Grassland Changes Research Articles

Soil moisture outweighs temperature for triggering the green-up date in temperate grasslands

Investigating grassland phenology and its relationship with climatic factors is crucial for understanding ecosystem responses to climate change. However, there have been few studies on the impact of soil moisture on grassland phenology. In this study, we extracted the green-up date in the Inner Mongolia grasslands, China, using the normalized difference vegetation index (NDVI) data from the Global Inventory Modeling and Mapping Studies (GIMMS) NDVI3g dataset (1982–2015) and the Moderate Resolution Imaging Spectroradiometer (2001–2015). We investigated the spatiotemporal pattern of the green-up date and its relationship with four climatic factors, including growing degree days, chilling days, soil moisture, and solar radiation. Most areas (67.1%) exhibited a trend towards earlier green-up date, but the significant trends (p < 0.05) were only found in 13.4% of the areas. For both datasets, the pixels with a negative regression coefficient of soil moisture accounted for more than 87% of the total area (more than 21% significantly, p < 0.05). Regarding the other factors, the sign of regression coefficients was not consistent among pixels. Thus, soil moisture correlated more significantly with the green-up date in temperate grasslands compared with the other climatic factors. This study provides the scientific basis for better understanding the mechanism of phenological response to climate change in temperate grasslands.

Is livestock grazing a key factor for changing vegetation patterns in lime rich coastal dunes in the Netherlands?

In 1990, livestock grazing was introduced in Meijendel, a 1800 ha lime-rich coastal dune area, at a density of 0.06–0.07 LLU.ha-1.year−1 (1:12–18 ha) to counteract encroachment of tall grasses and shrubland on dune grassland and increase the bare sand area. Monitoring was based on four digital orthophotos (1975–1990–2001-2009) with a high spatial resolution (pixel size 25 × 25 cm). The changes were tested using Generalized Estimating Equations. Habitat changes occurred, but contradicting our hypothesis, there was no significant impact from the grazing on bare sand, grassland or shrubland within 11 and 19 years post livestock introduction. (1) After several decennia of decreasing bare sand, there was a significant increase between 2001 and 2009, irrespective of livestock presence. (2) The changes in grasslands and shrublands are independent of the livestock, but dependent on distance to the coast. (3) Bare sand and shrub cover determine the space left for the dune grasslands. It appears other factors than livestock grazing must have induced the changes. Changes in climate conditions and nitrogen load might have stimulated bare sand. An interaction with the end of Marram planting in 1990 cannot be concluded from available data. The disease-led reduction of rabbit grazing from the mid-1950s led to an expansion of the dominant shrub Hippophae rhamnoides. However, Hippophae shrubland typically regresses to grasslands on its collapse after 25–40 years. Tree species like Crataegus, Betula and Quercus will gradually dominate the landscape for far longer. Active removal of these indigenous species is necessary to prevent future loss of dune grasslands.

RESEARCH ON THE VARIATION CHARACTERISTICS OF VEGETATION CHANGE AND ITS TERRAIN INFLUENCE FACTORS IN ALPINE GRASSLAND IN THE SOURCE REGION OF THE YELLOW RIVER

Abstract. The source region of the Yellow River is an important ecological barrier in China. Since the 1990s, under the influence of various factors, its runoff has decreased and the ecological environment has deteriorated, which has attracted great attention of governments. Vegetation is the general term of plant communities covering the surface, which is the natural link between the atmosphere, water and soil. It plays an important role in air regulation, soil conservation and maintaining the stability of the whole ecosystem. Therefore, the study on the differential characteristics and topographic influencing factors of alpine grassland change in the source region of the Yellow River can provide reference for the ecological environment protection in -this region in the future. Based on the remote sensing data of MODIS NDVI, we studied the spatial distribution pattern and temporal variation characteristics of vegetation coverage in the source region of the Yellow River from 2000 to 2009 by means of maximum synthesis method, pixel dichotomy model method and trend analysis method. Furthermore, combined with DEM topographic elevation data, we discussed the influence of topographic factors such as elevation, slope and aspect on fractional vegetation cover (FVC) change. The results showed that: (1) From 2000 to 2009, the FVC in the source region of the Yellow River fluctuated upward, showing the spatial distribution characteristics of the southeast region &gt; the central region &gt; the northwest region; (2) During the ten years from 2000 to 2009, the almost constant of FVC accounted for the largest area, and the areas with increasing FVC mainly concentrated in the northeast and northwest of the studied region, the areas with reduced vegetation coverage were scattered in various places in the studied region, mainly in the form of minimal patches or spots; (3) Different terrain factors had different effects on FVC and the effect of altitude on FVC changes was significantly greater than that of slope and aspect. With the increase of altitude, the proportion of significant reduction in FVC increased firstly and then decreased, while the proportion of significant increase in FVC was decreasing and the proportion of almost unchanged in FVC was increasing; With the increase of slope, the proportion in the above three cases (significant reduction, significant increase and almost unchanged in FVC) was increased, decreased gradually and fluctuated respectively. Under different aspect, the proportion in the above three cases varied little, fluctuating only within 1%.

