Regeneration Of Plant Communities Research Articles

Willow above, changes below: Seedless tree invader impacts riparian seed bank in the Patagonian ecotone

AbstractAimThe soil seed bank, an ecosystem component with a crucial role in the natural regeneration of plant communities, can be impacted by invasive non‐native plants. The impact of non‐native plants can be direct with the production of their own seeds or indirect without producing seeds, which has been less investigated. We determined the impact of an invasive seedless tree, non‐native willow (Salix × rubens), on the soil seed bank in a riparian ecosystem.LocationNorthwestern Patagonia, Argentina.MethodsIn autumn and spring 2022, we collected soil samples and estimated understorey cover, respectively, in plant communities invaded by willow and in uninvaded communities with a canopy dominated by native species. Over a year, we recorded the seedling emergence of soil samples to estimate the abundance, richness, and composition of the seed bank. We also compared the composition between the seed bank and understorey.ResultsTotal seed abundance and native woody species seed abundance decreased twofold and fourfold, respectively, in invaded plant communities in comparison with uninvaded communities. The most affected woody species was Ochetophila trinervis, a key tree species, because of its dominance in the canopy and understorey, and its role in various ecological processes (nitrogen cycling). In addition, willow invasion moderately changed the seed bank species composition producing species turnover. For both the seed bank and the understorey, species composition was more similar between invaded and uninvaded communities than between the seed bank and understorey. Willow invasion had more impact on understorey composition than on the seed bank.ConclusionsAlthough willows do not produce seeds regionally, their invasion negatively impacts the soil seed bank by replacing native woody canopy species that supply seeds to the seed bank. These impacts could result in notable changes in the structure of the plant communities and the ecosystem dynamics of riparian areas.

Thermal biology diversity of bee pollinators: Taxonomic, phylogenetic, and plant community‐level correlates

AbstractCommunity‐wide assembly of plant–pollinator systems depends on an intricate combination of biotic and abiotic factors, including heterogeneity among pollinators in thermal biology and responses to abiotic factors. Studies on the thermal biology of pollinators have mostly considered only one or a few species of plants or pollinators at a time, and the possible driving role of the diversity in thermal biology of pollinator asemblages at the plant community level remains largely unexplored. More specifically, it is unknown whether diversity in the thermal biology of bees, a major pollinator group worldwide, contributes to the assembly and maintenance of diverse bee communities; broadens the spectrum of possibilities available to bee‐pollinated plants; facilitates interspecific partitioning of ecological gradients across habitats, seasons, and time of day; and/or enhance plant pollination success through complementarity effects. The objectives of this study were to assess the diversity in thermal biology of the bee assemblage that pollinates plants in a Mediterranean montane area, evaluate its taxonomic and phylogenetic underpinnings, and elucidate whether there existed seasonal, daily, between‐habitat, or floral visitation correlates of bee thermal biology which could contribute to partition ecological gradients among plant and bee species. Thermal biology parameters were obtained in the laboratory (K, intrinsic warming constant) and the field (thoracic and ambient temperature at foraging site, Tth and Tair) on individual bees of a diverse sample (N = 204 bee species) comprising most bee pollinators of the regional plant community. Species‐specific thermal biology parameters were combined with quantitative field data on bee pollinators and flower visitation for the regional community of entomophilous plants (N = 292 plant species). Results revealed that the regional bee assemblage harbored considerable diversity in thermal biology features; that such diversity was mostly taxonomically, phylogenetically, and body‐size structured; and that the broad interspecific heterogeneity in thermal biology represented in the bee community as a whole eventually translated into daily, seasonal, among‐habitat, and flower visitation patterns at the plant community level. This lends support to the hypothesis that broad diversity in thermal biology of bees can enhance opportunities for bee coexistence, spatiotemporal partitioning of floral resources, and plant pollination success.

