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In this study, the vegetation and soils of different desertification landscapes (sandy grassland, and fixed, semi‐fixed, semi‐mobile, and mobile dunes) in the Hulun Buir Sandy Land were examined to quantify the impacts of desertification on plants, soils, and microbes, and the key limiting factors of restoration. Desertification caused soil quality to decline and led to an imbalance of nitrogen (N) and phosphorus (P) supplies (N:P ratios decreased significantly from 3.55–1.8, p < 0.05). Desertification did not change the stoichiometric relationships among plant carbon (C), N, and P at a community level, but promoted redistribution of nutrients from roots to aboveground tissues. The aboveground biomass N and P increased by 9.8% and 39.3%, respectively from grassland to mobile dunes, but these of the underground biomass decreased by 26.1% and 37.7%, respectively. N limitation (plant N:P < 10) occurred at the community level. Desertification led to the change of dominant species from perennial herbs to annual psammophytes, and plant diversity (from 1.15–0.79) and productivity (from 880.6 to 128.6 g m−2) first increased slightly (p > 0.05) and then decreased sharply (p < 0.05) with increasing desertification, but with no significant (p > 0.05) change of the microbial community. Redundancy analysis showed that the main environmental drivers were the soil N:P (with an explanation of 29.6%), followed by pH, electrical conductivity, and the soil's fine particles (with a total explanation of 24.3%). Based on these results, three reference frames were proposed for the restoration of the near‐original vegetation community. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSCs) are an integration of external photoautotrophs and internal heterotrophic communities. Sand burial is a ubiquitous disturbance that affects the biodiversity and ecological function of BSCs, but little is known about the influence of sand burial on microbial communities in arid sandy deserts. Here, based on a long-term field experiment and utilizing high-throughput sequencing, we assessed the influence of sand burial on bacterial and fungal communities inhabiting two typical successional stages of BSCs (cyanobacterial crusts for early successional stage and mixed crusts for late successional stage) at the three-sand buried depth (0, 0.5, and 10 mm) in the Tengger Desert, Northern China. We found that the diversity, abundance, and composition of the bacterial and fungal communities were all altered by the sand burial treatment. Different indicator taxa were identified in unburied and buried (shallow and deep) BSCs. Changes in soil properties caused by sand burial have been suggested as a possible cause of changes in the bacterial and fungal community composition in BSCs. [ABSTRACT FROM AUTHOR]

Sandy cropland ecosystems are major terrestrial ecosystems in semi-arid regions of northern China's Horqin Sandy Land, where they play an important role in the regional carbon balance. Continuous observation of the CO2 flux was conducted from 2014 to 2018 using the eddy covariance technique in a sandy maize cropland ecosystem in the Horqin Sandy Land. We analyzed carbon fluxes (the net ecosystem exchange (NEE) of CO2, ecosystem respiration (Reco), and the gross primary productivity (GPP) and their responses to environmental factors at different temporal scales using Random Forest models and correlation analysis. We found that the sandy cropland was a carbon sink, with an annual mean NEE of –124.4 g C m−2 yr−1. However, after accounting for carbon exports and imports, the cropland became a net carbon source, with net biome production ranging from –501.1 to –266.7 g C m−2 yr−1. At a daily scale, the Random Forest algorithm revealed that photosynthetic photon flux density, soil temperature, and soil moisture were the main drivers for variation of GPP, Reco, and NEE at different integration periods. At a monthly scale, GPP and Reco increased with increasing leaf area index (LAI), so the maize ecosystem's carbon sequestration capacity increased with increasing LAI. At an annual scale, water availability (precipitation and irrigation) played a dominant role in explaining inter-annual variability of GPP and Reco. Affected by climate (e.g., precipitation) and field management (e.g., cultivation, irrigation), carbon fluxes differed greatly between years in the maize system. [ABSTRACT FROM AUTHOR]

