Effects Of Grazing Research Articles

Effects of Sheep Grazing and Nitrogen Addition on Dicotyledonous Seedling Abundance and Diversity in Alpine Meadows

Seedling is a crucial stage in the growth and development of plants, and the expansion and persistence of plant populations can be achieved through seed regeneration. Sheep grazing, fertilization, light, soil moisture, vegetation diversity and biomass, and litter all have potential impacts on species regeneration. We measured vegetation diversity, annual net primary productivity (ANPP), litter, ground photosynthetically active radiation (PAR), and soil moisture of alpine meadows under sheep grazing and nitrogen addition treatments, and studied their effects on the dicotyledonous seedling abundance and diversity using linear regression models (LMs) and structural equation models (SEMs). We found that sheep grazing reduced ANPP, increased vegetation diversity and PAR, and decreased soil moisture. Fertilization increased ANPP and litter, decreased vegetation diversity and PAR, but had no effect on soil moisture. Sheep grazing and fertilization both reduced the abundance of dicotyledonous seedlings, and simultaneously fertilization can reduce the diversity of dicotyledonous seedlings, while sheep grazing had no effect on the diversity of dicotyledonous seedlings. LMs showed that vegetation diversity, ANPP, and litter, rather than light and soil moisture, affected dicotyledonous seedling abundance and diversity. SEMs revealed that sheep grazing and fertilization indirectly influenced seedling regeneration through vegetation diversity rather than ANPP and litter. Our research will increase our understanding of the dicotyledonous plant regeneration process in alpine grasslands and facilitate the development of strategies for management and protection of alpine grassland.

Seasonal Grazing Does Not Significantly Alter the Particle Structure and Pore Characteristics of Grassland Soil

Seasonal grazing is a recognized and sustainable approach to livestock management, but there is still a lack of comprehensive research on its impact on soil structure. This study utilizes advanced scanning electron microscopy technology to quantitatively evaluate the long-term effects of seasonal grazing on grassland soil structure, focusing on soil pore distribution characteristics and particle size. The investigation offers a detailed visual representation of the arrangement of soil particles at a micro-level. In both grazed and ungrazed plots (NG), soil particles ranging from 0.005 to 0.05 mm and 0.075 to 0.25 mm in size were predominant, constituting 20% and 60%, respectively. In plots subjected to seasonal grazing (grazing in June and August, G68, and grazing in July and September, G79), micro-particles (0.002–0.005 mm) and particles sized 0.05–0.075 mm were significantly lower compared to NG. Scanning electron microscope (SEM) images demonstrate structural differences, with NG displaying a higher proportion of small to medium-sized particles, more small pores, and fewer large pores. Analysis of pore size and morphology reveals the prevalence of large pores in both grazed and ungrazed plots. Continuous grazing plots exhibit significantly higher proportions of large pores compared to NG, while seasonal grazing plots show no significant differences. Correlation analyses indicate associations between soil physicochemical properties, particle size, and pore structure. Total soil nitrogen (TN), total soil carbon (TC), and soil moisture positively correlate with 0.005–0.05 mm particle proportions, while EC is negatively correlated with 0.05–0.075 mm particles. This study enhances our understanding of the effects of grazing practices on soil structure and provides scientific evidence for sustainable land management.

Temporal niche partitioning among sympatric wild and domestic ungulates between warm and cold seasons

The coexistence of sympatric species with similar ecological niches has been a central issue in ecology. Clarifying the daily activity patterns of sympatric wild ungulates can help understand their temporal niche differentiation and the mechanisms of coexistence, providing information for their conservation. The Baotianman National Nature Reserve in northern China is rich in wild ungulates, but little is known about the daily activity patterns of wild ungulates in the area, making it difficult to develop effective conservation strategies. We studied five representative wild ungulates (i.e. forest musk deer, Chinese goral, Reeve’s muntjac, Siberian roe deer, and wild boar) of the region using camera-trapping data, focusing on the seasonal daily activity patterns and effects of seasonal grazing of domestic sheep, to reveal their coexistence based on temporal ecological niche differentiation. Comparative analyses of the seasonal daily activity showed that forest musk deer exhibited a single-peak activity in the warm season. Other ungulates exhibited multipeak activity. All five ungulates differed significantly in daily activity patterns. Notably, wild boar and Reeve’s muntjac showed high overlap coefficients between the cold and warm seasons. In both cold and warm seasons, the five wild ungulates and domestic sheep displayed low overlap in their daily activity rhythms potentially indicating temporal ecological niche differentiation. The results suggest that temporal isolation might be a strategy for wild ungulates to avoid domestic sheep and reduce interspecific competition, and that temporal ecological niche differentiation potentially promoted the coexistence among the studied sympatric ungulates. This understanding may provide new insights for the development of targeted conservation strategies.

