Plant Functional Group Composition Research Articles

Intensive management and declines in soil nutrients lead to serious exotic plant invasion inEucalyptusplantations under successive short‐rotation regimes

AbstractThe ongoing expansion ofEucalyptusplantations is changing the development of the world's forests. But, it also threatens ecological security regionally and worldwide. The expansion effect on biodiversity and soil nutrients is a universal problem, which has always been heatedly debated. In order to evaluate the long‐term influence of intensive management ofEucalyptusplantations under successive short‐rotation regime on understory plant diversity, soil nutrients andEucalyptustree growth, we chose a chronosequence representing the first to the sixth rotation ofEucalyptusplantations arrayed in the majorEucalyptusplantation areas in southern China and analyzed plant diversity indices, composition of plant functional groups (PFGs), soil nutrient concentrations andEucalyptustree growth at the stand level. Our results reveal that intensive management exerts a long‐lasting negative effect on understory plant species diversity, soil nutrients andEucalyptustree growth over successive rotations. Changes in soil nutrient content related with C and P cycling and declines in soil total nitrogen and available phosphorus were related with understory PFGs degradation. Furthermore, the combination of declines in understory woody plants, grasses and soil N and P cycling indices led to serious exotic plant invasion in the understory. Our study suggests that serious alien plant invasions could threaten the biosecurity, soil and timber security inEucalyptusplantations. We suggest that reducing management intensity, converting mono‐culturedEucalyptusplantations into mixed plantations with indigenous tree species, and changing from successive short‐rotation to short‐, medium‐ and long‐term cyclic rotations are required to sustainably manage these plantations through improving plant diversity, restoring degraded soils and resisting plant invasions.

The oxygen isotope composition of bioavailable phosphate in soil reflects the oxygen isotope composition in soil water driven by plant diversity effects on evaporation

Abstract Despite the importance of phosphorus (P) for organisms, the contributions of different processes delivering P into the bioavailable pool in soil have not yet been unraveled mainly due to methodological constraints in separating physico-/geochemical from biological processes. Stable O isotope analyses of phosphate might help to disentangle these processes and recent method improvements now allow an application in terrestrial ecosystems. Plant diversity influences not only plant P uptake but also biological P release mechanisms in soil thereby potentially affecting stable isotope ratios of bioavailable P (δ18OPi). We calculated the degree of enzyme-mediated O incorporation into phosphate, determined the contributions of different biological processes (Pi mobilization from soil organic matter, microbial P turnover), and tested for plant diversity effects on δ18O values of phosphate and of soil water as well as on the processes involved in O incorporation. We added 18O-enriched and 18O-depleted water to separated subplots of 27 study sites differing in plant species richness and plant functional group composition. δ18O values of phosphate and soil water were measured before and six days after labeling. We calculated mixing models based on isotope fractionation published so far. The O incorporation factor a reflecting the proportional incorporation of O atoms from labeled water into phosphate molecules under field conditions averaged 0.33 (0.15–0.70). δ18O values of bioavailable phosphate indicated microbial P processing i.e., turnover and subsequent release of P in soil. Plant species richness was related to δ18O values of soil water via evaporation. Because of the complete exchange of O atoms in a phosphate molecule with ambient water during microbial P turnover in soil, plant species richness effects were also visible in δ18O values of bioavailable phosphate. In conclusion, our approach yielded new insights into the role of microorganisms in supplying bioavailable P. For the first time we could show that plant-community induced microclimate shapes δ18O values of bioavailable phosphate in soil indirectly by affecting δ18O values of soil water with which phosphate exchanges O. Therefore, stable O isotope analyses in phosphate represent a useful tool for unraveling complex plant-soil-microorganism interactions in the P cycle.

