Arid Desert Ecosystems Research Articles

A dataset of carbon and water fluxes in the extremely arid desert ecosystem in Guazhou County, Gansu Province (2019–2022)

A dataset of carbon and water fluxes in the extremely arid desert ecosystem in Guazhou County, Gansu Province (2019–2022)

A dataset of monthly litter recovery from the desert grassland in Southern Tarim Basin during 2010–2020

The Cele National Field Science Observation and Research Station of Desert Grassland Ecosystem of Xinjiang of Chinese Academy of Science (Hereinafter referred to as "Cele Station"), is located on the southern margin of the Tarim Basin bordered to the south by the Kunlun Mountains and to the north by the largest desert in China, the Taklimakan Desert. As a result of simple vegetation community and slow accumulation of soil organic matter, litter serves as an important source of nutrients in this area. Based on the long-term observations of desert plant communities at Cele station, we gathered monthly dynamic data of litter recovery in the desert grassland from Southern Tarim Basin from 2010 to 2020. Based on plant organs (branches, leaves, and fruits), the monthly dynamic data of litter recovery at the observation sites and plots were sorted out, and the annual changes of community and soil nutrients were recorded. Data were compiled in strict accordance with CERN bio-observation specifications. The data has undergone review and quality control by the quality control personnel of the station and sub-center. The results would provide basic data for further study of litter dynamics in the desert grassland from Southern Tarim Basin, and theoretical support for better understanding and assessing nutrient cycling in hyper–arid desert ecosystems.

Soil characteristics and plant functional traits under long-term conservation in arid desert ecosystems

Soil characteristics and plant functional traits under long-term conservation in arid desert ecosystems

The Influence of Induced Drought Stress on Germination of Cenchrus ciliaris L. and Cenchrus setigerus Vahl.: Implications for Rangeland Restoration in the Arid Desert Environment of Kuwait

Drought impacts in arid desert ecosystems can result in decreased ecosystem productivity and biodiversity. Implementation of restoration projects in arid desert environments is largely dependent on water availability and soil moisture condition. This study investigated the influence of induced drought stress by using polyethylene glycol (PEG-6000) solution on germination viz. Cenchrus ciliaris and Cenchrus setigerus as the important rangeland species. The water stress potential treatments were 0 (control), –0.5 MPa, –1.0 MPa, –1.5 MPa, and –2.0 MPa. The extent of seed germination was severely affected by decreased water stress potential. As drought increased, the percentage of germination decreased in both Cenchrus’ species. The water deficit at –0.5 MPa showed a significant (P < 0.001) reduction in the final germination percentage in the case of C. setigerus and C. ciliaris by 65% and 42.5%, respectively. At –1.0 MPa to –1.5 MPa, changes in intermediate germination were observed in C. ciliaris (from 35% to 17.5%, respectively) and C. setigerus (from 22.5% to 11.25% respectively). Higher levels of water stress (–2.0 MPa) prevented the survival of both species. Understanding the germination strategies of native desert plant species associated with drought stress and identifying favorable conditions during the germination process can be useful for restoration practices and rangeland management actions to improve desert ecosystems and maintain biodiversity.

The Function of Arbuscular Mycorrhizal Fungi Associated with Drought Stress Resistance in Native Plants of Arid Desert Ecosystems: A Review

Drought stress profoundly affects native desert plants’ survival and performance. Among all the abiotic stresses, drought is considered a major constraint that influences the structure and functions of desert ecosystems. Arid desert ecosystems are characterized by prolonged drought, extreme temperatures, high solar radiation, water scarcity, high salinity, scarcity of soil nutrients, and poor soil structure. Such extreme desert environments are the toughest regions on earth, which present enormous challenges in conserving plant survival, growth and reproduction. Despite the predominance of these environmental conditions, native desert plant species that grow in desert environments develop complex adaptation strategies and resistance mechanisms to ameliorate the abiotic and biotic stresses in the extreme environments including changes in biochemical, physiological, and morphological levels. Arbuscular mycorrhizal fungi (AMF) form positive symbiotic associations with a considerable percentage of terrestrial plants as their host, induce distinct impacts on plant growth and protect plants from abiotic stresses. However, it is necessary to advance our understanding of the complex mechanisms associated with AMF-mediated and other dark septate endophytes (DSE)-mediated amelioration of native desert plants’ drought stress resistance and associated biological adjustments such as changes in hormone balance, water and nutrient status, stomatal conductance and osmotic adjustment, antioxidant activity, and photosynthetic activity. This review provides an overview of the relationships of mycorrhiza and fungal endophytes involved in drought stress tolerance, summarizing the current knowledge and presenting possible mechanisms mediated by AMF to stimulate drought tolerance associated with native desert plants. We discuss the research required to fill the gaps and provide suggestions for future research.

