Functional traits and water transport strategies in lowland tropical rainforest trees

© 2015 Apgaua et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species' hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios

Environmental regulation of carbon isotope composition and crassulacean acid metabolism in three plant communities along a water availability gradient

Expression of crassulacean acid metabolism (CAM) is characterized by extreme variability within and between taxa and its sensitivity to environmental variation. In this study, we determined seasonal fluctuations in CAM photosynthesis with measurements of nocturnal tissue acidification and carbon isotopic composition (δ13C) of bulk tissue and extracted sugars in three plant communities along a precipitation gradient (500, 700, and 1,000 mm year−1) on the Yucatan Peninsula. We also related the degree of CAM to light habitat and relative abundance of species in the three sites. For all species, the greatest tissue acid accumulation occurred during the rainy season. In the 500 mm site, tissue acidification was greater for the species growing at 30% of daily total photon flux density (PFD) than species growing at 80% PFD. Whereas in the two wetter sites, the species growing at 80% total PFD had greater tissue acidification. All species had values of bulk tissue δ13C less negative than −20‰, indicating strong CAM activity. The bulk tissue δ13C values in plants from the 500 mm site were 2‰ less negative than in plants from the wetter sites, and the only species growing in the three communities, Acanthocereus tetragonus (Cactaceae), showed a significant negative relationship between both bulk tissue and sugar δ13C values and annual rainfall, consistent with greater CO2 assimilation through the CAM pathway with decreasing water availability. Overall, variation in the use of CAM photosynthesis was related to water and light availability and CAM appeared to be more ecologically important in the tropical dry forests than in the coastal dune

Patterns of Carbon Partitioning in Leaves of Crassulacean Acid Metabolism Species during Deacidification.

Carbohydrates stored during deacidification in the light were examined in 11 Crassulacean acid metabolism (CAM) species from widely separated taxa grown under uniform conditions. The hypothesis that NAD(P) malic enzyme CAM species store chloroplastic starch and glucans, and phosphoenolpyruvate carboxykinase species store extrachloroplastic sugars or polymers was disproved. Of the six malic enzyme species examined, Kalanchoe tubiflora, Kalanchoe pinnata, Kalanchoe daigremontiana, and Vanilla planifolia stored mainly starch. Sansevieria hahnii stored sucrose and Agave guadalajarana did not store starch, glucose, fructose, or sucrose. Of the five phosphoenolpyruvate carboxykinase species investigated, Ananus comosus stored extrachloroplastic carbohydrate, but Stapelia gigantea, Hoya carnosa, and Portea petropolitana stored starch, whereas Aloe vera stored both starch and glucose. Within families, the major decarboxylase was common for all species examined, whereas storage carbohydrate could differ both between and within genera. In the Bromeliaceae, A. comosus stored mainly fructose, but P. petropolitana stored starch. In the genus Aloe, A. vera stored starch and glucose, but A. arborescens is known to store a galactomannan polymer. We postulate that the observed variation in carbohydrate partitioning between CAM species is the result of two principal components: (a) constraints imposed by the CAM syndrome itself, and (b) diversity in biochemistry resulting from different evolutionary histories

Carbon isotope composition of canopy leaves in a tropical forest in Panama throughout a seasonal cycle

The seasonal variation in δ13C values was measured in leaves from 17 upper canopy, five mid-canopy and in four gap tree species, as well as in five epiphyte and five vine species, in a seasonally dry lowland tropical forest at Parque Natural Metropolitano near Panama City, Republic of Panama. No seasonal variation was detected in the δ13C values of mature exposed leaves from either the upper or mid-canopy. However, canopy position did influence the δ13C value. The mean isotopic composition of leaves from the mid-canopy was more negative than that of the upper canopy throughout the year. The δ13C value was also influenced by leaf development, with juvenile leaves on average 1.5‰ less negative than mature leaves. The five epiphyte species exhibited 13C values that were typical of crassulacean acid metabolism (CAM). Codonanthe uleana, with isotopic values of .19.9 to .22.1‰, is only the second species in the Gesneriaceae reported to express CAM, whereas values between .14.6 and .22.0‰ indicate that Peperomia macrostachya can exhibit different degrees of CAM. The isotopic composition of exposed mature leaves from the vines showed little interspecific variation and was similar to the upper-canopy leaves of the trees

Stable isotopes in leaf water of terrestrial plants

Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals incorporated into plant organic matter and atmospheric gases