Semi-arid Grassland Research Articles

Climate change drivers alter root controls over litter decomposition in a semi-arid grassland

Plant roots are the primary source of soil organic carbon (C) and critically support the growth and activities of microbes in the rhizosphere. Climate change factors may, however, modify root-microbial interactions and impact C dynamics in the rhizosphere. Yet, the direction and magnitude of interactive climate change effects, as well as the underlying mechanisms, remain unclear. Here we show evidence from a field experiment demonstrating that warming and precipitation changes strengthen root controls over litter decomposition in a semi-arid grassland. While warming and precipitation reduction suppressed microbial decomposition of root litter regardless of the root presence, precipitation increase stimulated litter decomposition only in the absence of roots, suggesting that plant competition for water constraints the activities of saprophytic microbes. Root presence increased microbial biomass but reduced microbial activities such as respiration, C cycling enzymes and litter decomposition, indicating that roots exert differential effects on microbes through altering C or water availability. In addition, nitrogen (N) input significantly reduced microbial biomass and microbial activities (respiration). Together, these results showed that alterations in soil moisture induced by climate change drivers critically modulate root controls over microbial decomposition in soil. Our findings suggest that warming-enhanced plant water utilization, combined with N-induced suppression of microbes, may provide a unique mechanism through which moderate increases in precipitation, warming and N input interactively suppress microbial decomposition, thereby facilitating short-term soil C sequestration in the arid and semi-arid grasslands.

NODULE CHARACTERISTICS OF THREE-YEAR-OLD CARAGANA MICROPHYLLA AND THEIR RESPONSES TO ENVIRONMENTAL CHANGES IN AN INNER MONGOLIA GRASSLAND

Aims Caragana microphylla widely spreads in Inner Mongolia grasslands as a dominant shrubby legume. Its nodule growth has been poorly addressed. Our objective is to examine nodule characteristics and their responses to different environmental factors to provide insights into their nitro-gen fixing and nitrogen cycling processes under future changing environments. Methods We conducted a field experiment in 2008 using open-top chambers at the Inner Mongolia Grassland Ecosystem Research Station of Chinese Academy of Sciences. We examined the number,weight and length of nodules of three-year-old C. microphylla individuals and their responses to nitro-gen addition,drought,water addition and elevated atmospheric CO2 concentration. Important findings Nodules were mainly distributed in lateral roots,and most had buff or brown color. Nodule shapes were diverse,being pyriform,globular,claviform,fusiform,and Y shaped. Root growth and nodule growth were significantly inhibited under the nitrogen addition treatment,resulting in roots being whitened and most nodules dead and black-brown. Drought depressed root nodulation,with mean length of nodules decreased significantly by 50.4% compared with that under normal water supply. Water addition stimulated root growth and nodule growth. Roots nodulated best under the com-bined treatment of water addition,elevated CO2 and non-nitrogen addition,with maximum mean length and weight of individual nodules and the maximum nodule weight per plant. Nodules in fibers relatively increased with increasing water supply. Nodule growth did not significantly respond to elevated CO2. Nodule number is more sensitive to environmental changes than nodule size,there are significant nitro-gen × water interactions on nodule number and weight per plant and the effects of three environmental factors on nodule growth are different. The negative effect of nitrogen is larger than the positive effects of water and elevated CO2. It is inferred that water is the major factor affecting the infection of rhizobia and the generation of nodules in this semiarid grassland ecosystem.

Photosynthetic carbon allocation to live roots increases the year following high intensity defoliation across two ecosites in a temperate mixed grassland

