Search Results (731)

Trehalose-6-phosphate (T6P) is a key signalling metabolite that integrates carbon availability with development and stress responses in plants. T6P levels are controlled by trehalose phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) enzymes; however, while TPS enzymes have been studied extensively, the physiological functions of individual TPPs remain incompletely understood. Here, we investigated the role of TPPI in Arabidopsis using loss-of-function tppi mutants, a complemented line (tppi+35S::TPPI), and TPPI-overexpressing (TPPI-OEX) plants. The tppi mutant exhibited delayed flowering accompanied by reduced expression of CO, FT, and SPL3, while complementation restored wild-type (WT) flowering time. TPPI-OEX plants displayed an intermediate flowering phenotype with moderate reductions in CO and FT expression. Under nitrogen starvation, tppi plants showed enhanced anthocyanin accumulation, altered nitrate reductase regulation, characterised by lower total enzyme activity but a higher activation state, and enhanced expression of nitrate assimilation and uptake genes (NIA1, NIA2, NRT1.1, and NRT2.1). TPPI deficiency also altered photosynthetic performance, with enhanced photosystem I (PSI) acceptor-side limitation, increased non-photochemical quenching (NPQ), and a tendency toward reduced photosystem II (PSII) electron transport, indicating altered photosynthetic electron transport and energy dissipation. Taken together, these results indicate that TPPI contributes to the regulation of flowering time, nitrogen responses, and photosynthetic performance, suggesting broader effects of TPPI on plant developmental and physiological processes. Full article

Photorespiration and drought-induced stomatal closure are two important physiological constraints that reduce carbon assimilation and productivity in C₃ forest trees under Mediterranean climatic conditions. Türkiye’s two dominant commercial pine species, Pinus brutia Ten. (Calabrian pine) and Pinus nigra J.F. Arnold subsp. pallasiana (Anatolian black pine), together cover approximately 8.15 million hectares. This study integrated published gas-exchange measurements, radiation-use efficiency estimates from MODIS, official forest inventory data, and dendrochronological growth records into a counterfactual accounting framework and propagated parameter uncertainty by Monte Carlo simulation (N = 40,000 draws). The two constraints jointly reduced weighted-mean net primary productivity (NPP) from a radiation-limited potential of 5.61 to an actual 3.46 Mg C ha⁻¹ yr⁻¹, a reduction of 37.9% (95% CI 32.2–43.4%). Decomposition shows that 47.7% of this loss is the obligate metabolic cost of C₃ carboxylation, which no silvicultural intervention can address, while 52.3%—20.1 of the 37.9 percentage points—is drought-attributable. Nationally, the deficit corresponds to 64.3 Mt CO₂ yr⁻¹ of forgone sequestration (47.8–81.2) and 34.4 Mm³ yr⁻¹ of forgone stemwood-volume equivalent (24.9–44.5), of which approximately 20.6 Mm³ would be merchantable, giving an annual economic deficit of USD 3.37 billion (2.40–6.48). Filtering the drought-attributable component for eligible area, recovery efficiency, additionality, leakage, and permanence yields approximately 1.0 Mt CO₂ yr⁻¹ of potentially issuable credits, fewer than two per cent of the headline figure. Eco-physiological suppression of this magnitude is currently invisible in national forest carbon accounting, and its recognition bears directly on dynamic baseline design and on the credibility of offsets generated from Mediterranean conifer forests. Full article

Soil salinity is an increasing constraint to crop production, yet little is known about the responses of culantro (Eryngium foetidum), a medicinal and culinary species of high economic value, to saline conditions. This study evaluated the effects of NaCl-induced salinity (0, 40, and 80 mM) on the growth, photosynthetic performance, pigment content, and vascular anatomy of E. foetidum cultivated in vitro. After 45 days, salinity significantly reduced shoot and root length, leaf number, chlorophyll fluorescence, net CO₂ assimilation, stomatal conductance, transpiration, carboxylation efficiency, and the contents of chlorophylls a and b, and carotenoids, with the strongest effects observed at 80 mM NaCl. In contrast, leaf area, biomass accumulation, specific leaf area, and intrinsic water-use efficiency were not significantly affected. Qualitative anatomical observations indicated apparent modifications in vascular organization under saline conditions, including narrower xylem vessels and phloem disorganization. Collectively, these findings demonstrate that salinity primarily impairs photosynthetic performance and vegetative growth while inducing morphological, physiological, and apparent anatomical responses in E. foetidum cultivated in vitro. This study provides the first integrated characterization of the responses of E. foetidum to in vitro salt stress, establishing a foundation for future investigations into the physiological mechanisms underlying salinity responses in this species. Full article

