Ectomycorrhizal symbiosis prepares its host locally and systemically for abiotic cue signaling.

Tree growth and survival are dependent on their ability to perceive signals, integrate them, and trigger timely and fitted molecular and growth responses. While ectomycorrhizal symbiosis is a predominant tree-microbe interaction in forest ecosystems, little is known about how and to what extent it helps trees cope with environmental changes. We hypothesized that the presence of Laccaria bicolor influences abiotic cue perception by Populus trichocarpa and the ensuing signaling cascade. We submitted ectomycorrhizal or non-ectomycorrhizal P. trichocarpa cuttings to short-term cessation of watering or ozone fumigation to focus on signaling networks before the onset of any physiological damage. Poplar gene expression, metabolite levels, and hormone levels were measured in several organs (roots, leaves, mycorrhizas) and integrated into networks. We discriminated the signal responses modified or maintained by ectomycorrhization. Ectomycorrhizas buffered hormonal changes in response to short-term environmental variations systemically prepared the root system for further fungal colonization and alleviated part of the root abscisic acid (ABA) signaling. The presence of ectomycorrhizas in the roots also modified the leaf multi-omics landscape and ozone responses, most likely through rewiring of the molecular drivers of photosynthesis and the calcium signaling pathway. In conclusion, P. trichocarpa-L. bicolor symbiosis results in a systemic remodeling of the host's signaling networks in response to abiotic changes. In addition, ectomycorrhizal, hormonal, metabolic, and transcriptomic blueprints are maintained in response to abiotic cues, suggesting that ectomycorrhizas are less responsive than non-mycorrhizal roots to abiotic challenges.

Root relative water content is a potential signal for impending mortality of a subtropical conifer during extreme drought stress.

Adaptation to future climates characterized by more frequent severe droughts requires enhanced mechanistic understanding of tree mortality. However, our knowledge of the physiological limits to withstand extreme drought, and how the coordination between water and carbon traits enhances survival, is still limited. Potted seedlings of Pinus massoniana were dehydrated to three target droughts (percentage loss of stem hydraulic conductivity of ca. 50%, 85%, and 100%; PLC50 , PLC85 and PLC100 ) and then relieved from these target droughts by fully rewatering. Predawn and midday water potentials (Ψ), relative water content (RWC), PLC and nonstructural carbohydrates (NSC) were monitored. During drought, Ψ and RWC declined as PLC increased. Root RWC declined more rapidly than other organ RWCs, particularly after PLC50 stress. All organ NSC concentrations were above predrought values. During rewatering, water trait recovery declined as drought increased, with no mortality at PLC50 but 75% mortality at PLC85 . The observed stem hydraulic recovery at PLC50 following rewatering was not correlated to NSC dynamics. Collectively, our results highlighted the primary role of hydraulic failure in Pinus massoniana seedling mortality by assessing mortality threshold and links among water status and water supply. Root RWC can be considered as a potential warning signal of P. massoniana mortality.

Unusual characteristics of the carbon cycle during the 2015-2016 El Niño.

The 2015-2016 El Niño was one of the strongest on record, but its influence on the carbon balance is less clear. Using Northern Hemisphere atmospheric CO2 observations, we found both detrended atmospheric CO2 growth rate (CGR) and CO2 seasonal-cycle amplitude (SCA) of 2015-2016 were much higher than that of other El Niño events. The simultaneous high CGR and SCA were unusual, because our analysis of long-term CO2 observations at Mauna Loa revealed a significantly negative correlation between CGR and SCA. Atmospheric inversions and terrestrial ecosystem models indicate strong northern land carbon uptake during spring but substantially reduced carbon uptake (or high emissions) during early autumn, which amplified SCA but also resulted in a small anomaly in annual carbon uptake of northern ecosystems in 2015-2016. This negative ecosystem carbon uptake anomaly in early autumn was primarily due to soil water deficits and more litter decomposition caused by enhanced spring productivity. Our study demonstrates a decoupling between seasonality and annual carbon cycle balance in northern ecosystems over 2015-2016, which is unprecedented in the past five decades of El Niño events.

