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Understanding the impact of agricultural land use on the soil prokaryotic communities in connected downslope sites is crucial for developing sustainable strategies to preserve ecosystem properties and mitigate agriculture's environmental impacts. In this study, we investigated topsoil samples collected at three time points in 2022 (March, June, and November) from two adjacent catenas, reaching from hillslope to floodplain. The catenas differed in land use (extensive grassland vs. extensive cropland) at the top and middle parts, while the floodplain remained an extensive grassland due to legal restrictions. Using quantitative real-time PCRs and metabarcoding, we assessed prokaryotic abundance and prokaryotic community composition. Results show higher bacterial abundance in the cropland-influenced floodplain part across all time points compared to the grassland-influenced floodplain part. Temporal dynamics revealed a progressive decrease in the shared prokaryotic communities of the floodplain parts, peaking at the summer sampling time point, indicating a significant influence of the respective management type of the agricultural sites over the bacterial and archaeal communities of the floodplain parts. Differential abundance analyses identified several nitrifying taxa as more abundant in the cropland-influenced floodplain. Upstream land use also influenced the prokaryotic network of the cropland-floodplain, with some cropland taxa becoming keystone taxa and altering network morphology, an effect not observed in the grassland-influenced floodplain. These findings suggest that upstream agricultural land use practices have exerted a long-term influence on the floodplain prokaryotic communities over the past three decades. Moreover, there is evidence suggesting that these prokaryotic communities may undergo a potential reset during winter, which requires further investigation. [ABSTRACT FROM AUTHOR]

Little research has been undertaken in Korean grasslands for approximately 40 years, despite their localized distribution and anthropogenic disturbances. To understand their structural characteristics and maintenance mechanisms, we investigated the grassland communities and their species diversity, interspecies interactions, and correlations between environmental factors and vegetation factor. Plant species richness was highest in grasslands subjected to unnatural fires (early seral stage) and lowest in grasslands with minimal disturbance, high altitude, and maintenance influenced by climatic factors (late seral stage). Furthermore, as succession progressed (early → mid → late seral stage), tall narrow-leaved grass communities and forb communities' abundance. Indicators distinguishing Korean grassland vegetation include Imperata cylindrica and Miscanthus sinensis, which are classified into eight vegetation communities. Species interactions were categorized into three groups, from early disturbance preference to, appearance of woody and late high– altitude adaptation. In addition, the number of communities increased at higher altitudes, steeper slopes, and lower vegetation heights. Thus, montane grasslands in Korea except for the vegetation is maintained by snowfall and strong winds, woody is expected to invade grassland, which could lead to the disappearance or permanent alteration of grasslands. [ABSTRACT FROM AUTHOR]

Spatial models are effective in obtaining local details on grassland biomass, and their accuracy has important practical significance for the stable management of grasses and livestock. To this end, the present study utilized measured quadrat data of grass yield across different regions in the main growing season of temperate grasslands in Ningxia of China (August 2020), combined with hydrometeorology, elevation, net primary productivity (NPP), and other auxiliary data over the same period. Accordingly, non-stationary characteristics of the spatial scale, and the effects of influencing factors on grass yield were analyzed using a mixed geographically weighted regression (MGWR) model. The results showed that the model was suitable for correlation analysis. The spatial scale of ratio resident-area index (PRI) was the largest, followed by the digital elevation model, NPP, distance from gully, distance from river, average July rainfall, and daily temperature range; whereas the spatial scales of night light, distance from roads, and relative humidity (RH) were the most limited. All influencing factors maintained positive and negative effects on grass yield, save for the strictly negative effect of RH. The regression results revealed a multiscale differential spatial response regularity of different influencing factors on grass yield. Regression parameters revealed that the results of Ordinary least squares (OLS) (Adjusted R2 = 0.642) and geographically weighted regression (GWR) (Adjusted R2 = 0.797) models were worse than those of MGWR (Adjusted R2 = 0.889) models. Based on the results of the RMSE and radius index, the simulation effect also was MGWR > GWR > OLS models. Ultimately, the MGWR model held the strongest prediction performance (R2 = 0.8306). Spatially, the grass yield was high in the south and west, and low in the north and east of the study area. The results of this study provide a new technical support for rapid and accurate estimation of grassland yield to dynamically adjust grazing decision in the semi-arid loess hilly region. [ABSTRACT FROM AUTHOR]

Aims: Livestock grazing is one of the most common utilization methods and exerts a significant effect on the carbon allocations between the above- and belowground components of a grassland ecosystem. The major aim of this study were to evaluate the proportions of 13C allocation to various C pools of the plant-soil system of a meadow steppe ecosystem in response to changes of stocking rate. Methods: In situ stable 13C isotope pulse labeling was conducted in a long-term grazing experiment with 4 stocking rate. Plant materials and soil samples were taken at eight occasions (0, 3, 10, 18, 31, 56 and 100 days after labeling) to analyze the decline in 13C over time, and their composition signature of 13C were analyzed by the isotope ratio mass spectrometer technique. Results: We found a significantly greater decline in assimilated 13C of shoot and living root for the heavily grazed swards compared to other stocking rates, with the highest relocation rate of 13C into soil C pool compared to other fractions. In addition, light grazing significantly allocated 13C assimilates in the belowground pool compared to other stocking rates, especially in the live root and topsoil C-pools. Conclusions: In this study, the effects of grazing on the carbon transfers and stocks within the plant-soil system of the meadow steppe were highly grazing pressure dependent. Plant-soil system in light stocking rate presented the highest C utilization efficiency, however, plants allocated more C to soil C pools with heavily stocking rate. [ABSTRACT FROM AUTHOR]

