Using a simple isotope mixing model, we evaluated the relative proportion of water vapour generated by plant transpiration and by soil evaporation at two sites in the Amazon basin. Sampling was carried out at two different soil covers (forest and pasture), in a seasonal tropical rainforest at eastern Amazon where major deforestation is the result of land‐use change, and compared to a less seasonal central Amazon forest. In both forests, vapour from transpiration was responsible for most, if not all, of the water vapour generated in the forest, while it could not be detected above the grassy pastures. Thus the canopy transpiration may be a major source of water vapour to the forest and perhaps to the atmosphere during the dry season. The results are discussed in relation to predictive models based on net radiation that usually are not able to distinguish between transpiration and evaporation.

Upland tropical forests have expanded and contracted in response to past climates, but it is not clear whether similar dynamics were exhibited by gallery (riparian) forests within savanna biomes. Because such forests generally have access to ample water, their extent may be buffered against changing climates. We tested the long-term stability of gallery forest boundaries by characterizing the border between gallery forests and savannas and tracing the presence of gallery forest through isotopic analysis of organic carbon in the soil profile. We measured leaf area index, grass vs. shrub or tree coverage, the organic carbon, phosphorus, nitrogen and calcium concentrations in soils and the carbon isotope ratios of soil organic matter in two transitions spanning gallery forests and savanna in a Cerrado ecosystem. Gallery forests without grasses typically show a greater leaf area index in contrast to savannas, which show dense grass coverage. Soils of gallery forests have significantly greater concentrations of organic carbon, phosphorus, nitrogen and calcium than those of savannas. Soil organic carbon of savannas is significantly more enriched in 13 C compared with that of gallery forests. This difference in enrichment is in part caused by the presence of C 4 grasses in savanna ecosystem and its absence in gallery forests. Using the 13 C abundance as a signature for savanna and gallery forest ecosystems in 1 m soil cores, we show that the borders of gallery forests have expanded into the savanna and that this process initiated at least 3000-4000 BP based on 14 C analysis. Gallery forests, however, may be still expanding as we found more recent transitions according to 14 C activity measurements. We discuss the possible mechanisms of gallery forest expansion and the means by which nutrients required for the expansion of gallery forest might accumulate.

Coastal ecosystems lie at the forefront of sea level rise. We posit that before the onset of actual inundation, sea level rise will influence the species composition of coastal hardwood hammocks and buttonwood (Conocarpus erectus L.) forests of the Everglades National Park based on tolerance to drought and salinity. Precipitation is the major water source in coastal hammocks and is stored in the soil vadose zone, but vadose water will diminish with the rising water table as a consequence of sea level rise, thereby subjecting plants to salt water stress. A model is used to demonstrate that the constraining effect of salinity on transpiration limits the distribution of freshwater-dependent communities. Field data collected in hardwood hammocks and coastal buttonwood forests over 11 years show that halophytes have replaced glycophytes. We establish that sea level rise threatens 21 rare coastal species in Everglades National Park and estimate the relative risk to each Climatic Change (2011) 107:81-108 species using basic life history and population traits. We review salinity conditions in the estuarine region over 1999-2009 and associate wide variability in the extent of the annual seawater intrusion to variation in freshwater inflows and precipitation. We also examine species composition in coastal and inland hammocks in connection with distance from the coast, depth to water table, and groundwater salinity. Though this study focuses on coastal forests and rare species of South Florida, it has implications for coastal forests threatened by saltwater intrusion across the globe.

TABLE 1. PALEOTEMPERATURE ESTIMATES FOR THE ARCTIC MIDDLE EOCENE Study MAT (ЊC) CMM (ЊC) Method of determination (Greenwood and Wing, 1995) 8.2-9.3 Ϫ2.0 to Ϫ0.8 Multiple regression model described by Wing and Greenwood (1993) (Basinger et al., 1994) 12-15 0-4 NLR (Wolfe, 1994) 13.7-17.2 3.3-8.6 CLAMP This study 13.2 Ϯ 2.0-Isotopic equilibrium between terrestrial carbonate and environmental water Note: MAT-mean annual temperature; CMM-cold month mean temperature; NLR-nearest living relative analogy; CLAMP-climate-leaf analysis multivariate program.

Measurements of internal gas phase CO2 concentration, stomatal resistance, and acid content were made in Crassulacean acid metabolism plants growing under The physiological significance of CAM is believed to result from the temporal separation of photosynthetic CO2 reduction and gas exchange with the atmosphere. Gas exchange with the atmosphere is restricted to the hours of darkness when the inevitable associated water loss is likely to be minimized. Photosynthetic CO2 reduction occurs without gas exchange with the atmosphere and hence without water loss. CO2 acquired at night is temporarily stored in malic acid and is consumed in photosynthetic reactions the following day.Earlier work (4, 5) has shown that CO2 may be released to the atmosphere surrounding CAM plants following illumination. This indicates that release of CO2 from malic acid is not directly caused by photosynthetic consumption of CO2 and suggests that there might be an accumulation of CO2 inside illuminated CAM tissues.Since CO2 concentration has effects on photosynthesis, respiration, photorespiration, and stomatal behaviour (1, 3, 6-8, 10) and inasmuch as it has been suggested that CO2 concentration is involved in the regulation of CAM (2) Gas Sampling. Disposable hypodermic syringes (2.0-ml capacity, 22-gauge needle) were used to withdraw gas samples (0.5-2.0 ml) from photosynthetic tissue. The syringe needle was inserted into the tissue through a globule of water standing on the surface of the plant or contained in a cup of Plasticine adhering to the plant. Taking samples by this method ensured, providing that stomata were closed, that any gas entering the syringe came from inside the plant and not from leakage around the needle. Furthermore, as the syringe was withdrawn from the plant this procedure ensured that any partial vacuum in the syringe was filled by water and not by gas from the atmosphere. If the syringe was sealed by plunging the needle deeply into a rubber stopper the sample could be stored for periods of up to 30 min without significant change in CO2 concentration. For the longer periods of storage required for field experiments (up to 30 h) gas samples, usually 1.0 ml, were injected through a serum bottle stopper into small glass vials which contained C02-free N2 and also sand to reduce the internal gas space.Measurement of CO2 Concentration. CO2 was separated from other atmospheric gases by GC of 0.5-ml samples at 70 C on a 2.15-m Porapak Q column using helium at a flow rate of 40 ml/