Remote sensing technology has been proved useful in mapping grassland vegetation properties. Spectral features of vegetation cover can be recorded by optical sensors on board of different platforms. With increasing popularity of applying unmanned aerial vehicle (UAV) to mapping plant cover, the study aims to investigate the possible applications and potential issues related to mapping leaf area index (LAI) through integration of remote sensing imagery collected by multiple sensors.

This paper applied the collected spectral data through field-based (FLD) and UAV-borne spectroradiometer to map LAI in a Sino–German experiment pasture located in the Xilingol grassland, Inner Mongolia, China. Spectroradiometers on FLD and UAV platforms were taken to measure spectral reflectance related to the targeted vegetation properties. Based on eight vegetation indices (VIs) computed from the collected hyperspectral data, regression models were used to inverse LAI. The spectral responses between FLD and UAV platforms were compared, and the regression models relating LAI with VIs from FLD and UAV were established. The modeled LAIs by UAV and FLD platforms were analyzed in order to evaluate the feasibility of potential integration of spectra data for mapping vegetation from the two platforms.

Results indicated that the spectral reflectance between FLD and UAV showed critical gaps in the green and near-infrared regions of the spectrum over densely vegetated areas, while the gaps were small over sparsely vegetated areas. The VI values from FLD spectra were greater than their UAV-based counterparts. Out of all the VIs, broadband generalized soil-adjusted vegetation index (GESAVI) and narrow-band nNDVI2 were found to achieve the best results in terms of the accuracy of the inversed LAIs for both FLD and UAV platforms. We conclude that GESAVI and nNDVI2 are the two promising VIs for both platforms and thus preferred for LAI inversion to carry spectra integration of the two platforms. We suggest that accuracy on the LAI inversion could be improved by applying more advanced functions (e.g. non-linear) considering the observed bias for the difference between the UAV- and FLD-inversed LAIs, especially when LAI was low.

Probabilistic models of species co-occurrences predict aggregated intraspecific spatial distributions that might decrease the degree of joint species occurrences and increase community richness. Yet, little is known about the influence of intraspecific aggregation on the co-occurrence of species in natural, species-rich communities. Here, we focus on early plant succession and ask how changes in intraspecific aggregation of colonizing plant species influence the pattern of species co-existence, richness and turnover.

We studied the early vegetation succession in a six ha constructed catchment within the abandoned part of a lignite mine in NE Germany. At two spatial scales (1- and 25-m2 plots), we compared for each pair of species the intraspecific degree of aggregation and the pattern of co-occurrence and compared observed relationships with temporal changes in important species functional traits.

The majority of species occurred in an aggregated manner, particularly in the first 2 years of succession. In pairwise comparisons, we found an excess of segregated species occurrences leading to a positive link between intraspecific aggregation and pairwise species segregation as predicted by the aggregation hypothesis, particularly at the lower spatial resolution. The degree of intraspecific aggregation was negatively correlated with the community-wide level of species spatial turnover and with plot species richness. Our results are the first direct confirmation that increasing intraspecific aggregation and interspecific competitive interactions counteract in shaping plant community structure during succession. The respective effects of aggregation were strongest at intermediate states of early succession.

Fire has important consequences on vegetation dynamics. In fire-prone areas, natural selection favors plant species, characterized by a large soil seed bank, and that their germination is stimulated by fire. Although seed germination stimulated by fire heat is common in the eastern Mediterranean Basin, only little is known about germination stimulation by smoke. We examined the interactive effect of aerosol smoke and fire history on the germinable soil seed bank (GSSB) community in eastern Mediterranean woodlands.

We collected soil samples from sites that have been subjected to different fire frequencies during the last four decades and exposed them to aerosol smoke, with or without watering. By documenting the seed germination patterns characterizing these samples, we could test for changes in the abundance and richness of the germinable seeds in the soil.