Changes in Grassland and Their Impact on Milk Production in Poland in the Context of Environmental Protection

Changes in Grassland and Their Impact on Milk Production in Poland in the Context of Environmental Protection

The scheme of nutrient addition affects vegetation composition and plant species richness in different ways: Results from a long-term grasslands experiment

The deposition of pollutants and agricultural fertilizers substantially increases nutrient supply to the environment. Nutrient addition may shift the nutrient limitation type of plants, e.g. from nitrogen (N)-limited to phosphorus (P)-limited. As the nutrient supply is expected to continue to grow, it is important to understand the patterns of nutrient limitation and their effects on species composition. The aim of this study was therefore to evaluate the long-term (39 years, 1968-2007) effects of varied fertilization schemes, i.e. N, P, PK, PK + 90 kg ha−1 N, and PK + 180 kg ha−1 N, on the species composition of a seminatural mountain grassland. In the first period of the experiment (13 years), NPK fertilization resulted in high yield and a considerably impoverished species composition, dominated by a single grass species (Holcus mollis). Plots fertilized with a single nutrient (N or P) developed a similar species composition to that of the control grassland (no fertilization) dominated by species typical of low-fertility habitats of the Nardo-Callunetea class. In the 1980s, the plots fertilized with NPK exhibited a considerable reduction in yield. Therefore, in the years 1993 and 1994 mowing was replaced by sheep grazing, and supplementary fertilization with micronutrients was applied. In 2007 the yield in the treatment fertilized with PK + 180 kg ha−1 N was not restored, but the number of species increased. The species composition in the PK treatment became more similar to that of the plots treated with NPK. In contrast, changes in grasslands fertilized with single nutrients (N or P) were insignificant. To conclude, the factor that most strongly affected species composition was the increase in productivity caused by the addition of basic macronutrients. The addition of N or P alone does not significantly affect species composition if other elements limit the productivity of the grassland.

Remote-Sensing Monitoring of Grassland Degradation Based on the GDI in Shangri-La, China

Grassland resources are important land resources. However, grassland degradation has become evident in recent years, which has reduced the function of soil and water conservation and restricted the development of animal husbandry. Timely and accurate monitoring of grassland changes and understanding the degree of degradation are the foundation for the scientific use of grasslands. The grassland degradation index of ground comprehensive evaluation (grassland degradation index, GDIg) is a digital expression of grassland growth that can accurately indicate the degradation of grasslands. In this research, the accuracy of GDIg in evaluating grassland degradation is discussed; the typical areas of grassland degradation in Shangri-La City, i.e., the towns of Jiantang and Xiaozhongdian, are selected as the research area. Through a field survey and spectroscopy combined with Huanjing-1 (HJ-1) satellite image data, grassland degradation was monitored in the study area from 2008 to 2017. The results show that: (1) GDIg based on six indicators, namely, above-ground biomass, cover level, height, biomass of edible herbage, biomass of toxic weeds, and species richness, can effectively indicate grassland degradation, with the accuracy of the degradation grade assessment reaching 98.6%. (2) The correlation between the GDIg and the grey values of 4 wavebands and 7 types of vegetation indexes derived from the HJ-1 is analysed, and the degraded grassland inversion model was built and revised based on HJ-1 data. The grassland degradation evaluation index of remote sensing (GDIrs) model indicates that grassland degradation is proportional to the ratio vegetation index (RVI). (3) The grassland area was 405.40 km2 in the initial monitoring period, accounting for 17.26% of the study area, while at the end of the monitoring period, the area was 338.87 km2, with a loss of 66.53 km2. From 2008 to 2017, the area of non-degraded and slightly degraded grassland in the study area presented a downward trend, with decreases of 59.87 km2 and 49.93 km2, respectively. In contrast, the area of moderately degraded grassland increased by 41.17 km2 from 91.58 km2 in 2008 to 132.74 km2 in 2017, accounting for 39.17% of the grassland. The area of severely degraded grassland was 78.32 km2, accounting for 23.11% of the grassland in 2017. (4) The degraded grasslands in the study area mainly transformed into the degradation-enhanced (deterioration) type. As the transformation rate gradually slows down, the current situation of grassland degradation is not hopeful.

