former grazed cultivated land use had five times higher Helichrysum abundance than former ‘wild’ land use. Soil pH, magnesium and phosphorus levels varied significantly across zones of historical land use but not between sites with and without Helichrysum species. Helichrysum splendidum was more abundant in soils with low soil phosphorus and magnesium concentrations. Our study demonstrates that historic grazing and cropping land uses through changes in soil nutrient properties can explain current Helichrysum species spread in protected areas. As such, conservation management plans would benefit from integrating mapping of former land uses to target interventions for problematic encroaching shrubs.

Forage taste agents manage plant communities through modifying grazing behavior of yak in alpine meadow

The use of taste agents to regulate the grazing behavior of livestock is a new attempt in pasture management, but the effects on grassland plant communities are not clear at present. Therefore, the following scientific questions need to be addressed: (1) how do different taste agents affected plant community structure by changing feed intake? (2) What was the mechanism of this effect? We proposed the following hypotheses: (1) Salt and sweetener increased feed intake of livestock and decreased the biomass of plant community, while bitters did the opposite. (2) Taste agents can regulate the relationship between plant species, and different taste agents can enhance or weaken the competitiveness of the different plants. In order to test the hypothesis, a grazing experiment with yaks was conducted in the alpine meadows of the Tibetan Plateau. Denatonium benzoate (Bitterant), NaCl (Salt), and sodium cyclamate (Sweetener) were sprayed onto the meadows twice a year, along with a control treatment of tap water. The results showed that (1) Salt increased the feed intake of yak significantly; bitterant decreased the feed intake of livestock and increased the biomass of plant community. (2) Salt increased the Pielou index of the plant community significantly. (3) The stability of plant community ranking from high to low is as follows: Control > Bitterant > Sweetener > Salt. (4) Bitterant and salt improved grazing tolerance of grassland and salt reduced the edibility of grassland. (5) The use of taste agents reduced the correlation between dominant species and led to the fragmentation of the relationship chain. The results of this study will provide a theoretical basis for using taste agents to regulate the community, species biodiversity management, restoration of degraded grassland, promoting utilization of grassland though controlling livestock selectivity.

Interannual hydrological changes affect plant communities across different elevation zones in plateau lakeshores: insights from Lake Erhai.

The relationship between wetland water level changes and plant community has been a research hotspot. However, the gradient changes and critical influencing factors of plateau lakeshore plants and soils during wet-dry alternation remain unclear. Here, we studied the variations in plants and soils along the Erhai lakeshore across three elevation ranges (1965.0-1965.3m, 1965.3-1965.6m, and 1965.6-1966.4m) during flooding and drought years. Our research aimed to elucidate the interrelationships and mechanisms among hydrology, soil properties, and plant dynamics. The results showed that (1) In drought years, the Shannon-Wiener index of plants significantly decreased across the three elevation ranges, and other plant diversity indices, biomass, and coverage also decreased to varying degrees; (2) except for soil pH, soil water (SW) and nutrient content decreased to varying degrees in the drought year; (3) SW was the primary factor influencing plant biomass, coverage, and diversity in the 1965.0-1965.3m and 1965.3-1965.6m ranges; nitrate nitrogen, C/N ratio, total phosphorus were the primary factors in the 1965.6-1966.4m ranges. The results of structural equation modeling revealed a significant and strong correlation between SW and plant biomass, coverage, and soil pH. This suggests that changes in SW directly impacted plant biomass accumulation, subsequently affecting coverage, and also played a role in regulating soil pH. This study identified the effects of hydrological inter-annual changes on plant communities and highlighted SW as a crucial driver. The strategies proposed in the results protect and improve the diversity and stability of lake ecosystems in Lake Erhai and other similar lakes.

Long-term effects of nitrogen enrichment in pollen chemistry of a plant species from Brazilian savannas, Pavonia rosa campestris

Human activities have substantially increased soil nutrient availability during the past decades, affecting plant community composition and plants' nutritional content. Several amino acids found in pollen, the main source of larval diet for bees, affect the development, health, and behaviour of this important group of pollinators. A better understanding of the consequences of global changes on pollen amino acid content can help explain and predict future impacts on bee populations and diversity. This is particularly relevant in regions that are highly exposed to fertilizers due to their importance for global food production, such as the Brazilian savannas (Cerrado), where soils are mostly dystrophic. Here, we use a long-term controlled fertilization experiment conducted in Cerrado and demonstrate that even after 10 years since the last fertilization addition, effects were still detectable on leaf and pollen chemical content. More specifically, pollen amino acid content of Pavonia rosa-campestris (Malvaceae), a species known to be important for the diet of several native bee species, changed because of nitrogen (N) addition. Not only did the overall amino acid content increase with N addition, but its profile was also affected, with the proportion of some amino acids increasing (e.g. isoleucine, leucine, serine, threonine), while decreasing for others (e.g. cysteine). These amino acids can have important effects on larval development and flower visitor behaviour. Further studies evaluating the effects on a diverse set of plant species and the consequent impacts on flower visitation and bee fitness are essential to better understand the full consequences of increased nitrogen availability in nutrient-limited ecosystems such as Cerrado.