Total GSSB density was higher in sites that were burned more frequently during the last four decades. Exposure to aerosol smoke increased the GSSB density, and this pattern was more pronounced in samples originating from sites burned more frequently, as well as among annual species. Notably, exposing wet samples to aerosol smoke caused a significant reduction in GSSB density and richness. These results highlight the importance of exploring germination responses using intact soil samples, rather than synthetic seed communities. Moreover, our findings emphasize the important role smoke plays in shaping post-fire succession processes in the Mediterranean Basin, mainly by stimulating the germination of annual species.

The accurate estimation of aboveground biomass in vegetation is critical for global carbon accounting. Regression models provide an easy estimation of aboveground biomass at large spatial and temporal scales. Yet, only few prediction models are available for aboveground biomass in rangelands, as compared with forests. In addition to the development of prediction models, we tested whether such prediction models vary with plant growth forms and life spans, and with the inclusion of site and/or quadrat-specific factors.

We collected dataset of aboveground biomass from destructive harvesting of 8088 individual plants belonging to 79 species in 735 quadrats across 35 sites in semi-steppe rangelands in Iran. A logarithmic transformation of the power-law model was used to develop simple prediction models for the easy estimation of aboveground biomass using plant coverage and vegetation density as predictors for the species-specific model, multispecies and plants of different growth forms and life spans. In addition, additive and multiplicative linear regression models were developed by using plant coverage and one categorical variable from the site and/or quadrat-specific factors.

The log-transformed power-law model based on plant coverage precisely predicted aboveground biomass across the whole dataset for either most of the species-specific model, multispecies or plants of the same growth forms (shrubs, forbs or graminoids) and life spans (annuals, biennials or perennials). The addition of vegetation density as a single or in a compound predictor variable had relatively poor performance compared with the model having plant coverage only. Although generalizing at the levels of plant group forms and/or life spans did not substantially enhance the model-fit and validation of the plant coverage-based multispecies model, the inclusion of plant growth forms or life spans as a categorical predictor variable had performed well. Generalized models in this study will greatly contribute to the accurate and easy prediction of aboveground biomass in the studied rangelands and will be also useful to rangeland practitioners and ecological modellers interested in the global relationship between biodiversity and aboveground biomass productivity across space and time in natural rangelands.

Aims

Plant community assembly in wetlands usually changes with elevation gradients, which may be due to the direct effect of flooding and indirect effects such as changes in soil properties and competition. However, the respective importance of each factor remains to be investigated.

We investigated patterns of plant diversity, community biomass and soil properties along an elevation gradient of a lakeshore meadow at Poyang Lake, China.

(i) With increasing elevation, species richness and Simpson diversity index decreased. Both aboveground biomass (AGB) and belowground biomass (BGB) increased with elevation, however, the BGB/AGB ratio also increased, which suggests a significant effect of belowground competition. (ii) Soil N content and soil N:P ratio increased, whereas soil pH decreased with elevation. Other soil properties showed no significant response. (iii) Structural equation modeling showed that variation of plant diversity was mainly explained by BGB. Thus, intensified belowground competition seems to be the primary mechanism causing lower plant diversity at higher elevations. (iv) These findings were further supported by the observed greater response ratio of N and P storage in plant communities than the response ratio of soil N and P content to elevation, suggesting that soil nutrient limitation and belowground nutrient competition increased with elevation. Our study has important implications to wetland management and biodiversity conservation under environmental change (e.g. changes in flooding regimes, eutrophication).

The Qinghai-Tibetan Plateau has a mean altitude exceeding 4000 m and covers about 2.5 million km2. More than 60% of this area is alpine grassland. Exclosures have been widely used in this region to study the sustainable use of grassland resources. We used patterns of functional trait diversity to infer the effects of exclosures on community assembly in alpine meadows.

We studied functional diversity using five traits under grazing and three enclosed (exclosure) plots (3, 8, and 18 years old) in an alpine meadow on the Qinghai-Tibetan Plateau. We quantified the strength of the community assembly processes by comparing the observed functional trait diversity with a null model that assumes random community assembly.