Purpose: Soil respiration (Rs) plays a crucial role in the terrestrial carbon cycle. We attempted to investigate how changes in water and nitrogen affect the Rs of grassland ecosystems through biotic and abiotic factors under the context of global change. Methods: We conducted a 4-year manipulative field experiment with a randomized complete block design in a 2 × 4 factorial consisting of two water addition levels and three nitrogen addition levels in a typical temperate grassland in China to explore the response of Rs to different water and nitrogen addition treatments in the growing season, and the potential factors controlling Rs were analyzed using structural equation modeling (SEM). Results: Water addition significantly enhanced the cumulative Rs in all years. The precipitation during the months of vigorous plant growth (May to July) was an important factor in determining the average Rs during the growing season. Nitrogen addition alone had no significant impacts on Rs except for short-term positive effects caused by low nitrogen addition (25 kg N ha−1 yr−1) during the period after nitrogen application in the first year. Although soil microbes and plant roots contributed to Rs, the main factors controlling Rs were still temperature and soil moisture. Conclusion: These findings indicate that water addition could promote Rs in semiarid grassland ecosystems. Changes in environmental factors could control Rs by affecting soil microorganisms and plant roots activity. [ABSTRACT FROM AUTHOR]

Silicon (Si) accumulation is known to alleviate various biotic and abiotic stressors in plants with potential ecological consequences. However, for dicotyledonous plants our understanding of Si variation remains limited. We conducted a comparative experimental study to investigate (1) interspecific variation of foliar Si concentrations across 37 dicotyledonous forbs of temperate grasslands, (2) intraspecific variation in foliar Si concentration in response to soil Si availability, the influence of (3) phylogenetic relatedness, and (4) habitat association to moisture. Foliar Si differed markedly (approx. 70-fold) across the investigated forbs, with some species exhibiting Si accumulation similar to grasses. Foliar Si increased with soil Si availability, but the response varied across species: species with higher Si accumulation capacity showed a stronger response, indicating that they did not actively upregulate Si uptake under low soil Si availability. Foliar Si showed a pronounced phylogenetic signal, i.e., closely related species exhibited more similar foliar Si concentrations than distantly related species. Significant differences in foliar Si concentration within closely related species pairs nevertheless support that active Si uptake and associated high Si concentrations has evolved multiple times in forbs. Foliar Si was not higher in species associated with drier habitats, implying that in dicotyledonous forbs of temperate grasslands high foliar Si is not an adaptive trait to withstand drought. Our results demonstrated considerable inter- and intraspecific variation in foliar Si concentration in temperate forbs. This variation should have pervasive, but so far understudied, ecological consequences for community composition and functioning of temperate grasslands under land-use and climate change. [ABSTRACT FROM AUTHOR]

In situ 13CO2 pulse labeling was conducted in temperate grasslands, managed by no grazing, rotational, or continuous overgrazing, to trace the allocation pattern and the dynamics of newly assimilated C into the plant-soil system. Forty-eight days after the labeling, the belowground 13C allocations under overgrazing were substantially lower than those under no grazing (55% for no grazing, 29% for rotational grazing, 36% for continuous grazing). Overgrazing reduced the relative amount of C incorporation into soil organic C (SOC). Overgrazing led to more C losses through shoot respiration (23%, 54%, 46% by no, rotational, and continuous grazing, respectively), but fewer losses via soil respiration (33%, 12%, 13% by no, rotational, and continuous grazing, respectively). Continuous grazing produced more C allocation to roots than rotational grazing (12% vs 4%), indicating that plants had stronger root C storage capacity under continuous than rotational grazing. The mean C residence time of the belowground rhizodeposits and C used for root respiration under rotational grazing (2.08 days) was longer than that under no grazing (1.47 days) or continuous grazing (1.37 days). Overgrazing decreased the C stocks in shoots but remained stable in roots. Meanwhile, overgrazing decreased the newly assimilated C allocation to belowground, creating a negative effect on C sequestration. Under overgrazing regimes, continuous grazing is more preferable in the investigated temperate grasslands than rotational grazing for C allocation and sequestration in soil. [ABSTRACT FROM AUTHOR]

Old fields are spreading in the world because of agriculture abandonment, and they show a persistence of exotic plant species with little recovery towards the original vegetation composition. Soil biota may also differ between old fields and native grasslands, but were comparatively less studied than plant communities, despite their importance in biogeochemical processes. Here we compared soil bacterial communities of exotic-dominated old fields with those of remnants of native grasslands in the Inland Pampa, Argentina, using the 16S rRNA gene amplicon sequencing approach. We also characterized plant communities, soil physico-chemical properties, and soil respiration. We expected more diverse soil bacterial communities, with higher heterogeneity, in remnant grasslands than in old fields because of a more diverse and more heterogeneous plant community. However, our results showed that soil bacterial communities had higher Shannon diversity in old fields than in remnant grasslands, but richness was not significantly different. Also we found different bacterial community compositions between grasslands even at a low taxonomic level. On the other hand, old fields harbored less heterogeneous bacterial communities than remnants, and bacteria and plant beta diversity were correlated. Despite contrasting plant and bacterial composition between old fields and remnant grasslands, soil physico-chemical properties were quite similar between grasslands. Overall, our results showed that bacterial communities in grassland soils were associated with changes in plant communities after agricultural abandonment. Plant-microbial feedbacks might regulate plant and soil bacterial community assemblage in old fields, yet further research is needed to demonstrate this potential feedback mechanism. [ABSTRACT FROM AUTHOR]