Livestock grazing is an important driver of the carbon (C) cycle in grasslands and could be a decisive factor determining whether grasslands are a net sink or source of C. However, short-term C dynamics in grassland ecosystems and its response to different grazing intensities remain unclear, especially under field conditions. Here we test the hypothesis that photosynthetic C allocation in the plant-soil system of grasslands is differentially affected by the intensity of grazing that occurred in the prior growing season. We studied the fate of new C assimilates, using a 13CO2 pulse-labeling technique, as they move from shoots to roots and soil in vegetation previously exposed to different defoliation (emulated grazing) intensities in two semiarid Mixed Prairie grassland ecosites having contrasting soil textures (sandy vs. loamy). Within 24 h after photosynthetic uptake, 34.5% of the labeled C was translocated out of shoots, with 21% of the labeled C found in the mineral soil. Plant communities treated with high intensity defoliation during the previous growing season had more of the newly fixed 13C translocate into live roots at both ecosites throughout the 25-day chase period, indicating a higher demand for photosynthetic C by the root system of heavily defoliated plants. Twenty-five days after labeling, 13C transfer into the top 30 cm mineral soil was consistently greater at the loamy (26% of total 13C remaining) than at the sandy ecosite (10.4% of 13C remaining). We conclude that conditioning with high intensity defoliation the prior growing season stimulated short-term C allocation to roots in these semi-arid grasslands. Although this response was independent of soil texture, more C was translocated belowground overall in the loamy ecosite. The effect of defoliation intensity and ecosite in regulating short-term C allocation in the plant-soil system in temperate grasslands should be incorporated into future models describing C cycling in grasslands when predicting C dynamics under different management strategies employing contrasting grazing intensities.

Stimulation of soil microbial functioning by elevated CO2 may surpass effects mediated by irrigation in a semiarid grassland

The functioning of microbial communities in response to elevated atmospheric carbon dioxide (eCO2) is one of the most important, but poorly understood, contributors to climate change feedbacks. The effect of soil moisture caused by eCO2 on soil microbial communities and functioning may be of high importance in water limited ecosystems. To address this knowledge gap, we measured the functional composition, structure, and functional processes of soil microbial communities under eCO2 and an irrigation treatment simulating water availability with eCO2 at two soil depths (0–5 cm and 5–15 cm) in a mixed-grass semiarid prairie. The overall functional diversity increased and the microbial composition and structure were significantly (P < 0.01) altered in response to eCO2 and irrigation treatments. A greater number of key functional genes involved in soil, i.e. carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling were stimulated under eCO2 than under irrigation treatment. Structural equation modeling (SEM) suggested that eCO2 significantly impacted soil microbial community structure by mediating both soil moisture and plant biomass, while irrigation influenced soil microbial community structure merely via regulation of soil moisture. Moreover, in this water-limited system, soil moisture mediated eCO2 effects on soil microbial functional structure were relatively more important than those mediated by plant activity. The present study further improves our understanding of how global climate change regulates soil microbial functional processes in a semiarid grassland ecosystem.

Rainfall-associated chronic N deposition induces higher soil N2O emissions than acute N inputs in a semi-arid grassland

Higher nitrogen (N) deposition and altered precipitation patterns are two important global change factors contributing to increasing atmospheric concentrations of greenhouse gas nitrous oxide (N2O). In most experiments manipulating global change factors, wet N deposition is simulated by acute N addition once or a few times per year, rather than chronic low N inputs associated to rainfalls as they occur in the field. Whether N deposition pattern (acute or chronic) matters for soil N2O emissions, and whether altered rainfall frequency and modified N deposition pattern have an interactive effect on soil N2O emissions, are still knowledge gaps. Here we used a full factorial design for a mesocosm experiment in a semi-arid grassland. The experimental factors included rainfall frequency (ambient number of rainfall events; +50% number of rainfall events; and -50% number of rainfall events), and N deposition pattern (no N deposition; acute N deposition with two N inputs; and chronic N deposition co-occurring with rainfall events). Our results showed that altered rainfall frequency had no effect on soil N2O emissions irrespective of N deposition pattern. In contrast, N deposition pattern matters for soil N2O emissions. As compared to no N addition, cumulative N2O emissions during the vegetation growing season were significantly increased by 36% for chronic N deposition, but not significantly for acute N deposition. The temporal dynamics of N2O fluxes also varied between acute and chronic N deposition. These findings suggest that acute N addition may underestimate the actual N deposition effect on N2O emissions in grasslands, and that N deposition pattern should be considered when building models of ecosystem-climate feedback.

