Semi-arid Grassland Of Inner Mongolia Research Articles

Distributions of trace elements with Long-term grazing exclusion in a semi-arid grassland of Inner Mongolia.

Trace elements are the essential mineral nutrients in grassland, however, we still know little about the distributions of trace elements in grassland with long-term grazing exclusion. The contents, stocks, and proportions of iron (Fe), aluminum (Al), manganese (Mn), and boron (B) in green plant-litter-root-soil were evaluated by enclosing for 18, and 39 years inside the fence (F18 and F39) and grazing outside the fence (F0) in Inner Mongolia grassland. The results showed that F18 and F39 decreased the stocks of Fe, Al, and Mn in green plant and root compared to F0 (p < .05), while increased the stocks of them in litter (p < .05). The stock of Fe, Al, and Mn in green plant at F39 was 28.6%, 13.9%, and 39.2% higher than that at F18. The stocks of four trace elements in first layer litter at F39 were increased by 12.7%-52.2% compared to F18, whereas the stocks of them in third layer litter were decreased by 32.2%-42.5%. The F18 obviously increased the stocks of Fe and Mn in soil, especially B (p < .05). While the stocks of these trace elements in soil at F39 were 9.1%-28.0% lower than that at F18, especially B (p < .05). In conclusion, the trace elements were mainly shifted from green plant and root to soil and third layer litter with 18-year grazing exclusion. Compared to 18-year grazing exclusion, the trace elements were shifted from third layer litter and soil to root with 39-year grazing exclusion.

Defoliation decreases soil aggregate stability by reducing plant carbon inputs and changing soil microbial communities

Soil aggregation and its stability are fundamental in ensuring soil function and ecosystem service provision, which can be greatly altered by ungulate disturbance, particularly the indirect effects from biomass removal by defoliation and direct effects from hoof trampling, but the mechanisms underlying the effect of defoliation and trampling on soil aggregation remains largely unexplored. Here, we conducted a 3-year manipulative experiment to investigate the effects of defoliation and trampling of ungulates and their interaction on soil aggregate stability in a semiarid grassland of Inner Mongolia, China. We found that defoliation rather than trampling dominantly affected soil aggregate stability. Defoliation disintegrated macroaggregates, reducing aggregate stability (-5 %), mainly attributed to the direct influence of a decline in plant inputs (aboveground biomass: −32 %) and the indirect effects of soil microbial biomass (-5 %). Moreover, compared to no defoliation plots, defoliation significantly decreased soil fungal diversity and altered fungal communities, particularly decreasing the relative abundance of Glomeraceae fungal taxa favorable to the formation of soil aggregates. Trampling only slightly attenuates the involvement of microorganisms (indirectly, −7 %) in aggregate formation by increasing soil compaction (directly, −4 %), and the positive effects from accelerating litter-derived C inputs due to trampling disturbance may counteract these limited negative effects. Our results highlight the negative effect of biomass removal by ungulates on soil aggregation, and suggest that the role of plant inputs and soil microbial properties on soil function and their correlation with soil aggregate stability needs to be explored under a diversity of grazing management strategies to refine management to improve soil conservation, C persistence and restore grasslands.

Light grazing alleviates aeolian erosion–deposition effects on microbial communities in a semi-arid grassland

BackgroundSoil erosion affects the stability of terrestrial ecosystems and ecosystem services by directly or indirectly impacting the cycling of soil materials and energy and reducing the fertility of grassland soils. However, research on microbial adaptation to grazing and soil erosion is limited, particularly in relation to grassland ecosystem restoration. Here, we assess microbial communities subjected to simulated soil erosion and grazing in a semi-arid grassland of Inner Mongolia, China.ResultsNo significant change was observed in soil variables. However, the structure of the soil microbial community underwent significant changes as a result of soil erosion and soil erosion plus grazing, leading to a significant increase in the relative abundance of Cyanobacteria (116.80% vs 116.38%). Wind erosion and deposition contributed to an increase in the network complexity of soil bacterial and fungal communities. However, much of this effect was alleviated by grazing. Simultaneously, aeolian processes and grazing regulate soil microbial community assembly, leading to inconsistent patterns of change in bacterial and fungal communities. Under wind erosion and deposition, the relative contribution of deterministic processes (4.44% vs 31.11%) in bacterial communities increased, while the relative contribution of stochastic processes (2.23% vs 20%) in fungal communities reduced. Grazing resulted in a decrease in the relative contribution of deterministic processes (8.89%) in the bacterial community and an increase in the relative contribution of stochastic processes (8.89%) in the fungal community.ConclusionThis study presents a comprehensive investigation of the response of soil microbial communities to aeolian erosion–deposition and grazing in a semi-arid grassland. Our findings indicate that microbial communities in the semi-arid grassland show resistance to external disturbances and that light grazing mitigates the effects of aeolian erosion–deposition on microbial communities, which is essential for maintaining the stability and biodiversity of grassland ecosystems.