Differential adaptation strategies to different levels of soil water deficit in two upland and lowland genotypes of rice: a physiological and metabolic approach.

BACKGROUND: Upland genotypes of rice are less sensitive to soil water deficit (SWD), making them suitable candidates for revealing the strategies underlying plant tolerance. The physiological factors, the biochemical traits needed to withstand oxidative stress, and the metabolite fluctuations of an upland genotype (Azucena) and an intolerant lowland genotype (IR64) genotype were measured under two levels of SWD (withholding water for 7- or 14 days) to identify SWD-responsive strategies associated with tolerance. RESULTS: After withholding water for 7 days, no significant changes in physiological and biochemical traits of Azucena were observed, whereas in IR64, significant decreases in physiological factors were recorded along with increases in oxidative-stress indicators. However, the root length of Azucena increased significantly, showing a clear stress avoidance strategy. Under a prolonged treatment (14 days), IR64 entered an oxidative-damage stage, whereas Azucena exhibited a highly efficient antioxidant system. Our metabolite analysis also revealed two different enriched pathways. After a 7-day SWD, the sugar levels were decreased in the leaves of Azucena but increased in IR64. The reduction in the sugar levels (up to 1.79-log2FC) in the Azucena leaves may be indicative of their transport to the roots, supplying the carbon source needed for root elongation. Under a 14-day treatment, proline and aspartate family members accumulated to the highest levels in Azucena, whereas an increase in the levels of aromatic amino acids with key roles in the biosynthesis of secondary metabolites was detected in IR64. CONCLUSION: The adaptation strategies identified in two types of rice genotypes in confronting SWD may assist researchers in finding the proper indicators for screening more tolerant genotypes. © 2019 Society of Chemical Industry.

Can the development of drought tolerant ideotype sustain Australian chickpea yield?

Terminal drought is a major problem in many areas where chickpea is grown on stored soil moisture. This is exacerbated by the lack of a targeted breeding approach focusing on key traits contributing to yield formation under water-limited conditions. There is no study to develop a chickpea ideotype and test it against commercial varieties under various management systems across the Australian grain belt. This study proposed a chickpea ideotype that can be grown in water deficit areas and compared its performance with commercial chickpea genotypes across the Australian grain belt. Important traits for ideotype construction and breeding were identified and tested against selected commercial varieties in silico in the Australian grain belt using the APSIM crop model. The key phenological, morphological and physiological traits were determined in the field at the University of Sydney's IA Watson Grains Research Centre near Narrabri for ideotype targeting. Five commercial chickpea genotypes (Sonali, PBA Hattrick, Kyabra, Tyson and Amethyst) were selected for evaluation against the chickpea ideotype. The constructed chickpea ideotype showed 76% resemblance to Sonali which performed well under water limited conditions. Simulated yield ranged from 760 to 3902 kg/ha across the Australian grain belt, with consistently higher yield in the ideotype compared with the commercial cultivars. The growing environments were grouped into three major clusters using the soil water deficit method with varying water stress levels. It is evident that grain filling is the most critical stage where soil moisture deficit caused chickpea yield losses up to 16.5% in the present study. By incorporating key target traits and targeting the right environment, chickpea yields can be sustained in the Australian grain belt or in an area having similar agro-ecological characteristics.

Cocoa agroforestry is less resilient to sub-optimal and extreme climate than cocoa in full sun.

