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Assessing the use of δ 13 C natural abundance in separation of root and microbial respiration in a Danish beech ( Fagus sylvatica L.) forest
Author(s) -
Formánek Pavel,
Ambus Per
Publication year - 2004
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1424
Subject(s) - beech , fagus sylvatica , chemistry , abundance (ecology) , respiration , botany , ecology , biology
Our understanding of forest biosphere–atmosphere interactions is fundamental for predicting forest ecosystem responses to climatic changes. Currently, however, our knowledge is incomplete partly due to inability to separate the major components of soil CO 2 effluxes, viz. root respiration, microbial decomposition of soil organic matter and microbial decomposition of litter material. In this study we examined whether the δ 13 C characteristics of solid organic matter and respired CO 2 from different soil‐C components and root respiration in a Danish beech forest were useful to provide information on the root respiration contribution to total CO 2 effluxes. The δ 13 C isotopic analyses of CO 2 were performed using a FinniganMAT Delta PLUS isotope‐ratio mass spectrometer coupled in continuous flow mode to a trace gas preparation‐concentration unit (PreCon). Gas samples in 2‐mL crimp seal vials were analysed in a fully automatic mode with an experimental standard error ±0.11‰. We observed that the CO 2 derived from root‐free mineral soil horizons (A, B W ) was more enriched in 13 C ( δ 13 C range −21.6 to −21.2‰) compared with CO 2 derived from root‐free humus layers ( δ 13 C range −23.6 to −23.4‰). The CO 2 evolved from root respiration in isolated young beech plants revealed a value intermediate between those for the soil humus and mineral horizons, δ 13 C root = −22.2‰, but was associated with great variability (SE ± 1.0‰) due to plant‐specific differences. δ 13 C of CO 2 from in situ below‐ground respiration averaged −22.8‰, intermediate between the values for the humus layer and root respiration, but variability was great (SE ± 0.4‰) due to pronounced spatial patterns. Overall, we were unable to statistically separate the CO 2 of root respiration vs. soil organic matter decomposition based solely on δ 13 C signatures, yet the trend in the data suggests that root respiration contributed ∼43% to total respiration. The vertical gradient in δ 13 C, however, might be a useful tool in partitioning respiration in different soil layers. The experiment also showed an unexpected 13 C‐enrichment of CO 2 (>3.5‰) compared with the total‐C signatures in the individual soil‐C components. This may suggest that analyses of bulk samples are not representative for the C‐pools actively undergoing decomposition. Copyright © 2004 John Wiley & Sons, Ltd.