High stocking rates effects in continuous season long grazing reduces the contribution of microbial necromass to soil organic carbon in a semi-arid grassland in Inner Mongolia

Livestock grazing strongly influences the accumulation of soil organic carbon (SOC) in grasslands. However, whether the changes occurring in SOC content under different intensities of continuous summer long grazing are associated with the changes in microbially-derived necromass C remains unclear. Here, we established a sheep grazing experiment in northern China in 2004 with four different stocking rates. Soil samples were collected after 17 years of grazing and analyzed for physical, chemical, and microbial characteristics. Grazing decreased SOC and microbial necromass carbon (MNC). Notably, grazing also diminished contributions of MNC to SOC. MNC declined with decreasing plant carbon inputs with degradation of the soil environment. Direct reductions in microbial necromass C, which indirectly reduced SOC, resulted from reduced in plant C inputs and microbial abundance and diversity. Our study highlights the key role of stocking rate in governing microbial necromass C and SOC and the complex relationships these variables.

Inner Mongolia grasslands act as a weak regional carbon sink: A new estimation based on upscaling eddy covariance observations

Clarifying temporal and spatial variations of carbon exchanges of arid and semi-arid grasslands, the most widespread terrestrial ecosystem in the Northern China, is critical to evaluate regional and national carbon balance. However, estimating the carbon sequestration capability of arid and semi-arid grasslands still remains a challenge due to large interannual variability and high sensitivity to human activities. In this study, based on 696 site-months of long-term eddy covariance observations from 7 sites, we estimated the regional carbon fluxes of the arid and semi-arid grasslands in Inner Mongolia, China with the random forest (RF) approach. The estimated carbon fluxes encompassed net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (ER), at a spatial resolution of 0.1°×0.1°. We found that Inner Mongolia grasslands acted as a weak carbon sink with a mean NEP of 2.43 ± 6.71 Tg C y−1 from 1982 to 2018. Fluctuations of precipitation during the peak growing season and leaf area index were the most important drivers for the interannual variations of regional carbon fluxes. During the dry period of 1999 to 2011, the grasslands switched from carbon sink to source resulting from a great drought-induced reduction in GPP than ER. Comparison of our RF carbon fluxes with the global datasets (FLUXCOM, CMIP6 models, and atmospheric inversion data of JenaCO2) showed that these products had limited agreement in terms of spatial and temporal variations, particularly for interannual variabilities of carbon fluxes, which highlights the importance of local long-term observations for regional evaluation and simulation of carbon budget.

Belowground soil and vegetation components change across the aridity threshold in grasslands

Grassland ecosystem functions are affected by global climate change and increasing aridity. Belowground components of soil and vegetation, such as specific root length, belowground biomass and soil organic carbon are important for maintaining these functions. However, aridity affects these components in different ways. This research evaluates changes in soil properties and plant attributes with aridity along a 2600 km aridity gradient in the arid and semiarid grasslands of Inner Mongolia. The aridity index was used considering the ratio of precipitation to potential evapotranspiration, where a higher value indicates greater aridity. Results showed an overall aridity threshold for grassland ecosystems of 0.67, where abrupt changes in belowground components were observed. The effect of aridity on specific root length changed from negative (−0.18) below the threshold to positive (0.24) above the threshold, with the emergence of coordination between aboveground and belowground plant characteristics. Aridity exhibited a negative effect on belowground biomass, increasing from −0.24 below the threshold to −0.55 above the threshold as the positive effect of relative grass abundance disappeared. The total effect of aridity on soil organic carbon showed a subtle change, but the driving pathways through which aridity affects changed from soil loss to aridity itself and vegetation cover at plot scale. These findings highlight how aridity affects belowground components in grassland ecosystems above and below the aridity threshold. They provide a basis for better understanding aridity-driven interactions in grassland ecosystems, and can be used to inform actions to protect grasslands under future climate change.

