Temperate Desert Ecosystems Research Articles

Unraveling community assembly in temperate desert ecosystems: Insights from multi‐seasonal surveys along the expressway

AbstractFor temperate desert ecosystems, understanding the maintenance mechanisms of biodiversity has become a central concern of policymakers, practitioners, and academicians, especially in the context of human disturbances. However, most of the past desert research is based on a single survey and single functional traits or phylogeny, and may lead to incomplete estimates of community assembly. To assess climate factors, soil factors, and human interference in the processes of dispersal assembly, filtering, and limiting similarity in community assembly, we selected 50 sites along the Beijing‐Xinjiang Expressway and conducted plant surveys at sites 0.5, 1.0, and 1.5 km away from the expressway twice, one in spring and one in autumn, and collected 31 functional traits and phylogenetic information of 74 species. We found that incomplete detection can lead to bias in biodiversity estimation due to seasonal surveys. Road disturbance at different distances had no significant effect on species composition and community assembly processes. The trade‐off between dispersal limitation and environmental filtering is the process of maintaining desert plant diversity. Precipitation directly determined the dispersal limitation and environmental filtering. Soil pH mediated the effect of temperature on biotic interaction in the dimension of phylogeny, while soil pH and organic carbon acted as intermediate factors affecting biotic interaction in functional traits. Our findings suggest that climate change, notably precipitation, has a more pronounced impact on desert plant communities than human disturbances. A multifaceted approach considering functional traits and phylogeny across seasons is essential for understanding species coexistence in desert ecosystems.

Divergent Nitrogen, Phosphorus, and Carbon Concentrations among Growth Forms, Plant Organs, and Soils across Three Different Desert Ecosystems

Quantifying the dryland patterns of plant carbon (C), nitrogen (N), and phosphorus (P) concentrations and their stoichiometric values along environmental gradients is crucial for understanding ecological strategies. To understand the plant adaptive strategies and ecosystem nutrient concentrations across three desert ecosystems (e.g., desert, steppe desert, and temperate desert), we compiled a dataset consisting of 1295 plant species across three desert ecosystems. We assessed the element concentrations and ratios across plant growth forms, plant organs, and soils and further analysed the leaf vs. root N, P, and N:P scaling relationships. We found that the leaf N, P, and C concentrations were significantly different only from those of certain other growth forms and in certain desert ecosystems, challenging the generality of such differences. In leaves, the C concentrations were always greater than the N and P concentrations and were greater than those in soils depending on the soil chemistry and plant physiology. Thus, the element concentrations and ratios were greater in the organs than in the soils. The values in the leaf versus the root N, P, and N:P scaling relationships differed across the three desert ecosystems; for example, αN (1.16) was greater in the desert, αP (1.10) was greater in the temperate desert ecosystem, and αN:P (2.11) was greater in the desert ecosystem. The mean annual precipitation (MAP) and mean annual temperature (MAT) did not have significant effects on the leaf elemental concentrations or ratios across the desert ecosystems. This study advances our understanding of plant growth forms and organs, which support resource-related adaptive strategies that maintain the stability of desert ecosystems via divergent element concentrations and environmental conditions.

The influence of precipitation timing and amount on soil microbial community in a temperate desert ecosystem.

