Vascular performance of woody plants in a temperate rain forest: lianas suffer higher levels of freeze-thaw embolism than associated trees

The success of lianas in tropical rain forests has been linked to their wide xylem vessels that confer much higher hydraulic conductivity than tropical trees. In contrast, the poorer representation of lianas in temperate forests and high elevations might reflect lower competitiveness there, because of the vulnerability of high-performance xylem to freeze–thaw embolism. Nevertheless, the empirical evidence that support this idea is surprisingly scarce. We assessed this hypothesis comparing the hydraulic performance of five lianas and nine trees coexisting in cold weather, by measuring wood traits, hydraulic conductivity, xylem embolism and root pressures. Vessel diameters of lianas were on average twice those of trees (51·3 vs. 23·2 μm), resulting in an 18-fold difference in mean specific hydraulic conductivity (15·5 vs. 1·05 kg s−1 m−1 MPa−1). Lianas on average suffered higher levels of freeze–thaw embolism than trees (29·9 vs. 12·8%), reducing their potential hydraulically supported competitive advantage; however, partially embolized lianas still had greater water transport capacity than trees. Specific hydraulic conductivity (Ks) was well correlated with vessel size in lianas but not in trees; however, plants with big vessels were more vulnerable to freeze embolism. Although all species of lianas developed root pressures and these tended to be higher than trees, root pressure were insufficient to repair embolism in plants > c. 7 m tall. The magnitudes of root pressure were well correlated with vessel size in lianas, but this relationship was not observed in trees. Synthesis: Our results show empirical evidence that hydraulic performance of temperate lianas exceed the performance of coexisting trees, in similar magnitude than its tropical counterparts. Nevertheless, this hydraulic advantage is reduced as a consequence of freeze embolism. Temperate lianas appear to employ a bet-hedging strategy entailing significant embolism in winter, but likely enabling rapid carbon gain during frost-free periods. Loss of winter carbon gain opportunities because of embolism may explain the low success of lianas in temperate rain forest. However, predicted future climatic scenarios could are likely to increase liana abundance in mid-latitudes and allow lianas to expand their ranges towards higher latitudes and elevations

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

Relationship between climbing plant dominance and ecophysiological traits in a temperate rainforest.

<p>Standardized regression coefficients (betas) of multiple regression analyses of climbing plant dominance across the light gradient against ecophysiological traits (<b>–for</b>: mean value of the trait in the closed-canopy mature forest; <b>–cha</b>: percentage of change in the trait between the mature forest and treefall canopy gaps). <b>Morphological traits</b> – Full model R² = 0.963; F_4,1 = 33.15; P<129. <b>Gas-exchange traits</b> – Full model R² = 0.997; F_4,1 = 387.59; P<0.038.</p

Dominance of climbing plant species across the light gradient and mean values of ecophysiological traits in a temperate rainforest.

<p>Overall dominance (<b>Dom</b>, average of relative frequency and relative density) of climbing plant species across the light gradient and mean values (± SE) of ecophysiological traits in mature forest (<b>for</b>) and canopy gaps (<b>gap</b>). The coefficient of variation (CV) among species for all variables is included (CV = standard deviation/mean, expressed in percentage).</p

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

The relationship between climbing plant dominance across the light gradient in the forest and the change in ecophysiological traits from the mature forest to canopy gaps.

<p><b>A</b>) Photosynthetic rate, A_max; <b>B</b>) dark respiration rate, R_d. Measurements were conducted in field plants. Each dot corresponds to a single species (n = 12 plants per species).</p