Functional group contributions to carbon fluxes in arctic-alpine ecosystems

ABSTRACTOngoing responses to climate change in arctic-alpine ecosystems, including the increasing dominance of deciduous shrubs, involve major shifts in plant functional group composition. Because rates of photosynthesis and respiration and their responses to temperature may vary among plant functional groups, a better understanding of their contributions to carbon fluxes will help improve predictions of how ecosystem changes will affect carbon source-sink relations in globally important tundra regions. We used a sequential harvest method to estimate growing season functional group contributions to net ecosystem exchange (NEE), ecosystem respiration (ER), and gross photosynthesis (GP) in alpine heath-, meadow-, and Salix-dominated shrub communities. We also partitioned ER into aboveground and belowground components in all three communities. Belowground efflux was the dominant component of ER in the heath and meadow communities (63 percent and 88 percent of ER, respectively) but contributed only approximately 40 percent of ER in the shrub community. The dominant functional group in each community contributed most to aboveground exchanges. Estimates for cryptogams were uncertain, but indicated a minor role for bryophytes and lichens in overall exchange. The results of our novel method of partitioning gas-exchange measurements suggest strong differences in the relative proportions of soil versus aboveground respiration and in the contributions of different functional groups in the net carbon exchange of three important arctic-alpine community types, with implications for changes in carbon dynamics as these systems respond to environmental change.

Plant functional composition and species diversity affect soil C, N, and P during secondary succession of abandoned farmland on the Loess Plateau

The relationships among soil C, N, and P, aboveground plants, and belowground organisms are well-known; however, the impact of the aboveground dynamics of plant communities and their ensuing effects on soil C, N, and P, particularly during secondary succession need clarification. This study explored the effects of plant functional composition and diversity on soil C, N, and P at different soil depths. Soil samples were collected at soil depths ranging from 0 to 60 cm from three grassland sites abandoned for 5, 17, and 30 years in the Yang Qing Chuan catchment. Soil properties and fine root biomass were determined for different soil depths, and the plant community characters at each site were also evaluated. The results revealed that the plant community transitioned from dominance by annual herb to dominance by perennial species during the succession, and the percentage of Leguminosae plants, plant diversity, and species richness increased with succession time. The soil water content, organic carbon, total nitrogen, total phosphorous, C:P ratio, and N:P ratio increased significantly with successional time and decreased significantly with soil depth. In contrast, the soil bulk density and pH decreased significantly with successional time and increased significantly with soil depth. Furthermore, the plant functional group composition and diversity significantly affected soil C, N, and P contents and ratios, but was sensitive to the vertical stratification of soil. Plant functional group composition had a stronger correlation to soil C, N, and P contents and ratios at soil depths of 0–20 cm than that of the 20–60 cm depth primarily due to the fact that the nutrients returned are mostly concentrated on the topsoil and seldom deposited in the deeper soils. However, plant diversity had a stronger impact on soil C, N, and P contents and ratios at soil depths of 20–60 cm than at 0–20 cm depth, because plant diversity exacerbates interspecific competition and forces the roots to grow deeper, which alters nutrients in the deep soil. In addition, the percentage of legumes can be used as a practical indicator of soil quality in the 0–20 cm layer during natural succession of abandoned farmlands. This study provides evidence that plant communities have a strong influence on soil C, N, and P, but that the pathways and degree of influence differ across vertically stratified soil.

Does plant diversity affect the water balance of established grassland systems?

AbstractEvidence from experimental grasslands indicated that plant biodiversity modifies the water cycle, but it is unclear if this is also true for established land‐use systems. Therefore, we investigated how actual evapotranspiration (ETa), downward flux (DF), and upward flux (UF) in soil are related with land use and plant diversity in agriculturally managed grassland. In three Central European regions (“Biodiversity Exploratories”), we studied 29 grassland plots (50 × 50 m; 9–11 plots per region) covering the land‐use classes pasture, mown pasture, and meadow, in at least triplicate per region. From 2010 to 2015, we measured soil moisture, meteorological conditions, plant species richness, cover, and number of species in the functional groups of grasses, herbs, and legumes, aboveground biomass and root biomass on each plot. Annual ETa, DF, and UF were calculated for two soil layers with a soil water balance model and statistically analysed for land‐use and biodiversity effects with analysis of variance. Water fluxes were not significantly affected by land‐use class. UF did not vary between plots with different species richness and plant functional group composition. DF from topsoil increased with increasing number of grass species. ETa from topsoil decreased with increasing species richness and with the number of herb or legume species, whereas ETa from subsoil increased. Our results demonstrate that plant diversity influences the soil depth partitioning of water use, but the complex drivers of this relationship in agriculturally managed grassland still need to be disentangled.