Soil variables driven by host plant and growth season affect soil microbial composition and metabolism in extremely arid desert ecosystems

Assessment changes of soil microbial community structure and function is important in understanding the response to desert ecosystem management. In present study, variations of soil microbial community and edaphic factors associated with five desert shrubs were determined in Anxi extremely arid desert in Northwest China in growing (summer), deciduous (autumn), and snowfall (winter) seasons. For that, the microbial composition and catabolic metabolism were examined using methods of phospholipid fatty acid (PLFA) and Biolog EcoPlate, respectively. Regardless of plant species and seasonal patterns, the microbial community was mostly dominated by gram-negative bacteria (GN); and the carbohydrates, amino acids and polymers were the main carbon sources for desert microbial metabolism. Microbial biomass and metabolic levels were significantly higher in both summer and winter than those of autumn. There was no correlation between soil microbial community and carbon utilization in winter; but GN was positively correlated with metabolism of amines carbon sources in summer, while fungal community presented the strongest correlation with suites of carbon sources’ metabolic levels in autumn, indicating the uncoupled relationship between microbial community and function in desert ecosystems. Desert shrubs significantly influenced the composition of soil microbial community, whereas the variation of microbial catabolic metabolism was most attributed to seasonality. Nevertheless, the effects of both plant species (21.3 %) and climate variation (84.9 %) interacted with soil properties, indicating the seasonality of soil nutrients predominately determined the changes in composition and metabolism of desert microbes. Both the comprehensive seasonal level and the intra-seasonal paired correlation analysis proved that phosphorus was the key factor in determining microbial community composition, while ammonia and nitrate nitrogen were more correlated to microbial functional metabolism. Additionally, soil moisture and organic carbon in desert environment also induced the shifts in ratio of fungi and bacterial communities. We conclude that the seasonal patterns of soil microbial community and metabolic function in extremely arid desert are predictable, and mainly influenced by specific soil factors driven by desert shrubs and climate factors. These findings will provide a basis for evaluating the management of soil resources and microbial function in desert environments.

Fractal features of soil grain-size distribution in a typical Tamarix cones in the Taklimakan Desert, China

Tamarix cones play key roles in preventing sand erosion and maintaining regional ecosystem stability. This study aimed to explore the characteristics of soil grain size distribution (GSD) in Tamarix cones across the Taklimakan Desert, verify the relationships between soil grain composition and the fractal dimension, and analyze the relationships between soil GSD and environmental factors. Soils of the Tamarix cones from 0 to 500 cm soil depth were sampled every 20 cm at four sites (Qiemo, Qira, Aral, and Tazhong) along the periphery to the hinterland of the Taklimakan Desert. A total of 300 soil samples were collected to measure soil grain sizes and soil properties. Soil grain size composition was dominated by silt and very fine sand, and the fraction of fine particles decreased and that of the coarse particles increased with soil depth, except for at Tazhong. This suggested that suspension-size particles are the main component of the soil GSD and decrease with the increasing depth in the profiles at the Tamarix cones. The soils were poorly and moderately poorly sorted. Kurtosis generally showed a mesokurtic peak, and the GSD was negatively skewed towards the coarser particles. The fractal dimensions of GSD decreased in the following order Qiemo (2.30) > Qira (2.07) > Aral (1.99) > Tazhong (1.96) because of the increase of coarse particles. The fractal dimension had a strong positive correlation with the clay and silt fractions, and a strong negative correlation with the sand fraction, indicating that the fractal dimension can reflect the characteristics of the soil GSD. The strong relationships between the fractal dimensions and selected soil properties indicate that the fractal dimension can not only quantify changes in soil properties, but also reflect the degree of desertification and degradation in the desert region. Considering the strong wind activities and different deposition sources in the Taklimakan Desert, this study provides a deep insight into the soil formation processes of Tamarix cones within extreme arid desert ecosystems.

