Meadow Steppe Of Inner Mongolia Research Articles

Moderate grazing increased carbon, nitrogen and phosphorus storage in plants and soil in the Eurasian meadow steppe ecosystem

The effects of grazing on the cycling of carbon (C), nitrogen (N) and phosphorus (P) in grassland ecosystems are complex. Uncertainty still exists as regards the allocation of C, N and P storage amounts in grazed ecosystems in Inner Mongolia, situated at the eastern end of the Eurasian dryland. Based on the long-term cattle grazing experimental platform in the Hulun Buir meadow steppe of Inner Mongolia, a 3-year (2019–2021) field control experiment was conducted to assess how the grazing intensity influenced the quantities of C, N and P stored in canopy biomass, root, litter and soil compartments. We examined the relationships between the different pools and their regulatory pathways at the ecosystem level across six grazing intensities. In general, grazing increased the aboveground N and P contents but decreased the aboveground biomass C content and nutrient storage amounts in aboveground biomass, roots and litter. The grazing intensity of 0.34 AU ha−1 increased soil organic carbon, total nitrogen and total phosphorus storage amounts, with the soil accounting for 98 % of total reserves on average. Grazing affected soil pH， nutrient contents, above- and belowground biomass and soil environmental factors such as soil bulk density, which in turn affected C, N and P storage in the ecosystem according to the results of the structural equation model; therefore, grazing intensity can be an important factor regulating the input and output of nutrients in the ecosystem. In the future, for adaptive management of grasslands, moderate grazing could effectively increase C, N and P storage in meadow steppe ecosystems and ensure the nutrient balance and long-term sustainable development.

Belowground Bud Bank Is Insensitive to Short-Term Nutrient Addition in the Meadow Steppe of Inner Mongolia

Belowground Bud Bank Is Insensitive to Short-Term Nutrient Addition in the Meadow Steppe of Inner Mongolia

Nitrogen and phosphorus additions alter foliar nutrient concentrations of dominant grass species and regulate primary productivity in an Inner Mongolian meadow steppe

Excessive nitrogen (N) inputs shift grassland productivity from nitrogen (N) to phosphorus (P) limitation. However, how plant nutrient concentrations and stoichiometric dynamics at community and species level responding to variable soil N and P availability, and their roles in regulating net primary productivity in meadow steppe remain unclear. To address this issue, we carried out an experiment with fifteen treatments consisting of factorial combinations of N (0, 1.55, 4.65,13.95, 27.9 g N m−2 yr−1) and P (0, 5.24,10.48 g P m−2 yr−1) for three years in a meadow steppe in Inner Mongolia. We examined concentrations and stoichiometry of C (carbon), N, P in plants and soils, and their associations with plant primary productivity. Results revealed mean community N:P ratios for shoots (12.89 ± 0.98) did not exceed 14 within the control treatment, indicating that plant growth was primarily N-limited in this ecosystem. Shoot N:P ratios were significantly increased by N addition (>16 when N application rate above 4.65 g N m−2 yr−1), shifting the community from N- to P-limited whereas significantly reduced by P addition (N:P ratios <14), further aggravating N limitation. N addition increased leaf-N concentrations whereas decreased leaf C:N ratios of all four species, but only the values for two graminoid species were significantly influenced by P addition. Leaf-P concentrations significantly increased for graminoids but significantly decreased for forbs with the application of N. VPA analysis revealed that aboveground components, especially in grass leaves, explained more variation in aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) than root and soil components. For grasses, leaf-N concentrations showed high association with ANPP, while leaf-P concentrations were associated with BNPP. These results highlight that N and P depositions could affect the leaf-nutrient concentrations of dominant grasses, and thereby potentially alter net primary productivity in meadow steppe.

Enhanced foliar 15 N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds.

Determining the abundance of N isotope (δ15 N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their 15 N signatures remains unclear. Here, the response of 15 N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH4 HCO3 , urea, and NH4 NO3 ) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ15 N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N2 -fixing species) showed significantly lower 15 N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ15 N of all three species increased with increasing N addition rates, with a sharp increase above an Naddition rate of ~10g N m-2 year-1 . Foliar δ15 N values were significantly higher when NH4 HCO3 and urea were added than when NH4 NO3 was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global Ndeposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.

