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Groundwater and its associated nutrients sustain the establishment and persistence of phreatophytes. Rapid root elongation immediately after germination is vital for desert species to access deep water sources to avoid water-deficit stress. However, the growth strategy and responses to nutrients and water of young phreatophyte seedlings before their roots reach the water table are poorly understood, especially in the scenarios of nitrogen (N) deposition and drought. We investigated how simulated N deposition and drought affect the plasticity of Alhagi sparsifolia seedlings by multiple eco-physiological mechanisms. Seedlings were planted under drought-stressed or well-watered conditions and subjected to various levels of N addition (0, 3.0, 6.0, or 9.0 gN·m -2  yr -1 ). The amounts of N and water independently or interactively affected the photosynthetic traits, drought tolerance characteristics, morphological traits, biomass allocation strategy, and nutrient distribution patterns among the plant organs. Moreover, changes mediated by N addition at the leaf level reflected the drought acclimation of the seedlings, which may be related to biomass and nutrient partitioning between organs. The roots were found to be more sensitive to variation of the N:phosphorus (P) ratio, and greater proportions of biomass, N, and P were allocated to resource-acquiring organs (i.e., leaves and fine roots) than to other tissues. A. sparsifolia adopts numerous strategies to tolerate drought, and additional N input was crucial to enhance the growth of drought-stressed A. sparsifolia, which was mainly attributable to its positive impact on the N and P uptake capacity mediated by increased biomass allocation to the roots., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Alnus cremastogyne, a broad-leaved tree endemic to south-western China, has both commercial and restoration importance. However, little is known of its morphological, physiological and biochemical responses to drought and phosphorous (P) application. A randomized experimental design was used to investigate how drought affected A. cremastogyne seedlings, and the role that P applications play in these responses. Drought had significant negative effects on A. cremastogyne growth and metabolism, as revealed by reduced biomass (leaf, shoot and root), leaf area, stem diameter, plant height, photosynthetic rate, leaf relative water content, and photosynthetic pigments, and a weakened antioxidative defence mechanism and high lipid peroxidation level. However, the reduced leaf area and enhanced osmolyte (proline and soluble sugars) accumulation suggests drought avoidance and tolerance strategies in this tree. Applying P significantly improved the leaf relative water content and photosynthetic rate of drought-stressed seedlings, which may reflect increased anti-oxidative enzyme (superoxide dismutase, catalase and peroxidase) activities, osmolyte accumulation, soluble proteins, and decreased lipid peroxidation levels. However, P had only a slight or negligible effect on the well-watered plants. A. cremastogyne is sensitive to drought stress, but P facilitates and improves its metabolism primarily via biochemical and physiological rather than morphological adjustments, regardless of water availability.