Different contributions of plant diversity and soil properties to the community stability in the arid desert ecosystem.

As a one of the focuses of ecological research, understanding the regulation of plant diversity on community stability is helpful to reveal the adaption of plant to environmental changes. However, the relationship between plant diversity and community stability is still controversial due to the scale effect of its influencing factors. In this study, we compared the changes in community stability and different plant diversity (i.e., species, functional, and phylogenetic diversities) between three communities (i.e., riparian forest, ecotone community, and desert shrubs), and across three spatial scales (i.e., 100, 400, and 2500 m2), and then quantified the contribution of soil properties and plant diversity to community stability by using structural equation model (SEM) in the Ebinur Lake Basin Nature Reserve of the Xinjiang Uygur Autonomous Region in the NW China. The results showed that: (1) community stability differed among three communities (ecotone community > desert shrubs > riparian forest). The stability of three communities all decreased with the increase of spatial scale (2) species diversity, phylogenetic richness and the mean pairwise phylogenetic distance were higher in ecotone community than that in desert shrubs and riparian forest, while the mean nearest taxa distance showed as riparian forest > ecotone community > desert shrubs. (3) Soil ammonium nitrogen and total phosphorus had the significant direct negative and positive effects on the community stability, respectively. Soil ammonium nitrogen and total phosphorus also indirectly affected community stability by adjusting plant diversity. The interaction among species, functional and phylogenetic diversities also regulated the variation of community stability across the spatial scales. Our results suggested that the effect of plant diversities on community stability were greater than that of soil factors. The asynchronous effect caused by the changes in species composition and functional traits among communities had a positive impact on the stability. Our study provided a theoretical support for the conservation and management of biodiversity and community functions in desert areas.

Great gerbil burrowing-induced microbial diversity shapes the rhizosphere soil microenvironments of Haloxylon ammodendron in temperate deserts

In the Gurbantunggut Desert of northwest China, the main habitat of Rhombomys opimus (great gerbil) is under the thickets of Haloxylon ammodendron, the main construction species. In the long-term coexistence, continuous gerbil activities (burrowing, defecating, and gnawing) limited the growth of H. ammodendron, affected the root microenvironment under the H. ammodendron forest, and weakened the desert ecosystem. However, there is a lack of general understanding about the response of desert soil microhabitats to such gerbil disturbance. Accordingly, this study examined the effects of different intensities of gerbil disturbance (none, mild, moderate, or severe disturbances) on soil nutrients content and used high-throughput sequencing to explore the change in diversity and structure of microbial communities (bacteria and fungi) in H. ammodendron rhizosphere at different soil depths (0–20, 20–40, and 40–60 cm). In the arid desert ecosystem, compared with the soil fungal community, the alpha diversity of the soil bacterial community was significantly affected by gerbil disturbance. Meanwhile, both soil depth and gerbil disturbance significantly impacted the beta diversity and relative abundance of soil bacterial and fungal communities. In addition, gerbil disturbance significantly altered the soil characteristics affecting the distribution and composition of soil microbial communities in H. ammodendron rhizosphere, especially the soil bacterial community. This survey provides evidence that remold impact of gerbil disturbance on soil microenvironment of H. ammodendron rhizosphere in desert ecosystems in northwest China, which helps to further understand the potential correlations with changes in the microbial community at a regional scale.

Effects of plant diversity and abiotic factors on the multifunctionality of an arid desert ecosystem.

