Desert Grassland Research Articles

Sustainable application of GF-6 WFV satellite data in desert steppe: A village-scale grazing study in China

This study investigated the vegetation growth and forage-livestock balance of desert grasslands at the village scale. This study was chosen to be conducted in the Ningxia Hui Autonomous Region, where desert grasslands are widely distributed and fragility of the environment. This paper establishes a model for estimating time series changes of above-ground biomass (AGB) in the study area based on remote sensing images from the Gaofen-6 satellite, combined with canopy spectra and AGB data of vegetated desert steppe areas. Next, the ecological carrying capacity and load of the desert steppe area were analyzed based on the number of sheep raised in different enclosures and the grazing methods employed. The status of the forage-livestock balance in the study area was assessed after measuring the crop yield of farmland. Finally, data and case support for grazing management in desert steppe were provided in combination with the research results. The study concluded that Gaofen-6 satellite images could quickly and accurately obtain information on vegetation growth and changes in desert grassland areas at a village scale. The available grazing time in a single year in the study area is inadequate to support current stocking levels. When ecological stability is the primary consideration, natural forage obtained through natural conditions cannot meet the needs of farmers for normal grazing and production activities. The suitable grazing time in the study area is limited in any year. The suitable maximum grazing intensity among all plots ranged from 0.334 to 2.541 sheep/ha. In the case of the balance between grass and livestock, the forage obtained from natural pastures could only satisfy 41.71% of the current stocking levels for sheep. Rotational grazing and subsidies for farmers help desert steppe to recover and achieve a forage-livestock balance.

Response of Grassland Soil Quality to Shallow Plowing and Nutrient Addition.

Due to differences in the soil environment and grassland management measures, the change characteristics of soil microbial entropy and soil comprehensive quality in different types of grassland may vary significantly. In this study, the spatial variation characteristics of grassland soil microbial entropy under shallow plowing and nutrient addition measures were studied using a networking experimental platform established in a temperate meadow steppe, typical steppe, and desert steppe in northern China. The grassland soil quality was comprehensively evaluated to provide a theoretical basis for the scientific and reasonable management of grasslands under global climate change. The results show that in the meadow steppe, shallow plowing and nutrient addition significantly decreased the soil microbial biomass carbon and microbial entropy in the region, resulting in a decrease in the comprehensive score of soil quality. In the typical steppe, due to the influence of shallow tillage measures, the microbial biomass of the grassland soil in the region was higher than that of the control group and its two treatments, and the comprehensive score of soil quality was ranked first among the four treatments. In the desert steppe, the interaction of shallow plowing and nutrient addition significantly increased the soil microbial entropy in the region. Under the nutrient addition measures, the soil microbial entropy of the desert steppe showed a downward trend. In addition, the soil C/N ratio of the desert grassland under nutrient addition measures increased significantly, and the comprehensive score of soil quality ranked first among the four treatments as the microbial entropy decreased significantly.

Comprehensive growth index monitoring of desert steppe grassland vegetation based on UAV hyperspectral.

The goal of this study was to establish a comprehensive growth index (CGI) of grassland vegetation for monitor the overall condition of the grassland. Taking the desert grassland in Otuoke Banner, Ordos City, Inner Mongolia as the research object, this study integrates five indicators. First, the optimal band of the unmanned aerial vehicle hyperspectral data is optimized using the correlation analysis, successive projection algorithm (SPA), optimum index factor method, and band combination index method. A dual-band spectral index in good correlation with the CGI is then constructed in the optimal band. Afterwards, a CGI characterization model is established in accordance with the partial least squares regression (PLSR) algorithm and its accuracy is analyzed. Finally, the CGI of the study area is estimated. The experimental results are as follows. 1) The R2 of models built using the training samples of the spectral indices corresponding to the optimal spectra screened by the SPA method was 0.7835, RMSE was 0.0712, and RE was 6.89%, less than 10%. The R2 of the Validation samples was 0.7698, RMSE was 0.0471, and RE was 6.36%, less than 10%, highest precision. 2) Models were built using the spectral indices corresponding to the optimal spectra screened by the SPA method, and the CGI mean values were inverted. A comparison of the mean measured CGI values of the sample quadrat of the test area showed that the mean relative error was 3.82%. The results show that the vegetation growth of desert-steppe grasslands can be adequately monitored, providing technical support for the rapid and accurate diagnosis of grassland conditions. However, there are still shortcomings in this study. 1) The research area for this study was mainly in the desert steppe in Otuoke Banner, Ordos, hence the relevance and universality of the findings need to be verified, and subsequent experiments need to be carried out on desert steppes in other regions or even other types of grasslands to test the universality of the model. 2) In this study, the influence of soil background and litter on the spectral reflectance is not considered in depth. In addition, the influence of sensor observation angle and solar elevation angle on the inversion model demands further investigation efforts.

