Semi-arid Steppe Of Inner Mongolia Research Articles

Analysis of spatial-temporal trends and causes of vapor pressure deficit in China from 1961 to 2020

Understanding the spatial-temporal trends and variability of vapor pressure deficit (VPD) is important for promoting climate protection and water management. This study was based on long-term series data of maximum/minimum air temperature (Tmax/Tmin) and relative humidity (RH) from 1740 meteorological stations in China from 1961 to 2020 to jointly analyze the spatial-temporal variation characteristics of VPD at different time scales, climate zones and extreme events and their influencing factor. The results showed an overall highly significant increasing trend in VPD, Tmax, and Tmin, with Sen's slope (SS) values of 0.0178 kPa/decade, 0.22 °C/decade, and 0.32 °C/decade, respectively. The opposite was true for RH (SS = −0.41%/decade). Moreover, the trends all changed abruptly around the year 2000. The VPD exhibited a highly significant upward trend in spring as well as at the junction of climatic zones and along the southeastern coast. This was particularly evident in the semi-arid steppe of Inner Mongolia (IM), the humid tropical south China (SC), and the semi-humid warm-temperate north China (NC) regions. For the frequency distribution of VPD extremes in each climate zone, the arid desert of northwest China (NWC)> > IM > NC. The frequency range was 758–910 days/decade, 249–410 days/decade, and 170–300 days/decade, respectively. Moreover, their average frequency of extreme events was 88 times/decade, 55 times/decade, and 38 times/decade respectively. The main meteorological factors affecting VPD taken together were Tmax, RH, Tmin, sunshine duration (N), and wind speed (U2) with mean importance values of 0.612, 0.351, 0.020, 0.016, and 0.001 respectively. Meanwhile, we found that VPD and reference crop evapotranspiration (ET0) were positively correlated and negatively correlated with soil water content and altitude. The maximum growth rate of VPD was observed in Cropland and Impervious environments. This research reveals the spatial-temporal characteristics of meteorological elements in China and provides a reference for scholars to formulate countermeasures against climate change.

Understanding the drivers of ecosystem multifunctionality in the Mongolian steppe: The role of grazing history and resource input

Predicting the comprehensive driver of ecosystem multifunctionality is crucial for effective grassland management. However, the underlying biotic and abiotic mechanisms of ecosystem multifunctionality under global change and land use remain poorly understood. In this study, a 3-year field experiment was conducted in a semi-arid steppe in Inner Mongolia to investigate the relative importance of different biotic and abiotic factors in regulating aboveground ecosystem multifunctionality (AEM) and belowground ecosystem multifunctionality (BEM) in response to resource input after long-term grazing. The experiment involved three grazing intensities (1.5 low, 4.5 moderate, and 9.0 high sheep/ha) with a 7-year difference in grazing history. Precipitation (W) and nitrogen deposition (N) were manipulatively increased during the growing season. The study focused on exploring the effects of various biotic factors (e.g. species richness, functional diversity, plant functional groups) and abiotic factors (e.g. soil environment variables) on AEM and BEM. The results revealed asymmetric responses of AEM and BEM to resource input. Resource input enhanced AEM, but not BEM. However, increasing grazing intensity substantially reduced BEM, though we noted that AEM and BEM decreased the most under moderate grazing. Interestingly, the study found consistent responses of single ecosystem functions and ecosystem multifunctionality to resource input across the three grazing blocks. Structural equation modeling (SEM) analysis indicated that species richness primarily enhanced AEM, while soil environment played a major role in promoting BEM across different grazing history intensities and the whole grazed system. Multiple biotic and abiotic factors with varying relative importance in different grazing history scenarios controlled AEM and BEM. Species richness exhibited a strong influence on AEM and BEM, but within a narrow effect threshold range, whereas soil environment had a lesser effect size but a wider threshold range. This study provides the first evidence that grazing history and resource enrichment jointly regulate AEM and BEM. The findings highlight the importance of considering biodiversity conservation, soil health, and land use history in management practices aimed at maintaining ecosystem multifunctionality under climate change and human activities scenarios.

