A simple stable carbon isotope method for investigating changes in the use of recent versus old carbon in oak.
Stable carbon isotope ratios from early-wood (EW) and late-wood (LW) are used to test competing models of carbon storage and allocation, providing a cost-effective alternative to measuring and dating non-structural carbohydrates in mature temperate broad-leaf forest trees growing under natural conditions. Annual samples of EW and LW from seven mature oaks (Quercus robur L.) from Scotland, covering AD 1924-2012, were pooled, treated to isolate alpha-cellulose and pyrolysed to measure the carbon isotope ratios. Late-wood values are strongly correlated with summer temperature of the year of growth and EW contains the same signal offset by 1 year. After a warm summer, isotopic ratios of EW are similar to those of the preceding LW, but following cold summers they are relatively enriched. The results conflict with established models of isotopic variation within oak tree rings but support 'two-pool' models for storage of non-structural carbohydrates, with EW formation, which occurs prior to budburst, preferentially using young reserves accumulated in the previous summer. Under poor growing conditions trees access older reserves. Slight average isotopic enrichment of EW may be explained by preferential accumulation of reserves during warmer summers rather than by isotopic enrichment during starch formation in non-photosynthetic tissue.
Department of Geography, Swansea University, Singleton Park, Swansea SA2 8PP,UK.
Danny
D
McCarroll
Department of Geography, Swansea University, Singleton Park, Swansea SA2 8PP,UK.
Matthew
M
Whitney
Department of Geography, Swansea University, Singleton Park, Swansea SA2 8PP,UK.
Giles H F
GHF
Young
Department of Geography, Swansea University, Singleton Park, Swansea SA2 8PP,UK.
Neil J
NJ
Loader
Department of Geography, Swansea University, Singleton Park, Swansea SA2 8PP,UK.
Mary H
MH
Gagen
D002247:Carbon Isotopes / Q000032:analysis*; D002482:Cellulose / Q000737:chemistry*; D029963:Quercus / Q000737:chemistry*; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000737:chemistry; D014934:Wood / Q000737:chemistry*
D002247:Carbon Isotopes; D002482:Cellulose
Quercus; carbon cycling; carbon dynamics; carbon isotopes; non-structural carbohydrates; oak; tree ring