Grazing weakens temporal stabilizing effects of diversity in the Eurasian steppe.

Many biodiversity experiments have demonstrated that plant diversity can stabilize productivity in experimental grasslands. However, less is known about how diversity–stability relationships are mediated by grazing. Grazing is known for causing species losses, but its effects on plant functional groups (PFGs) composition and species asynchrony, which are closely correlated with ecosystem stability, remain unclear. We conducted a six‐year grazing experiment in a semi‐arid steppe, using seven levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep per hectare) and two grazing systems (i.e., a traditional, continuous grazing system during the growing period (TGS), and a mixed one rotating grazing and mowing annually (MGS)), to examine the effects of grazing system and grazing intensity on the abundance and composition of PFGs and diversity–stability relationships. Ecosystem stability was similar between mixed and continuous grazing treatments. However, within the two grazing systems, stability was maintained through different pathways, that is, along with grazing intensity, persistence biomass variations in MGS, and compensatory interactions of PFGs in their biomass variations in TGS. Ecosystem temporal stability was not decreased by species loss but rather remain unchanged by the strong compensatory effects between PFGs, or a higher grazing‐induced decrease in species asynchrony at higher diversity, and a higher grazing‐induced increase in the temporal variation of productivity in diverse communities. Ecosystem stability of aboveground net primary production was not related to species richness in both grazing systems. High grazing intensity weakened the temporal stabilizing effects of diversity in this semi‐arid grassland. Our results demonstrate that the productivity of dominant PFGs is more important than species richness for maximizing stability in this system. This study distinguishes grazing intensity and grazing system from diversity effects on the temporal stability, highlighting the need to better understand how grazing regulates ecosystem stability, plant diversity, and their synergic relationships.

Plant Functional Group Composition on Restored Longleaf Pine—Wiregrass (Pinus palustris—Aristida stricta) Savannas with a History of Intensive Agriculture

ABSTRACT: We monitored plant community assembly during the first five years of longleaf pine—wiregrass (Pinus palustris—Aristida stricta) savanna restoration on four former bahiagrass (Paspalum notatum) pastures in peninsular Florida, which were restored via removal of exotic vegetation followed by mechanical planting with a wild-harvested native seed mix. We sampled randomly selected vegetation quadrats in each restored pasture annually, as well as randomly selected quadrats in each of four reference sites. All species were assigned to one of five functional groups (C4 graminoids, C3 graminoids, forbs, legumes, or shrubs) and one of three floristic quality categories (characteristic, pioneer, or weedy). Five years after restoration, we found that native C4 graminoids had supplanted the sod-forming P. notatum as the dominant graminoids on all sites. Restored sites had higher average C4 graminoid and forb cover than reference sites, but lower average species richness in both categories. Reference sites had...

Predicted risks of groundwater decline in seasonal wetland plant communities depend on basin morphology

In regions of the world where the climate is expected to become drier, meeting environmental water needs for wetlands and other dependent ecosystems will become increasingly challenging. Ecological models can play an important role, by quantifying system responses to reduced water availability and predicting likely ecological impacts. Anticipating these changes can inform both conservation and monitoring effort. We used water-plant functional group models to predict the effects of a declining water table for two wetland types reliant on the surface expression of groundwater but of contrasting basin morphology. Our interest was in quantifying the relative sensitivity of these wetland types to different amounts of groundwater decline. For the shallower, grass-sedge wetland, terrestrial plant probabilities increased markedly for declines between 0.25 and 0.5 m, but amphibious and submerged functional groups changed predictably, or not at all. However, mean inundated area reduced by over 70% for a 0.5 m groundwater decline, suggesting loss of area posed the greatest risk in this wetland type. In the deeper, steep-sided interdunal wetland, inundated area changed little, but models suggest clear transitions in plant functional group composition. Sedge-group probabilities increased sharply for declines between 0.25 and 0.5 m, while declines between 0.5 and 1.0 m predicted the loss of submerged species. As might be anticipated, the risks associated with groundwater level decline depend on basin morphology. However, by quantifying probable ways in which this will manifest in different wetland types, model predictions improve our ability to recognise and manage change.