Changes in plant species dominance maintain community biomass production under warming and precipitation addition in temperate steppe in Inner Mongolia, China

Dominant species play a crucial role in regulating plant community structure and productivity. Climate change affects community productivity by changing plant traits and resource use efficiency. However, the response of the productivity of a dominant species to warming and precipitation addition and the related effects on community biomass production in semi-arid grasslands remain unclear. We conducted a ten-year warming and precipitation addition study of a semi-arid steppe in Inner Mongolia, China. We examined the responses of community composition, biomass production, and trait and resource use efficiency of two dominant species, Leymus chinensis (rhizome grass) and Stipa krylovii. The results show that warming and precipitation increased the biomass of L. chinensis and decreased the biomass of S. krylovii. Community biomass production was unchanged under warming and precipitation from the contrasting changes in the two dominant species. Warming significantly increased the leaf area (LA) of L. chinensis and S. krylovii compared to that in ambient conditions, while it decreased the specific leaf area (SLA) and δ13C of S. krylovii. Increases in temperature stimulated biomass production of L. chinensis by affecting salicylic acid (SA) and GA (gibberellin), and they increased its competitive ability compared with that of S. krylovii. Our results highlight the different responses of L. chinensis and S. krylovii to environmental changes, which stabilised community productivity under warming and precipitation. Our study provides evidence that S. krylovii may be replaced by L. chinensis in steppe climates in the warmer and wetter future.

Opposite response of N2O emissions in different seasons to warming and precipitation addition on a temperate steppe

AbstractClimate change is an important issue that affects both global warming and precipitation, and the main cause is increased N2O emissions. Temperature and moisture are key factors in grassland ecosystem's response to climate change, and they can affect N2O fluxes. To clarify the impacts of warming and precipitation changes on N2O fluxes, an experiment was conducted in a semiarid steppe in Inner Mongolia, China over a nine‐year period (2011–2019). Plant productivity and soil nutrient dynamics were examined concurrently from 2017 to 2019, and N2O fluxes were monitored in response to different treatment conditions: control (C), warming (W), precipitation addition (P), and warming and precipitation addition (WP). The results showed that N2O emissions in the growing season were higher than those in the nongrowing season. Warming and precipitation addition had no significant effect on N2O fluxes compared with ambient conditions. Compared with P treatment, warming increased N2O flux in nongrowing season and decreased it in growing season. N2O flux was positively correlated with soil temperature and moisture (p < 0.05). Warming had a significant positive effect on soil NH4+‐N, whereas additional precipitation had a large positive effect on soil total nitrogen and soil nitrate nitrogen. With the WP treatment, soil microbial biomass nitrogen (MBN) and soil microbial biomass carbon (MBC) increased by 53.8% and 41.9%, respectively. The decrease in N2O emissions during the growing season in the W treatment compared with the P treatment may be largely attributed to the greater dominance of Leymus chinensis. The results highlight that changes in species dominance play an important role in regulating N2O emissions, and that the N2O fluxes in the nongrowing season account for a large proportion of the changes in N2O fluxes. Therefore, The warming effects on N2O emissions during nongrowing seasons should be further investigated.

The effect of precipitation timing on phylogenetic and functional community structure in a semi-arid steppe.