Reintroduction strategies for rare arable weeds in agricultural practice and their influence on yield

AbstractAgricultural intensification and changing landscape structure led to decreasing numbers of arable flora and fauna during the last decades. To counteract these declines, arable plant diversity needs to be restored. It is important to promote regional plant communities including endangered species to ensure adaption to agricultural landscapes. Therefore, this study examines the development of arable plant diversity, crop yield and the reintroduction success of rare arable plants (RAPs) under different practical farming strategies in cereals from 2019 to 2021 in southwestern Germany. Farming strategies varied regarding weed control intensity (none, mechanical, herbicide with and without efficiency gap), fertilisation (mineral and none) and row spacing (12.5 cm and 20 cm). Additionally, two different seed mixtures containing RAP and common species were used for reintroduction: one commercially available and another self‐composed. Reintroduction success was quite high with more than 80% establishment rate. Species numbers doubled in all treatments over time, except the one with herbicide application, with on average 8–10 species emerging from the soil seed bank. Reintroduction of RAP increased arable plant species richness further up to 37 species. The site‐adapted mixture showed in the end a site‐typical weed community. Yield was significantly lower in treatments with reintroduction via sown mixtures and no weed control, losing on average 65% yield. The reintroduction of RAP was successful and accompanied by an increasing floral diversity, however, with a simultaneous yield loss. Financial incentives or subsidies are therefore still necessary to compensate yield loss for reintroduction and conservation efforts.

Plant functional group interactions intensify with warming in alpine grasslands

Plant–plant interactions regulate plant community structure and function. Shifts in these interactions due to global climate change, mediated through disproportional increases of certain species or functional groups, may strongly affect plant community properties. Still, we lack knowledge of community‐level effects of climate‐driven changes in biotic interactions. We examined plant community interactions by experimentally removing a dominant functional group, graminoids, in semi‐natural grasslands in Southern Norway. To test whether the effect of graminoid removal varied with climate, the experiment was replicated across broad‐scale temperature and precipitation gradients. To quantify community‐level interactions across sites, we tested for changes in the remaining vascular community (i.e. forbs) cover, richness, evenness, and functional traits reflecting leaf‐economic investment and plant size over five years. The effect of graminoid removal on forb community structure and functioning varied over time, and along the climate gradients. Forb cover increased in response to graminoid removal, especially at warmer sites. Species richness increased following removal irrespective of climate, whilst evenness increased under warmer and wetter conditions irrespective of removal. No climate or removal effect was found for species turnover. Functional trait responses varied along the precipitation gradient – compared to controls, forb mean SLA decreased in drier conditions after graminoid removal. Leaf thickness increased under cooler and drier conditions irrespective of removal. These community structure alterations demonstrate stronger competitive interactions between forbs and graminoids under warmer conditions, whilst functional trait responses indicate a facilitative effect of graminoids under drier conditions. This indicates that both competition and facilitation regulate plant communities, suggesting complexity when scaling from populations to communities. Finally, both temperature and precipitation determine the direction and intensity of biotic interactions, with ecosystem‐wide implications for forb persistence and ecosystem functioning under future climates. Further work is needed to generalise the role of changing interactions in mediating community responses to climate change.

Effects of grazing disturbances on soil seed bank diversity in two vegetation types

Soil seed bank (SSB) play an essential role in the restoration and regeneration of plant communities. Grazing is a common disturbance factor that exerts an important effect on the diversity and composition of the SSB community in forests. Here, we evaluated the structure and composition of SSB along a grazing disturbance gradient of two types of vegetation (broad-leaved forests and mixed coniferous broad-leaved forests) in southwest China. A comparison of the similarity of SSBs with the above-ground vegetation strata (tree, shrub and herb layers) was also analyzed. The experiment revealed the germination of 25 species that belonged to 14 families and 24 genera. The density of SSBs did not show significant differences along the grazing disturbance. The alpha diversity of SSBs was the highest at moderate grazing intensity in broad-leaved forests, and not significantly different along disturbance intensities in mixed coniferous broad-leaved forests. No significant changes were observed in the species composition of SSB along the grazing gradients. Nonmetric multidimensional scaling analyses revealed low similarities between SSBs and above-ground vegetation, with the lowest similarity occurring under medium grazing disturbance intensity. Overall, our research offers significant insight into the response of SSBs to grazing in different vegetation types. It serves as a guide for designing grazing management strategies tailored to natural forests.

Rodents mediate the relationship between seed rain, seed bank, and plant community with increased grazing disturbance.

