Search Results (18)

Litter accumulation and small mammal disturbances create specific fine-scale microhabitats in grasslands. These microhabitats serve as safe sites and regeneration niches for subordinate plant species and are important in diversity maintenance. Previous experiments manipulating litter and disturbance and studying their effects on diversity revealed complex relationships. However, little is known about the realized net effects of these mechanisms in different types of grasslands. We conducted a long-term observational study exploring these patterns and their effects in successional and mature grasslands. We applied a specific mapping technique: the presences of litter, disturbance, and living plant species were recorded in 5 cm × 5 cm contiguous microquadrats along 52 m permanent transects. Sampling was repeated annually over 10 years. Spatial dynamics and associations with subordinate grassland specialists were evaluated using information theory models. Analyses were performed at increasing spatial and temporal scales. Varying associations were found across years. Negative associations dominated the relationships between litter and local diversity hotspots, while the relationships with disturbances were mainly neutral. When analyses were repeated at longer time scales, consistent negative associations were detected between litter and diversity hotspots. Long-term relationships between disturbance and diversity were negative in old-fields and positive in the natural grassland. To collect more representative and reliable data on the role of plant litter accumulation and small mammal disturbances, we recommend long-term annual monitoring and the application of temporal scaling based on cumulative diversity. Full article

Grazing affects soil organic carbon (SOC) through plant removal, livestock trampling, and manure deposition. However, the impact of grazing on SOC is also influenced by multiple factors such as climate, soil properties, and management approaches. Despite extensive research, the mechanisms by which grazing intensity influences SOC density in grasslands remain incompletely understood. This study examines the effects of varying grazing intensities on SOC density (0–30 cm) dynamics in temperate grasslands of northern China using field surveys and experimental analyses in a typical steppe ecosystem of Inner Mongolia. Results show that moderate grazing (3.8 sheep units/ha/yr) led to substantial consumption of aboveground plant biomass. Relative to the ungrazed control (0 sheep units/ha/yr), aboveground plant biomass was reduced by 40.5%, 36.2%, and 50.6% in the years 2016, 2019, and 2020, respectively. Compensatory growth failed to fully offset biomass loss, and there were significant reductions in vegetation carbon storage and cover (p < 0.05). Reduced vegetation cover increased bare soil exposure and accelerated topsoil drying and erosion. This degradation promoted the downward migration of SOC from surface layers. Quantitative analysis revealed that moderate grazing significantly reduced surface soil (0–10 cm) organic carbon density by 13.4% compared to the ungrazed control while significantly increasing SOC density in the subsurface layer (10–30 cm). Increased precipitation could mitigate the SOC transfer and enhance overall SOC accumulation. However, it might negatively affect certain labile SOC fractions. Elucidating the mechanisms of SOC variation under different grazing intensities and precipitation regimes in semi-arid grasslands could improve our understanding of carbon dynamics in response to environmental stressors. These insights will aid in predicting how grazing systems influence grassland carbon cycling under global climate change. Full article

The accurate assessment of the rise in nitrous oxide (N₂O) under global changes in grasslands has been hindered because of inadequate annual observations. To measure the seasonal response of N₂O emissions to increased water and nitrogen (N) deposition, one year round N₂O emissions were investigated by chamber weekly in the growing season and every two weeks in the non-growing season in semi-arid temperate grasslands northern China. The results showed the temperate semi-arid grassland to be a source of N₂O with greater variability and contribution during the non-growing season. The individual effects of water or N addition increased N₂O emissions during the growing season, while the effects of water or N addition depended on the N application rates during the non-growing season. Soil properties, particularly soil temperature and water-filled pore space (WFPS), played key roles in regulating N₂O emissions. Structural equation modeling revealed that these factors explained 71% and 35% of the variation in N₂O fluxes during the growing and non-growing season, respectively. This study suggested that without observations during the non-growing season it is possible to misestimate the annual N₂O emissions and the risk of N₂O emissions increasing under global change. This would provide insights for future management strategies for mitigating greenhouse gas emissions. Full article