Changes in the amount and timing of precipitation may affect plant species coexistence. However, little is known about how these changes in precipitation structure plant communities. Here, we conducted a 6-year field precipitation manipulation experiment in the semi-arid steppe of Inner Mongolia, China, to assess the importance of species extinction and colonization in community assembly by incorporating information on phylogenetic and functional relatedness. Our results demonstrated that the decline in plant species richness under decreasing precipitation in the late and entire growing season could be attributed to a decrease in species colonization and an increase in species loss, respectively. The increase in species richness under increasing precipitation in the late growing season was mainly caused by increases in colonizing species. The loss of species that were more closely related to other residents under decreasing precipitation in the late growing season did not alter patterns of phylogenetic overdispersion, and the colonization of species that were more distantly related to residents under increasing precipitation in the late growing season shifted functional relatedness from clustering to randomness. Increasing precipitation may weaken the strength of environmental filtering induced by water stress in this semi-arid steppe and thus increase the probability of successful colonization of functionally dissimilar species relative to residents. Our study suggests that incorporating information on the functional and phylogenetic relatedness of locally lost resident species and the colonization of new species into analyses of community assembly processes can provide new insights into the general responses of plant communities to global change.

Seasonal patterns of soil microbial community response to warming and increased precipitation in a semiarid steppe

Microorganisms are the basis for sustaining ecosystem function and are extremely sensitive to global warming and altered precipitation. Nevertheless, the seasonal pattern of the microbial response to a coupled effect of warming and increased precipitation is largely unknown. We set up a six-year manipulative experiment to verify changes in microbial response to warming (approximately 2 °C), increased precipitation (20 %), and their interactive effect in a semiarid steppe in Inner Mongolia. We detected changes in microbial species richness, diversity, community structure, and microbial interactions during different periods of the growing season. The results suggest that warming and increased precipitation had a stronger impact on the microbial community in the early growing season than in the mid- and late growing seasons. In the early growing season, warming significantly decreased bacterial diversity, while increased precipitation did not significantly affect the microbial community. The interactive effect of increased precipitation and warming significantly increased bacterial richness but decreased fungal richness and amplified the dissimilarities among bacterial and fungal communities. Compared to the early growing season, less microbial taxa significantly responded to warming and increased precipitation in the mid- and late growing seasons. Warming weakened species interactions, as evidenced by fewer nodes and links and lower complexity and robustness in the network. Increased precipitation strengthened species interactions and eased the warming-induced negative effect under the interactive effect. Our findings emphasize that more attention should be given to the changes in the microbial community in the early growing season of grassland in Inner Mongolia under future climate change scenarios.

Divergent effects of grazing versus mowing on plant nutrients in typical steppe grasslands of Inner Mongolia

Abstract Grazing and mowing are two major land use types in natural grasslands, which have intensive effects on nutrient cycling of grassland ecosystems by deposition of fecaluria nutrient versus removal of hay nutrient. Plant nutrients sensitively respond to the changes in nutrient cycling, while the information on the effects of diverse grazing versus mowing regimes on plant nutrients at different organs or levels are incomplete. A field experiment was conducted to compare the effects of continuous versus rotational grazing, and low versus high mowing frequencies on grassland ecosystems in a semiarid steppe of Inner Mongolia. Plant community characteristics and C, N and P concentrations of dominant species were determined across different managements. We found (i) plant community height and standing biomass significantly decreased with grazing intensity under both continuous and rotational grazing and under annual mowing. (ii) Plant shoot C concentration decreased, whereas N and P concentrations increased with grazing intensity in the two grazing regimes, while these concentrations showed no significant changes in response to the two mowing regimes. (iii) Plant community aboveground C, N and P pools significantly decreased with grazing intensity of both grazing regimes, but did not decrease with mowing frequency in the two mowing regimes. (iv) Plant root C, N and P concentrations showed little significant response to different grazing or mowing regimes, indicating a relatively bigger stability or slower response in plant root nutrients. Our study provides insights into the nutrient cycling in grazing and mowing grassland ecosystems from multiple perspectives.