Background and aims: Woody plant encroachment is a phenomenon of global concern in drylands due to demonstrated reductions in livestock carrying capacity. However, shrubs are known to contribute to the development of patches of enhanced fertility that might offset any negative effects of increasing grazing. We measured soil physical and chemical characteristics within shrub and open patches across a gradient in livestock grazing to explore how the relative effect of shrubs might change with increasing grazing-induced disturbance. Methods: Soil carbon, nitrogen phosphorus and bulk density were measured within 92 shrub patches and their paired interspaces at five sites ranging from long-grazed to long-ungrazed in a semiarid grassland encroached by the N-fixing shrub Caragana microphylla. We used a combination of linear and structural equation modelling to test whether shrubs might buffer any negative effects of overgrazing on soils. Results: Shrub soils were more porous, and had more organic carbon, nitrogen and phosphorus than interspace soils. Within both microsites, however, soil bulk density increased, and soil organic carbon and nutrients declined, with increasing grazing intensity. Grazing reduced interspace plant cover and height and exacerbated the negative effects of bulk density on soil carbon, whereas shrubs had the opposite effect. The relative importance of shrubs for soil carbon and nutrients increased with increasing grazing intensity but collapsed under extreme overgrazing. Conclusions: These findings highlight the effect of grazing in promoting shrub dominance, which can also prevent grassland degradation. However, any positive effects of grazing collapsed when sites were severely overgrazed. [ABSTRACT FROM AUTHOR]

Background and aims: The development of fertile patches within an infertile matrix is a common phenomenon in drylands. Shrub-centered expansion of fertile islands is generally attributed to processes of sediment erosion and deposition, but there have been fewer studies of how litter might contribute to the development of fertile islands in semiarid shrub grassland. Methods: We quantified the capture of two tumble plant species (Cleistogenes squarrosa, Salsola collina; also known as tumble weeds) by shrubs across ten sites across 38,000 km2 of a semiarid grassland encroached by Caragana microphylla. Results: Tumble plants are plants that blow across the grassland propelled by strong winds. Both tumble plant species were found over extensive areas of semiarid grassland, and their distribution coincides with the distribution of Caragana microphylla. Biomass production of both tumble plants averaged 12.2 g m−2 (range: 1.0 to 25.0 g m−2) and litter accumulation (amount accruing from wind-blown plants) of both tumble plants was significantly greater beneath shrubs (94.5 ± 28.9 g m−2 mean ± SE) than in the interspaces (3.3 ± 1.4 g m−2). Most of the material collecting under Caragana microphylla comprised tumble plants. Increases in the area of Caragana microphylla patches did not correspond to greater tumble plant capture. However, the supply of tumble plants was the strongest predictor of capture within shrub hummocks, suggesting that tumble plant capture is source limited rather than sink limited. Our structural equation model indicates that increases in grass cover and height were indirectly and negatively associated with tumble plant capture by reducing the tumble plant supply. Contrary to prediction, shrub height and shrub patch area had no overall effect on the tumble plant capture. Conclusions: Overall, we maintain that the capture of tumble plants by shrubs is an important self-maintaining mechanism of shrub-encroached grasslands. Tumble plant abundance is predicted to increase with increasing surface human disturbance and aridity. Therefore, the "shrub-litter island" effect is likely to be an important mechanism for maintaining and promoting the encroachment of shrubs into semiarid grasslands. [ABSTRACT FROM AUTHOR]

While emissions of nitric oxide (NO), ammonia (NH3) and nitrous oxide (N2O) from grassland soils have been increasingly well constrained, soil dinitrogen (N2) emissions are poorly understood. However, N2 losses might dominate total gaseous nitrogen (N) losses. Knowledge on N losses is key for the development of climate-adapted management that balances agronomic and environmental needs. Hence, we quantified all gaseous N losses from a montane grassland in Southern Germany both for ambient climatic conditions and for a climate change treatment (+ 2 °C MAT, − 300 mm MAP). Monthly measurements of soil N2 emissions of intact soil cores revealed that those exceeded by far soil N2O emissions and averaged at 350 ± 101 (ambient climate) and 738 ± 197 µg N m−2 h−1 (climate change). Because these measurements did not allow to quantify emission peaks after fertilization, an additional laboratory experiment was deployed to quantify the response of NH3, NO, N2O, and N2 emissions in sub daily temporal resolution to a typical slurry fertilization event (51 kg N ha−1). Our results revealed that total N gas losses amounted to roughly half of applied slurry-N. Surprisingly, N2 but not NH3 dominated fertilizer N losses, with N2 emissions accounting for 16-21 kg or 31-42% of the applied slurry-N, while NH3 volatilization (3.5 kg), N2O (0.2-0.5 kg) and NO losses (0-0.2 kg) were of minor importance. Though constraining annual N2 loss remained uncertain due to high spatiotemporal variability of fluxes, we show that N2 losses are a so far overlooked key component of the N balance in montane grasslands, which needs to be considered for developing improved grassland management strategies targeted at increasing N use efficiency. [ABSTRACT FROM AUTHOR]