Seed rain and the soil seed bank represent the dispersal of seeds in space and time, respectively, and can be important sources of recruitment of new individuals during plant community regeneration. However, the temporal dynamics of seed rain and the mechanisms by which the seed rain and soil seed bank may play a role in plant community regeneration with increased grazing disturbance remain unclear. Seed rain, soil seed bank, aboveground vegetation, and rodent density were sampled along a grazing gradient in an alpine marsh on the eastern Tibetan Plateau. We described the temporal dynamics of seed dispersal using Bayesian generalized mixed models, and nonmetric multidimensional scaling and the structural equation model were used to examine the effects of grazing disturbance on the relative role of seed rain and soil seed bank on aboveground plant community regeneration. The temporal dynamics of seed rain changed from a unimodal to a bimodal pattern with increased grazing disturbance. Both species diversity and seed density of the seed rain and seed bank increased significantly with increased grazing disturbance. Increased grazing disturbance indirectly increased the similarity of composition between seed rain, seed bank, and aboveground plant community by directly increasing species diversity and abundance of aboveground plant community. However, increased grazing disturbance also indirectly decreased the similarity of seed rain, soil seed bank, and aboveground plant community by directly increasing rodent density. The similarity between seed rain and aboveground plant community was greater than that of the soil seed bank and aboveground plant community with increased grazing disturbance. Grazing disturbance spreads the risk of seed germination and seedling establishment by changing the temporal dynamics of seed dispersal. Plants (positive) and rodents (negative) mediated the role of seed rain and soil seed bank in plant community regeneration. The role of seed rain in plant community regeneration is higher than the seed bank in disturbed alpine marshes. Our findings increase our understanding of the regeneration process of the plant community, and they provide valuable information for the conservation and restoration of alpine marsh ecosystems.

Modern vegetation-climate relationships for pollen assemblages across the mountainous regions of southwestern China: Implications for palaeoenvironmental reconstruction

A comprehensive understanding of modern pollen transport processes is a prerequisite for utilizing fossil pollen to elucidate the evolution of palaeoclimates and palaeoenvironments, especially in areas such as southwestern China where complex mountainous topography results in vegetation heterogeneity. In this paper, we selected four vertical profiles in mountainous regions of southwestern China, each with distinct plant communities, to investigate the relationship between modern pollen rain, vegetation types and vegetation cover, and to quantify the influence of environmental factors. Results show that pollen assemblages are generally representative of regional plant communities, although long-distant transport of arboreal pollen by valley winds can introduce signals from a much wider area. The calibrated arboreal pollen percentage (AP) and ratio of arboreal pollen to non-arboreal pollen (AP/NAP) serves as reliable quantitative proxies for vegetation cover, highlighting the importance of appropriate calibration when interpreting fossil pollen assemblages. Climate is the primary determinant of pollen distribution across these mountains, with mean temperature of the coldest month (MTCM) playing the most prominent contribution. Additionally, the impact of vegetation cover and soil nutrients on pollen distribution are also significant. Our modern study improves the accuracy of pollen interpretation for palaeoenvironmental reconstruction in mountainous regions of southwestern China.

Runoff and Erosion Following a Prescribed Fire on a Sagebrush-Steppe Rangeland in Idaho, USA

