Plant root mechanisms and their effects on carbon and nutrient accumulation in desert ecosystems under changes in land use and climate.

Deserts represent key carbon reservoirs, yet as these systems are threatened this has implications for biodiversity and climate change. This review focuses on how these changes affect desert ecosystems, particularly plant root systems and their impact on carbon and mineral nutrient stocks. Desert plants have diverse root architectures shaped by water acquisition strategies, affecting plant biomass and overall carbon and nutrient stocks. Climate change can disrupt desert plant communities, with droughts impacting both shallow and deep-rooted plants as groundwater levels fluctuate. Vegetation management practices, like grazing, significantly influence plant communities, soil composition, root microorganisms, biomass, and nutrient stocks. Shallow-rooted plants are particularly susceptible to climate change and human interference. To safeguard desert ecosystems, understanding root architecture and deep soil layers is crucial. Implementing strategic management practices such as reducing grazing pressure, maintaining moderate harvesting levels, and adopting moderate fertilization can help preserve plant-soil systems. Employing socio-ecological approaches for community restoration enhances carbon and nutrient retention, limits desert expansion, and reduces CO2 emissions. This review underscores the importance of investigating belowground plant processes and their role in shaping desert landscapes, emphasizing the urgent need for a comprehensive understanding of desert ecosystems.

Combining different species in restoration is not always the right decision: Monocultures can provide higher ecological functions than intercropping in a desert ecosystem.

Vegetation restoration in deserts is challenging due to these ecosystems' inherent fragility and harsh environmental conditions. One approach for active restoration involves planting native species, which can accelerate the recovery of ecosystem functions. To ensure the effectiveness of this process, carefully selecting species for planting is crucial. Generally, it is expected that a more diverse mix of species in the plantation will lead to the recovery of a greater number of ecosystem functions, especially when the selected species have complementary niche traits that facilitate maximum cooperation and minimize competition among them. In this study, we evaluated the planting of two native species from the hyper-desert of Taklamakan, China, which exhibit marked morpho-physiological differences: a phreatophytic legume (Alhagi sparsifolia) and a halophytic non-legume (Karelinia caspia). These species were grown in both monoculture and intercrop communities. Monoculture of the legume resulted in the highest biomass accumulation. Intercropping improved several ecosystem functions in the 50 cm-upper soil, particularly those related to phosphorus (P), carbon (C), and sulfur (S) concentrations, as well as soil enzyme activities. However, it also increased soil sodium (Na+) concentration and pH. Halophyte monocultures enhanced ecological functions associated with nitrogen concentrations in the upper soil and with P, S, C, and cation concentrations (K+, Ca2+, Mg2+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+), along with enzyme activities in the deep soil. It also maximized Na+ accumulation in plant biomass. In summary, we recommend legume monoculture when the primary goal is to optimize biomass accumulation. Conversely, halophyte monoculture is advisable when the objective is to extract sodium from the soil or enhance ecosystem functions in the deep soil. Intercropping the two species is recommended to maximize the ecosystem functions of the upper soil, provided there is no salinization risk. When planning restoration efforts in desert regions, it is essential to understand the impact of each species on ecosystem function and how complementary species behave when intercropped. However, these interactions are likely species- and system-specific, highlighting the need for more work to optimize solutions for different arid ecosystems.

Root morphological and physiological traits are committed to the phosphorus acquisition of the desert plants in phosphorus-deficient soils.