Variations in diversity, composition, and species interactions of soil microbial community in response to increased N deposition and precipitation intensity in a temperate grassland

BackgroundGlobal climate change has resulted in precipitation regimes exhibiting an increasing trend in rainfall intensity but a reduction in frequency. In addition, nitrogen (N) deposition occurs simultaneously in arid and semi-arid regions. Microbial biomass, diversity, composition, and species interactions are key determinants of ecological functions. We examined the effects of changes in precipitation intensity and N addition on the soil bacterial and fungal communities in a semi-arid grassland in Inner Mongolia, China.MethodsThe microbial biomass (bacterial PLFAs and fungal PLFAs) was determined through phospholipid fatty acid (PLFA) analysis, and microbial diversity (Shannon index and evenness index) was determined with high-throughput sequencing (16S and ITS). Species interactions were determined using a molecular ecological network analysis. The relationships between microbial community (bacterial community and fungal community) and environmental variables were examined by Mantel tests.ResultsWe found that N addition decreased fungal PLFA under moderate, high, and extreme precipitation intensity treatments and increased fungal community complexity under the high precipitation intensity treatment. Furthermore, N addition increased bacterial diversity under moderate and high precipitation intensity treatments. N addition caused greater environmental stress to the fungal community, which was dominated by deterministic processes.ConclusionsThe effects of N deposition on soil bacterial and fungal communities were altered by precipitation intensity. The changes in soil bacterial and fungal communities were different, implying that composition and functional traits adapt differently to projected global changes at a regional scale.

Estimation of grassland aboveground biomass combining optimal derivative and raw reflectance vegetation indices at peak productive growth stage

In this paper, field spectroradiometer and aboveground biomass (AGB) data were acquired at the harvest stage at two sites in semiarid grasslands in Inner Mongolia, China. Four forms of commonly used vegetation indices (VIs) using all possible combinations of narrow-band first derivative (FDR) and raw reflectance (RR) were calculated, and the best FDR-VIs and RR-VIs were chosen by a linear regression analysis against AGB. The stepwise multiple linear regression (SMLR) models using the optimal FDR-VIs, RR-VIs, and both FDR-VIs and RR-VIs as input variables were developed for estimating the AGB. Results demonstrated that the estimation performance using the best FDR-VIs were comparable with the best RR-VIs, while the accuracy has been further improved by combining the best FDR-VIs and RR-VIs (maximum decrease in RMSE of 44% and minimum RMAE of 4.7%). The approach was found to be an important step for more accurate and effective grassland AGB estimation.

Responses of Vegetation, Soil, and Microbes and Carbon and Nitrogen Pools to Semiarid Grassland Land-Use Patterns in Duolun, Inner Mongolia, China

Previous studies have observed that increased precipitation positively affects primary production in semiarid grasslands in Inner Mongolia, while soil carbon (C) and nitrogen (N) strongly influence how ecosystems respond to precipitation as well as anthropogenic disturbances under different management strategies. Therefore, in this study, we investigated the storage of organic C and N in four grassland sites with similar flora and landforms but with different grazing intensities to characterize how the storage and concentrations of C and N respond to relief from grazing pressure and precipitation. The concentrations of soil organic carbon (SOC), soil total nitrogen (STN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN), as well as the contents of soil bacteria and fungi in the 0–50 cm soil layers, were measured. The results showed that SOC, STN, MBC, and MBN storage varied greatly among the four grassland sites (p &lt; 0.05), with all decreasing significantly with grassland degradation and increasing greatly with the exclusion of grazing, i.e., the establishment of natural grassland (NG). More than 90% of C and 95% of N stored in the soil were lost due to heavy grazing, but the losses were smaller in other nutrient pools (including the aboveground biomass, litter, and roots). Interestingly, the proportion of the particle size fractions (clay, silt, and sand) had a stronger effect on limiting the soil and microbial nutrient pools compared to precipitation. The limited range of C and N storage found in these grassland soils indicated that enclosed fencing was a valuable management tool with a high potential to sequester C in the top meter of the soil, showing a stronger effect than precipitation. This study provides a theoretical basis for improving grassland recovery in semiarid areas that have been heavily grazed.

