Desert Grassland Research Articles

Afforestation with Pinus sylvestris var. mongolica remodelled soil bacterial community and potential metabolic function in the Horqin Desert

Soil bacteria have been widely investigated and their roles in terrestrial ecosystems are relatively well understood. The soil bacterial community and potential function are controlled by vegetation and bacteria are factors indicating changes in soil microenvironment. However, there is a knowledge gap regarding microbial influence and their use to predict the change in metabolic function after afforestation in desert ecosystem. Pinus sylvestris var. mongolica is the most important evergreen species in desertified northern China. Therefore, we used the 16S rRNA high-throughput sequencing and PICRUSt platform to identify the soil bacterial community and potential metabolic function across stand ages (HQh: half-mature forest, HQn: nearly-mature forest, HQm: mature forest) and control (CK, natural grassland) in the Horqin Desert. Soil characteristics were determined to clarify edaphic driving factors and reveal the effect of afforestation on bacteria. The results indicated that (1) The dominant soil bacterial community category was stable but potential metabolic function changed across stand ages. The dominant phyla and genera were Proteobacteria and Acidobacteria and Sphingomonas, RB41, respectively; the metabolic functions changed from carbohydrate to amino acid metabolism. (2) P. sylvestris plantations significantly increased soil bacterial diversity (P < 0.05). Catalase was significantly correlated with soil bacterial diversity (P < 0.05). (3) The driving factor of the bacterial community was Urease in the CK plot. Afforestation changed the soil organic matter (SOM) in HQh and HQn, but urease was restored in HQm. The dominant soil characteristics that affected potential metabolic function were soil porosity (SP) and total nitrogen (TN) in the CK plot, total phosphorous (TP) and SOM in HQh, catalase activity in HQn, and urease in HQm. The changes in dominant soil characteristics forecasted that afforestation broke traditional desert grassland ecological balance, established a new forest ecological balance by changing soil environment, and indicated that the potential metabolic pattern changed from resource acquisition to resource utilization. This may herald the creation of new ecosystems in deserts. Our results provide strong microbial evidence that evaluated the significance of afforestation in arid regions.

Climate warming-induced drought constrains vegetation productivity by weakening the temporal stability of the plant community in an arid grassland ecosystem

An investigation of the influences of climatic warming on ecosystem function and stability is crucial to project the impact of global climate change on terrestrial ecosystems. However, few studies have applied multiple warming treatments in arid ecosystems, which play a critical role in the global carbon cycle and are among the ecosystems most sensitive to future climatic change. To explore the effects of climatic warming on plant community function and stability, moderate warming and acute warming treatments were conducted in desert grassland, Inner Mongolia, China, using free-air temperature increase facilities. Aboveground net primary production (ANPP) of plant community significantly decreased with climatic warming, particularly in warmer years with drier conditions. The decrease in ANPP was mainly caused by decreased soil moisture induced by climatic warming. Climatic warming reduced the temporal stability of the plant community by weakening plant species asynchrony and shifting key functional groups, such as perennial vs annual grass and C3 vs C4 species. Our findings indicate that climatic warming could hamper plant community productivity via decreased soil moisture and constrain plant community functioning by weakening community stability. This result highlights that shifts in plant community composition and consequent functional changes can play a key role in predicting the responses of arid ecosystems to climatic change.

The responses of soil respiration to changed precipitation and increased temperature in desert grassland in northern China

Soil respiration (SR) is an important process and the largest source of carbon cycle of terrestrial ecosystems, which has a significant impact on global climate and environmental changes. The fluctuation of temperature and precipitation caused by climate change is a driving force for the dynamic change of SR. Therefore, we established the field experiment with 5 levels of precipitation by rainout shelters and 2 levels of temperature by Open-top Chamber (OTC) to determine the SR dynamic in the desert grassland in northwest China. The results show that: soil temperature (ST) and soil moisture (SM) are affected by changed precipitation and increased temperature, but not greatly. Overall, it can be seen that the SR continue to increase with the precipitation increasing and the temperature rising. SR has no significant correlation with above-ground living biomass (ALB), but is significantly correlated with root biomass (RB), so SR mainly comes from the root system, and ALB and RB both increase with rainfall rising. Soil physical and chemical properties are related to SR, but not significantly. These findings provide a reliable theoretical basis for formulating a reasonable response strategy in desert steppe ecosystems.