We found evidence for deterministic assembly processes for plant communities in exclosures. The changes in CWM of the five traits from grazing land to 18-year exclosure indicated that environmental filtering occurred due to the exclosures. Multivariate functional diversity (MFDis and MPDses), and functional diversity of individual traits, including that of leaf area, leaf weight and aboveground biomass (FDis of leaf area, leaf weight, and aboveground biomass), increased gradually from grazing land to the 18-year exclosure, and the values of the 18-year exclosure were significantly greater than null expectation. This can be interpreted to indicate that exclosures resulted in greater competitive interaction between species. These results suggest that the effect of exclosures on community assembly is more deterministic than stochastic in this meadow.

Studies of the climatic responses of plant assemblages via vegetation-based environmental reconstructions by weighted averaging (WA) regression and calibration are a recent development in modern vegetation ecology. However, the performance of this technique for plot-based vegetation datasets has not been rigorously tested. We assess the estimation accuracy of the WA approach by comparing results, mainly the root mean square error of prediction (RMSEP) of WA regressions for six different vegetation datasets (total species, high-frequency species and low-frequency species as both abundance and incidence) each from two sites.

Vegetation-inferred environment (plot elevation) calibrated over time is used to quantify the elevational shift in species assemblages. Accuracy of the calibrations is assessed by comparing the linear regression models developed for estimating elevational shifts. The datasets were also used for the backward predictions to check the robustness of the forward predictions.

WA regression has a fairly high estimation accuracy, especially with species incidence datasets. However, estimation bias at the extremes of the environmental gradient is evident with all datasets. Out of eight sets (each set with a model for total species, low-frequency species and high-frequency species) of WA regression models, the lowest RMSEPs are produced in the four models based on the total species datasets and in three models based on the high-frequency species only. The inferred environment mirrored the estimation precision of the WA regressions, i.e. precise WA regression models produced more accurate calibrated environmental estimates, which, in turn, resulted in regression models with a higher adjusted r2 for estimating the elevational shift in the species assemblages. Reliable environmental estimates for plot-based datasets can be achieved by WA regression and calibration, although the edge effect may be evident if species turnover is high along an extensive environmental gradient. Species incidence (0/1) data may improve the estimation accuracy by minimizing any potential census and field estimation errors that are more likely to occur in species abundance datasets. Species data processing cannot guarantee the most reliable WA regression models. Instead, generally optimal estimations can be achieved by using all the species with a consistent taxonomy in the training and reconstruction datasets.

Within biodiversity–ecosystem function experiments, it is widely understood that yields of some species rapidly decline when planted in monoculture. This effect may arise due to decreased access to soil nutrients or an increase in detrimental soil pathogens within monoculture plantings. To determine whether or not soil conditioning affects tall grass prairie species biomass production, we conducted a field experiment to assess species growth in conspecifically and heterospecifically conditioned soils and a greenhouse experiment to elucidate how conspecific soil biota affected species growth.

To test for species-specific soil effects, seedlings of the legume Astragulus canadensis, the cool-season grass Elymus canadensis, the forb Helianthus maximiliani and the warm-season grass Panicum virgatum were grown in field plots that had either been conspecifically or heterospecifically conditioned over 2 years. Plant growth was recorded over a single growing season, and soils were assessed for differences in their nematode (mesofauna) communities. Seedlings of these species were additionally grown over a 6-week period in conspecifically conditioned soil that was either untreated, heated to 60°C, sterilized (autoclaved at 120°C) or heated to 60°C and reinoculated with conspecific soil biota. The two heating treatments were used to compare growth responses between a low- and high-temperature soil treatment. The reinoculation treatment was used to assess the effect of soil biota in light of any nutrient changes that may have occurred with soil heating.