Sapindus delavayi (Franch.) Radlk. is a non-wood tree species of considerable ornamental, ecological, and medicinal value, and its fruits are rich in saponins, with notable cleansing and skin-care properties. However, this tree species is currently facing the dilemma of low fruit yield and unstable fruiting. Fertilization is an effective measure to improve this cultivation situation. Considering the harm of nitrogen fertilizer in soil, we designed four schemes to replace nitrogen fertilizer with organic fertilizers in this study, aiming to obtain the optimal fertilization combination for the growth of Sapindus delavayi (Franch.) Radlk. Three-year-old seedlings were subjected to applications of nitrogen fertilizer, organic fertilizer, and their combinations to evaluate their effects on plant physiological responses and soil physicochemical properties. Results revealed that the sole application of organic fertilizer significantly promoted the elongation of new shoots. Compared with the unfertilized control, the combined treatment of 30% organic fertilizer and 70% nitrogen fertilizer significantly increased soil nitrate nitrogen content by 161.54%, while ammonium nitrogen content decreased by 24.30%. Principal component analysis indicated that glutamine synthase (GS), glutamate synthase (GOGAT), and nitrate reductase (NR) were the major enzymes influencing leaf physiological responses. Therefore, we concluded that fertilization has affected the rate of nitrogen assimilation and altered the process of amino acid synthesis, thereby influencing the metabolism and maintenance of cellular function in Sapindus delavayi (Franch.) Radlk. Structural equation modeling further indicated that fertilization primarily influenced total carbon content in plant leaves by affecting soil organic matter and alkali-hydrolyzable nitrogen. These findings elucidate the regulatory relationship between plant physiological processes and soil properties under co-application of nitrogen and organic fertilizer, providing a scientific reference for field fertilization management of this tree species. Full article

Leaf senescence progressively remodels the photosynthetic apparatus, leading to impaired electron transport and declining carbon assimilation. Here, we investigated how dark-induced senescence (DIS) and exogenous 6-benzyladenine (BA) affect photosystem function, cyclic electron flow (CEF), photosynthetic protein remodeling and CO₂ assimilation in two barley (Hordeum vulgare L.) cultivars differing in their senescence characteristics, Carina (spring) and Lomerit (winter). DIS markedly reduced the chlorophyll content, PSI and PSII photochemistry, electron transport and CO₂ assimilation in both cultivars, although the underlying mechanisms differed. Carina maintained higher CEF despite stronger PSII inhibition, whereas Lomerit exhibited a greater decline in CEF accompanied by stronger donor- and acceptor-side limitations of PSI. These physiological responses coincided with the selective remodeling of proteins forming the PSI-associated electron transport network, including coordinated changes in cytochrome f, PGRL1, NdhS, FNR and photosystem antenna proteins, indicating the functional reorganization of photosynthetic electron transport rather than uniform chloroplast protein degradation. BA delayed senescence by preserving chlorophyll, maintaining PSI and PSII activity, sustaining CEF and partially alleviating the decline in CO₂ assimilation. The protective effects of BA were more pronounced in Carina and coincided with the more effective preservation of proteins associated with PSI-dependent electron transport. Collectively, our findings identify the selective stabilization of the PSI-associated electron transport network as a central mechanism underlying cytokinin-mediated delay of leaf senescence in barley and demonstrate that cultivar-dependent regulation of this network determines the effectiveness of cytokinin-mediated protection of photosynthesis. Full article