Global climate change may lead to changes in precipitation patterns. This may have a significant impact on the microbial communities present in the soil. However, the way these communities respond to seasonal variations in precipitation, particularly in the context of increased precipitation amounts, is not yet well understood. To explore this issue, a five-year (2012-2016) field study was conducted at the northeast boundary of the Ulan Buh Desert, examining the effects of increased precipitation during different periods of the growing season on both bacterial and fungal communities. The study included five precipitation pattern treatments: a control group (C), as well as groups receiving 50 and 100% of the local mean annual precipitation amount (145 mm) during either the early growing season (E50 and E100) or the late growing season (L50 and L100). The taxonomic composition of the soil bacterial and fungal communities was analyzed using Illumina sequencing. After 5 years, the bacterial community composition had significantly changed in all treatment groups, with soil bacteria proving to be more sensitive to changes in precipitation timing than to increased precipitation amounts within the desert ecosystem. Specifically, the alpha diversity of bacterial communities in the late growing season plots (L50 and L100) decreased significantly, while no significant changes were observed in the early growing season plots (E50 and E100). In contrast, fungal community composition remained relatively stable in response to changes in precipitation patterns. Predictions of bacterial community function suggested that the potential functional taxa in the bacterial community associated with the cycling of carbon and nitrogen were significantly altered in the late growing season (L50 and L100). These findings emphasize the importance of precipitation timing in regulating microbial communities and ecosystem functions in arid regions experiencing increased precipitation amounts.

Prediction of spatial distribution characteristics of ecosystem functions based on a minimum data set of functional traits of desert plants.

The relationship between plant functional traits and ecosystem function is a hot topic in current ecological research, and community-level traits based on individual plant functional traits play important roles in ecosystem function. In temperate desert ecosystems, which functional trait to use to predict ecosystem function is an important scientific question. In this study, the minimum data sets of functional traits of woody (wMDS) and herbaceous (hMDS) plants were constructed and used to predict the spatial distribution of C, N, and P cycling in ecosystems. The results showed that the wMDS included plant height, specific leaf area, leaf dry weight, leaf water content, diameter at breast height (DBH), leaf width, and leaf thickness, and the hMDS included plant height, specific leaf area, leaf fresh weight, leaf length, and leaf width. The linear regression results based on the cross-validations (FTEIW - L, FTEIA - L, FTEIW - NL, and FTEIA - NL) for the MDS and TDS (total data set) showed that the R2 (coefficients of determination) for wMDS were 0.29, 0.34, 0.75, and 0.57, respectively, and those for hMDS were 0.82, 0.75, 0.76, and 0.68, respectively, proving that the MDSs can replace the TDS in predicting ecosystem function. Then, the MDSs were used to predict the C, N, and P cycling in the ecosystem. The results showed that non-linear models RF and BPNN were able to predict the spatial distributions of C, N and P cycling, and the distributions showed inconsistent patterns between different life forms under moisture restrictions. The C, N, and P cycling showed strong spatial autocorrelation and were mainly influenced by structural factors. Based on the non-linear models, the MDSs can be used to accurately predict the C, N, and P cycling, and the predicted values of woody plant functional traits visualized by regression kriging were closer to the kriging results based on raw values. This study provides a new perspective for exploring the relationship between biodiversity and ecosystem function.

Bringing Antarctica to the lab: a polar desert environmental chamber to study the response of Antarctic microbial communities to climate change

Polar deserts contain unique and sensitive communities responsive to climate-associated habitat changes. However, unlike temperate desert ecosystems, characterizing and predicting the responses of polar ecosystems to environmental change remains a significant challenge due to logistical constraints. Here we aim to demonstrate the use of a custom-designed Polar Desert Environmental Chamber (PDEC) to perform off-continent experimental ecological research. We did so by characterizing the structure and composition of arid edaphic bacterial communities collected from the McMurdo Dry Valleys during a simulated wetting event. The results were discussed in light of previous field observations. Rapid structural and compositional changes were observed during wetting and re-drying treatments. Those were driven by changes in the relative abundance of coexisting taxa, which fluctuated asynchronously over time in response to the treatments. While selection was the main ecological factor influencing communities during dry conditions or the initial wetting, with prolonged exposure to wetness, neutral processes began to drive community assembly. Ultimately, these observations reflect different adaptative responses from microbial taxa to water stress, which can be argued as beneficial to increasing resilience in polar deserts. Our findings demonstrate that experiments conducted in PDEC provide valuable contextual data on community response to environmental change and can accelerate our ability to assess biological thresholds to change within polar desert ecosystems. We advocate that, with careful consideration of key emulated environmental attributes, laboratory-based Antarctic research can complement fieldwork to achieve a nuanced and evidence-based understanding of the ecology of Antarctica’s ice-free regions.

