Laticifers are specialized secretory cells that synthesize and store latex and provide a model for studying cellular specialization in plant metabolism. Euphorbia lathyris L. possesses non-articulated laticifers that produce triterpenoid-rich latex, but the mechanistic basis of laticifer specialization and latex metabolism remains unclear. Here, we generate the single-nucleus transcriptomic landscape of E. lathyris leaves and resolve a continuous laticifer trajectory with progressive activation of the mevalonate-derived triterpenoid pathway. Genes encoding the rubber biosynthetic complex, including cis-prenyltransferase (CPT), CPT-binding protein (CBP), and small rubber particle protein (SRPP), were specifically expressed in laticifers, indicating potential rubber formation. Ultrastructural and chemical analyses detect small rubber particles (similar to 150 nm) and a low-abundance cis-1,4-polyisoprene fraction in latex (0.30-0.47% w/w) with short average chain length (Mw approximate to 150-180 kDa). The streamlined repertoire of rubber biosynthetic pathway genes and the absence of Hevea-like rubber elongation factors (REFs) may be associated with the observed low rubber content and smaller molecular weight in E. lathyris. Network inference and validation identified a laticifer-specific DOF transcription factor, COGWHEEL1 (ElCOG1), that binds the promoters of ElCPT1 and butyrospermol synthase 1 (ElBUT1) and represses their activity, indicating a shared negative transcriptional control point acting on both the rubber-elongation and triterpenoid branches. In summary, this single-nucleus transcriptomic landscape of E. lathyris laticifers clarifies their metabolic specialization and establishes a framework for dissecting the regulatory programs of specialized secretory cells in latex-bearing plants.

Tropical tree species vary in photosynthetic temperature sensitivity, with species from warmer habitats or those acclimated to higher temperatures typically displaying higher thermal optima for net CO2 assimilation (Topt,Anet). Sustaining photosynthesis at elevated temperatures probably requires increased allocation of resources (ATP, NADPH, nitrogen, and carbon) towards heat stress management, particularly PSII repair. However, under extreme heat, repair demands may exceed available resources, potentially limiting acclimation. It is unclear whether higher Topt,Anet reflects inherently greater PSII heat stability. We studied 11 tropical tree species across a topographic (hilltop, slope, and valley) and thermal gradient (summer peaks: 46.1, 40.1, and 31.8 °C, respectively) in India's Central Western Ghats forest, measuring photosynthetic temperature responses and PSII thermal tolerance (T5, the temperature causing 5% PSII efficiency decline) at peak summer. We found an inverse correlation between T5 and Topt,Anet (P=0.005): lower Topt,Anet was associated with higher PSII heat stability (higher T5), and vice versa. This could suggest a trade-off between investing resources to achieve higher Topt,Anet and maintaining PSII heat stability. Species may struggle to simultaneously acclimate to elevated temperatures and remain resilient to extreme heat events. These findings have implications for understanding tropical forest tree responses to climate warming.

During development, cell fate determination hinges on the dynamic activities of multiple transcription factors (TFs), but how the activities of individual TFs contribute to developmental diversity remains incompletely understood. Here, we report that BZU2/ZmMUTE is responsible for the functional and spatial heterogeneity of the four-celled stomatal complexes in maize (Zea mays), in part through its liquid-liquid phase separation (LLPS) property. Genotypic and single-cell RNA-seq analyses confirmed previous findings that ZmMUTE is associated with lineage-specific gene expression during stomatal development, while providing additional resolution of cell-type-specific transcriptional programs. The intrinsically disordered region 4 (IDR4) promotes the formation of ZmMUTE condensates, which can recruit the ZmMUTE partner ZmSCRM and associate with transcriptionally active sites. These condensates are associated with enhanced DNA binding and target gene activation, potentially influencing the development of guard cells and subsidiary cells. IDR4 is also sufficient for conferring cell-to-cell mobility to AtMUTE, highlighting its conserved role in facilitating intercellular movement. Taken together, the dynamic behavior of ZmMUTE, owing to its condensational properties, appears to orchestrate cell-type-specific regulation, thereby enabling the emergence of the unique four-celled stomatal morphology.