Effects of Grazing, Extreme Drought, Extreme Rainfall and Nitrogen Addition on Vegetation Characteristics and Productivity of Semiarid Grassland.

Grassland use patterns, water and nutrients are the main determinants of ecosystem structure and function in semiarid grasslands. However, few studies have reported how the interactive effects of rainfall changes and nitrogen deposition influence the recovery of semiarid grasslands degraded by grazing. In this study, a simulated grazing, increasing and decreasing rainfall, nitrogen deposition test platform was constructed, and the regulation mechanism of vegetation characteristics and productivity were studied. We found that grazing decreased plant community height (CWMheight) and litter and increased plant density. Increasing rainfall by 60% from May to August (+60%) increased CWMheight; decreasing rainfall by 60% from May to August (-60%) and by 100% from May to June (-60 d) decreased CWMheight and coverage; -60 d, +60% and increasing rainfall by 100% from May to June (+60 d) increased plant density; -60% increased the Simpson dominance index (D index) but decreased the Shannon-Wiener diversity index (H index); -60 d decreased the aboveground biomass (ABG), and -60% increased the underground biomass (BGB) in the 10-60 cm layer. Nitrogen addition decreased species richness and the D index and increased the H index and AGB. Rainfall and soil nitrogen directly affect AGB; grazing and rainfall can also indirectly affect AGB by inducing changes in CWMheight; grazing indirectly affects BGB by affecting plant density and soil nitrogen. The results of this study showed that in the semiarid grassland of Inner Mongolia, grazing in the nongrowing season and grazing prohibition in the growing season can promote grassland recovery, continuous drought in the early growing season will have dramatic impacts on productivity, nitrogen addition has a certain impact on the species composition of vegetation, and the impact on productivity will not appear in the short term.

Distributions of medium mineral elements with long-term grazing exclusion in a semi-arid grassland of Inner Mongolia

• F18 and F39 altered distributions of medium mineral elements in plant and soil. • F18 and F39 shifted medium mineral elements from root to other parts. • Ca, Mg, and Si were shifted from soil to plant at F39 than F18. • Ca was shifted from root to litter at F39 than F18. • Mg, S, and Si were shifted from litter to root or green plant at F39 than F18. The variations of medium mineral elements in long-term grazing exclusion grassland have been few studied. Therefore, the contents, stocks, and proportions of calcium (Ca), magnesium (Mg), sulphur (S), and silicon (Si) in green plant-litter-root-soil continuum were evaluated by grazing exclusion for 18-, and 39-year (F18 and F39) and continue grazing (F0) in Mongolia grassland. Results showed that F18 and F39 decreased the stocks of Mg and Si in green plant and the stocks of Ca and Mg in 20–50 cm root ( p < 0.05). F18 and F39 increased the stocks of S in 0–100 cm soil and the stocks of elements in litter ( p < 0.05). Compared to F18, F39 increased the stocks of elements in 0–20 cm root, especially Si ( p < 0.05), and a 30.3 % higher of Ca stock in green plant was observed ( p < 0.05). The stock of Ca and Mg in 0–100 cm soil at F39 was 164.3 % and 72.6 % lower than that at F18, respectively ( p < 0.05). F39 decreased the stocks of Mg, S, and Si in incomplete- and complete decomposed litter relative to F18. We concluded that four elements were shifted from root to other parts with long-term grazing exclusion. However, Ca, Mg, and Si were shifted from soil to plant with grazing exclusion for 39 years relative to 18 years, and Ca was shifted from root to litter, and Mg, S, and Si were shifted from litter to root or green plant.