Drought in maternal environment boosts offspring performance in a subordinate annual grass

Drought can induce shifts in plant species or functional group abundances, which may favor coexisting subordinate species at the expense of previous dominants. Within-generation and transgenerational phenotypic plasticity can be important mechanisms to shape species responses to drought. Although a handful of studies have already investigated transgenerational plasticity in the context of drought, they provided variable results, and usually focused on species that currently dominate communities.We performed pot experiments with Secale sylvestre, a typical subordinate species in semiarid grasslands of Central Hungary. We tested if this annual grass shows reduced growth or reproduction in response to drought, and whether drought in the maternal environment affects offspring performance.For both maternal and offspring generations, plant height, shoot biomass, flowering onset, and seed number showed no within-generation plasticity in response to drought, and drought only decreased the seed mass of mother plants. In contrast, we found strong transgenerational effects on the overall performance of progenies, which changed with offspring age. At an early life stage, shoots were shorter for the offspring of drought-treated mothers than for the progenies of control mothers. This difference turned in the opposite direction later, and tiller number was also greater for the offspring of drought-treated mothers. Furthermore, the offspring of drought-treated mothers had over two-times higher adult shoot biomass and seed production compared to the offspring of control mothers. These beneficial transgenerational effects may help S. sylvestre to gain dominance in sand grasslands following dry years that decrease the abundance of perennial grasses, a vegetation change often observed in these grasslands after droughts.Our study provides the first evidence for positive transgenerational plasticity in response to drought for a subordinate species, which may be adaptive when the suppression of dominant species in the offspring environment is predictable from drought in the maternal environment.

Satellite estimates and subpixel variability of rainfall in a semi-arid grassland

Uncertainties in satellite rainfall estimation may derive from both the local rainfall characteristics and its subpixel variability. To study this issue, Micro Rain Radars and a rain gauge network were deployed within a 9-km satellite pixel in the semi-arid Xilingol grassland of China in summer 2009. The authors characterized the subpixel variability with the coefficient of variation (CV) and evaluated the satellite rainfall estimation for this semi-arid area. The results showed that rainfall events with a high CV were mostly convective with a small amount of rainfall. Spatially inhomogeneous rainfall was most likely to occur at the edges of small clouds producing rain. The performance of the TRMM (Tropical Rainfall Measuring Mission) 3B42V7 product for daily rainfall was better than that of the CMORPH (Climate Prediction Center morphing technique) and PERSIANN (Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks) products, although the TRMM product tended to overestimate rainfall in a lake area of the semi-arid grassland.摘要卫星估雨精度的不确定性受到当地降雨类型和像元内降雨非均匀性影响, 而结合这两个关键因素开展半干旱草原卫星估雨的研究有限. 2009年夏, 我们在中国锡林郭勒半干旱草原用多部微雨雷达和雨量计构建了9 km卫星像元降雨观测网, 观测了像元内降雨非均匀性(空间变异系数CV), 并评估了卫星估雨精度. 结果表明: (1) CV值受像元内平均降雨量, 降雨类型, 降雨云面积及移向等影响, 如高CV值的降雨过程大多为平均降雨量小, 对流性降雨过程, 降雨云边缘像元CV值较高; (2) TRMM 3B42V7 卫星估雨产品适用性较好, CMORPH和PERSIANN次之, 但TRMM 3B42V7易在半干旱草原湖泊处高估降雨.