Spatiotemporal fusion of multi-source remote sensing data for estimating aboveground biomass of grassland

Accurate estimation of aboveground biomass of grasslands is key to sustainable grassland utilization. However, most satellites cannot provide high temporal and spatial resolution data. Patterns of grassland dynamics associated with variability in climate conditions across spatiotemporal scales are yet to be adequately quantified. A spatiotemporal fusion model offers the opportunity to combine the resolution advantages of different remote sensing data to achieve a high frequency and high precision monitoring of vegetation. We test a flexible spatiotemporal data fusion (FSDAF) methodology to generate synthetic normalized difference vegetation index (NDVI) data from Moderate-Resolution Imaging Spectroradiometer (MODIS) and Landsat data sets. The methodology is tested for the semi-arid grassland of the Xilin River Basin, China. Based on NDVI data fusion and field measured aboveground biomass an aboveground biomass estimation model is established for the watershed. Exploring the temporal and spatial changes of biomass and its relationship with environmental factors. The results show that: (1) The FSDAF model performs well (R2 = 0.75) and has clear textural features. (2) The established Support Vector Machine Aboveground Biomass model not only ensured the accuracy of estimation (R2 = 0.78, RMSE = 15.43 g/m2), but also generated spatiotemporal maps of biomass with higher spatial (30 m) and temporal resolution (8 days). (3) The grassland aboveground biomass in this area decreases from southeast to northwest, and the grassland biomass reaches its peak at the end of July. The average biomass of different grasslands decreases in the order of meadow grassland > typical grassland > desert grassland. (4) Aboveground biomass increased linearly with increasing water content, organic carbon and total nitrogen, and was most sensitive to soil water content. During the early growing and rapid growing period, aboveground biomass is mainly affected by both air temperature and precipitation, while the effects of temperature and human activities gradually dominate in the middle and late growing periods. This study helps to improve the spatial and temporal resolution of dynamic monitoring of grassland biomass, and provides a scientific basis for grassland protection and management in arid and semi-arid regions.

The key to temperate savanna restoration is to increase plant species richness reasonably

Changes in species composition and diversity-productivity relationships during vegetation succession are of great significance for the restoration of degraded grasslands. However, the human intervention of grassland restoration mostly considers the single ecological (diversity) or production (biomass) function of grasslands, and does not fully consider the relationships between the two to improve the restoration effects. In this study, three vegetation types (desert grassland, sandy grassland and temperate savanna) were considered to simulate the three stages of restoration of degraded temperate savanna (early, middle and late restoration). Changes in species composition, diversity, and diversity-productivity relationships during the temperate savanna restoration were explored through spatiotemporal substitution. The results showed that with the progress of succession, xerophytes decreased significantly, mesophytes and hygrophytes increased, C4 plants decreased gradually, and C3 plants increased. The change of species richness was the main reason for community differences in the process of community succession, and species replacement mainly occurred between communities in the early and middle stages of succession. Species richness increased significantly from early to late stage of restoration. Latitude was significantly negatively correlated with species diversity. In the process of vegetation restoration, the impact of species richness, Pielou’s evenness, and β-diversity on biomass gradually developed positively and continued to increase, while the Simpson index showed the opposite effect. This study provides references for the restoration of temperate savanna and emphasizes the ecological and productive functions of the grassland should be taken into account in the restoration strategy.

Grassland ecosystem type drives AM fungal diversity and functional guild distribution in North American grasslands.

Nutrient exchange forms the basis of the ancient symbiotic relationship that occurs between most land plants and arbuscular mycorrhizal (AM) fungi. Plants provide carbon (C) to AM fungi and fungi provide the plant with nutrients such as nitrogen (N) and phosphorous (P). Nutrient addition can alter this symbiotic coupling in key ways, such as reducing AM fungal root colonization and changing the AM fungal community composition. However, environmental parameters that differentiate ecosystems and drive plant distribution patterns (e.g., pH, moisture), are also known to impact AM fungal communities. Identifying the relative contribution of environmental factors impacting AM fungal distribution patterns is important for predicting biogeochemical cycling patterns and plant-microbe relationships across ecosystems. To evaluate the relative impacts of local environmental conditions and long-term nutrient addition on AM fungal abundance and composition across grasslands, we studied experimental plots amended for 10 years with N, P, or N and P fertilizer in different grassland ecosystem types, including tallgrass prairie, montane, shortgrass prairie, and desert grasslands. Contrary to our hypothesis, we found ecosystem type, not nutrient treatment, was the main driver of AM fungal root colonization, diversity, and community composition, even when accounting for site-specific nutrient limitations. We identified several important environmental drivers of grassland ecosystem AM fungal distribution patterns, including aridity, mean annual temperature, root moisture, and soil pH. This work provides empirical evidence for niche partitioning strategies of AM fungal functional guilds and emphasizes the importance of long-term, large scale research projects to provide ecologically relevant context to nutrient addition studies.

