Responses of oak seedlings to increased herbivory and drought: a possible trade-off?

BACKGROUND AND AIMS: Anthropogenic disturbances are causing a co-occurring increase in biotic (ungulate herbivory) and abiotic (drought) stressors, threatening plant reproduction in oak-dominated ecosystems. However, we wonder whether herbivory could compensate for the adverse impact of drought by reducing evapotranspiration. Thus, we investigate the isolated and joint effects of herbivory and drought on oak seedlings of two contrasting Mediterranean species that differ in leaf habit and drought resistance. METHODS: California oak seedlings from the evergreen, and more drought-resistant, Quercus agrifolia and the deciduous Q. lobata (n=387) were assigned to a fully crossed factorial design with herbivory and drought as stress factors. Seedlings were assigned in a greenhouse to 3-4 clipping levels simulating herbivory and 3-4 watering levels, depending on the species. We measured survival, growth, and leaf attributes (chlorophyll, secondary metabolites, leaf area and weight) once a month (May-Sep) and harvested above- and below-ground biomass at the end of the growing season. KEY RESULTS: For both oak species, simulated herbivory enhanced seedling survival during severe drought or delayed its adverse effects, probably due to reduced transpiration resulting from herbivory-induced leaf area reduction and compensatory root growth. Seedlings from the deciduous, and less drought-resistant species, benefitted from herbivory at lower levels of water stress, suggesting different response across species. We also found complex interactions between herbivory and drought on their impact on leaf attributes. In contrast to chlorophyll content which was not affected by herbivory, anthocyanins increased with herbivory - although water stress reduced differences in anthocyanins due to herbivory. CONCLUSIONS: Herbivory seems to facilitate Mediterranean oak seedlings to withstand summer drought, potentially alleviating a key bottleneck in the oak recruitment process. Our study highlights the need to consider ontogenetic stages and species-specific traits in understanding complex relationships between herbivory and drought stressors for the persistence and restoration of multi-species oak savannas.

High water use efficiency due to maintenance of photosynthetic capacity in sorghum under water stress.

Environmental change requires more crop production per water use to meet the rising global food demands. However, improving crop intrinsic water use efficiency (iWUE) usually comes at the expense of carbon assimilation. Sorghum is a key crop in many vulnerable agricultural systems with higher tolerance to water stress (WS) than most widely planted crops. To investigate physiological controls on iWUE and its inheritance in sorghum we screened 89 genotypes selected based on inherited haplotypes from an elite or five exotics lines, containing a mix of geographical origins and dry vs. milder climates, which included different aquaporin (AQP) alleles. We found significant variation among key highly heritable gas exchange and hydraulic traits, with some being significantly affected by variation in haplotypes among parental lines. Plants with a higher proportion of the non-stomatal component of iWUE still maintained iWUE under WS by maintaining photosynthetic capacity, independently of reduction in leaf hydraulic conductance. Haplotypes associated with two AQPs (SbPIP1.1 and SbTIP3.2) influenced iWUE and related traits. These findings expand the range of traits that bridge the trade-off between iWUE and productivity in C4 crops, and provide possible genetic regions that can be targeted for breeding.

The intricacies of vegetation responses to changing moisture conditions.

A long-standing debate looks at whether air or soil dryness is more limiting to vegetation water use and productivity. The answer has large implications for future ecosystem functioning, as atmospheric dryness is predicted to increase globally while changes in soil moisture are predicted to be far more variable. Here, I review the complexities that contribute to this debate, including the strong coupling between atmospheric and soil dryness, and the widespread heterogeneity in vegetation hydraulic traits, acclimations, and adaptations to water stress. I discuss solutions to improve understanding and modeling of vegetation sensitivity to dryness, including how different types of observational data can be used together to gain insight into vegetation response to water stress across spatial and temporal scales.

Towards strategic interventions for global food security in 2050.