Methane and Nitrous Oxide Fluxes with Different Land Uses in the Temperate Meadow Steppe of Inner Mongolia, China

Background and aims: Grazing and mowing are widely adopted management practices for the semiarid steppe in China that profoundly affect the greenhouse gas (GHG) flux in grassland ecosystems. However, the general mechanisms for CH4 and N2O fluxes in response to grazing and mowing remain poorly understood. Thus, we conducted year-round flux measurements of CH4 and N2O fluxes to investigate the effect of grazing and mowing on CH4 and N2O fluxes. Methods: Using manual static chamber and gas chromatography, we measured the fluxes of CH4 and N2O from grazing-exclusion, grazing and mowing sites from June 2019 to June 2020 in the Hulunbuir Grassland, Inner Mongolia. Results: Grazing and mowing increased soil temperature and reduced soil water content and soil inorganic N content. Compared with grazing and mowing, lower mean CH4 uptake (−67.58 ± 8.9 μg m−2 h−1) and higher mean N2O emissions (29.17 ± 6.8 μg m−2 h−1) were found at the grazing-exclusion site. No pulse emissions of N2O were found for all sites during the spring thaw period (STP), and only two small N2O emission peaks due to soil thawing were captured on April 2nd and 5th. The contribution of the spring thaw to the total annual N2O budget was small and accounted for only 10%, 13% and 12% of the annual fluxes at the grazing-exclusion, grazing and mowing sites, respectively. Conclusion: Our results indicate that grazing and mowing enhance CH4 uptake and inhibit N2O emissions, primarily due to the increased soil temperature and reduced soil water content and soil inorganic N content. No apparent pulse N2O emissions were observed at any of the three sites during the STP in the Hulunbuir grassland.

Effects of exogenous organic/inorganic nitrogen addition on carbon pool distribution and transformation in grassland soil

AimsIncreases in nitrogen (N) deposition may significantly affect the organic carbon (OC) cycle in soil. The inconsistent findings of the influence of added N on soil OC pools highlight the need of quantifying responses of the OC pool distribution to N addition. Moreover, the influence of N addition with a mixture of organic and inorganic N on OC pool distribution and stabilization in grassland soil remains unclear. MethodsWe carried out a five-year field experiment with adding N to examine the effects of different types of N addition on soil OC pool distribution and transformation in a meadow steppe in Inner Mongolia. We applied N in the ratios of inorganic N (IN) and organic N (ON) at 10:0 (N1), 7:3 (N2), 5:5 (N3), 3:7 (N4), 0:10 (N5), and 0:0 (CK), respectively. We measured OC content in bulk soil, particulate organic matter (POM), and mineral-associated organic matter (MAOM) fractions. Additionally, a short-term soil incubation was conducted to assess potential OC mineralization. ResultsOur study showed no significant effect on soil organic carbon content of different ratios of IN/ON addition. N addition reduced microbial biomass C/N ratio, the fraction of mineral-associated organic matter, cumulative CO2 emission, and microbial metabolic quotient. Compared with ON addition alone, IN addition alone showed a stronger effect on the C in different soil fractions and soil OC mineralization. The particulate organic matter (POM) fraction was more sensitive to N addition than the mineral-associated organic matter (MAOM) fraction. ConclusionsOur results suggest that the contribution of N in organic and inorganic forms affecting OC pool distribution with different turnover rates should be considered when assessing the effects of N addition types on soil OC processes in grassland.