Many studies suggest that species diversity and abiotic factors promote ecosystem multifunctionality. However, whether ecosystem multifunctionality is impacted by phylogenetic diversity remains controversial. The present study tested this in an arid desert ecosystem in Ebinur Lake Basin using soil C:N ratio, soil pH, and soil salinity as abiotic factors, and species diversity and phylogenetic diversity as indicators of plant diversity. The effects of plant diversity and abiotic factors on single ecosystem functions (nutrient cycling, carbon stocks, water regulation, and wood production) and ecosystem multifunctionality were studied. We used structural equation modeling to assess the relationships among different functional groups and factors. The results showed that: (1) abiotic factors, particularly pH and C:N ratio in soil, had the strongest positive impact on multifunctionality (P < 0.001). The phylogenetic diversity and species diversity showed inconsistent changes, and their contribution to multifunctionality were not outstanding. (2) Abiotic factors were closely related to different ecosystem functions. Soil C:N had a significant positive effect on carbon stocks (P < 0.001), with an effect index of 0.89. Soil pH significantly enhanced nutrient cycling and water regulation. The role of plant diversity varied with the combination of different ecosystem functions. Phylogenetic diversity and species diversity influenced wood production, but showed opposite functions. (3) The importance of four single-ecosystem functions in an arid region was ranked as follows: carbon stocks > water regulation > nutrient cycling > wood production, emphasizing the importance of carbon elements in these ecosystems. These results improve our understanding of the drivers of multifunctionality in arid ecosystems, facilitating the elucidation of the influence of abiotic factors and phylogenetic diversity.

Effects of sand burial caused by ant nests on soil microbial biomass, basal respiration, and enzyme activity in/under biocrusts in vegetated areas of the Tennger Desert

AbstractSand burial of crusts, caused by ant burrowing, is a common phenomenon in desert landscapes, yet the potential impacts on soil processes are unknown. Three sand burial depths, 3.0–5.0 mm (deep burial), 1.0–1.5 mm (shallow burial), and 0 mm (control) affecting two dominant biocrusts (viz., cyanobacteria‐lichen crusts and moss crusts) sampled in the moist and dry seasons were selected to explore this issue in two vegetation areas of the Tennger Desert. We collected 180 samples from biocrust layers and topsoil to assess soil physicochemical properties, microbial biomass, basal respiration, and enzymes activities. The results showed that sand burial of crusts reduced soil microbial biomass, basal respiration, and enzyme activities, while deep burial caused a substantial decline in these parameters. Sand burial interfered with the biocrusts structure (e.g., rupture and flaking) and properties, subsequently causing soil‐nutrient deprivation and soil microclimate deterioration. These are major mechanisms for decreasing soil microbial biomass, basal respiration, and enzyme activities. Moss crusts had significantly higher levels of the microbial parameters than cyanobacteria‐lichen crusts following sand burial, indicating that biocrusts' tolerance to sand burial was synchronized with their progressive succession. In addition, soil microbial parameters were higher in natural vegetation areas than artificial vegetation areas following sand burial. Such observations suggest that high soil fertility could mitigate the negative effects of sand burial on soil processes. In conclusion, sand burial induces biocrust degradation and further disturbs surface soil processes in arid desert ecosystems.

Ecological uniqueness and the determinants in arid desert ecosystems of Northwest China

Ecological uniqueness has important theoretical and practical significance for biodiversity conservation, and it has become a popular research topic in recent years. Species richness and soil nutrients play important roles in ecological uniqueness, but it is still unclear how different life forms, multiple biodiversity attributes, and environmental factors affect ecological uniqueness. In this study, we conducted a community investigation to combine species diversity, functional diversity, phylogenetic diversity, and soil factors to evaluate the impact of biotic and abiotic factors on ecological uniqueness. We verified these different relationships in woody and herbaceous plants. Our results showed that the species contribution to beta diversity (SCBD) of herbaceous plants was higher than that of other species, and SCBD had a strong correlation with species abundance and leaf thickness. Ecological uniqueness can be explained by soil factors and community characteristics, but the relative importance and interpretation of these characteristics differ between communities and between woody and herbaceous plants. Soil factors and community characteristics explained more of the ecological uniqueness in woody plants than herbaceous plants and communities. The community ecological uniqueness was mainly affected by soil pH. Soil moisture content and phylogenetic diversity had extremely significant positive effects on the ecological uniqueness of woody plants, while species richness and functional richness had significant negative effects. pH had a significant positive effect on the ecological uniqueness of herbaceous plants, and soil moisture indirectly affected the herb ecological uniqueness by affecting pH. In brief, the result showed that SCBD is significantly related to plant abundance, functional traits and leaf nutrients. In addition to focusing on sites with high species richness, functional diversity, and phylogenetic diversity, a comprehensive analysis from the perspective of different life forms can fully reflect the ecological uniqueness and proceed with species protection.

