Mediterranean-type ecosystems occur in five regions worldwide and are characterized by intense summer drought that constrains plant carbon gain and water-use strategies. Along the leaf economics spectrum, herbs typically exhibit higher photosynthetic capacity but lower water-use efficiency than woody species due to greater stomatal (gₛ) and mesophyll conductance (gₘ). However, this expectation may not hold under the particularly arid summer conditions of the central Chilean matorral, where prolonged drought acts as a strong environmental filter on plant water-use strategies. Here, we evaluated photosynthetic capacity, diffusional and biochemical limitations, and intrinsic water-use efficiency (iWUE) in co-occurring herbs, shrubs, and trees. Using combined gas exchange, chlorophyll fluorescence, and carbon isotope composition (δ13C), we quantified gₛ and gₘ, partitioned photosynthetic limitations, and compared traditional iWUE with a mesophyll-integrated metric (iWUEmes). Herbs exhibited the highest area- and mass-based photosynthetic rates, whereas shrubs and trees showed progressively lower values, driven primarily by diffusional rather than biochemical limitations. Classical iWUE (Aₙ/gₛ) did not differ among functional groups, whereas iWUEmes showed a significant overall effect, with trees differing from herbs and shrubs, indicating divergence in carbon–water trade-offs. Evergreen trees, characterized by high leaf mass per area and low gₘ, experienced the strongest diffusional limitation. Overall, our findings demonstrate that mesophyll conductance plays a central role in regulating photosynthetic performance and water-use strategies, refining expectations derived from global trait-based frameworks and improving predictions of plant responses to increasing aridity in Mediterranean-type ecosystems.

Deficit irrigation severely constrains the early establishment of fruit tree plants, highlighting the need for practical technologies that enhance root performance under limited water availability. This study evaluated the physiological and biochemical responses of vegetatively propagated hazelnut plants (Corylus avellana L.) exposed to three irrigation regimes (full irrigation, 60% and 30% of field capacity) and treated with an alginate-based bioformulation produced using JetCutter technology and containing immobilized Bacillus safensis (PGPR).Water restriction induced typical drought responses, including increased proline accumulation, shifts in antioxidant enzyme activity, and higher abscisic acid (ABA) levels, confirming irrigation as the primary driver of plant responses. Under severe deficit irrigation (30% of field capacity), bioformulation-treated vegetatively propagated hazelnut plants exhibited greater root elongation, higher root proline accumulation, and improved overall plants performance compared with non-treated plants. Gas exchange parameters declined with increasing water restriction, while net photosynthesis did not differ significantly between treated and non-treated plants within irrigation levels.Root hormonal profiling revealed higher indole-3-acetic acid (IAA) levels in treated propagated plants under severe deficit irrigation, consistent with enhanced root development. Multivariate analyses confirmed irrigation level as the main factor structuring plant responses, but positioned bioformulation-treated vegetatively propagated plants closer to growth- and stability-associated traits under restricted water supply.Hence, these results support the potential of a JetCutter-derived alginate bioformulation as a practical tool to improve root system development and early establishment of hazelnut plants under irrigation water restriction.

During drought stress and subsequent recovery, plants adjust their water–carbon dynamics, typically increasing intrinsic water-use efficiency (iWUE) and mobilizing non-structural carbohydrate (NSC) pools. However, in tree species, the physiological and metabolic changes underlying these adjustments remains poorly understood because their larger size, slower turnover rates, and complex compartmentalization of carbon and water fluxes make difficult to capture coordinated whole-plant responses under natural drought–recovery cycles. In Porlieria chilensis, a species currently classified as vulnerable, we performed short- and long-term drought experiments, followed by recovery conditions in juvenile trees to investigate sugar-mediated responses associated with the dynamics of NSC, iWUE and primary metabolites by combining enzymatic activities, δ¹³C and δ¹⁸O, respiration rates and omics technologies. Long-term drought increased significantly iWUEmes (integrating mesophyll conductance and δ¹³C) due to stomatal closure, and decreased starch content coinciding with an inactivation of ADP-glucose pyrophosphorylase (AGPase) activity. Short-term recovery restored photosynthetic activities to pre-stress levels, while long-term recovery triggered the upregulation of several sugar-related enzymes to replenish NSC pools, and the accumulation of metabolites involved in osmotic regulation and polyamine metabolism. We concluded that a sugar futile cycle may help to sustain leaf carbon metabolism, supporting osmotic balance and carbon reserves during prolonged drought and recovery in this species. Overall, these findings improved understanding of carbon dynamics and stress-induced metabolic imprinting in woody species, providing insights for restoration strategies and predicting plant responses to climate change.