Aboveground net primary productivity and soil respiration display different responses to precipitation changes in desert grassland

AbstractPrecipitation (PPT) changes affect both aboveground vegetation dynamics and belowground carbon cycling processes, particularly in arid and semiarid regions. However, it remains unclear how extreme PPT variation can affect soil carbon sequestration potential. A 3-year PPT manipulation experiment with five levels (±40%, ±20% and ambient PPT) was conducted in a desert grassland of western Loess Plateau. Aboveground net primary productivity (ANPP) and soil respiration (Rs) were measured to examine whether the responses of ANPP and Rs to PPT changes displayed a double asymmetry model. The ANPP was more sensitive to extreme drought than extreme wet treatments in wet and dry years, which displayed a negative asymmetric model. The change in ANPP was mainly due to the direct effect of PPT change, and plant density variation also exerted some influence in the dry year. In contrast, Rs displayed a positive asymmetry response to PPT change in dry year. This may be ascribed to enhanced autotrophic respiration due to the enhanced positive responses of plant growth and ANPP to wet treatments as well as stronger birch effect of rainfall events on heterotrophic respiration. The saturating response of Rs to extreme drought (−40% PPT treatment) was also found in the dry year. Nevertheless, the response of Rs to PPT change displayed a negative asymmetry model in wet years. The contrasting models for ANPP and Rs in response to altered PPT regime suggest that extreme wet or dry treatments may increase soil C pools effluxes toward debt in this desert grassland.

Patterns of Genetic Divergence across Geographically Variable Populations of Xanthisma gracile (Asteraceae)

Premise of research. Numerous biotic and abiotic factors can contribute to local selection and lead to geographic structure and genetic divergence between populations. The southwestern United States contains many distinctive plant communities, ranging from woodlands to desert scrub, that are shaped by species adapting to local variation in elevation, precipitation, seasonality, and soils. Given this variation, species occurring across diverse habitats are expected to harbor high genetic diversity and exhibit significant genetic differences associated with environmental variation.Methodology. Here, we studied the genetic divergence of populations of Xanthisma gracile (Asteraceae) across Arizona using amplified fragment length polymorphisms and evaluated associations between genetic structure, geographic distance between populations, and variation in climatic factors. This species occurs in desert grasslands at low altitudes as well as in open pine forests at intermediate altitudes and exhibits phenotypic variation in plant height, leaf shape and pubescence, and floral traits.Pivotal results. We detected significant genetic structure across populations and found that a population from arid central Arizona is much more genetically distant than samples from northern and southern Arizona that occur in more mesic habitats. We also detected evidence for selection on numerous loci associated with variation in temperature and precipitation.Conclusions. Major changes have occurred across the Southwest since the Last Glacial Maximum, and genetic divergence in X. gracile across Arizona likely reflects selection for survival in climatically diverse habitats.

Effects of managed fire on a swale grassland in the Chihuahuan Desert

• Fire is considered a critical process for limiting shrub encroachment and maintaining grassland structure and functions. • Fire can be detrimental to grasses in upland settings of arid desert grasslands, but no studies have been performed in more productive swale grasslands. • Monitoring of a prescribed fire treatment in a swale grassland in southern New Mexico indicated that perennial grasses had not recovered after 5 years, even with above-average rainfall. Furthermore, indicators of erosion susceptibility increased, and shrubs resprouted rapidly.