Interactions among the Phenological Events of Winter Wheat in the North China Plain-Based on Field Data and Improved MODIS Estimation

Identification of complete drivers for phenology changes is crucial for developing prediction models of plant phenology. In addition to climatic factors, the interaction among phenological events has recently been reported as an important driver for the phenology changes of forests, savannas, and grasslands. However, open questions remain as to whether the phenological interaction exists in agricultural ecosystems, among which winter wheat plays a vital role in feeding human beings. In this study, we investigated the interaction among the phenological events of winter wheat in the North China Plain (NCP) using both field and satellite data. Considering the large discrepancies between the existing satellite estimation and field measurements of winter wheat phenology, we first improved the MODIS-based estimation of green-up date (GUD), heading date (HD), and maturity date (MD) through a re-calibrated relative threshold method (RTM) in the NCP. The GUD, HD, and MD were accurately estimated with the mean absolute errors (MAE) and root mean squared errors (RMSE) lower than 7.5 days, compared with the RMSEs ranging from 12.0 to 36.1 days in previous studies. Then, the relationships among the GUD, HD, and MD were analyzed using the field data collected at agricultural meteorological stations. The GUD (HD) showed a significantly positive correlation with the HD (MD). Quantitatively, a one-day earlier GUD (HD) would result in an earlier HD (MD) of 0.57 days (0.60 days). Furthermore, we applied the partial correlation analysis to the improved MODIS estimation of GUD, HD, and MD to investigate their interactions by considering the simultaneous influences from climatic factors. The results showed that the HD (MD) with 85.2% (94.5%) of all winter wheat pixels presented a significantly positive correlation with the GUD (HD). Meanwhile, the GUD (HD) with 84.2% (33.3%) of the entire winter wheat area presented a significantly negative correlation with pre-season temperature. These results suggest that both the climatic factors and phenological interactions should be included in the future development of winter wheat phenology models to improve the prediction accuracies.

Effect of grassland mosaic structure and dynamism on the reproductive habitat suitability for Alectoris graeca in central Apennines

Over the last several decades, the Mediterranean region has been subjected to mountain abandonment and farming cessation, leading to changes in vegetation and coenological features of grasslands, contextually to the strong decline of the rock partridge (Alectoris graeca). Our hypothesis was that the ongoing dynamic processes leading to the compositional changes of grasslands in central Apennines affect the habitat suitability for the singing male (territorial male defending its reproductive site). In 2015, we defined the presence/absence of spring territorial singing males in seven sites (1,250-2,400 m a.s.l.), by the census in 74 playback stations, distributed along 15 transects. We characterized the topography and the vegetation mosaic of such sites according to the collected topographic and vegetation cover data in 59 randomly selected plots (100 m × 100 m) along the transects. To understand the relations among the environmental variables and the effect of the composition and dynamism of the vegetation mosaics on the presence/absence of the singing male, we used principal components analysis and generalized linear mixed-effect modelling. Our results emphasized the marked overlap between the general environmental conditions, which proved to define the habitat suitability for A. graeca, and the characteristics of the site chosen by the singing male for starting the reproductive activities. Moreover, we found that the site suitability for the singing male decreases when the vegetation recovery processes are ongoing, because of the spread of coarse tall grasses-dominated communities and/or grassland types with dense turf. Tall grass-dominated communities and thick-turf grasslands exert their negative effect decreasing the habitat suitability for the singing male starting from low cover values. Therefore, it is conceivable that singing male’s suitable habitat will be dramatically restricted to the steepest south-facing slopes, where topographic and soil conditions do not allow the spread of grasslands with dense turf and of invasive/dominant tall grasses, increasing the threat to the species due to the effect of climate change on the vegetation features.