Terrestrial vegetation cover is a critical component of the global carbon cycle, annually assimilating a substantial fraction of anthropogenic CO₂ emissions. However, regional estimates of gross primary production (GPP) and net primary production (NPP) remain insufficiently studied, especially for ecologically sensitive areas such as the sub-Mediterranean landscapes of southeastern Crimea. The aim of this study is to calculate and map the spatio-temporal distribution of GPP and NPP across southeastern Crimea over the period 2001–2025 using Earth remote sensing data and geoinformation modeling. This study employed MODIS products (MOD17A2H collection 061) processed in the Google Earth Engine cloud platform, together with temperature and precipitation data (ClimateEU, CHIRPS). Statistical analysis included calculation of the carbon use efficiency (CUE) coefficient and correlation analysis. The results show that the mean GPP for southeastern Crimea is 1.13 kg C/m² and the mean NPP is 0.61 kg C/m², which exceed global average values. Maximum productivity is characteristic of natural forest communities (sessile oak, beech and juniper forests), whereas anthropogenically transformed landscapes (agricultural land, urban coenoses) exhibit the lowest values. The mean CUE is 0.54, with the highest values (0.63–0.66) recorded for agrocoenoses and steppes, and the lowest (0.49–0.57) for forests. A positive correlation between productivity and precipitation and a negative correlation with air temperature were identified, especially for forest ecosystems. This study fills a gap in regional primary productivity assessments and can serve as a basis for ecosystem monitoring under climate change and anthropogenic pressure. Full article

Soil moisture is a key forecast variable of land surface models. Direct assimilation of microwave brightness temperature data to optimize soil moisture initial fields is an effective approach to improve the simulation accuracy of soil moisture. However, most existing direct assimilation methods adopt physical radiative transfer models as observation operators, and their complex parametric errors greatly restrict the improvement in assimilation performance. This study introduces a high-precision MLP (Multilayer Perceptron)-based surrogate radiative transfer model as the observation operator. Combined with the Simplified Extended Kalman Filter (SEKF), it develops a direct radiance data assimilation system for the Common Land Model (CoLM). Assimilation experiments are conducted using brightness temperature data from the Microwave Radiation Imager (MWRI) onboard the FY-3D satellite. Their performance over China’s land areas is systematically assessed through comparison with the assimilation scheme based on the Community Microwave Emission Model (CMEM). The results show that the MLP-based assimilation scheme can effectively improve soil moisture simulation accuracy, yet the improvement varies across vegetation types: grassland areas achieve the largest error reduction (10.2%), while semidesert areas present the most prominent increase in the correlation coefficient (53.9%). Compared with the CMEM scheme, the MLP scheme exhibits better error stability and produces generally improved assimilation effects; specifically, in semidesert areas, the error decreases by 9.4%, and the correlation coefficient increases by 62.8%. This study demonstrates that deep learning-based observation operators have strong application potential for land surface data assimilation under complex physical mechanisms. Full article

Accurately simulating the spatiotemporal distribution of global atmospheric CO₂ remains challenging yet essential for reducing uncertainties in carbon source-sink inversions, quantifying the climate effects of heterogeneous CO₂ fields, and supporting the development of CO₂ observation networks. In this study, we simulated global atmospheric CO₂ concentrations (2010–2019) at a horizontal spatial resolution of 1° × 1° using the Aerosol and Atmospheric Chemistry Model of the Institute of Atmospheric Physics (IAP-AACM) without data assimilation, with initial fields and flux data from the CarbonTracker CT2022 (CT2022) reanalysis product. The simulations were comprehensively evaluated against CT2022 and observations from ground-based (NOAA GML), airborne (ObsPack), and satellite (OCO-2) platforms. The results indicate that across all evaluated surface stations, CT2022 exhibits poorer overall statistical performance (R = 0.69, RMSE = 5.37 ppm, MB = 2.05 ppm) primarily due to noticeable overestimations at unassimilated ground stations, while IAP-AACM maintains robust performance across the surface network (R = 0.84, RMSE = 2.62 ppm, MB = 0.28 ppm). Vertically, airborne observations across eight global campaigns confirm that IAP-AACM accurately reproduces the vertical distribution of CO₂, maintaining strong correlations (R = 0.72–1.00) and performance comparable to the CT2022 reanalysis (R = 0.86–1.00). In terms of total column CO₂ concentrations (XCO₂), IAP-AACM exhibits strong agreement with satellite retrievals annually (R = 0.97, RMSE = 1.08 ppm, MB = 0.26 ppm), with seasonal metrics remaining consistently robust across all four seasons (R = 0.96–0.97, RMSE = 0.98–1.20 ppm, MB = 0.13–0.37 ppm), demonstrating large-scale transport fidelity on par with the CT2022 reanalysis. Finally, across representative ObsPack land sites, unassimilated IAP-AACM achieves a high median correlation (R = 0.97), low error (RMSE = 2.01 ppm), and low mean bias (MB = −0.45 ppm), closely approaching the assimilated CT2022 reanalysis product (R = 0.98, RMSE = 1.40 ppm, MB = −0.07 ppm). Further analysis indicates that the optimized IAP-AACM exhibits robust performance under stable boundary layer conditions, where the revised diffusion scheme produces higher vertical diffusion coefficients that help mitigate excessive near-surface CO₂ accumulation during nighttime. Overall, the optimized IAP-AACM effectively simulates the spatiotemporal distribution of global atmospheric CO₂, serving as a reliable tool to support advanced research. Full article