Interannual variations in natural abundance of nitrogen stable isotopes in soil and plant and their implications in a meadow steppe

Nitrogen is the most limiting nutrient for ecosystems. The natural abundance of δ15N (15N/14N) can efficiently indicate ecosystem nitrogen cycling processes. We investigated the interannual variations in natural abundance of δ15N in soil-plant system and soil net nitrogen mineralization in a meadow steppe of Inner Mongolia. Results across the four sampling years (2017-2020) showed that the content of soil NO3--N (9.83-14.79 mg·kg-1) was significantly higher than that of NH4+-N (3.92-5.00 mg·kg-1) and that δ15N value of soil NH4+ (13.3‰-18.3‰) was significantly higher than that of NO3-(3.76‰-6.14‰). The δ15N value of soil NO3- was negatively correlated with soil NO3- content. The δ15N value of soil NH4+ was relatively higher in the dry years, while the δ15N value of soil NO3- significantly decreased in the wetter and drier years. Soil net mineralization and ammonification rates were significantly higher in the dry years than that of the wet years, while soil nitrification rates showed no correlation with annual precipitation. The δ15N values of plants were not related to that of soils, but nega-tively correlated with plant nitrogen content. Both δ15N values and nitrogen contents were significantly and positively correlated between the leguminous and non-leguminous plants, suggesting that legume could facilitate nitrogen uptake of non-leguminous plants. These results could provide supporting data for nitrogen cycling and their responses to changes in precipitation in grassland soil-plant systems.

Study of the occurrence of toxic alkaloids in forage grass by liquid chromatography tandem mass spectrometry

The toxic alkaloids in forage grass present a serious health hazard to humans and livestock, especially ergot alkaloids (EAs), pyrrolizidine alkaloids (PAs) and tropane alkaloids (TAs). Hence, there is a need for a simultaneous method that allows these dangerous plant toxins to be determined. A simple and effective method was developed to determine fifteen toxic alkaloids (EAs, PAs and TAs) in forage grass using the QuEChERS method and liquid chromatography tandem mass spectrometry (LC-MS/MS). The developed method was validated with average recoveries ranging from 63.10 to 102.10%, and relative standard deviations lower than or equal to 6.39% were obtained. Good linearity over the concentration range of 10-600 µg/kg dry matter (DM) was observed for the target alkaloids. The determination coefficients R2 calculated for each of the matrix calibration curves were greater than 0.99. The limits of detection and quantification were 5 µg/kg DM and 10 µg/kg DM, respectively. The reproducibility of the method was verified in three laboratories: all of the mean recoveries of 15 alkaloids were higher than 60%, and the relative standard deviations in alkaloids between laboratories were all less than 14.24%. The proposed method was applied to analyse 134 forage grass samples from the meadow steppe of Inner Mongolia to monitor toxic alkaloids. A significant difference in the frequency of contamination was found between different herbage species and different regions.

Effects of Grazing on the Grassland Vegetation Community Characteristics in Inner Mongolia

The continuous increase of livestock production in Inner Mongolia has caused severe degradation of the grassland ecosystems in recent years. Previous grazing experiments have shown a wide range of vegetation responses between the biome types on a global scale, but there is still a lack of sufficient studies to discern the relative responses of a given biome type. We conducted a meta-analysis of vegetation coverage (VC), plant density (PD), total biomass (TB), above-ground biomass (AGB), under-ground biomass (UGB) and Shannon–Weaver Index (SI) in different grassland types in Inner Mongolia obtained under conditions of different grazing intensities and durations. The results showed that grazing decreased VC, TB, AGB, UGB, and PD significantly. Compared to the global and national average values, the negative effects of grazing to steppe biomass in Inner Mongolia were higher than that on the global scale, while less pronounced than that in China. TB of the meadow steppe in Inner Mongolia increased by 40% under moderate grazing intensity and duration because of compensatory growth. SI of the desert and meadow steppe showed negative linear relationships with the grazing intensity in Inner Mongolia. The percentage changes in AGB, PD, and SI to grazing showed quadratic relationships with the mean annual temperature of the experimental year. With increasing mean annual precipitation, the negative effects of grazing on UGB and SI first decreased and then increased, with that of VC and grazing showing a cubic relationship.

