The response of soil methane (CH4) uptake to increased nitrogen (N) deposition and grazing management was studied in three types of steppe (i.e., meadow steppe, typical steppe, and desert steppe) in ...Inner Mongolia, China. The experiment was designed with four simulated N deposition rates such as 0, 50, 100, and 200kgNha−1, respectively, under grazed and fenced management treatments. Results showed that the investigated steppes were significant sinks for CH4, with an uptake flux of 1.12–3.36kgha−1 over the grass growing season and that the magnitude of CH4 uptake significantly (P<0.05) decreased with increasing N deposition rates. The soil CH4 uptake rates were highest in the desert steppe, moderate in the typical steppe, and lowest in the meadow steppe. Compared with grazed plots, fencing increased the CH4 uptake by 4.7–40.2% with a mean value of 20.2% across the three different steppe types. The responses of soil CH4 uptake to N deposition in the continental steppe varied depending on the N deposition rate, steppe type, and grazing management. A significantly positive correlation between CH4 uptake and soil temperature was found in this study, whereas no significant relationship between soil moisture and CH4 uptake occurred. Our results may contribute to the improvement of model parameterization for simulating biosphere-atmosphere CH4 exchange processes and for evaluating the climate change feedback on CH4 soil uptake.
The response of soil methane (CH4) uptake to increased nitrogen (N) deposition and grazing management was studied in three types of steppe (i.e., meadow steppe, typical steppe, and desert steppe) under grazed and fenced management in Inner Mongolia, China. Results showed that the continental steppe was CH4 sink (Fig. 2) with the values of 1.12–3.36kgha−1 over the grass growing season, which was significantly (P<0.05) decreased with increasing N deposition rates. The soil CH4 uptake rates were highest in the desert steppe, moderate in the typical steppe, and lowest in the meadow steppe. Compared with grazed plots, fencing increased the CH4 uptake by 4.7–40.2% with a mean value of 20.2% across the three different steppe types. The responses of soil CH4 uptake to N deposition in the continental steppe varied depending on the N deposition rate, steppe type, and grazing management. A significantly positive correlation between CH4 uptake and soil temperature was found in this study. Our results may contribute to the improvement of model parameterization for simulating biosphere-atmosphere CH4 exchange processes and for evaluating the climate change feedback on CH4 soil uptake.
Fig. 2 Seasonal variation in CH4 fluxes as affected by increasing N deposition in three different types of continental steppe under grazed and fenced conditions during the growing season from May to October 2012, i.e., meadow steppe grazed (a) and fenced (b), typical steppe grazed (c) and fenced (d), and desert steppe grazed (e) and fenced (f). Error bars indicate standard errors (n=3) of the mean. Display omitted
•The interaction of nitrogen deposition, steppe types, and fencing management on CH4 uptake was studied.•The steppe was a significant sink for CH4, significantly decreased (P<0.05) with increasing N deposition rates.•Soil CH4 uptake was the highest in desert steppe, intermediate in typical steppe, and the lowest in meadow steppe.
Due to insufficient palaeo-environmental records, the vegetation history and hydrology of the Tibetan Plateau during the Last Glacial Maximum (LGM) are uncertain. In this study, a 316-cm-long ...sediment core covering the last 33.8 thousand years recovered from Koucha Lake on the north-eastern Tibetan Plateau was analysed for pollen, along with total organic carbon (TOC) and total nitrogen (TN), to explore past vegetation and hydrology changes. Alpine desert was widely distributed around the lake with sparse vegetation cover between 33.8 and 16.8 cal ka BP, particularly in the LGM, as inferred from the extremely low pollen concentrations together with high proportions of desert pollen taxa and exogenous arboreal taxa. Alpine steppe developed around the lake thereafter and was replaced by alpine meadow at ca. 7 cal. ka BP, which reflects the increasing effective moisture during the mid and late Holocene. The ancient Koucha Lake existed from 33 to 29 cal ka BP as a shallow lake and probably dried out in the LGM with a sediment hiatus (presence of coarse gravel layer), as suggested by the high and low content of Pediastrum. The current Koucha Lake formed at ca. 20 cal. ka BP with an increase in water level at ca. 16.8 cal ka BP as revealed by faint stratification of the sediments along with higher pollen concentration and presence of Pediastrum and Botryococcus. Our research suggests that pollen concentration should be paid more attention when investigating past vegetation, and that pollen percentages are not comparable among samples with large differences in pollen concentrations.