Typical ephemeral plant—Erodium oxyrhinchum: growth response to snow change in temperate desert, Northwest China

AbstractSnow-cover changes in temperate desert ecosystems influence plant diversity, richness and distribution. The growth and distribution of herbaceous plants in these ecosystems are closely related to snow-cover depth, the most important water resource during the growth period due to water shortage during the dry season. However, the response to snow-cover change in winter remains unclear. The present investigation was undertaken to examine the influence of snow-cover change on the root growth of herbaceous species. The growth of desert typical ephemeral species, Erodium oxyrhinchum, was examined in Gurbantunggut Desert with four snow-cover depth treatments in winter. The four treatments were snow removal (−S), ambient snow, double snow (+S) and triple snow (+2S). The snow depth addition increased the abundance and growth rate of herbaceous plants. It also enhanced the biomass (including total and individual biomass) of these plants. The leaf area of E. oxyrhinchum increased significantly with snow addition, and the leaf dry matter content had an opposite trend. The study showed that the aboveground section of the plant was more sensitive to snow change than the underground. Snow change also influenced the root morphology. Snow removal resulted in the emergence of more lateral roots, whereas snow addition promoted the elongation of the main root for water and nutrient absorption. These results explain how changes in winter snow-cover depth alter plant growth, community structure and ecosystem function during the growing period in temperate desert ecosystems.

Species-dependent responses of root growth of herbaceous plants to snow cover changes in a temperate desert, Northwest China

Changes in snow cover can influence root growth and distribution of herbaceous species in water limiting desert ecosystems. However, how the growth of root systems of herbaceous species responds to snow cover changes remains unclear. Thus, the present study was aimed to examine the influence of snow cover changes on root growth of herbaceous species in a temperate desert of central Asia. Plots with four snow cover depth treatments in winter were investigated in the Gurbantunggut Desert. The four treatments were snow removal (− S), ambient snow, double snow (+ S), and triple snow (+ 2S). We examined the root growth of two typical herbaceous species: one ephemeral species, Erodium oxyrhinchum, and one annual species, Ceratocarpus arenarius. The root length of the annual plant was significantly reduced by snow removal compared with the ambient treatment. The specific root length and specific surface area of the ephemeral plants increased with increasing snow depth, whereas the annual plants showed the opposite trends. Snow removal significantly increased the root–shoot ratio of the annual plants, with no effects found in the ephemeral plants. The individual root biomass and total underground biomass of the two species had similar responses to the snow depth treatments, with the highest values found with the ambient treatment. These results can contribute to explaining to changing winter snow cover depth can alter plant growth, community structure, and ecosystem function in the growing season in temperate desert ecosystems.

Effects of exogenous nitrogen addition on litter decomposition and nutrient release in a temperate desert

A litterbag decomposition experiment was carried out in southern Gurbantunggut Desert, with four nitrogen treatments: N0(0 g N·m-2·a-1), N5(5 g N·m-2·a-1), N10(10 g N·m-2·a-1) and N20(20 g N·m-2·a-1). The aims were to examine the effects of exogenous nitrogen addition on decomposition rate and nutrient release of Tamarix ramosissima, Salicornia europaea and their mixture. Results showed that decomposition rates were significantly different among litter types. After 345 days, the decomposition rates of T. ramosissima, S. europaea and their mixture under different treatments were 0.64-0.70, 0.84-0.99 and 0.71-0.81 kg·kg-1·a-1, respectively. Both mono- and mixed-litters exhibited nutrient release during decomposition process, with the release rates being 60.6%-67.4%, 56.7%-62.6%, 57.4%-62.3%, 46.8%-63.0% for N, and 51.9%-77.9%, 59.9%-74.7%, 53.0%-79.9%, 52.3%-76.4% for P, respectively for the N0, N5, N10 and N20 treatments. Nitrogen addition did not affect litter decomposition rate. The dynamics of N and P during decomposition of different litter types showed different responses to nitrogen addition. Nitrogen addition inhibited N and P releases of S. europaea litter and P release of the mixed litter, but did not affect the nutrient release of T. ramosissima. The results suggested that nitrogen input would not promote litter decomposition in temperate desert ecosystems, but might retard the nutrient returning to soil system.