Accurate characterization of the role of the dry tropics in the global carbon cycle requires precise estimation of woody biomass changes due to ecological and anthropogenic change, including deforestation, forest degradation, regrowth, mortality and enhanced tree growth due to climate change. L-band Synthetic Aperture Radar (SAR) backscatter observations offer a reliable option to consistently map these processes as they are (i) available globally since 2007 (JAXA ALOS-1, ALOS-2 and ALOS-4), and (ii) sensitive to woody structure, such as aboveground biomass density (AGBD) up to similar to 100 t ha(-1). However, we lack multi-site empirical understanding of the scattering processes that determine the relationship between L-band SAR and woody vegetation structure in the dry tropics, and how this is mediated by soil properties. This study used observations from ground plots in Africa (n = 171), Australia (n = 6), and South America (n = 44) to understand the impact of vegetation structure and soil properties on spatially and temporally coincident fully-polarimetric L-band SAR data. Fully-polarimetric L-band SAR single-look complex data were converted to scattering mechanisms/parameters using van Zyl, Cloude-Pottier, and Freeman-Durden polarimetric decompositions to elucidate the physical mechanisms involved. Multivariate SAR-vegetation-soil relationships were analysed using a theory-informed structural equation modelling approach. The strongest positive effects on volume scattering come from stem density (stems ha(-1)) and mean stem biomass of trees, and soil water and sand content (standardized regression coefficients of 0.3, 0.1, 0.2 and 0.1, respectively). The only significant effect on surface scattering is from stem density (0.1). Significant effects on double bounce scattering are from stem density (0.3) and soil sand content (-0.2). Since AGBD is the product of stem density and mean stem biomass, this modelling framework points to a stronger effect from the number of trees rather than their size/biomass. Therefore, AGBD maps relying solely on radar intensity may not reflect significant changes when AGBD is increasing due to the growth of existing stems. Additionally, such maps might overestimate changes in AGBD when driven by the recruitment of new stems or loss of existing stems. Full-polarimetric observations allow the decomposition of the radar signal into volume scattering, surface scattering, and double bounce, enabling the inversion of structural equation models to retrieve both stem density and mean stem biomass. This provides a more comprehensive description of forest structure compared to retrieving only AGBD. As this approach depends on full-polarimetric data, its effectiveness is closely tied to the availability of such observations. Our findings underscore the value of recent and upcoming missions such as ALOS-4 PALSAR-3, BIOMASS and ROSE-L, and highlight the need to prioritise the acquisition of quad-pol SAR data to support future large-scale retrieval of vegetation structure attributes.

Trees of southern Amazonian forests face an increase in the duration and intensity of soil and atmospheric drought, which impose a higher risk of hydraulic failure in the water transport system, decreasing the water supply to foliage and increasing the risk of dehydration and death. However, it is not well understood how key hydraulic-related traits vary among southern Amazonian forests and whether Amazonian trees adjust them to be more drought tolerant along a gradient of increasing aridity. We measured leaf water potential (Psi leaf) in the dry season, xylem water potential associated with 50% (Psi 50) and 88% embolism formation, hydraulic safety margin (HSM50) and wood density (WD) in four forests at the southern edge of the Amazon. We compared our results with measurements from the literature for 10 additional forests distributed across the Amazon and subjected to different maximum cumulative water deficit (MCWD), a climate index for drought severity. For some analyses, species sampled within each forest were weighted by basal area to obtain community-weighted means (CWMs). Southern edge forests had high resistance to hydraulic failure, with more negative Psi 50 than other Amazonian forests. HSM50 across species correlated positively with predawn Psi leaf, suggesting that shallower rooting species in these forests face greater risk of hydraulic failure. Across all sites considered (southern and wider Amazon), HSM50_CWM did not correlate with MCWD, despite a more negative Psi 50_CWM with increasing MCWD. However, forests at the driest range of MCWD showed greater variability in hydraulic failure risk and contained more species potentially operating beyond their hydraulic limits. Synthesis. Although southern Amazonian forest species have undergone selection for high hydraulic resistance, they are not equally safe to hydraulic failure, highlighting the importance of site- and species-dependent factors. On a broader scale across the Amazon, tree communities in drier sites maintain HSM50_CWM similar to those in wetter sites. This may be the result of species turnover towards taxa with more negative Psi 50 or shifts in water use strategies, such as tight stomatal regulation, deeper rooting or seasonal leaf shedding.