Elymuscanadensis, H. maximiliani and P. virgatum growth was improved in field plots conditioned by the legume A. canadensis compared with their growth in conspecifically conditioned (home) soils. Despite variation (grass versus nongrass) in their soil nematode communities, there was no evidence to suggest that these three species were inhibited by conspecific or functionally conspecific soil conditioning in the field. Astragulus canadensis was the only species whose growth was reduced in conspecifically conditioned field soil. In the greenhouse, E. canadensis growth increased in all of the heat-treated soils, likely a response to a fertilization effect associated with soil heating. Panicum virgatum growth also increased among the heated soils. However, its growth decreased in heated soils where conspecific soil mesofauna were reintroduced, indicating that this grass may be inhibited by soil mesofauna. Finally, A. canadensis growth decreased in soils treated to fully remove soil biota and was not affected by reintroduction of soil mesofauna, suggesting that this species negatively responds to soil changes that occur with extreme heating. At least for the suite of tallgrass prairie species evaluated within this experiment, it appears that changes in soil chemistry and generalist soil biota, as opposed to increasing species-specific soil pathogens, more strongly contribute to temporal disparities in their performance.

Extreme climate events have become more severe and frequent with global change in recent years. The Chinese temperate steppes are an important component of the Eurasian steppes and highly sensitive and vulnerable to climatic change. As a result, the occurrence of extreme climate events must have strong impacts on the temperate steppes. Therefore, understanding the spatio-temporal trends in extreme climate is important for us to assess the sensitivity and vulnerability of Chinese temperate steppes to climatic changes. This research had two specific objects to (i) specify the temporal changes in extreme climate events across the whole steppe and (ii) compare the trend differences for extreme climate events in different types of steppes—meadow steppe, typical steppe and desert steppe.

To investigate extreme climate trends in the temperate steppes of China, 82 meteorological stations with daily temperature and precipitation data (1961–2013) were used. Meanwhile, eight core extreme climate indices (extreme high-temperature threshold, extreme low-temperature threshold, frost days, heatwave duration, heavy rainfall threshold, percentage of heavy rainfall, heavy rainfall days and consecutive dry days) from the Statistical and Regional Dynamical Downscaling of Extremes for European Regions (STARDEX) project were selected to analyse the trends in extreme climate across the whole temperate steppe and the three main types (meadow steppe, typical steppe and desert steppe) through time and space.

The results showed that (i) the changes in extreme climatic temperature events across the whole temperate steppe were obvious during 1961–2013. The frost days (?3.40 days/10 year [yr]) decreased significantly, while the extreme high-temperature threshold (0.24°C/10 yr), extreme low-temperature threshold (0.52°C/10 yr), and heatwave duration (0.58 days/10 yr) increased notably. The annual changes in extreme precipitation were small and not significant. (ii) Differences appeared in the extreme climatic trends in different types of steppes. The desert steppe showed strong climate extremes and underwent the most significant asymmetric warming compared with the meadow steppe and typical steppe. At the same time, the heatwave duration (0.62 days/10 yr) increased. In terms of the extreme precipitation, there was no significant trend among the three types of steppes. However, the fluctuations in extreme precipitation were the largest in the desert steppe compared to those in the typical steppe and meadow steppe.

Ubiquitous thermal acclimation of leaf respiration could mitigate the respiration increase. However, whether species of different plant functional groups showing distinct or similar acclimation justifies the simple prediction of respiratory carbon (C) loss to a warming climate.

In this study, leaf dark respiration (Rd) of illinois bundleflower (IB, legume), stiff goldenrod (GR, C3 forbs), indian grass, little bluestem and king ranch bluestem (IG, LB and KB, C4 grass) were measured with detached leaves sampled in a 17-year warming experiment.

The results showed that Rd at 20°C and 22°C (R20 and R22) were significantly lower in the warming treatment for all the five species. Lower R22 in warmed than R20 in control in GR, KB, LB and IG imply acclimation homeostasis, but not in IB. The significant decline in temperature sensitivity of respiration (Q10) of GR resulted in the marginal reduction of Q10 across species. No significant changes in Q10 of C4 grasses suggest different acclimation types for C3 forbs and C4 grass. The magnitude of acclimation positively correlated with leaf C/N. Our results suggest that non-legume species had a relative high acclimation, although the acclimation type was different between C3 forbs and C4 grasses, and the legume species displayed no acclimation in Rd. Thus, the plant functional types should be taken into account in the grassland ecosystem C models.

Anthocyanin accumulation is the main factor underlying why young plant leaves turn red, and plant growth follows the principle of maximizing the economic efficiency of energy. There is a need to verify the role of young plant leaves turning red and confirm whether anthocyanin accumulation overconsumes the energy of the plant.