Co-Regulation of Climate and Vegetation on Energy Balance and Partitioning Over a Semiarid Steppe in Inner Mongolia, China

Co-Regulation of Climate and Vegetation on Energy Balance and Partitioning Over a Semiarid Steppe in Inner Mongolia, China

Comparison of four bio-inspired algorithms to optimize KNEA for predicting monthly reference evapotranspiration in different climate zones of China

Accurate estimation of reference crop evapotranspiration (ET0) is of great significance to crop water use and agricultural water resources management. This study evaluated the performance of four bio-inspired algorithm optimized kernel-based nonlinear extension of Arps decline (KNEA) models, namely KNEA with grasshopper optimization algorithm (GOA-KNEA), KNEA with grey wolf optimizer algorithm (GWO-KNEA), KNEA with particle swarm optimization algorithm (PSO-KNEA), and KNEA with salp swarm algorithm (SSA-KNEA), on estimating monthly ET0 across China. Monthly meteorological data [including maximum air temperature (Tmax), minimum air temperature (Tmin), extra-terrestrial solar radiation (Ra), relative humidity (RH), global solar radiation (Rs), wind speed (U)] during 1966–2015 from 51 weather stations across the seven different climate zones of China were used for model training and testing. Four different combinations of meteorological data were applied as model input, and results from the FAO-56 Penman-Monteith formula were used as a control. Results showed that the GWO-KNEA model overall performed better than the other three coupling models, of which the GWO-KNEA2 model (i.e., the model with input combination 2) was the best (on average R2 = 0.9814, RMSE = 0.2143 mm d−1). The convergence rate and the population size of the GWO-KNEA model were also superior to the other three models. Among input combinations, models with combination 2 had the best overall performance, while models with combination 3 were the worst on average. In terms of the importance of each meteorological parameter contributing to model accuracy, Rs was greater than Ra, RH, or U. Among different climate zones, station specific models in the semi-arid steppe of Inner Mongolia showed the best estimating performance in general, while models in the Qinghai-Tibetan Plateau overall performed relatively poorly. The GOA-KNEA and SSA-KNEA models with the combination 4 showed large increases (29.7% and 28.7%, respectively), indicating a problem of overfitting. Conversely, the GWO-KNEA model was the most stable model with the smallest increase in RMSE during the testing phase (4.4–15.7%) among all models. In summary, taking the model's estimation accuracy, stability, convergence rate, and climate environment into account, our results suggest that GWO-KNEA would be a suitable model for estimating ET0 in different climate zones of China and the most practical input combination would be combination 2.

Belowground bud bank and its relationship with aboveground vegetation under watering and nitrogen addition in temperate semiarid steppe

In temperate perennial grasslands, the recruitment/regeneration of aboveground vegetation predominantly relies on belowground bud bank. Thus, understanding how belowground bud bank density and composition respond to global changes is essential to explain and predict plant community dynamics and ecosystem functions under global change context. The belowground bud bank and aboveground vegetation under the simulated precipitation changes and nitrogen deposition (by watering and N addition) were investigated in the temperate semiarid steppe of Inner Mongolia, China. N addition decreased total bud density but facilitated aboveground productivity, however, watering itself and its combination with N addition had little influence on total bud density. Different bud bank types showed specific responses to watering and N addition, especially, buds of grasses and forbs responded in an opposite way. Overall, shoot abundance were positively related to bud density, and showed similar responses with those of bud banks, especially for forbs, which are more sensitive to global changes. Our results imply that the changes in belowground bud bank might affect subsequent responses of plant communities to precipitation change and/or nitrogen deposition under future global change scenarios.

Effects of defoliation timing on plant nutrient resorption and hay production in a semi-arid steppe