Developmental dynamics and survival characteristics of the common horse bot flies (Diptera, Gasterophilidae, Gasterophilus) in desert steppe

The genus Gasterophilus (Diptera, Gastrophilidae) is an obligate parasite of the equine family that causes widespread myiasis in desert steppe. Based on four common naturally excreted Gasterophilus larvae collected systematically in the Karamaili Ungulate Nature Reserve from March to September 2021, this paper studies the population dynamics and ontogenetic laws of horse flies, and discuss the coexistence pattern and population dynamics prediction of horse flies. The results showed that the Gasterophilus larvae had obvious concentrated development period, and the time of population peaks was different, the earliest was G. nigricornis (late March), followed by G. pecorum-Ⅰ (mid-April), G. nasalis (late April), G. intestinalis (early May), G. pecorum-Ⅱ (mid-August). The order of development threshold temperature “Cnigricornis < Cpecorum-Ⅰ ≤ Cpecorum-Ⅱ < Cnasalis < Cintestinalis” is consistent with the peak order of different larval populations. The life history survival rate (L) was as follows: Lnigricornis (83.97%) ≥ Lintestinalis (81.25%) > Lnasalis (72.42%) ≥ Lpecorum-Ⅱ (71.65%) > Lpecorum-Ⅰ (39.23%). This study combined indoor experiments and field surveys revealed the development of horse fly populations with different life strategies in desert grasslands. Based on the different development threshold temperatures of several horse flies, the staggered population dynamics of Gasterophilus form continuous infection stress on the host. In addition, G. pecorum exhibited a univoltine bimodal population distribution in this area and led to two high-intensity host infections, which is one of the important reasons why it has become the dominant species of myiasis in desert steppe.

Spatial patterns and drivers of soil total nitrogen in anthropogenic shrub encroachment in desert steppe

Nitrogen is the most important driving factor in primary production and decomposition in arid and semi-arid ecosystems. The effects of shrub encroachment on nitrogen cycling have been investigated at the site scale but seldomly conducted at the landscape scale. Here, we selected 43 shrubland sites distributing across 3000 km2 area in temperate desert grassland in eastern Yanchi County of Ningxia Hui Autonomous. We investigated the spatial heterogeneity and driving factors of soil total nitrogen (STN) at the landscape scale by using geostatistical analysis and the geographical detector method. Our results showed that the average soil total nitrogen decreased in the order of 0–5 cm (0.21 g kg−1) &amp;gt; 5–15 cm (0.19 g kg−1) &amp;gt; 15–40 cm (0.18 g kg−1). Geostatistical analysis showed that soil total nitrogen exhibited the strong spatial autocorrelation in the 0–5 and 5–15 cm soil layers and the moderate spatial autocorrelation in the 15–40 cm soil layer. Furthermore, the geographic detector method indicated that soil physicochemical properties exhibited the stronger effects than these of topographic and vegetation biomass in determining the spatial distribution of soil total nitrogen. Specifically, soil water content in the 0–20 cm soil layer explained 35% of variation in soil total nitrogen spatial pattern in the 0–5 cm soil layer, while soil organic carbon content in the 15–40 cm soil layer explained 64% and 45% of variation in soil total nitrogen spatial patterns in the 5–15 cm and 15–40 cm soil layers, respectively. It was concluded that soil water content and organic carbon content primarily drove the formation of soil total nitrogen spatial heterogeneity in shrubland at the landscape scale, indicating that anthropogenic shrub encroachment evidently affected soil water content and redistribution in dryland.

Isotopic characteristics and sources of suspended particulate organic matter in a reservoir of Chinese desert grassland areas: the influence of dry and wet seasons and the role of atmospheric deposition.