Aims: In natural ecosystems, plants generally promote the acquisition of nitrogen (N) through the input of carbon (C) into the soil. The present study aimed to clarify how changes in C input affect N uptake by plants.Methods: In situ 15N labeling ((15NH4)2SO4 and K15NO3) was performed in grazed and ungrazed Leymus chinensis grasslands located in Inner Mongolia, northern China. Clipping and shading treatments were used to reduce C allocation to roots by limiting photosynthesis because grazing can produce such similar effect through defoliation.Results: Grazing increased the allocation of photosynthate to roots and the relative biomass of Carex duriuscula but decreased the relative biomass of L. chinensis. Grazing decreased 15N-NH4+ recovery (grazed: 30.9% vs. ungrazed: 39.3%) but increased 15N-NO3− recovery (grazed: 26.9% vs. ungrazed: 17.6%), which may be due to changes in the NH4+/NO3− ratio and species composition. Clipping and shading reduced 15N recovery, mainly because they decreased C supply for N uptake by reducing photosynthesis.Conclusions: These findings indicate that the reduction of the C input to soil decreases 15N recovery by plants in temperate grasslands, which contributes to our understanding of the trade-off between C and N and grassland N cycles. [ABSTRACT FROM AUTHOR]

Aims: As global climate warms and atmospheric nitrogen deposition increases, plants are likely to respond by altering community composition, thus affecting the nutrient cycle. Although it is well-known that feedback between plants and soils is linked by nutrient resorption occurring during senescence, our understanding of how long-term warming and nitrogen deposition (> 10 years) influence nutrient resorption remains limited.Methods: In a desert grassland in northern China, we explored the effects of warming and nitrogen fertilization on leaf nutrient resorption for three dominant species during two hydrologically contrasting years (wet with 52% above the long-term mean precipitation of 222 mm, and dry with precipitation 16% below the mean), based on a manipulative experiment initiated in 2006.Results: In the wet year, both warming and nitrogen fertilization significantly increased nitrogen and phosphorus concentrations in soils and plants and thus decreased resorption efficiency of both nitrogen and phosphorus with significant interactions, but these effects did not occur in the dry year. Changes in resorption efficiency were associated with plant available nitrogen and phosphorus in soils and water availability.Conclusions: Our study suggests that the responses of nutrient resorption to warming and nitrogen fertilization could be modified by natural precipitation variations in a desert grassland that is sensitive to abrupt changes in weather patterns. [ABSTRACT FROM AUTHOR]

Background and aims: The terrestrial biosphere's ability to capture carbon is dependent upon soil nitrogen (N) availability, which might reduce as CO increases, but global warming has the potential to offset CO effects. Here we examine the interactive impact of elevated CO (eCO) and warming on soil N availability and transformations in a low-fertility native grassland in Tasmania, Australia. Methods: Using ion exchange membranes, we examined soil nitrogen availability during the growing season from 2004 to 2010 in the TasFACE experiment. We also estimated soil N transformation rates using laboratory incubations. Results: Soil N availability varied strongly over time but was more than doubled by experimental warming of 2°C, an impact that was consistent from the fifth year of the experiment to its conclusion. Elevated CO reduced soil N availability by ~28%, although this varied strongly over time. Treatment effects on potential N mineralisation also varied strongly from year to year but tended to be reduced by eCO and increased by warming. Conclusions: These results suggest that warming should increase soil N availability more strongly than it is suppressed by eCO in low fertility grasslands such as this, stimulating terrestrial carbon sinks by preventing eCO-induced nitrogen limitation of primary productivity. [ABSTRACT FROM AUTHOR]

Background and aims: To test the hypothesis that dominant plant species could acquire different nitrogen (N) forms over a spatial scale and they also have the ability to compete for available N with microbes. Methods: A short-term N labeling experiment was conducted in the temperate grassland ecosystem of North China in July of 2013. Three N forms (NO NH and glycine) labeled with N were injected into the two soil depths (0-5 and 5-15 cm) surrounding each plant to explore N acquisition by plants and microbes. Three dominant plant species ( Artemisia frigida, Cleistogenes squarrosa and Artemisia capillaris) were investigated. Results: Two hours after N labeling, all three dominant plant species absorbed both organic and inorganic N, but different patterns were observed at two soil depths. Uptake of NO was significantly higher at 0-5 cm than at 5-15 cm soil depth among all the dominant plant species. N recovery by microbes was significantly higher than plants. However, N recovery by plants showed different patterns over soil depths. Conclusions: Dominant plant species in the temperate grassland have different patterns in acquisition of N added to soil in organic form and absorption of inorganic N, and microbes were more effectively than plants at competing for N in a short-term period. [ABSTRACT FROM AUTHOR]

High stocking densities on grazed pastures may promote nitrous oxide (NO) loss from soil to the atmosphere. However, studies of NO fluxes in cool-season pastures of North America are lacking. We performed two experiments in which measured NO fluxes were bootstrapped with re-sampling (n = 100, with 10,000 iterations), which allowed us to generate an empirical distribution of mean fluxes to understand how pasture management strategies might affect NO emissions. In Experiment 1, NO fluxes were estimated in southern Wisconsin pastures under rotational grazing, continuous grazing, haymaking, and no agronomic production. Nitrous oxide fluxes were significantly positive under rotational grazing at our research farm [21.6 (se = 10.3) μg m h], but not significantly different than zero under the other three treatments or rotationally grazed paddocks across eight working farms. In Experiment 2, we measured NO fluxes in eastern Nebraska before, during, and after two rotational grazing events under two N-input treatments-inorganic N fertilizer and supplemented dried distillers grains-and an unfertilized control. Nitrous oxide fluxes were positive (20-100 μg m h) in periods following rain, but otherwise not significantly different than zero. Post-grazing, NO emissions were lower from the control than fertilized or supplemented treatments. These experiments show cool-season pastures can be a source of NO to the atmosphere, but primarily following grazing events that coincide with significant precipitation. However, even though on-farm paddocks are in varying states of recovery from defoliation, farm scale emissions, although episodic, are likely to be positive in years with above average precipitation. [ABSTRACT FROM AUTHOR]

