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Predawn leaf water potential (LWP), the LWP between 09:00 and 10:30 h (termed minimum LWP), stem xylem hydraulic conductivity, foliar nitrogen, leaf gas exchange and leaf traits were measured on the same days in adults and 1-year-old to 7-year-old resprouts that had regrown after removing all the aboveground shoots. Height growth and accumulation of aboveground biomass quickly decreased with resprout age and there was no difference between 7-year-old resprouts and the uncut adults. Predawn LWP showed no significant difference between resprouts and adults, but the minimum LWP decreased gradually from −2.0 MPa in 1-year-old resprouts to −3.0 MPa in 7-year-old resprouts. The decrease in minimum LWP was associated with increased hydraulic resistance, as indicated by the gradual decrease in leaf area-specific hydraulic conductivity (KL) and sapwood area-specific hydraulic conductivity (KS) and the associated increase in stem native percentage loss of hydraulic conductivity in older than 2-year-old resprouts. The leaf nitrogen content per unit area (Narea) also decreased steadily from 3.6 g m−2 in 1-year-old resprouts to 1.7 g m−2 in 7-year-old resprouts. With the decline in LWP and Narea, the rate of leaf photosynthesis per unit area (Aarea) decreased from 20 μ mol m−2 s−1 in 1-year-old resprouts to 11 μ mol m−2 s−1 in 7-year-old resprouts. In adults, although KS decreased further compared with 7-year-old resprouts, the minimum LWP, KL, Narea and the rate of photosynthesis increased by 0.3 MPa, 29, 34 and 23%, respectively. The results show that a progressive loss of stem hydraulic conductivity and a steady decrease in foliar nitrogen with age were associated with a decrease in the photosynthetic rate of Caragana korshinskii Kom. resprouts, possibly changing the allocation of photosynthetic assimilates and slowing resprout height growth. [ABSTRACT FROM AUTHOR]

Ethylene, a plant hormone that significantly influences both plant growth and response to stress, plays a well-established role in stress signaling. However, its impact on stomatal opening and closure during dehydration and rehydration remains relatively unexplored and is still debated. Exogenous ethylene has been proven to induce stomatal closure through a series of signaling pathways, including the accumulation of reactive oxygen species, subsequent synthesis of nitric oxide and hydrogen sulfide, and SLOW ANION CHANNEL-ASSOCIATED 1 activation. Thus, it has been suggested that ethylene might function to induce stomatal closure synergistically with abscisic acid (ABA). Furthermore, it has also been shown that increased ethylene can inhibit ABA- and jasmonic acid-induced stomatal closure, thus hindering drought-induced closure during dehydration. Simultaneously, other stresses, such as chilling, ozone pollution, and K+ deficiency, inhibit drought- and ABA-induced stomatal closure in an ethylene synthesis-dependent manner. However, ethylene has been shown to take on an opposing role during rehydration, preventing stomatal opening in the absence of ABA through its own signaling pathway. These findings offer novel insights into the function of ethylene in stomatal regulation during dehydration and rehydration, giving a better understanding of the mechanisms underlying ethylene-induced stomatal movement in seed plants. [ABSTRACT FROM AUTHOR]

Leaf hydraulic traits are considered the key determinants of gas exchange and therefore affect species distributions along environmental gradients, but the patterns of leaf hydraulic traits and their associations with gas exchange across altitudinal gradients remain largely unknown.Here, we measured leaf hydraulic traits, gas exchange, leaf anatomical traits and plant size traits in two dominant alpine shrubs (Caragana jubata and Salix gilashanica) across an altitudinal gradient from 3100 to 3700 m.The findings indicated that with increasing altitude, both shrub species exhibited an increase in leaf hydraulic safety (more negative KleafP50), a decrease in leaf hydraulic efficiency (Kleaf‐max) and an increase in intrinsic water use efficiency (WUEi), thus allowing them to adapt to higher altitude habitats. The more negative KleafP50 was associated with a greater ratio of major to minor vein density (VLAmaj/VLAmin), the lower Kleaf‐max was associated with a lower minor vein density (VLAmin) and greater increase in WUEi arose from the small decrease in the photosynthetic rate relative to the stomatal conductance. However, C. jubata was consistent with the 'hydraulic safety strategy' with a great decrease in KleafP50, a small decrease in Kleaf‐max and a small increase in WUEi along with decreasing plant height and leaf area with increasing altitude. Whereas S. gilashanica was consistent with the 'photosynthetic efficiency strategy' with a small decrease in KleafP50, a greater decrease in Kleaf‐max and a greater increase in WUEi along with an increasing plant height and unchanged leaf area with increasing altitude.Overall, these findings provide new insights to improve understanding how shift in leaf hydraulic traits and their associations with gas exchange and plant size allow plants to adapt to high‐altitude habitats. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