Nonlinear carbon cycling responses to precipitation variability in a semiarid grassland

Changes in precipitation amount and variability would profoundly affect carbon (C) cycling in arid and semiarid grasslands. However, compared to the effects of precipitation amounts, little is understood about the impacts of precipitation temporal variability on terrestrial C cycling. To explore relationships between precipitation variability and C cycling processes and the underlying mechanisms, we conducted a 3-year field experiment and a 12-year model simulation, in which the constant seasonal precipitation amount was temporally manipulated with four and six levels of precipitation variability, respectively, in a semiarid grassland. Based on the manipulative experiment, we found various nonlinear relationships between C cycling processes and the coefficient of precipitation variability (Pcv), including a trinomial relationship for soil respiration (tipping point: 3 and 4.3), convex relationships for gross and net ecosystem production (peak at 3.5) as well as belowground biomass (peak at 4) and a nonlinear negative relationship for ecosystem respiration (peak at 2.5). Such relationships were regulated by seasonal averaged soil water content (SWC), early-growing season precipitation amount, soil inorganic nitrogen availability (SIN), and both SWC and SIN, respectively. However, these results from the manipulative experiment did not match those from the model simulation, in which ecosystem C cycling processes, dominated only by SWC responses, showed positive linear responses to Pcv. Our results mirror that the nonlinear responses of grassland C cycling to precipitation variability as regulate by SWC and SIN should be incorporated into models to forecast future ecosystem shifts under climate change.

Fungus-bacterium associations are widespread in fungal cultures isolated from a semi-arid natural grassland in Germany.

We report on a study that aimed at establishing a large soil-fungal culture collection spanning a wide taxonomic diversity and systematically screening the collection for bacterial associations. Fungal cultures were isolated from soil samples obtained from a natural grassland in eastern Germany and bacterial associations were assessed by PCR-amplification and sequencing of bacterial 16S rRNA. In addition, intraspecies genetic diversities of a subset of the isolated species were estimated by double-digest restriction associated DNA sequencing. A total of 688 fungal cultures, representing at least 106 fungal species from 36 different families, were obtained and even though clonal isolates were identified in almost all fungal species subjected to ddRAD-seq, relatively high genetic diversities could be observed in some of the isolated species. A total of 69% of the fungal isolates in our collection were found to be associated with bacteria and the most commonly identified bacterial genera were Pelomonas, Enterobacter and Burkholderia. Our results indicate that bacterial associations commonly occur in soil fungi, even if antibiotics are being applied during the isolation process, and provide a basis for the use of our culture collection in ecological experiments that want to acknowledge the importance of intraspecies genetic diversity.

Annual Net Primary Productivity of Different Functional Groups as Affected by Different Intensities of Rainfall Reduction in the Semiarid Grasslands of the Gauteng Province in South Africa

Rainfall variability is expected to change the soil water regime thereby impacting negatively on rangeland species composition, productivity and ecosystem services. The aim of this study was to assess the impact of different intensities of rainfall reduction (RR) on vegetation annual net primary productivity (ANPP). Twenty 7 × 7 m experimental plots with different intensities of RR structures consisting of transparent acrylic bands were built on a natural grassland. The interspaces between acrylic bands varied in size to intercept different intensities of ambient rainfall (0, 15, 30 and 60%) as RR treatments, with each RR treatment replicated five times in a complete randomised block design. A fixed 1 m2 quadrat was marked at the centre of each plot and the ANPP within the quadrats was determined by harvesting the quadrant at the end of the growing season. Generally, as compared to the control (ambient rainfall intensity) the overall grass ANPP (P &gt; 0.05) showed resilience to lower and moderate intensities of (15 and 30%) RR, but at a severe intensity of RR (60%) the ANPP was significantly reduced. Compared to the control the percentage contribution of grasses towards the overall ANPP increased at a lower intensity of RR (15%). In contrast, the percentage contribution of forbs towards the overall ANPP significantly reduced at lower intensity of RR. Within the grass species, however, those grasses that decrease when the veld is undergrazed or overgrazed (decreaser grass species) showed resilience at lower intensity (15 and 30%) of RR, while at a severe intensity of RR the ANPP of decreaser grasses were significantly reduced (1841 vs. 220 kg DM/ha). Those grasses that increase with undergrazing or overgrazing (increaser I or increaser II grass species) recorded a higher ANPP at moderate intensity of RR (30% RR) than at a higher intensity of RR, while the difference between 60% RR and 0% RR in terms of increaser grasses ANPP were not significant (P &gt; 0.05) (650 kg DM/ha). Up to 88% reduction in ANPP were recorded for decreaser grass species at severe intensity of RR as compared to the control the corresponding reduction in ANPP noted for increaser grasses were relatively less (up to 56% reduction in ANPP at 60% RR vs. 0% RR). Generally, the overall ANPP yield of the semiarid grassland in Gauteng province showed resilience to a low intensity of RR (15% RR) and moderate intensity of RR (30% RR) partly due to a shift in the species composition of grasses from decreasers to increasers ecological groups, as well as due to a decrease and an increased contribution of forb functional groups at a lower and moderate intensity of RR, respectively.

