Plant Life History Strategies Research Articles

Consistent pattern in scaling relationships of leaf dry mass versus area of woody species co-occurring in dry-hot and wet-hot habitats

The scaling relationships between leaf dry mass (LDM) and surface area (LA) can reflect the efficiency of light harvesting and photosynthesis, as well as the ability of plants to withstand biotic and abiotic stress. However, it remains little unknown whether plants alter the scaling relationships of LDM and LA, as along with leaf mass investment per unit area in common species growing in different habitats with high temperature and contrasting water availability. This study involved measuring LA, LDM, and leaf morphological traits (e.g., leaf thickness, dry mass per unit area, and density) in 14 woody species (10 tree species, 2 shrub species, and 2 liana species) that co-occur in wet-hot (WH) and dry-hot (DH) habitats in southwest China. Our results showed that the scaling exponents (α) of LDM vs. LA were consistently greater than 1.0 (indicating the increase in LA fails to keep pace with increasing LDM) for all 14 common species at both sites, irrespective of their growth forms. Furthermore, species exhibited a higher leaf mass investment per unit area and leaf density at the DH site compared to the WH site. These results suggest that the law of “diminishing returns” applies to the scaling relationships of LDM and LA in common species inhabiting both types of habitats. Additionally, plants at the DH site increased leaf mass and density investments, potentially reflecting an essential adaptation to strong selective pressure experienced by plant species in that habitat. This study provides new insights into the scaling relationships of LDM and LA in contrasting habitats, enriching our understanding of the plant life-history strategies and adaptations in response to climate change.

Plant life history strategies vary in subtropical forests with different disturbance histories: an assessment of biodiversity, biomass, and functional traits.

Disturbance alters environmental conditions in forests. Plants growing in forests with different disturbance histories in diverse environments may adopt varying life history strategies, but few studies focus on this effect. This study comprehensively investigated plant biodiversity, biomass, and functional traits in subtropical forests with two different disturbance histories in east China to explore differences in life history strategies. Biodiversity was slightly higher in disturbed compared to conserved forests. Significantly higher biomass was measured in conserved relative to disturbed evergreen broadleaved forests (P < 0.05). In conserved forests, leaf tissue density (LTD) was significantly higher and leaf thickness (LT), leaf dry matter content (LDMC), twig tissue density (TTD), twig dry matter content (TDMC), bark tissue density (BTD) and dry matter content (BDMC), and stem tissue density (STD) and dry matter content (SDMC) were significantly lower than in disturbed forests (P < 0.05). In terms of associated plant biodiversity, biomass, and functional traits, conserved forests adopted a resource acquisition strategy, reducing biodiversity and developing multiple functional traits such as high leaf area and specific leaf area and low LT, LDMC, TTD, TDMC, BTD, BDMC, STD, and SDMC to support a high biomass accumulation rate. Disturbed forests adopted a resource conservation strategy, enhancing biodiversity and developing converse trait combinations to lower the rate of biomass accumulation. A comprehensive investigation of plant biodiversity, biomass, and functional traits and subsequent assessment of plant life history strategies in conserved and disturbed forests will aid investigations of regional biodiversity and carbon reserves, contribute data to the TRY and Chinese plant trait databases, and improve ecological management and restoration efforts in east China.

Environmental heterogeneity promotes coexistence among plant life-history strategies through stabilizing mechanisms in space and time

