Use of stored carbon reserves in growth of temperate tree roots and leaf buds: analyses using radiocarbon measurements and modeling |
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| Authors: | J B GAUDINSKI †‡ M S TORN†§ W J RILEY† C SWANSTON¶ S E TRUMBORE&#; J D JOSLIN H MAJDI†† T E DAWSON‡ P J HANSON‡‡ |
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| Institution: | Department of Environmental Studies, University of California, Santa Cruz, CA, USA,;Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA,;Department of Integrative Biology, University of California, Berkeley, CA, USA,;Energy and Resources, University of California, Berkeley, CA, USA,;Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA, USA,;Department of Earth System Science, University of California Irvine, Irvine, CA, USA,;Belowground Forest Research, Apartado 104-5655, Santa Elena de Monteverde, Puntarenas, Costa Rica,;Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden,;Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA |
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| Abstract: | Characterizing the use of carbon (C) reserves in trees is important for understanding regional and global C cycles, stress responses, asynchrony between photosynthetic activity and growth demand, and isotopic exchanges in studies of tree physiology and ecosystem C cycling. Using an inadvertent, whole-ecosystem radiocarbon (14C) release in a temperate deciduous oak forest and numerical modeling, we estimated that the mean age of stored C used to grow both leaf buds and new roots is 0.7 years and about 55% of new-root growth annually comes from stored C. Therefore, the calculated mean age of C used to grow new-root tissue is ～0.4 years. In short, new roots contain a lot of stored C but it is young in age. Additionally, the type of structure used to model stored C input is important. Model structures that did not include storage, or that assumed stored and new C mixed well (within root or shoot tissues) before being used for root growth, did not fit the data nearly as well as when a distinct storage pool was used. Consistent with these whole-ecosystem labeling results, the mean age of C in new-root tissues determined using 'bomb-14C' in three additional forest sites in North America and Europe (one deciduous, two coniferous) was less than 1–2 years. The effect of stored reserves on estimated ages of fine roots is unlikely to be large in most natural abundance isotope studies. However, models of root C dynamics should take stored reserves into account, particularly for pulse-labeling studies and fast-cycling roots (<1 years). |
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| Keywords: | 14C carbon cycling carbon isotope carbon reserves fine-root turnover time mean age of carbon radiocarbon stored carbon |
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