We discuss the physical and enzymatic bases of carbone isotope discrimination during photosynthesis, noting how knowledge of discrimination can be used to provide additional insight into photosynthetic metabolism and the environmental influences on that process

Carbon Isotope Discrimination and Photosynthesis

Estimation of vegetation water content and photosynthetic tissue area from spectral reflectance: a comparison of indices based on liquid water and chlorophyll absorption features

Temporal variations in the stable carbon isotope composition (d 13 C) of leaves and current-year stems were examined in beech trees over one year. The d 13 C of both tissues were equal in the bud stage and started to diverge during growth, with values decreasing by 2·5 and 4·5‰ for stems and leaves, respectively. The dynamics of the d d d 13 C and content of non-structural sugars were also assessed. The beginning of the growth period was characterized by a decrease in starch content and high starch d 13 C values. Later in the season, the d 13 C of leaf soluble sugars progressively decreased from the end of May and the d d d 13 C of stem sucrose was at least 1·5‰ higher than that of leaves. The d 13 C of CO 2 respired by stem tissue increased during stem growth and exhibited large seasonal variations (from - 22·1 to - - 26·3‰). These values generally fell between those of starch and total organic matter. The results of the study showed that the d 13 C of stems is altered by two apparent fractionation steps: one during sugar transfer from leaves to stems and one during stem respiration. These results may have implications for analysis of isotopic signals in tree rings and forest ecosystems.

http://max2.ese.u-psud.fr/publications/2003dames_carbon.pdf

Carbon isotope composition of current‐year shoots from Fagus sylvatica in relation to growth, respiration and use of reserves

Carbon isotope discrimination (4) has been shown to be a valuable tool for long-term estimates of water-use efficiency, because this parameter is influenced by the ratio of intercellular to ambient CO 2 levels, which is in turn related to water-use efficiency. The objective of this study was to examine variation in 4-values of field materials and the extent to which changes in 4 might be interpreted as changes in water-use efficiency. On-line discrimination observations with four desert species confirmed theoretically expected relationships between 4 and the ratio of intercellular to ambient CO 2 concentrations, a prerequisite to applying 4-values to water-use efficiency (...)

Seasonal variation in the carbon isotopic composition of desert plants

Light is produced by changes in the energy level of electrons (when an electron changes from a high-energy, Or excited, State to a low-energy state, Its atom will emit a photon), but its dual nature makes it scientifically puzzling: it moves through space as a wave, but when it encounters matter it behaves like a particle, The quantum (Achenbach 2001). In practice “light” is used for the portion of the electromagnetic spectrum in the vicinity of visible light. In plant biology and ecology, photosynthetically active radiation (PAR), Which essentially coincides with visible light, Is probably the most relevant measure of light. The PAR region is where energy is most abundant (it represents on average 43% of the solar irradiance), And it is strong enough to drive electron transport in photosynthesis, Yet weak enough to avoid excessive damage to biological molecules. However, There exists no worldwide network for PAR measurements like the network of actinometric stations, Where global, Direct, diffuse and reflected solar radiation are measured using unified instruments and methodology and are metrologically based on the world radiometric reference (Ross and Sulev 2000). The dual nature of light, I.e., particle versus wave, Affects the way light in general and PAR in particular is measured. One group of sensors measures energy (e.g., W m−2), The other group quanta (e.g., μmol m−2 s−1).

Light Heterogeneity and Plants: from Ecophysiology to Species Coexistence and Biodiversity

Seasonal patterns in plant morphology, phenology, and physiology were monitored in several populations of Eriogonum inflatum, a desert ephemeral which produces a large photosynthetic inflorescence above a basal leaf rosette. Green stems accounted for 66–77% of whole plant photosynthetic surface area when integrated over a developmental cycle, whereas only 40–67% of the yearly transpirational water loss could be attributed to stems. Stems were found to have lower nitrogen and chlorophyll contents than leaves, and lower stomatal conductance under all physiological conditions encountered. However, because stems occur later in the year than leaves, comparison of physiological patterns was complicated by the two structures being exposed to different climatic regimes during their developmental cycles. Stems exhibited higher δ13C values than leaves, indicating that stems operated at higher water-use efficiencies than leaves, at least during periods when both leaves and stems were present. Higher water-use efficiency in stems of E. inflatum is attributed to both more conservative water use patterns and to their vertical orientation, allowing stems to remain photosynthetically active longer into the dry season after senescence of the horizontal leaf rosette.

Stem photosynthesis in a desert ephemeral, Eriogonum inflatum : Characterization of leaf and stem CO2 fixation and H2O vapor exchange under controlled conditions.

B. Gui-Ying

Papers

Stem photosynthesis in a desert ephemeral, Eriogonum inflatum : Characterization of leaf and stem CO2 fixation and H2O vapor exchange under controlled conditions.