This study aims to explore global food security, focusing on major cereal crops across different Agroecological Zones (AEZs). By projecting cereal production under different Shared Socioeconomic Pathways, insights into the challenges for achieving global food security by 2050 are drawn. The study identifies 'critical' risks in countries like Chad, Sudan, Algeria, Somalia, and Namibia in Africa, parts of Central Asia and the Middle East (Saudi Arabia), western USA, and Australia, due to high water stress combined with severe production deficits. However, implementing strategic interventions, like increasing harvested area, can significantly reduce these risks, potentially leading to surplus production in some regions. The regions still under cereal production deficit with such mitigation strategies are categorized in terms of risk to food security, considering water stress and import dependency. Iran, Venezuela, Sub-Saharan Africa, Saudi Arabia, parts of Southeastern Asia are projected to face persistent cereal production deficits and high import dependency by the mid-20th century. The study underlines the necessity for water-saving technologies and effective governance to balance crop production and water use, particularly in regions experiencing water scarcity.

Chronic mild cadmium exposure increases the vulnerability of tomato plants to dehydration.

Heavy metal contamination increases plant susceptibility to both biotic and abiotic stresses. However, the comprehensive impact of heavy metal pollution on plant hydraulics, which is crucial for plant productivity, and the interaction between heavy metal stress and environmental factors on plant health are not yet fully understood. In this study, we investigated the effects of cadmium exposure on plant-water relations and hydraulics of Solanum lycopersicum L., cultivar Piccadilly. Particular attention was given to leaf hydraulic conductance (KL) in response to cadmium pollution and dehydration. Cadmium exposure exhibited negligible impacts on tomato productivity but resulted in significant differences in pressure-volume derived traits. Leaves and roots of Cd-treated plants showed reduced wall stiffness compared to control samples. However, Cd-treated leaves had a less negative turgor loss point (Ψtlp), whereas Cd-treated roots exhibited more negative Ψtlp values due to lower osmotic potential at full turgor compared to control samples. Leaves and root cells of Cd-treated plants showed higher values of saturated water content compared to control plants, along with a distinct mineral profile between the two experimental groups. Despite similar leaf water potential thresholds for 50% and 80% loss of KL in control and cadmium-treated leaves, plants grown in cadmium-polluted soil showed higher leaf cell damages even under well watered conditions. This, in turn, affected the plant ability to recover from drought upon rehydration by compromising cell rehydration ability. Overall, the present findings suggest that under conditions of low water availability, cadmium pollution increases the risk of leaf hydraulic failure.

Hyperspectral Imaging Reveals Differential Carotenoid and Chlorophyll Temporal Dynamics and Spatial Patterns in Scots Pine Under Water Stress.

Drought-related die-off events have been observed throughout Europe in Scots pine (Pinus sylvestris L.). Such events are exacerbated by carbon starvation that is, an imbalance of photosynthetic productivity and resource usage. Recent evidence suggests that optically measurable photosynthetic pigments such as chlorophylls and carotenoids respond to water stress (WS). However, there is a lack of measurements using imaging spectroscopy, and the mechanisms linking xanthophyll-related changes in reflectance captured by the photochemical reflectance index (PRI) and chlorophyll changes in red edge position (REP) to WS are not understood. To probe this, we conducted a greenhouse experiment where 3-year-old Pinus sylvestris saplings were subjected to water limitation and followed using hyperspectral imaging (HSI) spectroscopy, water status and photosynthetic measurements. Carotenoids (e.g., xanthophyll cycle) and chlorophylls responded to WS, which was observed using the HSI-derived indices PRI and REP respectively. The spatial-temporal response in these two pigment-reflectance groupings differed. The spatial distribution of PRI represented the light intensity around the time of the measurement, whereas REP reflected the daily averaged light intensity over the experimental course. A further difference was noted upon rewatering, where the carotenoid-related PRI partially recovered but the chlorophyll-related REP did not.

Functional Analysis of Cucumis melo CmXTH11 in Regulating Drought Stress Tolerance in Arabidopsis thaliana.