The mechanism of soil nitrogen transformation under different biocrusts to warming and reduced precipitation: From microbial functional genes to enzyme activity

Soil nitrogen (N) mineralization is a microbially-mediated biogeochemical process that is strongly influenced by changing climates. However, little information is available on the mechanisms behind the response of N mineralization to prolonged warming coupled with drought in soils covered by biocrusts. We used open top chambers to investigate the rate of soil N transformation (ammonification, nitrification and mineralization), enzyme activity and gene abundance in response to warming coupled with reduced precipitation over three years (2016–2018). Warming and drought significantly reduced the N transformation rate, extracellular enzyme activity, and gene abundance in moss-covered soil. For cyanobacteria-covered soil, however, it inhibited enzyme activity and increased the abundance of the nitrification-related genes and therefore nitrification rate. Our treatments had no obvious effects on N transformation and enzyme activity, but reduced gene abundance in bare soil. Biocrusts may facilitate N transformation while the degradation of moss crust caused by climate warming will dampen any regulating effect of biocrusts on the belowground microbial community. Furthermore, belowground microbial communities can mediate N transformation under ongoing warming and reduced precipitation by suppressing ammonification- and nitrification-related gene families, and by stimulating nitrification-related gene families involved in cyanobacteria-covered soil. This study provides a basis for identifying the functional genes involved in key processes in the N cycle in temperate desert ecosystems, and our results further highlight the importance of different biocrusts organisms in the N cycle in temperate deserts as Earth becomes hotter and drier.

Seasonal nitrogen uptake strategies in a temperate desert ecosystem depends on N form and plant species.

Symbiotic plants might be able to regulate a limited nitrogen (N) pool, thus avoiding and reducing competition for resources, through the uptake of different chemical N forms. Our aim was to see whether coexisting herbs showed preference for different forms of N in a temperate desert. We conducted a situ experiment using the 15 N labeling method in the Gurbantunggut Desert of Northwestern China dominated by Erodium oxyrrhynchum, Hyalea pulchella, Nonea caspica and Lactuca undulata during their growing period (April and May). Four desert herb species preferentially relied on 15 N-NO3 for their N nutrition. Multi-factor analysis of variance (ANOVA) analysis results showed that species, N forms, months, and soil depths strongly affected N uptake rate. The uptake rate by herbs was higher in May than in April, and higher at 0-5 cm than at 5-15 cm soil layers. Erodium oxyrrhynchum, N. caspica and L. undulata showed different preference on N form over months. Erodium oxyrrhynchum and L. undulata changed their uptake preference from more 15 N-Glycine in April to more 15 N-NH4 in May. Although the N uptake rate of four desert herbs varied across different soil depths and months, all species absorbed more inorganic N compared with organic N. The higher preference for 15 N-NO3 and 15 N-NH4 over 15 N-Gly possibly reflects adaptation to different N forms in temperate desert.

Impact of elevated precipitation, nitrogen deposition and warming on soil respiration in a temperate desert

