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Wood density (WD) and other wood mechanical and structural properties may have a strong functional relationship with demographic patterns and allometry of trees. We analyzed the influence of WD, structural properties, architectural traits, and community-level attributes on growth rates (GRs) and mortality modes of canopy tree species in a subtropical forest of Argentina. Stem WD and the WD, strength, stiffness, toughness, and hardness of branches were measured in 10 canopy species. Architectural traits and liana load were also determined. Strength and hardness of branches were linearly correlated to branch WD, and GRs were linearly correlated to stem WD across species. At the individual level, trees with greater hardness and toughness in branches died mostly uprooted, and trees with greater branch stiffness and susceptibility to colonization by lianas were mostly broken. At the community level, the suppressed trees died mostly broken. The dominant trees with high local tree density died mostly broken, whereas more isolated trees died mostly uprooted. Mortality modes were determined not only by mechanical properties, but also by community properties such as liana load, crown canopy position, and number of neighboring trees. Other biophysical traits besides WD are important explanatory variables when dry wood is used to describe functional characteristics of trees. Key words: modulus of elasticity, modulus of rupture, wood density, mortality modes, architectural traits. La densite du bois (DB) et d'autres proprietes mecaniques et structurales pourraient avoir une etroite relation fonctionnelle avec les patrons demographiques et l'allometrie des arbres. Nous avons analyse l'influence de la DB, des proprietes structurales, des traits architecturaux et des attributs a l'echelle de la communaute sur le taux de croissance (TC) et la cause de mortalite des especes arborescentes dominantes dans une foret subtropicale en Argentine. La DB du tronc ainsi que la DB, la resistance, la rigidite, la tenacite et la durete des branches ont ete mesurees chez 10 especes dominantes. De plus, les traits architecturaux et la charge de lianes ont ete determines. La resistance et la durete des branches etaient lineairement correlees a la DB des branches et le TC etait lineairement correle a la DB du tronc chez l'ensemble des especes. A l'echelle individuelle, les arbres dont les branches avaient la plus grande durete et la plus grande tenacite sont le plus souvent morts renverses et ceux dont les branches avaient la plus grande rigidite et qui etaient les plus sujets a etre colonises par les lianes sont morts pour la plupart apres avoir ete casses. A l'echelle de la communaute, les arbres supprimes sont morts pour la plupart apres avoir ete casses. Les arbres dominants dont la densite etait localement elevee sont surtout morts apres avoir ete casses tandis que les arbres plus isoles son surtout morts apres avoir ete deracines. La faqon dont la mortalite est survenue etait determinee par les proprietes mecaniques mais aussi par les proprietes de la communaute, telles que la charge de lianes, la position de la cime dans le couvert et le nombre d'arbres avoisinants. D'autres traits biophysiques a part la DB sont d'importantes variables explicatives lorsque du bois sec est utilise pour decrire les caracteristiques fonctionnelles des arbres. [Traduit par la Redaction] Mots-cles: module d'elasticite, module de rupture, densite du bois, cause de mortalite, traits architecturaux. * S., Introduction Wood density (WD) and other mechanical properties such as elasticity and resistance to static or dynamic loads may have a strong functional relationship with demographic tree patterns (Poorter et [...]

Changes in water and nitrogen availability can affect the structure and function of arid ecosystems. How these resources affect aboveground primary productivity (ANPP) remains far from clear. We examined the N and water limitation of ANPP from the species to the community level and the response of ANPP to annual precipitation in a Patagonian steppe. We conducted a 7‐year field experiment with water addition (+W), nitrogen addition (+N) and +NW. Destructive methods for grasses and allometric relationships for shrubs were used to assess ANPP and vegetation indices (NDVI and MSAVI2) to estimate community ANPP. An increase in ANPP of one grass species (Papposstipa humilis) and a decrease of the grass Poa ligularis under +N were observed. Some shrub species exhibited mortality under nitrogen addition. Nitrogen exerted a positive effect on grass ANPP and amplified the sensitivity of grass ANPP to annual precipitation. However, +N had not effects on the shrub ANPP and shrub ANPP‐precipitation relationship. Water addition by itself had no effect on ANPP for either shrubs or grasses. However, shrubs responded positively to an unusually wet year regardless of treatment and were also more sensitive to changes in annual precipitation than grasses. Total ANPP increased significantly in +N relative to the C and +W but without changes in the sensitivity to annual precipitation. The results suggest that the responses of grasses and shrubs to water inputs are driven by soil moisture redistribution and rooting depth and that grass and community ANPP are more limited by N than by water. [ABSTRACT FROM AUTHOR]