Plant Allelopathy and Their Application in Gardens

The study of plant allelopathy is of extremely important research significance in agricultural and forestry production and management, as well as in ecological gardening applications in nature. Allopathies affects species composition in plant communities, It is one of the important factors affecting plant community succession. It is one of the important factors affecting plant community succession. In the application of garden landscape, the interaction and mutual restraint of communities are directly related to the final landscape effect. Therefore, by studying the effects of plants and garden applications, it is expected to provide reference value for garden landscape designers in the matching of garden landscape plants.

Pollinator-mediated effects of landscape-scale land use on grassland plant community composition and ecosystem functioning - seven hypotheses.

Environmental change is disrupting mutualisms between organisms worldwide. Reported declines in insect populations and changes in pollinator community compositions in response to land use and other environmental drivers have put the spotlight on the need to conserve pollinators. While this is often motivated by their role in supporting crop yields, the role of pollinators for reproduction and resulting taxonomic and functional assembly in wild plant communities has received less attention. Recent findings suggest that observed and experimental gradients in pollinator availability can affect plant community composition, but we know little about when such shifts are to be expected, or the impact they have on ecosystem functioning. Correlations between plant traits related to pollination and plant traits related to other important ecosystem functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning in response to changes in pollinator communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Despite calls to investigate community- and ecosystem-level impacts of reduced pollination, the study of pollinator effects on plants has largely been confined to impacts on plant individuals or single-species populations. With this review we aim to break new ground by bringing together aspects of landscape ecology, ecological and evolutionary plant-insect interactions, and biodiversity-ecosystem functioning research, to generate new ideas and hypotheses about the ecosystem-level consequences of pollinator declines in response to land-use change, using grasslands as a focal system. Based on an integrated set of seven hypotheses, we call for more research investigating the putative pollinator-mediated links between landscape-scale land use and ecosystem functioning. In particular, future research should use combinations of experimental and observational approaches to assess the effects of changes in pollinator communities over multiple years and across species on plant communities and on trait distributions both within and among species.

Short-term functional response to post-fire vegetation dynamic: A case study in a Mediterranean Pinus halepensis forest

Wildfire events significantly affect plant communities. Understanding the post-fire vegetation dynamics and how native and alien species interact to shape the composition and structure of the community is crucial to address conservation policy. Dispersal mechanisms and resource exploration strategies are two functional strategies which can explain variability in species response to disturbance. Here, we investigated how functional traits shape the short-term dynamic after a wildfire event in a Mediterranean pine forest. We collected plant co-occurrences and abundances in permanent plots of 100 m2 across four distinct sampling sessions (from late winter to early autumn, every 2 months). Functionally relevant traits including leaf traits and dispersal-related traits were also retrieved for the recorded species. We then derived the Grime's strategies of the recorded species from the collected leaf traits, and we computed the dispersal ability of each species as a function of the corresponding dispersal traits. To compare Grime's strategies and leaf traits across the monitoring cycles, we calculated the community weighted mean for each cycle as the average of species trait values in each plot. Further, we estimated variations in species abundances and species composition within each plot by using temporal turnover analysis, which showed a continuous post-fire increase in community-level vegetation cover and a strong compositional change driven by a spread of alien species. Associating these patterns to the recorded functional traits revealed that dispersal ability is crucial in post-fire recolonization. Moreover, ruderal species, being the most represented strategy soon after the fire, give way over time to more competitive species showing higher leaf area. Thus, short-term vegetation recovery involves different species-specific strategies that shape the ecological succession over time. Our case study highlights that knowledge about how functional traits drive plant colonization strategies is critical to assess the post-fire restoration status of Mediterranean pine forests.