HighlightsA spike in erosion occurred the year following a prescribed burn on a sagebrush-steppe rangeland.Two years after a prescribed burn on a sagebrush-steppe rangeland, burned plots had less runoff and erosion than unburned plots.Snowmelt processes may be important contributors to erosion in some sagebrush-steppe rangelands.Abstract. A study was carried out to compare runoff and erosion from natural rainfall on plots that had been treated with prescribed fire to unburned plots on a sagebrush-steppe rangeland in Southeast Idaho, U.S. Prescribed fire on rangeland sites is intended to maintain healthy shrub-steppe ecosystems but sometimes results in undesirable consequences such as increased runoff and soil erosion. Information is lacking on plot-scale erosion studies from natural precipitation in this ecosystem. Such plot-scale studies are needed to better understand sediment sources (uplands or channels) to support the management and modeling of rangeland watersheds. In this study, there were two treatments: four prescribed burn plots and three adjacent unburned control plots. Runoff and erosion were measured from natural rainfall for water years (WY) 2004 to 2010 following a prescribed burn in October 2003. Runoff and erosion were also measured from nearby unburned plots for WY 2005–2010. Ground cover on the burned plots averaged 57% (standard error (s.e. = 4%) in the summer of 2004, compared to 95% (s.e. = 5%) on the unburned plots. By the end of the study in 2010, ground cover had increased to 81% (s.e. = 4%) on the burned plots but decreased to 74% (s.e. = 5%) on the unburned plots. Annual runoff averaged 6 mm (s.e. = 7) from four burned plots, compared to 34 mm (s.e. = 8.7) from three unburned plots. In WY 2006, high rates of runoff from snowmelt on the unburned plots resulted in 122 mm (s.e. = 16) of runoff compared to only 12 mm (s.e. = 14) of runoff from the burned plots. An analysis of variance showed significant differences in runoff due to either precipitation (p = 0002) or year (p = 0.004) and treatment (burned vs. unburned; p=0.03). There were also significant differences in seasonal runoff (p = 0.05), as 90% of the measured runoff occurred in the spring, with all large runoff events associated with snowmelt. Erosion on the burned plots averaged 233 kg ha-1 (s.e. = 21) compared to 133 kg ha-1 (s.e. = 29) on the unburned plots. From two years after the burn and for the remainder of the study, there were no significant differences in erosion between burned and unburned plots (p < 0.05). Future studies are needed to link upland runoff and erosion with channel deposition, erosion, and sediment delivery, and more detailed studies on erosion associated with snowmelt on rangelands are needed to aid in the development of watershed modeling tools. Future studies should include observations of plant community regeneration in addition to ground cover, runoff, and sediment delivery. Keywords: Erosion, Hydrology, Prescribed fire, Rangelands.

Changes in plant species dominance maintain community biomass production under warming and precipitation addition in temperate steppe in Inner Mongolia, China

Dominant species play a crucial role in regulating plant community structure and productivity. Climate change affects community productivity by changing plant traits and resource use efficiency. However, the response of the productivity of a dominant species to warming and precipitation addition and the related effects on community biomass production in semi-arid grasslands remain unclear. We conducted a ten-year warming and precipitation addition study of a semi-arid steppe in Inner Mongolia, China. We examined the responses of community composition, biomass production, and trait and resource use efficiency of two dominant species, Leymus chinensis (rhizome grass) and Stipa krylovii. The results show that warming and precipitation increased the biomass of L. chinensis and decreased the biomass of S. krylovii. Community biomass production was unchanged under warming and precipitation from the contrasting changes in the two dominant species. Warming significantly increased the leaf area (LA) of L. chinensis and S. krylovii compared to that in ambient conditions, while it decreased the specific leaf area (SLA) and δ13C of S. krylovii. Increases in temperature stimulated biomass production of L. chinensis by affecting salicylic acid (SA) and GA (gibberellin), and they increased its competitive ability compared with that of S. krylovii. Our results highlight the different responses of L. chinensis and S. krylovii to environmental changes, which stabilised community productivity under warming and precipitation. Our study provides evidence that S. krylovii may be replaced by L. chinensis in steppe climates in the warmer and wetter future.

Mid-Term Effects of Fire on Soil Properties of North-East Mediterranean Ecosystems

Fire is a fundamental ecological process with a long history on Earth, determining the distribution of vegetation formations across the globe. Fire, however, does not only affect the vegetation but also the soil on which vegetation grows, creating a post-fire environment that differs significantly in terms of soil chemical and physical properties from the pre-fire environment. The duration of these alterations remains largely unknown and depends both on the vegetation condition and the fire characteristics. In the current study, we investigate the effect of fire on some chemical and physical properties 11 years after the event in four plant communities. Two of them constitute typical Mediterranean fire-prone plant communities, dominated by sclerophyllous Mediterranean shrubs, such as Quercus coccifera and Q. ilex, while the other two are not considered fire prone and are dominated by deciduous broadleaved species such as Q. petraea and Castanea sativa, respectively. The results indicate that fire affects the soil properties of the various communities in a different manner. Burned sites in the Q. coccifera community have a significantly lower concentration of organic matter, total nitrogen, and available magnesium. At the same time, they have a significantly higher concentration of sand particles and a lower concentration of clay particles. The effect of fire on the soil properties of the other three communities is less dramatic, with differences only in total phosphorus, organic matter, and total nitrogen. The results are discussed in relation to the site conditions and the post-fire regeneration of plant communities.