The relationship between water transport and photosynthesis represents the trade-off between carbon gain and water loss and was used to evaluate potential differences in water resource utilization among two dominant vegetation types of south Florida: subtropical evergreen broad leaf forests (hardwood hammocks) and pine woodlands (pine rocklands). We found consistent linear positive relationships between the quantum yield of photosystem II (ϕ PSII), an index of photosynthetic capacity, and hydraulic conductivity per sapwood area (k S) and per leaf area (k L) across all species. The slope of the ϕ PSII–k S relationship was steeper for hardwood hammock than for pine rockland species. Mean ϕ PSII was greater in pine rockland species and was greater for a given k L than in hardwood hammock species. These results are consistent with previous observations demonstrating that pine rocklands tend to have better access to stable water sources than hardwood hammocks. We also found greater photosynthetic carbon isotope discrimination with increasing k S and k L in pine rockland species, but not in hardwood hammock species, suggesting increased stomatal conductance with increasing k S and k L, consistent with greater water availability in pine rockland habitats. Our study thus utilizes relationships between water transport and photosynthesis to evaluate hydraulic constraints on physiological function between two contrasting vegetation types with contrasting stability of water sources.

Water availability is one of the factors affecting plant growth and development, especially in arid and semiarid environments. Changes in precipitation due climate change alter water availability to plants impacting on plant physiology. Numerous studies have focused on plant response to reduced precipitation and less on the effects of increased precipitation. The main objective of this study was to evaluate biophysical and physiological leaf traits in response to experimental water addition in four dominant shrubs and one grass species in a Patagonian steppe, during the dry season. The experiment consisted of two treatments: control and water addition, increasing the average annual rainfall by 25% during 6 years. We measured leaf wettability, water status, transpiration, photosynthesis, stomatal conductance, water use efficiency and foliar water uptake (FWU). In addition, we determined the phenotypic plasticity index of these evaluated traits. We expected lower FWU and higher transpiration and photosynthesis rates due changes in leaf surface properties under water addition treatment. All study species responded significantly to treatment with higher loss of water per transpiration and lower FWU. Also, all species increased photosynthesis rate and water use efficiency (WUE). However, water potential and leaf wettability did not change with higher precipitation. Thus, higher phenotypic plasticity was observed in functional than in morphological traits. Since functional traits were more sensitive than leaf surface traits, plants may quickly take advantage when environmental conditions tend to be more favourable to growth. Our findings suggest that plants of Patagonian steppe have adaptive ability to respond to environmental changes through plastic responses. [ABSTRACT FROM AUTHOR]

Stored water in inner tissues influences the plant water economy, which might be particularly relevant for trees facing increasing dry conditions due to climate change. We studied the water storage in the inner bark and the sapwood of Araucaria araucana (Molina) K. Koch. This species has an extremely thick inner bark and thus it can be used as a model system to assess the impact of internal water storage on plant water balance. Specifically, we analyzed the water circulation pathways in and out of the elastic water storages by using simultaneously frequency domain moisture sensors and dendrometers inserted in the inner bark and in the sapwood, and sap flow determinations during the dry season. The daily patterns of water content and expansion and contraction of the stem tissues were similar to the sap flow pattern. The whole-stem water content and diameter increased in the morning and decreased in the afternoon, contrary to the typical pattern observed in most tree species. An osmotic gradient favoring the water influx from sapwood to inner bark was observed in the morning. There were no lags in the onset of sap flow between different stem heights at the time that recharge of reservoirs occurred. Sap flow at 6 m height was higher than basal sap flow in the afternoon, when the sapwood water content started to decline followed by the water content of the inner bark. Inner bark and sapwood contributed 5–11% to total daily transpiration, allowing the maintenance of high water potentials in the dry season. Our results suggest that the stored water in the stems, the atypical dynamic of recharge and discharge of water from reservoirs and the high tissue capacitance may make an important contribution to the survival of A. araucana during drought periods by maintaining the water balance. [ABSTRACT FROM AUTHOR]