Amazon rainforests face intensifying water stress due to increases in vapour pressure deficit and changing hydrological regimes. Embolism resistance (Ψ50) is a critical metric of tree survival under drought conditions, it is defined as a plant's capacity to resist disruption of xylem water flow due to air bubble formation from water stress. However, measurements of Ψ50 are only available for a limited number of Amazon locations and species. Conversely, data on forest taxonomic composition are abundant across Amazonia, and if Ψ50 is conserved phylogenetically, these data could provide a way to scale-up drought resistance patterns. Here we evaluate Ψ50 measurements across non-flooded Amazonian tree taxa and reveal a moderate phylogenetic signal, with phylogenetic conservatism evident at the family-level. Notably, Fabaceae is amongst the most embolism-resistant tree families in Amazonia. Leveraging the phylogenetic signal we use species composition and tree size data from 448 forest plots across Amazonia to produce a macroecological assessment of Amazonian vulnerability to embolism. The resulting estimate spatial pattern reveals that forests in the Brazilian and Guiana Shield regions, where Fabaceae abundance is high, show strong resistance to embolism. In contrast, tree communities in Western Amazonia appear more vulnerable to embolism, suggesting a reduced capacity to withstand future drought conditions.

Understanding how the traits of lineages are related to diversification is key for elucidating the origin of variation in species richness. Here, we test whether traits are related to species richness among lineages of trees from all major biogeographical settings of the lowland wet tropics. We explore whether variation in mortality rate, breeding system and maximum diameter are related to species richness, either directly or via associations with range size, among 463 genera that contain wet tropical forest trees. For Amazonian genera, we also explore whether traits are related to species richness via variation among genera in mean species-level range size. Lineages with higher mortality rates—faster life-history strategies—have larger ranges in all biogeographic settings and have higher mean species-level range sizes in Amazonia. These lineages also have smaller maximum diameters and, in the Americas, contain dioecious species. In turn, lineages with greater overall range size have higher species richness. Our results show that fast life-history strategies influence species richness in all biogeographic settings because lineages with these ecological strategies have greater range sizes. These links suggest that dispersal has been a key process in the evolution of the tropical forest flora.

Understanding gene regulatory networks (GRNs) is essential for improving maize yield and quality through molecular breeding approaches. The lack of comprehensive transcription factor (TF)-DNA interaction data has hindered accurate GRN predictions, limiting our insight into the regulatory mechanisms. In this study, we performed large-scale profiling of maize TF binding sites. We obtained and collected reliable binding profiles for 513 TFs, identified 394,136 binding sites, and constructed an accuracy-enhanced maize GRN (mGRN+) by integrating chromatin accessibility and gene expression data. The mGRN+ comprises 397,699 regulatory relationships. We further divided the mGRN+ into multiple modules across six major tissues. Using machine-learning algorithms, we optimized the mGRN+ to improve the prediction accuracy of gene functions and key regulators. Through independent genetic validation experiments, we further confirmed the reliability of these predictions. This work provides the largest collection of experimental TF binding sites in maize and highly optimized regulatory networks, which serve as valuable resources for studying maize gene function and crop improvement.