Changes of soil bacterial and fungal community structure along a natural aridity gradient in desert grassland ecosystems, Inner Mongolia

Environmental aridity is increasing in several regions around the globe due to climate change. However, little is known about microbial diversity and community responses to aridity along grassland-to-desert gradients. We investigated soil bacterial and fungal diversity and composition, and associated environmental factors along an aridity gradient across grassland (G), desert-grassland (DG) and desert (D) in Inner Mongolia, Northern China. The results indicate that soil microbial diversity decreased significantly from G and DG to D. Bacteria were mostly dominated by the universal phyla Proteobacteria, Actinobacteria, Bacteroidetes and Acidobacteria. Fungal communities were dominated only by Ascomycota. Most bacterial species (58.7–69.1%) were found in all habitats with significant differences among the three vegetation types, while most soil fungal species occupied small geographic areas. Soil bacterial communities adapted to environmental changes through changes in proportions of their taxa, while fungi changed their rare taxa in response to the differences in local environments. Canonical correspondence analysis (CCA) indicated that soil C:N, salinity and regional temperature were the most important factors regulating microbial community composition. Structural equation models (SEM) revealed that C:N was the most important factor directly influencing soil microbial diversity, and SPEI was the most important factor indirectly influencing soil microbial diversity in the Mongolian desert-grassland ecosystem. Our results provide evidence that soil bacterial and fungal communities respond differently to the changes in the biotic and abiotic factors, reflecting different adaptive strategies for coping with climate change in desert grassland ecosystems.

Pulse Effect of Precipitation: Spatial Patterns and Mechanisms of Soil Carbon Emissions

The rapid and strong release of CO2 caused by precipitation (known as the pulse effect) is a common phenomenon that significantly affects ecosystem C cycling. However, the degree to which the pulse effect occurs overlarge regional scales remains unclear. In this study, we conducted continuous and high-frequency measurements of soil CO2 release rates (Rs) for 48 h after simulated precipitation, along a precipitation gradient of different grassland types (i.e., meadow, typical, and desert) in Inner Mongolia, China. Pulse effects were assessed using the maximum Rs (Rsoil–max) and accumulated CO2 emissions (ARs–soil). Strong precipitation pulse effects were found in all sites; however, the effects differed among grassland types. In addition, an apparent decrease in both Rsoil–max and ARs–soil was observed from the east to west, i.e., along the decreasing precipitation gradient. ARs–soil values followed the order: temperate meadow grassland (0.097 mg C g–1 soil) &amp;gt; typical temperate grassland (0.081 mg C g–1 soil) &amp;gt; temperate desert grassland (0.040 mg C g–1 soil). Furthermore, Rsoil–max and ARs–soil were significantly positively correlated with soil quality (SOC, POC, and N, etc.; P &amp;lt; 0.01). ARs–soil (P &amp;lt; 0.05) and ARs–SOC (P &amp;lt; 0.01) were significantly affected. ARs–soil and ARs–SOC were also positively correlated with soil microbial biomass significantly (P &amp;lt; 0.05). Rsoil–max and ARs–soil had similar spatial variations and controlling mechanisms. These results greatly support the substrate supply hypothesis for the effects of precipitation pulses, and provide valuable information for predicting CO2 emissions. Our findings also verified the significant effect of soil CO2 release from precipitation pulses on the grasslands of arid and semi-arid regions. Our data provide a scientific basis for model simulations to better predict the responses of ecosystem carbon cycles in arid and semi-arid regions under predicted climate change scenarios.

Genome-Wide Analysis and Expression Profiles of the Dof Family in Cleistogenes songorica under Temperature, Salt and ABA Treatment.

The DNA-binding with one zinc finger (Dof) family of plant-specific transcription factors has a variety of important functions in gene transcriptional regulation, development, and stress responses. However, the structure and expression patterns of Dof family have not been identified in Cleistogenes songorica, which is an important xerophytic and perennial gramineous grass in desert grassland. In this study, 50 Dof genes were identified in C. songorica and could be classified into four groups. According to genome-wide analysis, 46 of 50 Dof genes were located on 20 chromosomes, and the gene structure and conserved protein motif of these proteins were analyzed. In addition, phylogenetic analysis of Dof genes in C. songorica, Arabidopsis thaliana, Oryza sativa, and Brachypodium distachyon estimated the evolutionary relationships, and these genes were grouped into seven clusters. Moreover, the expression profiles of these Dof genes in C. songorica were analyzed in response to high/low temperature, salinity, and ABA treatments. These results will provide valuable information for future studies on gene classification, cloning, and functional characterization of this family in C. songorica.

Soil fertility evaluation and spatial distribution of grasslands in Qilian Mountains Nature Reserve of eastern Qinghai-Tibetan Plateau.