Legumes form symbioses with nitrogen-fixing bacteria, well studied metabolically but less so in terms of respiration. Symbiotic nitrogen fixation demands high respiratory ATP and carbon skeletons, linking nitrogen assimilation and both NADH- and ATP-dependent process to mitochondrial respiration. The plant mitochondrial electron transport chain contains two terminal oxidases that differentially fractionate against 18O, providing estimations in vivo of the energy efficiency of respiration. The regulation of N2 fixation by plant respiratory parameters remains unknown. To investigate the regulatory interactions of these two metabolic processes, we tested the effect of different plant N status and sources on respiratory parameters and nutrition in Lotus japonicus. Plants were grown with two levels of KNO3 fertilization (5 mM and 25 mM) and with the N2 fixing symbiotic bacteria Mesorhizobium loti, which induced the formation of root nodules (NP). Additionally, we characterized roots containing non-fixing nodules by growing plants that display spontaneous nodule formation (snf) (SNF). We evaluated the natural abundances of 13C and 15N, and 18O discrimination during respiration in leaves and roots using isotope-ratio mass spectrometry. NADH and nutrient content were measured using ultra-performance liquid chromatography and inductively coupled plasma spectrometry. We observed that cytochrome c oxidase activity was higher in nodulated roots capable of nitrogen fixation than in plants fertilized with high availability of nitrate, and that nitrogen status strongly associates to respiratory parameters. These findings highlight the role of cytochrome c oxidase in meeting the carbon and energy demands of symbiotic nitrogen fixation.

ABSTRACTLegumes are among the most utilised agronomic plant species due to their symbiotic association with N2‐fixing bacteria. Since N2 fixation entails high ATP cost, salt stress disrupts N2 fixation in the symbiont, but increases the production of osmolytes and antioxidant systems in the host plant. This results in competition for C allocation between osmoprotection in the host and continued supply to the symbiont for N acquisition, which may result in different plant responses to salinity. Two‐nodule types of plant species with contrasting carbon requirements for organic N2 fixation can be found within legume species; determinate and indeterminate. In this study, we tested responses of respiratory carbon metabolism, nitrogen assimilation and antioxidant machinery in leaves and roots of Phaseolus vulgaris (determinate nodules) and Pisum sativum (indeterminate nodules) 24 and 72 h after salt treatment (300 mM of NaCl). In P. sativum, we observed that nitrogenase activity was maintained at 24 h, but showed a strong decrease at 72 h together with cytochrome activity. On contrast, in P. vulgaris, respiration rates were maintained by an enhanced antioxidant activity under salinity although at the expense of nodule metabolism. Despite of the severity of the salt stress for N2 fixation, both species showed similar mechanisms to cope with salinity, like the maintenance of alternative respiration and increased antioxidant defence, that are worthy to be tested in the long term under field conditions.

