Colombia, one of the world’s leading coffee producers, is increasingly threatened by climate change. By 2050, some northern regions are projected to experience higher temperatures and reduced rainfall, posing risks to coffee production. Understanding how different coffee varieties respond to heat and drought is therefore essential for sustaining coffee production in the country. We evaluated the thermotolerance and drought response of two Coffea arabica L. varieties, Castillo and Caturra, under controlled conditions. Thermotolerance was quantified using T50, the temperature causing a 50

Theobroma cacao, one of Colombia's most socially significant crops, faces productivity challenges due to drought. This stress can reduce growth, leaf area, and stomatal conductance (Ks) and generate reactive oxygen species. Therefore, exploring solutions to enhance drought tolerance is crucial. This study aimed to (i) design a strategy to select fungal root endophytes with the potential to alleviate drought stress in plants; (ii) isolate fungi from Stenocereus spp. to induce drought tolerance in T. cacao genotype ICS95. In vitro drought tolerance screening identified five fungal isolates that exhibited the highest biomass production and less than 20% biomass loss under drought conditions compared with non-drought conditions. The soil of juvenile T. cacao plants was inoculated with these isolates, and physiological and morphological parameters were assessed, including leaf water potential (ΨL), Ks, proline content, and growth. The results showed a significant decrease in ΨL and Ks in juveniles under drought stress, which was observed across all five fungal isolates tested. However, juveniles inoculated with Phoma sp. exhibited significantly less negative ΨL than non-inoculated controls, suggesting that this fungus may be a potential inducer of drought tolerance in T. cacao ICS95. One intriguing result was that plants inoculated with this fungus accumulated less proline during the drought treatment. Under non-drought conditions, juveniles inoculated with Fusarium sp. exhibited a significant increase in specific leaf area under non-drought conditions compared to non-inoculated control. These findings suggest that fungal endophytes associated with Stenocereus spp. affect the physiological response of cacao juveniles under drought conditions.IMPORTANCETheobroma cacao is among the world's most valuable crops, yet its productivity is increasingly threatened by fluctuating rainfall and prolonged drought. Identifying sustainable strategies to mitigate these impacts is therefore critical. Xerophilic plants, such as Stenocereus spp., harbor diverse fungal endophytes adapted to arid environments, representing a promising source of microorganisms capable of enhancing stress tolerance in commercial crops. Our study demonstrates that cactus-derived endophytes could improve drought resilience in juveniles of cacao, in particular, the fungal endophyte Phoma sp. maintained less negative leaf water potential values under drought stress conditions and exhibited significantly lower proline accumulation compared to non-inoculated controls. Furthermore, under favorable conditions, some endophytes could promote growth by increasing leaf area compared to non-inoculated plants. These findings underscore the potential of fungal endophytes from arid ecosystems as biotechnological tools for sustainable cacao production. Further studies should explore the role of fungi when affecting plant proline metabolism.

Phaseolus vulgaris L. is a key food crop in tropical regions, where climate change is expected to increase the frequency and intensity of drought events. The use of plant growth-promoting bacteria (PGPB) offers a sustainable alternative to chemical fertilizers and may enhance crop resilience under water-limited conditions. We evaluated whether inoculation with Lysinibacillus sphaericus improves drought tolerance in P. vulgaris. Plants were assigned to four treatments: inoculated/non-inoculated × control/ drought, exposed to 14 days without irrigation, and monitored for leaf water potential (ΨL), stomatal conductance (gs), photosynthetic rate (Amass) and transpiration rate (E) every seven days, followed by seven days of recovery. Inoculated plants maintained higher ΨL, lower E and higher Amass under drought, resulting in greater total plant biomass primarily through increased leaf production. After rewatering, all inoculated plants fully recovered, whereas only one non-inoculated plant did. These results demonstrate that L. sphaericus enhances drought resilience in P. vulgaris, highlighting its potential as a biological tool for sustainable bean production with reduced chemical fertilizers under future climate scenarios. Further studies should investigate the specific physiological and biochemical mechanisms underlying this response–such as shifts in root architecture, osmolyte accumulation, and nutrient uptake–and evaluate impacts on yield and pod production under field conditions.

