Effects of nighttime warming and changing precipitation on soil microclimate in three temperate steppes along a precipitation gradient

BackgroundThe Mongolian steppe is one of the most important grasslands in the world but suffers from aridization and damage from anthropogenic activities. Understanding structure and function of this community is important for the ecological conservation, but has seldom been investigated.Methodology/Principal FindingsIn this study, a total of 324 quadrats located on the three main types of Mongolian steppes were surveyed. Early-season perennial forbs (37% of total importance value), late-season annual forbs (33%) and late-season perennial forbs (44%) were dominant in meadow, typical and desert steppes, respectively. Species richness, diversity and plant functional type (PFT) richness decreased from the meadow, via typical to desert steppes, but evenness increased; PFT diversity in the desert and meadow steppes was higher than that in typical steppe. However, above-ground net primary productivity (ANPP) was far lower in desert steppe than in the other two steppes. In addition, the slope of the relationship between species richness and PFT richness increased from the meadow, via typical to desert steppes. Similarly, with an increase in species diversity, PFT diversity increased more quickly in both the desert and typical steppes than that in meadow steppe. Random resampling suggested that this coordination was partly due to a sampling effect of diversity.Conclusions/SignificanceThese results indicate that desert steppe should be strictly protected because of its limited functional redundancy, which its ecological functioning is sensitive to species loss. In contrast, despite high potential forage production shared by the meadow and typical steppes, management of these two types of steppes should be different: meadow steppe should be preserved due to its higher conservation value characterized by more species redundancy and higher spatial heterogeneity, while typical steppe could be utilized moderately because its dominant grass genus Stipa is resistant to herbivory and drought.

Although numerous warming experiments have examined the impacts of elevated temperature on soil microbial activities, most are based on responses from a single site. To investigate how precipitation regime regulates warming effects on the carbon cycle, we conducted manipulative warming experiments in desert steppe, typical steppe, and meadow steppe along a precipitation gradient in northern China. Soil temperature, moisture, microbial biomass C (MBC), N (MBN), and microbial respiration were measured from 2006 to 2009. Soil moisture was significantly reduced by warming in the typical steppe but not affected in the desert and meadow steppe. Across the 4 years, warming decreased MBC and microbial respiration in the desert and typical steppe but not in the meadow steppe. The magnitude of warming-induced reductions in MBC and microbial respiration declined as site precipitation increased. Across the three sites, the changes in soil MBC, MBN, and microbial respiration were all positively correlated with annual precipitation and changes in belowground net primary productivity. Our results suggest that precipitation regime controls the response of soil microbial activity and biomass to warming, possibly by regulating soil moisture and substrate availability. With increasing precipitation, the stimulatory effects of warming on soil microbial activity and biomass outweigh the inhibitory effects due to declining soil moisture.

连续三年夜间增温和施氮对云杉外生菌根及菌根真菌多样性的影响

Asymmetric responses of soil respiration in three temperate steppes along a precipitation gradient in northern China revealed by soil-monolith transplanting experiment

The aim of this study was to investigate the dynamics of bacterial communities and natural fermentation quality in three steppe types [meadow steppe (MS); typical steppe (TS); and desert steppe (DS)] on the Mongolian Plateau. PacBio single molecule with real-time sequencing technology was applied to provide insights into the dynamics of the physicochemical characteristics and the complex microbiome of native grass after 1, 7, 15, and 30 days of fermentation process. The dry matter, crude protein, and water soluble carbohydrate (WSC) contents of the three groups slowly decreased after 1 day of fermentation process, and the lowest WSC concentration after 30 days of ensiling was detected in the DS group compared to that in the MS and TS groups. There was no significant effect of steppe types on lactic acid and butyric acid content (P>0.05). The pH was higher in the early stages of fermentation. After 30 days of fermentation, the pH of MS and DS dropped to ∼5.60, while TS was as high as 5.94. At different ensiling days, the pH of TS was significantly higher than that of MS (P<0.05). The ammonia nitrogen content of MS was significantly higher than TS and DS (P<0.05). During the whole fermentation process, Leuconostoc mesenteroides and Pseudocitrobacter faecalis were the main species of DS, while Enterobacter roggenkampii and Faecalibacterium prausnitzii dominated the fermentation process in MS and TS, respectively. The fermentation quality of native grass silage of different steppe types was less satisfactory, with the silage quality ranging from DS, MS, and TS in descending order. The epiphytic bacteria dominating the fermentation process differed between steppe types of silage. Leuconostoc mesenteroides as the main strain of DS had a modulating effect on pH and LA content, while the main strains of MS and TS (Enterobacter roggenkampii and Faecalibacterium prausnitzii) dominated the silage without significant effect on improving fermentation characteristics and nutritional quality.