ABSTRACT Determining the differences in flower hydraulic traits and structural resource allocation among closely related species adapted to low mean annual precipitation (MAP) can provide insight into plant adaptation to arid environments. Here, we measured the maximum flower hydraulic conductance (Kmax‐flower), water potential at induction 50% loss of Kmax‐flower (P50‐flower), flower pressure–volume parameters, dry mass of individual flowers and structural components (vexillum, wings, keels, stamens and sepals) of six Caragana species growing in regions ranging from 110 to 1400 mm MAP. Compared with species from high‐MAP environments, those from low‐MAP environments presented lower Kmax‐flower, more negative P50‐flower, osmotic potential at full turgor (πo) and turgor loss points (πtlp), and a greater bulk modulus of elasticity (ε). Consequently, a negative correlation between Kmax‐flower (hydraulic efficiency) and P50‐flower (hydraulic safety) was observed across Caragana species. Furthermore, the dry masses of individual flowers and structural components (vexillum, wings, keels, stamens and sepals) were greater in the species from the low‐MAP environment than in those from the high‐MAP environment. These findings suggest that greater flower hydraulic safety and drought tolerance combined with greater structural resource allocation promote drought adaptation in Caragana species to low‐MAP environments. [ABSTRACT FROM AUTHOR]

Wang et al. recently showed that, in soybean (Glycine max), root nodule formation is induced by a light-triggered signal that moves from the upper part of the plant to the roots. This novel signaling process opens a new area of research aimed to optimize the carbon–nitrogen balance in plant–rhizobium symbiosis. [ABSTRACT FROM AUTHOR]

Plastic pollution, particularly uncollected polythene fragments, has been identified as a significant driver of environmental change. This study investigated the effects of plastic fragments on soil multifunctionality (SMF) and bacterial communities in dryland ecosystems. The results showed that small and medium-sized fragments negatively impacted SMF, while large fragments had minimal effects. The study also found that the bacterial community characteristics and co-occurrence patterns played a crucial role in mediating the effects of plastic fragments on SMF. Overall, this research provides valuable insights into the long-term impacts of plastic pollution on soil ecosystems. [Extracted from the article]

While variation in mean annual precipitation (MAP) of the native habitat of a species has been shown to determine the ability of a species to resist a hydraulic decrease during drought, it remains unknown whether these variations in MAP also influence the ability of a species to recover and survive drought. Leaf hydraulic and gas exchange recovery following drought and the underlying mechanisms of these responses in six Caragana species from habitats along a large precipitation gradient were investigated during rehydration in a common garden. The gas exchange of species from arid habitats recovered more rapidly during rehydration after mild, moderate and severe drought stress treatments than species from humid habitats. The recovery of gas exchange was not associated with foliar abscisic acid concentration, but tightly related to the recovery of leaf hydraulic conductance (Kleaf). The recovery of Kleaf was associated with the loss of Kleaf during dehydration under mild and moderate drought stress, and to leaf xylem embolism formation under severe drought stress. Results pointed to the different ability to recover in gas exchange in six Caragana species post‐drought is associated with the MAP of the species in its native habitat. Summary Statement: Mean annual precipitation (MAP) has been shown to shape species' ability to resist a hydraulic dysfunction during drought. Our findings suggest that the ability to recover in gas exchange post‐drought as a strong driver in shaping species' distribution along a MAP gradient. [ABSTRACT FROM AUTHOR]