Bacterial, archaeal, and eukaryota diversity in mountainous areas varies along elevational gradients, but details remain unclear. Here, we use a next-generation sequencing method based on 16S/18S rRNA to reveal the soil microbial diversity and community compositions of alpine meadow ecosystems along an elevation span of nearly 2,000 m (1,936–3,896 m) in China's Qilian Mountains. Both bacterial and eukaryota diversity increased linearly with increasing elevation, whereas archaeal diversity increased, but not significantly. The diversity patterns of several phyla in the bacterial, archaeal, and eukaryota communities were consistent with the overall elevational trend, but some phyla did not follow this pattern. The soil microbial community compositions were shaped by the coupled effects of regional climate and local soil properties. Intradomain links were more important than interdomain links in the microbial network of the alpine meadows, and these links were mostly positive. The bacteria formed more connections than either archaea or eukaryota, but archaea may be more important than bacteria in building the soil microbial co-occurrence network in this region. Our results provide new visions on the formation and maintenance of soil microbial diversity along an elevational gradient and have implications for microbial responses to climate change in alpine ecosystems. [ABSTRACT FROM AUTHOR]

Caragana microphylla is a sand-fixing leguminous shrub with strong resistance to drought, cold, and low soil fertility. As a result, it plays an essential role in combating desertification in northern China, but little is known about its nutrient budget. Nutrient resorption is a key process in plant nutrient conservation and has marked ecological implications for plant fitness and ecosystem nutrient cycling. We studied the effects of both nitrogen (N) addition and reproductive effort on leaf N resorption of C. microphylla in a temperate semi-arid sandy land in China. The results showed that sprouting of the early leaves from over-wintered buds employs a strategy for slow returns on nutrient investment with smaller specific leaf area (SLA) and higher N resorption efficiency, whereas the late leaves, which sprout from current-year buds, employ a strategy for quick returns on nutrient investment with higher SLA and lower N resorption efficiency. N addition significantly increased the N resorption efficiency from early leaves while exerting no impact on late leaves, suggesting that the increased N recovery from early leaves is done to sustain the high N demands of late leaves. Reproductive effort did not affect the N resorption from early or late leaves due to the temporal separation between fruit production and leaf senescence. Taken together, our results demonstrate that C. microphylla has evolved different investment strategies for leaf N in early and late leaves to conserve nutrients and facilitate its growth in desertified environments. [ABSTRACT FROM AUTHOR]

Grasslands are major terrestrial ecosystems in arid and semiarid regions, and they play important roles in the regional carbon dioxide (CO2) balance and cycles. Sandy grasslands are sensitive to climate change, yet the magnitudes, patterns, and environmental controls of their CO2 flows are poorly understood for some regions (e.g., China's Horqin Sandy Land). Here, we report the results from continuous year-round CO2 flux measurements for 5 years from a sandy grassland in China's Horqin Sandy Land. The grassland was a net CO2 source at an annual scale with a mean annual net ecosystem CO2 exchange (NEE) of 49 ± 8 gCm-2yr-1 for the years for which a complete dataset was available (2015, 2016, and 2018). Annual precipitation had the strongest effect on annual NEE; grassland carbon sequestration increased with the increasing precipitation since NEE depended on annual precipitation. In the spring, NEE decreased (i.e., C sequestration increased) with increasing magnitude of effective precipitation pulses, total monthly precipitation, and soil temperature (Tsoil). In the summer, NEE was dominated by the total seasonal precipitation and high precipitation pulses (> 20 mm). In the autumn, NEE increased (i.e., C sequestration decreased) with increasing effective precipitation pulses, Tsoil , and near-surface soil water content (SWC) but decreased with increased SWC deeper in the soil. In the winter, NEE decreased with increasing Tsoil and SWC. The sandy grassland was a net annual CO2 source because drought decreased carbon sequestration by the annual plants. Long-term observations will be necessary to reveal the true source or sink intensity and its response to environmental and biological factors. [ABSTRACT FROM AUTHOR]

Tiantishan Grottoes, a famous site well known for its historical status in the spread of Buddhism art in ancient China, were selected for a comparison and analysis of microbial taxonomic characteristics on the wall paintings under different preservation conditions: in situ and ex situ conservation. A total of 12 samples were collected from three different cave wall paintings preserved in situ or ex situ . The 16/18S rRNA gene-based sequences revealed a high bacterial diversity and a relative low fungal abundance, including bacterial groups Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, Cyanobacteria, Acidobacteria, Deinococcus-Thermus and Fusobacteria; and fungal groups Ascomycota and Basidiomycota. Among them, two bacterial genera of the Promicromonospora and Planomicrobium and fungal order of the Sordariales and the family of Trichocomaceae were dominant in the samples preserved ex situ . Some of them have been reported at other cultural heritage sites and associated with the biodeterioration of cultural relics. The over-growth of these microbes led to the abundant filaments formed visible on the surface of the ex situ wall paintings, which preserved under museum conditions. Application of preservation materials including animal glue and wet gypsum to take them off from grottoes and strengthen, and subsequent long-term preservation under poor conditions in museums were mainly responsible for the microbial outbreaks. To avoid similar problems in the future, reasonable intervention measures and strict micro-environmental control must be implemented to the ex situ preservation of wall paintings. Our results have profound significance for clarify the occurrence of microbial invasions and mechanisms on the wall paintings; it is helpful to development a reasonable artificial intervention measures for conservation work of the wall paintings in the future. [ABSTRACT FROM AUTHOR]