Effects of water and nitrogen addition on ecosystem respiration across three types of steppe: The role of plant and microbial biomass

Simple SummaryThis study presents a large-scale field survey of the temperate steppes of Inner Mongolia, introducing a novel framework to classify vegetation based on root traits. The concept of root importance value was introduced, incorporating the architectural and functional indices of belowground roots, as well as the root life form spectrum. The present research reveals that these steppes can be categorized into three distinct community subtypes (meadow, typical, and desert steppe) and thirteen plant associations. The analysis uncovered a clear spatial gradient in root strategies, defining three ecological adaptation types. Furthermore, the key environmental drivers for each community were identified. Precipitation and soil nutrients are identified as key drivers shaping the spatial distribution of belowground root traits in meadow steppe. Water limitation was central in typical steppe, while desert steppe was influenced by altitude and temperature. This work provides a significant advance in understanding steppe ecosystems from a belowground perspective.The composition, architecture, and plant traits of temperate steppe communities are intricately associated with environmental factors. However, most studies primarily focus on aboveground observations, often overlooking the critical role of belowground root systems. Here we conducted a field survey at a large-regional scale to investigate the composition of temperate steppe communities and plant root traits. Cluster analysis, correspondence analysis and Pearson correlation coefficient matrix method were employed to classify vegetation associations based on plant community composition and root traits. The principal driving and limiting factors shaping plant root communities were systematically investigated. The results showed that the temperate steppe was categorized into three community subtypes: meadow steppe, typical steppe, and desert steppe, comprising five plant groups and thirteen plant associations. The RLFS analysis, based on belowground architectural and functional traits, demonstrated a spatial gradient differentiation with three ecological adaptations: tufted herbs, rhizome herbs, and non-tufted or rhizome herbs. Key environmental driving factors for meadow steppe included precipitation, soil carbon, nitrogen, and phosphorus content, while the average growing-season temperature as a limiting factor. The environmental driving factors for the typical steppe were not apparent, and the limiting factor was water. For the desert steppe, the environmental driving factors were altitude and average growing-season temperature. These findings reveal notable spatial heterogeneity and a distinct distribution pattern in community composition and vegetation classification based on belowground root traits in the Inner Mongolia steppes.

Growth controls over flowering phenology response to climate change in three temperate steppes along a precipitation gradient

Extreme climate events have become more severe and frequent with global change in recent years. The Chinese temperate steppes are an important component of the Eurasian steppes and highly sensitive and vulnerable to climatic change. As a result, the occurrence of extreme climate events must have strong impacts on the temperate steppes. Therefore, understanding the spatio-temporal trends in extreme climate is important for us to assess the sensitivity and vulnerability of Chinese temperate steppes to climatic changes. This research had two specific objects to (i) specify the temporal changes in extreme climate events across the whole steppe and (ii) compare the trend differences for extreme climate events in different types of steppes—meadow steppe, typical steppe and desert steppe. To investigate extreme climate trends in the temperate steppes of China, 82 meteorological stations with daily temperature and precipitation data (1961–2013) were used. Meanwhile, eight core extreme climate indices (extreme high-temperature threshold, extreme low-temperature threshold, frost days, heatwave duration, heavy rainfall threshold, percentage of heavy rainfall, heavy rainfall days and consecutive dry days) from the Statistical and Regional Dynamical Downscaling of Extremes for European Regions (STARDEX) project were selected to analyse the trends in extreme climate across the whole temperate steppe and the three main types (meadow steppe, typical steppe and desert steppe) through time and space. The results showed that (i) the changes in extreme climatic temperature events across the whole temperate steppe were obvious during 1961–2013. The frost days (−3.40 days/10 year [yr]) decreased significantly, while the extreme high-temperature threshold (0.24°C/10 yr), extreme low-temperature threshold (0.52°C/10 yr), and heatwave duration (0.58 days/10 yr) increased notably. The annual changes in extreme precipitation were small and not significant. (ii) Differences appeared in the extreme climatic trends in different types of steppes. The desert steppe showed strong climate extremes and underwent the most significant asymmetric warming compared with the meadow steppe and typical steppe. At the same time, the heatwave duration (0.62 days/10 yr) increased. In terms of the extreme precipitation, there was no significant trend among the three types of steppes. However, the fluctuations in extreme precipitation were the largest in the desert steppe compared to those in the typical steppe and meadow steppe.

Grassland degradation is serious in the Mongolian plateau, especially in Inner Mongolia, China. Accurate monitoring of grassland types and qualities is increasingly important for the purposes of grassland conservation and restoration. Using in situ hyperspectral reflectance data and ground-based ecological measurements, we explored the potential for large-scale monitoring grassland communities using imaging spectroradiometers. We compared the spectral reflectance of the major types of grasslands and field plots with/without livestock grazing. We also did statistical analysis about the relationship between hyperspectral indices and aboveground biomass (AGB) of the surveyed grassland communities. The results showed that: (1) the dominant plant species varied across meadow, typical, and desert steppe, and they also varied between fenced and grazed plots; (2) in situ hyperspectral data are useful for differentiating grassland communities of meadow, typical, and desert steppe and grassland communities with and without livestock grazing; and (3) the prediction accuracies of vegetation indices for AGB decreased from desert to typical and meadow steppe, and the results were contrary for the prediction accuracies of red edge inflection point (REIP). REIP may not be suitable for estimating AGB of the low-density grassland communities. The above results implied that care must be taken while using statistical models to link spectral and ecological measurements in large geographical scales since there is lack of portability over different types of grassland communities. This study provides foundations for future large-scale efforts of monitoring grassland communities in Inner Mongolia using imaging spectroradiometers.