The adaptive responses of Espeletia standleyana and E. santanderensis populations in a paramo in Northeastern Colombia (3350 m a.s.l.), were studied to characterize their spatial segregation. Their anatomical, morphofunctional and leaf biomass characteristics were determined and compared. We found that many traits such as depth of the stomatal crypts, number of vascular bundles, leaf and peduncle xylem vessel diameters, thickness of the mesophyll, leaf area, rosette height and diameter, leaf water content, leaf area index, and leaf biomass were significantly higher in E. standleyana (P< 0.05). Meanwhile, the diameter of the vascular bundles, width of stomatal crypts, number of leaves, specific leaf area, and percentage of sclerophylly were higher in E. santanderensis (P<0.05). Multifactorial segregation indicated highly differential expressions in their morphofunctional and leaf biomass characteristics, evidencing adaptations to their microhabitats. E. standleyana showed xeromorphic characters in response to the greater ambient fluctuations typical of the paramo, while E. santanderensis responded with scleromorphic traits related to lower soil organic matter and water content, characteristic of the high Andean forest-paramo ecotone. The high spatial heterogeneity of the paramos allows the development of microclimatic and edaphic mosaics that determine population segregation of these growth forms.

Glomalin-Related Soil Proteins (GRSP) are generally reported to originate from mycorrhizae, but there are suggestions that they may originate from various soil microorganisms. Biofertilizers aim to reduce the application of inorganic fertilizers, thereby improving soil health and positively influencing plant productivity. The objective of this study was to characterize GRSP in cultivated soil bioinoculated with a microbial consortium (MC) of the bacterial strains ME01 (Rhizobium tropici) + Leu2A (Bradyrhizobium japonicum). These strains were selected for their plant growth-promoting effects on Allium cepa L. under conditions of inorganic fertilization and water deficit. An onion crop was established with normal irrigation (NIr) (100

Synergistic studies of microorganisms in the last decade have been mostly directed towards their biofertilizing effects on growth and crop yield. Our research examines the role of a microbial consortium (MC) on physiological responses of Allium cepa hybrid F1 2000 under water and nutritional deficit in a semi-arid environment. An onion crop was established with normal irrigation (NIr) (100% ETc) and water deficit (WD) (67% ETc) and different fertilization treatments (MC with 0%, 50% and 100% NPK). Gas exchange (Stomatal conductance (Gs), transpiration (E) and CO2 assimilation rates (A)) and leaf water status were evaluated throughout its growth cycle. The MC + 50% NPK treatment with NIr maintained similar A rates to the production control. A. cepa decreased Gs by approximately 50% in the WD treatment. The highest water use efficiency (WUE) and an increase in the modulus of elasticity in response to water stress were obtained for the 100% NPK treatment under non-inoculated WD. The onion hybrid F1 2000 was tolerant to water stress and under non-limiting nutrient conditions, irrigation may be reduced. The MC facilitated the availability of nutrients under NIr allowing a 50% reduction in the application of high doses of fertilization without affecting yield, resulting in a suitable agroecological strategy for this crop.

Parasitic plants exhibit a clear competitive advantage acquiring resources, enabling them to occupy all major global ecosystems. Hemiparasites are capable of connecting to their hosts’ root or stem vascular systems through haustoria establishing a flow of water and nutrients between host and parasite. These parasitic associations have an important influence on biodiversity, consequently shaping plant communities through a reduction in growth and alteration of the competitive ability of parasitized hosts. Castilleja fissifolia L.f. (Orobanchaceae), the genus’ type species, is an abundant erect herb that inhabits the high tropical Andes and is commonly found in close spatial association with other plant species. Since many other species of the genus Castilleja have been described as hemiparasites, we sought to determine if C. fissifolia establishes parasitic relationships in the Venezuelan high Andes. And if so, to study its host range and facultative/obligate relations. Ten soil blocks which included C. fissifolia individuals were excavated from each of three sites in Piedras Blancas Paramo (PBP, 4250 m), taken to the laboratory and thoroughly examined to identify the presence of C. fissifolia -host interfaces. Instances in which one or more haustoria were found anchored to the roots of a potential host were recorded. C fissifolia acts as a non-specific hemiparasite of at least 44 plant species in PBP, including 25 eudicots, 18 monocots, and 1 pteridophyte, belonging to 16 plant families. These results represent the largest reported host range for any species within the genus Castilleja .