The study assessed the overall soil characteristics of grasslands on Qilian Mountains and rated the soil nutrient status with classification standard of the second national soil survey of China. Nemerow index method was used to evaluate the soil fertility of different grassland types. GIS was used to analyze the spatial distribution of the soil nutrients and provided a database for the grassland’s ecological protection and restoration. The study graded the soil organic matter (SOM), total N, and available K at level 2 (high) or above for most regions, available soil-P at level 4, while the soil bulk density, total porosity and pH were 0.77–1.32 g cm−3, 35.36–58.83% and 7.63–8.54, respectively. The rank of comprehensive soil fertility index was temperate steppe (TS) > alpine meadow (AM) > alpine steppe (AS) >upland meadow (UM) >alpine desert (AD)> lowland meadow (LM)> temperate desert steppe (TDS)> temperate desert (TD). The areas with high, medium and low soil fertility accounted for 63.19%, 34.24% and 2.57% of the total grassland area. Soil fertility of different grassland types had different main limiting factors, for instance, the pH, total N and SOM were the main factors limiting soil fertility in LM, while pH and available P were the main factors limiting soil fertility in UM, AM, TS and AS. In summary, the grassland soil fertility was generally at the mid-upper level, and the main limiting factors were found in the different types of the grasslands and their spatial distributions were figured out. Our findings also indicated that the typical grasslands and meadows may require phosphorus application, while for desert grasslands, both nitrogen and phosphorus were required to improve their comprehensive soil fertility and grassland productivity.

Evaluating the dynamics of grassland net primary productivity in response to climate change in China

Net primary productivity (NPP) has been considered as a direct indicator to access the terrestrial primary production. However, considerable uncertainties remain toward the response mechanism of NPP to climate change across annual and seasonal scales, especially for grassland ecosystems. In this study, the spatiotemporal dynamics of grassland NPP and its prominent climate-controlling factor were evaluated based on the CASA model and ground-based meteorological data across annual and seasonal scales in China from 1982 to 2016. Results showed that the annual mean grassland NPP was 294.58 gC·m−2·a−1 over the 35 years; the largest annual mean NPP was observed in Alpine sub-alpine meadow (235.72 ± 13.21 gC·m−2·a−1), while the smallest annual mean NPP value occurred in Desert grassland (97.27 ± 9.64 gC·m−2·a−1). Moreover, the multiyear mean grassland NPP showed a decreasing trend from the southeast to the northwest spatially. Temporally, grassland NPP exhibited a significant increasing trend (slope = 2.4 gC·m−2·a−1; p < 0.0001) over the whole study period; an abrupt change point across the grassland NPP time series was observed in 1999. Specially, 66.34% of the grassland area showed an increasing trend in NPP, and the areas with a significant increasing trend were concentrated in Qinghai-Tibet Plateau and the northern area of Xinjiang. Further climate factor analysis with NPP indicated that NPP positively correlated with precipitation and negatively correlated with temperature for the whole grassland area. In particular, the temperature was a dominant driver in NPP variations for Alpine sub-alpine meadow, Slope grassland and Alpine sub-alpine grassland, while precipitation controlled the most in NPP variations for Plain grassland and Desert grassland. The accumulation of grassland NPP in spring and autumn benefits from the increase in temperature, and precipitation promoted the accumulated NPP in summer and winter.

Assessing Sustainability Goals Using Big Data: Collaborative Adaptive Management in the Malpai Borderlands