Atmospheric methane oxidation is affected by grassland type and grazing and negatively correlated to total soil respiration in arid and semiarid grasslands in Inner Mongolia

Methane (CH4) is an important trace greenhouse gas and atmospheric CH4 uptake by high-affinity methanotrophs in grassland soil accounts for an important proportion of the terrestrial CH4 sink. However, our understanding of the comprehensive effects of grassland type and grazing treatment on active soil methanotrophs and atmospheric CH4 uptake is still under debate. This study investigates the impact of grazing on CH4 oxidation rate and active atmospheric CH4 oxidizing methanotroph communities in two arid and semiarid grassland ecosystems (meadow and desert) by detecting transcripts of methane monooxygenase (pmoA) genes. Atmospheric CH4 oxidation rates differed according to grassland type and grazing treatment. The highest activity was found in desert grasslands with moderate grazing and the lowest activity in meadow grasslands with exclosures. The differences in activities were linked with changes in abundance, composition and co-occurrence network patterns of active methanotrophs and CO2 production rate. Redundancy, correlation and random forest analyses indicated that pmoA transcripts, available phosphorus (AP), NO3−-N, and CO2 production rate were the most important factors predicting active methanotroph community composition and atmospheric CH4 oxidation activity in these grassland ecosystems. A glucose amendment incubation experiment showed that addition of glucose increased heterotrophic microbial respiration and inhibited atmospheric CH4 oxidation. This study provides evidence that CO2 production rate is an important factor associated with atmospheric CH4 oxidation activity in arid and semiarid grassland ecosystems and suggests that interactions between methanotrophs and other heterotrophs influence methanotroph activity in grassland ecosystems.

Seasonal and interannual variations of ecosystem photosynthetic characteristics in a semi-arid grassland of Northern China

Abstract The ecosystem apparent quantum yield (α), maximum rate of gross CO2 assimilation (Pmax) and daytime ecosystem respiration rate (Rd), reflecting the physiological functioning of ecosystem, are vital photosynthetic parameters for the estimation of ecosystem carbon budget. Climatic drivers may affect photosynthetic parameters both directly and indirectly by altering the response of vegetation. However, the relative contribution and regulation pathway of environmental and physiological controls remain unclear, especially in semi-arid grasslands. We analyzed seasonal and interannual variations of photosynthetic parameters derived from eddy-covariance observation in a typical semi-arid grassland in Inner Mongolia, Northern China, over 12 years from 2006 to 2017. Regression analyses and a structural equation model (SEM) were adopted to separate the contributions of environmental and physiological effects. The photosynthetic parameters showed unimodal seasonal patterns and significantly interannual variations. Variations of air temperature (Ta) and soil water content (SWC) drove the seasonal patterns of photosynthetic parameters, while SWC predominated their interannual variations. Moreover, contrasting with the predominant roles of Ta on α and Rd, SWC explained more variance of Pmax than Ta. Results of SEM revealed that environmental factors impacted photosynthetic parameters both directly and indirectly through regulating physiological responses reflected by stomatal conductance at the canopy level. Moreover, leaf area index (LAI) directly affected α, Pmax and Rd and dominated the variation of Pmax. On the other hand, SWC influenced photosynthetic parameters indirectly through LAI and canopy surface conductance (gc). Our findings highlight the importance of physiological regulation on the photosynthetic parameters and carbon assimilation capacity, especially in water-limited grassland ecosystems.

Preferences for different nitrogen forms in three dominant plants in a semi-arid grassland under different grazing intensities

Plant species generally absorb different nitrogen (N) forms from soil in ways that minimize N niche overlap, but whether and how grazing affects a plant’s preferred form of N remains unclear. Using the in-situ stable N isotope-labeling technique, we explored the preference of plants in taking up N of different chemical forms along an experimental gradient of grazing intensity in a semi-arid grassland in Inner Mongolia. 15N-labelled nitrate (NO3−), ammonium (NH4+) and glycine solutions were injected into the soil under nil (G0, as a control), light (G1) and heavy grazing (G2) grassland plots in June and August. Uptake of these three N forms was determined for three dominant plants, Leymus chinensis, Stipa grandis and Cleistogenes squarrosa. L. chinensis had the highest N acquisition capacity. Regardless of species, N absorption was higher in August than in June. While all three plant species absorbed glycine-N, they preferentially absorbed N in its inorganic forms (NO3−-N + NH4+-N), with NO3−-N having the highest uptake. Irrespective of grazing intensity, during peak growth (August) all three plant species preferred to absorb NO3−-N (the dominant N form) than NH4+-N or glycine-N. In contrast, in June plants differed in their preferred form of N uptake depending on the grazing treatment. Under heavy grazing (G2), all plants preferentially absorbed NO3−-N. Under light grazing (G1), all plants absorbing all three N chemical forms with no significant difference. Under no grazing (G0), L. chinensis preferentially absorbed NO3−-N but otherwise there was no significant effect of grazing intensity on the preferred form of N. Our results indicate that the three species of plants that we observed altered their N-uptake preference in response to grazing intensity differently in the early growth and vigorous growth stages. Plant N niche differentiation in time, space and chemical N forms needs to be explored systematically in future studies to aid understand of grazing effects on N processes in grassland ecosystem.

