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Plant traits are increasingly being used to improve prediction of plant function, including plant demography. However, the capability of plant traits to predict demographic rates remains uncertain, particularly in the context of trees experiencing a changing climate. Here we present data combining 17 plant traits associated with plant structure, metabolism and hydraulic status, with measurements of long‐term mean, maximum and relative growth rates for 176 trees from the world?s longest running tropical forest drought experiment. We demonstrate that plant traits can predict mean annual tree growth rates with moderate explanatory power. However, only combinations of traits associated more directly with plant functional processes, rather than more commonly employed traits like wood density or leaf mass per area, yield the power to predict growth. Critically, we observe a shift from growth being controlled by traits related to carbon cycling (assimilation and respiration) in well‐watered trees, to traits relating to plant hydraulic stress in drought‐stressed trees. We also demonstrate that even with a very comprehensive set of plant traits and growth data on large numbers of tropical trees, considerable uncertainty remains in directly interpreting the mechanisms through which traits influence performance in tropical forests. Made available in DSpace on 2021-01-12T09:05:37Z (GMT). No. of bitstreams: 1 nph.16972-2021.pdf: 1264820 bytes, checksum: 64adf8c9966954ff58dceff8df2c98cf (MD5) Previous issue date: 2021 Publicado Online em 27 set. 2020.

Made available in DSpace on 2022-05-01T06:02:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-08-15 As a result of anthropogenic pressure, three drives are expected to affect Brazilian savannas: an increase in the dry season, more frequent fire events, and defaunation. These drivers are a trigger for biodiversity loss and undermine the ecosystems services like carbon storage. Here our goal was to analyze how these drivers can affect the structure and dynamics of the savanna's tree species and how they impact the savanna's total estimating aboveground biomass (AGB). We analysed eight sites that comprise a physiognomic gradient from open savanna to savanna woodland. The species were classified by three traits: phenological strategies (deciduous or evergreen), fire resistance (resprouting or non-resprouting), and dispersal syndrome (animal or non-animal). Then, we modelled AGB loss in a dry season in the austral winter, a 2 °C increase in daily temperature, five fire events by decadal-series, and a defaunation scenario. Although climate change, change in fire frequency, and defaunation effects impact AGB separately, they also have a synergistic effect. This effect was observed in functional strategies and also in the total AGB of the community. In some cases, the total AGB loss exceeded 70%. The negative effects on performance were highest in species which were decidual, non-resprouting, and which employed animal dispersal for their seed. If different types of disturbances are not controlled in the near future, savanna communities will be dominated by evergreen, resprouters, and non-animal dispersed species, representing a steeply decline in the diversity of species and ecosystem functions. Department of Plant Biology Institute of Biology University of Campinas – UNICAMP, P.O. Box 6109 Department of Natural Sciences Maths and Education Centre for Agrarian Sciences Federal University of São Carlos (UFSCar), Rodovia Anhanguera - SP 330, km 174 Department of Ecological Modelling Helmholtz Centre for Environmental Research – UFZ, Permoserstraße 15 SBiK-F – Senckenberg Biodiversity and Climate Research Centre Georg-Voigt-Straße 14-16 Biological Sciences Unit Federal University of Jataí – UFJ, BR 364, km 192 Department of Environmental Dynamics National Institute of Amazonian Research – INPA Department of Biological Sciences Faculty of Sciences São Paulo State University – UNESP Department of Biological Sciences Faculty of Sciences São Paulo State University – UNESP

Future climate change predictions for tropical forests highlight increased frequency and intensity of extreme drought events. However, it remains unclear whether large and small trees have differential strategies to tolerate drought due to the different niches they occupy. The future of tropical forests is ultimately dependent on the capacity of small trees (

Whether tropical trees acclimate to long‐term drought stress remains unclear. This uncertainty is amplified if drought stress is accompanied by changes in other drivers such as the increases in canopy light exposure that might be induced by tree mortality or other disturbances. Photosynthetic capacity, leaf respiration, non‐structural carbohydrate (NSC) storage and stomatal conductance were measured on 162 trees at the world's longest running (15 years) tropical forest drought experiment. We test whether surviving trees have altered strategies for carbon storage and carbon use in the drier and elevated light conditions present following drought‐related tree mortality. Relative to control trees, the surviving trees experiencing the drought treatment showed functional responses including: (a) moderately reduced photosynthetic capacity; (b) increased total leaf NSC; and (c) a switch from starch to soluble sugars as the main store of branch NSC. This contrasts with earlier findings at this experiment of no change in photosynthetic capacity or NSC storage. The changes detected here only occurred in the subset of drought‐stressed trees with canopies exposed to high radiation and were absent in trees with less‐exposed canopies and also in the community average. In contrast to previous results acquired through less intensive species sampling from this experiment, we also observe no species‐average drought‐induced change in leaf respiration. Our results suggest that long‐term responses to drought stress are strongly influenced by a tree's full‐canopy light environment and therefore that disturbance‐induced changes in stand density and dynamics are likely to substantially impact tropical forest responses to climate change. We also demonstrate that, while challenging, intensive sampling is essential in tropical forests to avoid sampling biases caused by limited taxonomic coverage. Made available in DSpace on 2021-01-13T09:05:01Z (GMT). No. of bitstreams: 1 1365-2435.13689-2021.pdf: 1614823 bytes, checksum: 0ea046c5e0666a2e409e93fe849fd23e (MD5) Previous issue date: 2021 Publicado online em 29 set. 2020.