Collaborative adaptive management is a means to achieve social and ecological goals in complex natural resource management settings. Evaluation of collaborative management outcomes, however, is difficult at the scale of large landscapes. We developed an approach for such evaluations using long-term, spatio-temporal gridded or county-level datasets alongside local information on changes in ranch ownership. We applied this approach to evaluate the sustainability goals of the Malpai Borderlands Group (MBG) by comparing the MBG landscape to surrounding, similar desert grassland landscapes. We matched datasets, where possible, to management goals, including the preservation of ranching livelihoods, prevention of rangeland fragmentation by exurban development, sustaining the ecological role of fire, limiting or reversing woody plant encroachment into grasslands, sustaining rangeland productivity, and sustaining biodiversity. We found that the number of ranch families changed little since MBG was established, although several ranches were consolidated within some families or absentee owners, such that multiple families share other ranches. The number of beef cattle ranches declined within one MBG county, likely due to increasing depth to groundwater. Exurban development and rangeland-to-cropland conversion have been virtually nonexistent in the MBG landscape, while such conversions are common in adjacent landscapes. Coordinated fire planning with low fragmentation of rangeland has led to extensive fires in the MBG landscape, dwarfing the area burned in adjacent landscapes. The percent of land area exhibiting significant trends of increasing bare ground cover was intermediate in the MBG landscape compared with adjacent landscapes, while herbaceous and shrub cover exhibited significant trends in only a small fraction of the study region. Rangeland productivity exhibited significant declines in some landscapes, but declines were minimal in the MBG area. Our analysis suggests that collaborative adaptive management implemented by the MBG has aligned with their goals, but changing climate, water availability, and demography will become increasingly challenging.

Responses of soil nitrogen to the transition from desert grassland to shrubland in eastern Ningxia, China

In this study, desert grassland, grassland edge, shrubland edge, shrubland were selec-ted as four transition sites in a nearly 30 years typical desert grassland-shrubland mosaic formed by anthropogenic shrub introduction. Soil properties and soil microbial characteristics under vegetation patches and bare interspace in each site were investigated to examine the responses of soil nitrogen to the desert grassland-shrubland state transition. It was shown that the aboveground biomass increased with transition from desert grassland to shrubland. Annual herbs increased largely with the introduction of shrubs. Soil moisture, microbial biomass and total nitrogen and carbon decreased with the transition. The abundance of microogranisms was lower in grassland edge and shrubland edge, and then increased in shrubland, which was slightly higher than that of desert grassland. With respect to nitrogen, nitrate content reached the highest level of 28.45 mg N·kg-1 and ammonium reached the lowest level of 4.81 mg N·kg-1 in shrubland, which were significantly increased by 52.3% and decreased by 10.4% compared with desert grassland. In addition, soil moisture and microbial biomass nitrogen was positively correlated across all sites. The relationship between mine-ralized nitrogen and soil moisture was non-linear, as they were positively correlated in desert grassland and grassland edge, but negatively correlated in shrubland edge and shrubland. During the 30-year transition from desert grassland to shrubland, our results showed that soil total nitrogen and microbial biomass nitrogen were significantly decreased, but mineralized nitrogen, especially for nitrate, significantly increased over time, indicating that soil nitrification was inhibited in desert grassland but accelerated in shrubland.

Changes and controls of aboveground net primary production in response to grassland policy in Inner Mongolian grasslands of China

Over-reclamation of grassland resources has increasingly contributed to environmental degradation in China. With grassland degradation, actions have been taken to maintain or restore natural grasslands through efforts such as ecological engineering. Inner Mongolia is considered being one of the most severely degraded areas in China and consequently almost all of the national land restoration projects for environmental protection were implemented there, making it the province with the highest investment in environmental restoration programs in China. In this study, we use the estimation model relationship established between the vegetation index extracted from remote sensing images and the measured biomass in the field to inversely calculate the biomass in the study area. And then we focused on the changes in the aboveground net primary productivity (ANPP) of these grassland ecosystems, which is crucial for gaining a better understanding of grassland changes in the light of rapidly changing environmental policies and governance regimes in China. The interannual variation of ANPP fluctuated greatly (fluctuated from 87.81 g/m2 to 88.5234 g/m2 between 2000 and 2017). The grassland changes in the whole region are basically stable, but the changes in individual areas are more serious. The ANPP was negatively correlated with the mean annual temperature and positively correlated with the annual precipitation. The hydrothermal conditions directly affected the distribution and accumulation of ANPP along meadow, typical and desert grasslands. Different stages of grassland policy have different target orientations and have positive and negative impacts on ANPP.

