Effects of Wood Hydraulic Properties on Water Use and Productivity of Tropical Rainforest Trees

The efficiency of the water transport system in trees sets physical limits to their productivity and water use. Although the coordination of carbon assimilation and hydraulic functions has long been documented, the mutual inter-relationships between wood anatomy, water use and productivity have not yet been jointly addressed in comprehensive field studies. Based on observational data from 99 Indonesian rainforest tree species from 37 families across 22 plots, we analyzed how wood anatomy and sap flux density relate to tree size and wood density, and tested their combined influence on aboveground biomass increment (ABI) and daily water use (DWU). Results from pairwise correlations were compared to the outcome of a structural equation model (SEM). Across species, we found a strong positive correlation between ABI and DWU. Wood hydraulic anatomy was more closely related to these indicators of plant performance than wood density. According to the SEM, the common effect of average tree size and sap flux density on the average stem increment and water use of a species was sufficient to fully explain the observed correlation between these variables. Notably, after controlling for average size, only a relatively small indirect effect of wood properties on stem increment and water use remained that was mediated by sap flux density, which was significantly higher for species with lighter and hydraulically more efficient wood. We conclude that wood hydraulic traits are mechanistically linked to water use and productivity via their influence on sap flow, but large parts of these commonly observed positive relationships can be attributed to confounding size effects.

Drought or Severe Drought? Hemiparasitic Yellow Mistletoe (Loranthus europaeus) Amplifies Drought Stress in Sessile Oak Trees (Quercus petraea) by Altering Water Status and Physiological Responses

European oak species have long been considered relatively resistant to different disturbances, including drought. However, several recent studies have reported their decline initiated by complex changes. Therefore, we compared mature sessile oak trees (Quercus petraea (Matt.), Liebl.) infested versus non-infested by hemiparasitic yellow mistletoe (Loranthus europaeus Jacq.) during the relatively dry vegetation season of 2019. We used broad arrays of ecophysiological (maximal assimilation rate Asat, chlorophyll a fluorescence, stomatal conductance gS, leaf morphological traits, mineral nutrition), growth (tree diameter, height, stem increment), and water status indicators (leaf water potential Ψ, leaf transpiration T, water-use efficiency WUE) to identify processes underlying vast oak decline. The presence of mistletoe significantly reduced the Ψ by 1 MPa, and the WUE by 14%. The T and gS of infested oaks were lower by 34% and 38%, respectively, compared to the non-infested oaks, whereas the Asat dropped to 55%. Less pronounced but significant changes were also observed at the level of photosystem II (PSII) photochemistry. Moreover, we identified the differences in C content, which probably reduced stem increment and leaf size of the infested trees. Generally, we can conclude that mistletoe could be a serious threat that jeopardizes the water status and growth of oak stands.

Carbon-use strategies in stem radial growth of two oak species, one Temperate deciduous and one Mediterranean evergreen: what can be inferred from seasonal variations in the δ13C of the current year ring?

Tree ring synthesis is a key process in wood production; however, little is known of the origin and fate of the carbon involved. We used natural 13C abundance to investigate the carbon-use process for the ring development in a temperate deciduous (Quercus petraea (Matt.) Liebl.) and a Mediterranean evergreen (Quercus ilex L.) oak. The sapwood carbon reserves, phloem sucrose contents, stem respired CO2 efflux and their respective carbon isotope compositions (δ13C) were recorded over 1 year, in the native area of each species. The seasonal δ13C variation of the current year ring was determined in the total ring throughout the seasons, as well as in slices from the fully mature ring after the growth season (intra-ring pattern). Although the budburst dates of the two oaks were similar, the growth of Quercus ilex began 50 days later. Both species exhibited growth cessation during the hot and dry summer but only Q. ilex resumed in the autumn. In the deciduous oak, xylem starch storage showed clear variations during the radial growth. The intra-ring δ13C variations of the two species exhibited similar ranges, but contrasting patterns, with an early increase for Q. petraea. Comparison between δ13C of starch and total ring suggested that Q. petraea (but not Q. ilex) builds its rings using reserves during the first month of growth. Shifts in ring and soluble sugars δ13C suggested an interspecific difference in either the phloem unloading or the use of fresh assimilate inside the ring. A decrease in ring δ13C for both oaks between the end of the radial growth and the winter is attributed to a lignification of ring cell walls after stem increment. This study highlighted the differences in carbon-use during ring growth for evergreen and deciduous oaks, as well as the benefits of exploring the process using natural 13C abundance.

Estrutura da regeneração natural de Anadenanthera colubrina em fragmento de brejo de altitude em Bananeiras, PB

A destruição de habitats atrelada à fragmentação causa sérias consequências para qualquer tipo de vegetação, principalmente para a Mata Atlântica na Região Nordeste. Os Brejos de Altitudes Nordestinos são áreas que apresentam microclimas dissociantes das extensões onde estão inseridos. O conhecimento do potencial de regeneração natural é fundamental para a compreensão da dinâmica da vegetação. Este trabalho teve como objetivo avaliar a o recrutamento e a mortalidade de regenerantes de Anadenanthera colubrina ocorrente em fragmento florestal de Floresta Ombrófila Aberta. Em uma população de A. colubrina as parcelas foram demarcadas, onde existiam plantas matrizes, com plântulas regenerantes, sendo 10 parcelas fixas (10 m x 10 m), onde todos os exemplares dessa espécie menor ou igual a 1 m de altura foram marcados, numerados e acompanhados durante 9 meses. O diâmetro caulinar do táxon apresentou crescimento constante. O incremento médio mensal inicial em diâmetro foi de 1,8 mm e final de 2,3 mm e o incremento médio em altura foi de 20 cm no primeiro mês e 25,9 cm no último mês avaliado. A taxa de mortalidade chegou a 50%. Os fatores ambientais e antrópicos e a predação das sementes contribuem para a mortalidade dos regenerantes.Structure of natural regeneration in Anadenanthera colubrina altitude swamp fragment in Bananeiras, PB, BrazilThe habitats destruction linked to fragmentation causes serious consequences for vegetation in general, especially considering the Northeast Atlantic Forest. The Northeastern Swamps of Altitudes are areas with microclimates dissociating from extensions where they are inserted. Knowledge of the natural regeneration potential is the key to understanding the dynamics of vegetation. The study aimed to evaluate the recruitment and mortality of Anadenanthera colubrina regenerating occurring in Open Rain Forest fragments. In a population of A. colubrina, ten plots with 10 m x 10 m were established, near matrices plants. All specimens with 1 m height or lower were numbered and monitored for 9 months. The stem diameter of the taxon showed continuous growth. The monthly average increment in diameter was at first 1.8 mm and at the end 2.3 mm, and the average stem increment in height was 20 cm at the first month and 25.9 cm at the last month evaluate. The mortality rate reached 50%. Environmental and anthropogenic factors and seed predation contribute to mortality of regenerating individuals.Index terms: Abiotic factors; Recruitment; Mortality