• Bacteria and eukaryota diversity increased with increasing longitude and elevation. • Archaeal diversity decreased slightly with increasing elevation. • Some phyla diversity patterns are individually inconsistent with the overall trend. • Geographic distance contributed more than environmental factors to soil microbes. • More intra-domain than inter-domain links within the soil microbial network. Recent studies show that different microorganisms, especially bacteria and fungi, exhibit contrasting latitudinal, longitudinal, and altitudinal diversity patterns at a global scale, but little is known about biogeographic patterns in desert ecosystems. In this study, we chose a narrow geographic channel, namely the deserts of northern China's Hexi Corridor as the study area. Based on field survey and next-generation sequencing (Illumina MiSeq PE300 Platform), to map soil microbial geographic diversity patterns in this area and further determine the main driving factors responsible for shaping the soil microbial community. The results show that bacteria and eukaryotic diversity increased linearly with increasing longitude and altitude, but decreased with increasing latitude in the Hexi Corridor deserts, whereas archaeal diversity showed little change along these geographic gradients. Some individual phyla within the bacterial, archaeal, and eukaryota communities were not always consistent with collective trends, e.g., for the α-diversity of the ten most dominant bacterial phyla, only six phyla showed a statistically significant increase with altitude. The soil microbial community composition was jointly shaped by geographic distance and environmental variables (regional climatic factors and local edaphic variables). The effect of geographic distance on the soil microbial community composition was slightly stronger than that of the environmental variables. Intra-domain links were stronger than inter-domain links in the soil microbial network of the Hexi Corridor deserts, and these links were mostly positive. Although bacteria formed more connections than both archaea and eukaryotes, removing the archaea resulted in a lower natural connectivity, suggesting that the archaea were the core group for building this desert region's soil microbial co-occurrence network. Taken together, these findings deepen our understanding of regional-scale soil microbial diversity patterns in this desert ecosystem. [ABSTRACT FROM AUTHOR]

Microorganisms can accelerate the deterioration of stone monuments. In this study, we used next-generation sequencing (Illumina MiSeq PE300 Platform) to investigate the microbial biofilm communities that have developed on sandstone in two famous Buddhist cave temples, the Maijishan Grottoes and Tiantishan Grottoes, located on the historical Silk Road in western China. We found high bacterial diversity and relatively low eukaryota diversity based on 16S and 18S ribosomal RNA (rRNA) sequencing analysis. The dominant bacterial groups were Cyanobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, and Chloroflexi. The dominant eukaryota were Ascomycota, Basidiomycota, and Chytridiomycota. The most dominant genes among the bacteria were from Cyanobacteria (unclassified and no rank), Pseudonocardia , Kribbella, and Rubrobacter ; the dominant fungal genes were from unclassified Lecanorales and Capnodiales (unclassified and norank). These microbes form biofilms that will contribute to biodeterioration of the underlying sandstone. Combining with field monitoring and microscopic analysis, we determined that high bioreceptivity of the sandstone and locally available water were two important exogenous and endogenous factors that promoted microbial colonization, proliferation, and subsequent biofilm formation. The aforementioned microbes usually coexisted on the sandstone surfaces by building an inter-connected and dynamic community capable of adapting to and resisting the harsh local environmental conditions to survive and undergo succession. • A comparative analysis of microbial communities of stone biofilms of the two Grottoes. • High bioreceptivity of sandstone and available water are two of the most important factors for biofilm formation. • Strongly positive intra-domain connections contributed to resistance to harsh environment. [ABSTRACT FROM AUTHOR]