Clarifying the mechanisms underlying the recovery of gas exchange following drought is the key to providing insights into plant drought adaptation and habitat distribution. However, the mechanisms are still largely unknown. Targeting processes known to inhibit gas exchange during drought recovery, we measured leaf water potential, the leaf hydraulic conductance, stomatal reopening, abscisic acid (ABA) and the ethylene emission rate (EER) following moderate drought stress in seedlings of the globally pervasive woody tree Fraxinus chinensis. We found strong evidence that the slow stomatal reopening after rehydration is regulated by a slow decrease in EER, rather than changes in leaf hydraulics or foliar ABA levels. This was supported by evidence of rapid gas exchange recovery in plants after treatment with the ethylene antagonist 1-methylcyclopropene. These findings provide evidence to rigorously support ethylene as a key factor constraining stomatal reopening from moderate drought directly, thereby potentially opening new windows for understanding species drought adaptation. [ABSTRACT FROM AUTHOR]

Stomatal closure is regulated by plant hormones and some small molecules to reduce water loss under stress conditions. Both abscisic acid (ABA) and polyamines alone induce stomatal closure; however, whether the physiological functions of ABA and polyamines are synergistic or antagonistic with respect to inducing stomatal closure is still unknown. Here, stomatal movement in response to ABA and/or polyamines was tested in Vicia faba and Arabidopsis thaliana, and the change in the signaling components under stomatal closure was analyzed. We found that both polyamines and ABA could induce stomatal closure through similar signaling components, including the synthesis of hydrogen peroxide (H2O2) and nitric oxide (NO) and the accumulation of Ca2+. However, polyamines partially inhibited ABA‐induced stomatal closure both in epidermal peels and in planta by activating antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), to eliminate the ABA‐induced increase in H2O2. These results strongly indicate that polyamines inhibit abscisic acid‐induced stomatal closure, suggesting that polyamines could be used as potential plant growth regulators to increase photosynthesis under mild drought stress. [ABSTRACT FROM AUTHOR]

Plants secreted phytocytokine SMALL PHYTOCYTOKINES REGULATING DEFENSE AND WATER LOSS (SCREWs) and its receptor PLANT SCREW UNRESPONSIVE RECEPTOR (NUT) to counter abscisic acid (ABA)- and pathogen-induced stomatal closure (Liu et al.). This novel signaling process provides plants with a new strategy to increase immunity through disrupting an aqueous habitat for pathogen colonization. [ABSTRACT FROM AUTHOR]

Resprouting plants are distributed in many vegetation communities worldwide. With increasing resprout age post-severe-disturbance, new stems grow rapidly at their early age, and decrease in their growth with gradually decreasing water status thereafter. However, there is little knowledge about how stem hydraulic strategies and anatomical traits vary post-disturbance. In this study, the stem water potential (Ψ stem), maximum stem hydraulic conductivity (K stem-max), water potential at 50% loss of hydraulic conductivity (K stem   P 50) and anatomical traits of Caragana korshinkii resprouts were measured during a 1- to 13-year post-disturbance period. We found that the K stem-max decreased with resprout age from 1-year-old resprouts (84.2 mol m−1 s−1 MPa−1) to 13-year-old resprouts (54.2 mol m−1 s−1 MPa−1) as a result of decreases in the aperture fraction (F ap) and the sum of aperture area on per unit intervessel wall area (A ap). The K stem   P 50 of the resprouts decreased from 1-year-old resprouts (−1.8 MPa) to 13-year-old resprouts (−2.9 MPa) as a result of increases in vessel implosion resistance (t/b)2, wood density (WD), vessel grouping index (GI) and decreases in F ap and A ap. These shifts in hydraulic structure and function resulted in an age-based divergence in hydraulic strategies i.e. a change from an acquisitive strategy to a conservative strategy, with increasing resprout age post-disturbance. [ABSTRACT FROM AUTHOR]