Effects of cultivation and agricultural abandonment on soil carbon, nitrogen and phosphorus in a meadow steppe in eastern Inner Mongolia

Grassland conversion into cropland and further into abandoned land may result in substantial changes when such conversion neglects the historical context of the land use pattern in question in most cases. The objectives of this study were to examine the effects of land use shifts on soil organic carbon (OC), total nitrogen (TN) and total phosphorus (TP) in a meadow steppe in eastern Inner Mongolia. Four sites within 50 km were selected as replicates, and within each of the four sites, the plant and soil properties were investigated separately for three land use types, grassland, cropland and abandoned land from cropland, to reveal the effect of land use changes on soil nutrient contents and stocks. We found that cropland had the highest canopy biomass, whereas grassland maintained the highest root biomass. Significant decreases in OC and TN contents occurred mainly in the 0−20 cm soil layer with the conversion of grassland into cropland, whereas TP contents significantly increased in the 10−30 cm soil profile. Abandonment obviously increased the soil OC and TN contents in the 0−20 cm soil layer compared with cropland, although the levels of native grassland were not reached. The C:N, C:P and N:P ratios were highest in the entire soil profile for the grassland followed by the abandoned land and then the cropland. Changes in nutrient stocks with land use shifts showed similar trends as those in the relevant nutrient contents, but the change ratios of stocks among different land use types could be significantly underestimated due to the cultivation-compaction effect. Thus, we concluded that the abandonment and maintenance of native grasslands should be adopted to protect and maintain the soil organic matter and nitrogen in the meadow steppe of Inner Mongolia.

Soil extracellular enzyme activities and the abundance of nitrogen-cycling functional genes responded more to N addition than P addition in an Inner Mongolian meadow steppe

Nitrogen (N) and phosphorus (P) availability in soils commonly limit belowground biological processes in terrestrial ecosystems. Soil extracellular enzyme activities (EEAs) and microbial functional groups play critical roles in soil biological processes and nutrient cycling, yet their response to nutrient addition are poorly understood. To address this issue, we applied six fertilization treatments composed of combinations of N (0, 1.55, 13.95 g N m−2 yr−1) and P (0, 5.24 g P m−2 yr−1) for two years in a meadow steppe of Inner Mongolia. Soils were collected from each plot in July and August and analyzed for abundances of N-cycling genes and EEAs, and their relationships with treatments. The addition of N significantly increased C-acquisition enzyme activity and enzyme C:N and C:P ratios. Enzymatic stoichiometry indicated that N addition alleviated microbial demand for N, while it increased microbial C limitation. Microbial C and N limitation were significantly correlated with NH4+–N in July, yet they were correlated with soil water content (SWC) in August. The abundance of amoA significantly increased with N addition and was positively related to mineral-N accumulation. The abundance of denitrifier genes and gaseous N loss potential were accelerated by N addition in July, while a neutral effect was observed in August. Nitrate leaching potential was significantly increased by N addition, yet it declined with P addition in July. P addition also suppressed amoA abundance of ammonia oxidizing bacteria. Partial least squares path modelling indicated that N addition positively affected microbial-C limitation, soil N-loss potential and negatively affected microbial-N limitation. P addition negatively affected soil N-loss potential. Ultimately, this study highlights the importance of soil N availability in regulating microbial metabolism and soil N-loss potential, and enhances our understanding of the mechanisms responsible for variation in microbial nutrient cycling in meadow steppe soils.

Responses of soil potential carbon/nitrogen mineralization and microbial activities to extreme droughts in a meadow steppe

The mineralization of soil carbon (C) and nitrogen (N) is a critical process in the cycling of C and N in terrestrial ecosystems, which is strongly controlled by water availability. In this study, we collected soil samples in a 3-year extreme drought experiment in a meadow steppe in Inner Mongolia, freeze-dried these samples, and measured the potential C and N mineralization rates and water sensitivity of soil microorganism by incubating soils under soil water contents (SWC) of 3%, 8%, 13%, 18%, 25% and 35%. The results showed that averaged across different SWC, the extreme drought treatment of reducing 66% precipitation in growing season significantly increased potential N mineralization rate by 14.2%, but did not affect the potential C mineralization. Extreme drought significantly increased soil microbial biomass N and soil dissolved organic C by 26.8% and 26.9%, respectively. In both the control (natural rainfall) and extreme drought treatment, the potential C and N mineralization and microbial biomass C and N increased with SWC in the incubation, which was possibly caused by the enhanced substrate diffusion. Extreme drought also promoted the initial pulse response of C mineralization, implying the enhanced microbial response to water availability. Extreme drought significantly reduced the ratio of the potential soil C mineralization to the potential N mineralization, suggesting that extreme drought might weak the coupling of soil C and N. Extreme drought could cause different responses to soil water availability between soil C and N cycling. Extreme drought could enhance microbial response to increasing water availability, weak coupling between soil C and N, with consequences on nutrient cycling and primary productivity in the meadow steppe of northern China.