Cocoa agroforestry is perceived as potential adaptation strategy to sub-optimal or adverse environmental conditions such as drought. We tested this strategy over wet, dry and extremely dry periods comparing cocoa in full sun with agroforestry systems: shaded by (i) a leguminous tree species, Albizia ferruginea and (ii) Antiaris toxicaria, the most common shade tree species in the region. We monitored micro-climate, sap flux density, throughfall, and soil water content from November 2014 to March 2016 at the forest-savannah transition zone of Ghana with climate and drought events during the study period serving as proxy for projected future climatic conditions in marginal cocoa cultivation areas of West Africa. Combined transpiration of cocoa and shade trees was significantly higher than cocoa in full sun during wet and dry periods. During wet period, transpiration rate of cocoa plants shaded by A. ferruginea was significantly lower than cocoa under A. toxicaria and full sun. During the extreme drought of 2015/16, all cocoa plants under A. ferruginea died. Cocoa plants under A. toxicaria suffered 77% mortality and massive stress with significantly reduced sap flux density of 115 g cm-2  day-1 , whereas cocoa in full sun maintained higher sap flux density of 170 g cm-2  day-1 . Moreover, cocoa sap flux recovery after the extreme drought was significantly higher in full sun (163 g cm-2  day-1 ) than under A. toxicaria (37 g cm-2  day-1 ). Soil water content in full sun was higher than in shaded systems suggesting that cocoa mortality in the shaded systems was linked to strong competition for soil water. The present results have major implications for cocoa cultivation under climate change. Promoting shade cocoa agroforestry as drought resilient system especially under climate change needs to be carefully reconsidered as shade tree species such as the recommended leguminous A. ferruginea constitute major risk to cocoa functioning under extended severe drought.

Evaluation of the effects of mulch on optimum sowing date and irrigation management of zero till wheat in central Punjab, India using APSIM.

Machinery for sowing wheat directly into rice residues has become more common in the rice-wheat systems of the north-west Indo-Gangetic Plains of South Asia, with increasing numbers of farmers now potentially able to access the benefits of residue retention. However, surface residue retention affects soil water and temperature dynamics, thus the optimum sowing date and irrigation management for a mulched crop may vary from those of a traditional non-mulched crop. Furthermore, the effects of sowing date and irrigation management are likely to vary with soil type and seasonal conditions. Therefore, a simulation study was conducted using the APSIM model and 40 years of weather data to evaluate the effects of mulch, sowing date and irrigation management and their interactions on wheat grain yield, irrigation requirement (I) and water productivity with respect to irrigation (WPI) and evapotranspiration (WPET). The results suggest that the optimum wheat sowing date in central Punjab depends on both soil type and the presence or absence of mulch. On the sandy loam, with irrigation scheduled at 50% soil water deficit (SWD), the optimum sowing date was late October to early November for maximising yield, WPI and WPET. On the clay loam, the optimum date was about one week later. The effect of mulch on yield varied with seasonal conditions and sowing date. With irrigation at 50% SWD, mulching of wheat sown at the optimum time increased average yield by up to 0.5 t ha-1. The beneficial effect of mulch on yield increased to averages of 1.2-1.3 t ha-1 as sowing was advanced to 15 October. With irrigation at 50% SWD and 7 November sowing, mulch reduced the number of irrigations by one in almost 50% of years, a reduction of about 50 mm on the sandy loam and 60 mm on the clay loam. The reduction in irrigation amount was mainly due to reduced soil evaporation. Mulch reduced irrigation requirement by more as sowing was delayed, more so on the sandy loam than the clay loam soil. There was little effect of mulch on irrigation requirement for late October sowings. There were large trade-offs between irrigation input, yield, WPET and WPI on the sandy loam with regard to the optimum irrigation schedule. Maximum yield occurred with very frequent irrigation (10-20% SWD) which also had the greatest irrigation input, while WPI was highest with least frequent irrigation (70% SWD), and WPET was highest with irrigation at 40-50% SWD. This was the case with and without mulch. On the clay loam, the trade-offs were not so pronounced, as maximum yield was reached with irrigation at 50% SWD, with and without mulch. However, both WPET and WPI were maximum and irrigation input least at the lowest irrigation frequency (70% SWD). On both soils, maximum yield, WPET and WPI were higher with mulch, while irrigation input was slightly lower, but mulch had very little effect on the irrigation thresholds at which each parameter was maximised.

Threshold response of stomatal closing ability to leaf abscisic acid concentration during growth.