Increase in rainfall intensity promotes soil nematode diversity but offset by nitrogen addition in a temperate grassland

Precipitation regime in arid and semi-arid regions is exhibiting a trend of increase in rainfall intensity but reduction in frequency under global climate change. In addition, nitrogen (N) deposition occurs simultaneously in the same regions. Nematodes are the dominant soil biota in terrestrial ecosystems and are involved in various underground processes. How the diversity of nematode communities responds to changing precipitation regime and how N deposition regulates the responses remain unclear. Here, we performed a field experiment initiated in 2012 to examine the effect of changes in the precipitation regime (2 mm precipitation intensity, 5 mm precipitation intensity, 10 mm precipitation intensity, 20 mm precipitation intensity, and 40 mm precipitation intensity) and N addition (10 g N m−2 yr−1) on soil nematode community in a semi-arid grassland in Inner Mongolia of China. We found that the abundance and diversity of nematodes increased under the treatments with fewer but stronger precipitation events (the largest abundance of total nematodes was 1458.37 individuals/100 g dry soil occurred under 40 mm intensity treatment). However, N addition reduced nematode diversity under these treatments, which largely offset the positive effects of increased rainfall intensity alone. Soil pH and plant belowground biomass were the main factors affecting nematode diversity. Our results imply that, as a consequence of global climate change, an increase in the intensity of rainfall events in the coming decades may favor the nematode communities within arid and semi-arid ecosystems. However, this positive effect may be largely offset by soil acidification in the regions experiencing heavy N deposition.

Different Effects of Increased Water and Nitrogen on Seasonal Soil N2o Emissions from Native Semiarid Grassland in Inner Mongolia, China

Different Effects of Increased Water and Nitrogen on Seasonal Soil N2o Emissions from Native Semiarid Grassland in Inner Mongolia, China

Prediction of vegetation phenology with atmospheric reanalysis over semiarid grasslands in Inner Mongolia

Vegetation phenology is a sensitive indicator of climate change and vegetation growth. In the present study, two phenological phases with respect to vegetation growth at the initial and mature stages, namely, the start of the season (SOS) and the peak of the season (POS), were estimated from a satellite-derived normalized difference vegetation index (NDVI) dataset over a long-term period of 32 years (1983 to 2014) and used to explore their responses to atmospheric variables, including air temperature, precipitation, solar radiation, wind speed and soil moisture. First, the forward feature selection method was used to determine whether each independent variable was linear or nonlinear to the SOS and POS. In addition, a generalized additive model (GAM) was used to analyze the correlation between the phenological phases and each independent variable at different temporal scales. The results show that soil moisture and precipitation are linearly correlated with the SOS, whereas the other variables are nonlinearly correlated. Meanwhile, soil moisture, wind speed and solar radiation are found to be nonlinearly correlated with the POS. However, air temperature and precipitation reveal a significant negative correlation with the POS. Furthermore, it was concluded that the aforementioned independent variables from the previous year could contribute to approximately 63%–85% of the SOS variations in the present year, whereas the atmospheric variables from April to June could contribute to approximately 70%–85% of the POS variations in the same year. Finally, the SOS and POS predicted by the GAM exhibit significant agreement with those derived from the satellite NDVI dataset, with the root mean square error of approximately 3 to 5 days.