Responses of soil physicochemical properties and microbial characteristics to mowing and nitrogen addition in a meadow steppe in Inner Mongolia, China.

Frequent mowing and nitrogen enrichment can lead to the degradation of grassland ecosystem. It remains largely unknown that how the soil microbial characteristics, important bio-indicators of soil quality, respond to mowing and nitrogen enrichment. In this study, using a field experiment established in the meadow steppe in Hulunber, Inner Mongolia, we explored the responses of soil properties, microbial biomass, soil respiration, and soil enzyme activities to mowing and nitrogen addition during growing seasons. Mowing significantly reduced microbial biomass carbon, nitrogen and phosphorus, and soil respiration (basal respiration and substrate induced respiration), which might be caused by the moisture- and carbon-limitation. Mowing significantly reduced activities of the enzymes involved in nitrogen acquisition (N-acetyl-β-D-glucosaminidase) and phosphorus acquisition (acidic phosphomonoesterases), which supports the resource allocation theory. Soil pH was significantly reduced by N addition. However, microbial biomass showed no significant response to nitrogen input, implying that soil acidification induced by nitrogen inputs was not profound enough to affect microbial biomass. Nitrogen addition did not affect soil respiration and microbial enzymatic activities, inconsistent with results from most of previous studies conducted in typical steppe. Combination of mowing and nitrogen addition reduced the activity of acidic phosphomonoesterases, which might be due to the increased phosphorus availability under the combined treatment. Combination of mowing and nitrogen addition reduced microbial biomass phosphorus, but increased soil available phosphorus, corresponding to the lowered activity of acidic phosphomonoesterases under the combined treatment. Microbial biomass carbon, nitrogen and phosphorus, and soil respiration peaked in July, which was associated with the high temperature and precipitation in summer. Soil enzymatic activities were higher in the spring and summer than in the late growing season. In summary, our results indicated that mowing would result in the imbalance of soil nutrients and intensify the risk of grassland degradation. In contrary, nitrogen addition exerted no effects on microbial biomass and activity.

The burrow behavior and influenced factors of a prairie subterranean zokor (Myospalax psilurus).

The Transbaikal zokor (Myospalax psilurus) is a dominant rodent distributed in the meadow steppe of Inner Mongolia in northern China. Due to long history of evolution in subterranean environment, the zokor has an adaptive behavior: sealing burrow entrances. When a burrow is damaged, exposed entrances appear, and within a relatively short time, the zokor would be active in sealing the entrances to reduce risks to its survival. In general, it is thought that zokors avoid light and wind, which is consistent with their behavior of sealing burrow entrances. However, direct evidence from field experimental research has been lacking. This study set up 68 field sampling points in a meadow steppe in Inner Mongolia from August to September, 2014 and used a wind–light isolator to study the effects of wind and light factors on zokor burrow entrance sealing behavior. The results showed that there were no significant correlations between wind or light factors and the frequency of zokor burrow entrance sealing. Therefore, wind and light factors are not direct factors associated with zokors actively sealing burrow entrances.