Exploring the economic, social and environmental prospects for commercial natural annual grasslands by performing a sensitivity analysis on a multidisciplinary integrated model

This paper presents an integrated modelling study aimed at exploring the possible effects of drivers of change in commercial natural annual grasslands. We consider drivers as factors that affect the rangeland but are not affected by it. Thus, the stocking rate is not treated as a driver, but as an endogenous factor ultimately determined by drivers. This approach, which call for integrated multidisciplinary studies, is rare in the rangeland literature. We try to alleviate this lack by presenting and utilizing a novel multidisciplinary integrated system-dynamics model (108 equations) which represents an area of privately owned extensive farms, its farmers (their numbers and decisions), herds or flocks, herbage production, soil erosion and the linked local markets. By means of a global sensitivity analysis of this model we evaluated the sensitivities of key endogenous factors to the same percentage variation in 70 factors, including economic and climate drivers. The analysis considered the behaviours of 288,000 variants of the modelled system, each under a different 300-year driver scenario.We found that the environmental component of the model was almost exclusively sensitive to biophysical factors, whereas the socio-economic component was almost exclusively sensitive to socio-economic factors, despite the model takes account of key feedbacks connecting both components. Our results suggest that cautiously-managed commercial natural grasslands could socially and economically cope with climate change, especially in a scenario of rising prices of animal products, and also that, even though stocking rates would increase due to an increase in the demand for livestock products, the main threat to the provision of ecosystem services in the studied system would be climate change.

Effects of Community-Based Watershed Development on Landscape Greenness and Vegetation Cover in the Northwestern Highlands of Ethiopia

This study assesses the effects of community-based watershed development (CBWD) on landscape greenness and vegetation cover in the northwestern highlands of Ethiopia. It also evaluates implications of results on ecological conditions and rural livelihoods. Paired-sites comparison approach was used, and compared landscape greenness and vegetation cover at conserved (Tija Baji) and non-conserved (Tata) watersheds for the period 2000–2015. Landsat images for 2000 and 2015 were the datasets used, and analyzed using geographic information systems (GIS). Normalized difference vegetation index (NDVI) was employed to detect landscape greenness. The results showed that landscape greenness represented by high NDVI value (> 0.02) increased in the conserved watershed and decreased in the non-conserved watershed during the study period. The observed change in landscape greenness in both watersheds was due to the change in shrub land and grassland covers. Shrub land and grassland covers increased by 20.6 ha and 22.5 ha in the conserved watershed and decreased by 50 ha and 49.3 ha in the control watershed, respectively. The decreasing change in landscape greenness in the control watershed was due to the conversion of shrub land and grassland into cropland and bare land covers. Cropland and bare land covers in the control watershed increased by 41.9 ha and 26.7 ha, respectively. In contrast, these land covers declined by 30.4 ha and 23.3 ha in the conserved watershed, respectively. The observed changes in landscape greenness, cropland and bare land covers in the conserved watershed have important implications for the improvement of soil fertility, biodiversity, soil erosion and flood control, ground water recharge, carbon sequestration and on rural livelihood systems.

Plant communities are more sensitive than soil microbial communities to multiple environmental changes in the Eurasian steppe

Understanding species responsiveness to anthropogenic environmental changes benefits the guide to manage biodiversity. Microbes are traditionally thought to be more sensitive to environmental changes than plants. However, this hypothesis is supported by little empirical evidence. We compared plant and microbial responses to 13 types of simulated environmental changes (mowing (M), adding nitrogen (N), adding phosphorus (P), watering (W), warming (T) and combinations of these) in a steppe ecosystem. Contrary to our hypothesis, the microbial responses were generally smaller than the plant responses to different types of environmental changes, both at the community-abundance level and species/operational taxonomic unit (OTU)/gene level. This might be ascribed to the soil buffering capacity to environmental changes, and the rapid evolutionary adaptation for microbial communities. Furthermore, the responses at the community-abundance level were larger than at the species/OTU/gene level to 13 types of environmental changes, both in plant and microbial communities. Given that the community abundance representing the total number of all individuals of the organism within the community, the responses to environmental changes at the community-abundance level is likely to be larger than at the species/OTU/gene level. Plant biomass was more responsive to N addition, particularly in such N- limiting grassland ecosystem. Our findings highlight that plant communities are more responsive to environmental changes than microbial communities, contrary to the traditional viewpoint. Therefore, plant communities could be used as ecological indicators of anthropogenic environmental changes in grasslands.