We compared the different pigment contents, antioxidant capacities, leaf mass per area, photosynthetic characteristics, dark respiration rates, light compensation points (LCPs) and electron flow distribution of young and mature Schima superba leaves grown under full sunlight and 30% full sunlight conditions. We then examined the correlations between anthocyanins and total antioxidant capacity, photosynthetic pigments, dark respiration rates, LCPs by using linear regression. Finally, we analyzed Pearson correlation coefficients and used principal component analysis to evaluate the interactions of these functional indicators.

The young leaves of S. superba accumulated anthocyanins in full sunlight but not in 30% full sunlight. Anthocyanins substantially contributed to the total antioxidant capacity (accounting for 33.29%) in juvenile S. superba leaves. Young leaves containing more anthocyanin accumulated less reactive oxygen species after high light (HL) treatment. However, juvenile leaves accumulating anthocyanins showed 56.97% higher dark respiration rates, 24.79% higher LCPs and 5.32% higher allocations of electron flow to photorespiration and lower organic substance accumulation than did those without anthocyanins. These results suggest that young S. superba leaves must consume more energy to accumulate anthocyanins to adapt to HL environments. Therefore, plants sacrifice growth rate to ensure survival, which is a trade-off for their ability to respond to external environments.

For many terrestrial plants, nitrate is the most important form of available soil nitrogen for growth. However, many plant species, which grow on acidic, ammonium-dominated soils, exhibit a constantly low level of nitrate reductase activity (NRA). Little is known about NRA in high-mountain vascular plants in similar conditions. We tested the hypothesis that high-mountain vascular plants in acidic and ammonium-dominated habitats have low levels of NRA.

Twenty-six plant species of the families Asteraceae, Ericaceae, Poaceae, Polygonaceae, Salicaceae, Pinaceae, Ranunculaceae, Woodsiaceae, Cyperaceae, Juncaceae, Rosaceae and Urticaceae representing different growth forms were investigated in seven native and anthropogenic habitats of subalpine and alpine belts of the Karkonosze (Hercynian middle-mountains, Central Europe), with respect to leaf NRA and mineral nitrogen forms in soil. NRA was measured by an in vivo assay for the first time directly in the field using portable water bath.

An NRA study of vascular plants from high mountains is presented for the first time, and most of the studied subalpine and alpine species were subjected to field measurements for the first time ever. Differences among species, families, growth forms and habitats for NRA were found. These differences reflected mainly the taxonomical position and in part ecological preferences. PERMANOVA analysis confirmed that variance component showed that enzyme activities were mostly explained by plant species and habitat. Overall, the subalpine and alpine species from their native habitats are characterized by very low and low ability for nitrate metabolism. We also compared NRA with Ellenberg’s N values for the studied plants. Using a regression equation, N values of some species were calculated for the first time and corrected for the others.

Identifying factors that drive variation in herbivore effects on plant populations can provide insight for explaining plant distributions and for limiting weeds. Abiotic resource availability to plants is a key explanation for variation in herbivore effects on individual plants, but the role of resources in determining herbivore effects on plant populations is largely unexplored. We tested the hypothesis that soil nutrient availability drives variation in insect and mammal herbivore effects on tall thistle (Cirsium altissimum) population growth.

In a Kansas USA restored tallgrass grassland that experienced prescribed fires, we manipulated soil nutrients, through fertilizer addition, and presence of insect and mammal herbivores, using combinations of insecticide and fencing, in experimental plots. Over 7 years, we quantified herbivore damage to reproductive tall thistles, tall thistle seed production and population growth rates.

Seed production was reduced by insect herbivores and increased by fertilizer addition, but treatment effects were independent. Herbivore effects on tall thistle population growth depended upon soil nutrients in only one of seven annual transitions. Herbivores reduced thistle population growth in two of three annual transitions that included prescribed fire, whereas they reduced population growth in only one of four transitions without fire. Soil nutrient availability does not provide a general explanation for variation in herbivore effects on tall thistle population growth rates. Disturbance regime may be a more important aspect of ecological context for influencing herbivore effects on tall thistle populations in mesic grasslands.