BIOLOGY AND ECOLOGICAL ADAPTATIONS OF BLACKBUCK (ANTILOPE CERVICAPRA): A REVIEW

Blackbuck is the existing members of genus Antilope which is most elegant and graceful among all Antelopes of Asia with distinct sexual dimorphism. Blackbuck show endemism in Pakistan, Nepal and India occupying mainly the semi-arid grassland areas. The name of species attributes towards the dark brownish to blackish coat color of male species. While female and the young ones are tawny or yellow. Chin undersides of legs and chest are white in both male and female individuals. Males have whorled horns with 79cm length with absence in females. The average body length of this animal is 100-150cm with the tail length of 10-17cm. The average body weight for male is 20-57kg and for female 19-33kg. Thin grassy forests, open and semi-desert areas are good habitat for it. Being diurnal and herbivorous, it acts as both grazers and browsers. It is the fastest animal with an average speed of 80km/h. It remains reproductively functional whole year. Reproductive disorders including dystocia and different infectious diseases due to ectoparasites, endoparasites, bacteria and viruses affect these species. Habitat loss, stress, illegal killing and genetic troubles cause the species to be ‘Extinct in the Wildlife’ in Pakistan so conservation strategies are underway for species protection. It is indispensable for zoologists and conservational biologists to observe the species for its conservation and confronting threats. Review article highlighted necessary information about species, which will clear the way for further research on species.

The Development of Anxiety and Exploration in Two Species of the African Striped Mouse Rhabdomys.

Genes and the environment interact to produce complex, environmentally relevant behaviors. We tested whether the behavior of two sister species of striped mice originating from different habitats (semi-arid Rhabdomys pumilio and grassland R. bechuanae) are modulated by the early social rearing environment. We cross-fostered pups between the species, and at adulthood tested their exploratory behavior and anxiety in open field and novel object tests, and a plus maze. We expected that the early social rearing environment would alter the phenotype of both species. Regardless of treatment, R. bechuanae were more exploratory and slightly less anxious than R. pumilio. However, fostered individuals of both species showed no changes in exploratory and anxiety responses. Thus there may be a genetic influence on behavioral development, or the early rearing environments of R. pumilio and R. bechuanae are not sufficiently different to alter behavior.

Soil engineering by ants facilitates plant compensation for large herbivore removal of aboveground biomass.

The interplay between top-down and bottom-up processes determines ecosystem productivity. Yet, the factors that mediate the balance between these opposing forces remain poorly understood. Furthering this challenge, complex and often cryptic factors like ecosystem engineering and trait-mediated interactions may play major roles in mediating the outcomes of top-down and bottom-up interactions. In semiarid grasslands of northeastern China, we conducted a large-scale, three-year experiment to evaluate how soil engineering by ants and plasticity in plants independently and jointly influenced the top-down effects of grazing by a ubiquitous herbivore (cattle) on aboveground standing biomass of the dominant perennial grass, Leymus chinensis. Herbivory had strong top-down effects, reducing L. chinensis AB by 25% relative to baseline levels without cattle or ants. In contrast, soil engineering by ants facilitated weak bottom-up effects in the absence of herbivory. However, in the presence of herbivory, soil engineering effects were strong enough to fully offset herbivore removal of aboveground biomass. This outcome was mediated by L. chinensis's plasticity in reallocating growth from below- to aboveground biomass, a result linked to additive effects of engineers and herbivores increasing soil N availability and engineering effects improving soil structure. Soil engineering increased soil N by 12%, promoting aboveground biomass. Herbivores increased soil N by 13% via defecation, but this increase failed to offset their reductions in aboveground biomass in isolation. However, when combined, engineers and herbivores increased soil N by 26% and engineers improved soil bulk density, facilitating L. chinensis to shift resource allocations from below- to aboveground biomass sufficiently to fully offset herbivore suppression of aboveground biomass. Our results demonstrate that soil engineering and trait-mediated effects of plant plasticity can strongly mediate the outcome of top-down and bottom-up interactions. These cryptic but perhaps ubiquitous processes may help to explain the long-debated phenomenon of plant compensatory responses to large grazers.