Abstract Aims Nutrient resorption is a key plant nutrient conservation strategy, and its response to environmental and management changes is linked to nutrient cycling and production of ecosystems. Defoliation is a major pathway of mowing affecting plant nutrient resorption and production in grasslands, while the effect of defoliation timing has not been unexplored. The aim of this study was to examine the effect of defoliation timing on plant nutrient resorption and production in a steppe ecosystem. Methods We conducted a field experiment in a semi-arid steppe of Inner Mongolia including four treatments: early defoliation, peak defoliation, late defoliation and non-defoliation. We measured plant nitrogen (N) and phosphorus (P) resorption at species and community levels, and quantified plant N and P fluxes in resorption, litter return and hay output. Plant production in the mowing system was assessed by hay production and quality. Important Findings Peak and late defoliation, but not early defoliation, reduced plant community N and P resorption proficiency; and late defoliation reduced N resorption efficiency but not P resorption efficiency. Peak and late defoliation, but not early defoliation, reduced plant nutrient resorption flux and litter nutrient return flux. Defoliation timing did not alter root nutrient accumulation as nutrient uptake from soil likely compensated the deficit of nutrient resorption. Peak defoliation had the highest hay production and quality, while early defoliation had the lowest. Our results provide new insights into the nutrient cycling in mowing grassland, and imply that the mowing timing can be used as a tool to mediate the balance between conservation and production of steppes, and the early mowing before plant peak biomass period is recommended for conservation of the steppes while keeping sustainable pastoral production.

Distribution Characteristics of Soil Organic Phosphorus Fractions in the Inner Mongolia Steppe

Phosphorus (P) is one of the limiting nutrients in Inner Mongolia steppe soil, which seriously affect steppe productivity. Therefore, it is necessary to understand the distribution characteristics of organic P (Po) fractions and their influencing factors in Inner Mongolia steppe soil and to identify the contribution of Po fractions to soil available P (AP) to maintain the sustainable development of the Inner Mongolia steppe by improving the utilization rate of Po. The contents of soil Po fractions such as H2O-extractable Po (H2O-Po), NaHCO3-extractable Po (NaHCO3-Po), HCl-extractable Po (HCl-Po), NaOH-extractable Po (NaOH-Po), and phytate P (Phyt-P) were determined in soil samples (0–15 cm) from 15 sampling sites representing three types of grassland (i.e., desert steppe, typical steppe, and meadow steppe) in Inner Mongolia. The influencing factors of the soil Po fractions were determined by redundancy analysis (RDA). Soil Po content accounted for 61.0% of the total P (TP) on average. NaOH-Po was the main fraction of Po, accounting for 49.1% of Po on average; H2O-Po content accounted for the least amount of Po (mean 1.3 mg kg−1). H2O-Po and HCl-Po were not significantly different among the three steppes. The contents of NaHCO3-Po increased in the order of desert steppe < typical steppe < meadow steppe, and the trend of NaOH-Po and Phyt-P contents were desert steppe < meadow steppe < typical steppe. Pearson correlation analysis showed that NaHCO3-Po was positively correlated with AP (r = 0.86, p < 0.01). HCl-Po was negatively correlated with AP (r = − 0.56, p < 0.05). NaOH-Po and Phyt-P were significantly positively correlated with NaHCO3-extractable inorganic P (NaHCO3-Pi); Phyt-P was also negatively correlated with HCl-extractable Pi (HCl-Pi) (r = − 0.61, p < 0.05). These correlations were mainly caused by differences in steppe types and soil properties caused by climatic conditions, as shown by the result of RDA analysis. Soil Po plays an indispensable role in the supply of soil P in the semi-arid steppe of Inner Mongolia, where NaHCO3-Po and HCl-Po strongly contributed to AP. In addition, NaOH-Po and Phyt-P as a part of stable pools are important for providing P to other P pools. Po fractions in steppe soils were mainly regulated by climatic conditions and are closely related to the soil organic matter and pH.