Diverse Management Strategies Produce Similar Ecological Outcomes on Ranches in Western Great Plains: Social-Ecological Assessment

Experiments investigating grazing systems have often excluded ranch-scale decision making, which has limited our understanding of the processes and consequences of adaptive management. We conducted interviews and vegetation monitoring on 17 ranches in eastern Colorado and eastern Wyoming to investigate rancher decision-making processes and the associated ecological consequences. Management variables investigated were grazing strategy, grazing intensity, planning style, and operation type. Ecological attributes included the relative abundance of plant functional groups and categories of ground cover. We examined the environmental and management correlates of plant species and functional group composition using nonmetric multidimensional scaling and linear mixed models. After accounting for environmental variation across the study region, species composition did not differ between grazing management strategy and planning style. Operation type was significantly correlated with plant community composition. Integrated cow-calf plus yearling operations had greater annual and less key perennial cool-season grass species cover relative to cow-calf−only operations. Integrated cow-calf plus yearling ranches were able to more rapidly restock following drought compared with cow-calf operations. Differences in types of livestock operations contributed to variability in plant species composition across the landscape that may support diverse native faunal species in these rangeland ecosystems. Three broad themes emerged from the interviews: 1) long-term goals, 2) flexibility, and 3) adaptive learning. Stocking-rate decisions appear to be slow, path-dependent choices that are shaped by broader social, economic, and political dynamics. Ranchers described having greater flexibility in altering grazing strategies than ranch-level, long-term, annual stocking rates. These results reflect the complexity of the social-ecological systems ranchers navigate in their adaptive decision-making processes. Ranch decision-making process diversity within these environments precludes development of a single “best” strategy to manage livestock grazing.

Differential responses of soil bacteria, fungi, archaea and protists to plant species richness and plant functional group identity.

Plants are known to influence belowground microbial community structure along their roots, but the impacts of plant species richness and plant functional group (FG) identity on microbial communities in the bulk soil are still not well understood. Here, we used 454-pyrosequencing to analyse the soil microbial community composition in a long-term biodiversity experiment at Jena, Germany. We examined responses of bacteria, fungi, archaea, and protists to plant species richness (communities varying from 1 to 60 sown species) and plant FG identity (grasses, legumes, small herbs, tall herbs) in bulk soil. We hypothesized that plant species richness and FG identity would alter microbial community composition and have a positive impact on microbial species richness. Plant species richness had a marginal positive effect on the richness of fungi, but we observed no such effect on bacteria, archaea and protists. Plant species richness also did not have a large impact on microbial community composition. Rather, abiotic soil properties partially explained the community composition of bacteria, fungi, arbuscular mycorrhizal fungi (AMF), archaea and protists. Plant FG richness did not impact microbial community composition; however, plant FG identity was more effective. Bacterial richness was highest in legume plots and lowest in small herb plots, and AMF and archaeal community composition in legume plant communities was distinct from that in communities composed of other plant FGs. We conclude that soil microbial community composition in bulk soil is influenced more by changes in plant FG composition and abiotic soil properties, than by changes in plant species richness per se.