•A reliable pollen spectra covering last 33.8 ka completed for the northeastern Tibetan Plateau.•Hostile climate with sparse vegetation during the LGM revealed by pollen spectra and concentration.•Low lake level during the MIS 3 and LGM for the northeastern Tibetan Plateau.
•Heavy rainfall events determine GPP in water-limited grassland.•Rainfall interval affects GPP in temperature-limited grassland.•Heavy rainfall events affect GPP by recharging soil water at deeper ...layer.•Rainfall intervals affect GPP via changes in air temperature.
The impact of global climate change on precipitation regimes may bring about significant consequences to the productivity of grassland ecosystems. This study reports the effects of the characteristics of precipitation events (PEC, e.g., size, frequency, interval, and seasonal distribution of precipitation events) on gross primary productivity (GPP) based on long-term measurements of net ecosystem CO2 exchange and evapotranspiration by the eddy covariance technique in a water-limited temperate steppe in Inner Mongolia and a humid but temperature-limited alpine meadow in Tibet, China. We determined that the predominant characteristics of precipitation events that affected GPP differed remarkably between these two ecosystems. The number of heavy precipitation events (>10mmday−1) was the most important PEC to impact GPP in the temperate steppe. Years with more frequent heavy precipitation events favored higher GPP. However, in contrast with the case in the temperate steppe, precipitation interval was the factor that affected GPP most in the alpine meadow. GPP was higher as the precipitation intervals lengthened or their distribution shifted to fewer but longer intervals (concentrated distribution). Additionally, the mechanisms for the effects of PEC on GPP also differed between these two ecosystems. Compared with small events, heavy precipitation events recharged deeper soil layers in the temperate steppe, which was biologically more meaningful for plant transpiration (i.e., an increase in the ratio of transpiration to evapotranspiration), relief from drought stress (an increase in the duration of high soil water content), and thereby higher GPP. In contrast, mean air temperature was higher in the alpine meadow when the precipitation intervals increased or their distribution was more concentrated, leading to a longer period of higher temperature that was favorable to higher GPP. Our results imply that soil water is not the exclusive means of revealing the mechanism of precipitation affecting productivity; the corresponding changes in temperature along with precipitation events may also play a substantial role in temperature-limited grasslands.
The objective of this study was to examine the responses of nutrient quality and mineral elements of forages in different economic groups forages in the Qilian Mountains alpine meadows to different ...fertilization treatments. Eight fertilization treatments, potassium (K), nitrogen (N), zinc (Z), boric (B), copper (Cu), phosphorus (P), molybdenum (Mo), and selenium (Se), were sprayed onto forage roots, and no fertilizer was applied as a blank control (CK), with four replicates in each group. The forage trace element contents and nutritional quality of each economic group in to different treatments were determined in mid-August, and the trace element surplus and deficiency were analyzed. Compared with that in the control, the forage crude protein (CP) content in different economic groups under different fertilization treatments increased and fluctuated within the range of 7.7%-23.94%. The dry matter digestibility (DMD) ranged from 38.78% to 77.34% and showed no significant differences in DMD among treatments (
> 0.05). The DMD of legume forages was significantly higher than those of Gramineae grasses and sedges; there were no significant differences in forage acid detergent fiber (ADF) between any treatments and the control (
> 0.05), but ADF showed a decreasing trend in the treatments compared with that in the control. The P content increased by 81.81% in legumes (
< 0.05); however, it decreased by 38.46% and 61.29% in wilted grass and forbs (
< 0.05) and increased in Gramineae grasses and legumes under N treatment by 92.86% and 50% (
< 0.05), respectively. The Cu content under Cu, N, Zn, B and Se treatments increased significantly by 33.81%∼346.49% compared with that in the control. There were no significant differences in Zn content among the economic groups under different treatments (
> 0.05), but legumes showed better absorption of Zn. Consequently, the forages in this study were evaluated as having medium Cu (8.1-20 mg/kg), medium Se (0.11-1.0 mg/kg), and medium (30.1-60 mg/kg) to high (60.1-100 mg/kg) Zn contents. Comprehensive analysis showed that the application of different fertilizers could increase the CP and DMD of various forages, reduce ADF, and effectively improve the nutritional quality of pastures. The contents of N, Cu, Zn, and Se in forages increased under all treatments, and the contents of all forage elements were at appropriate levels. Applying K, N, P, Cu and Mo is beneficial to dominant species in Qilian Mountains alpine meadows.