The effects of topography on aboveground biomass and soil moisture at local scale in dryland grassland ecosystem, China

Water is the primary limiting factor for grassland vegetation in dryland regions. Topography is considered to play an important role in the distribution of soil moisture, which will significantly affect grassland ecosystems. To examine the response of soil water content (SWC) and aboveground biomass (AGB) of grassland vegetation to precipitation patterns and topography, a 6-year investigation was conducted during the period from 2012 to 2017 in a semiarid steppe of Inner Mongolia, China. The study area was divided into three parts based on the landscape position, i.e., top area (TA), slope area (SA) and bottom area (BA). The results suggested that SWC and AGB would be significantly affected by topography and precipitation patterns. A significant negative relationship was found between the SWC and the altitude of the sampling sites. In the dryer years (2013–2017), the AGB of the BA was significantly higher than that of the SA and TA. However, a non-significant difference was found for the AGB values between the three landscape positions in the wetter year (2012). During the growing season, variation of AGB and SWC was similar in 2014 but differed in 2015. AGB exhibited a significant positive relationship with SWC above a minimum value. Precipitation significantly affected the AGB of grassland, and moderate rainfall events were more effective than light rainfall events for grassland vegetation. Moreover, the distribution of species varied in different areas, which may result in the differences in the responses of AGB to soil moisture and precipitation. This study clarifies the effects of micro-topography on soil moisture and grassland ecosystems at a local scale in dryland regions, which provides useful information for grassland ecosystem management.

Comparison of neuron-based, kernel-based, tree-based and curve-based machine learning models for predicting daily reference evapotranspiration.

Accurately predicting reference evapotranspiration (ET0) with limited climatic data is crucial for irrigation scheduling design and agricultural water management. This study evaluated eight machine learning models in four categories, i.e. neuron-based (MLP, GRNN and ANFIS), kernel-based (SVM, KNEA), tree-based (M5Tree, XGBoost) and curve-based (MARS) models, for predicting daily ET0 with maximum/maximum temperature and precipitation data during 2001–2015 from 14 stations in various climatic regions of China, i.e., arid desert of northwest China (NWC), semi-arid steppe of Inner Mongolia (IM), Qinghai-Tibetan Plateau (QTP), (semi-)humid cold-temperate northeast China (NEC), semi-humid warm-temperate north China (NC), humid subtropical central China (CC) and humid tropical south China (SC). The results showed machine learning models using only temperature data obtained satisfactory daily ET0 estimates (on average R2 = 0.829, RMSE = 0.718 mm day−1, NRMSE = 0.250 and MAE = 0.508 mm day−1). The prediction accuracy was improved by 7.6% across China when information of precipitation was further considered, particularly in (sub)tropical humid regions (by 9.7% in CC and 12.4% in SC). The kernel-based SVM, KNEA and curve-based MARS models generally outperformed the others in terms of prediction accuracy, with the best performance by KNEA in NWC and IM, by SVM in QTP, CC and SC, and very similar performance by them in NEC and NC. SVM (1.9%), MLP (2.0%), MARS (2.6%) and KNEA (6.4%) showed relatively small average increases in RMSE during testing compared with training RMSE. SVM is highly recommended for predicting daily ET0 across China in light of best accuracy and stability, while KNEA and MARS are also promising powerful models.

Seasonal timing regulates extreme drought impacts on CO2 and H2O exchanges over semiarid steppes in Inner Mongolia, China

Climate models predict a substantial increase in the frequency of extreme drought, suggesting subsequent impacts on the carbon (C) and water cycles. Although many studies have investigated the impacts of extreme drought on ecosystem functioning, it remains unknown how the timing of extreme drought within a growing season may affect carbon and water cycling. Here we conducted a 3-year field experiment to investigate the influence of seasonal drought timing on ecosystem carbon and water exchange by excluding rainfall (for consecutive 30 days) during three periods of the growing season (May–June, July–August and August–September) in fenced and grazed sites of a semiarid temperate steppe in Inner Mongolia, China. In the fenced steppe, extreme drought reduced growing-season net CO2 uptake regardless of drought timing, while in the grazed steppe, early-growing season drought caused relatively larger reductions to net CO2 uptake than drought imposed later in the season. The effect of extreme drought on evapotranspiration (ET) was similar to that of CO2 exchange at the fenced site, with consistent reductions of seasonally-integrated ET for all treatments compared with the ambient condition. In contrast, at the grazed site, the response of ET to extreme drought was more variable, possibly due to the absence of litter and greater bare ground. Surprisingly, both gross and net carbon uptake declined with increasing ET at the grazed site, while the fenced site showed the positive water-carbon linkage typically seen in semiarid ecosystems. The different responses of CO2 and water exchanges for the fenced and grazed sites were regulated predominately by soil temperature and soil water content. Together, our results show that drought timing within the growing season can significantly alter drought impacts on ecosystem water and CO2 exchanges, and that grazing management may further mediate the response.