Drylands, comprising semi‐arid, arid, and hyperarid regions, cover approximately 41% of the Earth's land surface and have expanded considerably in recent decades. Even under more optimistic scenarios, such as limiting global temperature rise to 1.5°C by 2100, semi‐arid lands may increase by up to 38%. This study provides an overview of the state‐of‐the‐art regarding changing aridity in arid regions, with a specific focus on its effects on the accumulation and availability of carbon (C), nitrogen (N), and phosphorus (P) in plant–soil systems. Additionally, we summarized the impacts of rising aridity on biodiversity, service provisioning, and feedback effects on climate change across scales. The expansion of arid ecosystems is linked to a decline in C and nutrient stocks, plant community biomass and diversity, thereby diminishing the capacity for recovery and maintaining adequate water‐use efficiency by plants and microbes. Prolonged drought led to a −3.3% reduction in soil organic carbon (SOC) content (based on 148 drought‐manipulation studies), a −8.7% decrease in plant litter input, a −13.0% decline in absolute litter decomposition, and a −5.7% decrease in litter decomposition rate. Moreover, a substantial positive feedback loop with global warming exists, primarily due to increased albedo. The loss of critical ecosystem services, including food production capacity and water resources, poses a severe challenge to the inhabitants of these regions. Increased aridity reduces SOC, nutrient, and water content. Aridity expansion and intensification exacerbate socio‐economic disparities between economically rich and least developed countries, with significant opportunities for improvement through substantial investments in infrastructure and technology. By 2100, half the world's landmass may become dryland, characterized by severe conditions marked by limited C, N, and P resources, water scarcity, and substantial loss of native species biodiversity. These conditions pose formidable challenges for maintaining essential services, impacting human well‐being and raising complex global and regional socio‐political challenges. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Phosphorus (P) limitation and water stress can affect trees' growth, yet differing levels of nutrition under drought may have negative or positive effects on their growth and metabolism. This study aimed to evaluate the impact of P nutrition upon growth and metabolism in drought-stressed Phoebe zhennan (an endangered forest tree species) seedlings, to provide a basis for strengthening its conservation in the face of future climate change. A complete randomized design was used to investigate the effects of four different levels of P fertilization (no P, low P, moderate P, and high P) under water stress on the growth, photosynthesis, and nitrogen metabolism of P. zhennan. Drought-stressed seedlings under high P (HP) application had enhanced growth, while moderate P (MP) application improved their root biomass and leaf area only, whereas low P (LP) did not significantly affect any growth trait. Moreover, HP fertilization had positive effects on leaf relative water contents (LRWCs), while HP and MP both significantly improved photosynthetic traits vis-à-vis non-fertilized seedlings. The concentration of soluble sugars was significantly higher in non-fertilized than fertilized seedlings as were nitrogenous compounds (NO3− and NH4+) and nitrogen metabolic enzymes (NR, GDH, GOGAT, and GS) activities. Both NO3−and NH4+concentrations were significantly decreased under HP application compared with the non-fertilized counterparts. The plant traits improved under HP application counteracted the adverse impact of low nitrate availability and promoted seedling growth. Low-dose fertilization produces depressive effects in P. zhennan, but a high P concentration can overcome those negative effects to improve growth. [ABSTRACT FROM AUTHOR]

Soil macrofauna is vital for soil functions and soil-mediated processes in all ecosystems. However, environmental perturbations, such as drought, that threaten both the abundance and function of soil macrofauna remain mostly unexplored, particularly in an agroforestry system. We investigated the effects of drought on soil macrofauna abundance and vertical distribution under three different planting systems including two intercropping systems, comprising Chinese prickly ash (Zanthoxylum bungeanum) intercropped with soybean (Glycine max) (Z-G) or bell pepper (Capsicum annuum) (Z-C), and one monoculture system, comprising only Z. bungeanum (Z). Soil samples were collected at depths of 0–10, 10–20, and 20–30 cm, and soil macrofauna and chemical properties were analyzed. Soil dryness negatively affected soil macrofauna in all planting systems. Drought reduced the total macrofauna density, biomass, genera richness, and Pielou's evenness. Additionally, drought significantly decreased density and biomass of Drawida and Eisenia but had no effect on Carabid beetles. Soil macrofauna density was highest in the Z-G intercropping system and higher at 0–10 cm than at other soil depths. These results indicate that intercropping soybean rather than bell pepper increases the abundance and biomass of soil macrofauna, and drought remarkably impacts the response of soil macrofauna to planting systems. [ABSTRACT FROM AUTHOR]