It is essential to study the sources of suspended particulate organic matter (SPOM) for a comprehensive understanding of the carbon and nitrogen cycles in reservoir located in desert grassland areas. Atmospheric deposition is an important pathway for human and natural nutrients to enter water ecosystems. Previous studies have focused on hotspot areas, but neglected the impact of atmospheric deposition on reservoirs in desert grassland regions with little rainfall, long freezing periods, and a dusty climate. In this study, we measured the contents of organic carbon, total nitrogen, the isotopic composition (δ13C and δ15N), and the ratio of total organic carbon to total nitrogen (C/N ratios) for SPOM in the reservoir and its watershed across both dry and wet seasons using carbon and nitrogen isotope techniques. We also analyzed the sources of SPOM in the reservoir using the end-member mixing model. The results showed that the variation range in SPOM for δ13C was - 28.3 to - 21.8‰; for δ15N, it was 2.3 to 8.7‰; and the C/N ratios were 8.12 to 19.12. The variation range of δ13C for atmospheric particulate matter was - 20.0 to - 25.0‰; for δ15N, it was 2.3 to 11.9‰; and the C/N ratios ranged from 7.22 to 17.81. The main sources of carbon in the SPOM were atmospheric deposition and terrestrial C3 plants. The origins were significantly different between the wet and dry periods. Atmospheric nitrogen deposition and soil erosion were the primary sources of particulate nitrogen in the reservoir.

氮添加对宁夏荒漠草原植物初级生产力的影响机制

PDF HTML阅读 XML下载 导出引用 引用提醒 氮添加对宁夏荒漠草原植物初级生产力的影响机制 DOI: 10.5846/stxb202203100573 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目(2019YFE0117000);宁夏自然科学基金项目(2022AAC02010) Effects and mechanism of nitrogen addition on primary productivity in a desert grassland of Ningxia, China Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:许多研究探索了与全球变化相关的生态系统功能的变化,但对生态系统功能变化的机制与途径了解较少。初级生产力是生态系统功能的重要组分,但关于氮(N)添加下荒漠草原植物群落初级生产力如何变化以及变化机制尚未明确,N是否通过影响生物多样性来影响荒漠草原初级生产力？为此,本研究在荒漠草原开展了为期4年的N添加控制实验(2018-2021年),试验处理包括对照和4个N添加水平(5、10、20和40 g m-2 a-1),研究了N添加对荒漠草原物种多样性、功能多样性、初级生产力及其关系的影响。结果表明:(1)N添加处理(2018-2021年)改变了植物物种多样性及功能多样性,但年际间变化趋势不同。N添加处理第四年(2021年)荒漠草原植物功能多样性(Rao指数)、群落加权平均值-株高、功能均匀度和功能离散度均显著增加,而荒漠草原植物物种丰富度和Shannon-Wiener指数均显著降低。(2)N添加可以通过影响物种丰富度和功能多样性进而间接地促进荒漠草原初级生产力,但群落加权性状值-株高对初级生产力的影响是正效应,而物种丰富度和功能离散度对初级生产力的影响是负效应。(3)生物量比率假说更能解释荒漠草原植物群落初级生产力的变异。我们的研究表明了N添加主要通过改变群落内优势物种的功能性状来调节荒漠草原植物初级生产力。 Abstract:Many studies have explored changes in ecosystem functions related to global environmental changes, but little is known about the mechanisms and pathways behind the changes. Productivity is an important component of ecosystem functions. However, it is not clear how change and the mechanism of change of the primary productivity of desert grassland plant communities under nitrogen (N) addition; does N affect the productivity of desert grassland by affecting biodiversity? A manipulative N addition experiment located in the desert grassland has been conducted since 2018. The experimental treatment included five levels of N addition rate (i.e., control, 5, 10, 20 and 40 g m-2 a-1) with four replicates for each treatment. The plant functional traits, species richness and composition, and aboveground productivity were determined. In addition, species diversity, functional diversity and community weighted average traits were calculated. The results showed that: (1) the functional diversity (Rao index), community weighted average-height (CWM-height), functional evenness and functional dispersion of the desert grassland increased significantly in the fourth year of N addition treatment (2021), while the species richness and Shannon-Wiener index of the desert grassland decreased significantly. (2) N addition could indirectly promote the primary productivity of desert grassland by affecting species richness and functional diversity, but the impact of CWM-height on the primary productivity was a positive effect, while species richness and functional dispersion had a negative effect on productivity. (3) The biomass ratio hypothesis could better explain the variation of the primary productivity of desert grassland communities. Our results indicated that N addition regulated the primary productivity of desert grassland mainly by altering the functional traits of dominant species within the community. 参考文献 相似文献 引证文献

Effects of Inhabiting and Life Patterns on the UV Spectral Properties of Small Mammalian Herbivores’ Urine