Spatiotemporal environmental heterogeneity can promote species coexistence through stabilizing mechanisms such as the storage effect. These mechanisms require low density advantages and species-specific responses to heterogeneity. Theory based on organisms, which are short-lived and capitalize beneficial patches instantaneously, suggests that in the presence of spatiotemporal heterogeneity, stabilizing mechanisms should arise more commonly in space than in time.We used an individual-based model to investigate if spatiotemporal soil water heterogeneity promotes stable coexistence among annual and perennial plant life-history strategies, and which functional traits explain the requirements. Scenarios explicitly differed in the resource benefits offered by the range of soil water used to simulate heterogeneity.Our results show that spatiotemporal heterogeneity promoted stable coexistence solely among perennial life-history strategies. Perennial life form delayed population responses to heterogeneity, which resulted in population decoupling among life-history strategies in time as well as in space. Recovery from low density could be explained by a combination of one classical trait which stores the effects of favorable environmental conditions (longevity) and, unexpectedly, a fast resource acquisition strategy evidenced by high adult growth rate and short-term dormancy. Life-history strategy-specific responses emerged from functional differences in seedling competitive ability and seed dispersal distance alone or, additionally, from differences in the hydrological niche. Interestingly, life-history strategies which functionally differed only in dispersal distance coexisted irrespective of whether they experienced a difference in resource benefits themselves or coexisted with life-history strategies experiencing this difference.We show that spatiotemporal heterogeneity in a single abiotic factor promoted stable coexistence through stabilizing mechanisms. Our study highlights the need to study stabilizing mechanisms across different life-history strategies to better understand the effectiveness and dimensions of spatiotemporal heterogeneity in promoting coexistence.

Robust projections and consequences of an expanding bimodal growing season in the western United States

AbstractPlant growth is restricted to times of the year when actual evapotranspiration (AET) is greater than zero because AET requires both the presence of water in the soil and temperatures warm enough to allow transpiration. Locations where water rather than temperature limits plant growth, such as semi‐arid areas of the southwestern United States, often have a bimodal growing season, such that distinct AET (growth) peaks occur in the spring and late summer, with a period of very limited plant growth occurring during the intervening summer months. We hypothesized that future warming will increase the zone containing bimodal growth seasons, likely resulting in significant changes in the competitive relationships between plant species that differ in their tolerance of a bimodal seasonality. This will likely alter plant distributions. Using climate projections to drive a water balance model, we mapped geographic regions within the continental United States projected to experience bimodal growing seasons in the future. The area containing bimodal seasonality increased under all 13 general circulation models (GCMs) and two representative concentration pathways (RCPs) examined. This robust result (seen in all alternative futures examined) nevertheless showed considerable variability depending on the GCM examined. The bimodal zone was projected to increase 13%–212% (49,000–792,000 km2) by the late 21st century relative to 1981–2010 estimates. Climate futures that contained the greatest temperature increases and greatest precipitation decreases projected the greatest expansion in the bimodal zone. For plant species that depend on relatively long, consistent time periods that are favorable to growth each year, the projected shift in seasonality may be an acute disturbance that could cause widespread mortality. These changes will likely have cascading ecological and management implications, including changes in the dominant plant life history strategies that occur in affected areas.

Allometry of bud dynamic pattern and linkage between bud traits and ecological stoichiometry of Nitraria tangutorum under fertilizer addition.

Affected by the pressure and constraints of available resources, plant growth and development, as well as plant life history strategies, usually vary with environmental conditions. Plant buds play a crucial role in the life history of woody plants. Nitraria tangutorum is a common dominant woody species in desertified areas of northern China and its growth is critical to the desert ecosystem. Revealing the allometry of N. tangutorum aboveground bud fates and the linkage between bud traits and plant nutrient contents and stoichiometric ratios can be useful in understanding plant adaptation strategy. We applied seven nitrogen and phosphorus fertilizer addition treatments to natural N. tangutorum ramets in Ulan Buh Desert in three consecutive years. We surveyed three types of aboveground buds (dormant buds, vegetative buds, and reproductive buds) in each N. tangutorum ramet, then measured the plant carbon (C), nitrogen (N), and phosphorus (P) contents and ratios during three consecutive years. We specified that reserve growth potential (RGP), vegetative growth intensity (VGI) and sexual reproduction effort (SRE) are the three indices of bud dynamic pattern. The results showed that the bud dynamic pattern of N. tangutorum ramets differed significantly among different fertilizer addition treatments and sampling years. The allometry of RGP, VGI, and SRE was obvious, showing size dependence. The allometric growth relationship fluctuated among the sampling years. The linkage between bud traits and plant stoichiometric characteristics of N. tangutorum ramets showed close correlation with plant P content, C:P and N:P ratios, no significant correlation with plant C content, N content and C:N ratio. These results contribute to an improved understanding of the adaptive strategies of woody plants growing in desert ecosystems and provide insights for adoption of effective measures to restore and conserve plant communities in arid and semi-arid regions.

