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Warming, watering and elevated atmospheric CO₂-concentration effects have been extensively studied separately; however, their combined impact on plants is not well understood. In the current research, we examined plant growth and physiological responses of three dominant species from the Eurasian Steppe with different functional traits to a combination of elevated CO₂, high temperature, and four simulated precipitation patterns. Elevated CO₂ stimulated plant growth by 10.8–41.7 % for a C₃ leguminous shrub, Caragana microphylla, and by 33.2–52.3 % for a C₃ grass, Stipa grandis, across all temperature and watering treatments. Elevated CO₂, however, did not affect plant biomass of a C₄ grass, Cleistogenes squarrosa, under normal or increased precipitation, whereas a 20.0–69.7 % stimulation of growth occurred with elevated CO₂ under drought conditions. Plant growth was enhanced in the C₃ shrub and the C₄ grass by warming under normal precipitation, but declined drastically with severe drought. The effects of elevated CO₂ on leaf traits, biomass allocation and photosynthetic potential were remarkably species-dependent. Suppression of photosynthetic activity, and enhancement of cell peroxidation by a combination of warming and severe drought, were partly alleviated by elevated CO₂. The relationships between plant functional traits and physiological activities and their responses to climate change were discussed. The present results suggested that the response to CO₂ enrichment may strongly depend on the response of specific species under varying patterns of precipitation, with or without warming, highlighting that individual species and multifactor dependencies must be considered in a projection of terrestrial ecosystem response to climatic change.

Caragana korshinskii, a leguminous shrub, a common specie, is widely planted to prevent soil erosion on the Loess Plateau. The objective of this study was to determine how the plantation ages affected soil, leaf and root nutrients and ecological stoichiometry. The chronosequence ages of C. korshinskii plantations selected for this study were 10, 20 and 30 years. Soil organic carbon (SOC) and soil total nitrogen (STN) of C. korshinskii plantations significantly increased with increase in the chronosequence age. However, soil total phosphorous (STP) was not affected by the chronosequence age. The soil C: N ratio decreased and the soil C: P and N: P ratios increased with increasing plantation age. The leaf and root concentrations of C, N, and P increased and the ratios C: N, C: P, and N: P decreased with age increase. Leaf N: P ratios were >20, indicating that P was the main factor limiting the growth of C. korshinskii. This study also demonstrated that the regeneration of natural grassland (NG) effectively preserved and enhanced soil nutrient contents. Compared with NG, shrub lands (C. korshinskii) had much lower soil nutrient concentrations, especially for long (>20 years) chronosequence age. Thus, the regeneration of natural grassland is an ecologically beneficial practice for the recovery of degraded soils in this area.

Desertification is a major ecological challenge in China’s arid regions.  Caragana microphylla , a dominant sand-fixing shrub in the Hunshandake Desert, faces declining stability as plantations mature. Understanding its water use strategies and physiological adaptations across different forest ages is therefore essential for effective vegetation restoration in sandy ecosystems. Thus, the present study selects three- and eight-year-old  C. microphylla  plants in the Hunshandake sandy land as research objects. Hydrogen and oxygen stable isotope methods are used to identify plant water sources and calculate water use efficiency, while leaf functional traits (e.g., specific leaf area, C/N/P content) and long-term water use efficiency (via δ 13 C) were also measured. The results demonstrate that the primary water source for both three- and eight-year-old  C. microphylla  was 0–20 cm soil layer, and the surface water use efficiency of three-year-old  C. microphylla  is higher than that of eight-year-old plants. No significant difference is observed in long-term water use efficiency between both age groups. The nitrogen and phosphorus content in the leaves of eight-year-old  C. microphylla  decrease, while the C/N, C/P, and N/P increase. Therefore, eight-year-old  C. microphylla  plants maintain their growth needs by improving their nutrient utilization efficiency. The water use efficiency and nutrient use efficiency of  C. microphylla  exhibit synchronous adaptability. Future studies must consider not only the physiological and ecological adaptation of  C. microphylla  but also the impact of different restoration years on grassland communities and ecosystem functions.