Simulated NH4+-N Deposition Inhibits CH4 Uptake and Promotes N2O Emission in the Meadow Steppe of Inner Mongolia, China

Few studies are conducted to quantify the effects of enhanced N deposition on soil nitrous oxide (N2O) emission and methane (CH4) uptake in the meadow steppe of Inner Mongolia, China. A two-year field experiment was conducted to assess the effects of nitrogen (N) deposition rates (0, 10, and 20 kg N ha−1 year−1 as (NH4)2SO4) on soil N2O and CH4 fluxes. The seasonal and diurnal variations of soil N2O and CH4 fluxes were determined using the static chamber-gas chromatography method during the two growing seasons of 2008 and 2009. Soil temperature, moisture and mineral N (NH4+-N and NO3−-N) concentration were simultaneously measured. Results showed that low level of (NH4)2SO4 (10 kg N ha−1 year−1) did not significantly affect soil CH4 and N2O fluxes and other variables. High level of (NH4)2SO4 (20 kg N ha−1 year−1) significantly increased soil NO3−-N concentration by 24.1% to 35.6%, decreased soil CH4 uptake by an average of 20.1%, and significantly promoted soil N2O emission by an average of 98.2%. Soil N2O emission responded more strongly to the added N compared to CH4 uptake. However, soil CH4 fluxes were mainly driven by soil moisture, followed by soil NO3−-N concentration. Soil N2O fluxes were mainly driven by soil temperature, followed by soil moisture. Soil inorganic N availability was a key integrator of soil CH4 uptake and N2O emission. These results suggest that the changes of availability of inorganic N induced by the increased N deposition in soil may affect the CH4 and N2O fluxes in the cold semi-arid meadow steppe over the short term.

Nitrogen deposition influences the response of Potentilla tanacetifolia to phosphorus addition

Phosphorus is an essential macronutrient for all livingplants and plant production. Simultaneously, atmospheric nitrogendeposition also affects plant productivity at a global scale. However,few studies have investigated how plants respond to P addition whilesimultaneously considering N deposition. We investigated plant biomass,nutrient status and stoichiometric ratios on Potentilla tanacetifoliain response to P fertilization under contrasting N addition ratesin a typical meadow steppe in Inner Mongolia, China. Abovegroundbiomass of P. tanacetifolia increased under increasing levels of P fertilizationunder conditions of N addition. However, there was no significantchange in biomass when only phosphorus was added. Plantleaf and stem P concentrations increased linearly with P additionwhen there was no N addition. Our results suggest that increasedplant P nutrition under P addition will not turn into plant growthenhancement unless N demands are also satisfied. Nitrogen additionsignificantly increased leaf N concentrations, and leaf and seed N:Pratios, when there was no P fertilization. Nevertheless, the effects ofN addition were weakened, and eventually disappeared when P fertilizationrates increased. This indicates that N-induced alterationsof the plant nutrition status and stoichiometric ratios were P availability-dependent. Overall, our results suggest that multiple-nutrientconstraints and their interactions must be considered when assessingplant nutrient and growth responses to nutrient enrichment.

Effects of Simulated Nitrogen Deposition on Soil Net Nitrogen Mineralization in the Meadow Steppe of Inner Mongolia, China.

Effects of simulated nitrogen (N) deposition on soil net nitrogen mineralization (NNM) were examined in situ during two growing seasons, using the resin-core technique in the semiarid meadow steppe in Inner Mongolia, China. The aim of this study is to clarify the effect of N levels (0, 10, and 20 kg N ha−1yr−1) and forms (NH4 + and NO3 -) on soil mineral N and NNM. Our results showed that N levels had no significant differences on soil mineral N and NNM. In the first year, three N treatments ((NH4)2SO4, NH4Cl and KNO3) increased soil NH4 + concentrations but had no significant effects on soil NO3 - concentrations. In the second year, (NH4)2SO4 treatment increased soil NO3 - concentrations, NH4Cl and KNO3 treatments decreased them. Three N treatments significantly decreased soil NH4 + concentrations in the later stages of the second year. As for the soil NNM, three N treatments had no significant effects on the rates of soil NNM (R m) and net nitrification (R n) in the first year, but significantly decreased them in the second year. The contribution of N addition to Rm was higher from (NH4)2SO4 than from NH4Cl and KNO3. However, Soil R m was mainly affected by soil water content (SWC), accumulated temperature (Ta), and soil total N (TN). These results suggest that the short-term atmospheric N deposition may inhibit soil NNM in the meadow steppe of Inner Mongolia.