Purpose: Microbial processes driving nitrogen (N) cycling are hot topics in terms of increasing N deposition. Abundances of N-related functional genes (NFG) can be most responsive to N deposition and commonly used to represent N transformation rates. However, empirically simulated N deposition has been exclusively conducted through large and infrequent N fertilization, which may have caused contrasting effects on NFGs. Therefore, experiments with small and frequent N additions closed to natural deposition are necessary. Materials and methods: Independently manipulated N addition rates (i.e., 0, 5, 10, 15, 20, and 50 g N m year) and two frequencies (2 times per year addition as conventional large and infrequent N fertilization (2 N), and 12 times per year addition simulating small and frequent N deposition (12 N), respectively) were conducted in a long-term field experiment of a semiarid grassland in northern China. Quantification analysis using real-time PCR were carried out for NFGs, including nifH for N fixation, chiA for N mineralization, archaeal (AOA) and bacterial (AOB) amoA for nitrification, and narG, nirS, nirK, and nosZ for denitrification. Results and discussion: NFG abundances showed distinct sensitivities to N addition rates. The nifH, AOA- amoA, nirS, and nosZ gene abundances increased due to improved available N at low N rates, but suppressed by salt toxicity and acidification at high N rates. Large changes of chiA and AOB- amoA gene abundances highlighted their great sensitivities to the N enrichment. The abundance of AOB- amoA was more sensitive to N addition than AOA- amoA, but AOA- amoA dominated in absolute numbers and they predominated the ammonia-oxidation under different conditions. The N addition frequencies caused significant lower gene abundances of nifH, nirS, and nosZ under the 2-N frequency due to stronger suppression of acidification and salt toxicity and resulted in significant higher AOB- amoA gene abundances in response to higher N availability under the 2-N frequency. Conclusions: The NFGs abundances responded to N addition rates distinctly, highlighting that the driven processes involved in N cycling were altered by the N addition rates. The different effects of two N addition frequencies on NFG abundances demonstrated that conventional large and infrequent N fertilization cannot represent N deposition, and small and frequent N addition should be employed to project the effects of N deposition on microbial functional groups as well as on N transformations. [ABSTRACT FROM AUTHOR]

Soil respiration (Soil R) is one of the largest CO fluxes from terrestrial ecosystems to the atmosphere. The largely seasonal and daily patterns of Soil R in semiarid grassland ecosystems indicate that measurement time and frequency would have significant influences on the assessment of seasonal soil carbon release. Based on a three-year continuous measurement of Soil R in a semiarid grassland, we found that the Soil R value measured at around 10:00 o'clock local time was the closest to its daily mean, while the value at 14:00 o'clock was found to be the highest daily rate. A measurement frequency higher than every 10 days was necessary for estimating the seasonal Soil R and its temperature sensitivity ( Q) reasonably. Our study would be useful as guidelines for manual Soil R measurements and model data selection in semiarid temperate grasslands. [ABSTRACT FROM AUTHOR]

Aims: Major changes to rainfall regimes are predicted for the future but the effect of such changes on terrestrial ecosystem function is largely unknown. We created a rainfall manipulation experiment to investigate the effects of extreme changes in rainfall regimes on ecosystem functioning in a grassland system. Methods: We applied two rainfall regimes; a prolonged drought treatment (30 % reduction over spring and summer) and drought/downpour treatment (long periods of no rainfall interspersed with downpours), with an ambient control. Both rainfall manipulations included increased winter rainfall. We measured plant community composition, CO fluxes and soil nutrient availability. Results: Plant species richness and cover were lower in the drought/downpour treatment, and showed little recovery after the treatment ceased. Ecosystem processes were less affected, possibly due to winter rainfall additions buffering reduced summer rainfall, which saw relatively small soil moisture changes. However, soil extractable P and ecosystem respiration were significantly higher in rainfall change treatments than in the control. Conclusions: This grassland appears fairly resistant, in the short term, to even the more extreme rainfall changes that are predicted for the region, although prolonged study is needed to measure longer-term impacts. Differences in ecosystem responses between the two treatments emphasise the variety of ecosystem responses to changes in both the size and frequency of rainfall events. Given that model predictions are inconsistent there is therefore a need to assess ecosystem function under a range of potential climate change scenarios. [ABSTRACT FROM AUTHOR]

Numerous studies have focused on vegetation traits and soil properties in grassland, few of which concerned about effects of human utilization patterns on grassland yet. Thus, this study hypothesized that human disturbance (e.g., grazing, mowing and fencing) triggered significant variation of biomass partitioning and carbon reallocation. Besides, there existed some differences of species diversity and soil fertility. To address these hypotheses of grassland with diverse utilization patterns in Hulun Buir City, Inner Mongolia, China, we sampled in situ about aboveground biomass (AGB) and belowground biomass (BGB) to evaluate their biomass allocation. Species diversity and soil properties were also investigated. Subsequently, we discussed the relationship of species diversity with environmental conditions, using data collected from 23 sites during the ecological project period of Returning Grazing Lands to Grasslands (RGLG) program. The results were as follows: 1) both AGB and BGB were lower on grazing regime than those on fencing and mowing, but the ratio of root-to-shoot (R/S) was higher on grazing regime than the other two utilization patterns; 2) neither of evenness and Simpson Index was different significantly among all grassland utilization patterns in desert, typical, and meadow grassland at 0.05. In meadow grassland, species richness of fencing pattern was significantly higher than that of grazing pattern ( p < 0.05); 3) both of soil organic carbon content and soil available phosphorous content were increased significantly on fencing pattern than grazing pattern ( p < 0.05) in desert grassland, and mowing patterns increased the soil nutrients (soil organic carbon, soil total phosphorous, soil available phosphorous, and soil total nitrogen) significantly compared with grazing patterns ( p < 0.05) in typical grassland. However, there were no significant differences among utilization patterns in meadow grassland. In conclusion, both of AGB and BGB were increased significantly by fencing. Moreover, species diversity and soil nutrients can be promoted via mowing and fencing. This study suggested that implementation of Ecological Project played a positive role in sustainable grassland utilization of Hulun Buir City and a strong positive influence on the entire temperate grassland. [ABSTRACT FROM AUTHOR]