High mountain ecosystems are subjected to frequent freeze–thaw events all-year round, consequently plants have developed freezing resistance mechanisms to cope with extreme low temperatures. Additionally, these events have also been correlated with the risk of cavitation so that plants need to adapt their water transport system. Information on freezing resistance and xylem vessel characteristics along elevation gradients is scarce for neotropical high elevation species. In this study we aboard two specific questions: 1. Are there intraspecific differences in freezing resistance between low and high elevation populations of Senecio formosus Kunth? 2. Could an increase in freeze–thaw cycle frequency and lower freezing temperatures at higher elevations determine differences in xylem conduit traits between low and high elevation S. formosus populations? We expect greater freezing resistance and a safer water transport system, mainly shaped by narrower tracheary elements in higher elevation populations compared to lower ones. Freezing resistance (avoidance and tolerance) and tracheary elements were studied in S. formosus at its lower (3100 m) and upper (4200 m) distributional limits in the Venezuelan paramo. Freezing resistance was determined through injury and freezing temperature determinations; whereas xylem conduit characteristics dealt with were: vessel element and tracheid diameters,

Tropical high andean ecosystems, known as paramos, are unique because they are highly diverse, have a high number of endemic species, and play an essential role in different ecosystem services, but are especially susceptible to climate change. Most of the giant rosettes, a dominant growth-form in the paramos, depend on unique features like stems protected by marcescent leaves, voluminous stem pith, and leaf pubescence. However, Ruilopezia atropurpurea lacks these characteristics and must respond differently to endure the paramo extreme conditions. Additionally, unlike other rosettes, this species is found under contrasting exposed and understory microenvironments so that intraspecific plasticity is also expected. We evaluated the responses of R. atropurpurea in terms of leaf water relations, gas exchange, and morphological characteristics in temporal (seasonal and daily variations) and spatial (microsite differences) scales in a Venezuelan paramo. R. atropurpurea displayed lower leaf water potentials (minimum leaf water potentials of -1.5 MPa and -1.8 MPa at the turgor loss point), higher leaf conductance (620 mmol m-2s-1), transpiration (5 molm-2s-1), and CO2 assimilation (13 mmol m-2s-1) rates compared to other paramo giant rosettes. A reduction in leaf area and specific leaf area occurred from understory to exposed sites. R. atropurpurea diverges from the typical responses of most paramo giant rosettes to the extreme environmental conditions. This species’ morphological and physiological plasticity permits it inhabit under variable microclimatic conditions, but despite its confirmed plasticity, it is not able to reach higher elevations as other giant rosettes successfully have.

The páramo, a high tropical Andean ecosystem, presents very distinct climatic, floristic and ecological features. Paramo plants have adapted to pronounced daily temperature fluctuations, freezing temperatures any night of the year, high incoming radiation and seasonal unfavorable water availability conditions. Long fallow agricultural systems are common in the páramo, permitting partial recuperation of the vegetation through a secondary succession. Different hypothesis related to plant traits (water relations and gas exchange characteristics or biomass allocation patterns) during succession have been proposed. Particular traits have been associated to the stages along successional gradients from early species (traits related to high resource acquisition abilities) to late species (traits linked to internal conservation of resources). Our purpose was to study plant functional responses of different herbaceous species in an old-field succession in the high tropical Andes. Plant traits (specific leaf area (SLA), maximum CO2 assimilation rates (Amax), leaf nitrogen content (Nleaf), leaf water relations and biomass allocation) were studied in grasses and forbs along different successional stages. Clear trends in SLA, Amax on a mass basis, Nleaf and aboveground/belowground biomass allocation were found along the successional gradient for grasses, while patterns were not as well-defined for forbs in the latter two traits. No patterns in leaf water relations characteristics were observed for either plant-growth forms. Strategies associated to plant traits significantly influence plant species dominance and community assembly during secondary succession in tropical alpine open environments like the páramos. Plant traits linked to rapid growth (SLA, Amax and Nleaf) dominate during early succession. In contrast to previous studies, drought resistance traits were not found to dominate in late succession stages for either grasses or forbs.