Despite the progress in the measurement and accessibility of plant trait information, acquiring sufficiently complete data from enough species to answer broad-scale questions in plant functional ecology and biogeography remains challenging. A common way to overcome this challenge is by imputation, or 'gap-filling' of trait values. This has proven appropriate when focusing on the overall patterns emerging from the database being imputed. However, some applications force the imputation procedure out of its original scope, using imputed values independently from the imputation context, and specific trait values for a given species are used as input for computing new variables. We tested the performance of three widely used imputation methods (Bayesian hierarchical probabilistic matrix factorization, multiple imputation by chained equations with predictive mean matching, and Rphylopars) on a database of tropical tree and shrub traits. By applying a leave-one-out procedure, we assessed the accuracy and precision of the imputed values and found that out-of-context use of imputed values may bias the estimation of different variables. We also found that low redundancy (i.e. low predictability of a new value on the basis of existing values) in the dataset, not uncommon for empirical datasets, is likely the main cause of low accuracy and precision in the imputed values. We therefore suggest the use of a leave-one-out procedure to test the quality of the imputed values before any out-of-context application of the imputed values, and make practical recommendations to avoid the misuse of imputation procedures. Furthermore, we recommend not publishing gap-filled datasets, publishing instead only the empirical data, together with the imputation method applied and the corresponding script to reproduce the imputation. This will help avoid the spread of imputed data, whose accuracy, precision, and source are difficult to assess and track, into the public domain.

Climate change and landscape fragmentation have made fires the primary drivers of forest degradation in Southern Amazonia. Understanding their impacts is crucial for informing public conservation policies. In this study, we assessed the effects of repeated fires on trees with a diameter ≥10 cm across three distinct vegetation types in this threatened region: Amazonian successional forest (SF), transitional forest (TF), and ombrophilous forest (OF). Two anthropogenic fires affected all three vegetation types in consecutive years. We hypothesized that SF would be the least impacted due to its more open structure and the presence of fire-adapted savanna (Cerrado) species. As expected, SF experienced the lowest tree mortality rate (9.1%). However, both TF and OF were heavily affected, with mortality rates of 28.0% and 29.7%, respectively. Despite SF’s apparent fire resilience, all vegetation types experienced a significant net loss of species and individuals. These results indicate a fire-induced degradation stage in both TF and OF, characterized by reduced species diversity and structural integrity. Our findings suggest that recurrent fires may trigger irreversible vegetation shifts and broader ecosystem tipping points across the Amazonian frontier.

Understanding the capacity of forests to adapt to climate change is of pivotal importance for conservation science, yet this is still widely unknown. This knowledge gap is particularly acute in high-biodiversity tropical forests. Here, we examined how tropical forests of the Americas have shifted community trait composition in recent decades as a response to changes in climate. Based on historical trait-climate relationships, we found that, overall, the studied functional traits show shifts of less than 8% of what would be expected given the observed changes in climate. However, the recruit assemblage shows shifts of 21% relative to climate change expectation. The most diverse forests on Earth are changing in functional trait composition but at a rate that is fundamentally insufficient to track climate change.