Succession of soil bacterial community along a 46-year choronsequence artificial revegetation in an arid oasis-desert ecotone

How the bacterial community structure and potential metabolic functions will change after revegetation in arid desert ecosystems is still unknown. We used high-throughput pyrosequencing to explore changes in soil bacterial diversity, structure and metabolic pathways, and the key driving factors along a chronosequence of 46-year Haloxylon ammodendron revegetation in an oasis-desert ecotone in the northwestern China. Our results indicated that establishment of H. ammodendron on shifting sand dunes significantly changed the structure of bacterial communities and increased their diversity and richness. The main dominant phyla were Actinobacteria (32.1–41.3%) and Proteobacteria (19.2–27.0%); in that, α-Proteobacteria (16.4–20.7%) were the most abundant Proteobacteria. Kocuria coexisted at different succession stage after year 0, and their relative abundance ranged from 3.8–9.0%. Principal coordinates analysis (PCoA) showed that bacterial community from the same revegetation site grouped together and generally separated from each other, indicating that significant shifts in bacterial community structure occurred after revegetation. LEfSe analysis identified unique biomarkers in the soil samples from seven sites. Moreover, PICRUSt analysis indicated similar overall patterns of metabolic pathways in different succession stage. Redundancy analysis (RDA) showed that total carbon, pH and total phosphorus were major abiotic factors driving the structure of bacterial communities, which explained 57.5% of the variation in bacterial communities. Our findings advance the current understanding of plant-soil interactions in the processes of ecological restoration and desertification reversal.

Topsoil Nutrients Drive Leaf Carbon and Nitrogen Concentrations of a Desert Phreatophyte in Habitats with Different Shallow Groundwater Depths

Phreatophytes are deep-rooted plants that reach groundwater and are widely distributed in arid and semiarid areas around the world. Multiple environmental factors affect the growth of phreatophytes in desert ecosystems. However, the key factor determining the leaf nutrients of phreatophytes in arid regions remains elusive. This study aimed to reveal the key factors affecting the ecological stoichiometry of desert phreatophytes in the shallow groundwater of three oases at the southern rim of the Taklimakan Desert in Central Asia. Groundwater depth; groundwater pH and the degree of mineralization of groundwater; topsoil pH and salt concentration; topsoil and leaf carbon, nitrogen, and phosphorus concentrations of phreatophytic Alhagi sparsifolia grown at groundwater depths of 1.3–2.2 m in the saturated aquifer zone in a desert–oasis ecotone in northwestern China were investigated. Groundwater depth was closely related to the mineralization degree of groundwater, topsoil C and P concentrations, and topsoil salt content and pH. The ecological stoichiometry of A. sparsifolia was influenced by depth, pH and the degree of mineralization of groundwater, soil nutrients and salt concentration. However, the effects of soil C and P concentrations on the leaf C and N concentrations of A. sparsifolia were higher than those of groundwater depth and pH and soil salt concentration. Moreover, A. sparsifolia absorbed more N in the soil than in the groundwater and atmosphere. This quantitative study provides new insights into the nutrient utilization of a desert phreatophyte grown at shallow groundwater depths in extremely arid desert ecosystems.

Fungal Endophytic Community and Diversity Associated with Desert Shrubs Driven by Plant Identity and Organ Differentiation in Extremely Arid Desert Ecosystem.

Despite desert ecosystem being crucial to our understanding of natural geography, species evolution and global climate change, there is limited information on the dynamics of their composition and the diversity of endophytic fungi communities driven by plant identity and organ differentiation. Here, an extensive investigation of endophytic fungal microbiome in root, stem, and leaf organs associated with five xerophyte shrubs in an extremely arid desert, Northwest China, were examined. The fungal community dominated by Dothideomycetes and Pleosporales. Shrub species strongly drive the niche-based processes of endophytic fungi across the root, stem and leaf compartments. The diversity and composition of endophytic fungi in stem showed higher variability among plant species than leaf and root. The fungal communities in root libraries were more diverse and exhibited a remarkable differentiation of community composition. We further demonstrated the significant host preferences and tissue specificity of desert endophytic fungi, and unique specific taxa were also observed. The co-occurrence network revealed the coexistence of fungal endophytes in arid desert, and the root fungal network harbored the highest interspecies connectivity. Members of Pleosporales were the most common keystone species in the root fungal network. This is the first report of mycobiota in both plant species and organ differentiation in an extremely arid desert ecosystem.