Spatial pattern dynamics of darkling beetle communities at small scale in a desert grassland of alluvial fans in Helan Mountain, Northwest China

To understand the dynamics of spatial pattern of darkling beetle communities at the small scale, we surveyed the darkling beetle community using pitfall in a desert grassland of alluvial fans in Helan Mountain from May to October 2019. Based on the geostatistical analysis, we divided the 200 m×200 m study area equally into 100 grid squares and analyzed the spatial autocorrelation, spatial heterogeneity, spatial distribution pattern, and its relationship with topographic factors of the darkling beetle community. A total of 1086 individuals belonged to 10 species and 7 genera were collected. Community composition of darkling beetle had significant spatial and temporal variation. The diversity index of the community was the highest in May and lowest in July. The spatial autocorrelation of dominant species had obvious seasonal fluctuation, with a significantly spatial positive correlation in May, September, and October. Communities of darkling beetle and the dominant species showed strongly spatial heterogeneous, which were mainly determined by structural factors. The ordinary Kriging interpolation showed that the gradient distribution of beetle communities was obviously different among seasons, being the simplest in summer. The results of the cross variogram showed that the spatial relationships between different dominant species groups were mostly positive, and were mainly regulated by structural factors. Results of the canonical correspondence analysis (CCA) showed that the slope and elevation significantly affected the distribution of darkling beetles. Our results showed that the spatial heterogeneity of the darkling beetle showed significant seasonal variation, and thus provided a basis for understanding the mechanism and biodiversity of ground-dwelling beetle community in a desert grassland of alluvial fans.

Desert grassland dynamics in the last 20 years and its response to climate change in Xinjiang

Desert grassland dynamics in the last 20 years and its response to climate change in Xinjiang

NORTH AMERICAN PORCUPINE DISTRIBUTION IN THE PACIFIC NORTHWEST AND EVALUATION OF A NON-INVASIVE MONITORING TECHNIQUE

North American Porcupines (Erethizon dorsatum) have a broad geographic distribution across much of the continent, but recent evidence suggests that their populations may be declining in some areas, including the Pacific Northwest. Estimating baseline historical and contemporary distributions of Porcupines is necessary for initiating monitoring efforts and, if necessary, informing strategic conservation actions. We compiled 1905 occurrence records of Porcupines in Washington, Oregon, and northern California from 1908 to 2018. Using maximum entropy modeling (Maxent), we created historical and contemporary distribution models based on Porcupine records from 1981–2010 and 2012–2018, respectively, to match the temporal scale of available environmental predictor layers and suspected onset of the decline. Our models suggested a recent shift in the occupied environmental niche of Porcupines in the Pacific Northwest away from forested areas and towards desert scrub and grassland vegetation communities. In addition, we tested a non-invasive survey method for determining Porcupine presence and monitoring their status over time. Our trials suggested that sodium-soaked wood blocks may provide an inexpensive and minimally invasive technique to detect Porcupines, but further testing is needed to understand its effectiveness and limitations.

Temporal and Spatial Variations in NDVI and Analysis of the Driving Factors in the Desertified Areas of Northern China From 1998 to 2015

China faces some of the most serious desertification in the world, leading to many problems. To solve them, large-scale ecological restoration projects were implemented. To assess their effectiveness, we analyzed normalized-difference vegetation index (NDVI) data derived from SPOT VEGETATION and gridded climate datasets from 1998 to 2015 to detect the degrees of desertification and the effects of human and climate drivers on vegetation dynamics. We found that NDVI of desertified areas generally decreased before 2000, then increased. The annual increase in NDVI was fixed dunes (0.0013) = semi-fixed dunes (0.0013) &amp;gt; semi-mobile dunes (0.0012) &amp;gt; gobi (gravel) desert (0.0011) &amp;gt; mobile dunes (0.0003) &amp;gt; saline–alkali land (0.0000). The proportions of the area of each desert type in which NDVI increased were fixed dunes (43.4%) &amp;gt; semi-mobile dunes (39.7%) &amp;gt; semi-fixed dunes (26.7%) &amp;gt; saline–alkali land (23.1%) &amp;gt; gobi desert (14.4%) &amp;gt; mobile dunes (12.5%). Thus, the vegetation response to the restoration efforts increased as the initial dune stability increased. The proportion of the area where desertification was dominated by temperature (1.8%) was far less than the area dominated by precipitation (14.1%). However, 67.6% of the change was driven by non-climatic factors. The effectiveness of the ecological restoration projects was significant in the Loess Plateau and in the Mu Us, Horqin, and Hulunbuir sandy lands. In contrast, there was little effect in the Badain Jaran, Ulan Buh, and Tengger deserts; in particular, vegetation cover has declined seriously in the Hunshandake Sandy Land and Alkin Desert Grassland. Thus, more or different ecological restoration must be implemented in these areas.