The CmXTH11 gene, a member of the XTH (xyloglucan endotransglycosylase/hydrolase) family, plays a crucial role in plant responses to environmental stress. In this study, we heterologously expressed the melon gene CmXTH11 in Arabidopsis to generate overexpressing transgenic lines, thereby elucidating the regulatory role of CmXTH11 in water stress tolerance. Using these lines of CmXTH11 (OE1 and OE2) and wild-type (WT) Arabidopsis as experimental materials, we applied water stress treatments (including osmotic stress and soil drought) and rewatering treatments to investigate the response mechanisms of melon CmXTH11 in Arabidopsis under drought stress from a physiological and biochemical perspective. Overexpression of CmXTH11 significantly improved root growth under water stress conditions. The OE lines exhibited longer roots and a higher number of lateral roots compared to WT plants. The enhanced root system contributed to better water uptake and retention. Under osmotic and drought stress, the OE lines showed improved survival rates and less wilting compared to WT plants. Biochemical analyses revealed that CmXTH11 overexpression led to lower levels of malondialdehyde (MDA) and reduced electrolyte leakage, indicating decreased oxidative damage. The activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), were significantly higher in OE lines, suggesting enhanced oxidative stress tolerance. The CmXTH11 gene positively regulates water stress tolerance in Arabidopsis by enhancing root growth, improving water uptake, and reducing oxidative damage. Overexpression of CmXTH11 increases the activities of antioxidant enzymes, thereby mitigating oxidative stress and maintaining cellular integrity under water deficit conditions. These findings suggest that CmXTH11 is a potential candidate for genetic improvement of drought resistance in crops.

Unveiling the impact of organically activated biochar on physiological, biochemical, and yield attributes of maize under varied field moisture conditions.

Water deficiency in semiarid regions is a limiting factor that affects crop quality and yield. In Punjab, Pakistan, a 27% decline in maize yield was detected over the past two decades just because of water scarcity. Currently, no studies have reported the effects of organically activated biochar (AB) on crop productivity under natural field conditions. For this purpose, a field experiment in a split-split-plot design was conducted with three amendment levels (0, 2, and 4 tonnes ac-1), and three maize hybrids (DK-9108, DK-6321, and Sarhaab) under 100%, 70%, and 50% irrigation water (IW) of crop evapotranspiration (ETc). The AB significantly improved the soil's physical and chemical properties, and maximum improvement was recorded in 4 tonnes ac-1 AB amendment in organic matter (16.6%), total organic carbon (17%), phosphorus (11.43%), and available potassium (29.27%). The 4 tonnes ac-1AB amendment in soil had a significant impact on total chlorophyll content (0.3-1-fold in DK-6321), carotenoid content (3.9-4.4-fold in Sarhaab), and relative water content (30% and 21% in Sarhaab) under 50% irrigation water (IW) of ETc at V14th and R3 stages, respectively. Moreover, a significant decline in stress markers (proline content and sugar content) was detected at both growth stages in all maize hybrids in AB amended soil. The analysis of plant metabolites indicated increased intensities of phenolics, alkyl esters, and carbohydrates by 2.5-7%, 17-80%, and 40-43% in DK-6321 under 50% IW in 2-4 tonnes ac-1 AB amended soil, respectively. The highest improvement in growth and yield attributes among maize hybrids was detected in the order DK-6321¿DK-9108¿Sarhaab in 2-4 tonnes ac-1AB amended soil under 70% and 50% IW of ETc, respectively. Hence, this research might help to develop an effective soil amendment to restore degraded soils and improve maize growth under arid climatic conditions.

Sexual dimorphism at different life stages: early life sexual differences in root growth in Silene latifolia.

Male and female dioecious plants often show sexual dimorphism, differing in morphological, physiological and life-history traits. Most previous studies have focused on differences between males and females during or after reproduction, paying little attention to the pre-reproductive stages of the individuals. Here we assessed the response of male and female individuals of the dioecious plant Silene latifolia to abiotic stress at different life stages, including pre-reproductive (i.e. seedlings and young plants) and reproductive individuals. We measured growth, resource allocation and discrimination against 13C under nutrient deficiency, water stress, as well as their interaction. We observed sexual dimorphism in root growth, with female seedlings having longer main roots than male plants. Pre-reproductive male and female plants also responded differently, in terms of root allocation, to nutrient and water availability. At reproduction, females grew more roots than males when water was not limiting. These differences could help explain the female-skewed sex ratios found in natural populations of S. latifolia. We found no evidence of sexual dimorphism in aboveground dry mass, although females had longer leaves than males at the seedling stage. We conclude that sexual dimorphism in S. latifolia may occur not as a consequence of reproduction, but well before it.