Leaf abscisic acid concentration ([ABA]) during growth influences morpho-physiological traits associated with the plant's ability to cope with stress. A dose-response curve between [ABA] during growth and the leaf's ability to regulate water loss during desiccation or rehydrate upon re-watering was obtained. Rosa hybrida plants were grown at two relative air humidities (RHs, 60% or 90%) under different soil water potentials (-0.01, -0.06, or -0.08MPa) or upon grafting onto the rootstock of a cultivar sustaining [ABA] at elevated RH. Measurements included [ABA], stomatal anatomical features, stomatal responsiveness to desiccation, and the ability of leaves, desiccated to varying degrees, to recover their weight (rehydrate) following re-watering. Transpiration efficiency (plant mass per transpired water) was also determined. Soil water deficit resulted in a lower transpiration rate and higher transpiration efficiency at both RHs. The lowest [ABA] was observed in well-watered plants grown at high RH. [ABA] was increased by soil water deficit or grafting, at both RHs. The growth environment-induced changes in stomatal size were mediated by [ABA]. When [ABA] was increased from the level of (well-watered) high RH-grown plants to the value of (well-watered) plants grown at moderate RH, stomatal responsiveness was proportionally improved. A further increase in [ABA] did not affect stomatal responsiveness to desiccation. [ABA] was positively related to the ability of dehydrated leaves to rehydrate. The data indicate a growth [ABA]-related threshold for stomatal sensitivity to desiccation, which was not apparent either for stomatal size or for recovery (rehydration) upon re-watering.

A biomarker based on gene expression indicates plant water status in controlled and natural environments.

Plant or soil water status is required in many scientific fields to understand plant responses to drought. Because the transcriptomic response to abiotic conditions, such as water deficit, reflects plant water status, genomic tools could be used to develop a new type of molecular biomarker. Using the sunflower (Helianthus annuus L.) as a model species to study the transcriptomic response to water deficit both in greenhouse and field conditions, we specifically identified three genes that showed an expression pattern highly correlated to plant water status as estimated by the pre-dawn leaf water potential, fraction of transpirable soil water, soil water content or fraction of total soil water in controlled conditions. We developed a generalized linear model to estimate these classical water status indicators from the expression levels of the three selected genes under controlled conditions. This estimation was independent of the four tested genotypes and the stage (pre- or post-flowering) of the plant. We further validated this gene expression biomarker under field conditions for four genotypes in three different trials, over a large range of water status, and we were able to correct their expression values for a large diurnal sampling period.

Effect of Water Stress and Shading on Lime Yield and Quality.

The aim of this study was to test the combined effect of water stress and cropping system on yield and fruit quality in Bearss lime trees. For this purpose, two irrigation treatments were applied during stage II of fruit growth: control (well irrigated, automatically managed by soil water content sensors) and stress (non-irrigated), both under open-field and shaded conditions. Soil water status was assessed by determining soil water content and plant water status by measuring stem water potential (Ψstem), stomatal conductance (gs), and net photosynthesis (Pn). Yield parameters (kg and the number of fruits per tree and fresh mass per fruit) and fruit quality were assessed on two harvest dates. In addition, on the second harvest date, the content of metabolites and nutrients in the lime juice was analyzed. The results showed that soil water deficit induced 35% lower gs values in open-field than in shaded conditions. The highest kg and the number of fruits per tree were observed in the shaded system, especially on the first harvest date. The lowest yield was observed in stressed trees grown without netting. Slightly higher fresh mass and equatorial diameter were observed in shaded fruits than in open-field fruit. Soil water deficit increased fruit total soluble solids and decreased juice content, especially in open-field trees. Shaded conditions made the lime trees more resilient to soil water deficit, which led to higher yields and better external fruit quality traits. In addition, fruit precocity was significantly higher in the shaded system.

The prolonged effect of film mulch and P application on lucerne forage yield in a semiarid environment.

