The functional mechanism behind the latitudinal pattern of liana diversity: Freeze–thaw embolism reduces the ecological performance of liana species

Abstract There is a strong decrease in liana diversity along latitudinal and altitudinal gradients at a global scale, and there is a marked difference in liana diversity between tropical and temperate ecosystems. From these observations, it has been proposed that cold temperatures would restrict the ecological patterns of liana because of their vascular system's vulnerability to freeze–thaw embolism. Our objective was to establish the functional mechanism that drives the loss of liana diversity along a latitudinal temperature gradient. We evaluate the ecological performance of liana in 10 different species based on the apical growth rate, as well as functional traits associated with efficiency (maximum hydraulic conductivity and percentage conductivity lost) and safety of water transport (vessel diameter, vessel density, wood density, and root pressure). We found that at the colder (more southern) site within the latitudinal gradient, liana species showed lower performance, with a fivefold decrease in their apical growth rate as compared to the warmer (more northern) sites. We postulate that this lower performance results from a much lower water transport efficiency (26.1‐fold decrease as compared to liana species that inhabit warmer sites) that results from higher freeze–thaw (37.5% of PLC) and reduction of vessel diameter (3 times narrower). These results are unmistakable evidence that cold temperature restricts liana performance: in a cold environment, liana species exhibit a strong decrease in performance, low efficiency, and higher safety of water transport. Conversely, at warmer sites, we found that liana species exhibit functional strategies associated with higher performance, higher efficiency, and lower safety of water transport capacity. This trade‐off between efficiency and safety of water transport and their effects on performance could explain the latitudinal pattern of liana diversity

Tasas diarias de transpiración y relaciones hídricas en especies arbóreas con distinto nivel de sombra tolerancia en un bosque templado chileno Daily transpiration rates and hydraulic relationships in tree species with different shade-tolerance level in a Chilean temperate forest

En general se sabe que especies pioneras que sostienen altas tasas de crecimiento, transpiración y fotosíntesis son más tolerantes a la sequía y soportan mayores temperaturas, mientras que especies sombra tolerantes lo contrario. Sin embargo, no existen antecedentes respecto a los volúmenes diarios de agua transpirada a nivel de árbol en especies del bosque templado del sur de Chile, ni antecedentes respecto a la coordinación entre los rasgos funcionales involucrados en el transporte de larga distancia. El objetivo de este estudio fue cuantificar los volúmenes diarios de agua transpirada por cuatro especies arbóreas de diferente grado de sombra tolerancia en un bosque templado lluvioso del sur de Chile, así como evaluar su relación con diferentes rasgos funcionales asociados al transporte hídrico en tronco, ramas y hojas. Se encontró que existen diferencias significativas en las tasas diarias de transpiración entre especies, las que varían entre 0,07 y 0,01 lt cm-2dia-1 para Nothofagus dombeyi (Mirb.) Oerst. y Laureliopsisphilippiana (Looser) Schodde respectivamente. Contrario a lo esperado, ni la conductividad hidráulica específica (K ) ni la conductividad hidráulica foliar (K L) estuvieron bien correlacionadas con las tasas diarias de transpiración. Sin embargo, las especies menos tolerantes a la sombra presentaron rasgos asociados a una mayor tolerancia a la sequía y mientras que la semi-tolerante Eucryphia cordifolia Cav. estaría sufriendo importantes restricciones hídricas durante el verano.In general, pioneer species are known for supporting high transpiration, growth and photosynthesis rate, for being more drought tolerant and resist higher temperatures than shade-tolerant species. However, there is not information about rates of transpiration at the tree level in species of Chilean temperate forest, or about the coordination between hydraulic functional traits. We report here, transpiration rates of four tree species with different levels of shade tolerance in Chilean temperate rainforest, and explored some functional traits associated with water transport efficiency and drought tolerance. We found significant differences in daily transpiration rates ranging between 0.07 and 0.01 lcm-2day-1 in Nothofagus dombeyi (Mirb.) Oerst. and Laureliopsisphilippiana (Looser) Schodde respectively. Contrary to expectations, specific hydraulic conductivity (KS ) and leaf hydraulic conductivity (K L) were not well correlated with transpiration daily rates. However, the species less tolerant to shade showed traits associated with greater drought tolerance, while the semi-tolerant Eucryphia cordifolia Cav. showed important evidence of hydraulic restrictions during summer