Remote detection of water stress in cotton using a center pivot irrigation system-mounted sensor package.

Much research has been invested in infrared temperature (IRT)-based methods for cotton (Gossypium hirsutism L.) water stress detection using in-field sensors, but adoption of these is low, perhaps due to logistical challenges. Alternatively, the Water Deficit Index (WDI) was developed for crop water stress assessment using remote sensors not embedded in the canopy. The objective of this research was to evaluate the performance of a sensor package-including modern IRT and normalized difference vegetation index (NDVI) sensors facing downward at 45˚, and a mini weather station-attached unintrusively to a center pivot irrigation system for detecting cotton water stress using WDI. Sensor packages were evaluated in a two-year field study that included four irrigation treatments (0, 30, 60, and 90% ET replacement) and in two production cotton fields. Overall, the tested system was effective at distinguishing crop water stress among irrigation rates. Comparison of the results to a ground-based station and simulations indicated that WDI overestimated water stress at the highest irrigation rate, but performed well otherwise. Accuracy of the system could be improved by measuring canopy coverage (Fc) from the same vantage point as the IRT and NDVI sensors (from the pivot, downward at a 45˚ angle).

Pipe experiment elucidates biochar application depth affects nitrogen leaching under crop present condition.

Nitrogen leaching, resulting from the inefficient use of fertilizers, pollutes the environment, such as groundwater. Biochar can be applied to farmlands to mitigate nitrogen leaching. The effect depends on the application depth. However, the effect has not been examined under crop-farming conditions. Evaluating the interactions between biochar application depth and crop growth is indispensable for considering depth in the actual field. To address this, we conducted a pipe experiment with four treatments, no biochar (control), surface (0-5 cm), plow layer (0-30 cm), and subsurface (25-30 cm) applications, and compared the results with no-crop conditions from a previous study. Biochar application depth affected soil NO3--N and NH4+-N absorption ability and also influenced soil-water stress conditions, affecting crop growth. Surface biochar application improved nitrogen absorption and reduced soil-water stress, improving crop growth. The NO3--N leaching was reduced to 87.7%. Plow layer application worsened nitrogen absorption and resulted in frequent dry stress in the shallow-soil layer, preventing root growth in this layer. The NO3--N and NH4+-N leaching increased 106.4% and 264.1%, respectively. The effects of subsurface application were similar to those in the control. Selecting an appropriate application depth can simultaneously improve crop growth and reduce nitrogen leaching.

Substrate pH mediates growth promotion and resilience to water stress of Tilia tomentosa seedlings after Ectomycorrhizal inoculation.

Colonization by Ectomycorrhizal (EcM) fungi is key for the health and performance of plants under different stress scenarios, such as those faced by trees in urban environments. Because urban environments can be lacking EcM fungi, we here assessed the benefits of inoculating Tilia tomentosa seedlings in a pre-transplantation nursery context with the EcM fungi Lactarius deliciosus and Paxillus involutus, using substrates of different pH and facing water-stress. P. involutus had a more evident positive effect in T. tomentosa seedlings and had a good performance in both acidic and alkaline substrate. In acidic substrate the fungus increased the plant height by 0.91-fold, increased the mycorrhization rate by 3.23-fold, expansion rate by 5.03-fold and formation of secondary roots by 0.46-fold, compared to the non-inoculated control. This species also improved the phosphorus content of leaves, which revealed a promotion of nutrient uptake. In alkaline substrate P. involutus increased root dry weight by 3.92-fold and the mycorrhization parameters. In contrast, L. deliciosus only had a positive effect in the improvement of mycorrhization and expansion rates and phosphorus content in the root, effects visible only in alkaline substrate. When exposed to water-stress the increase of proline content was visible in acidic substrate for both fungi, L. deliciosus and P. involutus, and in alkaline substrate for the fungus P. involutus, a response indicative of the enhancement of defenses in stressing scenarios such as water scarcity. We conclude that fungal inoculation improves the vigour and resilience of Tilia seedlings and that it is of utmost importance to select a suitable EcM fungus and to consider the soil pH of the transplanting site. The inoculation approach can be a valuable tool to produce robust seedlings which may have a better performance when transplanted to the challenging urban environment.