Endophytic infection increases the belowground over-yielding effects of the host grass community mainly by increasing the complementary effects.

Increases in plant species diversity may increase the community diversity effect and produce community over-yielding. Epichloë endophytes, as symbiotic microorganisms, are also capable of regulating plant communities, but their effects on community diversity effects are often overlooked. In this experiment, we investigated the effects of endophytes on the diversity effects of host plant community biomass by constructing artificial communities with 1-species monocultures and 2- and 4-species mixtures of endophyte-infected (E+) and endophyte-free (E-) Achnatherum sibiricum and three common plants in its native habitat, which were potted in live and sterilized soil. The results showed that endophyte infection significantly increased the belowground biomass and abundance of Cleistogenes squarrosa, marginally significantly increased the abundance of Stipa grandis and significantly increased the community diversity (evenness) of the 4-species mixtures. Endophyte infection also significantly increased the over-yielding effects on belowground biomass of the 4-species mixtures in the live soil, and the increase in diversity effects on belowground biomass was mainly due to the endophyte significantly increasing the complementary effects on belowground biomass. The effects of soil microorganisms on the diversity effects on belowground biomass of the 4-species mixtures were mainly derived from their influences on the complementary effects. The effects of endophytes and soil microorganisms on the diversity effects on belowground biomass of the 4-species communities were independent, and both contributed similarly to the complementary effects on belowground biomass. The finding that endophyte infection promotes belowground over-yielding in live soil at higher levels of species diversity suggests that endophytes may be one of the factors contributing to the positive relationship between species diversity and productivity and explains the stable co-existence of endophyte-infected Achnatherum sibiricum with a variety of plants in the Inner Mongolian grasslands.

Climate and fragment area jointly affect the annual dynamics of seedlings in different functional groups in the Thousand Island Lake.

Habitat fragmentation and climate change are the two main threats to global biodiversity. Understanding their combined impact on plant community regeneration is vital for predicting future forest structure and conserving biodiversity. This study monitored the seed production, seedling recruitment and mortality of woody plants in the Thousand Island Lake, a highly fragmented anthropogenic archipelago, for 5 years. We analyzed the seed-seedling transition, seedling recruitment and mortality of different functional groups in the fragmented forests and conducted correlation analyses involving climatic factors, island area, and plant community abundance. Our results showed that: 1) shade-tolerant and evergreen species had higher seed-seedling transition, seedling recruitment and survival rate than shade-intolerant and deciduous species in time and space, and these advantages increased with the island area. 2) Seedlings in different functional groups responded differently to island area, temperature and precipitation. 3) Increasing active accumulated temperature (the sum of the mean daily temperature above 0 °C) significantly increased seedling recruitment and survival, and warming climate favored the regeneration of evergreen species. 4) The seedling mortality rate of all plant functional groups increased with the increase of island area, but the increasing strength weakened significantly with the increase of the annual maximum temperature. These results suggested that the dynamics of woody plant seedlings varied among functional groups, and can be regulated separately and jointly by fragmentation and climate.

Detecting long-term effects of mining-induced ground deformation on plant succession in semi-arid areas using a cellular automata model

Mining-induced ground deformation affects various plant communities in different ways. However, little is known about the effects of ground deformation on plant succession; no known quantitative approach currently exists to detecting the long-term effects. To address this issue, a plant community succession model based on cellular automata was developed. Plant succession over 30 years within a subsidence area in the Yungang mining area in China was simulated and compared under mining and non-mining scenarios, including under two sets of initial conditions (vegetated and bare). The normalized mean square error was applied to test the accuracy of the plant community succession model and to reveal the effects of ground deformation at the patch scale, which was 0.06–0.59 for simulated and observed plant patterns. Landscape indicators including contagion, patch cohesion, interspersion and juxtaposition, Shannon’s diversity, Shannon’s evenness, and aggregation indices were calculated and compared to reveal the effects of mine subsidence at the landscape scale. The results showed that the interspersion and juxtaposition, Shannon’s diversity, Shannon’s evenness, and aggregation indices were significantly influenced by ground deformation (P < 0.05) under vegetated conditions, indicating that ground deformation resulted in a loose, isolated, and mixed pattern of vegetation. In terms of the shrub and tree communities, the normalized mean square errors fluctuated at a high level under bare conditions, especially at the patch scale of 10 × 10 m, where it remained at greater than 0.5. Overall, mining-induced ground deformation had long-term effects on plant succession by limiting tree communities and promoting shrub communities, as well as by leading to a heterogenous vegetation pattern. Ground deformation altered the topography of the previously mined area, influencing hydrological processes such as rainfall, infiltration, and evaporation, which were closely related to plant succession. Although these long-term effects were not directly a result of ground deformation, changes in the topography of a subsidence area would interfere with the spontaneous succession of plant communities. Therefore, the long-term effects of mining-induced ground deformation should be considered during the ecological restoration of a mining area, which can promote the application of nature-based solutions and the natural regeneration of plant communities.