Plant pathogens are often hypothesized to promote species coexistence by generating conspecific negative density dependence (CNDD). However, the relative importance of fungal versus oomycete ...pathogens in maintaining plant species coexistence and community composition remains unresolved, despite their recognized effects on plant performance. Here, we use fungicide application to investigate how fungal versus oomycete pathogens affect plant species coexistence in an alpine meadow. We found that the severity of foliar fungal disease was density‐dependent at both intra‐ and interspecific levels. Fungal pathogen‐exclusion treatment successfully decreased the severity of foliar fungal diseases, with no detectable effects on root colonization by arbuscular mycorrhizal fungi or on soil chemical properties. Fungal pathogens were important factors shaping CNDD across 25 coexisting plant species. Exclusion of fungal pathogens significantly reduced plant species richness and Shannon's evenness. Treatments that excluded fungal pathogens also led to significant shifts in plant community composition toward more Poaceae and Cyperaceae. These results indicate that fungal pathogens, especially those affecting aboveground plant parts, may play a larger role in maintaining species coexistence and shaping community composition than has been previously recognized.
It has been widely demonstrated that farm management affects the plant species composition of grassland. The present study aimed to investigate the effect of farm management on plant species richness ...and composition in forty-nine small-scale farms breeding dairy cattle, located in the Eastern Italian Alps at two levels of precision: plot and farm levels. Data on housing system, quality scheme, farm productivity, income from milk yield and livestock density were collected through interviews with farmers. In each farm, botanical surveys were carried out in different plots representing the botanical composition of the farmland vegetation. Elevation, slope, type of use, number of hay cuts and type of fertilisation were also recorded. The botanical surveys of the plots on each farm were analysed to describe plant composition at the plot level, then merged to describe plant composition at the farm level. At both levels, grassland botanical composition was found to be affected by farm management. At the plot level, meadows cut 2 and 3 times per year did not exhibit any differences in plant richness, but they differed in plant species, botanical family and phytosociological class composition, with a general simplification of botanical composition. We found fewer phytosociological classes but not fewer plant species or botanical families in plots fertilised with slurry than in plots fertilised with manure or not fertilised, and a change in the botanical composition due to changes in the relative abundance of plant species. At the farm level, we observed a decrease in the number of plant species and phytosociological classes, and changes in plant composition, with increasing milk yield and livestock density. Changes in botanical composition were less evident at the farm level than at the plot level. However, protecting farms and their economic viability is a means of maintaining biodiversity at the plot level.
•Farm management influences grassland biodiversity patterns at different scales.•Cutting frequency affects plant species and phytosociological class composition.•Fertilization with slurry causes changes in plant species abundance.•Increasing milk production and self-sufficiency reduce plant species richness.
•Alpine gravelization by glacier melting seriously eroded downstream grassland.•Alpine gravelization decreased alpine grassland coverage, biomass density, and diversity.•Alpine gravelization ...initiated extreme soil aridity of hillside alpine grassland.•Alpine gravelization initiated disappearance of some species and plant functional groups.
Alpine gravelization by glacier melting may subsequently cause degradation of downstream vegetation. The thinning rates of glaciers outside ice sheet peripheries in some regions has doubled over the past 20 years.However, no study is available about the effects of alpine gravelization on alpine meadow ecosystem. Here, by investigating and measuring the community characteristics, soil moisture, and soil temperature of alpine meadows under three different gravel coverage levels (No gravel covered meadow, half gravel covered meadow, and fully gravel covered meadow),we examine the response of surface microhabitats and community to gravel cover on a typical hillside alpine meadow. Results showed that gravel cover significantly decreased soil/gravel ratio and topsoil moisture. Topsoil water content of the half-covered and the fully-covered gravel meadow was outstandingly low and reached<8% and 5%, respectively. Meanwhile, the larger decrease rates for coverage (−72.53%), above- and below-ground biomass (−76.61% and −94.09%), community density (−81.76%), species richness (−77.75%) and diversity (−55.98%) were found after gravel cover. Gravel cover induced the changes of the dominant species composition from Kobresia pygmaea to Setaria viridis, and ultimately to Trigonotis peduncularis and Ranunculus pedatifidus. Cyperaceae functional group species almost disappeared with increasing gravel coverage. In general, the increase in gravel coverage caused a decrease in soil water content, coverage, above-ground and under-ground biomass, community density, species richness, and the disappearance of Cyperaceae functional group species.Our results provide a new insight into the effect of alpine gravelization on soil water environment and alpine meadow degradation.
