Comparisons of δ13C of photosynthetic products and ecosystem respiratory CO2 and their responses to seasonal climate variability

Abstract

This study investigated the relationship between delta13C of ecosystem components, soluble plant carbohydrates and the isotopic signature of ecosystem respired CO2 (delta13CR) during seasonal changes in soil and atmospheric moisture in a beech (Fagus sylvatica L.) forest in the central Apennine mountains, Italy. Decrease in soil moisture and increase in air vapour pressure deficit during summer correlated with substantial increase in delta13C of leaf and phloem sap soluble sugars. Increases in delta13C of ecosystem respired CO2 were linearly related to increases in phloem sugar delta13C (r2=0.99, P<or=0.001) and leaf sugar delta13C (r2=0.981, P<or=0.01), indicating that a major proportion of ecosystem respired CO2 was derived from recent assimilates. The slopes of the best-fit lines differed significantly (P<or=0.05), however, and were about 0.86 (SE=0.04) for phloem sugars and about 1.63 (SE=0.16) for leaf sugars. Hence, changes in isotopic signature in phloem sugars were transferred to ecosystem respiration in the beech forest, while leaf sugars, with relatively small seasonal changes in delta13C, must have a slower turnover rate or a significant storage component. No significant variation in delta13C was observed in bulk dry matter of various plant and ecosystem components (including leaves, bark, wood, litter and soil organics). The apparent coupling between the delta13C of soluble sugars and ecosystem respiration was associated with large apparent isotopic disequilibria. Values of delta13CR were consistently more depleted by about 4 per thousand relative to phloem sugars, and by about 2 per thousand compared to leaf sugars. Since no combination of the measured pools could produce the observed delta13CR signal over the entire season, a significant isotopic discrimination against 13C might be associated with short-term ecosystem respiration. However, these differences might also be explained by substantial contributions of other not measured carbon pools (e.g., lipids) to ecosystem respiration or contributions linked to differences in footprint area between Keeling plots and carbohydrate sampling. Linking the seasonal and inter-annual variations in carbon isotope composition of carbohydrates and respiratory CO2 should be applicable in carbon cycle models and help the understanding of inter-annual variation in biospheric sink strength.

Age-related nutrient content and carbon isotope composition in the leaves and branches of Quercus aquifolioides along an altitudinal gradient

“…We also observed that there is a consistent trend of more negative d 13 C values in leaves when compared to branches. Similar patterns have been observed in a range of other studies (Terwilliger et al 2001;Scartazza et al 2004;Brandes et al 2006;Peuke et al 2006). On one hand, this may be a result of a higher lipid content in the membrane-rich chloroplasts, as it has been reported that lipids are depleted in 13 C compared with organic matter, acids, sugars and respired CO 2 (Hobbie and Werner 2004).…”

Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales

“…Carbon pools with shorter turnover times and thus a better-defined origin such as leaf soluble sugars (Brugnoli and Farquhar, 1988), phloem allocated carbon (e.g. Gessler et al, 2004;Scartazza et al, 2004) or even dark-respired δ 13 CO 2 of recent photosynthates (Barbour et al, 2011b) are therefore better indicators for recent changes in WUE ia , as outlined below (Sect. 2.2).…”

“…Within the last ten years it was, however, shown that the transport of newly assimilated carbon within the plant and from the plant to the rhizosphere can also be followed by natural abundance stable isotope techniques (e.g. Scartazza et al, 2004;Brandes et al, 2006;Wingate et al, 2010b …”

Variation génétique de la productivité, de caractères foliaires et de la discrimination isotopique vis-à-vis du carbone chez des hybrides de peuplier cultivés sur des sites contrastés

“…Discs were dried at 60 • C during two days, weighted and specific leaf area (SLA, cm 2 g −1 ) was computed. During the same period, phloem sap was collected from each tree with the method described by Scartazza et al (2004) and modified by Gessler et al (2004). On July 19, from 11:00 a.m. to 5:00 p.m., a thin strip of bark (2 cm long and 1 cm wide) still attached to the trunk was removed and plunged into tubes filled with 1 mL pure water for 4 h. This mixture was membrane filtered (0.45 μm pore size, Millipore), put into tin capsules and oven-dried at 60 • C over one day.…”