Soil organic carbon (OC) storage across regions is influenced by climate and parent materials, which determine soil properties like clay content and mineralogy. Within homogeneous soil regions, land use and management practices are further important controls for soil OC contents and turnover. Here, we studied the impact of study region, land use (forest, grassland), forest management (spruce and beech forest under age-class management, unmanaged beech forest), and grassland management (meadow, mown pasture, unmown pasture) on stocks and turnover (based on ΔC values) of soil OC in density frations of topsoil horizons. Samples were taken from 36 plots in the regions Hainich-Dün (HAI) and the Schwäbische Alb (ALB) in Germany. They were separated into two light fractions (free light fraction (LF1), occluded light fraction (LF2)) and the mineral-associated organic matter (MOM) fraction using sodium polytungstate with a density of 1.6 g cm. Overall most soil OC was stored in the MOM fraction (73%). Soil OC concentrations and stocks in the MOM fraction differed between study regions, probably due to larger amounts of pedogenic Al- and Fe-oxides in the ALB than in the HAI region. Within each region, forest soils stored significantly higher proportions of total OC in the two LF (33±1.9 %) than grassland soils (20±2.3 %). Different management of forests and grasslands affected the C:N ratio of density fractions, but not OC storage. While modelled soil OC turnover in the MOM was longest of all fractions, all fractions had average ΔC values above atmospheric values, suggesting a significant fast-cycling component in all of them. Different from stocks, turnover of OC in the MOM fraction were not affected by study region or contents of pedogenic oxides. Radiocarbon contents in the LF were higher for forest than for grassland sites, indicating faster turnover of OC at grassland sites. However, some of the observed difference could originate from different average lifetimes of roots in forests and grasslands. Applying different lag-times for OC input for forests and grasslands significantly reduced the differences in modelled turnover times. Lower ΔC values of mown pastures than pasture soils in both regions suggest a management effect on soil C turnover in grasslands.We conclude that OC storage in the MOM of topsoil layers is more affected by regional differences in soil texture and mineralogy than by land use and management, while its turnover could not be explained with the studied soil properties. Soil OC storage and turnover in the two LFs is influenced by land use (forest or grassland) and management, but ecosystem specific lag-times have to be considered for modelling OC turnover in these fractions. [ABSTRACT FROM AUTHOR]

Understanding the patterns of forage quantity and quality and investigating the factors influencing these patterns are essential for the development of animal husbandry. However, there is very little field evidence focused on these issues at a large spatial scale. In the current study, we analyzed forage quantity and quality at 177 sites distributed in all the major grassland types across China, and explored the relationship between forage quantity and quality based on consistent sampling protocols. We also investigated potential factors influencing forage quality patterns across China. Our study indicates the Tibetan grasslands had both higher quantity and quality forage than the Inner Mongolian grasslands, and alpine meadow had the best quantity and quality forage because of the meadow's high productivity and the crude protein and nitrogen free extract content of the meadow forage. For the main vegetation formations, Kobresia tibetica meadows and Achnatherum splendens steppes had the highest quantity, while Kobresia pygmaea meadows and Kobresia humilis meadows had the best quality. We also found that although environmental factors, such as temperature and soil fertility, could affect physiological processes and so influence forage quality, the large scale patterns of change were mainly a result of the differences in vegetation types. Finally, we reported a negative relationship between forage quantity and quality: higher forage quantity means more crude fiber but less ether extract and crude protein. These findings improve our understanding on the spatial patterns of forage quantity and quality, and provide solid evidence related to the future development of animal husbandry. [ABSTRACT FROM AUTHOR]

Grasslands account for 40 % of the Chinese land area. About 80 % of the total grasslands are in the northern temperate zone. These grassland ecosystems provide goods and services to the local people and play an important role in the global carbon cycle. Remote sensing and ecosystem modeling approaches have been used to quantify the carbon budget of these grasslands. However, the intensive site measurements and meteorological data acquired in these ecosystems in the last few decades have not been adequately used to improve ecosystem model capabilities, in turn, better quantify their carbon budget. In this study an effort was made to examine the carbon budget and its spatial-temporal variation of the temperate grasslands in China from 1951 to 2007 using a process-based biogeochemistry model. It was found that the regional grasslands acted as a small carbon sink at 11.25 g C m year in the study area of 64.96 million hectares with a high inter-annual variability ranging from −124 to 122.7 g C m year during the study period. As a result, the temperate grasslands sequestered about 410 Tg C in their vegetation and soils during the study period. The carbon sink occurred in typical steppe in central Inner Mongolia within the 300-400 mm rainfall zone and forest steppe in central and western China. By contrast, forest steppe in northeastern China mainly acted as a carbon source. Three major ecosystem types of forest steppe, typical steppe and desert steppe account for 54, 34, and 12 % of the total sink (7.3 Tg C year) during 1951-2007, respectively. Soil moisture and evapotranspiration had a dominant effect on carbon budget in the typical steppe and the forest steppe while both water conditions and nitrogen mineralization rate were the major factors in the desert steppe. At a decadal scale, the air temperature significantly increased by 0.4 °C and annual precipitation insignificantly decreased by 0.2 mm; the regional carbon sink increased by 2.2 Tg C per decade during the period 1951-2007. However, further sensitivity analysis suggests that the sink of temperate grasslands will be reduced if the climate gets warmer and drier during this century since the increasing net primary production does not keep up with the increase of heterotrophic respiration. [ABSTRACT FROM AUTHOR]