Small area and low connectivity constrain the diversity of plant life strategies in temporary ponds

AbstractAim(i) To determine whether area and connectivity of temporary ponds can predict plant species diversity, and the diversity and abundance of different plant life histories; (ii) To explore whether pond connectivity with the river prior to river regulation predicts better plant diversity patterns than current pond connectivity, suggestive of possible effects of connectivity loss.LocationEastern Carpathian Mountains, Romania, Europe.MethodsWe fitted linear and generalized linear models (LM and GLM) to examine whether pond area and current distance from the Olt River predict plant species richness, Shannon diversity and relative cover of different social behaviour types and overall plant species richness and Shannon diversity. Using historical maps, we measured pond distance from the river ca. 60 years before the Olt River was regulated, and we refitted the LM and GLM models using pond area and past distance from the river as independent variables.ResultsTotal plant species richness increased with pond area, and it decreased with the distance from the river, but total plant Shannon diversity index was affected, positively, only by pond area. The strength of responses to pond area and connectivity of species richness, Shannon diversity and relative cover varied across the different social behaviour types. Past and current distances between ponds and riverbeds had similar effects on plant diversity, with some evidence for stronger effect of the present connectivity on specialist species Shannon diversity and a weaker effect on disturbance tolerants, generalists and competitors.Main ConclusionsPond area and connectivity with the landscape are important predictors of the diversity of plant life history strategies, and therefore, useful tools in pond conservation. Consistent species richness and Shannon diversity responses of wetland specialists to pond area and connectivity make this life history type well suited for monitoring pond condition.

Do the same genus plants have consistent adaptation strategies in cold-wet environments? A case study of leaf suitability of 19 Syringa species

Carbon cost-benefit theory indicates that leaf photosynthesis benefit and structure cost have scaling relationship. However, this relationship has not been tested in the perennial cold-wet regions. Shorter growing seasons in cold-wet climates severely limit plant growth, making it important to explore the light interception and economic strategies for the survival of plants in this region. We measured leaf area (LA), leaf fresh mass (LFM) and leaf dry mass (LDM) of 19 Syringa species around Xi’ning city to explore leaf scaling relationship and adaptation strategies. Our results showed that LA, LFM and LDM varied among species, with the coefficients of variation (CV) among species being 64.61%, 76.43% and 65.94%, respectively. For all species, LDM with LFM and LA showed isometric growth, and only LA and LFM followed allometric growth with a scaling exponent greater than 1 (p < 0.05). Linear correlation indicated that, with the increase of LA, the scaling constant tended diminishingly. Ultimately, according to the CSR (Competitor - Stress tolerator - Ruderal) strategy division, nineteen plants were divided into strategy CS (competitor & stress tolerator) and strategy S/CS (stress tolerator/competitor & stress tolerator). What’s more, LA, LFM and LDM of CS strategy plant were all significantly greater than S/CS strategy. In conclusion, plants in cold-wet habitats tend to have a more conservative economic strategies; and combined with the CSR theory, these plants are more competitive and stress tolerators. More attention should be paid to the effects of harsh environments on plant life history strategies.

Wood density relates negatively to maximum plant height across major angiosperm and gymnosperm orders.