Abstract. Soil respiration (Rs) is the most important source of carbon dioxide emissions from soil to atmosphere. However, it is unclear what the interactive response of Rs would be to environmental changes such as elevated precipitation, nitrogen (N) deposition and warming, especially in unique temperate desert ecosystems. To investigate this an in situ field experiment was conducted in the Gurbantunggut Desert, northwest China, from September 2014 to October 2016. The results showed that precipitation and N deposition significantly increased Rs, but warming decreased Rs, except in extreme precipitation events, which was mainly through its impact on the variation of soil moisture at 5 cm depth. In addition, the interactive response of Rs to combinations of the factors was much less than that of any single-factor, and the main response was a positive effect, except for the response from the interaction of increased precipitation and high N deposition (60 kg N ha−1 yr−1). Although Rs was found to show a unimodal change pattern with the variation of soil moisture, soil temperature and soil NH4+-N content, and it was significantly positively correlated to soil dissolved organic carbon (DOC) and pH, a structural equation model found that soil temperature was the most important controlling factor. Those results indicated that Rs was mainly interactively controlled by the soil multi-environmental factors and soil nutrients, and was very sensitive to elevated precipitation, N deposition and warming. However, the interactions of multiple factors largely reduced between-year variation of Rs more than any single-factor, suggesting that the carbon cycle in temperate deserts could be profoundly influenced by positive carbon–climate feedback.

Water-use efficiency in response to simulated increasing precipitation in a temperate desert ecosystem of Xinjiang, China

Water-use efficiency (WUE) is a key plant functional trait that plays a central role in the global cycles of water and carbon. Although increasing precipitation may cause vegetation changes, few studies have explored the linkage between alteration in vegetation and WUE. Here, we analyzed the responses of leaf WUE, ecosystem carbon and water exchanges, ecosystem WUE, and plant community composition changes under normal conditions and also under extra 15% or 30% increases in annual precipitation in a temperate desert ecosystem of Xinjiang, China. We found that leaf WUE and ecosystem WUE showed inconsistent responses to increasing precipitation. Leaf WUE consistently decreased as precipitation increased. By contrast, the responses of the ecosystem WUE to increasing precipitation are different in different precipitation regimes: increasing by 33.9% in the wet year (i.e., the normal precipitation years) and decreasing by 4.1% in the dry year when the precipitation was about 30% less than that in the wet year. We systematically assessed the herbaceous community dynamics, community composition, and vegetation coverage to explain the responses of ecosystem WUE, and found that the between-year discrepancy in ecosystem WUE was consistent with the extent to which plant biomass was stimulated by the increase in precipitation. Although there was no change in the relative significance of ephemerals in the plant community, its greater overall plant biomass drove an increased ecosystem WUE under the conditions of increasing precipitation in 2011. However, the slight increase in plant biomass exerted no significant effect on ecosystem WUE in 2012. Our findings suggest that an alteration in the dominant species in this plant community can induce a shift in the carbon- and water-based economics of desert ecosystems.

Divergent variations in concentrations of chemical elements among shrub organs in a temperate desert.

Desert shrubs, a dominant component of desert ecosystems, need to maintain sufficient levels of nutrients in their different organs to ensure operation of various physiological functions for the purpose of survival and reproduction. In the present study, we analyzed 10 elements in leaves, stems, and roots of 24 dominant shrub species from 52 sites across a temperate desert ecosystem in northwestern China. We found that concentrations of all 10 elements were higher in leaves than in stems and roots, that non-legumes had higher levels of leaf Na and Mg than did legumes, and that Na was more concentrated in C4 leaves than in C3 leaves. Scaling relationships of elements between the photosynthetic organ (leaf) and non-photosynthetic organs (stem and root) were allometric. Results of principal components analysis (PCA) highlighted the important role of the elements responsible for osmoregulation (K and Na) in water utilization of desert shrubs. Soil properties and taxonomy explained most variation of element concentrations in desert shrubs. Desert shrubs may not be particularly susceptible to future change in climate factors, because most elements (including N, P, K, Ca, Mn, Zn, and Cu) associated with photosynthesis, osmoregulation, enzyme activity, and water use efficiency primarily depend on soil conditions.