It has been suggested that a trade‐off between hydraulic efficiency and safety is related to drought adaptation across species. However, whether leaf hydraulic efficiency is sacrificed for safety during woody resprout regrowth after crown removal is not well understood. We measured leaf water potential (ψleaf) at predawn (ψpd) and midday (ψmid), leaf maximum hydraulic conductance (Kleaf‐max), ψleaf at induction 50% loss of Kleaf‐max (KleafP50), leaf area‐specific whole‐plant hydraulic conductance (LSC), leaf vein structure and turgor loss point (πtlp) in 1‐ to 13‐year‐old resprouts of the aridland shrub (Caragana korshinskii). ψpd was similar, ψmid and KleafP50 became more negative, and Kleaf–max decreased in resprouts with the increasing age; thus, leaf hydraulic efficiency clearly traded off against safety. The difference between ψmid and KleafP50, leaf hydraulic safety margin, increased gradually with increasing resprout age. More negative ψmid and KleafP50 were closely related to decreasing LSC and more negative πtlp, respectively, and the decreasing Kleaf‐max arose from the lower minor vein density and the narrower midrib xylem vessels. Our results showed that a clear trade‐off between leaf hydraulic efficiency and safety helps C. korshinskii resprouts adapt to increasing water stress as they approach final size. A trade‐off between leaf hydraulic efficiency and safety is proposed to be related to drought adaptation, but it is still under debate. Here, leaf hydraulic efficiency clearly traded off against safety in resprouts of Caragana korshinskii, thus helping resprouts adapt to increasing water stress. [ABSTRACT FROM AUTHOR]

It is important to understand the changes in microbial properties of plant rhizospheres to elucidate the interaction between heavy metals and plant communities. In this study, high throughput sequencing method was used to analyze the effects of heavy metals on rhizosphere microbial community structure of the autochthonous plant Salsola collina in the Jinchuan mining area. The operational taxonomic units (OTU) number and species diversity, and richness of the bacterial community in the rhizosphere of Salsola collina were higher than those of the bulk soil. Proteobacteria, Actinobacteria, and Firmicutes were the major bacterial phyla, and Salsola collina, Kaistobacter, Citrobacter, Acinetobacter and Pseudomonas were the main genera. Principal component analysis (PCA) and unweighted pair group method using arithmetic average (UPGMA) cluster analysis showed that there were significant differences in bacterial community structure between site and between rhizosphere and bulk soil. The moisture content, total nitrogen, phosphorus, magnesium, nickel, chromium, lead, and zinc contents, and pH had significant effects on species richness of the bacterial community, with total phosphorus content having a significant effect on species diversity. The finding of this study could be used as an important guideline for bioremediation of heavy metals in mining area. [ABSTRACT FROM AUTHOR]

Summary: Plants control water‐use efficiency (WUE) by regulating water loss and CO2 diffusion through stomata. Variation in stomatal control has been reported among lineages of vascular plants, thus giving rise to the possibility that different lineages may show distinct WUE dynamics in response to water stress.Here, we compared the response of gas exchange to decreasing leaf water potential among four ferns and nine seed plant species exposed to a gradually intensifying water deficit. The data collected were combined with those from 339 phylogenetically diverse species obtained from previous studies.In well‐watered angiosperms, the maximum stomatal conductance was high and greater than that required for maximum WUE, but drought stress caused a rapid reduction in stomatal conductance and an increase in WUE in response to elevated concentrations of abscisic acid. However, in ferns, stomata did not open beyond the optimum point corresponding to maximum WUE and actually exhibited a steady WUE in response to dehydration. Thus, seed plants showed improved photosynthetic WUE under water stress.The ability of seed plants to increase WUE could provide them with an advantage over ferns under drought conditions, thereby presumably increasing their fitness under selection pressure by drought. [ABSTRACT FROM AUTHOR]

Drought is a cyclical phenomenon in natural environments. During dehydration, stomatal closure is mainly regulated by abscisic acid (ABA) dynamics that limit transpiration in seed plants, but following rehydration, the mechanism of gas exchange recovery is still not clear. In this study, leaf water potential (ψleaf), stomatal conductance (gs), leaf hydraulic conductance (Kleaf), foliar ABA level, ethylene emission rate in response to dehydration and rehydration were investigated in four Caragana species with isohydric (Caragana spinosa and C. pruinosa) and anisohydric (C. intermedia and C. microphylla) traits. Two isohydric species with ABA‐induced stomatal closure exhibited more sensitive gs and Kleaf to decreasing ψleaf than two anisohydric species which exhibited a switch from ABA to water potential‐driven stomatal closure during dehydration. Following rehydration, the recovery of gas exchange was not associated with a decrease in ABA level but was strongly limited by the degradation of the ethylene emission rate in all species. Furthermore, two anisohydric species with low drought‐induced ethylene production exhibited more rapid recovery in gas exchange upon rehydration. Our results indicated that ethylene is a key factor regulating the drought‐recovery ability in terms of gas exchange, which may shape species adaptation to drought and potential species distribution. Drought is a cyclical phenomenon in natural environments. During dehydration, stomatal closure is mainly regulated by abscisic acid (ABA) dynamics that limit transpiration in seed plants, but the mechanisms of gas exchange recovery are still not clear following rehydration. The results in this study indicate that ethylene is a key factor regulating the drought‐recovery ability in terms of gas exchange, which may shape species adaptation to drought and potential species distribution. [ABSTRACT FROM AUTHOR]