BACKGROUND: Phosphorus (P) deficiency in desert ecosystems is widespread. Generally, desert species may allocate an enormous proportion of photosynthetic carbon to their root systems to adjust their P-acquisition strategies. However, root P-acquisition strategies of deep-rooted desert species and the coordination response of root traits at different growth stages to differing soil P availability remains unclear. In this study, a two-year pot experiment was performed with four soil P-supply treatments (0, 0.9, 2.8, and 4.7 mg P kg-1 y-1 for the control, low-, intermediate-, and high-P supply, respectively). Root morphological and physiological traits of one- and two-year-old Alhagi sparsifolia seedlings were measured. RESULTS: For two-year-old seedlings, control or low-P supply significantly increased their leaf Mn concentration, coarse and fine roots' specific root length (SRL), specific root surface area (SRSA), and acid phosphatase activity (APase), but SRL and SRSA of one-year-old seedlings were higher under intermediate-P supply treatment. Root morphological traits were closely correlated with root APase activity and leaf Mn concentration. One-year-old seedlings had higher root APase activity, leaf Mn concentration, and root tissue density (RTD), but lower SRL and SRSA. Two-year-old seedlings had higher root APase activity, leaf Mn concentration, SRL and SRSA, but a lower RTD. Root APase activity was significantly positively correlated with the leaf Mn concentration, regardless of coarse or fine roots. Furthermore, root P concentrations of coarse and fine roots were driven by different root traits, with root biomass and carboxylates secretion particularly crucial root traits for the root P-acquisition of one- and two-year-old seedlings. CONCLUSIONS: Variation of root traits at different growth stages are coordinated with root P concentrations, indicating a trade-off between root traits and P-acquisition strategies. Alhagi sparsifolia developed two P-activation strategies, increasing P-mobilizing phosphatase activity and carboxylates secretion, to acclimate P-impoverished in soil. The adaptive variation of root traits at different growth stages and diversified P-activation strategies are conducive to maintaining the desert ecosystem productivity.

Fine-root traits are devoted to the allocation of foliar phosphorus fractions of desert species under water and phosphorus-poor environments.

Traits of leaves and fine roots are expected to predict the responses and adaptation of plants to their environments. Whether and how fine-root traits (FRTs) are associated with the allocation of foliar phosphorus (P) fractions of desert species in water- and P-poor environments, however, remains unclear. We exposed seedlings of Alhagi sparsifolia Shap. (hereafter Alhagi) treated with two water and four P-supply levels for three years in open-air pot experiments and measured the concentrations of foliar P fractions, foliar traits, and FRTs. The allocation proportion of foliar nucleic acid-P and acid phosphatase (APase) activity of fine roots were significantly higher by 45.94 and 53.3% in drought and no-P treatments relative to well-watered and high-P treatments, whereas foliar metabolic-P and structural-P were significantly lower by 3.70 and 5.26%. Allocation proportions of foliar structural-P and residual-P were positively correlated with fine-root P (FRP) concentration, but nucleic acid-P concentration was negatively correlated with FRP concentration. A tradeoff was found between the allocation proportion to all foliar P fractions relative to the FRP concentration, fine-root APase activity, and amounts of carboxylates, followed by fine-root morphological traits. The requirement for a link between the aboveground and underground tissues of Alhagi was generally higher in the drought than the well-watered treatment. Altering FRTs and the allocation of P to foliar nucleic acid-P were two coupled strategies of Alhagi under conditions of drought and/or low-P. These results advance our understanding of the strategies for allocating foliar P by mediating FRTs in drought and P-poor environments.

Soil microbial functional profiles of P-cycling reveal drought-induced constraints on P-transformation in a hyper-arid desert ecosystem.

Soil water conditions are known to influence soil nutrient availability, but the specific impact of different conditions on soil phosphorus (P) availability through the modulation of P-cycling functional microbial communities in hyper-arid desert ecosystems remains largely unexplored. To address this knowledge gap, we conducted a 3-year pot experiment using a typical desert plant species (Alhagi sparsifolia Shap.) subjected to two water supply levels (25 %-35 % and 65 %-75 % of maximum field capacity, MFC) and four P-supply levels (0, 1, 3, and 5 g P m-2 y-1). Our investigation focused on the soil Hedley-P pool and the four major microbial groups involved in the critical phases of soil microbial P-cycling. The results revealed that the drought (25 %-35 % MFC) and no P-supply treatments reduced soil resin-P and NaHCO3-Pi concentrations by 87.03 % and 93.22 %, respectively, compared to the well-watered (65 %-75 % MFC) and high P-supply (5 g P m-2 y-1) treatments. However, the P-supply treatment resulted in a 12 %-22 % decrease in the soil NH4+-N concentration preferred by microbes compared to the no P-supply treatment. Moreover, the abundance of genes engaged in microbial P-cycling (e.g. gcd and phoD) increased under the drought and no P-supply treatments (p < 0.05), suggesting that increased NH4+-N accumulation under these conditions may stimulate P-solubilizing microbes, thereby promoting the microbial community's investment in resources to enhance the P-cycling potential. Furthermore, the communities of Steroidobacter cummioxidans, Mesorhizobium alhagi, Devosia geojensis, and Ensifer sojae, associated with the major P-cycling genes, were enriched in drought and no or low-P soils. Overall, the drought and no or low-P treatments stimulated microbial communities and gene abundances involved in P-cycling. However, this increase was insufficient to maintain soil P-bioavailability. These findings shed light on the responses and feedback of microbial-mediated P-cycling behaviors in desert ecosystems under three-year drought and soil P-deficiency.