• 4300 km long transects were established in the ecologically fragile areas of China. • Soil C:N:P stoichiometry in ecologically fragile areas was well-constrained. • C:N:P stoichiometry differed among the areas in response to environmental changes. • Climate and vegetation factors were the key drivers of soil C:N:P stoichiometry. Researchers are paying increasing attention to soil stoichiometry (carbon:nitrogen:phosphorus (C:N:P) ratios) in efforts to explore biogeochemical cycles, but little is known about the spatial pattern, implications, and driving factors of this stoichiometry in large, ecologically fragile areas. To explore these factors, we established three transects that covered a total length of about 4300 km in ecologically fragile areas of China, and sampled at intervals of about 25 km. These transects covered the karst area and the agro-pastoral ecotone of southwestern China, the Qinghai-Tibet Plateau, the Loess Plateau, and the forest-grassland ecotone. We collected 312 soil samples to a depth of 30 cm from 156 plots. The soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the ecologically fragile areas showed strong coupling relationships. Soil C:N:P was 51:4:1 to a depth of 30 cm, which is lower than the average global C:N:P (111:8:1). SOC and TN concentrations at 0 to 20 cm were significantly higher than that at 20 to 30 cm, but TP did not differ significantly among depths. SOC, TN, and TP concentrations were highest in the agro-pastoral ecotone, and were lowest in the Loess Plateau. C:N, C:P, and N:P were highest in the karst area. C:N were lowest in the Qinghai-Tibet Plateau, and C:P and N:P were lowest in the Loess Plateau. The spatial pattern of C, N, and P stoichiometry along environmental gradients was variable. The contributions to explaining the soil stoichiometry were highest for climate (21.7%), vegetation (8.9%), soil properties (6.4%), and topography (0.6%) to a depth of 20 cm, versus vegetation (35.9%), climate (5.3%), soil properties (3.3%), and topography (2.1%) at 20 to 30 cm. The results provide new insights into the biogeochemical cycles of C, N, and P and guidance for their impacts on ecological restoration in ecologically fragile areas. [ABSTRACT FROM AUTHOR]

Two subterranean ancient Chinese tombs of over 1700 years old, one from the Jin Dynasty and another from the Han Dynasty, were investigated in relation to black spots associated with microbiological deterioration of brick mural paintings within. The objectives of this study were to characterize the diversity of culturable fungal communities and assess the biodeteriorative potential of the isolated fungi. Culture-dependent methods using four different types of media were used for fungal isolation and specialized agar plates were used for biodeteriorative analyses by monitoring calcite dissolution, proteolytic activity, pH change, and biomineralization capabilities the isolated strains. Physical characterization of the mural samples and biomineralization were carried out using scanning electron microscopy combined with energy dispersive and X-ray diffraction analyses, while fungal acid production was analysed using High-performance liquid Chromatography (HPLC). Results showed that most of the 22 fungal strains isolated belonged to the Penicillium and Aspergillus genera. Differences in fungal community diversity between the two tombs may be attributed to variations in their interior temperature and relative humidity, however the history and drawing techniques used could also be contributing factors. Penicillium aurantiogriseum , Aspergillus versicolor and Penicillium olsonii were found in both tombs, representing the core microflora found in the black spots, thus these three fungi may be the sources of the black spots. More than 68% of the isolated fungi showed proteolytic activity and 27% of the strains produced acids, leading to dissolution of calcium carbonate and decreased pH value. Among the isolates, 5 out of 6 acid-forming fungal strains could also promote biomineralization. Penicillium was the main genus found to form acid and promote biomineralization. These fungi with biodeterioration and biomineralization characteristics were abundant in the black spots, indicating that formation of black spots was relevant to their presence and activity. These results suggest that thriving fungi, primarily driven by the local microenvironment, pose a high risk to brick wall paintings. • Filamentous fungi contribute to the formation of black spots on mural paintings. • The decay of mural paintings through proteolysis, carbonate dissolution, acid production, and biomineralization. • The formation of black spots on mural is influenced by the surrounding microenvironmental conditions. • Using different methods in tandem should be a prerequisite for the precise assessment of fungal threats to mural paintings. [ABSTRACT FROM AUTHOR]