Annually variable but synchronous production of large seed crops (‘masting’) is a widespread phenomenon in temperate trees. Mounting concerns about the impacts of anthropogenic climate change (ACC) on plant reproduction gives urgency to our need to understand better the role of climate on tree reproduction, and in particular, mast events. Unlike our understanding of reproductive phenology however, there is little consensus regarding how climate affects plant reproductive effort or indeed the actual environmental triggers that underpin masting behaviour.

We used a 27-year record of acorn yield from a population of 12 Quercus robur trees located in southern England to compare masting frequency and post-dispersal acorn yield each year for each tree, with long-term weather data over the same period. We focussed on discrete or sequential climate cues (temperature, precipitation and frost days) as likely predictors of oak reproduction.

Annual post-dispersal acorn crop varied greatly; i.e. no acorns in 14 of the 27 years, but there was no sequential pattern of crop versus non-crop years indicating that weather, rather than resource limitation alone, dictated the timing of reproduction. Crop years were instead most closely associated with relatively cool late summer conditions in the preceding year, followed by anomalous summer warmth within crop year. Acorn yield increased following dry April and above-average May and June temperatures within crop year. Although our results support a general association between warm late spring and summer conditions, and crop frequency and yield, respectively, the influence of cooler later summer conditions in the year prior to masting highlights how a combination of weather cues may dictate the occurrence of mast years. Consequently, our results corroborate not only the hypothesis that temperature differentials between consecutive years, not absolute temperatures, may be the better predictor of mast seeding events but lend support also to the suggestion that reproductive failure and resource accumulation resulting from a climate-linked environmental veto, drives future reproductive synchronization in temperate tree species.

Elevated anthropogenic nitrogen (N) deposition could alter N status in temperate steppe. However, threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems. Research on the natural abundance of ¹⁵N (δ¹⁵N) could greatly help provide integrated information about ecosystem N status. The goal of this study was to investigate the suitability of measurements of δ¹⁵N of major ecosystem N pools and several key species, plant ¹⁵N fractionation, together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia.

We carried out a N addition experiment during 2011–14 on a Stipa krylovii steppe in Inner Mongolia, Northern China. We investigated the response of several key N transformation processes, vegetation and soil properties to N addition. Aboveground biomass and belowground biomass (BGB) δ¹⁵N, root and foliar δ¹⁵N of three dominant species (Artemisia frigida, S. krylovii and Leymus chinensis), δ¹⁵N of soil total N and soil KCl-extractable NO₃^?-N were determined. The responses of isotope fractionation during plant N uptake and reallocation to N addition were also determined.

Our results suggest that the N addition rate of 5g N m^?2 yr^?1 could be regarded as threshold of early N saturation in this S. krylovii steppe as indicated by an increase in plant fractionation and a decrease in plant δ¹⁵N. When N input rate is >10 g N m^–2 yr^–1, increased N deposition can lead to an apparent reduction in species richness and BGB as well as an increase in NO₃^? in extractable soil pools <30-cm soil profile. With N addition, S. krylovii and A. frigida undergo earlier N status shift from N limitation toward N excess compared with L. chinensis, contributing to L. chinensis out-competing other species. Overall, this study provides a better understanding of N status change in temperate steppe based on isotope evidence and several other functional variables and contributes to predicting the responses of temperate steppe to future global N deposition scenario.

Riparian plant diversity is sensitive to changes in groundwater in arid regions. However, little is known about how plant diversity responds to changes in environment along riverside-desert gradients in riparian ecosystem. Our objectives were to (i) identify riparian plant diversity along riverside-desert gradients in Tarim desert riparian forests, (ii) analyze the impact of environment variables on plant diversity, (iii) determine the optimum groundwater depth for different plant life-forms.

Six transects 90 quadrats (with each size 100 m × 100 m) distributed vertically to river bed along riverside-desert gradients ~30 km in length were surveyed. At each quadrat, the morphological features of riparian plant communities were measured, and the groundwater depth, soil water, soil salinity, soil nutrient were also monitored at same sites.