Depth-dependent responses of soil bacterial communities to salinity in an arid region.

Soil salinization adversely affects soil fertility and plant growth in arid region worldwide. However, as the drivers of nutrient cycling, the response of microbial communities to soil salinization is poorly understood. This study characterized bacterial communities in different soil layers along a natural salinity gradient in the Karayulgun River Basin, located northwest of the Taklimakan desert in China, using the 16S rRNA Miseq-sequencing technique. The results revealed a significant filtering effect of salinity on the bacterial community in the topsoil. Only the α-diversity (Shannon index) in the topsoil (0-10 cm) significantly decreased with increasing salinity levels, and community dissimilarity in the topsoil was enhanced with increasing salinity, while there was no significant relationship in the subsoil. BugBase predictions revealed that aerobic, facultatively anaerobic, gram-positive, and stress-tolerant bacterial phenotypes in the topsoil was negatively related to salinity. The average degree and number of modules of the bacterial co-occurrence network in the topsoil were lower under higher salinity levels, which contrasted with the trends in the subsoil, suggesting an unstable bacterial network in the topsoil caused by higher salinity. The average path length among bacterial species increased in both soil layers under high salinity conditions. Plant diversity and available nitrogen were the main drivers affecting community composition in the topsoil, while available potassium largely shaped community composition in the subsoil. This study provides solid evidence that bacterial communities adapt to salinity through the adjustment of microbial composition based on soil depth. This information will contribute to the sustainable management of drylands and improved predictions and responses to changes in ecosystems caused by climate change.

Patterns of carbon, nitrogen, and phosphorus stoichiometry of three life-form desert plants and responses to soil and microbial biomass factors in a hyper-arid desert ecosystem.

Plant, soil, and microbial biomass ratios of carbon (C), nitrogen (N), and phosphorus (P) are crucial in maintaining stability of desert ecosystems. Nevertheless, variation in relations of elemental ratios between different life forms of plants and soil and microbial biomass in desert ecosystems remains unclear. In a hyper-arid desert ecosystem, C, N, and P concentrations and ratios were analyzed in the plant-soil-microbial biomass system of three perennial desert species (Alhagi sparsifolia Shap. [Herb, Fabaceae], Karelinia caspica Pall. [Herb, non-Fabaceae], and Tamarix ramosissima Ledeb. [Shrub]). Concentrations of N and P in Alhagi sparsifolia leaf, stem, and root were significantly greater than those in Karelinia caspica and Tamarix ramosissima, whereas plant C and soil organic C (SOC) were highest with Tamarix ramosissima. Alhagi sparsifolia and Tamarix ramosissima were P-limited, whereas Karelinia caspica was N-limited. According to correlation analysis, SOC rather than soil total P (STP) regulated plant N:P ratios, and microbial biomass C, N, and P rather than SOC, soil total N, and STP regulated plant C:N:P ratios. Soil water content also affected plant nutrient balance. Thus, in a hyper-arid desert ecosystem, the plant-soil-microbial biomass system and the balance of C, N, and P are closely related, and the role of soil microbial biomass in affecting plant nutrient balance should receive increased attention.

Potential role of root-associated bacterial communities in adjustments of desert plant physiology to osmotic stress.