Soil salinity and bacterial spot of tomato (BST), caused by Xanthomonas perforans, are major abiotic and biotic stresses limiting tomato production, particularly in Florida. While their individual effects are well documented, the impact of soil salinity on BST has not yet been investigated. This greenhouse study evaluated how increasing irrigation water salinity (electrical conductivity [EC] = 0.5, 3, 5, or 7 dS m⁻¹) affected tomato growth, physiology, BST severity, fruit quality, and transcriptomic responses. Salinity reduced plant growth and BST severity but did not directly affect X. perforans populations. Results indicated that reduced plant physiological activity (net CO₂ assimilation [A], transpiration [E], and stomatal conductance [g_s]) contributes to lower disease levels. Increased salinity led to more solute concentrations, altered sugar metabolism, and improved perceived taste, as supported by taste panel, osmolality, and transcriptomic analyses. They also showed that transcriptional responses to salinity (EC = 7 dS m⁻¹) and X. perforans infection were strongly time-dependent. Salt-treated plants exhibited fewer differentially expressed genes following inoculation, whereas comparisons between EC 7-treated and control plants revealed extensive salinity-induced reprogramming. KEGG analysis indicated enrichment of photosynthesis, carbon metabolism, amino acid biosynthesis, and ribosome pathways, while defense-related pathways, including MAPK signaling and plant–pathogen interaction, were downregulated, suggesting that tomato prioritized adaptation to salinity over pathogen defense. Full article

Moss-dominated biological soil crusts are associated with carbon and nitrogen cycling in dryland and alpine sandy ecosystems, but functional differentiation among closely related moss species and their mixed assemblages remains unclear. We used shotgun metagenomic sequencing to compare below-crust soil associated with Didymodon constrictus (Mitt.) K. Saito (D. constrictus) crusts (mossC), ferrugineus (Schimp. ex Besch.) M.O. Hill (D. ferrugineus) crusts (mossF), and visually co-dominated mixed crusts (mossM) in the Gonghe Basin on the northeastern Qinghai–Tibet Plateau. Fifteen spatially separated quadrats per category were pooled into three composite biological replicates (effective n = 3). KEGG, CAZy, and targeted carbon- and nitrogen-cycling annotations showed category-associated differences in relative gene representation. MossC had greater mean representation of glycoside hydrolases and several complex-carbon-processing functions, mossF had greater representation of nitrogen-assimilation and acetate-related functions, and mossM had greater representation of selected carbon-degradation, nitrogen-mineralization, and dissimilatory-nitrate-reduction functions. The full RDA model explained 58.4% of functional variation (adjusted R² = 0.334; exact permutation p = 0.028340), with single-variable associations retained for total carbon and soil water content. Genus-level taxonomic dissimilarity correlated with KEGG, CAZy, carbon-cycling, and nitrogen-cycling dissimilarities after FDR correction. MossM showed both positive and negative descriptive deviations from the approximate unweighted midpoint of mossC and mossF, but no inferential test was applied to these deviations. The small number of composite replicates, visually estimated moss proportions, edaphic confounding, and absence of activity measurements limit causal and confirmatory interpretation. Full article

Microalgal growth-promoting bacteria (MGPBs) represent a promising strategy to enhance biomass productivity, yet the mechanistic basis of these mutualistic interactions remains poorly understood. Here, we isolated a new MGPB, Cupriavidus oxalaticus MEYA8, and characterized its mutualistic interaction with the model microalga Chlamydomonas reinhardtii. Co-cultivation at an optimal MEYA8: Chlamydomonas ratio greatly enhanced microalgal cell density and chlorophyll content, which reached 2.1-fold and 1.6-fold those of the control, respectively, with markedly improved photosynthetic efficiency across both photosystems. Transwell assays confirmed that this promotion is mediated by diffusible metabolites rather than direct cell contact. Metabolites and multi-omics analyses revealed that MEYA8 can produce compounds similar to indole-3-acetic acid (IAA) and is adapted to the microalgal phycosphere by preferentially utilizing organic acids and amino acid derivatives. In response, Chlamydomonas upregulated proteins involved in photosynthetic electron transport, energy metabolism, and nitrogen assimilation, consistent with the observed enhancement in photosynthetic performance. These findings suggest a metabolically reciprocal interaction model: MEYA8 supplies diffusible growth-promoting factors such as IAA-like compounds to enhance Chlamydomonas photosynthesis and growth, while Chlamydomonas provides organic substrates that sustain bacterial proliferation. Our work provides new insights into algal–bacterial mutualism and may provide a new microbial resource for engineering microalgal and beneficial bacterial consortia. Full article