Vegetation Mapping by Using GPM/DPR over the Mongolian Land

Mongolian steppe is one of the largest and important ecosystems. The degradation of grassland and the expansion of desert are occurring due to drought and desertification processes. We attempted monitoring of the broad-scale vegetation in Mongolia by a space-borne precipitation radar, which may complement typical approaches of vegetation monitoring (such as NDVI). We utilized the Global Precipitation Mission’s (GPM) dual-frequency precipitation radar (DPR). We characterized backscatter (σ0) of GPM/DPR’s two microwave bands (Ku and Ka) with respect to the dominant vegetation zones (forest, grassland, desert). Both Ku and Ka radars’ σ0 values were investigated for incidence angle dependency and the seasonal variation. As a result, the use of multi-angle, multi-band observations of GPM/DPR could help to characterize the vegetation zones. Especially, the σ0 at incidence angles between 1° and 8° represented useful characteristics of vegetation. Based on it, by using unsupervised clustering, we produced annual maps describing vegetation zones from 2014 to 2018. The result indicated that Mongolia experienced extensive changes in grassland and desert areas during the study years.

Influence of climate changes on the potential distribution of a widespread grassland species in South America

The consequences of Quaternary climatic fluctuations on plant evolutionary history have been well documented in North America and Europe but have been far less studied in the Neotropical region. Diversification patterns in South American grasslands have been neglected, especially in the Pampas. In this study, we applied an ensemble-modeling framework and a bioregionalization method to test the hypothesis that Petunia axillaris subspecies responded differently to past climate changes in the South American grasslands. Scenarios for the future were projected to better understand the consequences of climatic shifts on the species’ survival. Our results revealed that each subspecies is currently distributed in different bioregions and displays substantial geographic separation as a consequence of past climate oscillations. The projected future scenarios suggest that all subspecies would be affected by habitat fragmentation. This could influence the genetic structuring among P. axillaris populations, as the diversity of grasslands species depends on the genetic characteristics of the remaining populations over the fragmented regions. These results reinforce the importance of considering intraspecific diversity when planning conservation efforts in grasslands in southern South America.

Community carbon and water exchange responses to warming and precipitation enhancement in sandy grassland along a restoration gradient.

Temperature increasing and precipitation alteration are predicted to occur in arid and semiarid lands; however, the response mechanism of carbon and water exchange at community level is still unclear in semiarid sandy land. We investigated the responses of carbon and water exchanges to warming and precipitation enhancement along a sand dune restoration gradient: mobile sand dunes (MD), semifixed sand dunes (SFD), and fixed sand dunes (FD). The average net ecosystem productivity (NEP) and evapotranspiration (ET) between May and August increased by 98% and 59%, respectively, from MD to SFD, while they had no significant differences between FD and the other two habitats. Warming inhibited ecosystem NEP, ET, and water use efficiency (WUE) by 69%, 49% (p < .001), and 80%, respectively, in SFD, while it nearly had no significant effects in MD and FD. However, precipitation addition by 30% nearly had no significant effects on community NEP, ET, and WUE, except for warming treatment in FD. In general, precipitation addition of 30% may still not be enough to prevent drought stress for growth of plants, due to with low water holding capacity and high evaporation rates in sandy land. Temperature increase magnified drought stress as it increased evapotranspiration rates especially in summer. In addition, community NEP, ET, and WUE were usually influenced by interactions between habitats and temperature, as well as the interactions among habitats, temperature, and precipitation. Species differences in each habitat along the restoration gradient may alter climate sensitivity of sandy land. These results will support in understanding and the prediction of the impacts of warming and precipitation change in semiarid sandy grassland.