Soil amino acids are of great importance for nitrogen cycling and plant nutrition, especially in the nitrogen-limited ecosystems. However, the factors that influence amino acid pools in alpine meadow ...soils remain unclear. The aims of this study were to answer the following questions: (1) Do soil amino acid pools under different vegetation cover show appreciable differences in their concentration and composition during the growing season? (2) Is the pool size of soil amino acids in the alpine meadow smaller or larger than those in other ecosystems? Soils were sampled from three sites dominated by three typical types of plants (Kobresia graminifolia, Polygonum viviparum and Elymus nutans) in a Tibetan alpine meadow, respectively, during the growing season. Soils were extracted with water and 2M KCl solution, respectively, and amino acids were quantitatively determined by high performance liquid chromatography. The results show that the pool size of soil exchangeable amino acids extracted by 2M KCl in this alpine meadow is comparable to those in other N-limited ecosystems. The pool size of soil amino acids across the three sites displayed temporal dynamics during the growing season, with the pool size increased from May to July and decreased in August. The P. viviparum soil had the largest amino acid pool among the three sites in May, whereas the largest pool in July and August was found in the K. graminifolia soil. The composition of the soil amino acid pools across the sites changed over the season, with acidic amino acids being abundant (63.6–84.3%) in spring, and neutral amino acids dominating (53.7–66.0%) in summer. The three sites shared five dominant amino acids (lysine, glutamic acid, leucine, alanine, and serine) through June to August; however, the other dominant amino acids (glycine, valine and threonine) varied among the sites and the months. These results suggest that the concentration and composition of amino acid pools in the Tibetan alpine meadow soils could be significantly influenced by the vegetation cover. Additionally, soil sampling time and extraction methods could also exert pronounced effect on the results. The information obtained in this study may help in understanding the influence of plant-soil feedback on soil amino acid pools, and the mechanisms of organic nitrogen uptake by alpine plants.
•Soil amino acids in alpine meadow are abundant.•Soil amino acid concentrations varied seasonally.•Acidic amino acids were dominant in spring; neutral amino acids were dominant in summer.•Amino acids were the most abundant in the Kobresia graminifolia soil.•The three plant sites shared five dominant amino acids.
1. It is well known that climate change alters abiotic factors (temperature and water availability) that directly affect ecosystem properties. However, less is known about the indirect impacts of ...climate change on ecosystem structure and function. Here, we show that experimental warming may deteriorate ecosystems via trophic interactions. 2. In a Tibetan alpine meadow, plant species composition, size, coverage and above-ground biomass were investigated to reveal the effect of artificial warming (c. 1 °C mean annual temperature at the soil surface), which was accomplished using warmed and ambient open top chambers. In addition, rodent damage to plants was assessed. 3. The dicot forb silverweed Potentilla anserina increased significantly, while other species groups remained unchanged or decreased in plant community dominance rank after 2 years of artificial warming. The change in community structure was attributed to the difference in biomass allocation and growth form among species. 4. In the third year, plateau zokors Myospalax fontanierii, a widespread rodent herbivore, damaged plants in the warmed chambers, while leaving plants in the ambient chambers mostly undamaged. Above-ground biomass was found to be smaller in the warmed chambers than the controls in the third year, in contrast to the trend of the first 2 years. In addition, zokor burrow density was positively correlated with silverweed biomass and its dominance within communities, which was consistent with findings of independent field investigations that silverweed-dominated plots were more likely to be visited and damaged by the zokors than sites-dominated by grass species. 5. Synthesis and applications. The top-down negative effect of zokor damage on above-ground biomass in the warmed chambers was induced by the bottom-up effect of changes in species composition and community structure on zokor foraging behaviour, which were driven by artificial warming. Such trophic interactions may invalidate some predictions of ecological effects by current species-climate envelope models. Furthermore, because management measures including increasing the water table, planting grass and moderate cattle grazing may prevent silverweed dominance, we suggest that these interventions could be employed to control zokor damage in alpine meadows that are predicted to be drier and warmer in the future.
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