A First Look at the Relationship Between Large Herbivore-Induced Landscape Modifications and Ixodes ricinus Tick Abundance in Rewilding Sites.

Background: While the influence of landscape and microclimatic conditions on tick populations is well-documented, there remains a gap in more specific data regarding their relationship to rewilding efforts with large herbivore activity. Objective: This pilot study, spanning from 2019 to 2021, explores the effects of naturalistic grazing by large semi-wild ungulates on tick abundance in the Milovice Reserve, Czechia. Methods: Tick collection was observed using flagging techniques at two distinct sites of rewilding area: one grazed, actively utilized by animals involved in the rewilding project, and one ungrazed, left fallow in neighboring areas utilized only by wild animals. Transects, each measuring 150 m in length and 5 m in width (750 m2), were established at these two sampling locations from March to September between 2019 and 2021. To minimize potential bias resulting from tick movement, a 300 m buffer zone separated the two sites. Data analysis employed a generalized estimating equations (GEE) model with negative binomial regression. The study assessed potential variations in tick abundance between selected transects, considering factors such as plant cover seasonality, temperature, and humidity. Results: During the collection periods, we gathered 586 live ticks, with 20% found in grazed areas and 80% in ungrazed areas. Notably, tick abundance was significantly higher in ungrazed areas. Peaks in tick abundance occurred in both grazed and ungrazed areas during spring, particularly in April. However, tick numbers declined more rapidly in grazed areas. Microclimatic variables like temperature and humidity did not significantly impact tick abundance compared to landscape management and seasonal factors. Conclusion: Rewilding efforts, particularly natural grazing by large ungulates, influence tick abundance and distribution. This study provides empirical data on tick ecology in rewilded areas, highlighting the importance of landscape management and environmental factors in tick management and conservation. Trophic rewilding plays a crucial role in shaping ecosystems and tick population dynamics in transformed landscapes.

Effects of macroalgae and sea urchin grazing pressure on zoantharians growth under laboratory conditions

In the context of ocean warming, thermophilic organisms such as zoantharians are expanding and altering shallow benthic habitats. Here, a four-month laboratory experiment was performed to examine the influence of three types of macroalgae morphotypes common in the Canary Islands (turf algae, Lobophora spp., and crustose coralline algae) on the growth of two zoantharian species, Palythoa caribaeorum and Zoanthus pulchellus. Additionally, the grazing effects of echinoids Diadema africanum and Paracentrotus lividus were assessed as facilitators of substrate colonization by means of controlling macroalgae cover. Colony and algal coverages were measured at the beginning, middle and end of the experiment, and increments were calculated. Results indicated a general decrease in zoantharian colony sizes in contact with different algal types in the absence of sea urchins. However, P. caribaeorum colonies showed significant growth in the presence of D. africanum, highlighting the ecological importance of sea urchins in zoantharian population proliferation and subsequent community modification. This study represents the first investigation into zoantharian-macroalgae interactions under controlled conditions.

Shifts in soil C stabilization mechanisms are linked to reindeer-induced changes in plant communities and associated fungi in subarctic tundra