Three distinct vegetation communities were identified based on cover and richness in the tree, shrub and herb layers: the riparian zone, the transitional zone and the desert margin zone. Twelve species were indicators of the three vegetation communities. Riparian plant diversity was influenced by groundwater depth, distance from river, soil moisture content, soil salinity and soil nutrient by redundancy analysis. In response to groundwater depth, the optimal groundwater depths for species diversity, evenness and shrub cover were 2.8, 2.7 and 3.7 m, respectively. Therefore, maintaining high plant diversity requires managers to ensure stable groundwater depth for different plant life-forms rather than for some of them.

Many invasive alien plant species are clonal and can greatly propagate and spread through clonal integration (sharing resources between connected ramets) in heterogeneous and variable environments. Here, we tested whether water variability influences clonal integration of invasive alien plant species and consequently facilitates their growth and dominance in a native community.

We selected four typical invasive clonal plant species in China. Connected (with clonal integration) and disconnected (without clonal integration) clonal fragments were established either under constant watering or variable watering condition in an experimental native plant community consisting of three naturally co-occurring grassland species. Proximal part of the container received high nutrient and distal part received low nutrient.

Clonal integration significantly increased biomass, aboveground mass and belowground mass of invasive alien plants in the proximal ramets, the distal ramets and the whole clone and decreased the growth of native community. Interestingly, clonal integration significantly increased the growth of invasive plants in variable watering. The positive effect of clonal integration was stronger in variable watering than in constant watering. Invasive plants with clonal integration had high biomass proportion (>0.6) in the whole community. Our results suggest that invasive clonal plants benefit more from clonal integration in variable water environments when established in a native community, and to some extent, clonal integration potentially contribute greatly to the invasiveness of alien clonal plants when they enter a new community with resource variability.

Snow cover occupies large percentage of land surface in Tibetan Plateau. Snow cover duration (SCD) during non-growing seasons plays a critical role in regulating alpine vegetation’s phenology by affecting the energy budgets of land surface and soil moisture conditions. Different period’s snow cover during non-growing season may have distinct effect on the vegetation’s phenology. Start of season (SOS) has been observed advanced under the ongoing climate change in the plateau, but it still remains unclear how the SCD alters the SOS. This study attempts to answer the following questions: (i) What is the pattern of spatial and temporal variations for SCD and grassland SOS? (ii) Which period’s SCD plays a critical role in grassland’s SOS?

The remote sensing datasets from the Moderate Resolution Imaging Spectroradiometer (MODIS) were utilized to compute the SOS and SCD on the Tibetan Plateau over 2003–15. The Asymmetric Gaussian function was applied to extract SOS. We also explored the spatial pattern and temporal variation of SOS and SCD. Then, by using linear correlation coefficients, we investigated the driving effects of different period’s non-growing season SCD on SOS.

The non-growing season SCD slightly decreased during 2003–15, while SOS exhibited an overall advancing trend. Advanced trends in SOS were observed in the eastern plateau, and the delayed trends were mainly founded in western plateau. Snow cover area exhibited two separate peaks during autumn and late winter over the plateau. Extended SCD regions mainly distributed in middle-east of the plateau, while shrunken SCD distributed in other regions of the plateau. SCD of different seasons caused distinct effects on vegetation SOS. Lengthened autumn SCD advanced SOS over the eastern plateau. The slightly lengthened SCD postponed SOS over the western plateau. In the wet meadow regions, advanced SOS was positively associated with SCD during the entire non-growing season, whereas for the dry steppe, SCD over the preseason played a more dominant role. The SCD of previous autumn and winter also showed lag effect on SOS over meadow regions to a certain extent. This study confirmed the importance of SCD to phenological processes at the beginning of growing season and further suggested that role of SCD should be discriminated for different periods and for different heat-water conditions. With the lag effects and SCD’s distinct effect of different seasons considered, predictions on the Tibetan Plateau’s spring phenology could be improved.