Moderately prolonged dry intervals between precipitation events promote production in Leymus chinensis in a semi-arid grassland of Northeast China

BackgroundClimate change is predicted to lead to changes in the amount and distribution of precipitation during the growing seasonal. This “repackaging” of rainfall could be particularly important for grassland productivity. Here, we designed a two-factor full factorial experiment (three levels of precipitation amount and six levels of dry intervals) to investigate the effect of precipitation patterns on biomass production in Leymus chinensis (Trin.) Tzvel. (a dominant species in the Eastern Eurasian Steppe).ResultsOur results showed that increased amounts of rainfall with prolonged dry intervals promoted biomass production in L. chinensis by increasing soil moisture, except for the longest dry interval (21 days). However, prolonged dry intervals with increased amount of precipitation per event decreased the available soil nitrogen content, especially the soil NO3−-N content. For small with more frequent rainfall events pattern, L. chinensis biomass decreased due to smaller plant size (plant height) and fewer ramets. Under large quantities of rain falling during a few events, the reduction in biomass was not only affected by decreasing plant individual size and lower ramet number but also by withering of aboveground parts, which resulted from both lower soil water content and lower NO3−-N content.ConclusionOur study suggests that prolonged dry intervals between rainfall combined with large precipitation events will dramatically change grassland productivity in the future. For certain combinations of prolonged dry intervals and increased amounts of intervening rainfall, semi-arid grassland productivity may improve. However, this rainfall pattern may accelerate the loss of available soil nitrogen. Under extremely prolonged dry intervals, the periods between precipitation events exceeded the soil moisture recharge interval, the available soil moisture became fully depleted, and plant growth ceased. This implies that changes in the seasonal distribution of rainfall due to climate change could have a major impact on grassland productivity.

Spatial patterns and ecological drivers of soil nematode β-diversity in natural grasslands vary among vegetation types and trophic position.

Understanding biogeographic patterns of community assemblages is a core objective in ecology, but for soil communities these patterns are poorly understood. To understand the spatial patterns and underlying mechanisms of β-diversity in soil communities, we investigated the β-diversity of soil nematode communities along a 3,200-km transect across semi-arid and arid grasslands. Spatial turnover and nested-resultant are the two fundamental components of β-diversity, which have been attributed to various processes of community assembly. We calculated the spatial turnover and nested-resultant components of soil nematode β-diversity based on the β-partitioning framework. Distance matrices for the dissimilarity of soil nematode communities were computed using the 'Sørensen' method. We fitted negative exponential models to compare the distance decay patterns in nematode community similarity with geographic distance and plant community distance in three vegetation types (desert, desert steppe and typical steppe) and along the whole transect. Variation partitioning was used to distinguish the contribution of geographic distance and environmental variables to β-diversity and the partitioned components. Geographic distance and environmental filtering jointly drove the β-diversity patterns of nematode community, but environmental filtering explained more of the variation in β-diversity in the desert and typical steppe, whereas geographic distance was important in the desert steppe. Nematode community assembly was explained more by the spatial turnover component than by the nested-resultant component. For nematode feeding groups, the β-diversity in different vegetation types increased with geographic distance and plant community distance, but the nested-resultant component of bacterial feeders in the desert ecosystem decreased with geographic distance and plant community distance. Our findings show that spatial variation in soil nematode communities is regulated by environmental processes at the vegetation type scale, while spatial processes mainly work on the regional scale, and emphasize that the spatial patterns and drivers of nematode β-diversity differ among trophic levels. Our study provides insight into the ecological processes that maintain soil biodiversity and biogeographic patterns of soil community assemblage at large spatial scales.