The affiliation between vegetation phenology and seasonal climate (start and end times of the growing season, or SOS and EOS) provides a basis for acquiring insight into the dynamic response of terrestrial ecosystems to the effects of climate change. Although climate warming is an important factor affecting the advancement or delay of plant phenology, understanding the sensitivity of phenology to seasonal variation in climate factors (e.g., local air temperature, precipitation) is generally lacking under different climate backgrounds. In this study, we investigated the interannual variability of grassland phenology and its spatial variation in temperate regions of China based on satellite-derived products for the normalized difference vegetation index (NDVI) and weather data acquired from 2001 to 2020. We found that due to differences in local climate conditions, the effects of seasonal warming and precipitation on phenology were divergent or even opposite during the 20 years. The sensitivities of the start of growing season (SOS) to both spring temperature and last-winter precipitation was controlled by mean annual precipitation in terms of spatial variation. The SOS in the semi-humid (200–400 mm) region was most sensitive to spring temperature, advancing 5.24 days for each 1 °C rise in the average spring temperature (p < 0.05), while it was most sensitive to last-winter precipitation in arid regions (<200 mm), with SOS advancing up to 2.23 days for every 1 mm increase in the last-winter precipitation (p < 0.05). The end of growing season (EOS) was sensitive to autumn temperature, being delayed 10.13 days for each 1 °C rise in the average autumn temperature in regions with temperatures between −10 °C and −5 °C (p < 0.05). The uncertainty in the determination of the EOS could conceivably be greater than the determination of the SOS due to the dual effects of pre-autumn climate and growth constraints induced by declining fall temperatures. The effect of atmospheric warming on grassland phenology was lessened with increased atmospheric and soil aridity, suggesting that the interaction of regional drought and climate warming is an important source for local-to-regional differences and uncertainties in grass phenological response. Full article

The high spatial and temporal resolution of recently developed evapotranspiration (ET) products facilitates agricultural water-savings in irrigated areas as well as improved estimates of crop yield, especially in arid and semi-arid regions. However, cloud cover interferes with ET estimates, in particular when using thermal-infrared-based models in temperate and tropical regions. Previous studies have shown that the two-source energy balance (TSEB) model coupled with soil moisture (TSEB-SM) has great potential for estimating surface ET by overcoming this issue. In this study, the TSEB-SM model was first used to generate a spatiotemporally continuous 1 km daily ET dataset across the Heihe River Basin in China from 2000 to 2020, which was then evaluated against four spatially distributed sites (Arou, Huazhaizi, Daman, and Sidaoqiao) and further compared with the two most widely used daily ET datasets (PML-V2 (Penman–Monteith–Leuning) and SEBAL (surface energy balance algorithm for land)). The results showed that the newly developed ET dataset agrees well with ground-based observations and outperforms the PML-V2 and SEBAL products in precisely characterizing the seasonal fluctuations and spatial distribution as well as the spatiotemporal trends of ET. In particular, ET in the Heihe River Basin exhibits clear regional differences. The upstream and midstream grassland and irrigated oasis areas provide much higher annual ET than the downstream desert areas, with a difference of up to 600 mm/year. A three-cornered hat (TCH)-based pixel-by-pixel analysis further demonstrated that the TSEB-SM and PML-V2 products have substantially smaller relative uncertainties as compared to SEBAL ET. In general, the proposed ET datasets are expected to be more beneficial for irrigation scheduling and to provide more efficient water management across the Heihe River Basin. Full article

The northern foothills of Yinshan Mountain are situated in northern China’s agricultural and pastoral ecotone, serving as a crucial ecological barrier. To comprehensively assess the impact of grassland resource restoration in this region since the initiation of the Grain-for-Green conversion project in 2000, this study analyzes the spatiotemporal characteristics of precipitation use efficiency (PUE) and investigates climate-driven factors during 2001–2021. The results showed that the grassland types at the north foot of Yinshan could be divided into four categories: warm-arid, warm subtropical semidesert (WSS), warm temperate-arid, warm temperate zonal semidesert (WZS), warm temperate-semiarid, warm temperate typical steppe (WTS), and warm temperate-subhumid forest steppe (WFT). The NPP of the four grassland species were 151.34 (WSS), 196.72 (WZS), 283.33 (WTS), and 118.06 gC·m⁻² (WFT), and correspondingly, the PUE of the four grassland species were 0.66 (WSS), 0.66 (WZS), 0.80 (WTS), and 0.57 gC·m⁻²·mm⁻¹ (WFT). From 2001 to 2021, PUE in grassland showed an overall upward trend, rising from 0.57 to 0.99 gC·m⁻²·mm⁻¹. The trend analysis found that the vegetation ecological area of the northern foot of Yinshan became better, of which 54.36% was improved and 15.72% was degraded. It is worth pointing out that WSS had the highest degree of improvement, while WFT was in a degraded state. The climate driving force analysis shows that the regional contribution of precipitation is 19.57%, temperature is 28.33%, potential evapotranspiration is 13.65%, wind speed is 10.79%, and saturated vapor pressure is 27.66%. Full article