Seasonality of pollinators in montane habitats: Cool‐blooded bees for early‐blooming plants

AbstractUnderstanding the factors that drive community‐wide assembly of plant‐pollinator systems along environmental gradients has considerable evolutionary, ecological, and applied significance. Variation in thermal environments combined with intrinsic differences among pollinators in thermal biology have been proposed as drivers of community‐wide pollinator gradients, but this suggestion remains largely speculative. We test the hypothesis that seasonality in bee pollinator composition in Mediterranean montane habitats of southeastern Spain, which largely reflects the prevalence during the early flowering season of mining bees (Andrena), is a consequence of the latter's thermal biology. Quantitative information on seasonality of Andrena bees in the whole plant community (275 plant species) and their thermal microenvironment was combined with field and laboratory data on key aspects of the thermal biology of 30 species of Andrena (endothermic ability, warming constant, relationships of body temperature with ambient and operative temperatures). Andrena bees were a conspicuous, albeit strongly seasonal component of the pollinator assemblage of the regional plant community, visiting flowers of 153 different plant species (57% of total). The proportion of Andrena relative to all bees reached a maximum among plant species which flowered in late winter and early spring, and declined precipitously from May onward. Andrena were recorded only during the cooler segment of the annual range of air temperatures experienced at flowers by the whole bee assemblage. These patterns can be explained by features of Andrena's thermal biology: null to weak endothermy; ability to forage at much lower body temperature than strongly endothermic bees (difference ~ 10°C); low upper tolerable limit of body temperature, beyond which thermal stress presumably precluded foraging at the warmest period of year; weak thermoregulatory capacity; and high warming constant enhancing ectothermic warming. Our results demonstrate the importance of lineage‐specific pollinator traits as drivers of seasonality in community‐wide pollinator composition; show that exploitation of cooler microclimates by bees does not require strong endothermy; and suggest that intense endothermy and precise thermoregulation probably apply to a minority of bees. Medium‐ and large‐sized bees with low upper thermal limits and weak thermoregulatory ability can actually be more adversely affected by climate warming than large, hot‐blooded, extremely endothermic species.

Seed dispersal by duikers in selectively logged rainforests: Overlooked dispersal of an important animal community

Seed dispersal by frugivores is a key process which is necessary for the regeneration of plant communities. The decrease in the abundance of fruit-eating mammals due to anthropogenic pressures impacts on the proper functioning of forest ecosystems.In this study, for the first time we evaluate seed dispersal by duikers (Bovidae, frugivores and the most hunted animals of the rainforests of central Africa: Congo basin), using germination trials of seeds contained in their dung and rumen. The influence of selective timber harvesting on this dispersal was also examined by comparing duiker community occupancy between a logged and an unlogged site.Our results revealed a community of four duiker species Cephalophus silvicultor, Philantomba congica and two species of ‘red’ duiker (C. callipygus and C. castaneus). A total of 79 plant species (5481 seedlings) were found in the dungs of all duikers and a total of 37 species (5225 seedlings) were observed in the rumens of red duikers and P. congica. Phyllanthus sp. and Musanga cecropioides were the dominant taxa in dung and rumen contents respectively. Taxa of high commercial value such as Erythrophleum suaveolens, Milicia excelsa and Nauclea diderrichii were also observed. The lack of a clear difference between the plant communities dispersed by the duiker species (assessed by β-diversity) showed that they play redundancy rather than complementary dispersal roles.Duikers play an underestimated role in the restoration of environments disturbed by logging or shifting cultivation as most of the species observed are pioneer colonizing species. Furthermore duiker communities appear to be affected little by selective logging.

