Explore the vast range of titles available.

Plant function requires effective mechanisms to regulate water transport at a variety of scales. Here, we develop a new theoretical framework describing plant responses to drying soil, based on the relationship between midday and predawn leaf water potentials. The intercept of the relationship (Λ) characterizes the maximum transpiration rate per unit of hydraulic transport capacity, whereas the slope (σ) measures the relative sensitivity of the transpiration rate and plant hydraulic conductance to declining water availability. This framework was applied to a newly compiled global database of leaf water potentials to estimate the values of Λ and σ for 102 plant species. Our results show that our characterization of drought responses is largely consistent within species, and that the parameters Λ and σ show meaningful associations with climate across species. Parameter σ was ≤1 in most species, indicating a tight coordination between the gas and liquid phases of water transport, in which canopy transpiration tended to decline faster than hydraulic conductance during drought, thus reducing the pressure drop through the plant. The quantitative framework presented here offers a new way of characterizing water transport regulation in plants that can be used to assess their vulnerability to drought under current and future climatic conditions.

Tree species adopt diverse drought resistance strategies, which are crucial for the ability of karst vegetation to adapt to drought stress. However, our understanding of how to differentiate these strategies remains limited, particularly with respect to identifying indicator traits that can accurately distinguish the drought resistance strategies used by different species. In this study, we use principal component analysis based on functional traits to distinguish the drought resistance strategies of Platycladus orientalis and Broussonetia papyrifera ; we identify key indicator traits reflecting differences in drought resistance strategies by analyzing the correlations of the same traits across different plant species. Most importantly, in this study, stomatal transpiration efficiency is proposed as a novel trait. Principal component analysis based on functional traits can distinguish plant drought resistance strategies. A correlation analysis of the indicators revealed that 2,2-diphenyl-picrylhydrazyl radical-scavenging activity, Δcrown width, stomatal transpiration efficiency, and water use efficiency can serve as critical markers to differentiate the drought resistance strategies of plants. Notably, the stomatal transpiration efficiency of P. orientalis and B. papyrifera exhibited entirely opposite trends under drought stress ( r = -0.38); however, investigations of additional tree species are needed to further verify the reliability of stomatal transpiration efficiency as an indicator of different plant drought resistance strategies. These findings improve our ability to effectively differentiate karst plant drought resistance strategies and understand the mechanisms involved.

To predict the dynamics of tropical rainforest ecosystems in response to climate change, it is necessary to understand the drought tolerance and related mechanisms of trees in tropical rainforests. In this study, we assessed the ecophysiological responses of seedlings of six dipterocarp species ( Dipterocarpus pachyphyllus, Dryobalanops aromatica, Shorea beccariana, S. curtisii, S. parvifolia , and S. smithiana ) to experimental short-term drought conditions. The seedlings were initially grown in plastic pots with sufficient irrigation; irrigation was then stopped to induce drought. Throughout the soil-drying period, we measured various ecophysiological parameters, such as maximum photosynthetic and transpiration rates, stomatal conductance, water-use efficiency, predawn water potential, the maximum quantum yield of photosystem II ( F v /F m ), leaf water characteristics (using pressure-volume curves), leaf water content, and total sugar and starch contents. In all six dipterocarp species studied, the F v /F m values dropped sharply when the soil water content fell below 8%. However, there were interspecific differences in physiological responses to such a decrease in soil water content: S. parvifolia and S. beccariana actively controlled their stomata during drought to reduce water consumption via an isohydric response, but showed an increase ( S. parvifolia ) or no change ( S. beccariana ) in leaf drought tolerance; Di. pachyphyllus and Dry. aromatica maintained photosynthesis and transpiration close to the wilting point during drought without reducing water consumption via an anisohydric response, and also increased their leaf drought tolerance over the drying period; and S. curtisii and S. smithiana maintained their photosynthetic capacity without stomatal closure, but showed no change or a slight decrease in leaf drought tolerance. Our results indicate that extreme drought can cause the death of dipterocarp seedlings via various drought response, which could substantially impact the future distribution, population dynamics, and structure of tropical rainforests.

Pinus (~113 species, generally early-seral) and Quercus (~435 species, generally late-seral), currently co-occur over a wide range of climates and biomes in the Northern Hemisphere. Climate change is expected to threaten the coexistence dynamics of pine and oak species. Here, we analyze the responses of Pinus and Quercus to water stress, with the objective of determining how they vary globally in their responses to drought at the genus level. The results show that pines tend to tightly close stomata before stress becomes severe and may deplete their stored carbon; on the other hand, oaks begin stomatal control at a lower water potential and hence do not suffer from carbon depletion. Pines exhibit a wider hydraulic safety margin (average: 3.33 MPa) than oaks (average: 1.41 MPa) because of lower Ψ50 (average: −3.62 MPa) and earlier stomatal closure (average: −2.19 MPa). For oaks, stomatal closure and Ψ50 occur at −2.61 MPa and −3.07 MPa, respectively. We discuss and show that these contrasting drought responses are consistent with their seral roles. While the difference in the basic strategies to drought in the two genera is unmistakable, the species studied are still too few to make convincing generalizations. Research is also needed on other components related to drought adaptations.