Introduction: Limited water and soil phosphorus (P) availability often hampers lucerne productivity in semiarid regions. Plastic film mulch and P application typically enhance young lucerne (2-3 years) productivity by increasing soil water use and P availability. However, the prolonged impact of film mulch and P application on lucerne productivity as the stand ages remains unclear. Methods: This study conducted a 9-year field experiment on the semiarid Loess Plateau to investigate how film mulch and P application affect lucerne forage yield, soil water content, and soil fertility. The field experiment used a split-plot design with randomized blocks, in which the whole plots were with (M1) and without plastic film mulch (M0), and the split plots were four P rates (0 (P0), 9.7 (P1), 19.2 (P2), and 28.8 (P3) kg P ha-1). Results and discussion: The M1 treatment produced significantly higher lucerne forage yields than the M0 treatment during the first five years, but the yield-increasing effect of film mulch gradually diminished over time, with no effect in Years 6-8, and lower yields than the M0 treatment in Year 9. Phosphorus fertilization significantly increased forage yield after Year 3 in the M0 treatment, but only in Years 3-5 in the M1 treatment. In Years 2-5, film mulch significantly increased soil organic carbon, total nitrogen (N), inorganic N, and microbial biomass carbon in P0, P1, and P2 but not in P3. However, in Years 7-9, film mulch significantly decreased soil available potassium (K), organic carbon mineralization, lucerne density, and shoot K concentration, but did not reduce soil N and P availability at any level P of application. Moreover, plastic film mulch significantly increased the soil water content at 0-300 cm deep from Year 7 onwards. In conclusion, film mulch ceased to enhance lucerne production beyond year 6, which could not be attributed to soil water content, N or P availability but was partially associated with reduced soil K availability. Consequently, future research should focus on soil K availability, and K addition should be considered after five years in lucerne pastures mulched with plastic film in semiarid areas.

The Process of Soil Desiccation under Haloxylon ammodendron Plantations: A Case Study of the Alxa Legue Desert, China.

Haloxylon ammodendron is a desert shrub widely used as a windbreak and for sand fixation, and it has achieved remarkable results in China. However, in desert areas, large-scale afforestation increases soil water consumption and forms a dried soil layer (DSL), the development of which seriously threatens the sustainable development of the ecosystem. In this study, soil moisture in the 0-400 cm soil profile was measured in selected 5-, 11-, 22-, 34-, and 46-year-old plantations of Haloxylon ammodendron plantations in Alxa Legue, China, and three soil desiccation evaluation indices were calculated-the soil desiccation index (SDI), DSL thickness (DSLT), and DSL soil water content (DSL-SWC)-to analyze the change pattern of the soil water content for different stand ages. The results showed that the shallow water layer (0-200 cm) was depleted sharply in the first five years of Haloxylon ammodendron plantation growth, but no DSL developed; the inflection point of soil water content change appeared after 10 years of growth, after which the shallow soil water was depleted and the drying process of the deep soil water content was significantly faster than that in the early growth period. The deep soil layer (200-400 cm) was depleted seriously after 22 years of afforestation, the soil drying phenomenon was obvious, and the DSL developed from the 172 cm soil layer. After 46 years of afforestation, the DSL was fully developed and the DSL-SWC was only 0.034 cm3 cm-3. Priority should thus be given to the use of less water-consuming shrub species; alternatively, after 5 years of growth of Haloxylon ammodendron plantations, certain water control measures should be taken to maintain the soil water balance.

Controlling gully- and revegetation-induced dried soil layers across a slope-gully system.