Trends in soil microclimate and modeled impacts on germination timing in the sagebrush steppe

AbstractPast and projected changes in climate affect soil microclimate, impacting seeds that use soil moisture and soil temperature as cues for germination. Seed germination and plant establishment are among the most important processes regulating plant community assembly in response to climate change. Changes in germination timing expose seedlings to new abiotic and biotic risk factors that can affect recruitment success. Species with seed dormancy strategies to avoid harsh winter conditions could experience more mortality if changes in germination timing cause early germination and subsequent exposure to freezing conditions. We analyzed soil microclimate trends in the sagebrush steppe from 1979 to 2017 using a soil physics model (SHAW) and calculated the germination timing of native species used in restoration efforts with wet‐thermal response curves from lab trials. We applied the germination curves to modeled soil microclimate at 10 sites in the sagebrush steppe. Our results indicate that warmer and wetter fall seasons have become more prevalent and will likely lead to accelerated germination of several native restoration species in the sagebrush steppe. Changes to spring soil conditions favor slightly more germination in early spring, but strong trends of earlier onset of spring soil conditions were not evident. Trends in climate have created drier and warmer summer seedbed conditions, likely to increase stress on seedlings. Historic cycles of alternating slow or fast germination appeared less frequently during the last 12 years of the study (2004–2016). Seedbed microclimate trends will likely impact seedling establishment by altering germination timing and exposing seeds to more harsh abiotic conditions, likely resulting in decreased recruitment of native species and increased abundance of invasive annual grasses.

Grazing alters seedling emergence number, dynamics, and diversity of herbaceous plants in a semiarid sandy grassland

AbstractOvergrazing in semiarid grassland is a major cause of vegetation degradation. Understanding the changes in seedling patterns driven by grazing is crucial to unveiling mechanisms of plant community regeneration and succession in grazed grassland. However, the dynamics of seedling emergence and species diversity under grazing are rarely studied. This study used periodical field investigation to examine the variation in seedling emergence, plant diversity, species composition, and seedling survival of herbaceous plants under four grazing intensities, including light (LG), moderate (MG), heavy (HG), and non‐grazed (NG), in a semiarid sandy grassland. The results showed that seedling number and density were significantly higher in HG plots, while the seedling survival rate was significantly lower in HG, and that seedling emergence dynamics varied with grazing. Seventy‐five percent of the seedlings in HG emerged during early spring in April, while approximately 50% of the seedlings in LG, MG, and NG emerged in May. Differences in species richness and diversity varied with growth stages and the diversity was always higher in LG than in other grazing habitats during the main growing season. Annual forb seedlings increased while annual grass seedlings decreased after grazing with no perennial grass seedlings in HG. Our study suggests that high seedling emergence but low seedling survival rate, and simple species composition especially the disappearance of perennial plants caused by HG may be an important factor leading to vegetation degradation in the semiarid grazed grassland.

Nonlinear response of the soil seed bank and its role in plant community regeneration with increased grazing disturbance

Abstract The soil seed bank represents valuable rebuilding capital that may rescue an ecosystem from state transition once vegetation has crossed an apparent threshold from the desired to degraded state. However, almost no research has explored the response of transient and persistent seed banks and their role in plant community regeneration along a gradient of wetlands from intact to a seriously degraded state due to increased grazing disturbance. Seven grazing disturbance levels from nondisturbed to highly degraded alpine marsh ecosystems were selected on the eastern Tibetan Plateau. Akaike information criterion (AIC) was used to select the best‐fit model to predict the response of the plant community, soil seed bank and Bray–Curtis dissimilarity index to increased grazing disturbance. Both the plant community and seed bank showed a nonlinear change with increasing grazing disturbance. Species richness and seed density of the transient seed bank first decreased and then increased with increased disturbance, but the persistent seed bank showed a reverse trend, with an obvious threshold. Species composition of the persistent and transient seed banks exhibited little change compared to the plant community as disturbance increased. Similarities between both the persistent and transient seed banks and plant community also showed a nonlinear change with increased disturbance, while the persistent seed bank had a higher similarity with the plant community than the transient seed bank. Synthesis: At high grazing disturbance, persistent seed banks are more important than transient seed banks in plant community regeneration. Alpine wetland ecosystems have intrinsic resilience because the persistent seed bank has a pool of species above the threshold. However, ecosystem resilience declines if the species pool of the persistent seed bank is depleted below the threshold. The restoration potential of the seed bank has limits, and it will gradually be exhausted when species losses due to increased grazing intensity exceed the threshold of state transition.