Increasing temperatures in the tropics will reduce performance of trees and agroforestry species and may lead to lasting damage and leaf death. One criterion to determine future forest resilience is to evaluate damage caused by temperature on Photosystem-II (PSII), a particularly sensitive component of photosynthesis. The temperature at which 50% of PSII function is lost ( T 50 ) is a widely used measure of irreversible damage to leaves. To assess vulnerability to high temperatures, studies have measured T 50 or leaf temperatures, but rarely both. Further, because extant leaf temperature records are short, duration of exposure above thresholds like T 50 has not been considered. Finally, these studies do not directly assess the effect of threshold exceedance on leaves. To understand how often, and how long, leaf temperatures exceed critical thresholds, we measured leaf temperatures of forest and agroforestry species in a tropical forest in the Western Ghats of India where air temperatures are high. We quantified species-specific physiological thresholds and assessed leaf damage after high-temperature exposure. We found that leaf temperatures already exceed T 50 . However, continuous exposure durations above critical thresholds are very skewed with most events lasting for much less than 30 min. As T 50 was measured after a 30-min exposure, our results suggest that threshold exceedances and exposure durations for lasting damage are currently not reached and will rarely be reached if maximum air temperatures increase by 4°C. Consistent with this, we found only minor indications of heat damage in the forest species. However, there were indications of heat-induced reduction in PSII function and damage in the agroforestry leaves which have lower T 50 . Our findings suggest that, for forest species, while high-temperature thresholds may be surpassed, durations of exposure above thresholds remain short, and therefore, are unlikely to lead to irreversible damage and leaf death, even under 4°C warming.

Microclimate differences in water availability can drive seasonal water use and photosynthetic variation among co-occurring tropical tree species, especially in forests with strongly seasonal climates. We studied a tropical forest site in the Western Ghats, India, and characterised seasonal differences in photosynthetic CO2 assimilation rates (Anet) among nine tree species with contrasting leaf habit and topographic affinities: deciduous species in dry hilltops, dry-affinity evergreens on slopes and wet-affinity evergreens in valleys. Surface soil moisture was lowest in hilltops, intermediate on slopes and highest in valleys, with higher levels during the wet period compared to the dry period. As expected, deciduous species on dry hilltops showed higher photosynthetic rates at the thermal optimum (Topt) during the wet period, while evergreen species showed no overall seasonal differences. Interestingly, evergreen species with a dry affinity on hill slopes showed higher Anet at the thermal optimum during the dry period compared to the wet period, despite lower soil moisture. This suggests that these species either have sufficient water availability during the dry period or possess a warmer thermal niche preference/adaptation. Across species, stomatal conductance (gs) at Topt was generally higher during the wet period, except for one evergreen species. Our findings illustrate seasonal differences in photosynthesis among tropical tree species across different leaf habits and topographic affinities.

1. Leaf and wood functional traits of trees are related to growth, reproduction, and survival, but the degree of phylogenetic conservatism in these relationships is largely unknown. In this study, we describe the variability of strategies involving leaf, wood and demographic characteristics for tree genera distributed across the Amazon Region, and quantify phylogenetic signal for the characteristics and their relationships. 2. Leaf and wood traits are aligned with demographic variables along two main axes of variation. The first axis represents the coordination of leaf traits describing resource uptake and use, wood density, seed mass, and survival. The second axis represents the coordination between size and growth. Both axes show strong phylogenetic signal, suggesting a constrained evolution influenced by ancestral values, yet the second axis also has an additional, substantial portion of its variation that is driven by functional correlations unrelated to phylogeny, suggesting simultaneously higher evolutionary lability and coordination. 3. Synthesis. Our results suggest that life history strategies of tropical trees are generally phylogenetically conserved, but that tree lineages may have some capability of responding to environmental changes by modulating their growth and size. Overall, we provide the largest-scale synopsis of functional characteristics of Amazonian trees, showing substantial nuance in the evolutionary patterns of individual characteristics and their relationships.

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.