Spider Community Variability and Response to Restoration in Arid Grasslands of the Pacific Northwest, USA.

Simple SummarySpiders contribute greatly to biodiversity and play important roles in terrestrial food webs, yet we know very little about the types of spiders that live in semi-arid grasslands in the Pacific Northwest, USA. As interest in the conservation of biodiversity and restoration of these imperiled ecosystems grows, it is imperative that we not only describe spider communities (i.e., groups of interacting species) in these areas, but also investigate environmental factors that influence them, and how they respond to restoration. This information can help guide land managers as they design restoration and management plans. Our goals were threefold: (1) describe variability in spider communities in three semi-arid grasslands of the Pacific Northwest, (2) identify environmental variables that may influence spider communities, and (3) determine whether spiders or environmental variables differ between actively vs. passively restored sites. We found that spider communities varied greatly among three superficially similar locations and patterns corresponded to differences in elevation and cover of invasive grass, litter, biological soil crust, and flowering plants. We found no differences between spider communities in active and passive restoration treatments, indicating that if the primary goal of restoration is to increase biodiversity, additional factors must also be manipulated.Grassland restoration in North America has intensified but its impact on major invertebrate groups, including spiders, is unclear. We studied three grassland locations in the Pacific Northwest, USA, to (1) describe variability in spider communities, (2) identify environmental variables that may underlie patterns in spider communities, and (3) determine whether spiders and environmental variables differ between actively (removal of disturbances, then plant with natives) vs. passively restored sites (removal of disturbance only). We found spider richness, diversity, and composition differed among the three locations but abundance did not. Sites with more litter and invasive grass cover had more spiders while sites at higher elevation and with more forb and biological soil crust cover had increased spider richness and diversity. Spider community composition was associated with elevation and litter cover. Surprisingly, no spider community or environmental variables differed between actively and passively restored sites, except that litter cover was higher in passively restored sites. This study demonstrates that even in superficially similar locations, invertebrate communities may differ greatly and these differences may prevent consistent responses to active vs. passive restoration. If increasing biodiversity or the abundance of invertebrate prey are goals, then environmental factors influencing spider communities should be taken into account in restoration planning.

Soil properties and microbial abundance explain variations in N2O fluxes from temperate steppe soil treated with nitrogen and water in Inner Mongolia, China

Microbe-mediated soil nitrification and denitrification processes affect the variations in soil N2O fluxes. Researchers are concerned about how the abundances of nitrifiers and denitrifiers and the N2O fluxes from temperate semi-arid grassland soil vary as nitrogen (N) and water inputs vary. In this study, we report the results from a field experiment that was set up in a temperate semi-arid grassland area in northern China in May 2017. In August 2018, we collected samples to investigate how a range of physical, chemical and biological characteristics of soil, including the pH, moisture, dissolved organic carbon content (DOC) and available N content, N2O fluxes, and the abundances of ammonia oxidizers and denitrifiers in the soil, changed after N (4 g N·m−2·year−1 NH4NO3) and water (112.5 mm·year−1) were added over a period of 1 year. We analyzed the abundances of AOA amoA, AOB amoA, nirS, nirK and nosZ using quantitative PCR. We found that the soil N2O emissions were negatively affected by the water additions, but were not affected by the N additions. We also found that the AOA amoA and nosZ genes responded positively to the N additions. Watering had a positive effect on the nirS gene abundance, while N additions and water together intensified the effect of only water on the nirS gene abundance. The nirS gene abundance, soil pH, and DOC content explained 46.1%, 20.1% and 12.0% of the variations in the soil N2O fluxes, respectively. These results provide improved insights into how microorganisms affect N cycling, and may be used to help predict how soil N2O fluxes might change in the future, as N deposition and precipitation change.