Plant growth-promoting rhizobacteria (PGPR) have significant potential for enhancing soil quality and plant growth; however, their agricultural application is limited by challenges such as immobilization and desiccation vulnerability. Background: This study addressed PGPR solid formulation by applying JetCutter-assisted immobilization technology to PGPR strains isolated from the rhizosphere of hazelnut (Corylus avellana). Methods: Four immobilized PGPR strains were evaluated under controlled greenhouse conditions: Serratia proteamaculans, Pseudomonas mohnii, Pseudomonas baetica, and Bacillus safensis. Their effects on root development, gas exchange parameters, dissolved organic carbon (DOC), and soil enzymatic activities (phosphatase, urease, protease, and β-glucosidase) were assessed. Principal component analysis (PCA) was used to identify the top-performing strain. Results: Treatment with encapsulated bacteria resulted in a 27% increase in DOC compared to controls (p < 0.05), while phosphatase and urease activities increased by 35% and 28%, respectively. Root length and volume improved by 18% and 22%, respectively, with PCA identifying P. baetica as the most effective strain. Conclusions: Immobilized Gram-negative PGPR strains enhanced root development and soil biochemical activity in hazelnuts, whereas B. safensis enhanced photosynthesis but had minimal impact on soil properties. These results highlight functional differences and support the use of PGPR immobilization to promote early plant establishment.

Galls induced by Espinosa nothofagi (Hymenoptera) on Nothofagus obliqua (Nothofagaceae) buds exhibit tissue compartmentalization, with an inner compartment (IC) specialized for larval nutrition and an outer compartment (OC) associated with defense and protection. Although previous studies have linked reactive oxygen species (ROS) to functional specialization in galls, comprehensive analyses of oxidative stress and antioxidant systems in distinct gall compartments are still limited. Additionally, N. obliqua is a deciduous species with active secondary growth in spring, which coincides with gall development and potentially influences host redox dynamics. This study evaluated ROS production, lipid peroxidation (MDA), and the activity of enzymatic and nonenzymatic antioxidant systems in gall compartments and nongalled stems (NGS). We hypothesized that ROS and antioxidant systems in galls are compartmentalized according to their function and that secondary growth in NGS leads to ROS accumulation, which is counteracted by antioxidant defenses. Both histochemical and quantitative analyses revealed low oxidative stress in the IC, which was supported by elevated dehydroascorbate reductase activity. The OC presented increased H₂O₂ levels and superoxide dismutase and glutathione reductase activities, indicating exposure to environmental stressors. NGS resulted in the highest ROS levels, which were associated with intense cambial activity, along with strong enzymatic antioxidant responses. The colocalization of H₂O₂ and flavonoids suggests that these compounds act as effective ROS scavengers in both galls and NGS. Although each organ relies on distinct strategies, all effectively prevent membrane damage through efficient enzymatic and flavonoid-based antioxidant mechanisms. These findings demonstrate the functional compartmentalization of oxidative stress and defense, highlighting the role of redox balance during secondary growth and gall development.

Purpose: This study aimed to comprehensively evaluate the effects of elevated carbon dioxide (CO2) levels on wheat root biomass production, root exudates, and bacterial community structure. Methods: Wheat was evaluated in a closed system growth chamber under two CO2 conditions (CO2 550 and CO2 1000 ppm) at two growth stages (four and eight weeks). Leaf enzymatic activity (glutamate dehydrogenase and nitrate reductase), gas exchange parameters, aerial and root biomass, organic acids exuded by roots, soil microbial activity, community composition and structure, and diversity (richness and Shannon’s index) were evaluated. Results: In the fourth week of growth, CO2 1000 resulted in a decrease in net photosynthesis. However, root biomass increased by 107

Microplastics (MPs) alter soil properties and plant physiology and pose a significant risk to crop health and food quality. This study assessed the effects of MPs (polyamide-PA, low-density polyethylene-LDPE, and polypropylene-PP) on Andisol and Raphanus sativus L. as a model plant. Plant characteristics, including growth, chlorophyll content, oxidative stress, antioxidant capacity, and bioactive compound profiles, were evaluated. In addition, the effects on soil nutrients, microbiological properties, and bacterial nitrogen-cycling gene abundance were studied, revealing alterations in both soil and plants. Soil pH increased up to 4.3%, whereas dissolved organic carbon and polyphenol levels decreased, particularly in the PA (26%) and PP (29%) treatments. LDPE and PP increased beta-glucosidase activity (14% and 23%, respectively) and basal soil respiration (25% and 26%, respectively). Nitrogen-cycling genes nifH, amoA, and nirS were notably more abundant in PP-treated soils, with increases of 79%, 76%, and 62%, respectively. In R. sativus , PA and LDPE increased SPAD values by 9.9% and increased biomass in rootlets (155% in PA, 60% in LDPE) and radishes (125% in PP). Oxidative stress levels in radishes increased by 63% and 73% after exposure to LDPE and PP, respectively. MPs altered glucosinolate profiles in leaves and rootlets. Furthermore, PA and LDPE modified anthocyanin profiles in leaves, whereas PP altered the profile in radishes. This study highlights the impact of MPs on soil and plant physiology, identifying polyphenols and microbial biomass carbon as key predictors of R. sativus response.

