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Summary: Leaf economic spectrum (LES) relationships have been studied across many different plant lineages and at different organizational scales. However, the temporal stability of the LES relationships is largely unknown. We used the wild blueberry system with high genotypic diversity to test whether trait–trait relationships across genotypes demonstrate the same LES relationships found in the global database (GLOPNET) and whether they are stable across years.We studied leaf structure, photosynthesis, and leaf nutrients for 16 genotypes of two wild blueberry species semi‐naturally grown in a common farm in Maine, USA, across 4 yr.We found substantial variation in leaf structure, physiology, and nutrient traits within and among genotypes, as well as across years in wild blueberries. The LES trait–trait relationships (covariance structure) across genotypes were not always found in all years. The trait syndrome of wild blueberries was shifted by changing environmental conditions over the years. Additionally, traits in 1 yr cannot be used to predict those of another year.Our findings show that LES generally holds among genotypes but is temporally unstable, stressing the significant influence of trait plasticity in response to fluctuating environmental conditions across years, and the importance of temporal dimensions in shaping functional traits and species coexistence. [ABSTRACT FROM AUTHOR]

Summary: Both mistletoes and their hosts are challenged by increasing drought, highlighting the necessity of understanding their comparative hydraulic properties. The high transpiration of mistletoes requires efficient water transport, while high xylem tensions demand strong embolism resistance, representing a hydraulic paradox.This study, conducted across four environments with different aridity indices in Yunnan, China, examined the xylem traits of 119 mistletoe–host species pairs.Mistletoes showed lower water use efficiency, indicating a more aggressive water use. They also showed lower hydraulic efficiency (lower vessel diameter and theoretical hydraulic conductivity) but higher safety (lower vulnerability index and higher conduit wall reinforcement, vessel grouping index, and wood density) compared with their hosts, supporting the trade‐off between efficiency and safety. Environmental variation across sites significantly affected xylem trait comparisons between mistletoes and hosts. Additionally, the xylem traits of mistletoes were strongly influenced by host water supply efficiency. The overall xylem trait relationships in mistletoes and hosts were different.These findings stress the impact of host and site on the hydraulic traits of mistletoes, and suggest that mistletoes may achieve high transpiration by maintaining high stomatal conductance under low water potentials. This study illuminates the distinctive adaptation strategies of mistletoes due to their parasitic lifestyle. [ABSTRACT FROM AUTHOR]

Climate change is raising concerns about how forests will respond to extreme droughts, heat waves and their co-occurrence. In this greenhouse study, we tested how carbon and water relations relate to seedling growth and mortality of northeastern US trees during and after extreme drought, warming, and combined drought and warming. We compared the response of our focal species red spruce (Picea rubens Sarg.) with a common associate (paper birch, Betula papyrifera Marsh.) and a species expected to increase abundance in this region with climate change (northern red oak, Quercus rubra L.). We tracked growth and mortality, photosynthesis and water use of 216 seedlings of these species through a treatment and a recovery year. Each red spruce seedling was planted in containers either alone or with another seedling to simulate potential competition, and the seedlings were exposed to combinations of drought (irrigated, 15-d 'short' or 30-d 'long') and temperature (ambient or 16 days at +3.5 °C daily maximum) treatments. We found dominant effects of the drought reducing photosynthesis, midday water potential, and growth of spruce and birch, but that oak showed considerable resistance to drought stress. The effects of planting seedlings together were moderate and likely due to competition for limited water. Despite high temperatures reducing photosynthesis for all species, the warming imposed in this study minorly impacted growth only for oak in the recovery year. Overall, we found that the diverse water-use strategies employed by the species in our study related to their growth and recovery following drought stress. This study provides physiological evidence to support the prediction that native species to this region like red spruce and paper birch are susceptible to future climate extremes that may favor other species like northern red oak, leading to potential impacts on tree community dynamics under climate change. [ABSTRACT FROM AUTHOR]

Polyploidization is hypothesized to improve the freezing resistance of plants in cold regions. However, adaptive strategies and key physiological mechanisms involved in the freezing resistant ability of polyploids remain unclear. In Actinidia chinensis (kiwifruits), the tetraploids and hexaploids occupy higher altitude habitats with colder climates than the diploids, providing a study system to investigate mechanisms responsible for differentiation in freezing resistance between cytotypes. We characterized environmental conditions of their natural distribution areas, and measured leaf‐level traits of cold damages and water relations at typical sites of each cytotype along an altitudinal gradient. Polyploids showed lower semi‐lethal temperature (LT50) than ice nucleation temperature (INT), reflecting a tolerance strategy to cope with freezing events in the plateau regions. More negative turgor loss points and larger cell elastic modulus of polyploids could help to alleviate damages from freezing‐induced cell dehydration, thus strengthening their tolerance to lower subzero temperatures (lower LT50). The increased supercooling capacity of polyploids (lower INT) might correlate with less extracellular ice formation due to lower osmotic potential at full turgor, apoplastic water fraction and tissue capacitance. Our study uncovers a greater cold tolerance in polyploid kiwifruits than diploids, and suggests the potential linkage between freezing tolerance and water relations. Taken together, such a divergence in stress resistance may underlie the niche shift of polyploid plants towards harsh environments. [ABSTRACT FROM AUTHOR]

To better understand the dynamics and functional roles of root pressure, we represent a novel and the first complete analytical model for root pressure, which can be applied to complex roots/shoots. The osmotic volume of a single root is equal to that of the vessel lumen in fine roots and adjacent apoplastic spaces. Water uptake occurs via passive osmosis and active solute uptake (Js*, osmol s−1), resulting in the osmolyte concentration Cr (mol·kg−1 of water) at a fixed osmotic volume. Solute loss occurs via two passive processes: radial diffusion of solute Km (Cr− Csoil) from fine roots to soil, where Km is the diffusional constant and Csoil is the soil–solute concentration, and the mass flow of solute and water into the plant from the fine roots. The proposed model predicts the quadratic function of root pressure (Pr), Pr2+bPr+c=0, where b and c are the functions of plant hydraulic resistance, soil water potential, solute flux and gravitational potential. The model demonstrates the root pressure‐mediated distribution of water through the hydraulic architecture of a 6.8‐m‐tall bamboo shoot. This model provides a theoretical basis to test the functional roles of root pressure in shaping the hydraulic architecture and refilling potential xylem embolisms. Summary statement: An analytical solution for root pressure is derived and illustrated by applying it to the measured hydraulic architecture of a 7‐m bamboo shoot. [ABSTRACT FROM AUTHOR]