The seasonal and successional variations of carbon release from biological soil crust-covered soil

Biological soil crusts play key roles in global carbon cycles in terms of carbon exchange between pedosphere and the atmosphere, yet few explorations have been conducted regarding how seasonal variations and successional patterns of the crusts influence C release in temperate desert ecosystems. The carbon release of four soil cover types (mobile dune sand, algae-, mixed- and moss-crusted) was measured in PVC mesocosms both before, in relatively dry conditions, and immediately after natural rainfall events. Intact crusts at a 10 cm level were removed from the southeast edges of Tengger Desert, China. Amounts of released C from the four soil cover types accounted for 18.4%–23.1%, 46.9%–52.3%, and 27.7%–31.1% of total C released in the spring, summer, and fall seasons, respectively. The annual C release amounts were 56.6 gCm−2 yr−1 for the mobile dune sand, 67.9 gCm−2 yr−1 for the algae-crusted soil, 90.3 and 128.8 gCm−2 yr−1 for the mixed-crusted soil and moss-crusted soil. Linear regression analyses suggest a significant positive relationship between seasonal accumulative rainfall and carbon release amounts. These findings indicate that variations in the amount of seasonal rainfall and the succession of the crusts significantly change the carbon output patterns in the sandy desert ecosystem.

Effects of increasing precipitation on soil microbial community composition and soil respiration in a temperate desert, Northwestern China

Soil microbial communities play a critical role in soil carbon cycling and influence soil carbon–climate feedbacks. However, little information exists regarding the response of soil microbial communities in temperate desert ecosystems to projected increases in precipitation and the resulting effects on soil carbon emissions. A three-year precipitation addition experiment was conducted to explore the responses of soil respiration (Rs), microbial respiration (Rm) and microbial community composition to low (extra 15%) and medium (extra 30%) precipitation increases in a temperate desert ecosystem. Rs, Rm, microbial biomass carbon (MBC) and nitrogen (MBN), and microbial PLFAs consistently increased with increasing precipitation. Rs and Rm were positively correlated with MBC and microbial PLFAs. However, precipitation addition had no impacts on microbial community composition and fungal to bacterial PLFAs ratio. These results suggest that projected precipitation increase may synergistically increase bacterial and fungal abundance, and stimulation of microbial biomass can increase soil carbon release in desert ecosystems.

Biological soil crusts influence carbon release responses following rainfall in a temperate desert, northern China

AbstractHow soil cover types and rainfall patterns influence carbon (C) release in temperate desert ecosystems has largely been unexplored. We removed intact crusts down to 10 cm from the Shapotou region, China, and measured them in PVC mesocosms, immediately after rainfall. C release rates were measured in soils with four cover types (moss‐crusted soil, algae‐crusted soil, mixed (composed of moss, algae, and lichen)‐crusted soil, and mobile dune sand). We investigated seven different rainfall magnitudes (0–1, 1–2, 2–5, 5–10, 10–15, 15–20, and >20 mm) under natural conditions. C release from all four BSCs increased with increasing rainfall amount. With a rainfall increase from 0 to 45 mm, carbon release amounts increased from 0.13 ± 0.09 to 15.2 ± 1.35 gC m−2 in moss‐crusted soil, 0.08 ± 0.06 to 6.43 ± 1.23 gC m−2 in algae‐crusted soil, 0.11 ± 0.08 to 8.01 ± 0.51 gC m−2 in mixed‐crusted soil, and 0.06 ± 0.04 to 8.47 ± 0.51 gC m−2 in mobile dune sand, respectively. Immediately following heavy rainfall events (44.9 mm), moss‐crusted soils showed significantly higher carbon release rates than algae‐ and mixed‐crusted soils and mobile dune sands, which were 0.95 ± 0.02, 0.30 ± 0.03, 0.13 ± 0.04, and 0.51 ± 0.02 μmol CO2 m−2 s−1, respectively. Changes in rainfall patterns, especially large rain pulses (>10 mm) affect the contributions of different soil cover types to carbon release amounts; moss‐crusted soils sustain higher respiration rates than other biological crusts after short‐term extreme rainfall events.