In this study, we conducted a global assessment of the sensitivity of vegetation greenness (VGS) to precipitation and to the estimated Lagrangian precipitation time series of oceanic (PLO) and terrestrial (PLT) origin. The study was carried out for terrestrial ecosystems consisting of 9 biomes and 139 ecoregions during the period of 2001–2018. This analysis aimed to diagnose the vegetative response of vegetation to the dominant component of precipitation, which is of particular interest considering the hydroclimatic characteristics of each ecoregion, climate variability, and changes in the origin of precipitation that may occur in the context of climate change. The enhanced vegetation index (EVI) was used as an indicator of vegetation greenness. Without consideration of semi-arid and arid regions and removing the role of temperature and radiation, the results show the maximum VGS to precipitation in boreal high-latitude ecoregions that belong to boreal forest/taiga: temperate grasslands, savannas, and shrublands. Few ecoregions, mainly in the Amazon basin, show a negative sensitivity. We also found that vegetation greenness is generally more sensitive to the component that contributes the least to precipitation and is less stable throughout the year. Therefore, most vegetation greenness in Europe is sensitive to changes in PLT and less to PLO. In contrast, the boreal forest/taiga in northeast Asia and North America is more sensitive to changes in PLO. Finally, in most South American and African ecoregions, where PLT is crucial, the vegetation is more sensitive to PLO, whereas the contrast occurs in the northern and eastern ecoregions of Australia. Full article

Soil nematode communities can offer valuable indicators for monitoring the status of soil ecosystems. However, their potential for assessing soil restoration under revegetation has been neglected in temperate arid and semiarid areas. This study examined the characteristics of soil nematode communities and their relationships with soil physicochemical properties under five typical revegetation approaches in the semiarid Loess Plateau of China. The results showed that planting an artificial Caragana korshinskii forest led to the recovery of the soil food web, which significantly increased soil nematode abundance (138.10 ± 11.60 inds./100 g dry soil) and community diversity (Shannon-Wiener diversity: 2.48 ± 0.13; trophic diversity: 3.08 ± 0.02), associated with the high contents of SOC and NH₄⁺-N. However, establishing an artificial Prunus sibirica forest improved neither soil properties nor nematode community characteristics, reflecting poor soil ecosystem restoration. After establishing an artificial Prunus davidiana forest (PD) and an artificial Medicago sativa grassland (MS), substantial increases in herbivorous and fungivorous nematodes were observed, respectively, likely due to the accumulation of particular genera that fed on roots (e.g., Pratylenchus) or their symbiotic fungi (e.g., Tylencholaimus), which might result in the deterioration (in MS) or restoration (in PD) of the soil food webs. Natural grassland restoration greatly improved soil properties (i.e., SOC, NH₄⁺-N, microbial biomass carbon) but did not change the nematode community obviously, probably due to top-down predation in natural habitats. In conclusion, the characteristics of nematode communities can effectively indicate the restoration of soil food webs and identify their possible driving forces under revegetation, which have important implications for vegetation restoration in arid and semiarid regions. Full article

The existence of residences and roads is an important way in which human activity affects wind erosion in arid and semiarid environments. Studies assessing the impact of these elements on wind erosion have only focused on limited plots, and their threat of erosion to the surrounding environment has been ignored by many studies. This study was based on spatially overlayed analysis of independent wind erosion distribution simulated by the revised wind erosion equation (RWEQ) and remote-sensing-image-derived residence and road distribution data. Wind erosion at different distances from residences and roads was quantified at the landscape scale of a typical temperate grassland ecosystem, explicitly demonstrating the crucial impacts of both elements on wind erosion. The results showed that wind erosion weakened as the distance from residences and roads increased due to the priority pathways of human activities, and the wind erosion around the residence was more severe than around the road. Human activities in the buffer zones 0–200 m from the residences most frequently caused severe wind erosion, with a wind soil loss of 25 t ha⁻¹ yr⁻¹ and a wind soil loss of approximately 5.25 t ha⁻¹ yr⁻¹ for 0–60 m from the roads. The characteristics of wind erosion variation in the buffer zones were also affected by residence size and the environments in which the residences were located. The variation in wind erosion was closely related to the road levels. Human activities intensified wind erosion mainly by affecting the soil and vegetation around residences and roads. Ecological management should not be limited to residences and roads but should also protect the surrounding environments. The findings of this study are aimed towards a spatial perspective that can help implement rational and effective environmental management measures for the sustainability of wind-eroded ecosystems. Full article