It is well known that avian predators can use prey excretions such as urine and feces to track their prey, and the urine and feces of small mammalian herbivores can reflect ultraviolet (UV) light and emit fluorescent light. There are still some debates as to whether UV visibility of small mammalian herbivores’ urine is used as a hunting cue by avian raptors. Some studies in Europe have demonstrated that diurnal raptors are capable of utilizing these cues to target key prey species. However, researchers in Australia have argued that raptors do not use the UV visibility of urine while hunting. To our knowledge, there are no reports from Asia concerning the ultraviolet spectral characteristics of small mammal herbivores’ urine. This study examined the UV spectral properties of urine from 6 small mammal herbivores species by comparing the UV reflectance and fluorescence spectra of urine from small mammalian herbivores living in plateau meadows, plateau shrubs, open marshland, farmland, and semi-desert grassland in China. In addition, we compared the UV spectral properties of urine from ground-dwelling species of rodents and subterranean species to determine whether ultraviolet visibility of small mammal herbivores’ urine could be used as a visual signal by Asian vole-eating raptors. The results showed that: 1) the SC370 values of urine from four small mammal herbivores species were ordered as plateau pika (plateau meadow) > root voles (plateau bush) > reed voles (swampland) > Brandt’s vole (desert grassland); and 2) UV fluorescence peak intensity and the wavelengths of urine from ground-dwelling species (such as the root vole, plateau pika, or Brandt’s vole) were significantly higher than those of subterranean-dwelling species (mandarin vole and plateau zokor). These results indicate that UV visibility of small mammal herbivores’ urine may act as a visual cue for raptors.

黄土高原草地植物多样性与群落稳定性的关系及其驱动因素

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土高原草地植物多样性与群落稳定性的关系及其驱动因素 DOI: 10.5846/stxb202203010475 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 黄土高原干旱胁迫下白羊草根系分泌物介导的土壤氮转化机制项目（42177449）；陕西省基础研究计划项目（2021JM-605） Relationship between grassland plant diversity and community stability and its driving factors on the Loess Plateau Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:植物多样性对维持生态功能的稳定发挥具有重要作用。以黄土高原不同植被带草地为研究对象，基于野外调查和实验分析，探究黄土高原不同植被带草地植物多样性与群落稳定性特征和二者之间的关系以及影响因素。结果表明：黄土高原草地群落结构特征（地上生物量、地下生物量）与植物多样性具有明显的纬度分布格局，草地植物多样性和生物量均表现出自东南向西北沿森林草原带-森林带-草原带-草原荒漠带逐渐递减趋势。森林草原带草地植物多样性和群落稳定性显著高于森林带、草原带和草原荒漠带；植物多样性与群落稳定性之间存在显著正相关关系，可以作为衡量群落稳定性的指标，其稳定性大小表现为森林草原带 > 森林带 > 草原带 > 草原荒漠带。降雨量是影响植物多样性和群落稳定性的主要因素，并通过改变土壤含水量影响群落稳定性。研究结果揭示了草地植物多样性与群落稳定性之间的关系及驱动机制，为维持黄土高原草地生态系统的群落稳定性提供了科学依据。 Abstract:Plant diversity plays an important role in maintaining the stability of ecological functions. Based on field investigation and empirical analysis, this study took the grassland in different vegetation zones of the Loess Plateau as the research object, explored the characteristics of plant diversity and community stability, assessed the relationship between the two indicators, and further revealed the essential drivers that affected the relationships. The results showed that the characteristics of community structure (aboveground biomass, underground biomass) and plant diversity (richness, diversity and evenness) in grassland on the Loess Plateau had an obvious latitudinal distribution pattern, and the diversity and biomass of grassland plant showed the following trend from southeast to northwest:forest steppe belt > forest belt > grassland belt > desert grassland belt. The plant diversity and community stability of grassland in forest steppe belt were significantly higher than those in the other belts; There was a significantly positive correlation between plant diversity and community stability, suggesting that the plant diversity could be used as an index to estimate the stability.The order of stability was forest-steppe belt>forest belt>steppe belt>steppe desert belt. Rainfall was the main factor that influenced plant diversity and community stability, further affecting community stability by changing soil moisture content. The results of this study revealed the relationship between grassland plant diversity and community stability and the underlying driving mechanism, which provided a scientific basis for maintaining the community stability of grassland ecosystem on the Loess Plateau. 参考文献 相似文献 引证文献

基于多特征融合与无人机高光谱的荒漠草原退化物种分类

Accurate spatial distribution of grassland degradation indicator species is of great significance for grassland degradation monitoring. In order to realize the intelligent remote sensing grassland degradation monitoring task, this paper collects remote sensing data of three degradation indicator species of desert grassland, namely, constructive species, dominant species, and companion species, through the UAV hyperspectral remote sensing platform, and proposes a multi-feature fusion (MFF) classification model. In addition, vertical convolution, horizontal convolution, and group convolution mechanisms are introduced to further reduce the number of model parameters and effectively improve the computational efficiency of the model. The results show that the overall accuracy and kappa coefficient of the model can reach 91.81% and 0.8473, respectively, and it also has better classification performance and computational efficiency compared to different deep learning classification models. This study provides a new method for high-precision and efficient fine classification study of degradation indicator species in grasslands.