Groundwater Depths Affect Phosphorus and Potassium Resorption but Not Their Utilization in a Desert Phreatophyte in Its Hyper-Arid Environment.

Nutrients are vital for plant subsistence and growth in nutrient-poor and arid ecosystems. The deep roots of phreatophytic plants are necessary to access groundwater, which is the major source of nutrients for phreatophytes in an arid desert ecosystem. However, the mechanisms through which changes in groundwater depth affect nutrient cycles of phreatophytic plants are still poorly understood. This study was performed to reveal the adaptive strategies involving the nutrient use efficiency (NUE) and nutrient resorption efficiency (NRE) of desert phreatophytes as affected by different groundwater depths. This work investigated the nitrogen (N), phosphorus (P), and potassium (K) concentrations in leaf, stem, and assimilating branch, as well as the NUE and NRE of the phreatophytic Alhagi sparsifolia. The plant was grown at groundwater depths of 2.5, 4.5, and 11.0 m during 2015 and 2016 in a desert-oasis transition ecotone at the southern rim of the Taklimakan Desert in northwestern China. Results show that the leaf, stem, and assimilating branch P concentrations of A. sparsifolia at 4.5 m groundwater depth were significantly lower than those at 2.5 and 11.0 m groundwater depths. The K concentrations in different tissues of A. sparsifolia at 4.5 m groundwater depth were significantly higher than those at 2.5 and 11.0 m groundwater depths. Conversely, the NRE of P in A. sparsifolia was the highest among the three groundwater depths, while that of K in A. sparsifolia was the lowest among the three groundwater depths in 2015 and 2016. The N concentration and NUE of N, P, and K in A. sparsifolia, however, were not influenced by groundwater depth. Further analyses using structural equation models showed that groundwater depth had significant effects on the P and K resorption of A. sparsifolia by changing soil P and senescent leaf K concentrations. Overall, our results suggest groundwater depths affect P and K concentrations and resorption but not their utilization in a desert phreatophyte in its hyper-arid environment. This study provides a new insight into the phreatophytic plant nutrient cycle strategy under a changing external environment in a hyper-arid ecosystem.

Variability in condensation water and its determinants in arid regions of north‐western China

AbstractCondensation water plays an important ecohydrological role in arid and semi‐arid regions. However, little is known about the factors determining the formation of condensation over long term, especially in desert oases in arid areas. During 2005–2014, we investigated the main limiting factors in formation of condensation water for five different surfaces (interdune, dune top, flat vegetation‐free sand, artificial grassland and plantation forest), sand particle sizes, and temperature and humidity control experiment in a typical arid region of north‐western China. Results showed that changes in microhabitat resulting from different surface conditions had a significant influence on the amount of condensation water in arid desert ecosystem. Except for sand particle sizes 0.2–0.02 and 2–0.2 mm, the amount of average daily condensation for different sand particle sizes differed significantly (P &lt; 0.05) and decreased with an increase in sand particle size. Air temperature (AT), relative humidity (RH), air and surface temperature range (RT) and wind speed (WS) can significantly (P &lt; 0.05) affect the formation of condensation water in arid regions, and the thresholds of condensation water formation were RH &gt; 25% and WS &lt; 3.50 m s−1. Such effects, however, differed among the different surfaces due to different conditions of soil characteristics, microhabitats and regional climate. These results suggest that the influence of site characteristics, microhabitats and regional climate on the formation of condensation water should attract more attention and that both the relative importance and the interactions among different determining factors will contribute to a better understanding of the mechanistic determinants for the formation of condensation water in arid areas.