Effects of community structure on precipitation‐use efficiency of grasslands in northern Tibet

AbstractQuestions(1) What are the primary factors determining the precipitation‐use efficiency (PUE) in northern Tibet; (2) how does PUE respond to the gradients of biotic and abiotic factors; and (3) how do the composition and structure of plant functional groups (PFGs) affect PUE?LocationNorthern Tibet, China.MethodsA community survey of species composition, cover and above‐ground net primary productivity (ANPP) was conducted within 1 m × 1 m plots in 62 slightly disturbed sites. The effects of community features (total cover, cover of PFGs and species richness) and environmental factors [mean annual precipitation (MAP), mean annual temperature, surface soil bulk density, pH and C and N content] on PUE were identified through Pearson's correlation analyses, hierarchical partitioning and ordinary regressions.ResultsAlong the precipitation gradient, ANPP and PUE increased exponentially. Among the community features, total cover and cover of PFGs, including forbs and sedges, were the primary factors that determined PUE. The three cover variables, together with species richness, positively affected PUE and accounted for 47.6% of the total variation in PUE. Among the environmental factors, MAP, surface soil pH and N content were the most significantly related to PUE and accounted for 29.9% of the total contribution.ConclusionCommunities with high cover, species richness and nutrient content, but low soil bulk density, presented the highest PUE. At a regional scale, PUE depended mainly on plant cover, especially the cover of PFGs, namely, forbs and sedges. Environmental factors, including MAP and surface soil N and C content, positively affected PUE, whereas soil pH and bulk density negatively affected PUE. Our results highlight the importance of considering community structure to understand PUE variations in natural alpine grasslands.

Grazing intensity differentially regulates ANPP response to precipitation in North American semiarid grasslands.

Grazing intensity elicits changes in the composition of plant functional groups in both shortgrass steppe (SGS) and northern mixed-grass prairie (NMP) in North America. How these grazing intensity-induced changes control aboveground net primary production (ANPP) responses to precipitation remains a central open question, especially in light of predicted climate changes. Here, we evaluated effects of four levels (none, light, moderate, and heavy) of long-term (>30yr) grazing intensity in SGS and NMP on: (1) ANPP; (2) precipitation-use efficiency (PUE, ANPP : precipitation); and (3) precipitation marginal response (PMR; slope of a linear regression model between ANPP and precipitation). We advance prior work by examining: (1) the consequences of a range of grazing intensities (more grazed vs. ungrazed); and (2) how grazing-induced changes in ANPP and PUE are related both to shifts in functional group composition and physiological responses within each functional group. Spring (April-June) precipitation, the primary determinant of ANPP, was only 12% higher in NMP than in SGS, yet ANPP and PUE were 25% higher. Doubling grazing intensity in SGS and nearly doubling it in NMP reduced ANPP and PUE by only 24% and 33%, respectively. Increased grazing intensity reduced C3 graminoid biomass and increased C4 grass biomass in both grasslands. Functional group shifts affected PUE through biomass reductions, as PUE was positively associated with the relative abundance of C3 species and negatively with C4 species across both grasslands. At the community level, PMR was similar between grasslands and unaffected by grazing intensity. However, PMR of C3 graminoids in SGS was eightfold higher in the ungrazed treatment than under any grazed level. In NMP, PMR of C3 graminoids was only reduced under heavy grazing intensity. Knowing the ecological consequences of grazing intensity provides valuable information for mitigation and adaptation strategies in response to predicted climate change. For example, moderate grazing (the recommended rate) in SGS would sequester the same amount of aboveground carbon as light grazing because ANPP was nearly the same. In contrast, reductions in grazing intensity in NMP from moderate to light intensity would increase the amount of aboveground carbon sequestrated by 25% because of increased ANPP.

Soil microbial community composition and its driving factors in alpine grasslands along a mountain elevational gradient