Transformer attention network and unmanned aerial vehicle hyperspectral remote sensing for grassland rodent pest monitoring research

The proliferation of grassland rodents has aggravated the degradation process of desert grassland. Additionally, it carries many viruses that threaten human and animal health. Accurate spatial distribution in grassland between rodent populations, vegetation, and bare soil is essential for developing rodent control measures. However, the traditional survey method of grassland rodent pest information is time-consuming and costly, and the period is long. In addition, satellite remote sensing cannot meet the accuracy requirements for the identification of grassland rat holes due to the limitation of spatial resolution. To realize intelligent grassland rodent infestation monitoring, this paper adopts an unmanned aerial vehicle hyperspectral remote sensing platform for data acquisition. Meanwhile, a transformer attention network (TAN) is proposed for grassland rodent infestation information extraction. The network adopts a two-stage feature extraction structure that effectively improves the classification performance of the model. In each stage, first, local features are extracted by a fixed convolution kernel to enhance detailed texture features; second, the extracted local features are refined using the contour convolution module to enrich feature information at the edges of the feature map; finally, the transformer attention module is used to focus on the global pixels, thus suppressing background information and enhancing effective information output. The results show that the overall accuracy (OA), average accuracy, and kappa coefficient of the TAN network can reach 97.71%, 98.44%, and 0.9538, respectively. Compared with several networks, such as two-dimensional CNN, three-dimensional CNN, HybridSN, and CTN, the OA values of the TAN network were improved by 2.59%, 2.45%, 2.94%, and 1.03%, respectively. The results of this study effectively improve the efficiency of the grassland rodent information survey and provide a solid theoretical basis for the investigation and statistics of grassland rodent infestation.

Two awn-development-related peptides, GAD1 and OsEPFL2, promote seed dispersal and germination in rice

In nature, seed dispersal and germination are crucial for plant survival and propagation. Elaborate mechanisms have evolved that enhance the success of these events ( Peart, 1981 Peart M.H. Further experiments on the biological significance of the seed-dispersal units in grasses. J. Ecol. 1981; 69: 425-436https://doi.org/10.2307/2259677 Crossref Google Scholar ; Bewley, 1997 Bewley J.D. Seed germination and dormancy. Plant Cell. 1997; 9: 1055-1066https://doi.org/10.1105/tpc.9.7.1055 Crossref PubMed Scopus (2151) Google Scholar ), and the widespread distribution of grass species has been associated with the evolution of these traits. Many of these mechanisms are associated with characteristics that are intrinsic to the seed, such as awn development, seed shattering, and germination ( Ntakirutimana et al., 2019 Ntakirutimana F. Xiao B. Xie W. Zhang J. Zhang Z. Wang N. Yan J. Potential effects of awn length variation on seed yield and components, seed dispersal and germination performance in Siberian Wildrye. Plants. 2019; 8: 561https://doi.org/10.3390/plants8120561 Crossref Scopus (11) Google Scholar ). Awns and/or other seed appendages often help mature seeds to disperse widely and germinate under various challenging environments ( Elbaum et al., 2007 Elbaum R. Zaltzman L. Burgert I. Fratzl P. The role of wheat awns in the seed dispersal unit. Science. 2007; 316: 884-886https://doi.org/10.1126/science.1140097 Crossref PubMed Scopus (441) Google Scholar ). For example, the awns of wheat react to a change in humidity and propel the seeds into moist soil to facilitate seed germination ( Elbaum et al., 2007 Elbaum R. Zaltzman L. Burgert I. Fratzl P. The role of wheat awns in the seed dispersal unit. Science. 2007; 316: 884-886https://doi.org/10.1126/science.1140097 Crossref PubMed Scopus (441) Google Scholar ). It has also been shown that awn length has a remarkable correlation with seed germination in some grass species ( Ntakirutimana et al., 2019 Ntakirutimana F. Xiao B. Xie W. Zhang J. Zhang Z. Wang N. Yan J. Potential effects of awn length variation on seed yield and components, seed dispersal and germination performance in Siberian Wildrye. Plants. 2019; 8: 561https://doi.org/10.3390/plants8120561 Crossref Scopus (11) Google Scholar ; Liu et al., 2018 Liu W. Wang T. Zhang S. Ding L. Wei Z. Grazing influences Stipa breviflora seed germination in desert grasslands of the Inner Mongolia Plateau. PeerJ. 2018; 6: e4447https://doi.org/10.7717/peerj.4447 Crossref Scopus (9) Google Scholar ). However, it is not known whether the pathways that promote awn development and regulate seed germination rate are linked or whether rice awns contribute to successful seed germination in nature.