A rainfall enrichment system suitable for open field experiments in arid and semi-arid ecosystems

The predicted changes in precipitation patterns because of global change have profound effects on terrestrial ecosystems. In the present study, the principle and design details of a rainfall enrichment system (RAINES) for open field experiments in semi-arid and arid ecosystems are shown. The rainfall intensity, validity and uniformity of this experimental facility were also tested. During the period from 2008 to 2010, our data showed that the RAINES was able to simulate rainfall events with different rainfall sizes, frequencies and timing. The greatest advantage of the RAINES was its high uniformity in rainfall distribution over a relatively large experimental surface area (&gt;90 m2), which was important for experimental studies of semi-arid and arid ecosystems where vegetation distribution is sparse. The rainfall validity of RAINES was steadily at 66% or higher as long as the hydraulic pressure exceeded 1.4 KPa and the wind speed was below 2.5 m s-1. Since the RAINES is light-weight, inexpensive and versatile enough to be used to simulate various rainfall events with needed properties in remote fields, it is able to provide reliable simulated rainfall in the field for studying possible responses of soil and vegetation processes to rainfall change in arid and semi-arid ecosystems. The application of the RAINES will improve our understanding on the relationship between water availability and ecosystem processes in arid and semi-arid ecosystems, which will provide useful knowledge for the protection, restoration and sustainable management of semi-arid and arid desert ecosystems world.

Uncertainty in gap filling and estimating the annual sum of carbon dioxide exchange for the desert Tugai forest, Ebinur Lake Basin, Northwest China.

In most eddy covariance (EC) studies, carbon flux measurements have a high defect rate for a variety of reasons. Obtaining the annual sum of carbon dioxide exchange requires imputation of data gaps with high precision and accuracy. This study used five methods to fill the gaps in carbon flux data and estimate the total annual carbon dioxide exchange of the Tugai forest in the arid desert ecosystem of Ebinur Lake Basin, Northwest China. The Monte Carlo method was used to estimate the random error and bias caused by gap filling. The results revealed that (1) there was a seasonal difference in the friction velocity threshold of nighttime flux, with values in the growing season and non-growing season of 0.12 and 0.10 m/s, respectively; (2) the five gap-filling methods explained 77–84% of the data variability in the fluxes, and the random errors estimated by these methods were characterized by non-normality and leptokurtic heavy tail features, following the Laplacian (or double-exponential) distribution; (3) estimates of the annual sum of carbon dioxide exchange using the five methods at the study site in 2015 ranged from −178.25 to −155.21 g C m−2 year−1, indicating that the Tugai forest in the Ebinur Lake Basin is a net carbon sink. The standard deviation of the total annual carbon dioxide exchange sums estimated by the five different methods ranged from 3.15 to 19.08 g C m−2 year−1, with bias errors ranging from −13.69 to 14.05 g C m−2 year−1. This study provides a theoretical basis for the carbon dioxide exchange and carbon source/sink assessment of the Tugai forest in an arid desert ecosystem. In order to explore the functioning of the Tugai forest at this site, a greater understanding of the underlying ecological mechanisms is necessary.

Rainfall amount and timing jointly regulate the responses of soil nitrogen transformation processes to rainfall increase in an arid desert ecosystem

Climate models predict greater rainfall will occur in the arid and semiarid regions of Northwest China, where nitrogen (N) cycling is particularly sensitive to changes in rainfall regimes. Yet, how increasing rainfall regulates soil N transformation processes in these water-limited regions is still not well understood. We conducted a manipulative experiment in a desert ecosystem in Northwest China, whereby we simulated five different scenarios of future rain regimes (natural rains plus 0%, 25%, 50%, 75% and 100% of the local mean annual precipitation) each month from May to September in 2009. We examined in situ net N mineralization and soil N availability in both vegetated and bare soils, as well as leaf litter N release for the dominant shrub species Nitraria tangutorum monthly after each rain addition. We found that increased water availability via the simulated rain addition significantly decreased total net N mineralization rates over the growing season in both vegetated and bare soils. A larger amount of litter N was released after rain addition in vegetated soils, which could contribute to the higher concentrations of inorganic N in vegetated soils compared to bare soils. Furthermore, we found that the responses of soil N transformation processes to rain additions showed great seasonality, and thus both rainfall amount and timing jointly regulate the responses of soil N transformation processes to rainfall increase under future rainfall scenarios in this arid desert ecosystem. Over the growing season, rainfall addition reduced soil inorganic N concentrations but favored plant N uptake and microbial N immobilization. We suggest that the cycling of N will be greatly changed under future rainfall regimes, which may have consequences for ecosystem stability and functioning in this “N-conserving” desert ecosystem.