Understanding the vertical distribution patterns of soil microbial community and its driving factors in alpine grasslands in the humid regions of the Tibet Plateau might be of great significance for predicting the soil microbial community of this type of vegetation in response to environmental change. Using phospholipid fatty acids (PLFA), we investigated soil microbial community composition along an elevational gradient (3094 similar to 4131 m above sea level) on Mount Yajiageng, and we explored the impact of plant functional groups and soil chemistry on the soil microbial community. Except for Arbuscular Mycorrhizal fungi (AM fungi) biomarker 18:2 omega 6,9 increasing significantly, other biomarkers did not show a consistent trend with the elevational gradient. Microbial biomass quantified by total PLFAs did not show the elevational trend and had mean values ranging from 1.64 to 4.09 mu mol per g organic carbon (OC), which had the maximum value at the highest site. Bacterial PLFAs exhibited a similar trend with total PLFAs, and its mean values ranged from 0.82 to 1.81 mu mol (g OC)(-1). The bacterial to fungal biomass ratios had the minimum value at the highest site, which might be related to temperature and soil total nitrogen (TN). The ratios of Gram-negative to Gram-positive bacteria had a significantly negative correlation with soil TN and had the maximum value at the highest site. Leguminous plant coverage and soil TN explained 58% of the total variation in the soil microbial community and could achieve the same interpretation as the whole model. Other factors may influence the soil microbial community through interaction with leguminous plant coverage and soil TN. Soil chemistry and plant functional group composition in substantial amounts explained different parts of the variation within the soil microbial community, and the interaction between them had no impact on the soil microbial community maybe because long-term grazing greatly reduces litter. In sum, although there were obvious differences in soil microbial communities along the elevation gradient, there were no clear elevational trends found in general. Plant functional groups and soil chemistry respectively affect the different aspects of soil microbial community. Leguminous plant coverage and soil TN had important effects in shaping soil microbial community.

Understory plant functional groups and litter species identity are stronger drivers of litter decomposition than warming along a boreal forest post-fire successional gradient

Increasing surface temperatures due to climate change have the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how ecosystem functioning may be affected by interactions between warming and other drivers, such as plant functional group composition and environmental context. In this study, we investigated how vascular plant litter decomposition and nutrient release were affected by experimental warming, moss removal and shrub removal along a post-fire boreal forest successional gradient. Our results show that litter decomposition and nutrient loss were primarily driven by understory plant functional group removal. The removal of mosses generally reduced litter mass loss and increased litter phosphorus (P) loss, while shrub removal typically increased litter mass loss and in one litter species reduced immobilization of P. Litter nitrogen (N) loss was unaffected by plant functional group removal. Warming interacted with successional stage and species identity of the litter decomposed, but these effects were uncommon and generally weak. As climate change advances, moss cover is expected to decrease, while shrub cover is expected to increase. Taken together with our results, this suggests that lower moss cover will decrease leaf litter decomposition rates and increase P release from litter, while increasing shrub cover will decrease decomposition rates and may reduce P release from litter. Our results demonstrate that in the short term, the direct effects of warming and successional stage will play a relatively minor role in driving litter decomposition processes in the boreal forest. In the long term, as the climate warms, temperature and its indirect effects via changes in the understory vegetation will play an important role in driving litter decomposition, thereby potentially altering C storage and nutrient cycling.

Functional composition of plant communities determines the spatial and temporal stability of soil microbial properties in a long‐term plant diversity experiment

Stable provisioning of ecosystem functions and services is crucial for human well‐being in a changing world. Two essential ecological components driving vital ecosystem functions in terrestrial ecosystems are plant diversity and soil microorganisms. In this study, we tracked soil microbial basal respiration and biomass over a time period of 12 years in a grassland biodiversity experiment (the Jena Experiment) and examined the role of plant diversity and plant functional group composition for the spatial and temporal stability of soil microbial properties (basal respiration and biomass) in bulk‐soil. Spatial and temporal stability were calculated as the inverse coefficient of variation (CV−1) of soil microbial respiration and biomass measured from soil samples taken over space and time, respectively. We found that 1) plant species richness consistently increased soil microbial properties after a time lag of four years since the establishment of the experimental plots, 2) plant species richness had minor effects on the spatial stability of soil microbial properties, whereas 3) the functional composition of plant communities significantly affected spatial stability of soil microbial properties, with legumes and tall herbs reducing both the spatial stability of microbial respiration and biomass, while grasses increased the latter, and 4) the effect of plant diversity on temporal stability of soil microbial properties turned from being negative to neutral, suggesting that the recovery of soil microbial communities from former arable land‐use takes more than a decade. Our results highlight the importance of plant functional group composition for the spatial and temporal stability of soil microbial properties, and hence for microbially‐driven ecosystem processes, such as decomposition and element cycling, in temperate semi‐natural grassland.