Arctic tundra ecosystems store a significant proportion of the global soil organic carbon (C). However, warming-induced shrub encroachment and reindeer (Rangifer tarandus L.) grazing regimes promoting graminoid vegetation may strongly influence tundra soil C stability. Here, we studied how reindeer grazing intensity and experimental warming affect soil C stabilization in a tundra ecosystem. We hypothesized that under light grazing, persistent complexes formed by fungal necromass (FNM) and condensed tannins (CT) from shrub roots stabilize the soil C, whereas, under heavy grazing, the soil C stabilization is affected by glomalin-related soil proteins (GRSP) produced by arbuscular mycorrhizal fungi of graminoids. In addition, we expect warming to mediate grazing effects, diminishing the potential for C stabilization.Our results show no effect of grazing on stable C concentration, however, under light grazing the labile C concentration was higher. We found higher concentrations of chitin and tannins under light grazing, indicative of soil C stabilization potential through FNM-CT complexes. By contrast, we found more root ergosterol under heavy grazing, suggesting a high abundance of endophytes, usually melanized, and a slightly higher GRSP concentration. Warming did not cause changes in stable C concentration but was associated with changes in the soil chemical quality, pointing to a decrease of lignin, polypeptides, and polysaccharides.We conclude that different soil C stabilization mechanisms operate under light and heavy grazing pressures and that these mechanisms are closely linked to changes in the vegetation and the fungi typically associated with them.

Assessing Microbial Diversity in Páramo Soils (Multistrategy Analysis): Effects of Potato Farming and Livestock Grazing in Nevados National Natural Park, Colombia

High Andean Páramos are very fragile neotropical ecosystems. Moreover, biodiversity in these areas is threatened by the anthropic activities of agriculture, cattle raising, and mining and has been little studied. Changes associated with potato farming and livestock grazing on microorganisms of Páramo soil of the Nevados National Natural Park (Nevados NNP) were assessed by (1) determination of physical and chemical properties (physicochemical matrix) and enzymatic activities associated (enzymatic activity matrix) with different biogeochemical cycles (C, N, and P); (2) microbial community functional diversity via evaluation of functional groups associated with carbon, nitrogen, and phosphorus cycles using cultivation-dependent techniques (arable functional group matrix and most probable number matrix); and (3) microbial diversity using cultivation-independent techniques that employ the hypervariable V5–V6 region of the 16S rRNA gene and pyrosequencing (16S-454 genus matrix and 16S-454 OTU matrix). Four of the six evaluated matrices (physicochemical, enzymatic activities, most probable number, and arable functional groups) revealed significant differences according to land use. The strategy adopted by the arable functional group matrix, in which the diversity of nitrogen fixation, phosphate solubilization, and cellulolytic compounds was evaluated, showed the most significant impacts of the different factors (land use, season, and elevation), especially those caused by potato cultivation and livestock. These results indicate that the initial impacts of potato farming and livestock grazing on the microbial community in El Bosque Village are better detected by functional diversity analysis than by molecular analysis of the 16S rRNA gene V5–V6 variable region. The results may have been caused by the type of molecular marker used in the analyses and the type of agricultural practices used by peasant farmers, which affect the functional diversity of the soil community. Among these practices are the maintenance of fallow periods greater than 7 years between each potato crop and the small proportion of cattle in relation to the total land area of the village. As the findings can be interpreted as an indicator of the early impacts of potato cultivation and livestock on microbial diversity, the effects of implementing community management plans, applying agroecological models, retaining biocultural memory, and changing agrarian structure are relevant for mitigating future changes.

Sheep dung deposition disrupted the soil microbiome in degraded grassland but not in non-degraded grassland

Grazing is the most extensive land use in grassland worldwide, wherein the soil microbiome is known to support multiple ecosystem functions. Yet, the experimental impact of livestock grazing and dung deposits on the soil microbiome in degraded grassland remains poorly understood. We examined the effects of sheep dung depositions on the bacterial and fungal microbiome of two grasslands: non-degraded and degraded (long-term overgrazing) in northern China. Specifically, sheep dung was experimentally added to the soil and its effects on the soil microbial community were determined 3 months later (corresponding to livestock excreta deposited throughout the entire growing season of grassland, June to September). Our results showed that sheep dung additions showed negative effects on the soil microbiome of already degraded grassland, while with a diminished impact on the non-degraded grassland. In particular, dung deposition decreased soil microbial Shannon index, notably significantly reducing fungal diversity in degraded grassland. Moreover, sheep dung deposition modifies soil bacterial community structure and diminishes bacterial community network complexity. The alteration of soil pH caused by sheep dung deposition partially explains the decline in microbial diversity in degraded grassland. However, sheep dung did not alter the relative abundance and community composition of bacterial and fungal dominant phyla either in the non-degraded or in the degraded grassland. In conclusion, the short-term deposition of sheep dung exerted a detrimental influence on the microbial community in degraded grassland soil. It contributes new experimental evidence regarding the adverse effects of livestock grazing, particularly through dung deposition, on the soil microbiome in degraded grassland. This knowledge is crucial for guiding managers in conserving the soil microbiome in grazed grasslands.