Effects of livestock grazing intensification on plant communities of Patagonian drylands increase with increasing aridity

AbstractQuestionLivestock grazing affects plant communities in drylands worldwide. However, our current understanding of the Patagonian drylands has primarily been derived from comparing exclosures with grazing conditions or from single‐site grazing gradients. The pending question is: do impacts of grazing intensification on Patagonian plant communities change along aridity gradients?LocationPatagonia, Argentina.MethodsWe surveyed vegetation cover of perennial species in paddocks with different sheep‐grazing pressure (ungrazed, lightly, moderately, and intensively grazed, based on long‐term stocking rates), in three plant communities located along a regional aridity gradient: a semi‐desert (arid), a shrub–grass steppe (semi‐arid), and a grass steppe (dry sub‐humid). In these communities, we analyzed the effects of grazing pressure on the total cover of vegetation, the cover of dominant plant life‐forms (grasses and shrubs), the plant species diversity, and the traits of dominant plant species.ResultsIntensification of sheep grazing significantly decreased total vegetation cover in the semi‐desert, but not in the steppes. Although grazing decreased the cover of grasses (particularly of the highly preferred ones) in all communities, in the shrub–grass and grass steppes this reduction was offset by an increase in the cover and size of shrubs. Plant diversity was not consistently affected by grazing pressure in these communities. Traits of dominant plant species partially explained community responses to grazing intensification.ConclusionsLivestock grazing intensification reduces the forage quantity and quality of Patagonian plant communities, but the severity depends on plant community types. In semi‐deserts (the most arid), grasses were drastically affected, while in the steppes, the grazing effects on grasses were low and partially compensated by an increase in the cover and size of shrubs, which fulfill critical roles other than forage provision. It is fundamental that grazing pressure be adapted to forage resource availability for each community type to achieve sustainable management in the context of climate change.

Bamboo expansion promotes radial growth of surviving trees in a broadleaf forest.

Considerable evidence indicates that some trees are more vulnerable than others during bamboo (Phyllostachys edulis) expansion, which can affect plant community structure and alter the environment, but there has been insufficient research on the growth status of surviving individuals in colonized forests. In this study, we compared the annual growth increment, growth rate, and onset, cessation, and duration of radial growth of Alniphyllum fortunei, Machilus pauhoi, and Castanopsis eyrei in a bamboo-expended broadleaf forest (BEBF) and a bamboo-absent broadleaf forest (BABF) using high-resolution point dendrometers. We found that the annual radial growth of A. fortunei, M. pauhoi, and C. eyrei was 22.5%, 172.2%, and 59.3% greater in BEBF than in BABF, respectively. The growth rates of M. pauhoi and C. eyrei in BEBF were significantly higher than in BABF by13.9 μm/d and 19.6 μm/d, whereas A. fortunei decreased significantly by 7.9 μm/d from BABF to BEBF. The onset and cessation of broad-leaf tree growth was later, and the growth duration was longer in BEBF compared to BABF. For example, A. fortunei and M. pauhoi in BEBF had more than one month longer growth duration than in BABF. Additionally, the nighttime growth rates of some surviving broad-leaf trees in BEBF was significantly higher than that in BABF. These results suggest that the surviving trees have plasticity and can adapt to atmospheric changes and competitive relationships after expansion of bamboo in one of two ways: by increasing their growth rates or by modifying onset and cessation of growth to extend the growth duration of trees or avoid the period of intense competition with bamboo, thereby growing better. Our research reveals for the first time how the growth of surviving broad-leaf trees adjusts to bamboo expansion. These results provide insights into how biological expansions impact primary production and have implications for forest management in the Anthropocene.

Shifting enzyme activity and microbial composition in sediment coregulate the structure of an aquatic plant community under polyethylene microplastic exposure

It has been shown that microplastics (MPs) interfere with critical biological processes (including development, growth and fitness); however, there is no information about the impact of MPs on plant productivity and community structure in freshwater ecosystems. Here, we investigated the effects of two sizes (MIC: 20–300 μm, MAC: 2–3 mm) and three concentrations (0.03 %, 0.3 %, and 0.6 %) of low-density polyethylene MPs on submerged plant communities. The results showed that plant responses to MPs were species specific, which can affect plant community structure. For canopy-forming species (Hydrilla verticillata), total biomass increased by 4 %–46 % and relative abundance increased by 23 %–34 % under MP exposure, while rosette-forming species (Vallisneria natans) decreased by 44 %–67 % in total biomass and relative abundance decreased by 54 %–71 %. Myriophyllum spicatum growth was largely unaffected by MPs. Community diversity was negatively correlated with MAC treatments, and the community root to shoot ratio decreased by 40 %, while community productivity increased by 41 % at a 0.6 % MAC concentration. Although MPs did not change the microbial community composition, alpha diversity was reduced at the 0.6 % concentration. It is worth noting that 0.6 % is a higher concentration than most field sediment investigations. During the experiment, the activity of functional enzymes related to carbon and nitrogen increased under most MP treatments. Structural equation modelling showed that MIC changed the community structure mainly by driving sediment enzyme activity, while MAC changed the community structure mainly by driving plant growth. The results implied that MPs may affect sediment enzymatic activities, microbial alpha diversity and aquatic plant growth, potentially altering the diversity and stability of aquatic ecosystems.