Mechanisms of grazing management impact on preferential water flow and infiltration patterns in a semi-arid grassland in northern China

Grazing management is widely used to control grassland degradation in Inner Mongolia. However, the correlation between the soil physical properties, root traits, and infiltration patterns of different types of grazing management has seldom been studied. To reveal the effect of grazing management on water infiltration and preferential flow behavior, we first investigated the soil and plant properties in a grazing exclusion (19 years, GE), cold-season grazing (19 years, CG), and free-grazing grassland (19 years, FG) in a semi-arid grassland in Inner Mongolia. Dye tracer infiltration was adopted to obtain the water infiltration patterns from different types of grazing management. Finally, root biomass and root morphological traits were measured in a field experiment. The results showed that the plant height, vegetation coverage, richness index, Shannon-Wiener index, soil water content, total porosity, and mean weight diameter were higher at the GE site than at the FG site, whereas soil bulk density and sand content were lower at the GE site than at the FG site (P < 0.05). In addition, the root mean diameter, specific root length, and root mass density were higher at the GE site than at the FG site. As a result, differences in these root traits and soil and vegetation properties affected the preferential water flow behavior in the three types of grassland. The preferential flow evaluation index (PFI) of the GE, CG, and FG sites was 0.89, 0.30, and 0.15, respectively, which indicated that more obvious preferential flow occurred at the GE site than at the CG and FG sites. These findings highlight that the long-term GE enhanced plant density and root biomass, which could potentially promote the natural restoration of soil pores and preferential water infiltration. Therefore, local governments and herders should implement GE rather than other grazing management practices to prevent grassland degradation.

Heavy rainfall in peak growing season had larger effects on soil nitrogen flux and pool than in the late season in a semiarid grassland

Increasing heavy rainfalls can strongly affect ecosystem nitrogen (N) cycling processes and thereby alter soil N fluxes and pools. However, the effects of heavy rainfalls on soil N fluxes and pools are poorly understood, particularly with regards to high rainfall timing under field conditions. We conducted a 3-year (2014–2016) manipulative experiment in which heavy rainfall was imposed in middle (plant peak growing stage) or late (plant senescent growth stage) growing season in a semiarid grassland of Inner Mongolia, China to explore the responses of N2O fluxes and soil total N contents and the underlying microbial mechanisms. Mid-season heavy rainfall promoted soil N2O emissions by 65% on average across the three years, attributable mainly to increases in denitrifying nirK and nirS abundances induced large denitrification at higher soil water contents. However, archaeal and bacterial amoA and narG genes did not change significantly due probably to counteracting effects of increased soil water content (positive) and soil pH (negative). Mid-season heavy rainfall led to 17% reduction in soil total N by the end of the last year of the study (2016), partly due to the enhanced accumulated N2O emissions over the three years. In contrast, late-season heavy rainfall did not change N2O emissions and soil total N contents even though soil water content, soil pH and nirK and nirS abundance were significantly increased, perhaps due to limitation by low temperature. Timing of the heavy rainfall events during the plant growing season strongly influenced their impacts on soil N fluxes and pools and heavy rainfalls in the peak stage of plant growth may potentially cause a positive feedback to global warming and exacerbate N limitation in terrestrial ecosystems.

Linking leaf traits to the temporal stability of above- and belowground productivity under global change and land use scenarios in a semi-arid grassland of Inner Mongolia

The biotic drivers for the temporal stability of aboveground net productivity (ANPP) in natural ecosystems are well understood. However, knowledge gaps still exist regarding the relative importance of biotic and abiotic drivers regulating the temporal stability of aboveground productivity (ANPP), belowground net productivity (BNPP), and community net productivity (NPP) under global change and land use scenarios. Thus, in this study, we aimed to study the effects of increased water and nitrogen availability on temporal stability of ANPP, BNPP, and NPP and underlying mechanisms at sites with different long-term grazing histories in typical grasslands of the Inner Mongolia. The results suggested that resource addition affected the ANPP stability, but it did not change the stability of BNPP and NPP, which were all mediated by grazing histories. Most importantly, our study further indicated that species asynchrony, primarily contributed to the stability of ANPP and NPP by weakening their variation, and species asynchrony was regulated directly by plant diversity-related variables and indirectly by soil variables which were affected by resource addition and grazing history. In addition, an increase of ANPP stimulated under resource addition was a secondary contributor to ANPP stability. Specifically, the community-weighted mean of specific leaf area (CWM SLA) regulated the ANPP stability indirectly by promoting species asynchrony, while functional diversity of leaf area and SLA both directly controlled the BNPP stability. Findings of our study demonstrate that different mechanisms drove temporal stability of above- and belowground productivity. Our study has important implications for maintaining the temporal stability of community productivity and for establishing sustainable management practices of semi-arid grasslands under global change and land use scenarios.