Eucalyptus grandis is the most widely planted tree species worldwide and can face severe drought during the initial months after planting because the root system is developing. A complete randomized design was used to study the effects of two water regimes (well‐watered and water‐stressed) and phosphorus (P) applications (with and without P) on the morphological and physio‐biochemical responses of E. grandis. Drought had negative effects on the growth and metabolism of E. grandis, as indicated by changes in morphological traits, decreased net photosynthetic rates (Pn), pigment concentrations, leaf relative water contents (LRWCs), nitrogenous compounds, over‐production of reactive oxygen species (ROS) and higher lipid peroxidation. However, E. grandis showed effective drought tolerance strategies, such as reduced leaf area and transpiration rate (E), higher accumulation of soluble sugars and proline and a strong antioxidative enzyme system. P fertilization had positive effects on well‐watered seedlings due to improved growth and photosynthesis, which indicated the high P requirements during the initial E. grandis growth stage. In drought‐stressed seedlings, P application had no effects on the morphological traits, but it significantly improved the LRWC, Pn, quantum efficiency of photosystem II (Fv/Fm), chlorophyll pigments, nitrogenous compounds and reduced lipid peroxidation. P fertilization improved E. grandis seedling growth under well‐watered conditions but also ameliorated some leaf physiological traits under drought conditions. The effects of P fertilization are mainly due to the enhancement of plant N nutrition. Therefore, P can be used as a fertilizer to improve growth and production in the face of future climate change. [ABSTRACT FROM AUTHOR]

The use of phosphorus (P) to alleviate soil nutrient deficiency alters resources in plant and microbial communities, but it remains unknown how mixed and monospecific planting of forest tree species shape soil microbial structure and functions in response to drought and its interplay with phosphorus addition. We investigated the microbial structure and chemical properties of forest soils planted with P. zhennan monoculture, A. cremastogyne monoculture, and their mixed cultures. The three planting systems were exposed to drought (30–35% water reduction) and the combination of drought with P. A well-watered treatment (80–85% water addition) of similar combinations was used as the control. Planting systems shaped the effects of drought on the soil microbial properties leading to an increase in nitrate nitrogen, urease activity, and microbial biomass carbon in the monocultures, but decrease in mixed cultures. In the monoculture of P. zhennan, addition of P to drought-treated soil increased enzyme activities, the concentration of dissolved organic nitrogen, and carbon, leading to increase in the total bacteria, G+ bacteria, and arbuscular mycorrhizal fungi. Except in the drought with P addition treatment, the impact of admixing on total phospholipid fatty acids (PLFAs), bacterial PLFA, and fungi PLFA was synergistic in all treatments. Our findings indicated that in monoculture of P. zhennan and its mixed planting with A. cremastogyne, greater biological activities could be established under drought conditions with the addition of P. [ABSTRACT FROM AUTHOR]

Drought and excess water are divergent weather conditions, predicted to strongly affect the physiology of plants. The present study investigated the effects of varying drought stress imposed at different stages of growth and development on the three most cultivated Capsicum species in Africa. This was with a view to elucidating the physiological and biochemical responses of these plants to aftermath of drought and to further ascertain the most critical stage of drought in them . Capsicum spp. were exposed to four drought regimes by withholding water to 80–85%, 55–60%, 40–45% and 30–35% water holding capacity (WHC) respectively representing control, light, moderate and severe drought stress conditions. Results showed that moderate and severe drought induced significant reduction in leaf relative water content (LRWC), relative growth rate (RGR), carotenoid, chlorophyll “ a ”, “ b ” and total chlorophyll content of the study plants at the vegetative stage, particularly in Capsicum chinense . C. chinense exposed to severe drought stress had highest LAR and leaf weight ratio (LWR) at flowering and fruiting stages. Furthermore, C. chinense under moderate and severe drought treatment had higher phenol content at vegetative stage. Irrespective of the growth stage, no pinch of capsaicin content was detected in C. annum. Capsaicin content of C. chinense exposed to drought stress at vegetative stage was significantly lower (p < 0.05) than those exposed to the same drought stress at fruiting stage. The present findings revealed that Capsicum chinense was more tolerant to drought stress than the other two species. Data presented in this study suggest that the three-capsicum species are likely to be more susceptible to the aftermath of drought at the vegetative stage than at either the fruiting or the flowering stage. [ABSTRACT FROM AUTHOR]