Photosynthesis of two moss crusts from the Tengger Desert with contrasting sensitivity to supplementary UV-B radiation

Predicting the effects of increased ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion on temperate desert ecosystems requires better knowledge of the ecophysiological response of common moss species. The aim of the current work was to determine whether elevated UV-B radiation affected photosynthetic performance and chloroplast ultrastructure of two moss crusts and whether response differences were observed between the crusts. In laboratory experiments, Bryum argenteum and Didymodon vinealis, which show microdistributions and are dominant in soil crusts at the Tengger Desert, Northern China, were subjected to four levels of UV-B radiation of 2.75 (control), 3.08, 3.25, and 3.41 W m−2 for 10 days, simulating 0, 6, 9, and 12% of stratospheric ozone at the latitude of Shapotou, respectively. The results showed that chlorophyll a fluorescence parameters (i.e., the maximal quantum yield of PSII photochemistry, the effective quantum yield of PSII photochemistry, and photochemical quenching coefficient), pigment contents, soluble protein contents, and the ultrastructure were negatively influenced by elevated UV-B radiation and the degree of detrimental effects significantly increased with the intensity of UV-B radiation. Moreover, results indicated that B. argenteum was probably more sensitive to supplementary UV-B radiation than D. vinealis. Therefore, we propose the use of B. argenteum crusts as a bioindicator of responses to elevated UV-B radiation.

Nitrogen fixation in biological soil crusts from the Tengger desert, northern China

Biological soil crusts (BSCs) are the primary source of soil nitrogen in dry areas. We investigated the nitrogenase activity of three BSC types from the Tengger desert in responses to stimulated precipitation, temperature, and irradiance intensity. In addition, potential seasonal nitrogen fixation by BSCs was estimated using meteorological records. The nitrogenase activity of BSCs ranged from 2.6 to 16.6 mmol m−2 h−1 in this desert, and nitrogenase activity was significantly dependent on crust type, precipitation, and temperature, but not on irradiance. Cyanobacterial–algal crusts showed the highest nitrogenase activity (16.6 mmol m−2 h−1), followed by lichen crusts (6.9 mmol m−2 h−1), and moss crusts (2.6 mmol m−2 h−1). Cyanobacterial–algal crusts demonstrated maximum nitrogenase activity with 1.54 mm of precipitation, while the maximum activity for lichen and moss crusts occurred at 1.83 mm and 0.65 mm, respectively. The optimum temperature for nitrogenase activity ranged from 15 to 30 °C. Based on meteorological data, the potential nitrogen input was estimated to be 3.7–13.2 g m−2 a−1, and the high nitrogen fixation in this region resulted from the perfect match of optimum climate to the favorable environmental factors for BSC nitrogenase activity. This study demonstrated that BSCs are the main nitrogen input source in this temperate desert ecosystem. In particular, cyanobacterial–algal crusts, which are the first colonizers of the desert ecosystem, may mediate the majority of nitrogen fixation to facilitate soil nitrogen accumulation in these infertile soils.

Simulating Soil Freezing and Thawing of Temperate Desert Ecosystem on the Qinghai-Tibet Plateau

Understanding the soil freezing and thawing processes of temperate desert ecosystem on the Qinghai-Tibet Plateau, especially considering that soil freezing and thawing is very sensitive to climate changes. Little changes of soil freezing or thawing may lead to changes in water and heat transition in soils and thus affect the structure and function of ecosystems. SHAW, as a physically based, Land-surface model, provides a useful tool for understanding and analyzing soil freezing and thawing processes. In this paper, using the measured data of temperate desert ecosystem in Dachaidan assessed the model performance in simulating soil freezing and thawing processes. Comparison of the simulated results by SHAW to the measured data showed that in the initial stage of freezing the simulated frozen depth was thinner than the measured; in the thawing period the simulated thawing rate was higher than the measured due to the overestimated soil temperature below 10cm; however, for the most cold stage (the stable frozen stage), the simulated matched quite well with the measured. For the maximum frozen depth the simulation only overestimated by as much as 4%. On the whole, the SHAW model performed satisfactorily. This provides a good base for further application of LSMs to the temperate desert ecosystem on the Qinghai-Tibet Plateau.