Summary: Clarifying the coordination of leaf hydraulic traits with gas exchange across closely‐related species adapted to varying rainfall can provide insights into plant habitat distribution and drought adaptation.The leaf hydraulic conductance (Kleaf), stomatal conductance (gs), net assimilation (A), vein embolism and abscisic acid (ABA) concentration during dehydration were quantified, as well as pressure–volume curve traits and vein anatomy in 10 Caragana species adapted to a range of mean annual precipitation (MAP) conditions and growing in a common garden.We found a positive correlation between Ψleaf at 50% loss of Kleaf (KleafP50) and maximum Kleaf (Kleaf‐max) across species. Species from low‐MAP environments exhibited more negative KleafP50 and turgor loss point, and higher Kleaf‐max and leaf‐specific capacity at full turgor, along with higher vein density and midrib xylem per leaf area, and a higher ratio of Kleaf‐max : maximum gs. Tighter stomatal control mediated by higher ABA accumulation during dehydration in these species resulted in an increase in hydraulic safety and intrinsic water use efficiency (WUEi) during drought.Our results suggest that high hydraulic safety and efficiency combined with greater stomatal sensitivity triggered by ABA production and leading to greater WUEi provides drought tolerance in Caragana species adapted to low‐MAP environments. [ABSTRACT FROM AUTHOR]

Brassinosteroids (BRs) are well recognized for their defensive role in plants under abiotic stress conditions, but 28-homobrassinolide (HBR)-induced tolerance to drought stress has not been reported in soybean (Glycine max L.). The present study investigated the effect of HBR on soybean seedlings under drought stress. Drought stress suppressed growth and photosynthetic systems while increased the proline, glycine betaine (GB), anthocyanin, total phenolic (TP), and total flavonoid (TF) levels in soybean seedlings. HBR restricted reactive oxygen species (ROS) accumulation and decreased the hydrogen peroxide (H2O2) and malondialdehyde (MDA) content by triggering the antioxidant systems. HBR acts as a shield in soybean, protecting the plant against the harmful effects of methylglyoxal (MG) effects by upregulating the enzymes glyoxalase I, (Gly I;15%) and glyoxalase II (Gly II;29.1%) compared to the levels in drought stressed seedlings. Overall, HBR improved drought tolerance in soybean seedlings by modulating osmolytes, the AsA–GSH cycle, and enzyme activities. [ABSTRACT FROM AUTHOR]

We evaluated the importance of conserved water use in drought adaptation in soybean [ Glycine max (L.) Merr.], and identified the traits involved in this mechanism. Eight soybean genotypes, four landraces and four recent cultivars, were collected and yield performance in the field was determined and used in pot experiments to evaluate the yield performance and the water use pattern under three soil moisture treatments imposed from 40 days after sowing: well-watered [WW, soil water content (SWC) maintained between 85%–100% field capacity (FC)]; water stress (WS, water withheld until SWC decreased to 30% FC, rewatered to 100% FC and water withheld again to 30% FC); and terminal water stress (TWS, water withheld until maturity). The recent cultivars all out-yielded the landraces in two different years in the field and under well-watered conditions in the pot experiment. Among the eight soybean genotypes, J19 and ZH – two recent cultivars with lower daily water use before flowering, but higher use after flowering – had the best yield performance in the WS and TWS treatments in the pot experiment and in the field. These two soybean genotypes and J19, another recent cultivar, had higher grain yield, hundred-grain weights and water use efficiency for grain yield (WUE G ) in the WS treatments than the other genotypes, and higher hundred grain weights, higher WUE G , higher pod numbers and the only significant grain yield in the TWS treatment. J19 and ZH had low root length densities (RLD), low leaf areas at flowering, and transpiration decreased at high plant available soil water content under drought. Thus, we conclude that reducing RLD and restricting water loss contributed to conserved water use and improved yield performance and WUE G in water-limited conditions. [ABSTRACT FROM AUTHOR]