Effects of Simulated NH4+Deposition on CO2Fluxes in the Hulun Buir Meadow Steppe of Inner Mongolia, China

Abstract: Atmospheric nitrogen (N) deposition may affect carbon (C) sequestration in terrestrial ecosystem. The main objective of this paper was to test the hypothesis that N addition would increase CO2 emission in the N limited meadow steppe in Inner Mongolia, China. Response of CO2 fluxes to simulated N deposition was studied in the growing season of 2008 and 2009 by static chamber and gas chromatograph techniques. Parallel to the flux measurements, soil temperature, soil moisture, TOC, DOC, soil NH4 + and NO3 - were measured at the same time. The results indicated that two-year N additions had no significant effect on NH4 +, but slightly increased NO3 - in the later period. The HN treatment tended to increase CO2 fluxes in the two years, and LN treatment tended to decrease CO2 fluxes in 2008, and shifted to increase CO2 fluxes in later growing season of 2009. N addition significantly increased the aboveground biomass and root biomass. The correlation between CO2 fluxes and moisture or temperature facto...

Litter mixing significantly affects decomposition in the Hulun Buir meadow steppe of Inner Mongolia, China†

Aims We explored the decomposition rates of single- and mixed-species litter, the litter-mixing effect and the effect of component litters in a mixture on decomposition. Methods In a litter bag experiment, shoot litters from two dominant grasses (Leymus chinensis and Stipa baicalensis) and one legume (Melissitus ruthenica) were decomposed separately and as a mixture from May 2010 to September 2011 in the Hulun Buir meadow steppe of Inner Mongolia, China. We separated the litter mixture into its individual component litters (i.e. the different single-species litters) and analyzed the changes in litter mass remaining and litter nitrogen (N) remaining during single-and mixed-species litter decomposition. Important Findings (i) Litter mixing had significant positive effects on litter decomposition. The litter-mixing effect was strongest for the mixture of S. baicalensis and L. chinensis litters, followed by the mixture of S. baicalensis and M. ruthenica litters. (ii) Single-species component litters decomposed faster in the mixtures than separately (positive effect), but these effects were not significant for legume species M. ruthenica litter. Relative to single-species litter decomposition, the decomposition rates of the two grass (S. baicalensis and L. chinensis) litters significantly increased when they were mixed with each other or with M. ruthenica litter. (iii) For each species litter type, the percentage of litter N remaining during decomposition (NR) differed between the single-species litter and mixed litter treatments. The NR of S. baicalensis litter was higher when it was decomposed in the mixture than in isolation. However, the NR of L. chinensis litter was lowest in its mixture with M. ruthenica among the treatments. Regardless of its decomposition in the mixture or in isolation, the NR of M. ruthenica litter varied little among treatments. There was a significant positive relationship between the NR and percentage of initial litter mass remaining in both the single litter and mixed litter treatments. These results suggest that N transfer may happen among component litters in mixture and further affect the decomposition.

Effects of Species and Low Dose Nitrogen Addition on Litter Decomposition of Three Dominant Grasses in Hulun Buir Meadow Steppe

Atmospheric nitrogen (N) deposition caused by anthropogenic activities may alter litter decomposition and species composition, and then affect N cycling and carbon (C) sequestration in an ecosystem. Using the litterbag method, we studied the effects of N addition (CK: no N addition; low-N: 1 g N m-2 y-1; high-N: 2 g N m-2 y-1) on changes in mass remaining of shoot litter decomposition of three grasses (Stipa baicalensis, Carex pediformis and Leymus chinensis) over 28 months in the Hulun Buir meadow steppe of Inner Mongolia. The results showed that the addition of high and low N had no significant effect on the decomposition of single-species litter, but low N addition slightly inhibited the decomposition of litter mixtures. In addition, litter decomposition was strongly species dependent. Our results suggest that species type is likely the main determinant of litter decomposition, and low N deposition in natural ecosystems does not influence single-species litter decomposition.