Lianas (woody vines) are important components of tropical forests and are known to compete with host trees for resources, decrease tree growth and increase tree mortality. Given the observed increases in liana abundance in some forests and their impacts on forest function, an integrated understanding of carbon dynamics of lianas and liana-infested host trees is critical for improved prediction of tropical forest responses to climate change. Non-structural carbohydrates (NSC) are the main substrate for plant metabolism (e.g., growth, respiration), and have been implicated in enabling tree survival under environmental stress, but little is known of how they vary among life-forms or of how liana infestation impacts host tree NSC. We quantified stem total NSC (NSC) concentrations and its fractions (starch and soluble sugars) in trees without liana infestation, trees with more than 50% of the canopy covered by lianas, and the lianas infesting those trees. We hypothesized that i) liana infestation depletes NSC storage in host trees by reducing carbon assimilation due to competition for resources; ii) trees and lianas, which greatly differ in functional traits related to water transport and carbon uptake, would also have large differences in NSC storage, and that As water availability has a significant role in NSC dynamics of Amazonian tree species, we tested these hypotheses within a moist site in western Amazonia and a drier forest site in southern Amazonia. We did not find any difference in NSC, starch or soluble sugar concentrations between infested and non-infested trees, in either site. This result suggests that negative liana impact on trees may be mediated through mechanisms other than depletion of host tree NSC concentrations. We found lianas have higher stem NSC and starch than trees in both sites. The consistent differences in starch concentrations, a long term NSC reserve, between life forms across sites reflect differences in carbon gain and use of lianas and trees. Soluble sugar concentrations were higher in lianas than in trees in the moist site but indistinguishable between life forms in the dry site. The lack of difference in soluble sugars between trees and lianas in the dry site emphasize the importance of this NSC fraction for plant metabolism of plants occurring in water limited environments. Abstract in Portuguese and Spanish are available in the supplementary material.

O presente trabalho analisou as mudanças de uso e cobertura da terra na localidade, de forma espacial e temporal, nos anos de 2000 e 2020, por meio da plataforma Google Earth Engine (GEE). Utilizou-se a imagem do satélite Landsat-5/TM relativo ao ano de 2000 e imagem do satélite Landsat-8/OLI-TIRS referente ao ano de 2020. Os resultados apontam que houve uma redução de 135,91 km² de cobertura vegetal, correspondendo a 10,51% de perda proveniente das atividades antrópicas que ocorreram em Garrafão do Norte, especialmente, em relação à agricultura com os cultivos de dendê, mandioca e laranja e à pecuária com as pastagens, pois juntos apresentam um aumento de 198,06% que equivalem a 305,02 km² de área antropizada. Portanto verificou-se que o município de Garrafão do Norte segue o padrão de desenvolvimento econômico dos municípios amazônicos, onde acontece a diminuição das áreas florestais para a ampliação de suas atividades produtivas, como o cultivo de dendê, sendo este um dos principais geradores do desflorestamento da região, caracterizando o cenário do Antropoceno na Amazônia.

Already threatened by deforestation, the Brazilian Cerrado-a complex and biodiverse tropical savannah that provides important ecosystem services-could experience climate warming of 1-5 degrees C by 2100. This could negatively impact sexual reproduction (considered particularly sensitive to temperature stress) in native plant species, potentially limiting the production of viable pollen, fruits, and seeds; however, such impacts are largely unstudied in wild tropical species. To investigate the potential effects of higher temperatures on Cerrado species reproduction, developing inflorescences of common and widespread tree Byrsonima pachyphylla (Malpighiaceae) were passively heated in situ from an early bud stage (by 3-4 degrees C during the daytime). Viability of pollen samples (analyzed through in vitro pollen germination and differential pollen staining) and fruit set (the proportion of hand-pollinated flowers that developed into mature fruit) were compared between heated and control (ambient temperature) inflorescences, hypothesizing that both would be lower in heated inflorescences. However, higher daytime temperatures had no impact on viable pollen production, suggesting a strong resilience to warming. Nevertheless, fruit set was significantly reduced, which could have serious implications for future species recruitment and potentially Cerrado community structure, insect and animal food chains, and human populations, especially if representative of other Cerrado species. To the best of our knowledge, this experiment is the first manipulative warming of Cerrado vegetation in situ. It provides initial insights into the effects that increasing temperatures could have on future reproductive success and demonstrates the importance of considering reproduction when evaluating the possible impacts of climate change on tropical ecosystems.

Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1-6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth's 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world's most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.