Legume-based intercropping has the potentials for improving nitrogen (N) behavior in semiarid cereal production. Yet, it is unclear how the intercropped legume mediates the fate and benefits of fertilizer N in plastic film mulched cereal field. A two-year field experiment was conducted with cropping patterns, including maize monoculture, soybean monoculture and maize-soybean intercropping, with N levels (0, 180 and 225 kg N ha−1 for maize; 0 and 40 kg N ha−1 for soybean), and with and without plastic film mulching in maize. Both data qualification from the methods of N-difference and 15N isotope tracer confirmed that maize had a great enhancement of NUE when intercropped with soybean. The use of 180 kg N ha−1 with film mulching for intercropped maize resulted in the highest NUE with 61% 15N recovery, 40% N agronomic efficiency and 91 kg grain kg−1 N partial productivity. Under no mulching, intercropped maize with 180 kg N ha−1 had a 28% higher 15N recovery and 43% less 15N loss with 12% more fertilizer 15N allocation into maize grain than monoculture maize with 225 kg N ha−1. To some extent, this effect was amplified by film mulching. Interestingly, film mulching caused an overuse of soil-derived N in maize, and in this regard, an influence of 67.3% was eliminated by soybean-based intercropping. This deficiency of N was compensated by enhancing the use of fertilizer-derived N and soybean-transferred N (30 kg N ha−1) under low-N rate. The intercropping pattern FM180S40, i.e. film mulched maize with 180 kg N ha−1 and soybean with 40 kg N ha−1, had the highest N fertilization efficiency (FNER=1.29) due to the high land use efficiency (LER=1.19) and maize yield (14 Mg ha−1) with less N fertilizer use. Soybean-based intercropping and film mulching sustained a 20% reduction of N fertilizer based on the optimized N level (225 kg N ha−1) for dryland maize. This further induced a great intercropping advantage of N fertilization efficiency via high NUE of maize and positive processes of NUE formation in maize strips. This study highlights the key role of intercropped soybean in boosting N fertilization benefits and reducing N loss in semiarid film-mulched agriculture systems. [Display omitted] • Cereal NUE mechanism in legume-supported intercropping system was studied. • Labelled-15N confirmed the enhancements of maize NUE when intercropped with soybean. • More labelled-15N was translocated into maize grain for higher N fertilizer benefits. • Intercropped soybean significantly declined the overuse of soil-derived N by film mulched maize. • Intercropped soybean reduced fertilizer N loss for film mulched maize under low N conditions. [ABSTRACT FROM AUTHOR]

• Leaf N and leaf traits are key indicators of shifting photosynthesis (A). • Leaf traits explain the eco-physiological strategies to climate changes. • A mass is highly vulnerable to desert grass-shrubland and warm-temperate forest. • Variability in storage-N required for plant/leaf survival and maintenance. • Mass-based A and dark-respiration with N mass showed stronger affinity compared to area-based. Leaf functional traits profoundly impact the function of diverse-biomes under different environmental conditions. Thus, it is urgent to deeply understand how leaf traits and leaf nitrogen (N) develop photosynthesis adaptive-strategies across functional groups and biomes. We compiled information from previous studies on six diverse-biomes under different climates to determine the difference in functional groups (forbs, deciduous-shrubs, deciduous-trees, and evergreen-needle) and related traits: photosynthesis (A mass , A area), dark respiration (dR mass , dR area), N mass , N area , leaf life-span (LL), specific leaf area (SLA), and diffusive conductance (G s). Then, we used non-linear modeling to examine the A-dR responses to leaf N. Among the biomes, desert grass-shrubland (Colorado) and warm temperate forest (South Carolina) had lower A mass , N mass with lower SLA, while humid temperate forest (North Carolina) displayed higher A mass , N mass with higher SLA, indicating that species in desert grass-shrubland and warm temperate biomes adapt conservative strategies while humid temperate species adapt acquisitive strategies for leaf maintenance against limited N and climate conditions. Among functional groups, forbs had higher A mass , dR mass and N mass , deciduous-shrubs and trees had intermediate A mass , dR mass , and N mass , while evergreen-needle had lower A mass , dR mass with lower N mass. Forbs had minimum storage N (A store), deciduous-shrubs and trees had intermediate A store , while evergreen-needle had the highest A store. We concluded that forbs needed a minimum N-investment for leaf maintenance followed by deciduous and evergreen-needle. These results reveal that leaf N and leaf traits support adaptive-strategies for A-dR that regulate leaf maintenance and photosynthesis capacity under limited resources and environmental conditions. [ABSTRACT FROM AUTHOR]