Plants have developed various strategies to deal with abiotic stresses throughout their lifetimes. However, environmental stresses can have long-lasting effects, positively modifying plant physiological responses to subsequent stress episodes, a phenomenon known as preconditioning or stress memory. Intriguingly, this memory can even be transmitted to offspring, referred to as "inter- or transgenerational memory". Chenopodium quinoa is a pseudocereal that can withstand several abiotic stresses, including nitrogen (N) limitation. This research highlights the critical role of maternal N conditions in shaping the physiological and metabolic responses of their offspring. Mother quinoa plants (F0) were grown under High N (HN) or Low N (LN) conditions. LNF0 plants exhibited lower panicle biomass, net photosynthesis, and yield compared to HNF0 plants. Seeds from LNF0 retained proteins, reduced amino acids' levels, and increased lipids (such as PI 34:2), especially phosphatidylcholines, and their unsaturation level, which was associated with faster germination compared to HNF0 seeds. Offsprings seedlings (F1) grown under either HN or LN had similar proteins and amino acid proportions of their seeds. However, LNF0LNF1 seedlings displayed significantly higher biomass and number of root tips. These changes were significantly correlated with transpiration, net photosynthesis, and stomatal conductance, as well as with starch content, suggesting higher CO2 fixation at the whole plant level in LNF0LNF1 plants. Our findings suggest that quinoa transmits maternal environmental stress information to its offspring, modulating their resilience. This work underscores the potential of utilizing maternal environmental conditions as a natural priming tool to enhance crop resilience against nutritional stress.

"Memory imprint" refers to the process when prior exposure to stress prepares the plant for subsequent stress episodes. Seed priming is a strategy to change the performance of seedlings to cope with stress; however, mechanisms associated with the metabolic response are fragmentary. Salinity is one of the major abiotic stresses that affect crop production in arid and semiarid areas. Chenopodium quinoa Willd. (Amaranthaceae) is a promising crop to sustain food security and possesses a wide genetic diversity of salinity tolerance. To elucidate if the metabolic memory induced by seed halo-priming (HP) differs among contrasting saline tolerance plants, seeds of two ecotypes of Quinoa (Socaire from Atacama Salar, and BO78 from Chilean Coastal/lowlands) were treated with a saline solution and then germinated and grown under different saline conditions. The seed HP showed a more positive impact on the sensitive ecotype during germination and promoted changes in the metabolomic profile in both ecotypes, including a reduction in carbohydrates (starch) and organic acids (citric and succinic acid), and an increase in antioxidants (ascorbic acid and α-tocopherol) and related metabolites. These changes were linked to a further reduced level of oxidative markers (methionine sulfoxide and malondialdehyde), allowing improvements in the energy use in photosystem II under saline conditions in the salt-sensitive ecotype. In view of these results, we conclude that seed HP prompts a "metabolic imprint" related to ROS scavenger at the thylakoid level, improving further the physiological performance of the most sensitive ecotype.