Woody plant encroachment reduces density of most grassland specialists in a desert grassland but has limited influence on nest survival

AbstractWoody plants are proliferating in grassland ecosystems worldwide, altering distributions and demography of many imperiled species. The transition from grassland to shrubland is especially prevalent in semiarid regions, but the influence of woody plant encroachment (WPE) on birds that breed in desert grasslands is poorly understood, which reduces the potential for developing effective conservation actions for this imperiled group. During 2013–2015, we surveyed breeding birds on 140 10-ha plots in southeastern Arizona, USA, that spanned a gradient of encroachment (0–37% cover) by Prosopis (mesquite), which has invaded grasslands worldwide. We evaluated the effect of WPE on density, nest placement, and nest survival at 3 spatial scales (within 1.5 m and 5 m of the nest and at the 10-ha plot) for common species and 3 species groups: obligate grassland specialists (n = 7 species), facultative grassland specialists (n = 17), and species not typically associated with grasslands (n = 42). Density of the obligate species group decreased by 30% across the gradient of shrub (0.5–2 m tall) cover and by 23% across the gradient of tree (&amp;gt;2 m tall) cover. For 3 of 4 obligate species, density decreased by ≥50% when tree cover increased from 0 to 15%. In contrast, density of the facultative species group nearly tripled as tree cover increased from 0 to 22%. Obligate species placed nests 3.5 times farther from trees than facultative species (51.9 vs. 14.8 m). WPE influenced nest survival for 2 species but effects were inconsistent across spatial scales: nest survival of Grasshopper Sparrow (Ammodramus savannarum) decreased with increasing cover of trees on plots and shrubs within 5 m of the nest, and nest survival of Mourning Dove (Zenaida macroura) increased with increasing cover of shrubs on plots. Our results demonstrate that many grassland obligates are affected adversely even by small increases in woody cover. Consequently, restoration efforts should focus on early stages of WPE (i.e., cover &amp;lt;10% and shrubs &amp;lt;2 m tall) when removal of woody plants is more effective and less expensive relative to later stages.

Scale effect of climate factors on soil organic carbon stock in natural grasslands of northern China

Changes in grassland soil organic carbon stock (SOCS) may significantly affect the regional climate and carbon cycle of terrestrial ecosystems. However, how the impact of climate factors on SOCS and the dominant climate factors are regulated by the area scale of grasslands remains unclear. To understand the scale effects of climate on SOCS and how to accurately estimate SOCS at different scales, three area scales were defined by extending grassland types on the basis of meadow, typical and desert grasslands (Scale I (average area 37.22 × 104 km2) included each of these three types of grasslands, Scale II (average area 74.45 × 104 km2) was achieved by a pairwise combination of these three types of grasslands. Scale III (area 111.67 × 104 km2) was an aggregate of these three types of grasslands), the relationship between climate factors (i.e., mean annual precipitation, mean annual temperature, annual maximum temperature, annual minimum temperature, mean annual ground temperature, mean annual humidity, annual sunshine duration, annual maximum depth of accumulated snow, and the number of snow-covered days) and SOCS at the three scales were explored in the grasslands of northern China. Our results indicated that the total SOCS in grasslands at the three scales was ordered as desert grassland < meadow grassland < typical grassland. Of the nine climate factors, mean annual precipitation, positively correlated with SOCS, was the most significant climatic factor for all three scales. The dominant climatic factors of the SOCS differed across grassland area scales (i.e., MAP and MAH for meadow grassland, AMAT, MAP, NSD, and MAH for typical grassland, MAP, NSD, MAH, AMAT, and ASD for meadow-typical grassland scale, MAP, MAT, and MAGT for typical-desert grassland scale, MAP and MAT for meadow-typical-desert grassland scale). The impact of climate factors on the SOCS decreased as the scale increased. It is essential to screen appropriate climate predictors according to a given area scale when assessing regional SOCS. Multiple climate factors are better predictors for accessing SOCS at a small scale. At a large scale, however, dominant climatic factors are predictors that are more efficient.