Biological soil crust (BSC) establishment as a nature-based strategy (NbS) may restore the functionality of degraded soils in semiarid agroecosystems. However, this issue is little documented. To address this issue, a BSC-inoculated (broken-skin inoculation, moss) field experiment was conducted in a semiarid alfalfa (Medicago sativa L.) field in 2018 and 2019, with the treatments as follows: 1) conventional flat planting (control), 2) flat planting with BSC inoculation (BSC), 3) ridge-furrow planting (RF) and 4) sectional ridge-furrow planting (SRF). The result showed that compared with the control, alfalfa biomass was evidently increased in BSC, RF and SRF treatments at the second growing season. Relative to the control, the BSC treatment harvested the highest soil total porosity, mean weight diameter, and macroaggregate proportion (>2 mm) (p < 0.05; significantly greater than RF and SRF). Also, the BSC inoculation remarkably improved soil microbial biomass carbon (C) & nitrogen (N), soil organic C and total N by 46%, 35%, 16% and 29% respectively, also significantly greater than RF and SRF (p < 0.05). This phenomenon was tightly correlated with the optimized soil C fractions as affected by the BSC inoculation, since dissolved organic C, oxidizable organic C, particulate organic C, light fraction organic C and heavy fraction organic C were promoted by 17%, 29%, 13%, 40% and 14% in the BSC treatment respectively, relative to the control (p < 0.05). Therefore, the BSC inoculation significantly improved soil quality in alfalfa field. This outcome was closely associated with the increased soil cohesion and microaggregate proportion, and decreased soil C-N ratio under the BSC. The optimized physiochemical properties boosted C mineralization and the utilization of soil C & N by microbial organisms. Therefore, the BSC establishment can act as a promising NbS to conserve the degraded soils in semiarid agroecosystems. [Display omitted] • Biological soil crust (BSC) as nature-based strategy was tested in alfalfa field. • BSC improved stability of soil physical structure relative to flat planting. • BSC significantly enhanced soil liable carbon and microbial carbon & nitrogen. • BSC showed ecological advantages over natural ridge-furrow planting strategies. • BSC is a promising nature-based strategy to restore the degraded semiarid soils. [ABSTRACT FROM AUTHOR]

The self-thinning rule defines a straight upper boundary line on log-log scales for all possible combinations of mean individual biomass and density in plant populations. Recently, the traditional slope of the upper boundary line, −3/2, has been challenged by −4/3 which is deduced from some new mechanical theories, like the metabolic theory. More experimental or field studies should be carried out to identify the more accurate self-thinning exponent. But it's hard to obtain the accurate self-thinning exponent by fitting to data points directly because of the intrinsic problem of subjectivity in data selection. The virtual dynamic thinning line is derived from the competition-density (C-D) effect as the initial density tends to be positive infinity, avoiding the data selection process. The purpose of this study was to study the relationship between the virtual dynamic thinning line and the upper boundary line in simulated plant stands. Our research showed that the upper boundary line and the virtual dynamic thinning line were both straight lines on log-log scales. The slopes were almost the same value with only a very little difference of 0.059, and the intercept of the upper boundary line was a little larger than that of the virtual dynamic thinning line. As initial size and spatial distribution patterns became more uniform, the virtual dynamic thinning line was more similar to the upper boundary line. This implies that, given appropriate parameters, the virtual dynamic thinning line may be used as the upper boundary line in simulated plant stands. [ABSTRACT FROM AUTHOR]