Changes in size-dependent Chlorophyll a concentration and group-specific picophytoplankton abundance in short-term nutrient-addition experiments in the Equatorial Eastern Indian Ocean

To clarify the changes in phytoplankton community and influencing factors in short-term nutrient-addition experiments in the Equatorial Eastern Indian Ocean, we conducted three experiments (one in situ-like experiment, one on-deck experiment with deep seawater, and one on-deck experiment with surface seawater). Our findings indicate that when nutrients were added, there was a more significant increase in the chlorophyll a (chl a) concentrations of microphytoplankton (>20 μm) compared to those of nanophytoplankton (2-20 μm) and picophytoplankton (<2 μm). The chl a concentrations for phytoplankton <20 μm only exhibited significant increases in the on-board incubation of surface seawater collected at 1300 hr when grazing stress have likely been weak. In picophytoplankton, occasional increases in the abundances of Synechococcus were found, while the abundances of Prochlorococcus and eukaryotic picophytoplankton (Peuk) did not increase significantly. It results likely from the preference of grazing effect by herbivores and bottle effects. Additionally, the Prochlorococcus from 75 m was more adapted to weak light, thus its abundance sharply decreased when incubated under high light. We suggest that the nutrient effects have greater influence on microphytoplankton, but other factors, such as grazing and light, might contribute more to <20 μm phytoplankton. Furthermore, bottle effects should be considered when conducting incubation experiments.

Grazing increases the positive feedback of legumes while decreasing the negative feedback of grass

AbstractHerbivore grazing affects plant growth and community structure in grasslands. This effect could be directly through foraging and dung/urine return or indirectly through plant–soil feedbacks (PSFs). Addressing the grazing effect on the feedback of plants can explicate the causes of community changes in the grazing system. However, how grazing and PSF interact to affect plant growth remains unclear. Here, we conducted a classic PSF experiment. In the conditioning stage, two native plant species (a grass Bromus inermis and a legume Medicago sativa) were planted in the field with four simulated grazing treatments (ambient, mowing, dung/urine addition, and mowing + dung/urine addition) in a meadow grassland of northern China. In the feedback stage, B. inermis and M. sativa were planted in the soils (both unsterilized and sterilized) from each treatment in the field experiment. Plant biomass of M. sativa showed positive feedback while B. inermis showed negative feedback across all the simulated grazing treatments. Simulated grazing (mowing and dung/urine addition) increased the positive feedback of M. sativa, while decreasing the negative feedback of B. inermis. The addition of dung/urine to the soil was found to have a significantly stronger impact on plant growth feedback compared to the effect of mowing. Dung/urine addition enriches the soil with higher levels of available nitrogen and phosphorus. Our results suggested that legume plants should have positive PSFs while grass should have negative feedback, which might be amplified by grazing because of the dung/urine fertilization effect. Our study improves the understanding of PSF effects on plant growth and community change in grazed grassland.

The effect of livestock grazing on plant diversity and productivity of mountainous grasslands in South America - A meta-analysis.

Mountainous grasslands in South America, characterized by their high diversity, provide a wide range of contributions to people, including water regulation, soil erosion prevention, livestock feed provision, and preservation of cultural heritage. Prior research has highlighted the significant role of grazing in shaping the diversity and productivity of grassland ecosystems, especially in highly productive, eutrophic systems. In such environments, grazing has been demonstrated to restore grassland plant diversity by reducing primary productivity. However, it remains unclear whether these findings are applicable to South American mountainous grasslands, where plants are adapted to different environmental conditions. To address this uncertainty, we conducted a meta-analysis of experiments excluding livestock grazing to assess its impact on plant diversity and productivity across mountainous grasslands in South America. In alignment with studies in temperate grasslands, our findings indicated that herbivore exclusion resulted in increased aboveground biomass but reduced species richness and Shannon diversity. The effects of grazing exclusion became more pronounced with longer durations of exclusion; nevertheless, they remained resilient to various climatic conditions, including mean annual precipitation and mean annual temperature, as well as the evolutionary history of grazing. In contrast to results observed in temperate grasslands, the reduction in species richness due to herbivore exclusion was not associated with increased aboveground biomass. This suggests that the processes governing (sub)tropical grassland plant diversity may differ from those in temperate grasslands. Consequently, further research is necessary to better understand the specific factors influencing plant diversity and productivity in South American montane grasslands and to elucidate the ecological implications of herbivore exclusion in these unique ecosystems.