The assimilation capacity of the biosphere and the sustainability of the living resources are enhanced by the efficient and continued contribution of the vegetation from all ecoregions of the Earth. The urban greenery fulfills many regulatory ecosystem services (RES) as well. In this regard, the importance of urban green spaces (UGS) in helping to reduce the adverse impacts of overcrowding and changing climate is of pertinence. Lack of quantitative information from urban settings in different climatic regions seriously constrains the recognition of the important role UGS play in carbon storage and sequestration. To assess how the UGS is aiding the retention of carbon, which is photosynthetically assimilated into biomass and/or sequestered, relevant field parameters were collected from 4010 trees belonging to 34 different species, different hedge plants, and groundcover grasses spread in 24,991 m² area in three parks of Panaji city, India. Standard methods were followed to derive carbon stock and sequestration rates by trees, hedge plants, and groundcover. Notwithstanding wide differences between tree species, the weighted mean of CO₂ sequestered per tree averaged 55 kg y⁻¹ (ca. 78.82 tons ha⁻¹) in Panaji city. Accordingly, the CO₂ sequestration potential of trees, in the UGS of Panaji (by 76,751 trees) and Tumkur (with an estimated 38,152 trees) cities, respectively, was 4221.31 tons y⁻¹ ha⁻¹ and 2098 tons ha⁻¹ y⁻¹ @ 55 kg tree⁻¹ y⁻¹. It is apparent from this first-time study that calculated tree carbon biomass and species-wise yearly carbon sequestration rates (CSRs) of 78.82 tons ha⁻¹ y⁻¹ and that of carbon production rates of 31.77 tons ha⁻¹ y⁻¹ are far higher than the previously reported CSR estimates variously from 1 to 8 tons ha⁻¹ y⁻¹ and carbon production rates 3.23 to 6.55 tons ha⁻¹ y⁻¹. The hedge row carbon biomass averaged 13.18 tons ha⁻¹ and sequestration of 48.38 tons ha⁻¹ y⁻¹ CO₂. Similarly, occupying over 42% of the UGS, the groundcover carbon biomass averaged 14.69 tons ha⁻¹ with sequestration of 53.92 tons CO₂ ha⁻¹ y⁻¹. Combined CSP of existing trees, groundcover, and hedge plants in Panaji and Tumkur city UGS apparently neutralize carbon footprint of over 4550 and 2200 Indians at an annual per capita emission of 1.94-ton. It is thus undeniable that in our global fight against climate change, the addition of inputs and data from studies like these can aid in planning mitigation measure as well as in fulfilling local/regional sustainability plans and needs. Full article