Effects of Precipitation Changes on Plant Community Diversity and Soil C:N:P Ecological Stoichiometric Characteristics in a Desert Steppe of China

Studying the influence of precipitation patterns on plant community diversity, soil C:N:P ecological stoichiometric characteristics, and the relationships between key soil factors and plant community diversity is of great significance for the protection of plant community diversity in desert grasslands. This paper was studied in the desert steppe of the west of Loess Plateau using a three-year precipitation manipulation experiment (40% reduction in precipitation, 20% reduction in precipitation, natural precipitation, 20% increase in precipitation, and 40% increase in precipitation), explored the influence of changes in precipitation in dry and wet years on the diversity of plant community and soil C:N:P ecological stoichiometric characteristics. And we also explored the relationship between soil C:N:P ecological stoichiometric characteristics and the key soil factors and the diversity of plant community under changes in precipitation. The results showed that in a normal year and the drier year (2013 and 2015), Patrick richness and Shannon-Wiener diversity index were significantly low under the 20% reduction treatment compared with the control and 40% increase treatments, respectively. During the wetter year, Patrick richness and Shannon-Wiener diversity index were no different between any of the precipitation treatments. In the normal year and the drier year, the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents and the carbon-nitrogen ratio (C:N), carbon-phosphorus ratio (C:P), and nitrogen-phosphorus ratio (N:P) all decreased with an increase in precipitation (the decrease in the C:N ratio was statistically significant). During the wetter year, SOC, TN, C:P, and N:P increased with an increase in precipitation. During the normal year, precipitation treatments had no significant influence on soil water content, having a limited influence on the plant community. TN, N:P, SOC, C:N, and microbial biomass nitrogen (MBN) had a more prominent influence on plant community diversity. In the wetter year, precipitation was abundant leading to a rise in soil nutrients. Water was not the most important factor limiting to plant growth whereas soil water content, soil nutrients, and ecological stoichiometric characteristics jointly regulate plant community diversity. In the drier years, precipitation treatments had a significant impact on soil water content, whereby an increase in precipitation led to high losses of soil nutrients. Therefore, soil water content was the most important factor affecting plant community diversity during drier years. These observations indicate that under dry and wet years, plant community diversity and soil C:N:P ecological stoichiometric characteristics have variable responses to precipitation and soil C:N:P effect on plant community were also different. These results provide a theoretical basis for the protection and management of desert steppe systems under future projected changes in precipitation.

Estimation of shrubland aboveground biomass of the desert steppe from optical and C-band SAR data

Accurately estimating the shrubland aboveground biomass (AGB) of the desert steppe and understanding its dynamic changes are vitally important for studying the regional carbon cycle and sustainable use of grassland resources. Synthetic aperture radar (SAR) data are seldom applied to estimate shrubland AGB, particularly in arid and semiarid desert steppe landscapes. The main objective of this study was to model shrubland AGB in arid and semiarid desert steppe regions with HJ1B and RADARSAT-2 C-band data. The main species was Caragana microphylla, one of the most widespread shrubs in desert grasslands. Three regression models based on stepwise multiple linear regression (SMLR), partial least squares regression (PLSR) and random forest regression (RFR) were developed between the measured AGB and radar backscatter coefficient, vegetation indices and texture information. The three methods were compared, and their performance was evaluated for the estimation of shrubland AGB from HJ1B and RADARSAT-2 data. The results show that SAR can produce higher accuracy with R2 = 0.34–0.42 than PLSR and RFR in arid and semiarid desert steppe regions. The RF results were slightly worse than those of SMLR and PLSR for sparse vegetation. The use of C-band SAR data to monitor dynamic changes in shrubland AGB in northern China will be of great value.