Soil fauna is closely linked to ecological functions such as biogeochemical cycling, soil structure, ecosystem sustainability and trophic interactions. However, little consideration has been given to how desertification influences the abundance and diversity of soil fauna in arid areas. In this study, soil fauna was sampled in four desert habitats (gravel, sand, salt and mud desert) in northwest China. At the same time, the plant traits, geographic location and soil properties were investigated. We also measured contribution of environmental factors explained faunal community diversity and abundance, and by what pathways desertification controls soil fauna. The results showed that total abundance and diversity of soil fauna in the mud desert were significantly (P < 0.05) higher than salt, sand and gravel deserts. Soil fauna diversity, composition and community were more sensitive to desertification-induced changes in soil properties than to changes in plant traits and geographic locations (changes in soil properties explained 68.9 % and 73.7 % of the variation in diversity and abundance of soil fauna community, respectively). Among them, the available phosphorus, volumetric water content had a significant positive effect on community diversity and abundance, while pH had a significant negative effect (P < 0.01). The results of piecewise structural equation modeling imply that desertification may have mainly indirect impacts on soil fauna community, and that direct effects are almost zero. In summary, regardless of the type of desertification, it will affect the material cycle, energy flow and information transfer of ecosystems by destroying the soil habitats and vegetation conditions, and will affect the structure and diversity of soil fauna from the bottom up., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Biological soil crusts (biocrusts) are considered "desert ecosystem engineers" because they play a vital role in the restoration and stability maintenance of deserts, including those cold sandy land ecosystems at high latitudes, which are especially understudied. Microorganisms participate in the formation and succession of biocrusts, contributing to soil properties' improvement and the stability of soil aggregates, and thus vegetation development. Accordingly, understanding the composition and successional characteristics of microorganisms is a prerequisite for analyzing the ecological functions of biocrusts and related applications. Here, the Hulun Buir Sandy Land region in northeastern China-lying at the highest latitude of any sandy land in the country-was selected for study. Through a field investigation and next-generation sequencing (Illumina MiSeq PE300 Platform), our goal was to assess the shifts in diversity and community composition of soil bacteria and fungi across different stages during the succession of biocrusts in this region, and to uncover the main factors involved in shaping their soil microbial community. The results revealed that the nutrient enrichment capacity of biocrusts for available nitrogen, total nitrogen, total phosphorus, total content of water-soluble salt, available potassium, soil organic matter, and available phosphorus was progressively enhanced by the succession of cyanobacterial crusts to lichen crusts and then to moss crusts. In tandem, soil bacterial diversity increased as biocrust succession proceeded but fungal diversity decreased. A total of 32 bacterial phyla and 11 fungal phyla were identified, these also known to occur in other desert ecosystems. Among those taxa, the relative abundance of Proteobacteria and Cyanobacteria significantly increased and decreased, respectively, along the cyanobacterial crust-lichen-moss crust successional gradient. However, for Actinobacteria, Chloroflexi, and Acidobacteria their changed relative abundance was significantly hump-shaped, increasing in the shift from cyanobacterial crust to lichen crust, and then decreasing as lichen crust shifted to moss crust. In this process, the improved soil properties effectively enhanced soil bacterial and fungal community composition. Altogether, these findings broaden our understanding about how soil microbial properties can change during the succession of biocrusts in high-latitude, cold sandy land ecosystems., (© 2024. The Author(s).)