The practice of producing more vigorous seedlings represents a competitive advantage at the time of transplanting a crop, and the use of combined biofertilizers are a sustainable ecological alternative. The objective of this research was to select a microbial consortium for the production of F1 2000 hybrid onion seedbeds under shade-house conditions. Five rhizobacterial strains of the genera Rhizobium (ME01 strain), Bradyrhizobium (Leu2A and YE1 strains), Ochrobactrum (ES1 strain) and Pseudomonas (Alf strain), which have shown favorable effects on pepper and lettuce seedlings. These rhizobacteria were inoculated in a mixed manner (microbial consortium) in onion as follows: Alf+ES1, ME01+ES1, ES1+Leu2A, Alf+Leu2A, YE1+ES1, ME01+Alf, YE1+Alf, ME01+YE1, YE1+Leu2A, ME01+Leu2A, using a soil from San Juan de Lagunillas-Mérida, Venezuela under shade-house conditions for 60 days. The following variables were determined: number of leaves, pseudostem base diameter, aerial and root length, aerial and root fresh and dry weight. Additionally, a CO2 assimilation curve under different light levels was carried out on the seedlings of the selected consortium to observe their photosynthetic response. The consortium ME01 + Leu2A (Rhizobium tropici + Bradyrhizobium japonicum) increased all studied variables, especially the pseudostem base diameter, essential for onion cultivation, and yielded higher seedlings CO2 assimilation rates. The use of this microbial consortium is recommended as an option for agricultural production under seedbed conditions.

In a scenario of world population increase and climate change, an efficient use of water is key for agricultural production. Onion is one of the most profitable crops and can adapt to particular conditions of water stress. The objective of this research was to determine growing degree-days and accumulated radiation under non-stress conditions and yield of an F1 2000 hybrid of onion (Allium cepa L.) under water deficit (WD) and biofertilization in a semi-arid environment. An established nutrient requirement of 247 kg N, 240 kg P2O5(105 kg P), 240 kg K2O (199 kg K), and two irrigation factors were applied: normal irrigation with a daily and WD with a 3 d interval irrigation frequencies. The effect of biofertilization was evaluated through the inoculation of a microbial consortium (MC) in combination with four NPK fertilizer treatments. The crop accumulated 1334 degree-days and 1188 MJ m−2·d−1at the time of harvest at 71 d after transplanting. The yield was 36 t·ha−1, similar under both irrigation conditions; and the WD treatment resulted in a 35% water savings, a 47% and 65% increase in water use efficiency and modulus of elasticity, respectively. The MC resulted in a 50% NPK savings under non-limiting water conditions and produced a similar yield compared with the 100% NPK non-inoculated control. The lower irrigation frequency together with the 100% NPK fertilization dose without the MC and the use of the microorganisms and the 50% NPK treatment without water stress are recommended as agrosustainable practices for onion production.

Nitrogen nutrition considerably influences the process of growing and producing potato crops. The aim of this study was to determine the effects of nitrogen nutrition on the pattern of biomass and nitrogen partitioning during the growth of potato crop in Mérida, Mérida, Venezuela. Experimental land plots were set, with a randomized blocks design, and with three different fertilization treatment settings for the "Granola" cultivar. The first one without nitrogen (0-N), the next one with 133 Kg N Ha-1 (133-N), and the last one with 400 Kg N Ha-1 (400-N). In the main phenological stages of the crop, biomass and nitrogen levels were measured for each organ. The performance of the tubers and the total biomass are strongly influenced by the availability of nitrogen and assimilatory biomass. The total biomass production, as well as the biomass and nitrogen partitioning to each organ, showed the following sequence: 400-N > 133-N > 0-N. However, biomass and nitrogen partitioning to the roots and stolons was higher in the treatment with limited nitrogen levels. Proportional changes among aboveground and belowground biomass are adaptive responses to nitrogen deficit conditions, which, in their turn, are determining factors in crop production.