Cultivation is one of the most important human activities affecting the grassland ecosystem besides grazing, but its impacts on soil total organic carbon (C), especially on the liable organic C fractions have not been fully understood yet. In this paper, the role of cropping in soil organic C pool of different fractions was investigated in a meadow steppe region in Inner Mongolia of China, and the relationships between different C fractions were also discussed. The results indicated that the concentrations of different C fractions at steppe and cultivated land all decreased progressively with soil depth. After the conversion from steppe to spring wheat field for 36 years, total organic carbon (TOC) concentration at the 0 to 100 cm soil depth has decreased by 12.3% to 28.2%, and TOC of the surface soil horizon, especially those of 0-30 cm decreased more significantly (p<0.01). The dissolved organic carbon (DOC) and microbial biomass carbon (MBC) at the depth of 0-40 cm were found to have decreased by 66.7% to 77.1% and 36.5% to 42.4%, respectively. In the S. baicalensis steppe, the ratios of soil DOC to TOC varied between 0.52% and 0.60%, and those in the spring wheat field were only in the range of 0.18%-0.20%. The microbial quotients (qMBs) in the spring wheat field, varying from 1.11% to 1.40%, were also lower than those in the S. baicalensis steppe, which were in the range of 1.50%-1.63%. The change of DOC was much more sensitive to cultivation disturbance. Soil TOC, DOC, and MBC were significantly positive correlated with each other in the S. baicalensis steppe, but in the spring wheat field, the correlativity between DOC and TOC and that between DOC and MBC did not reach the significance level of 0.05. [ABSTRACT FROM AUTHOR]

Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha year; MN, 100 kg N ha year; LN, 50 kg N ha year) on soil respiration compared with non-fertilization (CK, 0 kg N ha year), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments ( Q varied within 1.70-1.74) but was slightly reduced in MN treatment ( Q = 1.63). N fertilization increased soil CO emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN and MN ( P < 0.05) and reached a marginally significant level for LN ( P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July-September 2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007-June 2008). The annual total soil respiration was 53, 57, and 24% higher than in the CK plots (465 g m year). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July-September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year ( P > 0.05). [ABSTRACT FROM AUTHOR]

Two, two-factor experiments manipulated species and functional form plant richness and the spatial scaling of either nitrogen (N) or phosphorous (P) in restored tallgrass prairie in North Dakota, USA. Nitrate (NO) leaching was measured in these plots and analyzed for its response to the treatment factors and measured plant community parameters. Nitrate extracted from anion exchange resin was regressed against the first principal component of species and functional form richness, the spatial scaling of N or P, the measured biomass of the functional forms used and the plot values for plant parameters based on weighted averages by species biomass. The treatments applied in the N and P experiments were 1, 2, 5, 10, or 20 plant species taxa, and the application of fertilizer in a random fractal pattern with either fine-scale or coarse-scale heterogeneity. Nitrate leaching decreased with plant diversity and increased by a factor of two going from fine-scale to coarse-scale N. It was also related to a number of plant functional parameters, and was positively correlated with the biomass of late successional C grasses ( Koeleria cristata (Lam.) Beauv., Poa pratensis L., Stipa comata Trin. & Rupr., and Stipa viridula Trin.), which are known from previous studies to have negative mycorrhizal responsiveness and are characterized by high root lateral spread per unit of root biomass. Our results show that while plant diversity has a highly significant influence on plant community uptake of NO, this effect is mediated by the scaling of soil N and the functional traits of the species comprising the plant assemblage. [ABSTRACT FROM AUTHOR]

The number of genetically distinct individuals within a community is a key component of biodiversity and yet its impact at different trophic levels, especially upon the diversity of functionally important soil microorganisms is poorly understood. Here, we test the hypothesis that plant communities that are genetically impoverished will support fewer species of root-associated fungi. We used established grassland mesocosms comprising non-sterile natural soil supporting defined communities of 11 clonally-propagated plant species. Half of the mesocosms contained one genotype per species and half 16 genotypes per species. After 8 years growth, we sampled roots from the mesocosms and measured root-associated fungal richness and diversity using terminal restriction fragment length polymorphism (T-RFLP). Contrary to our hypothesis, we found that the roots of genetically impoverished communities contained more species of fungi and had greater diversity compared to genetically rich communities. Analysis of the plant species composition of the mesocosm communities indicated that genotypic diversity affects root-fungal diversity indirectly through its influence upon plant species diversity. Our findings highlight the need to include feedbacks with plant intraspecific diversity into existing models describing the maintenance of soil biodiversity. [ABSTRACT FROM AUTHOR]

Climate change is known to influence interannual variation in grassland aboveground net primary productivity (ANPP), or seasonal biomass, but direct, long-term ground observations are rare. We present a 22-year (1982–2003) measurement series from the Inner Mongolia grassland, China, to examine the effect of climate change on interannual variations in ANPP and monthly aboveground biomass (MAB). ANPP exhibited no increase over 1982–2003 but there was an association with previous-year precipitation. MAB in May increased by 21.8% from 47.8 g m−2 (averaged for 1982–1984) to 58.2 g m−2 (2001–2003), whereas there was no significant variation in June, July and August, and a decrease of 29.7% in September. The MAB increase in May was correlated with increases in precipitation and temperature in the preceding months. These findings suggest that the effects of climate change on grassland production vary throughout the growing season, with warmer and wetter springs resulting in increased biomass early in the growing season, and drier falls causing a decrease in biomass late in the growing season. [ABSTRACT FROM AUTHOR]