Chenopodium quinoa Willd. is a native species that originated in the High Andes plateau (Altiplano) and its cultivation spread out to the south of Chile. Because of the different edaphoclimatic characteristics of both regions, soils from Altiplano accumulated higher levels of nitrate (NO3-) than in the south of Chile, where soils favor ammonium (NH4+) accumulation. To elucidate whether C. quinoa ecotypes differ in several physiological and biochemical parameters related to their capacity to assimilate NO3- and NH4+, juvenile plants of Socaire (from Altiplano) and Faro (from Lowland/South of Chile) were grown under different sources of N (NO3- or NH4+). Measurements of photosynthesis and foliar oxygen-isotope fractionation were carried out, together with biochemical analyses, as proxies for the analysis of plant performance or sensitivity to NH4+. Overall, while NH4+ reduced the growth of Socaire, it induced higher biomass productivity and increased protein synthesis, oxygen consumption, and cytochrome oxidase activity in Faro. We discussed that ATP yield from respiration in Faro could promote protein production from assimilated NH4+ to benefit its growth. The characterization of this differential sensitivity of both quinoa ecotypes for NH4+ contributes to a better understanding of nutritional aspects driving plant primary productivity.

Two main leaf types are recognized among vascular plant species: compound and simple. Compound leaves are believed to be photosynthetically more productive than simple ones, by diluting mass tissue in more projected area. Conversely, simple leaves are believed to be more stress-tolerant by packing mass tissue in less projected area during stress like drought. Nevertheless, convective cooling is more efficient in compound than simple leaves, a process that could alleviate water loss in drought periods. In Central Chile, woody species with simple and compound leaves coexist. This zone is facing a mega-drought event, causing browning and tree mortality. However, how severe droughts affect photosynthetic traits on both leaf-type species have not been addressed so far. We measured photosynthetic traits in well-watered and drought conditions in three compound and three simple leaf species, and drought response ratios were obtained. We hypothesized that with no water limitation compound leaf species will show higher net photosynthesis (AN) than simple leaf species associated with a higher mesophyll conductance (gm). Opposite results are expected for simple leaf species due to their stress-tolerant physiology, showing fewer changes in their photosynthetic traits. We found that gm and AN were larger in compound leaf species in well-watered conditions. With drought, both leaf-type species were negatively affected despite foliar temperature in compound leaf species was 4 °C lower. Our result suggests that regardless of leaf shape the matorral species in Central Chile will be seriously affected in their AN due to the megadrought currently affecting this zone.

The alternative oxidase pathway (AOP) is associated with excess energy dissipation in leaves of terrestrial plants. To address whether this association is less important in palustrine plants, we compared the role of AOP in balancing energy and carbon metabolism in palustrine and terrestrial environments by identifying metabolic relationships between primary carbon metabolites and AOP in each habitat. We measured oxygen isotope discrimination during respiration, gas exchange, and metabolite profiles in aerial leaves of ten fern and angiosperm species belonging to five families organized as pairs of palustrine and terrestrial species. We performed a partial least square model combined with variable importance for projection to reveal relationships between the electron partitioning to the AOP (τa) and metabolite levels. Terrestrial plants showed higher values of net photosynthesis (AN) and τa, together with stronger metabolic relationships between τa and sugars, important for water conservation. Palustrine plants showed relationships between τa and metabolites related to the shikimate pathway and the GABA shunt, to be important for heterophylly. Excess energy dissipation via AOX is less crucial in palustrine environments than on land. The basis of this difference resides in the contrasting photosynthetic performance observed in each environment, thus reinforcing the importance of AOP for photosynthesis.

The interaction of the alternative oxidase (AOX) pathway with nutrient metabolism is important for understanding how respiration modulates ATP synthesis and carbon economy in plants under nutrient deficiency. Although AOX activity reduces the energy yield of respiration, this enzymatic activity is upregulated under stress conditions to maintain the functioning of primary metabolism. The in vivo metabolic regulation of AOX activity by phosphorus (P) and nitrogen (N) and during plant symbioses with Arbuscular mycorrhizal fungi (AMF) and Rhizobium bacteria is still not fully understood. We highlight several findings and open questions concerning the in vivo regulation of AOX activity and its impact on plant metabolism during P deficiency and symbiosis with AMF. We also highlight the need for the identification of which metabolic regulatory factors of AOX activity are related to N availability and nitrogen-fixing legume-rhizobia symbiosis in order to improve our understanding of N assimilation and biological nitrogen fixation.