Nitrogen fertilization has positive effects on growth and production of potato crop. The objective of this study was to assess the differences of the photosynthetic response and biomass partitioning patterns during the main phenophases of the potato cultivar Capiro under different nitrogen nutrition fertilization treatments in the tropical Andes of Mérida, Venezuela. Plots of 40 m2 (2,625 plants m-2) were established under a random block design with three replications by nitrogen fertilization treatment: 0, 100, 200, and 300 kg. N ha-1. Photosynthesis and biomass were measured in the different organs in the main phenological stages of the crop. The results indicate that photosynthesis tends to increase slightly with the nitrogen supply; although the differences were not always significant and, decreases during crop growth. Tubers yield it was markedly influenced by the nitrogen fertilization. The total biomass production, as well as biomass allocation in different organs showed differences between treatments, maintaining the following order: 300-N> 200-N> 100-N> 0-N. When analyzing the biomass accumulation curves, it is estimated that the application of 250 kg N ha-1 as mineral fertilizer is enough to reach optimal production yields.

Background: Tropical mountain ecosystems of the Northern Andes have long fascinated researchers because of the unique conditions associated with cold climates in equatorial latitudes. More than six decades have elapsed since the beginning of systematic ecological research in the Venezuelan paramos, making them one of the best-studied tropical alpine regions in the world. Aims: We review the conceptual development and state of the art of ecological research in the Venezuelan paramos, with emphasis on environmental and plant ecology research, presenting a general framework for the studies included in this special issue. Methods: We provide a historical sketch of the periods that have marked ecological studies in the Venezuelan paramos. Then, we synthesise research on environmental drivers, plant population and community ecology, ecosystem functioning, the response of the paramo to climate change and human disturbance; we finally consider agroecology and conservation. Results and conclusions: This review demonstrates the significant contributions made to alpine ecology in key areas such as biodiversity/ecosystem function changes during succession, nutrient cycling, species interactions and socio-ecological research. We indicate the need to develop a more integrated view of the links between evolutionary processes, functional diversity, community dynamics and ecosystem services both in natural and human-impacted areas.

Background: Tropical high mountains present extreme daily temperature variations, frequent high air evaporative demands and seasonal differences in soil water availability. Plants have adapted to these conditions through different avoidance-tolerance mechanisms. This review focuses on plant-growth forms and their adaptive strategies. Aims: This integrated review of p?ramo plant traits aims at contributing to understanding the functioning of plant-growth forms and their significance on ecosystem properties under environmental climate and land-use changes. Methods: Plant responses are presented along avoidance-tolerance gradients considering three main aspects: freezing resistance, water relations and gas exchange characteristics. Results from 45 herbaceous and 42 woody species along elevational gradients in the Venezuelan high Andes were analysed. Results: Leaf supercooling is the common avoidance response of woody plants to night-time freezing temperatures, while herbaceous plants tolerate frost. Trees and caulescent rosettes maintain more positive leaf water potentials under water deficit conditions compared to more tolerant herbaceous species. All plant growth-forms showed strong stomatal control under dry-season conditions. Conclusions: P?ramo plant growth-forms may be separated according to an avoidance-tolerance gradient in response to water deficit and low temperature resistance. Woody growth-forms tend to avoid both freezing and water stress, while herbaceous forms tolerate frost and resist an unfavourable water status. Grasses and cushion plants are at the tolerant extreme of the gradient and coincide in that both reach the highest elevations in the p?ramo. Andean giant rosettes are freezing avoidant, particularly susceptible to water deficit and the most vulnerable, of all growth-forms, to changing environmental conditions.

Background: Stomatal response functions of dominant plant species can provide insights into the behaviour of ecosystems under environmental stress, and provide tools for modelling their response to climate change. However, they remain little studied in tropical Alpine ecosystems. Aims: Our objective was to formulate and compare stomatal response functions for two dominant paramo species with different adaptive strategies to drought, the stress-tolerant shrub Hypericum laricifolium, and the stress avoiding giant rosette Espeletia schultzii and thus enable making projections as to their future fitness in a changing climate. Methods: A reanalysis of data found in the literature and new ecophysiological and micrometeorological measurements were used to fit and test new stomatal response functions to environmental variables for these two species. Results: The response functions of vapour pressure differences between leaf and air showed an exponential decrease for both species, while for photosynthetically active radiation (PAR), peak-form response functions provided the best fit. The response function for leaf water potential was linear for the drought-tolerant shrub and decreased exponentially for the stress avoiding giant rosette. Several thresholds prior to stomatal closure were also included in the functions. Conclusions: Although stress-avoiding and stress-tolerant strategies are both successful in the Andean paramo, the response functions suggest that the tolerant shrub could be more resistant to more intense drought.

