Narcy Anai Pereira-Zaldívar

Numerous plant species can actively pressurize water in their xylem. It has been hypothesized that regular peaks in positive pressure help plants to remove xylem embolism and to replenish water reservoirs. This may happen after rewatering when plants have suffered from soil water deficit (WD) and/or following diurnal cycles under well-watered (WW) conditions. Using X-ray microcomputed tomography (µCT), we tested these hypotheses in tomato plants by quantifying xylem functionality and internal water pools in stems of 35 plants subjected to WD intensities before and after rewatering and 14 WW plants. Positive xylem pressure was detected in only 30% of the WD plants after rewatering, with a majority of this 30% showing no or rare events of xylem embolism repair. However, all WD tomato plants restored their internal water pools after rewatering, independently of their ability to generate detectable positive xylem pressure. In WW plants, positive xylem pressure was consistently generated and allowed for repair of the few embolized vessels. The ability of tomato plants to rehydrate non-xylary parenchyma tissues after WD and to repair embolisms under WW conditions sheds new light on alternative water-use mechanisms of herbaceous species to recover from drought.

As drought events become more severe, understanding drought‐tolerance traits in crops is vital for food security. Brassica oleracea L., a widely consumed vegetable (including cabbage, cauliflower, and broccoli), has seen a rise in cultivation, but the response of different genotypes to drought remains poorly studied. Here, we investigated the mechanisms underlying drought resistance in seven genotypes of B. oleracea (two grandparental lines and five F2 genotypes) by examining stem anatomical and hydraulic traits, as well as stomatal characteristics, leaf dimensions, and stomatal regulation under drought conditions. Detailed measurements of stem anatomical traits were obtained using light and electron microscopy, while stem hydraulic vulnerability was assessed using the Optical Vulnerability method. The seven genotypes displayed contrasting water‐use and hydraulic strategies. Under well‐watered conditions, initial stomatal conductance ( g _sΨ0 ) showed considerable variation independent of their leaf and stomata size and density, while the leaf water potential at 90% stomatal closure ( Ψg _s90 ) was similar among genotypes. Stomatal safety margins (SSM) were positive across genotypes, confirming coordination between stomatal regulation and xylem hydraulics, and mainly driven by stem P ₅₀ , which was approximately 1 MPa lower in the most tolerant genotype. Embolism resistance was best explained by the thickness of the intervessel pit membrane, highlighting the importance of including anatomical traits in plant drought tolerance studies. To conclude, the intraspecific variation observed in anatomical, hydraulic and stomatal traits among our B. oleracea genotypes indicates potential adaptability to drought and suggests that more drought‐tolerant genotypes could be identified within this crop species through targeted, human‐mediated crosses.

As the human population grows and droughts become more frequent and intense, identifying drought-responsive anatomical and ecophysiological traits in crops is critical to safeguard food production in a world that is becoming more demanding for plant growth. Solanum lycopersicum (tomato) is a major herbaceous crop species in which stem woodiness increases with age, especially in the basal stem regions, providing an opportunity to investigate how developmental changes in stem structure influence plant–water relations under drought. In this study, we investigated a 2-month and a 4-month old batch of two woody knockout mutant genotypes (double SOC1-like, quadruple FUL SOC1-like), as well as the wild type Solanum lycopersicum var. Moneyberg, to assess how differences in stem woodiness from genetic modification and plant age influence total plant drought tolerance. Therefore, we quantified a suite of drought-responsive anatomical traits and monitored ecophysiological traits from stems and/or leaves under well-watered and/or drought conditions. These traits included stem lignification, intervessel pit membrane thickness, stomatal traits, plant water potential dynamics, and resistance to drought-induced embolism. Overall, our results show that drought tolerance increases with plant age, primarily through enhanced resistance to drought-induced embolism in the stem, which correlates with increasing stem lignification at the basal stem. Stomata control plays a minor role, as resistance to drought-induced embolism drives major differences in the stomatal safety margin. When comparing developmental stages, variation in embolism resistance and woodiness in stems explains drought tolerance differences within genotypes, whereas intervessel pit membrane thickness is the primary driver of drought tolerance differences among genotypes. These findings demonstrate the dynamic role of drought-associated plant traits at the species level, highlighting once again the remarkable ability of plants to adapt to their environmental conditions.

Complex trichomes in the leaves of epiphytic Bromeliaceae absorb water and nutrients, while also facilitating long distance water transport along the leaf surface, a phenomenon previously characterized for two Tillandsia species. This study aimed to determine trichome traits that govern external water transport speed, and its relation to life form, xylem transport capacity and environmental conditions. Using near-infrared optical techniques, we characterized trichome-mediated transport in 19 species and analyzed its association with trichome and vascular traits, functional group, and habitat parameters. External leaf water transport was observed in 10 species, all of which were atmospheric life forms (nebulophytes and pseudobulbs). Transport speed positively correlated with trichome area, wing length, and degree of overlap. Species with higher trichome overlap had lower xylem capacity (Kx) and tracheid diameter and numbers, suggesting that the atmospheric life form is related to secure, inefficient vascular systems, which may be partly compensated with external transport. External transport was more common in species from habitats with high maximum vapor pressure deficits and low aridity indices, suggesting it enhances water uptake by rapidly redistributing water across available trichomes before evaporation can occur.

The Bromeliaceae family has been used as a model to study adaptive radiation due to its terrestrial, epilithic, and epiphytic habits with wide morpho-physiological variation. Functional groups described by Pittendrigh in 1948 have been an integral part of ecophysiological studies. In the current study, we revisited the functional groups of epiphytic bromeliads using a 204 species trait database sampled throughout the Americas. Our objective was to define epiphytic functional groups within bromeliads based on unsupervised classification, including species from the dry to the wet end of the Neotropics. We performed a hierarchical cluster analysis with 16 functional traits and a discriminant analysis, to test for the separation between these groups. Herbarium records were used to map species distributions and to analyze the climate and ecosystems inhabited. The clustering supported five groups, C₃ tank and CAM tank bromeliads with deep tanks, while the atmospheric group (according to Pittendrigh) was divided into nebulophytes, bromeliads with shallow tanks, and bromeliads with pseudobulbs. The two former groups showed distinct traits related to resource (water) acquisition, such as fog (nebulophytes) and dew (shallow tanks). We discuss how the functional traits relate to the ecosystems inhabited and the relevance of acknowledging the new functional groups.