The Neogene environment and paleovegetation of today’s semi-arid and arid Central Asia remain elusive. Little is known about the effect of paleoclimatic change on the distribution and ecological response mechanisms of aquatic plants, especially on the Tibetan Plateau. Here, we report a new species of Nelumbo Adanson, including leaves, receptacles, and fruits, namely Nelumbo delinghaensis sp. nov., from the Upper Youshashan Formation of the upper Middle Miocene in the northern Qaidam Basin on the Tibetan Plateau. The new species comprises centrally peltate leaves with 12–15 actinodromous primary veins and a receptacle embedded with ca. 15–30 fruits, with an unlobed central disc. Megafossils of lotus from northwest China broaden the geographical and stratigraphic ranges of Nelumbo. Our findings suggest that a large freshwater lake body surrounded by temperate forests and grassland developed in the Qaidam Basin during the late Middle Miocene, in sharp contrast to the present desert vegetation. The climate used to be sufficiently warm and moist enough to support a forest-steppe ecosystem with abundant freshwater bodies. Full article

Climate conditions can significantly alter the vegetation net primary productivity (NPP) in many of Earth’s ecosystems, although specifics of NPP–climate condition interactions, especially time-lag responses on seasonal scales, remain unclear in ecologically sensitive forest–grassland ecotones. Based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) and meteorological datasets, we analyzed the relationship between NPP and precipitation, temperature, and drought during the growing season (April–August), considering the time-lag effect (0–5 months) at the seasonal scale in Hulunbuir, Inner Mongolia, China from 2000 to 2018. The results revealed a delayed NPP response to precipitation and drought throughout the growing season. In April, the precipitation in the 4 months before (i.e., the winter of the previous year) explained the variation in NPP. In August, the NPP in some areas was influenced by the preceding 1~2 months of drought. The time-lag effect varied with vegetation type and soil texture at different spatial patterns. Compared to grass and crop, broadleaf forest and meadow exhibited a longer legacy of precipitation during the growing season. The length of the time-lag effects of drought on NPP increased with increasing soil clay content during the growing season. The interaction of vegetation types and soil textures can explain 37% of the change in the time-lag effect of the NPP response to PPT on spatial pattern. Our findings suggested that preceding precipitation influences vegetation growth at the early stages of growth, while preceding drought influences vegetation growth in the later stages of growth. The spatial pattern of the time lag was significantly influenced by interaction between vegetation type and soil texture factors. This study highlights the importance of considering the time-lag effects of climate conditions and underlying drivers in further improving the prediction accuracy of NPP and carbon sinks in temperate semiarid forest–grassland ecotones. Full article

Investigating relationships between climatic factors and plant δ¹³C of both C₃ and C₄ plants simultaneously is critical for accurately predicting the effects of climate change on plant ecophysiology and ecosystem functioning and reconstructing past vegetation and climate conditions. We selected common C₃ and C₄ plants in temperate grasslands in Inner Mongolia, China, i.e., Stipa spp., Carex spp., Leymus chinensis and Cleistogenes spp., and investigated the relationships between climatic factors and plant δ¹³C of each genus/species. The results showed that precipitation, especially growing season precipitation (GSP), was the dominant factor affecting plant δ¹³C in this region. For C₃ plants, there were significantly negative relationships between precipitation and plant δ¹³C. For C₄ plants, plant δ¹³C of Cleistogenes spp. firstly increased, then decreased with precipitation at a breakpoint GSP 204.84 mm. Our findings emphasize that C₄ plant δ¹³C is sensitive to precipitation, but responses are species-specific and environment-specific, and suggest that C₄ plant δ¹³C can be used as a proxy for water use efficiency (WUE), but care should be taken in evaluating WUE. Moreover, our findings provide basic information for accurately predicting the effects of climate change on ecosystem structure and function and reconstructing past vegetation and climate conditions from bulk materials in arid and semiarid regions. Full article