Impacts of different fencing periods and grazing intensities on insect diversity in the desert steppe in Inner Mongolia

For the past several decades, both species biodiversity and productivity of desert steppe have been reduced due to excessive use and climate factors. To counteract this, Chinese government has supported large-scale grassland ecological restoration programs since the year 2000. The policy needs a standard for the evaluation of the effects of such restorative measures on the grasslands after decades. Grassland insect diversity plays an important role in the maintenance of plant species and functional diversity. To understand the relation of grazing management and insect diversity, we use a complete two factor design, two fencing periods (3 or 7 years) and three grazing intensities (0, 6, or 12 sheep per ha), to examine the response of the insect diversity to fencing and grazing in desert steppe. We found almost no significant differences in either plant or insect species diversity between the sites fenced for 3 and 7 years, as the pressure of grazing increased, insect diversity decreased to a greater extent at 7-year enclosure sites than at 3-year sites. We recommend the most suitable grazing intensity for the sustainability of biodiversity of the desert steppe in Inner Mongolia is light grazing (8 sheep/ha 0.5 yr−1), and the most suitable fencing period is three years, which suggest that policies that remove livestock from the desert grassland for long periods (7 + years) are not beneficial for maintaining insect diversity, and heavy grazing lead ecological environment weaker and insect diversity decreasing. Thus, periodic livestock grazing is important in the design of management actions to preserve biodiversity.

Plant species richness on the Tibetan Plateau: patterns and determinants

Whether current hypotheses for geographic patterns of species richness (SR) have a strong explanatory power for the Tibetan Plateau (TP) with extreme climatic conditions remains unclear. In comparison with the classic ‘water–energy dynamics hypothesis', the unique climate factors (e.g. extreme low temperature and low oxygen partial pressure) on the TP likely significantly affect the spatial variation of SR. Here, we investigate geographic patterns and determinants of SR on the TP through a systematic field investigation. We systematically analyzed a total of 2013 plant communities covering 11 different vegetation types on the TP. To compare this SR with that of other sites across the globe, we compiled a global database containing information on 87 forest and 3660 grassland plots. The SR per 400 m2 in the forests and shrubs and that per 1 m2 in alpine grasslands and deserts was 62.76 (± 1.80 SE), 44.53 (± 7.57 SE), 16.84 (± 0.39 SE) and 3.62 (± 0.55 SE), respectively. The SR of forests and shrubs decreased with latitude and altitude, whereas that of alpine grasslands and deserts showed a unimodal pattern along the altitudinal gradient. Unique climate factors, such as extreme low temperature, mean diurnal temperature and oxygen partial pressure, act synergistically with water–energy dynamics and influence the spatial pattern of SR on the TP. Furthermore, the tree SR on the TP was lower than that of global tropical and subtropical broadleaf forests but higher than that of temperate conifer forests. Alpine meadows had a higher SR than other sites; however, the SR in alpine desert grasslands and alpine deserts was lower. Our findings provide novel insights into the mechanisms underlying the spatial variation in plant diversity, especially on plateaus and in high‐latitude regions. Our findings and the SR map with 1 km resolution provide important benchmarks for biodiversity conservation and may help to improve predictions of the effect of climate change on biodiversity.

Response of soil C-, N-, and P- acquisition enzymes to moisture pulses in desert grassland to shrubland state transition

Grassland-shrubland state transition causes profound effects on soil nutrients and microorganisms, yet little is known about how these soil characteristics are influenced by rainfall and litter changes during transition. Here, we examined water (high or low moisture pulse) and litter (grass or shrub) effects on these soil characteristics in grassland-shrubland mosaics consisting of desert grassland (DG), grassland edge (GE), shrubland edge (SE), and shrubland (SL) sites. The results showed that the transition of DG-GE-SE-SL significantly reduced soil moisture, total carbon (C), total nitrogen (N), total phosphorus (P), microbial biomass carbon, and microbial biomass nitrogen, revealing evident soil degradation during this transition. After applying water and litter, soil microbial respiration (SMR) and the activities of all enzymes were promoted to varying degrees among the sites. Specifically, SMR was promoted under a low moisture pulse but suppressed under a high moisture pulse along the transition from DG to SL. Two C-acquisition enzymes, cellobiohydrolase and β-1,4-glucosidase, became increasingly active from DG to SL. Another C-acquisition enzyme of β-1,4-xylosidase and an N-acquisition enzyme of leucine aminopeptidase showed the strongest preferences for low moisture pulses in SL. These results indicated that shrub encroachment retained certain microbes with an advanced ability to acquire to C and N from dry and infertile soil in SL. Although a P-acquisition enzyme of alkaline phosphatase showed a decreasing trend along the transition from DG to SL, similar like those C- and N- acquisition enzymes, it was not sensitive to varying moisture levels, suggesting that alkaline phosphatase was affected by other soil physicochemical properties rather than soil moisture. The joint analysis of soil extracellular enzymes and nutrients indicated that microbial biomass carbon played a more important role than other soil characteristics in determining soil extracellular enzyme activities along the transition from DG to SL. Future research on dissecting soil microbial communities is warranted to better understand the microbiological mechanisms behind these phenomena in the shrub encroachment process.