A Meta‐analysis of the Willingness to Pay for Cultural Services from Grasslands in Europe

AbstractWe investigate the willingness to pay (WTP) for cultural ecosystem services from grasslands using a meta‐analysis based on 32 eligible research papers that provide in total 79 estimates. The average WTP (corrected for purchasing power) across these studies is 38 Euros per person per year. Yet, our analysis reveals that the transfer of these results needs careful evaluation. More specifically, it is essential to frame the monetary valuation exercise in relation to the direction of grassland change. A switch from cropland to grassland reduces WTP by 90 Euros while an increase in less‐intensive land‐use in mountain regions raises WTP by 53 Euros. We conclude that for an adequate consideration of grasslands in holistic ecosystem services assessments, the direction of grassland change is important.

Land use modulates the effects of climate change on density but not community composition of Collembola

Collembola are highly abundant and diverse soil animals and play key roles in litter decomposition and nutrient cycling. Given their functional significance, it is important to understand their responses to human-induced global changes, such as climate change and land-use intensification. Here, we utilized an experimental field study, to test the interactive effects of climate (ambient vs. future) and land use (five land-use regimes, from extensively-used meadow to conventional farming) on three eco-morphological life forms of Collembola: epedaphic, hemiedaphic, and euedaphic species. We found that the effects of climate change on Collembola density were modulated by land use, and that the responses of different life forms to climate × land use interaction differed in magnitude and/or direction. The densities of total and hemiedaphic Collembola significantly decreased under organic farming and marginally increased in grasslands under future climatic conditions, whereas epedaphic Collembola tended to decrease their density with climate change in grasslands. In contrast, the density of euedaphic Collembola significantly increased with climate change in intensively-used grasslands. Further, we found that grasslands (especially extensively-used meadow) support the most abundant Collembola communities, with high species richness but low evenness. Multivariate analyses revealed independent effects of climate change and land-use intensification on Collembola community composition. Together, our findings indicate that the effects of climate change on Collembola communities depend on their life forms and land-use types. Surface-dwelling Collembola are more vulnerable to land use and climate change than those living in deeper soil layers. This may slow down the process of soil-surface litter decomposition in a changing world.

Divergent shifts in peak photosynthesis timing of temperate and alpine grasslands in China

The changing climate is shifting the seasonality of photosynthesis in vegetation, including the start (SOS), end (EOS), and length (LOS) of the growing season, and the peak photosynthesis timing (PPT). While the SOS, EOS, and LOS have been widely investigated, the PPT of grasslands – as a proxy for the response of seasonal plant photosynthesis to climate change – has been overlooked. In this study, we propose a hybrid generalized additive model (HGAM) method to extract PPT using the Vegetation Photosynthesis Model (VPM)-based gross primary production (GPP) product, and we examine the dynamics, drivers, and consequences of PPT changes in temperate and alpine grasslands in China over 2000–2016. We found that the PPTs in temperate and alpine grasslands have exhibited advancing (with −0.68 days yr−1, p < 0.05) and delaying (with 0.29 days yr−1, p = 0.158) trends, respectively. In addition, preseason precipitation and soil moisture were positively correlated with the PPT in temperate and alpine grasslands, respectively, while the preseason temperature consistently controlled the PPT changes in both grasslands. Furthermore, we found that an earlier PPT was associated with higher annual production in the temperate grasslands but not in the alpine grasslands in China. The divergent PPT patterns indicated the varied adaptation characteristics to climatic constraints in the temperate and alpine grasslands and also caused different consequences on carbon uptake. This study highlights the importance of PPT in understanding the spatiotemporal dynamics of vegetation photosynthesis and the carbon cycle under a changing climate.

Dominant plant species influence nematode richness by moderating understory diversity and microbial assemblages