Combined metabolome and transcriptome analysis reveal the mechanism of water stress in Ophiocordyceps sinensis.

BACKGROUND: Ophiocordyceps sinensis (O. sinensis) is the dominant bacterium in the asexual stage of Chinese cordyceps, and its growth usually suffers from water stress. Thus, simulating its ecological growth environment is crucial for artificial cultivation. This study aimed to reveal the mechanism underlying the water stress tolerance of Ophiocordyceps sinensis (O. sinensis) by combining metabolomic and transcriptome analyses to identify crucial pathways related to differentially expressed genes (DEGs) and metabolites (DEMs) involved in the response to water stress. RESULTS: Gene coexpression analysis revealed that many genes related to 'betalain biosynthesis', 'tyrosine metabolism', 'linoleic acid metabolism', 'fructose and mannose metabolism', and 'starch and sucrose metabolism' were highly upregulated after 20d-water stress. Metabolomic analysis revealed that many metabolites regulated by these genes in these metabolic pathways were markedly decreased. On the one hand, we surmised that carbohydrate metabolism and the ß-oxidation pathway worked cooperatively to generate enough acyl-CoA and then entered the TCA cycle to provide energy when exposed to water stress. On the other hand, the betalain biosynthesis and tyrosine metabolism pathway might play crucial roles in response to water stress in O. sinensis by enhancing cell osmotic potential and producing osmoregulatory substances (betaine) and antioxidant pigments (eumelanin). CONCLUSIONS: Overall, our findings provide important information for further exploration of the mechanism underlying the water stress tolerance of O. sinensis for the industrialization of artificial cultivation of Chinese cordyceps.

Mapping of quantitative trait loci (QTL) in Brassica napus L. for tolerance to water stress.

Brassica napus L. plants are sensitive to water stress conditions throughout their life cycle from seed germination to seed setting. This study aims at identifying quantitative trait loci (QTL) linked to B. napus tolerance to water stress mimicked by applications of 10% polyethylene glycol-6000 (PEG-6000). Two doubled haploid populations, each consisting of 150 genotypes, were used for this research. Plants at the two true leaf stage of development were grown in the absence (control) or presence (stress) of PEG-6000 under controlled environmental conditions for 48 h, and the drought stress index was calculated for each genotype. All genotypes, along with their parents, were genotyped using the Brassica Infinium 90K SNP BeadChip Array. Inclusive composite interval mapping was used to identify QTL. Six QTL and 12 putative QTL associated with water stress tolerance were identified across six chromosomes (A2, A3, A4, A9, C3, and C7). Collectively, 2154 candidate genes for water stress tolerance were identified for all the identified QTL. Among them, 213 genes were identified as being directly associated with water stress (imposed by PEG-6000) tolerance based on nine functional annotations. These results can be incorporated into future breeding initiatives to select plant material with the ability to cope effectively with water stress.

Drought tolerance and recovery capacity of two ornamental shrubs: Combining physiological and biochemical analyses with online leaf water status monitoring for the application in urban settings.

When plants are transferred from nursery to urban environments, they often face drought stress due to inadequate maintenance, such as insufficient irrigation. Using drought tolerant species may help mitigate the adverse impact of drought stress in urban settings. Additionally, utilizing novel technologies for water status monitoring may help optimize irrigation schedules to prevent transplanting failures. This study investigated the physiological and biochemical responses of two ornamental shrubs, Photinia x fraseri and Viburnum tinus, subjected to water stress of increasing severity and rewatering. Water relations, gas exchanges, chlorophyll fluorescence and biochemical analyses were conducted alongside real-time monitoring of water status using leaf-water-meter sensors (LWM). The progression of water stress had a notable negative impact on leaf gas exchanges and water relations in both species. Notably, P. fraseri avoided photoinhibition by reducing chlorophyll content and actual efficiency of PSII. Adjustments in leaf phenolic compounds played a significant role in enhancing drought tolerance of both species due to their antioxidant and photoprotective properties. Upon rewatering, both species exhibited complete recovery in their physiological functions, underscoring their remarkable tolerance and resilience to drought stress. Additionally, LWM sensors efficiently tracked the dehydration levels, exhibiting a rising trend during the water stress progression and a subsequent decline after rewatering for both species. These findings confirm the reliability of LWM sensors in monitoring physiological status of plants in outdoor contexts, making them a suitable tool for use in urban settings.