The future of tropical forests is dependent on the capacity of young trees to adjust to drought. We evaluated multiple hydraulic traits indicative of the drought tolerance of small trees across nine common genera at the world’s longest-running tropical throughfall exclusion experiment and compared their responses with surviving large canopy trees. Small understorey trees increased specific hydraulic conductivity by 56.3% and leaf:sapwood area ratio by 45.6% in response to the drought treatment. However, understorey trees in both a control and the throughfall exclusion treatment had significantly lower minimum stomatal conductance and maximum hydraulic leaf-specific conductivity relative to the large trees, as well as significantly greater hydraulic safety margin (HSM) and PLC and embolism resitance, occupying a distinctly different hydrualic niche. The greater HSM of small understorey trees relative to large canopy trees likely enables them to adjust other aspects of their hydraulic systems to take advantage of increases in light availability in the understorey, driven by drought-induced mortality of canopy trees. Our results suggest that small understorey trees can adjust their hydraulic systems in response to changes in water and light availability and this has major implications for the regeneration potential of tropical forests following droughts.

The response of small understory trees to long‐term drought is vital in determining the future composition, carbon stocks and dynamics of tropical forests. Long‐term drought is, however, also likely to expose understory trees to increased light availability driven by drought‐induced mortality. Relatively little is known about the potential for understory trees to adjust their physiology to both decreasing water and increasing light availability. We analysed data on maximum photosynthetic capacity (J max, V cmax), leaf respiration (R leaf), leaf mass per area (LMA), leaf thickness and leaf nitrogen and phosphorus concentrations from 66 small trees across 12 common genera at the world’s longest running tropical rainfall exclusion experiment and compared responses to those from 61 surviving canopy trees. Small trees increased J max, V cmax, R leaf and LMA (71%, 29%, 32%, 15% respectively) in response to the drought treatment, but leaf thickness and leaf nutrient concentrations did not change. Small trees were significantly more responsive than large canopy trees to the drought treatment, suggesting greater phenotypic plasticity and resilience to prolonged drought, although differences among taxa were observed. Our results highlight that small tropical trees have greater capacity to respond to ecosystem level changes and have the potential to regenerate resilient forests following future droughts.

The fate of tropical forests under future climate change is dependent on the capacity of their trees to adjust to drier conditions. The capacity of trees to withstand drought is likely to be determined by traits associated with their hydraulic systems. However, data on whether tropical trees can adjust hydraulic traits when experiencing drought remain rare. We measured plant hydraulic traits (e.g. hydraulic conductivity and embolism resistance) and plant hydraulic system status (e.g. leaf water potential, native embolism and safety margin) on >150 trees from 12 genera (36 species) and spanning a stem size range from 14 to 68 cm diameter at breast height at the world's only long-running tropical forest drought experiment. Hydraulic traits showed no adjustment following 15 years of experimentally imposed moisture deficit. This failure to adjust resulted in these drought-stressed trees experiencing significantly lower leaf water potentials, and higher, but variable, levels of native embolism in the branches. This result suggests that hydraulic damage caused by elevated levels of embolism is likely to be one of the key drivers of drought-induced mortality following long-term soil moisture deficit. We demonstrate that some hydraulic traits changed with tree size, however, the direction and magnitude of the change was controlled by taxonomic identity. Our results suggest that Amazonian trees, both small and large, have limited capacity to acclimate their hydraulic systems to future droughts, potentially making them more at risk of drought-induced mortality.

Summary CO 2 efflux from stems (CO 2_stem) accounts for a substantial fraction of tropical forest gross primary productivity, but the climate sensitivity of this flux remains poorly understood.We present a study of tropical forest CO 2_stem from 215 trees across wet and dry seasons, at the world's longest running tropical forest drought experiment site.We show a 27% increase in wet season CO 2_stem in the droughted forest relative to a control forest. This was driven by increasing CO 2_stem in trees 10–40 cm diameter. Furthermore, we show that drought increases the proportion of maintenance to growth respiration in trees > 20 cm diameter, including large increases in maintenance respiration in the largest droughted trees, > 40 cm diameter. However, we found no clear taxonomic influence on CO 2_stem and were unable to accurately predict how drought sensitivity altered ecosystem scale CO 2_stem, due to substantial uncertainty introduced by contrasting methods previously employed to scale CO 2_stem fluxes.Our findings indicate that under future scenarios of elevated drought, increases in CO 2_stem may augment carbon losses, weakening or potentially reversing the tropical forest carbon sink. However, due to substantial uncertainties in scaling CO 2_stem fluxes, stand‐scale future estimates of changes in stem CO 2 emissions remain highly uncertain.

CO2 efflux from stems (CO2_stem) accounts for a substantial fraction of tropical forest gross primary productivity, but the climate sensitivity of this flux remains poorly understood. We present a study of tropical forest CO2_stem from 215 trees across wet and dry seasons, at the world?s longest running tropical forest drought experiment site. We show a 27% increase in wet season CO2_stem in the droughted forest relative to a control forest. This was driven by increasing CO2_stem in trees 10?40 cm diameter. Furthermore, we show that drought increases the proportion of maintenance to growth respiration in trees > 20 cm diameter, including large increases in maintenance respiration in the largest droughted trees, > 40 cm diameter. However, we found no clear taxonomic influence on CO2_stem and were unable to accurately predict how drought sensitivity altered ecosystem scale CO2_stem, due to substantial uncertainty introduced by contrasting methods previously employed to scale CO2_stem fluxes. Our findings indicate that under future scenarios of elevated drought, increases in CO2_stem may augment carbon losses, weakening or potentially reversing the tropical forest carbon sink. However, due to substantial uncertainties in scaling CO2_stem fluxes, stand-scale future estimates of changes in stem CO2 emissions remain highly uncertain. Made available in DSpace on 2018-05-16T00:50:06Z (GMT). No. of bitstreams: 1 nph.15024.pdf: 1143269 bytes, checksum: 404bd137e49ad064956acba1b262b8d4 (MD5) Previous issue date: 2018-05-15