γ-aminobutyric acid (GABA) is a non-protein amino acid involved in various physiological processes; it aids in the protection of plants against abiotic stresses, such as drought, heavy metals, and salinity. GABA tends to have a protective effect against drought stress in plants by increasing osmolytes and leaf turgor and reducing oxidative damage via antioxidant regulation. Guard cell GABA production is essential, as it may provide the benefits of reducing stomatal opening and transpiration and controlling the release of tonoplast-localized anion transporter, thus resulting in increased water-use efficiency and drought tolerance. We summarized a number of scientific reports on the role and mechanism of GABA-induced drought tolerance in plants. We also discussed existing insights regarding GABA's metabolic and signaling functions used to increase plant tolerance to drought stress. [ABSTRACT FROM AUTHOR]

Ozone (O3) is a gaseous environmental pollutant that can enter leaves through stomatal pores and cause damage to foliage. It can induce oxidative stress through the generation of reactive oxygen species (ROS) like hydrogen peroxide (H2O2) that can actively participate in stomatal closing or opening in plants. A number of phytohormones, including abscisic acid (ABA), ethylene (ET), salicylic acid (SA), and jasmonic acid (JA) are involved in stomatal regulation in plants. The effects of ozone on these phytohormones' ability to regulate the guard cells of stomata have been little studied, however, and the goal of this paper is to explore and understand the effects of ozone on stomatal regulation through guard cell signaling by phytohormones. In this review, we updated the existing knowledge by considering several physiological mechanisms related to stomatal regulation after response to ozone. The collected information should deepen our understanding of the molecular pathways associated with response to ozone stress, in particular, how it influences stomatal regulation, mitogen-activated protein kinase (MAPK) activity, and phytohormone signaling. After summarizing the findings and noting the gaps in the literature, we present some ideas for future research on ozone stress in plants [ABSTRACT FROM AUTHOR]

• ABA is involved in stomatal closure in ferns, gymnosperms and angiosperms. • P type and R type ABA responses occur during dehydration and rehydration in gymnosperms as well as angiosperms. • Increasing and decreasing behaviour of foliar ABA content in angiosperms during dehydration. The variation in stomatal movement across vascular plants in response to abscisic acid (ABA) has received great attention in recent years. This review is an attempt to better understand the role of ABA in the stomatal movement of seed and seedless plants under dehydration and rehydration. Seed plants, i.e., gymnosperms and angiosperms, have two divergent ABA responses, the peaking type (P-type) and rising type (R-type), to induce stomatal closure under sustained drought stress. However, in the case of ferns and lycophytes, stomata of almost all species exhibit insensitive (I-type) behaviour to ABA. Consequently, seed plants have evolved an optimized water use efficiency to improve their succession in terrestrial ecosystems. During rehydration, the recovery of gas exchange is constrained by ABA accumulation under drought in R-type plants and constrained by hydraulics in P- and I-type plants. Thus, future studies should investigate the mechanisms underlying the divergence in stomata in response to ABA, focusing on P-type vs. R-type ABA responses in seed plants, the competition of seed plants, and the interaction between ABA and hydraulic pathways during rehydration. [ABSTRACT FROM AUTHOR]

In recent years, research on spermine (Spm) has turned up a lot of new information about this essential polyamine, especially as it is able to counteract damage from abiotic stresses. Spm has been shown to protect plants from a variety of environmental insults, but whether it can prevent the adverse effects of drought has not yet been reported. Drought stress increases endogenous Spm in plants and exogenous application of Spm improves the plants' ability to tolerate drought stress. Spm's role in enhancing antioxidant defense mechanisms, glyoxalase systems, methylglyoxal (MG) detoxification, and creating tolerance for drought-induced oxidative stress is well documented in plants. However, the influences of enzyme activity and osmoregulation on Spm biosynthesis and metabolism are variable. Spm interacts with other molecules like nitric oxide (NO) and phytohormones such as abscisic acid, salicylic acid, brassinosteroids, and ethylene, to coordinate the reactions necessary for developing drought tolerance. This review focuses on the role of Spm in plants under severe drought stress. We have proposed models to explain how Spm interacts with existing defense mechanisms in plants to improve drought tolerance. [ABSTRACT FROM AUTHOR]