Deviation Between δ13C and Leaf Intercellular Co2 in Salix Interior Cuttings Developing Under Low Light

This is the publisher's official version. It is also available electronically from: http://www.jstor.org/stable/10.1086/322892.Leaf δ13C values of perennial species are sometimes less negative than model‐predicted δ13C values derived from instantaneous measures of pi/pa. It has been hypothesized that the less negative δ13C values could be caused by 13C‐enriched stored carbon imported during the early stages of leaf growth. The δ13C values of newly emerging leaves could thus represent δ13C values of stem‐stored carbohydrates and may also provide integral measures of pi/pa at the end of the past growing season. We tested these hypotheses by sprouting cuttings of Salix interior under wet and dry soil‐moisture conditions in a controlled environmental chamber. Plants were defoliated after 56 d, and watering treatments were then reversed for half of the plants in each treatment. The δ13C values of newly emerging leaves did not correlate with pi/pa ratios of newly emerging leaves or of mature leaves prior to defoliation, thereby indicative that δ13C values of newly emerging leaves are not a simple reflection of prior pi/pa. Also, the δ13C values of newly emerging leaves were more enriched in 13C relative to the δ13C values of stem carbohydrates in the treatments where water regimes were reversed. Newly emerging leaves after defoliation had higher δ13C values despite the lower instantaneous water‐use efficiency and similar values of pi/pa to older photosynthetic leaves. Large differences between observed and model‐predicted pi/pa values also occurred in older, more mature leaves, and this may be because large proportions of their total mass were derived from carbon import

Conditions environnementales, biosynthèses, diagenèse : contribution analytique de la RMN 2H en milieu anisotrope

International audienc

Conditions environnementales, biosynthèses, diagenèse : contribution analytique de la RMN 2H en milieu anisotrope

International audienc

Regeneration and Growth drier Logging Florida Pondcypress Domes

ABSTRACT. Recovery of vegetation after logging 16 small (1-5 ha), undrained pondcypress domes in north central Florida was analyzed. One dome was undisturbed and the others had been logged from a few months to 45 years before the study began. Densities of young (<2 yr old) pondcypress (Taxodium distichurn var. nutans (Ait.) Sweet) were higher in domes that were recently logged than in older domes, whereas densities of other young woody plants were similar regardless of when a dome had been logged. Pondcypress saplings were significantly more abundant in domes logged 3 years before the study, and had sprouted after the domes were logged. There were no striking differences in canopy composition between older (15-45 yr) logged domes and historical descriptions ofunlogged domes. In general, no differences in tree species composition (importance values, relative and absolute densities, frequencies and dominances of major species, and species diversity) were found among the domes. Also, selective logging did not result in a growth release among remaining trees. Over a period of 45 years or less, pondcypress domes appeared to recove

Changes and their possible causes in δ 13 C of dark-respired CO 2 and its putative bulk and soluble sources during maize ontogeny

International audienceThe issues of whether, where, and to what extent carbon isotopic fractionations occur during respiration affect interpretations of plant functions that are important to many disciplines across the natural sciences. Studies of carbon isotopic fractionation during dark respiration in C-3 plants have repeatedly shown respired CO2 to be C-13 enriched relative to its bulk leaf sources and C-13 depleted relative to its bulk root sources. Furthermore, two studies showed respired CO2 to become progressively C-13 enriched during leaf ontogeny and C-13 depleted during root ontogeny in C-3 legumes. As such data on C-4 plants are scarce and contradictory, we investigated apparent respiratory fractionations of carbon and their possible causes in different organs of maize plants during early ontogeny. As in the C-3 plants, leaf-respired CO2 was C-13 enriched whereas root-respired CO2 was C-13 depleted relative to their putative sources. In contrast to the findings for C-3 plants, however, not only root- but also leaf-respired CO2 became more C-13 depleted during ontogeny. Leaf-respired CO2 was highly C-13 enriched just after light-dark transition but the enrichment rapidly decreased over time in darkness. We conclude that (i) although carbon isotopic fractionations in C-4 maize and leguminous C-3 crop roots are similar, increasing phosphoenolpyruvate-carboxylase activity during maize ontogeny could have produced the contrast between the progressive C-13 depletion of maize leaf-respired CO2 and C-13 enrichment of C-3 leaf-respired CO2 over time, and (ii) in both maize and C-3 leaves, highly C-13 enriched leaf-respired CO2 at light-to-dark transition and its rapid decrease during darkness, together with the observed decrease in leaf malate content, may be the result of a transient effect of light-enhanced dark respiration