Recent Methods for Evaluating Crop Water Stress Using AI Techniques: A Review.

This study systematically reviews the integration of artificial intelligence (AI) and remote sensing technologies to address the issue of crop water stress caused by rising global temperatures and climate change; in particular, it evaluates the effectiveness of various non-destructive remote sensing platforms (RGB, thermal imaging, and hyperspectral imaging) and AI techniques (machine learning, deep learning, ensemble methods, GAN, and XAI) in monitoring and predicting crop water stress. The analysis focuses on variability in precipitation due to climate change and explores how these technologies can be strategically combined under data-limited conditions to enhance agricultural productivity. Furthermore, this study is expected to contribute to improving sustainable agricultural practices and mitigating the negative impacts of climate change on crop yield and quality.

Osmotolerant plant growth promoting bacteria mitigate adverse effects of drought stress on wheat growth.

Drought stress represents a major constraint with significant impacts on wheat crop globally. The use of plant growth-promoting bacteria (PGPB) has emerged as a promising strategy to alleviate the detrimental impacts of water stress and enhance plant development. We investigated 24 strains from diverse ecosystems, assessed for PGP traits and tolerance ability to abiotic stresses (drought, salinity, temperature, pH, heavy metals, pollutants, herbicides, and fungicides). The most effective bacterial strains Providencia vermicola ME1, Pantoea agglomerans Pa, Pseudomonas knackmussi MR6, and Bacillus sp D13 were chosen. Furthermore, these strains exhibited PGP activities under osmotic stress (0, 10, 20, and 30% PEG-6000). The impact of these osmotolerant PGPBs on wheat (Triticum durum L.) growth under drought stress was assessed at two plant growth stages. In an in vitro wheat seed germination experiment, bacterial inoculation significantly enhanced germination parameters. In pot experiments, the potential of these bacteria was evaluated in wheat plants under three treatments: Well-watered (100% field capacity), moderate stress (50% FC), and severe stress (25% FC). Results showed a significant decline in wheat growth parameters under increasing water stress for uninoculated seedlings. In contrast, bacterial inoculation mitigated these adverse effects, significantly improving morphological parameters and chlorophyll pigment contents under the stress conditions. While malondialdehyde (lipid peroxidation) and proline contents increased significantly with drought intensity, they decreased after bacterial inoculation. The antioxidant enzyme activities (GPX, CAT, and SOD) in plants decreased after bacterial inoculation. The increased root colonization capacity observed under water stress was attributed to their ability to favorable adaptations in a stressful environment. This study highlighted the potential of selected PGPB to alleviate water stress effects on wheat, promoting practical applications aimed at enhancing crop resilience under conditions of water shortage.

Combining proximal and remote sensing to assess 'Calatina' olive water status.

Developing an efficient and sustainable precision irrigation strategy is crucial in contemporary agriculture. This study aimed to combine proximal and remote sensing techniques to show the benefits of using both monitoring methods, simultaneously assessing the water status and response of 'Calatina' olive under two distinct irrigation levels: full irrigation (FI), and drought stress (DS, -3 to -4 MPa). Stem water potential (Ψstem) and stomatal conductance (gs) were monitored weekly as reference indicators of plant water status. Crop water stress index (CWSI) and stomatal conductance index (Ig) were calculated through ground-based infrared thermography. Fruit gauges were used to monitor continuously fruit growth and data were converted in fruit daily weight fluctuations (ΔW) and relative growth rate (RGR). Normalized difference vegetation index (NDVI), normalized difference RedEdge index (NDRE), green normalized difference vegetation index (GNDVI), chlorophyll vegetation index (CVI), modified soil-adjusted vegetation index (MSAVI), water index (WI), normalized difference greenness index (NDGI) and green index (GI) were calculated from data collected by UAV-mounted multispectral camera. Data obtained from proximal sensing were correlated with both Ψstem and gs, while remote sensing data were correlated only with Ψstem. Regression analysis showed that both CWSI and Ig proved to be reliable indicators of Ψstem and gs. Of the two fruit growth parameters, ΔW exhibited a stronger relationship, primarily with Ψstem. Finally, NDVI, GNDVI, WI and NDRE emerged as the vegetation indices that correlated most strongly with Ψstem, achieving high R2 values. Combining proximal and remote sensing indices suggested two valid approaches: a more simplified one involving the use of CWSI and either NDVI or WI, and a more comprehensive one involving CWSI and ΔW as proximal indices, along with WI as a multispectral index. Further studies on combining proximal and remote sensing data will be necessary in order to find strategic combinations of sensors and establish intervention thresholds.