Effects of nitrogen addition and mowing on rodent damage in an Inner Mongolian steppe.

Rodent damage is a serious threat to sustainable management of grassland. The effects of nitrogen (N) deposition and grassland management on rodent damage have been scarcely studied. Here, we reported the effects of 2 years of N addition and mowing on burrow density and damage area of Citellus dauricus in a semiarid steppe in Inner Mongolia. N addition significantly aggravated, while mowing alleviated rodent damage in the grassland under study. Burrow density and damage area increased 2.8‐fold and 4.7‐fold, in N addition plots compared to the ambient N addition treatment, respectively. Conversely, mowing decreased burrow density and damage area by 75.9% and 14.5%, respectively, compared to no mowing plots. Observed changes in rodent damage were mainly due to variations in plant community cover, height, and aboveground net primary productivity. Our findings demonstrate that N addition and mowing can affect the rodent density and activity in grassland, suggesting that the effects of a changing atmospheric composition and land use on rodent damage must be considered in order to achieve better grassland management.

Recovery succession drives the convergence, and grazing versus fencing drives the divergence of plant and soil N/P stoichiometry in a semiarid steppe of Inner Mongolia

Understanding the plant and soil elemental stoichiometry during grassland dynamics is important for developing measures to enhance the restoration of degraded grassland. A number of restoration practices have been applied in the degraded typical steppe grassland in Inner Mongolia, either for research purpose or as actual restoration projects. However, the effects of different restoration measures on soil and plant N/P stoichiometry remain unclear. Here we explored the effects of three restoration measures (i.e., natural recovery, NR; shallow ploughing, SP; and harrowing HA) on the N, P stoichiometry of plant and soil in a typical steppe of Inner Mongolia, by comparing plant and soil N, P content and N/P ratio among the grasslands restored through NA, SP and HA, and that under sustained animal grazing (GR). Long-term restoration increased aboveground plant biomass, litter accumulation and changed soil and plant N/P ratio. Soil N and P contents in restored grassland (NR, SP or HA) were higher than those under grazing (GR); the restored grasslands shared a common slope of N-P linear regression, which was significantly greater than that of grazing grassland. Plant N content and N/P ratio decreased firstly and then increased during the restoration of degraded grassland. Soil N limitation is greater than soil P limitation in typical steppe of Inner Mongolia. Soil N limitation is smaller in naturally recovered grassland and grazing grassland than in the restored grassland following shallow ploughing and harrowing. The restoration succession over 26-years after the exclusion of animal grazing have changed the N-P coupling relation in grassland soil, with a common N-P relation converged under grassland that are treated with different restoration measures.

Effects of warming and increased precipitation on net ecosystem productivity: A long-term manipulative experiment in a semiarid grassland

