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Oil palm plantations are rapidly expanding in the Brazilian eastern Amazon. Further expansion of irrigated oil palm plantations may occur because they may improve productivity during drought events compared to rainfed-only plantations. To investigate the importance of irrigation to alleviate drought-induced stress on palm trees, and its potential as a management alternative, we monitored transpiration (T , mm day–1) in a five-year-old oil palm plantation during an extreme drought caused by the El-Niño Southern Oscillation (ENSO) event in the Amazon basin. Our study spanned over the dry season (DS) and the wet season (WS), using an ongoing irrigation experiment (control with no irrigation, drip and sprinkler irrigation), to identify how differences in water supply affect the oil palm T during a period of reduced precipitation induced by ENSO. Our results indicate that independently of the irrigation system, T was higher in the DS, compared to the WS. Higher soil moisture in both the irrigation treatments, relative to the control plot, allowed for 23% higher average T relative to the control plot. The vapor pressure deficit (VPD) variation presented a higher effect over oil palm transpiration than photosynthetic active radiation. In both irrigation systems, a higher rate of transpiration with increases in VPD was observed than in the control plot during ENSO drought. Additionally, within individual palm fronds, we also observed differences in VPD tolerance (higher for lower and older leaves) and avoidance (higher for upper and newer leaves). Results indicate that irrigation increased fruit production by 35% and 26% in the sprinkler and drip irrigation systems, respectively. Overall, these results demonstrate the potential role of irrigation to alleviate water stress and maintain productivity of palm oil plantations during periods of moisture stress, while highlighting the possible feedback of increasing transpiration on water balance and hydrologic regulation. • Oil palm transpiration was measured during an extreme drought induced by El-Niño in Eastern Amazon. • Oil palm trees with reduced water supply are very sensitive to drought. • Different irrigation regimes allowed oil palm trees to support transpiration at higher vapour pressure deficits. [ABSTRACT FROM AUTHOR]

Comparisons among methods are essential to validate plant traits measured across studies. However, a rigorous analysis is a complex task that needs to take into account not only the principle of the method and its correct use, but also inherent intraspecific trait variability, something we feel is not fully considered by Sergent et al. (2020). They compared the Bench dehydration, MicroCT, and Pneumatic methods using three long-vesseled species and found divergence among these methods. As a key finding, Sergent and colleagues reported unreliable estimates of Ψ 50 for Olea europaea when using the Pneumatic method in a such long-vesseled species. Here, we tested this finding by measuring independently vulnerability curves for O. europaea. Our results reinforce the viability of the Pneumatic method to estimate embolism vulnerability in long-vesseled species, as already found by others. Briefly, we also discuss important procedures when using the Pneumatic method and encourage further experiments, as the only way to know better the limitations of available methods and improve our understanding about plant water relations. [ABSTRACT FROM AUTHOR]

• Desiccation tolerant species and non-desiccation tolerant species display contrasting carbon and water-use strategies to survive during dry periods. • The mild drought condition had an effect on on leaf functioning and biomass accumulation only for desiccation tolerant species. • Under severe drought conditions, both species presented similar non-structural carbohydrate dynamics. • Desiccation tolerant species recovered functioning upon re-watering, whereas the non-desiccation tolerant species died. Desiccation tolerance (DT) is the ability of plants to tolerate low leaf water content from which they can recover when water becomes available. DT species mostly occur in seasonally-dry environments, tropical rocky outcrops such as the campos rupestres. Velloziaceae, a prominent family in the campos rupestres , comprises both DT and non-DT species. We tested if DT Vellozia nivea was associated with low productivity under mild drought conditions and survival under extreme drought. We measured traits related to drought resistance (turgor loss point – Ψ TLP), plant functioning and productivity (e.g., gas exchange, biomass), non-structural carbohydrate dynamics and mortality in two species, one DT and one non-DT Vellozia species in two water-stress experiments simulating mild and extreme drought. Both species had similar survival rates under mild drought conditions, but the DT species had a lower productivity. Under extreme drought, the dynamics of non-structural carbohydrates was similar in both species but only the non-DT species died, and the cause of mortality was likely hydraulic dysfunction, as they died after reaching Ψ TLP. All individuals of the DT species desiccated when they reached Ψ TLP but rehydrated after re-watering. We show that the DT strategy in V. nivea implies a costs in terms of productivity, specially under mild drought conditions, but it allows survival under extreme drought, indicating a trade-off between productivity and survival in the DT species. Climate change predictions with more frequent and severe droughts will likely affect the abundance and distribution of DT and non-DT taxa. [ABSTRACT FROM AUTHOR]