Wood density is a crucial plant functional trait related to plant life history strategies. Its ecological importance in small-stature growth forms (e.g., shrubs) has not been extensively examined. Given that hydraulic conduit dimensions vary positively with plant height and that there is a negative relationship between conduits' diameter and wood density, I hypothesized an also negative relationship between wood density and plant height. Knowing that bark and pith proportions are significant in small-diameter stems, I additionally disentangled the contribution of wood, bark, and pith to stem density. I determined density in small-diameter stems across 153 species spanning all major angiosperm and gymnosperm orders by considering a diversity of growth forms (trees, treelets, shrubs, vines, and hemiparasites). Stem cross sections were dissected to consider the densities of wood with bark and pith; wood with pith and without bark; wood with bark and no pith; and wood without bark and pith. Secondary growth was also measured. Trees showed similar wood densities as non-self-supporting vines, and both showed significantly less dense wood than treelets, shrubs, and hemiparasites. General comparisons showed that wood was significantly denser than all other tissues, and these differences did not depend on growth form. Wood density was significantly and negatively related to growth rate and pith area proportions but not to bark thickness proportion. An implicit negative relationship between maximum plant height and stem density emerges as a property of plants likely linked to hydraulic conductive size.

Functional traits of leaves with different ages of Taxus wallichiana var. chinensis saplings.

Variations of functional traits with leaf age reflect plant life history strategy and indicate allocation pattern and trade-off characteristics in the limiting resource. In this study, leaves with different ages of Taxus wallichiana var. chinensis saplings were taken as experimental materials. Fourteen leaf functional traits of leaves at three differebt ages were measured in order to reveal changes of the saplings' ecological strategies with leaf aging. The results showed that one-year-old leaves had significantly higher specific leaf area than two- and three-year-old lea-ves, while three-year-old leaves had significantly greater leaf thickness, leaf area, volume, fresh weight and dry weight than leaves at other ages. In addition, one-year-old leaves had significantly greater nitrogen content (N), phosphorus content (P) and N:P than two- and three-year-old leaves, but lower C:N than three-old-year leaves. The slope of allometric relationship between leaf water content and dry weight, leaf thickness and leaf area of one-year-old leaves, leaf thickness and leaf area of three-year-old leaves were all significantly lower than 1.0. Two-year-old leaves showed significantly allometric relationships between many leaf traits, with slope being not equal to 1.0. In conclusion, one-year-old leaves of T. wallichiana var. chinensis saplings tended to have higher photosynthetic capacity, two-year-old leaves had stronger dry matter accumulation, and three-year-old leaves would construct defense system. The coordination and complementation of functional traits among leaves with different ages might have great significance for maintaining individual homeostasis and survival.

Twig biomass allocation of Betula platyphylla in different habitats in Wudalianchi Volcano, northeast China.

Understanding the response of biomass allocation in current-year twigs is crucial for elucidating the plant life-history strategies under heterogeneous volcanic habitats. We aimed to test whether twig biomass allocation, within-leaf biomass allocation, and the size-number trade-off of Betula platyphylla would be influenced. We measured twig traits of B. platyphylla in Wudalianchi volcanic kipuka, the lava platform, and Shankou lake in northeastern China using standardized major axis analyses. The results showed that the leaf number, total lamina mass (TLAM), stem mass (SM), and twig mass (TM) were significantly different between the three habitats and were greatest in kipuka with abundant soil nutrients. TLAM and SM scaled allometrically with respect to TM, while the normalization constants of the lava platform differ significantly between kipuka and Shankou lake, which showed that under certain TM, leaves gain more biomass in the lava platform. However, within the leaf, individual lamina mass (ILM) scaled isometrically with respect to individual petiole mass (IPM) in kipuka and the lava platform, but ILM scaled allometrically to IPM in Shankou lake. Our results indicated that inhabitats influenced the twig traits and biomass allocation and within-leaf biomass allocation are strategies for plants to adapt to volcanic heterogeneous habitats.

Putting non-structural compounds on the map of plant life history strategies: a commentary on Schoonmaker et al.