Plants possess the ability to adapt to osmotic stress by adjusting their physiology and morphology and by cooperating with their root-associated (rhizosphere and endosphere) microbial communities. However, the coordination of host self-regulation with root-associated microorganisms at the community level, especially for desert plants, remains unclear. This study investigated the morphophysiological responses of seedlings from the desert plant Alhagi sparsifolia Shap to osmotic stress, as well as the relationships between these adaptations and their root-associated bacterial communities. The results indicated that osmotic stress contributed to a reduction in height and increased levels of reactive oxygen species (ROS) and malondialdehyde (MDA). In response, A. sparsifolia exhibited a series of morphophysiological adjustments, including increased ratio of root to shoot biomass (R/S) and the number of root tip, enhanced vitality, high levels of peroxidase (POD), ascorbate peroxidase (APX), and glutathione (GSH), as well as osmolytes (proline, soluble protein, and soluble sugar) and modification in phytohormones (abscisic acid (ABA) and jasmonic acid (JA)). Additionally, osmotic stress resulted in alterations in the compositions and co-occurrence patterns of root-associated bacterial communities, but not α-diversity (Chao1). Specifically, the rhizosphere Actinobacteria phylum was significantly increased by osmotic stress. These shifts in root-associated bacterial communities were significantly correlated with the host's adaptation to osmotic stress. Overall, the findings revealed that osmotic stress, in addition to its impacts on plant physiology, resulted in a restructuring of root-associated microbial communities and suggested that the concomitant adjustment in plant microbiota may potentially contribute to the survival of desert plants under extreme environmental stress.

l-Ergothioneine Exhibits Protective Effects against Dextran Sulfate Sodium-Induced Colitis in Mice.

Background: Ulcerative colitis (UC) is a chronic disease of the intestinal tract in which excessive activation of inflammatory response is correlated. l-Ergothioneine (EGT) widely existing in mushrooms has various physiological activities. In this study, the protective effects of EGT on dextran sulfate sodium (DSS)-induced colitis mice were investigated. Results: It was observed that EGT administration, especially at the high dose level, prevented the body weight loss, the colon shortening, and the increase in disease activity index and spleen index caused by DSS. Moreover, EGT supplementation attenuated DSS-induced gut barrier damage by enhancing the expression of tight-junction protein and recovering the loss of gut mucus layer. Furthermore, EGT considerably decreased the colonic myeloperoxidase (MPO) activity induced by DSS, but no significant differences were observed in the concentrations of IL-6 and TNF-α in colon tissues. Additionally, EGT downregulated the populations of CD4+ T cells and macrophages, indicating that EGT stabilized the immune response caused by DSS. Conclusion: Together these results suggest that EGT can alleviate DSS-induced colitis and provide important insights concerning the potential anticolitis activity of such food products.

Foliar P-Fractions Allocation of Karelinia caspia and Tamarix ramosissima Are Driven by Soil and Groundwater Properties in a Hyper-Arid Desert Ecosystem.

The allocation patterns of foliar phosphorus (P) fractions across various vegetation types generally reflect the adaptability to P-impoverished environments. However, the allocation of foliar-P fractions within the desert herb Karelinia caspia (K. caspica) and shrub Tamarix ramosissima (T. ramosissima) in soils with different environment-P availability and the impact of soil and groundwater properties on foliar-P fractions allocation remain unclear. The foliar-P fractions (metabolites-P, nucleic acid-P, structural-P, and residual-P) of K. caspica and T. ramosissima and the properties of 0-60 cm deep soil under their canopy and groundwater were determined at four different environment-P sites. Results found that as environment-P availability decreased, both plants allocated the higher proportions of foliar-P to nucleic acid-P than to metabolites-P and structural-P. With the exception of residual-P, foliar-P fractions were markedly higher for K. caspica than T. ramosissima. Soil Olsen-P, NO3 --N, soil water content, electrical conductivity (EC), groundwater EC, and total dissolved solids (TDSs) played an important role in allocating foliar P-fractions for both K. caspica and T. ramosissima. Compared with K. caspica, the foliar-P fractions of T. ramosissima were more tightly bounded to groundwater than soil properties. Overall, these findings show how desert plants flexibility take advantage of the foliar-P in low environment-P availability and illustrate the foliar-P fractions allocation of desert plants is driven by soil and groundwater properties.