Predicting parameters of degradation succession processes of Tibetan <i>Kobresia</i> grasslands

Abstract. In the past two decades, increasing human activity (i.e., overgrazing) in the Tibetan Plateau has strongly influenced plant succession processes, resulting in the degradation of alpine grasslands. Therefore, it is necessary to diagnose the degree of degradation to enable implementation of appropriate management for sustainable exploitation and protection of alpine grasslands. Here, we investigated environmental factors and plant functional group (PFG) quantity factors during the alpine grassland succession processes. Principal component analysis (PCA) was used to identify the parameters indicative of degradation. We divided the entire degradation process into six stages. PFG types shifted from rhizome bunchgrasses to rhizome plexus and dense-plexus grasses during the degradation process. Leguminosae and Gramineae plants were replaced by sedges during the advanced stages of degradation. The PFGs were classified into two reaction groups: the grazing-sensitive group, containing Kobresia humilis Mey, and Gramineae and Leguminosae plants, and the grazing-insensitive group, containing Kobresia pygmaea Clarke. The first group was correlated with live root biomass in the surface soil (0–10 cm), whereas the second group was strongly correlated with mattic epipedon thickness and K. pygmaea characteristics. The degree of degradation of alpine meadows may be delineated by development of mattic epipedon and PFG composition. Thus, meadows could be easily graded and their use adjusted based on our scaling system, which would help prevent irreversible degradation of important grasslands. Because relatively few environmental factors are investigated, this approach can save time and labor to formulate a conservation management plan for degraded alpine meadows.

Nitrogen and phosphorus co-limitation and grazing moderate nitrogen impacts on plant growth and nutrient cycling in sand dune grassland

Atmospheric nitrogen (N) deposition alters plant biodiversity and ecosystem function in grasslands worldwide. This study examines the impact of 6years of nutrient addition and grazing management on a sand dune grassland. Results indicate that co-limitation of N and phosphorus (P) moderates the impact of realistic rates of N addition (7.5, 15kgNha1year−1). Combined NP addition (15kgN+10kgPha−1year−1) was the only nutrient treatment to differ significantly from the control, with greater above-ground biomass (mainly moss), and enhanced N and P mineralisation rates. Grazing management altered plant functional group composition, reduced above-ground biomass and meso-faunal feeding rates, and decoupled N and P mineralisation. There were no synergistic effects of grazing and N treatment. Although NP co-limitation apparently prevents adverse impacts of N deposition above the critical load, excess N is likely to be stored in moss biomass and soil, with unknown future consequences. CapsuleThis study shows that at realistic levels of N addition, NP co-limitation in a dune grassland appears to prevent adverse impacts of N on plant growth and nutrient cycling.

Long‐term effects of plant diversity and composition on plant stoichiometry

Plant elemental composition can indicate resource limitation, and changes in key elemental ratios (e.g. plant C:N ratios) can influence rates including herbivory, nutrient recycling, and pathogen infection. Although plant stoichiometry can influence ecosystem‐level processes, very few studies have addressed whether and how plant C:N stoichiometry changes with plant diversity and composition. Here, using two long‐term experimental manipulations of plant diversity (Jena and Cedar Creek), we test whether plant richness (species and functional groups) or composition (functional group proportions) affects temporal trends and variability of community‐wide C:N stoichiometry.Site fertility determined the initial community‐scale C:N ratio. Communities growing on N‐poor soil (Cedar Creek) began with higher C:N ratios than communities growing on N‐rich soil (Jena). However, site‐level plant C:N ratios converged through time, most rapidly in high diversity plots. In Jena, plant community C:N ratios increased. This temporal trend was stronger with increasing richness. However, temporal variability of C:N decreased as plant richness increased. In contrast, C:N decreased over time at Cedar Creek, most strongly at high species and functional richness, whereas the temporal variability of C:N increased with both measures of diversity at this site.Thus, temporal trends in the mean and variability of C:N were underlain by concordant changes among sites in functional group proportions. In particular, the convergence of community‐scale C:N over time at these very different sites was mainly due to increasing proportions of forbs at both sites, replacing high mean C:N (C4 grasses, Cedar Creek) or low C:N (legumes, Jena) species. Diversity amplified this convergence; although temporal trends differed in sign between the sites, these trends increased in magnitude with increasing species richness. Our results suggest a predictive mechanistic link between trends in plant diversity and functional group composition and trends in the many ecosystem rates that depend on aboveground community C:N.SynthesisWe compared the effect of plant diversity on the temporal dynamics of community stoichiometry in two long‐term grassland diversity experiments: the Cedar Creek and Jena Experiments. Changes in community C:N ratios were accelerated by increasing diversity at both sites, but in opposite directions depending on soil fertility. Stoichiometry changes were driven by shifts of functional group composition differing in their elemental compositions, the identity of the functional groups depending on the site. Thus, we highlighted that community turnover constrained the effect of diversity on plant stoichiometry at both sites