Mechanisms for the construction of plant communities in the Gurbantunggut Desert, China

Analysis of the phylogenetic structure of a community based on the phylogenetic relationships among species in the community can reflect the ecological process of community composition and determine the mechanism of plant community construction. In this study, we analyzed the characteristics of the phylogenetic structure and diversity of plant communities in the Gurbantunggut Desert and their interactions with soil factors and explored the mechanisms of species maintenance in the communities. The results showed that the ecological traits of plants were conserved, habitat filtering was the primary process affecting plant communities, and the diversity of phylogeny was ranked as fixed dunes > semifixed dunes > mobile dunes. At different slope positions within the dune, there is greater phylogenetic diversity at the bottom and lower slope, and habitat filtering dominates community construction, with the dominant role of habitat filtering in the community diminishing as the slope position rises. The phylogenetic diversity of plant communities of different life types is ranked as short-lived plants > small trees and shrubs > annual and perennial herbs. On the bottom and lower slopes, short-lived plants and annual and perennial herbaceous communities are mainly influenced by habitat filtering. Habitat filterability decreased with increasing slope position. On the upper slopes and at the top, competitive exclusion effects between small trees and shrubs dominated. Our analysis shows that soil water content and organic carbon affect phylogenetic diversity mainly by influencing community species richness and that the interaction between soil water content, grain size and plant diversity leads to clustering of species with similar soil preferences, which in turn affects the phylogenetic structure of the community. In addition, the change from habitat filtering to intraspecific competition in plant community construction from the bottom to the top of the slope is mainly influenced by short-lived plant communities, and this type of plant needs to be given priority consideration in the conservation and restoration of desert plant communities.

Effects of long‐term mowing on species diversity, biomass and composition of plant community in a semi‐arid grassland in northeastern China

AbstractQuestionsHow does long‐term, moderate‐intensity mowing affect plant community diversity, biomass, and composition in semi‐arid grasslands? And what are the underlying mechanisms that drive differences in plant community structure and functions between mowed and unmowed grasslands?LocationA semi‐arid grassland in Jilin Province, northeastern China.MethodsIn a 30‐year experiment, we investigated long‐term effects of mowing on the grassland ecosystem in northeastern China by comparing plant community diversity, biomass, and composition between mowed and unmowed permanent plots across six grasslands.ResultsLong‐term mowing did not affect plant species richness, but increased species evenness by 29%. Mowing had little effects on above‐ground (shoot) and below‐ground (root) biomass. The unchanged above‐ground biomass in the mowed areas was attributed to a trade‐off between biomass of grasses and forbs: mowing significantly increased forb biomass by 50%, but reduced grass biomass by 20% and the grass to forb biomass ratio by 46%. Mowing also reduced biomass of the dominant Leymus chinensis grass by 24% and litter biomass by 56%. Regression analyses indicated that the species evenness was negatively affected by L. chinensis biomass and litter biomass.ConclusionsThis study demonstrates that, although long‐term moderate mowing has limited effects on plant species richness and plant biomass, such a managed strategy can greatly reduce the dominance of grass species and allow the growth of forb species, leading to a higher species evenness in the plant community. This win–win situation promotes forage production for farmers while increasing plant diversity for conservation, suggesting that current mowing tactics can be a sustainable management practice in this ecosystem. However, the continuous loss of plant litter because of mowing may have negative influences on soil nutrient availability in the long run. From this perspective, a short‐term halt in mowing or fertilization that allows plants and soil nutrients to recover could represent a more optimal protocol for management.