Can livestock grazing dampen density‐dependent fluctuations in wild herbivore populations?

Abstract Conservation policy for the high mountains of Asia increasingly recognises the need to encompass large multi‐use landscapes beyond the protected area network. Due to limited long‐term research in this region, our understanding of even fundamental processes, such as factors regulating large mammal populations is poor. Understanding the factors that regulate animal populations, especially those generating cyclicity, is a long‐standing problem in ecology. Long‐term research across multiple taxa (mainly from Europe and North America) has focussed on the relative roles of food and predation in generating cyclicity in population dynamics. It remains unclear how trophic interactions that are influenced by anthropogenic stressors can affect population dynamics in human‐modified landscapes. We present a 10‐year study to compare the effects of livestock grazing on density‐dependent dynamics in two populations of bharal, Pseudois nayaur, in the Himalayas. We combine this with a mechanistic understanding of whether density dependence in these two sites acts predominantly by affecting adult survival or recruitment. We compared and quantified density dependence in the bharal population by fitting Bayesian Gompertz state‐space models. We found evidence for negative density dependence which indicates possible cyclic dynamics in the bharal population of the site (Tabo) with low livestock density. The population dynamics of this site were driven by recruited offspring—with a 2‐year density‐dependent lag effect—rather than adult survival. In the site with high livestock density (Kibber), this density dependence was not detected. We postulate the potential role of excessive grazing by livestock in affecting offspring recruitment, thereby affecting the bharal population in Kibber. Synthesis and applications: Our results suggest that conservation action to facilitate wild herbivore population recovery, such as the development of protected areas and village reserves, needs to account for density‐dependent regulation. Sites with trophy hunting require continuous monitoring to understand the effects of density dependence so that appropriate hunting quotas can be formulated.

Best management practices for winter care of the cow herd – confinement versus open grazing

The objective of this study was to evaluate whether the effects of winter grazing or confinement for winter care of beef cows in Iowa would have any impact on the physical condition of the cow or the calf born to the cow in spring.  It appears that where feedstuff quality is similar between scenarios, there was no difference.  

Effects of grazing on functional diversity along secondary succession in a tropical dry forest (Caatinga, Brazil)

AbstractAimLivestock production is among the main anthropogenic disturbances in seasonally dry tropical forests. However, its effects on plant functional composition in dry forests is poorly understood. Our goal was to analyze the variation in both functional composition and functional diversity of plant communities under goat grazing and at different ages of fallow in a tropical dry forest.LocationBrazilian dry forest (Caatinga) in Rio Grande do Norte State, northeastern Brazil.MethodsWe measured the height, leaf area, and specific leaf area of all shrub‐tree and herbaceous species along a gradient of stocking rate, years of grazing, and age of fallow. Additionally, we quantified the foliar contents of nitrogen, phosphorus, and tannins in the tree shrub layer. We tested the effects of grazing and deforestation using linear mixed models.ResultsOur findings suggest that the functional diversity of plant communities in the Caatinga is not altered when goat grazing and secondary succession are examined independently. However, the interaction of both factors has affected the functional diversity, particularly in the herbaceous layer. Although grazing influenced specific traits in the shrub‐tree layer, the overall functional diversity remained unaltered by grazing, succession, or their interaction.ConclusionsGrazing does not interfere with the natural succession process nor diminish the functional diversity of plant communities in the Caatinga. Therefore, with appropriate management, grazing can coexist with the conservation goals of the Caatinga.