Occupancy and diet of the Indian desert fox Vulpes vulpes pusilla in a Prosopis juliflora invaded semi-arid grassland

Encroachment by woody invasive plants has been recognized as a major driver of structural change in grasslands ecosystems. The impact of invasive plant-mediated changes on mammalian species from higher trophic levels is relatively less understood. This study aims to understand the impact of woody encroachment on the ecology of a relatively understudied mesopredator, the Indian desert fox Vulpes v. pusilla in a semi-arid saline grassland ecosystem in Western India. We examined the site occupancy of the Indian desert fox at the landscape level, and den site selection at the micro-habitat scale. We also examined the diet of desert foxes during winter and summer season. We found that at the landscape level the desert fox selects more open Suaeda saline habitats over dense invasive Prosopis juliflora dominated habitats. At the scale of the den, proximity to water and vegetation cover were the main drivers of den site selection. Similar to other arid zone foxes, insects, plant materials and small mammals were the main components of the diet of Indian desert fox. Given its selection of open habitats, invasive shrub encroachment is likely to result in a loss of habitat as well as resources for this species, potentially impacting on the conservation status of this already range-restricted species in India.

Soil nutrients and variation in biomass rather than native species richness influence introduced plant richness in a semi-arid grassland

Several different hypotheses account for the success of introduced species in new environments. Experimental studies show a negative native-exotic richness relationship (NERR), while observational studies suggest that this relationship is usually positive. Increased resource availability and environmental variation can also enable introduced species to establish in new environments. We conducted an observational study in a semi-arid grassland in the Thompson-Nicola District of British Columbia to examine the biotic and abiotic factors that account for variation in introduced and native species richness.In each of 12 sites, an 8 × 8 m area was set up, containing 64, 1-m2 plots. We identified and categorized plant species in each site into introduced and native species. We tested the relationship between introduced species richness and native species richness at the 1-m2 sampling grain and at sampling grains up to 64 m2. We also analysed the relationship between native and introduced species, and within-plot biomass, and between native and introduced species and variation in biomass. For a representative subset of four sites, we tested the relationship between introduced and native species richness and nitrogen, phosphorus and potassium.We found no NERR at the 1 m2 sampling grain, nor for the other sampling grains up to 64 m2. Introduced species richness increased with phosphorus and nitrogen availability, and was also positively related to biomass heterogeneity.Our results indicate that introduced species richness in these grasslands is likely influenced by phosphorus and nitrogen, and by variation in vegetation biomass, but not by native species. More non-native plants are likely to occupy nutrient-rich plots compared to nutrient-poor plots in these grasslands. Variation in biomass can leave gaps for the establishment of introduced species. These results should inform management considerations for the control of invasive species to optimize preservation of grasslands.

Effects of Phylogenetic Relatedness on Fluctuation-Dependent and Fluctuation-Independent Coexistence Mechanisms in Multispecies Communities.

AbstractEvolutionary relatedness may hinder stable coexistence due to similar niches and nonlinear responses to competition. The mechanisms driving stability may respond differently to phylogenetic distance. Related species may be synchronic (have similar demographic responses over time), affecting fluctuation-dependent mechanisms: the storage effect should destabilize coexistence, and relative nonlinearity should be stronger due to increased fluctuations in competition. We tested these hypotheses using invasion analysis based on a model parameterized for 19 plant species from a semiarid grassland. Although weakly, coexistence stability increased with phylogenetic distance. Stabilization through fluctuation-independent niche differentiation was stronger between distant relatives as a result of weaker competition. Synchronicity was higher between close relatives, having the expected negative effects on the storage effect's contribution to coexistence. Relative nonlinearity was strong at both ends of the phylogenetic relatedness gradient but not in the middle. This may be the result of different nonlinear responses between distant relatives and of stronger fluctuations in competition due to synchronicity between closer relatives. The effect of phylogenetic distance on coexistence was almost negligible when pairwise species were analyzed, in accordance with previous research. Phylogenetic distance became more important as more species interacted, however, suggesting that evolutionary relatedness may be influential in species-rich communities.