Effects of fine‐scale surface heterogeneity on rock outcrop plant community structure

AbstractQuestionsTo what extent do fine‐scale substrate variations affect the structure and diversity of rock outcrop vascular plant communities? How can we define the appropriate scale to measure fine‐scale substrate heterogeneity in rocky systems?LocationNine rock outcrops in the Iron Quadrangle, a priority area for biodiversity conservation in southeast Brazil.MethodsGeomorphology and rock mechanics methods were adapted to determine the appropriate scale to measure rock surface heterogeneity on granitoid, quartzitic and ironstone (canga) outcrops. Then, a roughness index was calculated from 60 microtopographic profiles in each lithotype to investigate the response of the plant community to this scale. The relation between surface heterogeneity and plant community richness, abundance, total plant cover and dominant species cover was quantified through linear regressions. A cluster analysis compared the percentage cover of functional groups in each outcrop, and diversity profiles were built based on Rényi's alpha. PERMANOVA was used to test for significant difference in the relative cover among the functional groups.ResultsThe roughness index, scaled at 1 cm, had the best power to diagnose the presence of vascular plants. High surface heterogeneity was caused by high frequency of fissures, cracks and rock fragments. Linear regression models indicated that the community parameters are strongly related to variations in surface roughness. The community patterns revealed by the cluster analysis and the diversity profiles matched those of the roughness analysis. Dominant functional groups differed strongly between ‘smooth’ and ‘coarse’ microtopography. Desiccation‐tolerant species prevailed in smooth outcrops, while sclerophytes and graminoids were better represented in coarse outcrops.ConclusionsThe composition of plant functional groups was affected by rock microrelief, and roughness was a significant predictor of plant community parameters. Functional group proportions reflected different adaptive plant strategies to two main stressful bedrock features: water shortage and mechanical resistance to root growth.

Grassland Arthropods Are Controlled by Direct and Indirect Interactions with Cattle but Are Largely Unaffected by Plant Provenance.

Cattle grazing and invasion by non-native plant species are globally-ubiquitous changes occurring to plant communities that are likely to reverberate through whole food webs. We used a manipulative field experiment to quantify how arthropod community structure differed in native and non-native California grassland communities in the presence and absence of grazing. The arthropod community was strongly affected by cattle grazing: the biovolume of herbivorous arthropods was 79% higher in grazed than ungrazed plots, whereas the biovolume of predatory arthropods was 13% higher in ungrazed plots. In plots where non-native grasses were grazed, arthropod biovolume increased, possibly in response to increased plant productivity or increased nutritional quality of rapidly-growing annual plants. Grazing may thus affect plant biomass both through the direct removal of biomass, and through arthropod-mediated impacts. We also expected the arthropod community to differ between native and non-native plant communities; surprisingly, arthropod richness and diversity did not vary consistently between these grass community types, although arthropod abundance was slightly higher in plots with native and ungrazed grasses. These results suggest that whereas cattle grazing affects the arthropod community via direct and indirect pathways, arthropod community changes commonly associated with non-native plant invasions may not be due to the identity or dominance of the invasive species in those systems, but to accompanying changes in plant traits or functional group composition, not seen in this experiment because of the similarity of the plant communities.