Background: Woody bamboos of the genus Chusquea grow along a broad range of elevations in the Venezuelan Andes. Their growth-form and density vary along the cloud forest – páramo gradient. In this article, we related ecophysiological traits and population genetic diversity information to explain the distribution of growth-form patterns of Chusquea in the Merida Andes, Venezuela. Aims: We quantified differences in the ecophysiological response and genetic diversity of scandent cloud forest and shrub-like páramo bamboos of the genus Chusquea, taking in account the differences in their flowering patterns, growth-form and habitat. Methods: We related low temperature resistance, water relations and leaf gas exchange variables to the growth-form, habitat, flowering patterns and genetic diversity in species of Chusquea. The genetic diversity study was based on Inter Sequence Simple Repeats and Random Amplified Polymorphic DNA markers analysis of cloud forest and páramo populations. Results: Scandent cloud forest and shrub-like páramo species of Chusquea had a very similar ecophysiological response for all the variables analysed during wet and dry seasons and were capable of enduring freezing temperatures through moderate supercooling. Species associated with the cloud forest – páramo gradient maintained low stomatal conductance and transpiration rates that favoured high leaf water potentials, without limiting photosynthetic rates. Shrub-like bamboos growing above the continuous forest line had a small decline in net photosynthesis rates, associated with an increase in water use efficiency. Both scandent and shrub-like bamboos had a remarkably high genetic diversity, comparable to non-clonal species. Conclusions: Species of Chusquea in the Venezuelan Andes are a physiologically relatively homogeneous group across a broad elevation gradient. Population genetic diversity appears to be more related with their flowering pattern and habitat conditions than with their growth form.

Nitrogen fertilization has considerable effects on growth and yield of potato crop. Leaf expansion is one of the most important growth parameters that can be used to optimize nitrogen fertilization management in agroecological practices. We evaluated the effect of nitrogen fertilization on the leaf area index (LAI) of potato crop during different phenological stages by two different methods. Experimental plots were established in a randomized block design with the following treatments: no nitrogen supply (0-N), 133 kg N ha-1 (133-N), and 400 kg N ha-1 (400-N), using the Granola variety, at the Andes region, Merida city, Venezuela. We measured leaf area at the main phenological stages of the crop using a plant canopy analyzer. LAI showed significant differences among treatments and phenological stages, except during the emergence stage. The maximum LAI values were obtained 55 days after emergence: 400-N (1.42±0.16) > 133-N (0.92±0.21) > 0-N (0.34±0.08). Nitrogen fertilization had a significant effect on the development of LAI in potato crop along its different phenological stages.

Strong daily temperature variations, seasonal soil water availability and high air evaporative demands play an essential role in adaptive responses of tropical high elevation mountain plants. Giant rosettes are a perfect example of successful adaptations to these conditions, representing an important life-form of high elevation tropical mountains in the Andes, Hawaii and Africa, a well-known case of convergent evolution. Adaptive radiation resulted in a substantially large number of giant rosette species in the 'paramos', a local name given for tropical alpine Andean vegetation. Plant functional responses: plant water relations, gas exchange characteristics and freezing resistance in giant rosettes are described in order to understand their responses to extreme environmental conditions characteristic of high elevation tropical habitats. Giant rosettes have a large capacitance (water-storage pith) and strong stomatal control to cope with periods of water deficit, resulting in the maintenance of high leaf water potentials on a daily and seasonal basis. Maximum net CO2 assimilation rates are variable among species (3-10 mu mol m(-2) s(-1)), all showing photosynthetic decreases from wet to dry seasons. Giant rosettes rely on permanent supercooling of the leaves together with insulating structures protecting stems and apical buds to cope with freezing damage. Even though the general aspect and plant morphology of giant rosettes is similar across all high elevation tropical regions, responses to similar selective pressures resulted in different physiological characteristics in freezing resistance mechanisms, e.g. tolerance versus avoidance, and thermal balance of the rosette. Giant rosette responses under changing global environments are also discussed. The emphasis in the description of physiological and morphological characteristics will be on South American giant rosettes due to the large number of studies and the large number of species occurring in this region.