The seminal works of J. Philip Grime established that long-lived plants, like trees, have evolved a continuum of life strategies, spanning from competitors to stress tolerators, that optimize the capture and use of resources under habitats ranging from high to low productivity, respectively (Grime 1977, 2006). Competitors succeed in productive habitats by quickly capturing resources and colonizing space; resources are invested in new biomass to foster further capture. Conversely, the stress- tolerant strategy succeeds in unproductive habitats through a slow and costly-to-construct biomass, which does not require high rates of resource inputs but at the same time is highly resistant against potential losses of the invested resources (e.g., herbivory). These two strategies are comparable to the two end points of the leaf- or plant-economic spectrum, spanning from slow-growing–resource conservative to fast-growing–resource acquisitive (Reich et al. 1997, Westoby et al. 2002, Diaz et al. 2004...

Are we missing the forest for the trees? Conspecific negative density dependence in a temperate deciduous forest.

One of the central goals of ecology is to determine the mechanisms that enable coexistence among species. Evidence is accruing that conspecific negative density dependence (CNDD), the process by which plant seedlings are unable to survive in the area surrounding adults of their same species, is a major contributor to tree species coexistence. However, for CNDD to maintain community-level diversity, three conditions must be met. First, CNDD must maintain diversity for the majority of the woody plant community (rather than merely specific groups). Second, the pattern of repelled recruitment must increase in with plant size. Third, CNDD should extend to the majority of plant life history strategies. These three conditions are rarely tested simultaneously. In this study, we simultaneously test all three conditions in a woody plant community in a North American temperate forest. We examined whether understory and canopy woody species across height categories and dispersal syndromes were overdispersed-a spatial pattern indicative of CNDD-using spatial point pattern analysis across life history stages and strategies. We found that there was a strong signal of overdispersal at the community level. Across the whole community, larger individuals were more overdispersed than smaller individuals. The overdispersion of large individuals, however, was driven by canopy trees. By contrast, understory woody species were not overdispersed as adults. This finding indicates that the focus on trees for the vast majority of CNDD studies may have biased the perception of the prevalence of CNDD as a dominant mechanism that maintains community-level diversity when, according to our data, CNDD may be restricted largely to trees.

Natural variation in plant telomere length is associated with flowering time.

Telomeres are highly repetitive DNA sequences found at the ends of chromosomes that protect the chromosomes from deterioration duringcell division. Here, using whole-genome re-sequencing and terminal restriction fragment assays, we found substantial natural intraspecific variation in telomere length in Arabidopsis thaliana, rice (Oryza sativa), and maize (Zea mays). Genome-wide association study (GWAS) mapping in A. thaliana identified 13 regions with GWAS-significant associations underlying telomere length variation, including a region that harbors the telomerase reverse transcriptase (TERT) gene. Population genomic analysis provided evidence for a selective sweep at the TERT region associated with longer telomeres. We found that telomere length is negatively correlated with flowering time variation not only in A. thaliana, but also in maize and rice, indicating a link between life-history traits and chromosome integrity. Our results point to several possible reasons for this correlation, including the possibility that longer telomeres may be more adaptive in plants that have faster developmental rates (and therefore flower earlier). Our work suggests that chromosomal structure itself might be an adaptive trait associated with plant life-history strategies.

Mohammed Armani.

Mohammed Armani.

Plant traits and vegetation data from climate warming experiments along an 1100\u2009m elevation gradient in Gongga Mountains, China

Functional trait data enhance climate change research by linking climate change, biodiversity response, and ecosystem functioning, and by enabling comparison between systems sharing few taxa. Across four sites along a 3000–4130 m a.s.l. gradient spanning 5.3 °C in growing season temperature in Mt. Gongga, Sichuan, China, we collected plant functional trait and vegetation data from control plots, open top chambers (OTCs), and reciprocally transplanted vegetation turfs. Over five years, we recorded vascular plant composition in 140 experimental treatment and control plots. We collected trait data associated with plant resource use, growth, and life history strategies (leaf area, leaf thickness, specific leaf area, leaf dry matter content, leaf C, N and P content and C and N isotopes) from local populations and from experimental treatments. The database consists of 6,671 plant records and 36,743 trait measurements (increasing the trait data coverage of the regional flora by 500%) covering 11 traits and 193 plant taxa (ca. 50% of which have no previous published trait data) across 37 families.