Nitrogen Addition Affects Ecosystem Carbon Exchange by Regulating Plant Community Assembly and Altering Soil Properties in an Alpine Meadow on the Qinghai-Tibetan Plateau.

Nitrogen (N) deposition can affect the global ecosystem carbon balance. However, how plant community assembly regulates the ecosystem carbon exchange in response to the N deposition remains largely unclear, especially in alpine meadows. In this study, we conducted a manipulative experiment to examine the impacts of N (ammonium nitrate) addition on ecosystem carbon dioxide (CO2) exchange by changing the plant community assembly and soil properties at an alpine meadow site on the Qinghai–Tibetan Plateau from 2014 to 2018. The N-addition treatments were N0, N7, N20, and N40 (0, 7, 20, and 40 kg N ha–1year–1) during the plant growing season. The net ecosystem CO2 exchange (NEE), gross ecosystem productivity (GEP), and ecosystem respiration (ER) were measured by a static chamber method. Our results showed that the growing-season NEE, ER and GEP increased gradually over time with increasing N-addition rates. On average, the NEE increased significantly by 55.6 and 65.2% in N20 and N40, respectively (p < 0.05). Nitrogen addition also increased forage grass biomass (GB, including sedge and Gramineae) by 74.3 and 122.9% and forb biomass (FB) by 73.4 and 51.4% in N20 and N40, respectively (p < 0.05). There were positive correlations between CO2 fluxes (NEE and GEP) and GB (p < 0.01), and the ER was positively correlated with functional group biomass (GB and FB) and soil available N content (NO3––N and NH4+–N) (p < 0.01). The N-induced shift in the plant community assembly was primarily responsible for the increase in NEE. The increase in GB mainly contributed to the N stimulation of NEE, and FB and the soil available N content had positive effects on ER in response to N addition. Our results highlight that the plant community assembly is critical in regulating the ecosystem carbon exchange response to the N deposition in alpine ecosystems.

Intraspecific more than interspecific diversity plays an important role on Inner Mongolia grassland ecosystem functions: A microcosm experiment

Biodiversity changes in terrestrial communities continue in the context of global changes. However, the interactive effects of the changes in diversity at inter- and intraspecific levels as well as cascading effects from plant to soil microorganisms on ecosystem functioning under climate changes remains largely unexplored. Using grassland species in the semi-arid Inner Mongolia Steppe, we conducted a microcosm experiment to assess how drought treatment (non-drought and drought conditions), species diversity (2, 4, and 7 species) and genotypic diversity of the dominant species Leymus chinensis (1, 3, and 6 genotypes) affected ecosystem functions directly or indirectly via regulating plant community functional structure [community-weighted mean (CWM) and functional dispersion (FDis)] and soil microbial diversity (Shannon–Wiener index). Drought treatment, species and genotypic diversity significantly and interactively affected soil N, P cycle and soil multifunctionality as well as soil microbial diversity. Drought treatment significantly affected biomass, soil C cycle, CWM and soil microbial diversity. Species diversity significantly affected soil N cycle, CWM and FDis, and genotypic diversity significantly affected all soil functions and soil microbial diversity. CWM regulated the responses of all ecosystem functions except soil N cycle to the changes in soil moisture and species diversity, which supports the mass ratio hypothesis. The cascading effect from genotypic diversity to soil microbial diversity was significant on belowground biomass but not on any of the other ecosystem functions observed in this study. These findings highlight the importance of genotypic diversity of the dominant species L. chinensis in affecting belowground ecosystem functioning as well as soil microbial diversity, which should not be ignored for grassland protection and management. This study provides further insights into biodiversity and ecosystem functioning mechanisms in semi-arid grasslands in the context of global climate changes.