Above- and belowground biomass allocation not only influences growth of individual plants, but also influences vegetation structures and functions, and consequently impacts soil carbon input as well as terrestrial ecosystem carbon cycling. However, due to sampling difficulties, a considerable amount of uncertainty remains about the root: shoot ratio (R/S), a key parameter for models of terrestrial ecosystem carbon cycling. We investigated biomass allocation patterns across a broad spatial scale. We collected data on individual plant biomass and systematically sampled along a transect across the temperate grasslands in Inner Mongolia as well as in the alpine grasslands on the Tibetan Plateau. Our results indicated that the median of R/S for herbaceous species was 0.78 in China's grasslands as a whole. R/S was significantly higher in temperate grasslands than in alpine grasslands (0.84 vs. 0.65). The slope of the allometric relationship between above- and belowground biomass was steeper for temperate grasslands than for alpine. Our results did not support the hypothesis that aboveground biomass scales isometrically with belowground biomass. The R/S in China's grasslands was not significantly correlated with mean annual temperature (MAT) or mean annual precipitation (MAP). Moreover, comparisons of our results with previous findings indicated a large difference between R/S data from individual plants and communities. This might be mainly caused by the underestimation of R/S at the individual level as a result of an inevitable loss of fine roots and the overestimation of R/S in community-level surveys due to grazing and difficulties in identifying dead roots. Our findings suggest that root biomass in grasslands tended to have been overestimated in previous reports of R/S. [ABSTRACT FROM AUTHOR]

ABSTRACT / Nitrous oxide (N2O) emissions from temperate grasslands are poorly quantified and may be an important part of the atmospheric N2O budget. In this study N2O emissions were simulated for 1052 grassland sites in the United States using the NGAS model of Parton and others (1996) coupled with an organic matter decomposition model. N2O flux was calculated for each site using soil and land use data obtained from the National Resource Inventory (NRI) database and weather data obtained from NASA. The estimates were regionalized based upon temperature and moisture isotherms. Annual N2O emissions for each region were based on the grassland area of each region and the mean estimated annual N2O flux from NRI grassland sites in the region. The regional fluxes ranged from 0.18 to 1.02 kg N2O N/ha/yr with the mean flux for all regions being 0.28 kg N2O N/ha/yr. Even though fluxes from the western regions were relatively low, these regions made the largest contribution to total emissions due to their large grassland area. Total US grassland N2O emissions were estimated to be about 67 Gg N2O N/yr. Emissions from the Great Plains states, which contain the largest expanse of natural grassland in the United States, were estimated to average 0.24 kg N2O N/ha/yr. Using the annual flux estimate for the temperate Great Plains, we estimate that temperate grasslands worldwide may potentially produce 0.27 Tg N2O N/yr. Even though our estimate for global temperate grassland N2O emissions is less than published estimates for other major temperate and tropical biomes, our results indicate that temperate grasslands are a significant part of both United States and global atmospheric N2O budgets. This study demonstrates the utility of models for regional N2O flux estimation although additional data from carefully designed field studies is needed to further validate model results. [ABSTRACT FROM AUTHOR]

Population, biomass and secondary net production of aboveground insects were studied in a temperate grassland from February 1986 to january 1987. The live shoot biomass varied from 12·4±0·67 to 84·8 g m and the aboveground net primary production was 190·3 g m yr. A total of 65 species belonging to 33 families of 10 insect orders were collected. Herbivores (77·6%) were the most dominant insects followed by Omnivores (12%), Predators (5%), Saprophages (5%) and Parasites (0·4%). Maximum population density and biomass were 9·8 m and 254 mg m, respectively. Cumulative secondary net production was 1·144 g m. [ABSTRACT FROM AUTHOR]

Background: Global climate change is projected to increase temperature and alter precipitation pattern, which could affect grassland ecosystem. Long-term observation at a field experiment can be a powerful approach to explore the impacts of climate change on biomass productivity in grassland. In attempting to understand how climatic variability regulates biomass productivity, we analyzed long-term records of temperature and precipitation to examine how variation of temperature and precipitation across 19 years affect biomass productivity.Methods: We established the experiment with 64 plots in two blocks and planted 31 species in 30 different mixtures. We harvested aboveground biomass twice a year, sorted biomass by functional groups, and weighed dry biomass. The site was mown after each harvest. We did not apply any fertilizer and water. Using linear regression model, we examined the influences of growing season temperature and precipitation on biomass productivity.Results: The results showed that aboveground biomass productivity in September and annual were significantly increased in post-drought (2003-2015). The relationships of aboveground biomass productivity with growing season precipitation were significantly positive. The results showed that aboveground biomass productivity in June and annual were sensitive to growing season temperature. The relationships of aboveground biomass productivity of the functional group of grasses with early growing season temperature were significantly negative. Early growing season precipitation had a significant positive effect on aboveground biomass productivity of the functional groups of grasses and legumes. Post-drought aboveground biomass productivity of the functional groups of grasses in June and September were declined, whereas legumes significantly increased, which suggests that the role of dominant grasses may shift by legumes with global climate change.Conclusions: Our results highlight that early and late growing temperature and precipitation variability may reduce the aboveground biomass productivity in grassland. Our study implies that the combination of several functional groups is essential for the maintenance of stable productivity in temperate grassland ecosystem. [ABSTRACT FROM AUTHOR]