Distribution and abundance of herbivorous reef fishes on a barrier reef system in the Florida Keys and Dry Tortugas, Florida

Herbivorous reef fishes control algal growth and are critical for maintaining reef health. Grazing effects vary due to community composition, so a diverse herbivore community is important for preventing phase shifts from coral to algal-dominated reefs. However, herbivore communities and grazing effects vary spatially, resulting in non-uniform distribution of algal mitigation across the seascape. Therefore, understanding how habitat influences herbivore communities is essential for predicting the spatial distribution of these species' ecological services. This study used underwater visual surveys (n = 5455) to examine how habitat influences spatial patterns of herbivorous fish densities and species richness in the Florida Keys and Dry Tortugas, Florida. Herbivorous fishes were ubiquitous, and communities were dominated by small herbivores such as damselfishes (Pomacentridae), gobies (Gobiidae), surgeonfishes (Acanthuridae), and small- to medium-bodied parrotfishes (subfamily Scarinae). A suite of factors influenced herbivorous fish communities but boosted regression tree results showed that habitat relief, depth, and spatial location within the Florida Keys and Dry Tortugas were the most important factors. In general, herbivore occurrence, density, and species richness increased as percent of low relief hardbottom habitat (<0.2 m high) decreased. In addition, density and occurrence of herbivores generally increased at shallower depths. Spatial location influenced the density of herbivores with potential hotspots predominantly located in the Upper Keys and the Dry Tortugas Bank. These data provide a valuable understanding of the spatial distribution of herbivorous reef fishes, and aid management decisions regarding the protection and sustainability of herbivore resources and the ecosystems that rely on them.

Effects of Grazing on vegetation in the Gobi desert region of Mongolia

Mongolia is a massive, semi-arid country in Central Asia with a huge territory of 1,500,000 km2, with rangeland making up around 75% of the country's territory. These rangelands have supported herders and grazing animals for millennia. The transition from nomadic to stationary livestock husbandry in Mongolia’s rangeland has resulted in major changes in vegetation communities due to increased livestock numbers. The primary objective of this study is to examine the impacts of grazing on the vegetation of rangelands in the desert steppe ecosystem. The purpose of this study is to examine the impacts of livestock grazing by measuring vegetation standing crop biomass, vegetation cover, and species' richness. The study was carried out in Khanbogd soum (district), Umnugovi aimag, the southern province of Mongolia. To assess the grazing impact, we sampled fourteen winter camps of herders who are members of the four herder groups, who were located at 1000 m and 2000 m from each. In total, we sampled 28 plots in two consecutive years. Our results indicate that aboveground biomass, cover, and species' richness did not differ with increasing distance from winter camps. Similar grazing pressures were shown at 1,000 and 2,000 meters away from the winter camps as well.

Compositional and functional analysis of the bacterial community of Mediterranean Leptosols under livestock grazing

The composition and functioning of soil bacterial communities, as well as their responses to multiple perturbations, are not well understood in the terrestrial ecosystems. Our study focuses on the bacterial community of erosive and poorly developed soils (Haplic Leptosols) in Mediterranean rangelands of Extremadura (W Spain) with different grazing intensities. Leptosols from similar natural conditions were selected and sampled at two depths to determine the soil properties as well as the structure and activity of bacterial communities. As grazing intensified, the soil C and N content increased, as did the number and diversity of bacteria, mainly of fast-growing lineages. Aridibacter, Acidobacteria Gp6 and Gp10, Gemmatimonas, and Segetibacter increased their abundance along the grazing-intensity gradient. Firmicutes such as Romboutsia and Turicibacter from livestock microbiome also increased. In functional terms, the KEGG pathways enriched in the soils with moderate and high grazing intensity were ABC transporters, DNA repair and recombination proteins, the two-component system, and the degradation of xenobiotics. All of these proved to be related to stronger cell division and response mechanisms to environmental stressors such as drought, warming, toxic substances, and nutrient deprivation. Consequently, the bacterial community was affected by grazing, but appeared to adapt and counteract the effects of a high grazing intensity. Therefore, a clearly detrimental effect of grazing was not detected in the bacterial community of the soils studied.