The balance between ecosystem carbon dioxide (CO2) uptake and release determines the level of carbon (C) sequestration in terrestrial ecosystems and its potential impact on CO2 concentration in the atmosphere. However, how changes in temperature and precipitation will affect the relationships of net ecosystem productivity (NEP) with gross primary productivity (GPP) and ecosystem respiration (ER) remains unclear. In this study, a nine-year field manipulative experiment was conducted with elevated temperature and increased precipitation in a semiarid steppe of Inner Mongolia, China. Experimental warming reduced GPP and ER by almost the same amount, leading to a slight change in NEP (−0.16μmolm−2s−1), whereas increased precipitation stimulated GPP more than ER during the growing seasons, resulting in an enhanced NEP (+0.63μmolm−2s−1). In addition, seasonal patterns of ecosystem C fluxes and the NEP-GPP or NEP-ER relationships were not altered by experimental warming. However, increased precipitation delayed the peak of GPP during the growing seasons and enhanced the correlation between NEP and GPP in the steppe ecosystem. The enhanced control of GPP over NEP under the increased precipitation suggests that ecosystem C sequestration is attributed more to C uptake than C release when water availability is improved in the semiarid grassland. Our findings provide an insight into the response mechanism of ecosystem C flux to warming and precipitation change in semiarid grasslands, and facilitate the projection of terrestrial ecosystem C dynamics and climate feedbacks in the future.

Arbuscular mycorrhizal fungi regulate soil respiration and its response to precipitation change in a semiarid steppe.

Arbuscular mycorrhizal fungi (AMF) are critical links in plant–soil continuum and play a critical role in soil carbon cycles. Soil respiration, one of the largest carbon fluxes in global carbon cycle, is sensitive to precipitation change in semiarid ecosystems. In this study, a field experiment with fungicide application and water addition was conducted during 2010–2013 in a semiarid steppe in Inner Mongolia, China, and soil respiration was continuously measured to investigate the influences of AMF on soil respiration under different precipitation regimes. Results showed that soil respiration was promoted by water addition treatment especially during drought seasons, which induced a nonlinear response of soil respiration to precipitation change. Fungicide application suppressed AMF root colonization without impacts on soil microbes. AMF suppression treatment accelerated soil respiration with 2.7, 28.5 and 37.6 g C m−2 across three seasons, which were mainly caused by the enhanced heterotrophic component. A steeper response of soil respiration rate to precipitation was found under fungicide application treatments, suggesting a greater dampening effect of AMF on soil carbon release as water availability increased. Our study highlighted the importance of AMF on soil carbon stabilization and sequestration in semiarid steppe ecosystems especially during wet seasons.

Do sheep grazing patterns affect ecosystem functioning in steppe grassland ecosystems in Inner Mongolia?

Overgrazing has driven degradation and desertification of semi-arid grasslands in Northern China over recent decades. Selective grazing by sheep influences sward structure by inducing heterogeneous vegetation patterns comprising overgrazed hotspots and areas rejected by grazing sheep. In this study, we examined the effects of grazing intensity (ungrazed, light and heavy grazing in 2008 and 2010) and grazing system (a mixed system involving continuous grazing alternating annually with hay making vs. a continuous system involving continuous utilization of the same area for grazing) on plant biomass distribution and ecosystem functioning after 4 years and 6 years of controlled grazing in a semi-arid steppe of Inner Mongolia, China. The spatial biomass distribution was determined by sward height measurements converted to biomass and afterwards visualized in biomass distribution semivariograms. Within each of the different areas: grazed (i.e., areas frequently grazed by sheep), rejected (i.e., areas largely avoided by grazing sheep) and fenced (i.e., areas from which grazing had been excluded by fencing), plant species and soil parameters were sampled in order to analyze the mechanisms and effects of grazing patterns on ecosystem functioning. The results revealed a more homogeneous biomass distribution in the ungrazed and heavily grazed plots compared to lightly grazed plots, in which heterogeneous biomass distribution patterns included both overgrazed hotspots and rejected areas. The patch vegetation patterns were consistent between years only under light grazing intensity. However, patch vegetation patterns in the continuous system did not necessarily indicate negative effects on grassland ecosystem functioning. Within the 6 years of grazing experiment, it appears that patchy structure rather than homogeneous patterns showed higher biodiversity, significant variations in litter, soil water content and soil temperature and smaller effects on belowground biomass and carbon storage. Therefore, heterogeneous patchy vegetation patterns are likely to moderate grassland recovery and optimize ecosystem functioning by forming resource islands with sufficient water and nutrients in the short run.