The introduction of exotic plants and improper management strategies with regard to plant species can change the soil-water balance of deep soils, which in turn results in the formation of a dried soil layer (DSL) within the soil profile. The Loess Plateau (LP) of China has a complex terrain; however, only a few studies have evaluated the effects of the gully-induced DSL patterns, especially in hilly and gully regions of the northern LP. In this study, we collected soil-water content data to a depth of 5 m at 40 sampling sites in a slope-gully system to investigate and characterize DSLs and their spatial patterns. Results show that the DSL indices vary greatly in different slope positions. The thickness of DSLs (DSLT) and quantitative index (QI) in the gully were significantly (p < 0.05) higher than those in the non-gully areas. The relative contribution of soil properties was higher than those of terrain factors in the gully, whereas the contribution of terrain factors was higher than those of soil properties under shrubland. Gullies contributed to the complex spatial DSL patterns in the slope-gully system. Partial least squares regression (PLSR) was used to detect the relative significance of 10 selected environmental factors that affect spatial DSL patterns. Variable importance in projection (VIP) demonstrated that soil properties, especially Clay and Silt content, significantly influenced the DSL formation depth (DSLFD), DSLT, and QI. Land-use and slope position were the most important factors that influenced the mean soil-water content (SWC) within DSLs (DSL-SWC), which exhibited the highest VIP values. PLSR models simulated DSL indices accurately in DSL-SWC; the values for variation in response (R2) and goodness of prediction (Q2) were 0.94 and 0.92, respectively. Therefore, our findings provide a helpful base reference for DSL management and reclamation of hill and gully regions of the LP.

Plant survival under drought stress: Implications, adaptive responses, and integrated rhizosphere management strategy for stress mitigation.

In many regions of the world, the incidence and extent of drought spells are predicted to increase which will create considerable pressure on global agricultural yields. Most likely among all the abiotic stresses, drought has the strongest effect on soil biota and plants along with complex environmental effects on other ecological systems. Plants being sessile appears the least resilient where drought creates osmotic stress, limits nutrient mobility due to soil heterogeneity, and reduces nutrient access to plant roots. Drought tolerance is a complex quantitative trait controlled by many genes and is one of the difficult traits to study and characterize. Nevertheless, existing studies on drought have indicated the mechanisms of drought resistance in plants on the morphological, physiological, and molecular basis and strategies have been devised to cope with the drought stress such as mass screening, breeding, marker-assisted selection, exogenous application of hormones or osmoprotectants and or engineering for drought resistance. These strategies have largely ignored the role of the rhizosphere in the plant's drought response. Studies have shown that soil microbes have a substantial role in modulation of plant response towards biotic and abiotic stress including drought. This response is complex and involves alteration in host root system architecture through hormones, osmoregulation, signaling through reactive oxygen species (ROS), induction of systemic tolerance (IST), production of large chain extracellular polysaccharides (EPS), and transcriptional regulation of host stress response genes. This review focuses on the integrated rhizosphere management strategy for drought stress mitigation in plants with a special focus on rhizosphere management. This combinatorial approach may include rhizosphere engineering by addition of drought-tolerant bacteria, nanoparticles, liquid nano clay (LNC), nutrients, organic matter, along with plant-modification with next-generation genome editing tool (e.g., CRISPR/Cas9) for quickly addressing emerging challenges in agriculture. Furthermore, large volumes of rainwater and wastewater generated daily can be smartly recycled and reused for agriculture. Farmers and other stakeholders will get a proper knowledge-exchange and an ideal road map to utilize available technologies effectively and to translate the measures into successful plant-water stress management. The proposed approach is cost-effective, eco-friendly, user-friendly, and will impart long-lasting benefits on agriculture and ecosystem and reduce vulnerability to climate change.

Soil Water Deficit and Fertilizer Placement Effects on Root Biomass Distribution, Soil Water Extraction, Water Use, Yield, and Yield Components of Soybean [Glycine max (L.) Merr.] Grown in 1-m Rooting Columns.