During the process of dune vegetation restoration, understanding how grazing disturbance affects the relationship between plant species is a critical issue in ecological studies. However, there is insufficient evidence on the changes in the interaction between dominant shrubs and understory vegetation under grazing behavior. We aimed to study how grazing and dune stabilization affects the relationship between Caragana microphylla and understory vegetation. We established fencing at various stages of dune stabilization and proceeded to compared the performance indicators (e.g., richness and biomass) and the relative interaction index of understory vegetation and different functional groups along the dune stability under grazing and fencing conditions. Results showed that C . microphylla had facilitation on understory plants, and increased with dune stability, while the facilitation of Caragana microphylla on understory vegetation was stronger under grazing conditions. As sand dune stabilization increases, the facilitation of C . microphylla on understory vegetation diversity decreases significantly. However, there was no significant difference in the facilitation of C . microphylla on understory vegetation biomass at different stages of sand dune stabilization. This is related to the survival strategy of perennials being less tolerant to environmental stress than annuals, because grazing increased the richness of both annuals and perennials while reducing the overall biomass, and in the later stages of sand dune stabilization, and the facilitation of C . microphylla on perennials was higher than on annuals. Our study highlights the importance of the responses of different life-form groups to environmental factors and grazing disturbance during the process of sand dune vegetation restoration, as they play a crucial role in shaping the development of the relationship between understory vegetation and dominant shrubs.

Understanding the response of soil properties and bacterial communities in rhizosphere soil to aridity and dune types is fundamental to desertification control. This study investigated soil properties and bacterial communities of both rhizosphere and bulk soils of Caragana microphylla from four sites with different aridity indices, and one site with three different types of dunes. All sites were located in the desert regions of northern China. The results indicated that compared with the bulk soil, the soil nutrient content of rhizosphere, especially the content of total phosphorus, was generally significantly improved in different desertification environments. The bacterial richness and diversity were also higher than those of bulk soil, especially in arid regions and fixed dunes. Firmicutes, Actinobacteria, Proteobacteria, and Acidobacteria were the most dominant phyla in all samples. The regression analyses showed that at different sites, soil total organic C, total N, Na+, and total P played key roles in determining the bacterial community structure while total organic carbon, electronic conductivity, pH and total phosphorus were the dominant factors at the different dunes. The results further revealed that the dominant phyla strongly affected by environmental factors at different sites were Acidobacteria, Gemmatimonadetes, and Actinobacteria among which, Acidobacteria and Gemmatimonadetes were negatively correlated with Na+ content. At different types of dunes, Actinobacteria, Planctomycetes, and Gemmatimonadetes were particularly affected by environmental factors. The increased abundance of Actinobacteria in the rhizosphere soil was mainly caused by the decreased soil pH.

Shrub encroachment induced by global change and human disturbance strongly affects ecosystem structure and function. In this study, we explore the degree to which invading leguminous shrubs affected neighboring grasses, including via the transfer of fixed nitrogen (N). We measured N concentrations and natural abundance ¹⁵N of shoot tissues from three dominant grasses from different plant functional groups across seven distances along a local transect (up to 500 cm) to the leguminous shrub, Caragana microphylla. C. microphylla did transfer fixed N to neighboring grasses, but the amount and distance of N transferred were strongly species-specific. Shoot N concentrations decreased significantly with distance from C. microphylla, for a rhizomatous grass, Leymus chinensis, and a bunchgrass, Achnatherum sibiricum. However, N concentrations of another bunchgrass, Stipa grandis, were higher only directly underneath the shrub canopy. Shoot δ¹⁵N values of L. chinensis were enriched up to 500 cm from the shrub, but for S. grandis were enriched only below the shrub canopy. In contrast, δ¹⁵N of A. sibiricum did not change along the 500-cm transect. Our results indicated the rhizomatous grass transferred fixed N over long distances while bunchgrasses did not. The presence of C. microphylla increased the shoot biomass of L. chinensis but decreased that of S. grandis and A. sibiricum. These findings highlight the potential role of nutrient-acquisition strategies of neighboring grasses in moderating the interspecific variation of fixed N transfer from the leguminous shrub. Overall, leguminous shrubs have either positive or negative effects on the neighboring grasses and dramatically affect plant community composition and structure.

In close agreement with visible germination, orthodox seeds lose desiccation tolerance (DT). This trait can be regained under osmotic stress, but the mechanisms are poorly understood. In this study, germinating seeds of Caragana korshinskii Kom. were investigated, focusing on the potential modulating roles of reactive oxygen species (ROS) in the re-establishment of DT. Germinating seeds with 2 mm long radicles can be rendered tolerant to desiccation by incubation in a polyethylene glycol (PEG) solution (−1.7 MPa). Upon PEG incubation, ROS accumulation was detected in the radicles tip by nitroblue tetrazolium chloride staining and further confirmed by confocal microscopy. The PEG-induced re-establishment of DT was repressed when ROS scavengers were added to the PEG solution. Moreover, ROS act downstream of abscisic acid (ABA) to modulate PEG-mediated re-establishment of DT and serve as a new inducer to re-establish DT. Transcriptomic analysis revealed that re-establishment of DT by ROS involves the up-regulation of key genes in the phenylpropanoid–flavonoid pathway, and total flavonoid content and key enzyme activity increased after ROS treatment. Furthermore, DT was repressed by an inhibitor of phenylalanine ammonia lyase. Our data suggest that ROS play a key role in the re-establishment of DT by regulating stress-related genes and the phenylpropanoid–flavonoid pathway.