Atmospheric N deposition alleviates the unfavorable effects of drought on wheat growth

Drought and atmospheric nitrogen deposition (AND) become increasingly serious in recent decades owing to the progressively rising anthropogenic activities. Thus, it is significant to assess the effects of combined drought and AND on plant morphological and physiological performance (MorPhyPer) to better elucidate the mechanisms that drive the successful plant life-history strategies under the combined drought and AND. The objective of this study is to evaluate the combined drought [imitated by polyethylene glycol-6000 (PEG 6000) solution] with different degrees and AND [a mixed N with a 1: 1: 1 ratio of NH4–N: NO3–N: CO(NH2)2–N] with different concentrations on MorPhyPer of wheat (Triticum aestivum L.) via the garden-pot cultivation under the condition with natural light for nearly sixty days. Results showed that drought dramatically reduced MorPhyPer of wheat. This phenomenon may be attributed to the gradually enhanced osmotic pressure generated by the dehydrated condition, the enhanced degrees of reactive oxygen species, the raised level of plant cell cytoplasm membrane peroxidation, and/or the downgraded plant enzymatic defensive ability. AND notably improved MorPhyPer of wheat mostly owing to the relieved N deficiencies. The combined drought and AND antagonistically affect plant supporting ability, leaf photosynthetic area, and belowground growing competitiveness of wheat. The reason may be due to the increased belowground moisture content under the combined drought and AND which can improve the efficiency and capacity of nutrients absorption (mainly absorb more N nutrients) by root and transport to the aboveground portion and subsequently raise the level of drought resistance. The reason may be also attributed to the enhanced leaf photosynthetic area which can capture more sunlight and increase the tolerance to the adverse environment. Accordingly, AND notably alleviated the unfavorable effects of drought on MorPhyPer of wheat basically.

Fire can promote germination, recruitment and seed bank accumulation of the threatened annual grass Arthraxon hispidus

Disturbance plays an important role in plant life history strategies and has been documented as both enhancing and threatening populations of the vulnerable grass Arthraxon hispidus (Thunb.) Makino (hairy jointgrass) on the NSW north coast. Mechanical disturbance (slashing) is often used in A. hispidus conservation management, but many Australian plants are adapted to fire-based disturbance regimes. In this study we undertook a field burning experiment, along with soil seed bank sampling and germination trials, to explore how fire influences A. hispidus population dynamics in terms of plant recruitment and seed bank fluctuations. We found that winter burning strongly promoted A. hispidus spring germination without entirely depleting the residual seedbank. Although drought affected our field study population, burning also led to increased adult cover and substantial seed bank replenishment the following autumn. Exposure to a smoke treatment almost doubled the germination rate of A. hispidus seeds in nursery trials. Our study suggests that appropriate burning regimes can help to maintain this species in the landscape, by both structural and chemical mechanisms, by enhancing plant recruitment and facilitating seed bank accumulation. However, some A. hispidus plants also successfully germinated, established, and reproduced in unburnt plots during our study, suggesting that populations of this species can persist without disturbance in some habitats, such as native wetland communities. We found that A. hispidus has a multi-year seed longevity and a persistent seed bank, providing the species a degree of resilience in the event of unpredictable disturbance regimes and climatic anomalies.

