Vertical and seasonal variation in the δ13C of leaf-respired CO2 in a mixed conifer forest

Abstract

The C-isotopic composition (delta C-13) of leaf respiration (delta(LR)) has previously been shown to vary among functional groups, plant organs and times of day. We here investigated vertical and seasonal variation in delta(LR) through deep (similar to 35 m) forest canopies. We measured delta(LR), delta C-13 of leaf bulk organic matter (delta(LB)), specific leaf area, net photosynthesis (A) and dark respiration in shade, middle and sun foliage in four conifer species from May to August. We used Keeling plots to estimate delta(LR); we developed a novel technique for ensuring that the respiratory substrate was not changing over the course of the measurement. Variables delta(LR) and delta(LB) displayed a vertical pattern in Abies grandis, Pseudotsuga menziesii and Thuja plicata, but were independent of canopy position in Larix occidentalis. Vertical gradients in delta(LB) (3.6 parts per thousand) and delta(LR) (2.8 parts per thousand) were similar. The respiratory enrichment (delta(LR)-delta(LB)) was smaller in expanding (3 parts per thousand) than mature (4-8 parts per thousand) foliage. There was a linear relationship between the respiratory enrichment and A. Our data support the hypothesis that delta(LR) values are related to patterns of C allocation among metabolic pathways. We demonstrated that considerable variation in delta(LR) occurs vertically through the canopy (3 parts per thousand gradient) and seasonally (3-7 parts per thousand). Understanding sources of variation in respiratory signals is fundamental to comprehending C dynamics and for global model applications.

Keywords

canopy gradients; carbon isotopes; conifers; leaf respiration; ontogeny; photosynthesis; seasonal variation; specific leaf area

Published in

Tree Physiology
2011, Volume: 31, number: 4, pages: 414-427 Publisher: OXFORD UNIV PRESS

SLU Authors

• Marshall, John

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.1093/treephys/tpr026

Permanent link to this page (URI)

https://res.slu.se/id/publ/89252