The Mongolian steppes with a long history of nomadic pastoralism cover a large area of the Palaearctic steppe biome and are still relatively intact. As livestock number has increased over the last two decades, grazing has been considered as the main reason of pasture degradation. However, the impact of grazing on vegetation dynamics, and its interaction with climate, is still not clear. We reviewed 44 publications in Mongolian language, covering 109 sites in five main steppe types, i.e., desert, dry, meadow, mountain, and high mountain steppe, with a mean annual precipitation and temperature range from 120 to 370 mm and from −6 to +5°C, respectively. We calculated relative changes in vegetation cover, species richness, and aboveground biomass from heavily grazed with respect to lightly/non-grazed conditions. Multiple linear regression models were used to test the impact of environmental factors, i.e., mean annual precipitation, coefficient of variation for precipitation, mean annual temperature and elevation. Grazing had a stronger effect on the vegetation of dry, desert and high mountain steppes, whereas its effect was less pronounced in the meadow and mountain steppes with mesic climate and high productivity. Vegetation cover, species richness and aboveground biomass were reduced by heavy grazing in the dry, desert and high mountain steppes. In the meadow steppes, grazing reduced vegetation cover, but increased richness and had nearly no effect on biomass. In the mountain steppe, richness and cover were not affected, but biomass was reduced by heavy grazing. Additionally, grazing effects on biomass tended to be more pronounced at sites with higher amounts of annual precipitation, and effects on cover changed from negative to positive as elevation increased. In conclusion, grazing effects in Mongolian steppes are overall negative in desert, dry and high mountain steppes, but no or even positive effects are found in meadow and mountain steppes. Especially, heavy grazing showed a detrimental effect on all vegetation variables in desert steppes, indicating the existence of combined pressure of climate and grazing in arid habitats, making them potentially sensitive to overgrazing and climate change. Grassland conservation and management should consider characteristics of different steppe types and give importance to local environmental conditions.

Spatial patterns of soil organic carbon fractions and their control in temperate grasslands of China

There are still great uncertainties about effects of climate warming and no-tillage on soil carbon, nitrogen, phosphorus and potassium contents and pH in alpine farmlands. A warming (control; daytime warming, DW; nighttime warming, NW; all-day warming, DW + NW) and no-tillage (no-tillage vs. tillage) experiment was conducted in an alpine farmland of the Lhasa, Xizang since 2015. Soil organic carbon, total nitrogen, total phosphorus, total potassium (TK), available nitrogen, available phosphorus, available potassium, dissolved organic carbon (DOC), active organic carbon, particulate organic carbon (POC), light fraction organic carbon, and heavy fraction organic carbon contents and pH at four depths (0–5, 5–15, 15–25, and 25–35 cm) were measured. Warming effects on concerned soil variables differed with warming time, soil depth, and no-tillage. No-tillage effects on concerned soil variables differed with warming-time (daytime, nighttime, and all-day warming) and soil depths. Therefore, daytime warming and nighttime warming have different effects on soil variables, although the effects of nighttime warming on soil variables are not always greater than those of daytime warming. Effects of daytime warming and nighttime warming on soil variables are not simple addition or subtraction effects. There are interactions between diurnal asymmetrical warming and no-tillage on soil variables.

Aridity modifies the responses of plant stoichiometry to global warming and nitrogen deposition in semi-arid steppes

Understanding how species sort themselves into communities is essential to explain the mechanisms that maintain biodiversity. Important insights into potential mechanisms of coexistence may be obtained from observation of non-random patterns in community assembly. The spatial niche overlap (Pianka index) and co-occurrence (c-score) patterns in carabid species in three types of steppes (desert steppe, typical steppe, and meadow steppe) in China was investigated. Non randomness was tested using null models. Niche overlap values were significantly higher than expected by chance in the desert steppe, where vegetation cover is less abundant and less uniformly distributed, which possibly forces species to concentrate in certain places. In the typical and meadow steppes, results were influenced by the scale of the analysis. At a broad scale, niche separation was found as a result of species segregation among different sectors (habitats) within these steppes, but when the analysis was conducted at a finer scale, species appeared to be no more segregated than expected by chance. The high co-occurrence averages found in the meadow and typical steppes indicate that the distributions of the species found in a site may be negatively affected by the presence of other species, which suggests that some species tend to exclude (or reduce the abundance of) others. The very low c-score average observed in the desert steppe suggests that competition is not involved there. Thus, in more homogeneous landscapes (such as the typical and meadow steppes), competition might play some role in community structure, whereas spatial variation in the abundances of species is more driven by the uneven spatial distribution of vegetation in the landscape where productivity is lower and less uniformly distributed.