Typical small-pot culture systems are not ideal for controlled environment phenotyping for drought tolerance, especially for root-related traits. We grew soybean plants in a greenhouse in 1-m rooting columns filled with amended field soil to test the effects of drought stress on water use, root growth, shoot growth, and yield components. There were three watering treatments, beginning at first flower: watered daily to 100% of the maximum soil water holding capacity (control), 75% (mild drought stress), or 50% (drought stress). We also tested whether applying fertilizer throughout the 1-m soil depth instead of only in the top 30 cm would modify root distribution by depth in the soil profile and thereby affect responses to drought stress. Distributing the fertilizer over the entire 1-m soil depth altered the root biomass distribution and volumetric soil water content profile at first flower, but these effects did not persist to maturity and thus did not enhance drought tolerance. Compared to the control (100%) watering treatment, the 50% watering treatment significantly reduced seed yield by 40%, pod number by 42%, seeds per pod by 3%, shoot dry matter by 48%, root dry matter by 53%, and water use by 52%. Effects of the 75% watering treatment were intermittent between the 50 and 100%. The 50% treatment significantly increased root-to-shoot dry matter ratio by 23%, harvest index by 17%, and water-use efficiency by 7%. Seed size was not affected by either fertilizer or watering treatments. More than 65% of the total root dry matter was distributed in the upper 20 cm of the profile in all watering treatments. However, the two drought stress treatments, especially the mild drought stress, had a greater proportion of root dry matter located in the deeper soil layers. The overall coefficient of variation for seed yield was low at 5.3%, suggesting good repeatability of the treatments. Drought stress imposed in this culture system affected yield components similarly to what is observed in the field, with pod number being the component most strongly affected. This system should be useful for identifying variation among soybean lines for a wide variety of traits related to drought tolerance.

MdHB-7 Regulates Water Use Efficiency in Transgenic Apple (Malus domestica) Under Long-Term Moderate Water Deficit.

Improved water use efficiency (WUE) promotes plant survival and crop yield under water deficit conditions. Although the plant-specific HD-Zip I transcription factors have important roles in plant adaptation to various abiotic stresses, including water deficit, their functions in regulating WUE of apple (Malus domestica) are poorly understood. We characterized the role of MdHB-7 in WUE regulation by subjecting MdHB-7 transgenic plants to long-term moderate soil water deficit. The long-term WUE (WUEL) of transgenic apple plants with MdHB-7 overexpression or MdHB-7 RNA interference (RNAi) differed significantly from that of control plants. Upregulation of MdHB-7 caused reduced stomatal density, whereas the suppression of MdHB-7 increased stomatal density under both normal and long-term moderate soil water deficit conditions. Moderate reduction in stomatal density helped to improve the WUE of MdHB-7 overexpression transgenic plants, especially under water deficit conditions. MdHB-7 overexpression plants maintained high rates of photosynthesis that were conducive to the accumulation of biomass and the improvement of WUEL. MdHB-7 overexpression also alleviated the inhibition of root growth caused by long-term moderate soil water deficit and improved root vitality and hydraulic conductivity, which were essential for improving plant WUEL. By contrast, MdHB-7 RNA interference reduced the WUEL of transgenic plants by inhibiting these factors under normal and long-term moderate soil water deficit conditions. Taken together, our results provide solid evidence for a crucial role of MdHB-7 in the regulation of apple WUEL and provide new insights for improving the WUE of apple plants under moderate soil water deficit.

A transcriptomic analysis reveals the adaptability of the growth and physiology of immature tassel to long-term soil water deficit in Zea mays L.

Drought is a key threat to maize growth and yield. Understanding the mechanism of immature tassel (IT) response to long term drought is of paramount importance. Here, the maize inbred line PH6WC was tested under well-watered (CK) and two water deficit treatments (WD1 and WD2). The final IT length in the WD1 and WD2 treatments decreased by nearly 6.2% and 21.2% compared to the CK, respectively, and the average accumulation rate IT dry matter was 1.5-fold and 1.8-fold slower, respectively. Furthermore, RNA sequencing analysis was conducted on the IT sampled at 30 days after the WD treatments. In total, the cellular component in gene ontology (GO) analysis suggested that the differentially expressed genes were significantly enriched in three common terms (apoplast, plant-type cell wall, and anchored component of membrane) among the CK vs WD1, CK vs WD2, and WD1 vs WD2 comparisons. Next, a co-expression network analysis identified 44 modules that contained global expression genes. Finally, by combining the GO analysis with modules, nine genes involved in carbohydrate metabolism and the antioxidant system were screened out, and the six corresponding physiological parameters were all significantly increased under the WD treatments. These results showed that, although the IT length and dry matter decreased, the IT enhanced the adaptation to drought by regulating their own genetic and physiological changes.