Grazing effects on the relationship between plant functional diversity and soil carbon sequestration regulated by livestock species

Abstract Grazing exerts a profound influence on both the plant diversity and productivity of grasslands, while simultaneously exerting a significant impact on regulating grassland soil carbon sequestration. Moreover, besides altering the taxonomic diversity of plant communities, grazing can also affect their diversity of functional traits. However, we still poorly understand how grazing modifies the relationship between plant functional diversity (FD) and soil carbon sequestration in grassland ecosystems. Here, we conducted a grazing manipulation experiment to investigate the effects of different grazing regimes (no grazing, sheep grazing (SG) and cattle grazing (CG)) on the relationships between plant FD and soil carbon sequestration in meadow and desert steppe. Our findings showed that different livestock species changed the relationships between plant FD and soil organic carbon (SOC) in the meadow steppe. SG decoupled the originally positive relationship between FD and SOC, whereas CG changed the relationship from positive to negative. In the desert steppe, both SG and CG strengthened the positive relationship between FD and SOC. Our study illuminates the considerable impact of livestock species on the intricate mechanisms of soil carbon sequestration, primarily mediated through the modulation of various measures of functional trait diversity. In ungrazed meadows and grazed deserts, maintaining high plant FD is conducive to soil carbon sequestration, whereas in grazed meadows and ungrazed deserts, this relationship may disappear or even reverse. By measuring the traits and controlling the grazing activities, we can accurately predict the carbon sequestration potential in grassland ecosystems.

Clams on stilts: a phytoplankton bioassay investigating effects of wastewater effluent amendments and Corbicula fluminea grazing

Shallow-water habitats are being restored in the Sacramento-San Joaquin River Delta with the goal of enhancing phytoplankton production and food availability for higher trophic levels. However, elevated grazing pressure from the non-native freshwater clam Corbicula fluminea and localized depletions of dissolved inorganic nitrogen may limit phytoplankton biomass accumulation in restored habitats. To evaluate interactions between nutrients and grazing on phytoplankton productivity and biomass accumulation, Sacramento River water high or low in phytoplankton biomass was amended with wastewater effluent, presence of C. fluminea, or both, in 48 h in situ incubations. We measured changes in chl a concentration, phytoplankton community composition, and photosynthetic efficiency as well as carbon and nitrogen uptake rates as indicators of phytoplankton responses. Diatoms dominated phytoplankton communities before and after incubation. Chl a concentrations increased 0.7 and 7.4 times in the high and low phytoplankton biomass controls, respectively, and 4.5 and 14 times in the high and low phytoplankton biomass effluent-added treatments, respectively. In the clam treatments, chl a accumulation was suppressed to near zero regardless of effluent additions or initial phytoplankton biomass. In treatments with clams and effluent combined, phytoplankton photosynthetic efficiency was nearly 50% lower than in the effluent-only treatments, suggesting phytoplankton were stressed in the presence of clams. This experiment demonstrated that the presence of clams can prevent the accumulation of phytoplankton biomass, both directly by clam filtering and indirectly by depressing phytoplankton photosynthetic efficiency and rate of growth. We recommend that future wetland restoration projects promoting increased phytoplankton biomass assess clam settlement likelihood as well as nutrient availability.

Efecto del pastoreo en la composición y la diversidad florística durante el barbecho en El-Tarf, Argeli

In the El-Tarf region, located in northeastern Algeria, fallow lands are frequently used as grazing grounds for sheep flocks, where they are left all day with a significant grazing load. Limited studies conducted to assess the effects of grazing have yielded varied and sometimes contradictory results, thus underscoring the need for reliable local data. The study aims to assess the impact of grazing on the floristic richness, diversity, production, and chemical composition of fallow lands in the El-Tarf region (northeast Algeria). Measurements were taken during the optimal vegetation period from March to June over a period of 2 years (2019 and 2020). The experimental design included a single factor: grazing intensity (no grazing, moderate grazing, and intense grazing). The results indicated that grazing reduced floristic richness and diversity (Maximum Diversity, Shannon and Weaver Index, Evenness Index), but it did not have an effect on coverage. The non-grazed fallow land is richer, hosting 23 herbaceous species distributed among 8 botanical families, with the most represented being Asteraceae (39 %), followed by Poaceae (26 %). The Fabaceae, on the other hand, display a more modest representation, accounting for only 13 %.Grazing also decreased significantly the biomass and total aboveground herbaceous phytomass, with improvements noted in non-grazed conditions, recording values of 3.80 t.DM.ha-1 and 1.77 t.DM.ha-1, respectively. In addition, grazing had a significant impact on chemical composition, with the highest values recorded for moderate grazing, reaching 14.7 % for total nitrogen content and 11.66 % for mineral content.