Vegetation restoration can be effective in containing gully head advance. However, the effect of vegetation restoration type on soil aggregate stability and erosion resistance at the head of the gully is unclear. In this study, five types of vegetation restoration— Pinus tabulaeformis (PT), Prunus sibirica (PS), Caragana korshinskii (CKS), Hippophae rhamnoides (HR), and natural grassland (NG, the dominant species is Leymus chinensis )—in the gully head were studied. Soil aggregate composition and nutrient contents in the 0–20, 20–40, and 40–60 cm soil layers were also determined, and the soil stability parameters were used to evaluate the soil conditions. The soil erodibility (K) was then determined by measuring the granulometric composition and organic matter. The results showed that the particle size of soil aggregates under different vegetation restoration types was mainly < 0.25 mm, and the percentage of aggregate disruption (PAD) was 22.08–76.07%. This further indicated that in Loess hilly and gully regions, water-stable aggregates were more reflective of the stability of soil aggregates in a gully head under vegetation restoration. The > 0.25 mm aggregates (R > 0.25 mm ), geometric mean diameter (GMD), and mean weight diameter (MWD) values of the three soil layers were the highest in PT and the lowest in NG, while the opposite was true for fractal dimension (D) and the percentage of aggregate disruption (PAD). The K ranged from 0.052 to 0.065 t·hm 2 ·h·MJ − 1 mm − 1 ·hm − 2 . GMD can be used to characterize the anti-erosion ability of soil, and increasing the soil organic carbon, total nitrogen, and clay content can effectively reduce soil erodibility. The comprehensive analysis indicated that the soil aggregates of arbors planted in the gully head had the highest stability and anti-erodibility, followed by shrubs and grasslands, and can be used to evaluate vegetation restoration measures in gully heads.

The Gonghe Basin region of the Tibet Plateau is severely affected by desertification. Compared with other desertified land, the main features of this region is windy, cold and short growing season, resulting in relatively difficult for vegetation restoration. In this harsh environment, identification the spatial distribution of soil nutrients and analysis its impact factors after vegetation establishment will be helpful for understanding the ecological relationship between soil and environment. Therefore, in this study, the 12-year-old C. intermedia plantation on sand dunes was selected as the experimental site. Soil samples were collected under and between shrubs on the windward slopes, dune tops and leeward slopes with different soil depth. Then analyzed soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP) and available potassium (AK). The results showed that the spatial heterogeneity of soil nutrients was existed in C. intermedia plantation on sand dunes. (1) Depth was the most important impact factor, soil nutrients were decreased with greater soil depth. One of the possible reasons is that windblown fine materials and litters were accumulated on surface soil, when they were decomposed, more nutrients were aggregated on surface soil. (2) Topography also affected the distribution of soil nutrients, more soil nutrients distributed on windward slopes. The herbaceous coverage were higher and C. intermedia ground diameter were larger on windward slopes, both of them probably related to the high soil nutrients level for windward slopes. (3) Soil \"fertile islands\" were formed, and the \"fertile islands\" were more marked on lower soil nutrients level topography positions, while it decreased towards higher soil nutrients level topography positions. The enrichment ratio (E) for TN and AN were higher than other nutrients, most likely because C. intermedia is a leguminous shrub.

Shoot elongation is one of the main plastic responses of plants to burial, a ubiquitous stress factor in dry ecosystems. Yet, intraspecific variation in this response to burial and the extent to which this variation is functionally coordinated with variation in other trait responses are largely unknown. We subjected seedlings of the shrub Caragana intermedia from 18 maternal parents (i.e. different half-sib families) to repeated partial burial to investigate how burial affects shoot growth, stem mechanical traits and associated plasticity. Burial increased both stem elongation and diameter growth of plants, but decreased biomass production. Half-sib families had different rates of shoot elongation, and differed in their response to burial with respect to biomechanical stem properties. Across half-sib families, the magnitude of these responses in mechanical traits was positively correlated with the magnitude of the stem elongation response. These results indicate that plasticity in different stem traits in response to sand burial and intraspecific variation therein are functionally coordinated with respect to mechanical stability. The results emphasize the importance of considering functionally coordinated traits when analyzing phenotypic plasticity in plants.