Combining infiltration holes and level ditches to enhance the soil water and nutrient pools for semi-arid slope shrubland revegetation.

Active vegetation restoration has been proposed as an effective approach for restoring degraded ecosystems. Soil water and nutrient deficits hinder slope revegetation in arid and semi-arid areas. However, few studies have discussed rainfall runoff utilization and soil nutrient conservation within the context of slope vegetation restoration. In this study, the effects of combining infiltration holes and level ditches on the soil water storage, organic matter, and total nitrogen were analyzed on the slopes of shrubland and bare land. The results showed that the combined measures significantly increased the average soil water content above the 100 cm soil layer and mitigated soil desiccation below 220 cm in the shrubland. Meanwhile, the combined measures obviously increased the soil organic matter and total nitrogen above the 60 and 40 cm soil layers in bare land and shrubland, respectively. Overall, combining infiltration holes and landscape engineering measures is an effective approach for enhancing the soil water and nutrient pools of slopes. Our findings provide an effective engineering measure to combat soil water and nutrient deficits for slope vegetation restoration in arid and semi-arid areas.

Short-term nitrogen dynamics are impacted by defoliation and drought in Fagus sylvatica L. branches.

The predicted recurrence of adverse climatic events such as droughts, which disrupt nutrient accessibility for trees, could jeopardize the nitrogen (N) metabolism in forest trees. Internal tree N cycling capacities are crucial to ensuring tree survival but how the N metabolism of forest trees responds to intense, repeated environmental stress is not well known. For 2 years, we submitted 9-year-old beech (Fagus sylvatica L.) trees to either a moderate or a severe prolonged drought or a yearly removal of 75% of the foliage to induce internal N cycling changes. During the second year of stress, in spring and summer, we sprayed 15N-urea on the leaves (one branch per tree). Then, for 14 days, we traced the 15N dynamics through the leaves, into foliar proteins and into the branch compartments (leaves and stems segments), as well as its long-distance transfer from the labeled branches to the tree apical twigs. Defoliation caused a short- and mid-term N increase in the leaves, which remained the main sink for N. Whatever the treatment and the date, most of the leaf 15N stayed in the leaves and was invested in soluble proteins (60-68% of total leaf N). 15N stayed more in the proximal part of the branch in response to drought compared with other treatments. The long-distance transport of N was maintained even under harsh drought, highlighting efficient internal N recycling in beech trees. Under extreme constraints creating an N and water imbalance, compensation mechanisms operated at the branch level in beech trees and allowed them (i) to maintain leaf N metabolism and protein synthesis and (ii) to ensure the seasonal short- and long-distance transfer of recycled leaf N even under drastic water shortage conditions.

Deep rooted apple trees decrease groundwater recharge in the highland region of the Loess Plateau, China.

Unlike recharge in shallow rooted ecosystems, estimating the groundwater recharge beneath deep rooted plants that absorb water from deep soil remains difficult. The purpose of this research is to develop an approach to estimate the groundwater recharge beneath deep-rooted vegetation by combining water mass balance and chloride mass balance (CMB) and to quantify how the conversion of shallow-rooted cropland to deep-rooted apple orchards changes groundwater recharge. The proposed groundwater recharge rate under deep-rooted vegetation in this study is the difference between the groundwater recharge rate in a cropland (obtained using CMB) and the mean annual soil water storage deficit beneath an adjacent deep-rooted vegetation. The results show that the conversion from cropland (shallow-rooted) to apple orchard (deep-rooted) decreased soil water storage by 776, 1106, and 1117mm, corresponding to 19, 20, and 26-year-old apple orchards, respectively. Groundwater recharge beneath cropland, on average, was 58mmyr-1, which amounts to 10% of the average annual precipitation. Groundwater recharge beneath the apple orchards were variable, but all being <3% of the average annual precipitation. The conversion of cropland to apple orchards lead to a substantial decrease in groundwater recharge, potentially threatening the sustainability of the land use change.