The coupling between carbon (C):nitrogen (N):phosphorus (P) stoichiometry in plant leaves is closely related to ecological functions such as photosynthesis, growth, and biogeochemical cycling. To explore the biogeographic patterns, nutrient limitations, and the relationships between leaf and soil stoichiometry, as well as the factors influencing leaf stoichiometry, we quantified community-level leaf C:N:P stoichiometry in trees, shrubs, and herbs along transects with a total length of about 4300 km. The leaf C:N:P ratios of trees, shrubs, and herbs were approximately 349:13:1, 267:14:1, and 226:12:1, respectively. Leaf C:N:P stoichiometry differed significantly (p < 0.05) among the life forms. Compared with global and Chinese scales, the C, N, and P concentrations were higher and C:N, C:P, and N:P ratios were lower. The leaf C:N:P stoichiometry patterns along a latitude gradient differed among life forms. There was no significant correlation between leaf N and soil total N, whereas leaf P of all three life forms increased significantly with increasing soil total P. Those results suggested a community-level N limitation for trees, shrubs, and herbs growth. Environmental factors explained 43.9, 26.5, and 6.1 % of leaf stoichiometric variations for trees, shrubs, and herbs, respectively. However, the key environmental driving factors gradually changed from climatic factors for trees and shrubs to soil factors for herbs. The results provide new insights into community-level biogeographical patterns and potential factors of leaf stoichiometry among plant life forms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Soil extracellular enzyme activity (EEA) stoichiometry reflects the dynamic balance between microorganism metabolic demands for resources and nutrient availability. However, variations in metabolic limitations and their driving factors in arid desert areas with oligotrophic environments remain poorly understood. In this study, we investigated sites in different desert types in western China and measured the activities of two C-acquiring enzymes (β-1,4-glucosidase and β-D-cellobiohydrolase), two N-acquiring enzymes (β-1,4-N-acetylglucosaminidase and L-leucine aminopeptidase), and one organic-P-acquiring enzyme (alkaline phosphatase) to quantify and compare the metabolic limitations of soil microorganisms based on their EEA stoichiometry. The ratios of log-transformed C-, N-, and P-acquiring enzyme activities for all deserts combined were 1:1.1:0.9, which is close to the hypothetical global mean EEA stoichiometry (1:1:1). We quantified the microbial nutrient limitation by means of vector analysis using the proportional EEAs, and found that microbial metabolism was co-limited by soil C and N. For different desert types, the microbial N limitation increased in the following order: gravel desert < sand desert < mud desert < salt desert. Overall, the study area's climate explained the largest proportion of the variation in the microbial limitation (17.9 %), followed by soil abiotic factors (6.6 %) and biological factors (5.1 %). Our results confirmed that the EEA stoichiometry method can be used in microbial resource ecology research in a range of desert types, and that the soil microorganisms maintained community-level nutrient element homeostasis by adjusting enzyme production to increase uptake of scarce nutrients even in extremely oligotrophic environments such as deserts., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The leaf calorific value (LCV) is an important trait that indicates how efficiently a plant utilizes natural resources to capture energy. However, little is known about the LCV characteristics of plants in arid and hyper-arid environments. To investigate the spatial patterns and variations in LCV of desert plants and their possible causes, we collected 343 leaf samples of 52 species along a 1000-km transect in the desert area of northwestern China. We analyzed the gross calorific value (GCV), ash-free calorific value (AFCV), carbon content (CC), nitrogen content (NC), and ash content (AC) of the leaves. The mean leaf GCV and AC were 16.2 kJ g -1 (range from 8.9 to 20.1 kJ g -1 ), and 189.8 mg g -1 (range from 61.5 to 495.1 mg g -1 ) respectively, which differ significantly from the values for plants growing in more humid areas of China. Succulence was the dominant trait that drove the differences in leaf GCV and AFCV among plant functional groups. Succulent plants had significantly lower leaf GCV and AFCV, and significantly higher AC, than non-succulent plants, indicating that the investment of energy for succulent plants in response to drought stress may be lower than that for non-succulent plants. Among the biological factors that affected LCV, the CC and AC were the main determinants of leaf GCV, whereas CC and NC were the main determinants of leaf AFCV. Drought stress is an environmental constraint that has a direct negative effect on both leaf GCV and AFCV, but its contribution may be weaker than phylogenetic effects. Our results suggest that LCV is a useful leaf trait that can be used to evaluate plant-environment interactions from an energy perspective., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Sandy cropland ecosystems are major terrestrial ecosystems in semi-arid regions of northern China's Horqin Sandy Land, where they play an important role in the regional carbon balance. Continuous observation of the CO 2 flux was conducted from 2014 to 2018 using the eddy covariance technique in a sandy maize cropland ecosystem in the Horqin Sandy Land. We analyzed carbon fluxes (the net ecosystem exchange (NEE) of CO 2 , ecosystem respiration (R eco ), and the gross primary productivity (GPP) and their responses to environmental factors at different temporal scales using Random Forest models and correlation analysis. We found that the sandy cropland was a carbon sink, with an annual mean NEE of -124.4 g C m -2 yr -1 . However, after accounting for carbon exports and imports, the cropland became a net carbon source, with net biome production ranging from -501.1 to -266.7 g C m -2 yr -1 . At a daily scale, the Random Forest algorithm revealed that photosynthetic photon flux density, soil temperature, and soil moisture were the main drivers for variation of GPP, R eco , and NEE at different integration periods. At a monthly scale, GPP and R eco increased with increasing leaf area index (LAI), so the maize ecosystem's carbon sequestration capacity increased with increasing LAI. At an annual scale, water availability (precipitation and irrigation) played a dominant role in explaining inter-annual variability of GPP and R eco . Affected by climate (e.g., precipitation) and field management (e.g., cultivation, irrigation), carbon fluxes differed greatly between years in the maize system., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)