Contrasting stem water uptake and storage dynamics of water-saver and water-spender species during drought and recovery.

Drought is projected to occur more frequently and intensely in the coming decades, and the extent to which it will affect forest functioning will depend on species-specific responses to water stress. Aiming to understand the hydraulic traits and water dynamics behind water-saver and water-spender strategies in response to drought and recovery, we conducted a pot experiment with two species with contrasting physiological strategies, Scots pine (Pinus sylvestris L.) and Portuguese oak (Quercus faginea L.

Do H and O in leaf water reflect environmental drivers differently?

We compiled hydrogen and oxygen stable isotope compositions (δ H and δ O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ H was more closely correlated with δ H of xylem water or atmospheric vapour, whereas leaf water δ O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ O.

Evidence for distinct isotopic compositions of sap and tissue water in tree stems: consequences for plant water source identification.

The long-standing hypothesis that the isotopic composition of plant stem water reflects that of source water is being challenged by studies reporting bulk water from woody stems with an isotopic composition that cannot be attributed to any potential water source. The mechanism behind such source-stem water isotopic offsets is still poorly understood. Using a novel technique to extract selectively sap water from xylem conduits, we show that, in cut stems and potted plants, the isotopic composition of sap water reflects that of irrigation water, demonstrating unambiguously that no isotopic fractionation occurs during root water uptake or sap water extraction.

Contrasting ecophysiological strategies related to drought: the case of a mixed stand of Scots pine (Pinus sylvestris) and a submediterranean oak (Quercus subpyrenaica).

Submediterranean forests are considered an ecotone between Mediterranean and Eurosiberian ecosystems, and are very sensitive to global change. A decline of Scots pine (Pinus sylvestris L.) and a related expansion of oak species (Quercus spp.

Short-term dynamics of evaporative enrichment of xylem water in woody stems: implications for ecohydrology.

In ecohydrology, it is generally assumed that xylem water reflects the water source used by plants. Several studies have reported isotopic enrichment within woody tissues, particularly during dormancy periods or after long periods of inactivity. However, little is known about the short-term dynamics of this process.

Circadian rhythms have significant effects on leaf-to-canopy scale gas exchange under field conditions.

Background: Molecular clocks drive oscillations in leaf photosynthesis, stomatal conductance, and other cell and leaf-level processes over ~24 h under controlled laboratory conditions. The influence of such circadian regulation over whole-canopy fluxes remains uncertain; diurnal CO and HO vapor flux dynamics in the field are currently interpreted as resulting almost exclusively from direct physiological responses to variations in light, temperature and other environmental factors. We tested whether circadian regulation would affect plant and canopy gas exchange at the Montpellier European Ecotron.

Isotope-ratio infrared spectroscopy: a reliable tool for the investigation of plant-water sources?

Stable isotopes are extensively used as tracers for the study of plant-water sources. Isotope-ratio infrared spectroscopy (IRIS) offers a cheaper alternative to isotope-ratio mass spectroscopy (IRMS), but its use in studying plant and soil water is limited by the spectral interference caused by organic contaminants. Here, we examine two approaches to cope with contaminated samples in IRIS: on-line oxidation of organic compounds (MCM) and post-processing correction.