Belowground assemblages are tightly linked to the aboveground vegetation, and often differ between plant species and vegetation types due to direct and indirect influences. However, the relative contribution of these direct and indirect influences of plants on belowground organisms differs among taxa and remains poorly understood. We established a plant removal experiment to better understand the effects of dominant plant species on nematode assemblages in an alpine meadow on the Tibetan plateau. We quantified plant community diversity, soil microbial assemblage richness and edaphic properties to explore how a dominant shrub and graminoids affect nematode assemblage structure and community-weighted mean (CWM) biomass using structural equation modelling (SEM). We found contrasting responses of nematode richness and CWM biomass of nematodes to the removal of shrubs and graminoids, including an intriguing interaction between them. The latter indicates that interactions between shrubs and graminoids modify nematode communities rather than their independent effects. Our results further suggest that dominant plants predominantly indirectly influence nematode richness through changes in biotic variables, specifically understory diversity, and bacterial and fungal richness. However, the dominant plants had no direct and limited indirect effects on CWM nematode biomass, which instead increased with soil nitrogen content, and decreased with soil pH, carbon and ammonium content. Our results provide insight into the relative role of direct and indirect influences on belowground assemblages and highlight the importance of dominant plants in maintaining belowground diversity. By contrast, edaphic properties appear more important to belowground biomass, likely reflecting longer term influences of the plant community on resource availability and quality. Vegetation changes in grassland, such as reduced dominance of shrubs and graminoids, might therefore reduce soil biodiversity relatively rapidly but contribute to longer term impacts through changes in biogeochemical cycles.

Assessing the effects of climate variation and human activities on grassland degradation and restoration across the globe

Abstract While quantitative assessment of ecosystems degradation is quite addressed in the literature, quantitatively separating the relative contribution of climate variation and human activities to grassland ecosystem degradation is still limited, although well recognized as a key knowledge for a better understanding of the degradation mechanisms and for more efficient control of degradation processes. In this study, actual net primary productivity (ANPP) was selected as an indicator to investigate the grassland dynamics from 2000 to 2013. In addition, potential NPP (PNPP) and human-induced NPP (HNPP), which was calculated as the difference between PNPP and ANPP, were used to differentiate the relative impacts of climate variation and human activities on grassland degradation/restoration, respectively. Results showed that 60.94% of the total global area of grassland experienced restoration over the study period, with an increase in NPP by 1864.81 Tg C across the globe. The restored areas induced by climate variation and human activities accounted for 45.73% and 34.99% with an increases in NPP by 852.75 Tg C and 652.50 Tg C, respectively. By contrast, nearly 39.06% of the global grassland area experienced degradation. This degradation was associated with a noticeable decrease in ANPP by 325.53 Tg C. While 45.45% of the degraded grassland areas were influenced by climate variation, human activities were accounted for around 40.11% of this degradation. The relative effect of the two factors (i.e. climate variation and human activities) on grassland changes was found to vary greatly among the studied six continents. While human activities exerted larger impacts than climate variation on grassland degradation in North America and Europe, climate variation was the dominant factor for grassland restoration in Asia, Europe, Oceania and North America, which can be mainly attributed to the increase in precipitation during the study period. The findings of the current study improved our understanding of the relative impacts of climate variation and human activities on grassland degradation and restoration at the global scale.

Cattle grazing alters the interaction of seed-borne fungi and two foliar pathogens of Leymus chinensis in a meadow steppe

Intensive grazing by herbivores lead to major ecological changes in natural grasslands, including severe degeneration. However, the understanding of how grazing affects the incidence of pathogenic and saprotrophic fungi on leaves and seeds of dominant plant species in grasslands is limited. In this study, the presence of two fungal pathogens that cause lesions on leaves of a dominant grass species of the Hulunber meadow steppe in northeast China, Leymus chinensis, as well as saprotrophic fungi associated with lesions, was investigated in plots with different grazing intensities treatments (0, 0.42, 0.63, 0.83, 1.25, and 1.67 cattle ha−1). In addition, seeds of L. chinensis were harvested from plants of the different grazing intensities and the presence of seed-borne fungi, including pathogenic and saprotrophic fungi, were examined by fungal isolation. The results indicated that with the increase of grazing intensity, the incidence of two fungal diseases on leaves of L. chinensis, leaf blotch diseases caused by Leptosphaeria avenaria and Parastagonospora nodorum, decreased. On seeds, the two most frequently isolated fungi were Le. avenaria and P. nodorum, from 57.2% and 40.6% of seeds respectively. At the highest grazing plots, the frequency of isolation of these two fungi to 23.1 and 15.6% respectively. By contrast, the frequency of isolation of Epicoccum nigrum in the highest grazing plots was 88.9%, approximately 10-fold of that in control plots. In dual-culture studies, E. nigrum isolates had inhibitory effects on the growth of isolates of the two leaf pathogens.