Drought has been approved to affect the process of terrestrial ecosystems from different organizational levels, including individual, community, and ecosystem levels; however, which traits play the dominant role in the resistance of plant to drought is still unclear. The experiment was conducted in semi-arid temperate grassland and included six paired control and drought experimental plots. The drought treatment was completely removed from precipitation treatments from 20 June to 30 August 2013. At the end of the growing season in 2013, we removed the rain cover for ecosystem recovery in 2014. The results demonstrated that drought treatment increased the coverage of and abundance Heteropappus altaicus, Potentilla bifurca, and Artemisia scoparia by 126.2–170.0% and 63.4–98.9%, but decreased that of Artemisia frigida, Dontostemon dentatus, and Melissilus ruthenicu by 46.2–60.2% and 49.6–60.1%. No differences in coverage and abundance of Agropyron cristatum, Stipa kiylovii, and Cleistogenes squarrosa were found between control and drought treatment. The coverage and abundance of Stipa kiylovii have exceeded the original level before the drought stress, but Heteropappus altaicus still had not recovered in the first year after the disturbance. Our findings indicate that plant functional traits are important for the understanding of the resistance and resilience of plants to drought stress, which can provide data support for grassland management. Full article

Shrub encroachment, i.e., shrub emergence or an increase in woody plant cover, has been widely observed in arid and semiarid grasslands and savannas worldwide since the 2000s. However, until now, there has been a clear division of opinion regarding its ecological implications. One view is that shrub encroachment is an indicator of ecological degradation, and the other is that shrub encroachment is a sign of the restoration of degraded ecosystems. This division leads to completely different judgments about the states and transition phases of shrub-encroached ecosystems, which further affects decisions about their conservation and management. To determine whether ecosystems experiencing shrub encroachment are degrading or are in a postdegraded restoration stage, the spatial distributions and interactions of woody plants after shrub encroachment were investigated in this study. An Ulmus pumila-dominated temperate savanna-like ecosystem with significant shrub encroachment in the Otindag Sandy Land, Inner Mongolia, China, was selected as the research area, and woody plants were surveyed within a 25-hectare (500 × 500 m) plot. Spatial point pattern analysis was employed to analyze the distribution patterns of the woody plants. The results indicated different patterns for U. pumila trees, i.e., a random distribution pattern for old trees (with a diameter at breast height (DBH) of more than 20 cm) and aggregated distribution patterns for medium (5 cm ≤ DBH < 20 cm) and juvenile trees (DBH < 5 cm) at scales of 0–9 and 0–12 m, respectively. For most shrubs, there was significant aggregation at a scale of 0–6 m. However, there were significant negative relationships between old U. pumila trees (DBH ≥ 20 cm) and most shrub species, such as Caragana microphylla and Spiraea aquilegifolia. In contrast, there were positive relationships between juvenile trees (DBH < 5 cm) and most shrub species. These results suggest that, to some extent, shrub encroachment may have disrupted the normal succession pattern in the U. pumila community in this area, and without conservation, the original tree-dominated temperate savanna-like ecosystem may continue to deteriorate and eventually become a shrub-dominated temperate savanna-like ecosystem. Full article

It is important to accurately evaluate ecosystem respiration (RE) in the alpine grasslands of the Tibetan Plateau and the temperate grasslands of the Inner Mongolian Plateau, as it serves as a sensitivity indicator of regional and global carbon cycles. Here, we combined flux measurements taken between 2003 and 2013 from 16 grassland sites across northern China and the corresponding MODIS land surface temperature (LST), enhanced vegetation index (EVI), and land surface water index (LSWI) to build a satellite-based model to estimate RE at a regional scale. First, the dependencies of both spatial and temporal variations of RE on these biotic and climatic factors were examined explicitly. We found that plant productivity and moisture, but not temperature, can best explain the spatial pattern of RE in northern China’s grasslands; while temperature plays a major role in regulating the temporal variability of RE in the alpine grasslands, and moisture is equally as important as temperature in the temperate grasslands. However, the moisture effect on RE and the explicit representation of spatial variation process are often lacking in most of the existing satellite-based RE models. On this basis, we developed a model by comprehensively considering moisture, temperature, and productivity effects on both temporal and spatial processes of RE, and then, we evaluated the model performance. Our results showed that the model well explained the observed RE in both the alpine (R² = 0.79, RMSE = 0.77 g C m⁻² day⁻¹) and temperate grasslands (R² = 0.75, RMSE = 0.60 g C m⁻² day⁻¹). The inclusion of the LSWI as the water-limiting factor substantially improved the model performance in arid and semi-arid ecosystems, and the spatialized basal respiration rate as an indicator for spatial variation largely determined the regional pattern of RE. Finally, the model accurately reproduced the seasonal and inter-annual variations and spatial variability of RE, and it avoided overestimating RE in water-limited regions compared to the popular process-based model. These findings provide a better understanding of the biotic and climatic controls over spatiotemporal patterns of RE for two typical grasslands and a new alternative up-scaling method for large-scale RE evaluation in grassland ecosystems. Full article