Alhagi sparsifolia Harbors a Different Root-Associated Mycobiome during Different Development Stages.

The mycobiome in the rhizosphere and within the roots benefits the nutrition and function of host plants. However, compared with the bacterial community, root-associated mycobiomes of desert plants and the forces that drive their assemblage are limited. Here, we investigated the mycobiomes in bulk soil, rhizosphere, and root compartments of Alhagi sparsifolia Shap., a phreatophyte species dominating in Central Asia. The internal transcribed spacer (ITS) gene phylogenetic profiles displayed significantly diverse mycobiomes across three compartments and host growth times, together explaining 31.45% of the variation in the community composition. The community structure of the perennial stage was markedly different from that of other stages (30 days to 2 years old). Along the soil-plant continuum, the α-diversity (estimated by Chao1) decreased gradually, while concomitantly increasing the community dissimilarity and the influence of edaphic factors. Specific leaf area, soil water content, and soil organic matter levels were common factors driving the composition of the three mycobiome communities. A more complex and connected network was observed in the root community compared with the other compartments. Overall, our work suggests that an age-sensitive host effect restructured the desert-plant-root-associated mycobiome, and that edaphic factors and host growth strategy may play potential roles in this process.

Alhagi sparsifolia: An ideal phreatophyte for combating desertification and land degradation.

The upcoming launch of the post-2020 biodiversity framework entails elucidating the future priorities and strategies for conserving biodiversity on a regional and global scale. Desertification has caused significant environmental and socio-economic problems in many arid and semiarid areas of the world. Phreatophytes increase nutrient levels and water reserves in the ground below them and are essential resources for other plants and animals. Factors that can enhance or reduce the island effect of phreatophytes are worthy of research since they can contribute to the survival and growth of this group of plants. Furthermore, these plants substantially impact the whole environment and boast necessary evolutionary adaptations for sustaining islands of life in the arid landscape to prevent complete desertification. Alhagi sparsifolia is a semi-shrub legume and a typical desert phreatophyte. The main objective of this review is to disseminate research-based knowledge and improve awareness of this important plant species and provide a framework that could effectively improve regional socio-ecological environments, particularly in controlling desertification, thereby enhancing human welfare. First, we synthesized knowledge of the physiological acclimation of this species, above all in terms of water and nutrient use, the impact of salinity, and its response to different light environments and temperatures. Then, we analyzed the socio-ecological services that A. sparsifolia offers, highlighted the anthropogenic threats to its habitats, and strategies for its sustainable utilization and management. We conclude that more knowledge of how A. sparsifolia interacts with groundwater will contribute significantly to elucidating the possible effects of climate change and human activities on the sustainable use of groundwater. Protected areas must be set up, and key knowledge shared to combat desertification and improve people's welfare as a means of guaranteeing sustainable development. An integrative socio-ecological approach must be adapted to improve understanding of this valuable phreatophyte's importance and sustainable use and fulfill Sustainable Development Goals (SDGs).

Optimization and Characterization of Polyphosphate Fertilizers by Two Different Manufacturing Processes.

To explore how different reaction parameters affect the major features of short-chain ammonium polyphosphate (APP) fertilizers, a batch of manufacturing experiments were conducted under two different manufacturing processes [phosphoric acid (PA)-urea and monoammonium phosphate (MAP)-urea]. The APP features including polymerization degree, polymerization rate, solubility, and N and P recovery rates were significantly varied and influenced by the molar ratio of raw materials (P:N), reaction temperature, time, and pressure under different manufacturing conditions. In the MAP-urea process, the optimized APP products were gained under the combination condition of molar ratio = 1.6:1, T = 130 °C, and t = 45 min, while this happened in molar ratio = 1:1.7, T = 180 °C, and t = 60 min in the PA-urea process. Comprehensively, the features of APP fertilizers produced by the MAP-urea process were better than those produced by the PA-urea process. Our results provide valuable references for manufacturing high-quality short-chain APP fertilizers.