Home-field advantage effects in litter decomposition is largely linked to litter quality

Climate change and associated environmental alterations affect plant communities, potentially decoupling links between plants and their associated soil microbial communities. This may in turn affect processes like litter decomposition, an important function that controls nutrient and carbon cycling as well as many other ecosystem processes. Microbial decomposers have been proposed to specialize, being able to easier decompose litter from its ‘home’ community than litter from other communities, in what is termed the home field advantage (HFA) hypothesis. We report a litter decomposition experiment including four alpine meadow communities spread along a geographical gradient that ranged from the Atlas in Morocco to the Iberian Peninsula to the Swiss Alps. We tested whether litter decomposition rate would differ depending on litter and soil origin, expecting interactions between litter and soil microbial communities to be at the core of responses. We expected to find HFA in all four alpine communities. HFA ranged from very negative to neutral to positive along our geographical gradient, in a variation that could be attributed to the interaction of microbial communities with soil and plant traits, and linked to the relative abundance of microbial groups performing specific functions. Litter decomposition depended on litter quality and on the fungal community, which seemed adapted to deal with poor-quality, recalcitrant litter, leading to HFA. Climate plays a role as well, indirectly through plant community composition. Phyllosphere communities competed with soil communities when in interaction, a fact that may have blurred results of some previous HFA experiments. In summary, there is a clear HFA in systems with low-quality litter that requires a specialised fungal community to maximize decomposition. By contrast, high-quality, easy to decompose litter would be dealt with by any decomposer community, not showing evidence of HFA.

Spatial Heterogeneity Effects on Meta-Community Stability of Annual Plants from a Coastal Dune Ecosystem.

Spatial heterogeneity affects plant community composition and diversity. It is particularly noticeable in annual plant communities, which vary in space and time over short distances and periods, forming meta-communities at the regional scale. This study was conducted at the coastal dune ecosystem in Nizzanim nature reserve, Israel. This study aimed to analyze the effect of the spatial heterogeneity, which is expressed in differences in the fixation levels of the dunes and patches outside and beneath the dominant Artemisia monosperma shrubs, on the characteristics of the annual plant meta-community and its temporal stability, considering the mechanisms that may affect it. Thirteen dunes were studied: three mobile, seven semi-fixed, and three fixed dunes. Data on the annual plants were collected during the spring seasons of 2006, 2007, 2009, 2014, 2015, and 2016. For each dune, 72 quadrats of 40×40 cm were sampled yearly, with 24 quadrats per slope aspect (windward, leeward, and crest), 12 under the shrub, and 12 in the open. The results indicate that the transition from mobile dunes through semi-fixed to fixed dunes is characterized by an increase in annual plant cover, species richness, species diversity, changes in plant communities, and stability driven by the asynchrony of species population fluctuations. Asynchrony affected the stability of the meta-community of this ecosystem in patches beneath the shrubs but not in the open patches.

Land-use history, fire regime, and large-mammal herbivory affect deer-preferred plant diversity in longleaf pine woodlands

Since ecological systems often experience multiple disturbances, understanding changes in important ecological interactions, such as plant-herbivore interactions, may require studies capable of disentangling the unique and interactive effects of multiple forms of disturbance. For example, understanding how mammalian herbivores affect plant communities may require understanding how widespread past disturbances, such as agricultural land use, interact with contemporary disturbances, such as prescribed fire. We tested if past agricultural land use and contemporary fire regime modified the effects of mammalian herbivory on focal plant communities by measuring the richness of plant species preferred by deer at 26 longleaf pine woodlands containing paired open and large-mammal exclusion plots. Land-use history significantly affected the community composition of deer-preferred species, and focal species were 8.19 times more likely to be present in post-agricultural sites than non-agricultural sites. Large-mammal herbivory only affected plant species richness in woodlands with low fire frequencies wherein focal species were on average 2.23 times more likely to be present in exclusion plots than open plots. These results suggest that past and present disturbances can mediate contemporary plant-animal interactions and may explain spatial patterns in the intensity of large-mammal herbivory. Our findings also suggest that common management practices, such as use of prescribed burns, may indirectly promote plant species richness by reducing deer herbivory.

Explore the soil factors driving soil microbial community and structure in Songnen alkaline salt degraded grassland.