Most Citrus spp. trees in China are cultivated in acidic soils with low soil organic matter and high Al³⁺. The mechanisms of humic acid (HA) to alleviate Al³⁺ stress in plants remain unclear. ‘Sour pummelo’ (Citrus grandis (L.) Osbeck) seedlings were exposed to 0.5 (HA0.5), 0.1 (HA0.1), or 0 (HA0) mM sodium humate and 1.2 (Al1.2) or 0 (Al0) mM AlCl₃·6H₂O for 128 days. Thereafter, the research examined biomass; Al and mineral nutrients; leaf photosynthetic performance; and leaf and root nonstructural carbohydrates, reactive oxygen species metabolism, and related physiological parameters. Al1.2 significantly reduced whole plant dry weight (DW), root DW, leaf CO₂ assimilation (A_CO2), and chlorophyll a + b concentration by 61%, 45%, 61%, and 35%, respectively, at HA0, but only 48%, 17%, 44%, and 11%, respectively, at HA0.5. Further analysis suggested that the addition of HA endowed Citrus with Al resilience by the following several aspects: (a) lessened tissue (leaf, stem, and root) concentrations of Al and enhanced capacity to maintain macronutrient (S, K, Mg, Ca, N, and P) homeostasis at Al1.2; (b) improved capacity to combat oxidative stress at Al1.2; and (c) enhanced A_CO2 and growth at Al1.2. Further analysis indicated that HA-mediated alleviation of growth decline caused by Al1.2 involved (a) reduced ability to absorb Al and less root-to-shoot Al transport and (b) increased ability to maintain macronutrient homeostasis and to combat oxidative stress; and that HA-mediated alleviation of leaf chlorophyll and A_CO2 decline and photosynthetic electron transport chain impairment involved less leaf Al concentration and improved leaf macronutrient homeostasis. To conclude, the addition of HA lowered roots’ ability to absorb Al and tissue Al concentration and subsequently mitigated Al-toxic impairment to root growth and function, thereby enhancing the ability of plants to maintain macronutrient homeostasis, and hence alleviating Al1.2-stimulated oxidative damage and inhibition of A_CO2 and growth. Full article

The frequency and magnitude of droughts are increasing concurrently with atmospheric CO₂ concentration, with profound consequences for plant carbon assimilation. However, the interactions and the underlying physiological mechanism are still not fully understood. To fill the knowledge gap, we exposed Chinese fir (Cunninghamia lanceolata) saplings to two CO₂ concentrations (400 and 800 ppm, representing ambient and elevated CO₂) and two soil water regimes (70% and 40% field capacity; well-watered and drought-stressed conditions) in a factorial design. Net photosynthetic rate (A_n), chlorophyll fluorescence, photosynthetic pigments, oxidative stress indicators, and antioxidant enzyme activities were measured four times over a 45-day treatment period. Under well-watered conditions, elevated CO₂ significantly increased A_n by 61.5%. However, drought stress substantially reduced A_n by 75.0% under ambient CO₂ and by 75.6% under elevated CO₂, whereas no statistically significant CO₂-induced increase was detected under drought conditions. Furthermore, drought stress caused marked reductions in stomatal conductance, transpiration, chlorophyll content, and photosystem II (PSII)-related parameters, together with increased malondialdehyde, proline, and antioxidant enzyme activities. Variance partitioning analysis suggested that stomatal regulation (SR), photosynthetic capacity (PC), and stress response (STR) jointly explained 71% of the variation in A_n. Structural equation modeling further suggested that drought stress restricted the photosynthetic benefits of elevated CO₂ primarily through stomatal closure, concurrently associated with stress-related declines in pigment stability and photochemical performance. These findings suggest that the carbon sink potential of Chinese fir plantations under future CO₂-enriched climates may be strongly constrained by water deficits. Full article

Water scarcity caused by irregular rainfall and high evapotranspiration rates in the Brazilian semi-arid region is one of the main factors limiting watermelon cultivation, underscoring the need for irrigation strategies capable of mitigating the adverse effects of water deficit. This study aimed to evaluate the effects of foliar salicylic acid application on the induction of water-deficit tolerance in watermelon plants subjected to water restriction at different phenological stages under semi-arid conditions. The experiment was conducted using a randomized block design in a split-plot arrangement, with five irrigation management strategies based on crop evapotranspiration (ETc) and four salicylic acid (SA) concentrations, with three replications and three plants per plot. Water deficit adversely affected the morphophysiological traits of the plants and the physical and chemical attributes of ‘Crimson Sweet’ watermelon fruits, with water restriction during the vegetative and flowering stages causing the most severe effects. Foliar application of salicylic acid at concentrations ranging from 1.2 to 2.6 mM increased relative water content by 9.4%, reduced electrolyte leakage by 11.60%, and enhanced CO₂ assimilation by 18.82%, instantaneous water-use efficiency in 128.10%, and instantaneous carboxylation efficiency by 46.92%. Salicylic acid concentrations within this range also improved plant water status, gas exchange, photosynthetic pigment content, growth, and the physical and chemical attributes of the fruits. In contrast, concentrations above 2.6 mM reduced gas exchange, photosynthetic pigment accumulation, chlorophyll a fluorescence, and the physical and chemical quality of ‘Crimson Sweet’ watermelon fruits. Thus, salicylic acid may be an alternative to modulate the tolerance of watermelon plants under water deficit during phenological phases. Full article