Cross‐scale drivers of plant trait distributions in a fragmented forest landscape

During community assembly, plant functional traits are under selective pressure from processes operating at multiple spatial scales. However, in fragmented landscapes, there is little understanding of the relative importance of local‐, patch‐ and landscape‐scale processes in shaping trait distributions. Here, we investigate cross‐scale influences of landscape change on traits that dictate plant life history strategies in re‐assembling plant communities in a fragmented landscape in eastern China. Using forest dynamics plots (FDPs) on 29 land‐bridge islands in which all woody plants have been georeferenced and identified to species, we characterized and derived two composite measures of trait variation, representing variation across the leaf economics spectrum and plant size. We then tested for trait shifts in response to local‐, patch‐ and landscape‐scale factors, and their potential cross‐scale interactions. We found substantial community‐wide trait changes along local‐scale gradients (i.e. forest edge to interior): more acquisitive leaf economic traits and larger sized species occurred at edges, with a significant increase in trait means and trait range. Moreover, there were significant cross‐scale interaction effects of patch and landscape variables on local‐scale edge effects. Altered spatial arrangement of habitat in the surrounding landscape (i.e. declining habitat amount and increasing patch density), as well as decreasing area at the patch level, exacerbated edge effects on traits distributions. We suggest that synergistic interactions of landscape‐ and patch‐scale processes, such as dispersal limitation, on local‐scale environmental filtering at edges, together shape the spatial distributions of plant life history strategies in fragmented plant communities.

A unified framework for plant life-history strategies shaped by fire and herbivory.

Fire and herbivory both remove aboveground biomass. Environmental factors determine the type and intensity of these consumers globally, but the traits of plants can also alter their propensity to burn and the degree to which they are eaten. To understand plant life-history strategies associated with fire and herbivory we need to describe both response and effect functional traits, and how they sort within communities, along resource gradients, and across evolutionary timescales. Fire and herbivore functional traits are generally considered separately, but there are advances made in understanding fire that relate to herbivory, and vice versa. Moreover, fire and herbivory interact: the presence of one consumer affects the type and intensity of the other. Here, we present a unifying conceptual framework to understand plant strategies that enable tolerance and persistence to fire and herbivory. Using grasses as an example, we discuss how flammability and fire tolerance, palatability, and grazing tolerance traits might organize themselves in ecosystems exposed to these consumers, and how these traits might have evolved with reference to other strong selective processes, like aridity. Our framework can be used to predict both the diversity of life-history strategies and plant species diversity under different consumer regimes.

Using Functional Trait Diversity Patterns to Disentangle the Processes Influencing the Recovery of Subalpine Grasslands Following Abandonment of Agricultural Use

Grasslands in the Qinghai-Tibetan Plateau, as in much of the world, are increasingly degrading due to agriculture exploitation. Restoring such grasslands or facilitating recolonization to create late-successional communities requires an understanding of how communities within grasslands are structured within a secondary succession series. Here we studied community assembly using species abundance, soil nutrient levels, three functional traits (photosynthesis rate, seed mass and seed germination rate) in two comparable chronosequences of sub-alpine grasslands in the Qinghai-Tibetan Plateau. These grasslands range from ‘natural grassland’ (without human managements), to those that have been excluded from agricultural exploitation for 4 to 13 years. We were interested in shifts in functional trait diversity (FD; the value and range of functional traits in a community) and trait dispersion represented by the differences between observed FD and the expectation under neutral assembly. We found that a series of abiotic and/or biotic filters significantly influenced the success of species in different successional states, leading to systematic shifts in plant life history strategies from traits that indicated high relative growth rate to traits that signified highly competitive ability. We also found comparable community assembly processes between 13-year and natural grasslands, where hierarchical competition led to the exclusion of forb species by graminoid species and facilitation induced by legume species. Our results have three implications for degraded subalpine grasslands caused by agriculture exploitation in Qinghai Tibetan plateau. First, in the course of the abandonment of agricultural use and the return from degraded to natural grasslands, deterministic processes induced a shift in plant strategies from rapid relative growth rate under low N competition to slow relative growth rate under high N competition. Second, active seeding of graminoid and legume species may reduce the hierarchical competition, which in turn speedup recovery from agriculture exploitation. Finally, monitoring FD and trait dispersion patterns may be a good way to evaluate the restoration efforts in degraded grasslands caused by agriculture exploitation in Qinghai Tibetan plateau, due to the close connection of functional attributes (e.g., growth, colonization, recruitment and resource competition) and natural state of this ecosystem.