Saline-alkali degradation in grassland significantly affects plant community composition and soil physical and chemical properties. However, it remains unclear whether different degradation gradients affect soil microbial community and the main soil driving factors. Therefore, it is important to elucidate the effects of saline-alkali degradation on soil microbial community and the soil factors affecting soil microbial community in order to develop effective solutions to restore the degraded grassland ecosystem. In this study, Illumina high-throughput sequencing technology was used to study the effects of different saline-alkali degradation gradients on soil microbial diversity and composition. Three different gradients were qualitatively selected, which were the light degradation gradient (LD), the moderate degradation gradient (MD) and the severe degradation gradient (SD). The results showed that salt and alkali degradation decreased the diversity of soil bacterial and fungal communities, and changed the composition of bacterial and fungal communities. Different degradation gradients had different adaptability and tolerance species. With the deterioration of salinity in grassland, the relative abundance of Actinobacteriota and Chytridiomycota showed a decreasing trend. EC, pH and AP were the main drivers of soil bacterial community composition, while EC, pH and SOC were the main drivers of soil fungal community composition. Different microorganisms are affected by different soil properties. The changes of plant community and soil environment are the main factors limiting the diversity and composition of soil microbial community. The results show that saline-alkali degradation of grassland has a negative effect on microbial biodiversity, so it is important to develop effective solutions to restore degraded grassland to maintain biodiversity and ecosystem function.

Contrasting effects of urbanization and fire on understory plant communities in the natural and wildland–urban interface

AbstractAs human populations expand and land‐use change intensifies, terrestrial ecosystems experience concurrent disturbances (e.g., urbanization and fire) that may interact and compound their effects on biodiversity. In the urbanizing landscapes of the southern Appalachian region of the United States of America (US), fires in mesic forests have become more frequent in recent years. However, 80 years of forest management practices aimed at fire suppression in this region may have decreased landscape resistance or resilience to high‐severity fires. At the same time, housing development is rapidly expanding in the wildland–urban interface, creating opportunities to examine the combined effects of urbanization and fire disturbances on plant communities when fires occur. Here, we investigated how understory plant communities were affected by a fire that varied in severity at sites in Gatlinburg, TN, and in the adjacent Great Smoky Mountains National Park. Our goal was to investigate the individual and combined effects of fire and urbanization on plant community composition in the second growing season after a fire. Overall, we found a significant interaction effect of fire severity and urbanization on total plant abundance and richness, such that increasing fire severity was associated with lower abundance and richness in natural areas but higher abundance and richness in exurban areas. Shannon diversity was significantly affected by fire severity and urbanization, but not interactively. Plant composition was affected by fire severity, urbanization, and their interaction effects. Understory plant communities in exurban locations (low‐density residential areas near protected lands) were resilient following the pulse disturbance event (fire), likely because of their consistent exposure to a press disturbance (urbanization). Our study indicates a press disturbance may change the way a subsequent pulse disturbance affects plant communities. Our findings contribute new insights into how disturbances can interact to alter patterns of biodiversity in the southeastern US.

Drought neutralizes positive effects of long‐term grazing on grassland productivity through altering plant–soil interactions

Abstract Livestock grazing is among the most intensive land‐use activities in grasslands, and can affect plant communities directly or indirectly via grazing‐induced soil legacies. Under climate change, grasslands are threatened globally by recurrent drought. However, the extent to which drought influences grazing‐induced soil legacy effects on plant biomass production and community composition remains largely unexplored. We grew five naturally co‐occurring plant species (three dominants and two subordinates) in mixed communities in a glasshouse experiment in live and sterilized soil that had or had not been subjected to 19 years of grazing; these plant communities were then exposed to a subsequent drought. We tested the treatment effects on plant community biomass, proportional above‐ground biomass of individual species, arbuscular mycorrhizal (AM) fungal root colonization, and soil nutrient availability. Under drought‐free conditions, soils from grazed plots produced significantly higher plant above‐ground and total community biomass compared to soils from ungrazed plots. In contrast, plant above‐ground and total community biomass were similar between grazed and ungrazed soils under drought conditions. Similarly, soils from grazed plots increased the proportional biomass of dominant species but decreased the proportion of subordinate species; however, the proportional biomass of dominant and subordinate species was similar between grazed and ungrazed soils under drought conditions. Soil NO3−‐N in grazed soil was significantly higher compared to ungrazed soil. Drought dramatically increased soil NO3−‐N in sterilized soil and had a more pronounced increase in grazed soil than in ungrazed soil. Arbuscular mycorrhizal fungal root colonization from grazed soil was lower compared to ungrazed soil. Drought significantly increased the soil available phosphorus concentration, as well as plant community AM fungal root colonization. Synthesis. Our study suggests that drought can neutralize positive grazing effects on plant community biomass production via altered plant–soil interactions. Also, we found that drought can alleviate the negative effects of grazing legacies on subordinate species by reducing competitiveness of dominant species. Our study provides new insights for understanding the underlying mechanisms of grazing effects on grassland productivity under climate change. Read the free Plain Language Summary for this article on the Journal blog.