Parametrization of lower limit temperature in crop water stress index model: A case study of Quercus variabilis plantation.

The lower limit temperature in the crop water stress index (CWSI) model refers to the canopy temperature (Tc) or the canopy-air temperature differences (dT) under well-watered conditions, which has significant impacts on the accuracy of the model in quantifying plant water status. At present, the direct estimation of lower limit temperature based on data-driven method has been successfully used in crops, but its applicability has not been tes-ted in forest ecosystems. We collected continuously and synchronously Tc and meteorological data in a Quercus variabilis plantation at the southern foot of Taihang Mountain to evaluate the feasibility of multiple linear regression model and BP neural network model for estimating the lower limit temperature and the accuracy of the CWSI indicating water status of the plantation. The results showed that, in the forest ecosystem without irrigation conditions, the lower limit temperature could be obtained by setting soil moisture as saturation in the multiple linear regression mo-del and the BP neural network model with soil water content, wind speed, net radiation, vapor pressure deficit and air temperature as input parameters. Combining the lower limit temperature and the upper limit temperature determined by the theoretical equation to normalize the measured Tc and dT could realize the non-destructive, rapid, and automatic diagnosis of the water status of Q. variabilis plantation. Among them, the CWSI obtained by combining the lower limit temperature determined by the dT under well-watered condition calculated by the BP neural network model and the upper limit temperature was the most suitable for accurate monitoring water status of the plantation. The coefficient of determination, root mean square error, and index of agreement between the calculated CWSI and measured CWSI were 0.81, 0.08, and 0.90, respectively. This study could provide a reference method for efficient and accurate monitoring of forest ecosystem water status.

Genome­wide identification of the SWEET gene family in grape (Vitis vinifera L.) and expression analysis of VvSWEET14a in response to water stress.

Sugars are considered primary metabolites that determine the flavor and quality of grape berries, also playing a crucial role in the plants to resist stress. Sugars Will Eventually be Exported Transporters (SWEETs) gene family has been previously reported to be involved in the growth and development of grape, while the changes in transcriptional levels under water stress remain unclear. In this study, sixteen grape SWEETs members were identified and annotated based on their homologous genes in Arabidopsis and tomato, they were classified into four clades (Clades I to IV) with VvSWEETs by phylogenetic analysis. The highly conserved motifs and gene structures of VvSWEETs indicate that they are closely evolutionary conservation. Chromosomal localization and synteny analysis found that VvSWEETs were unevenly distributed on 11 chromosomes, and the VvSWEET5a, VvSWEET5b, VvSWEET14b and VvSWEET14c existed a relatively recent evolutionary relationship. Promoter cis-acting elements showed that the clade III has more ABRE motif, especially the VvSWEET14a. The regulation of VvSWEETs is mainly influenced by the Dof and MYB families, which are associated with grape ripening, while VvSWEET14a is closely related to the bHLH, MYB, NAC, and bZIP families. RT-qPCR data and subcellular localization show that VvSWEET14a was highly induced under early water stress and is located in the vacuole membrane. The instantaneous transformation assay identified that this gene could promote to transport hexose in the vacuole to maintain normal osmotic pressure. In summary, our study provides a basis for further research on SWEET genes function and regulatory mechanism in the future, and lays the foundation for stress resistance breeding of Vitis vinifera. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01501-1.