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Variation in the degree of coupling between δ 13 C of phloem sap and ecosystem respiration in two mature Nothofagus forests
Author(s) -
Barbour Margaret M.,
Hunt John E.,
Dungan Roger J.,
Turnbull Matthew H.,
Brailsford Gordon W.,
Farquhar Graham D.,
Whitehead David
Publication year - 2005
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.2005.01329.x
Subject(s) - canopy , photosynthesis , ecosystem , respiration , biology , phloem , botany , carbon cycle , photosynthetic capacity , ecology , environmental science
Summary• Day‐to‐day variability in the carbon isotope composition of phloem sap (δ 13 C hd ) and ecosystem respiratory CO 2 (δ 13 C R ) were measured to assess the tightness of coupling between canopy photosynthesis (δ 13 C hd ) and ecosystem respiration (δ 13 C R ) in two mature Nothofagus solandri (Hook. f.) forests in New Zealand.• Abundant phloem‐tapping scale insects allowed repeated, nondestructive access to stem phloem sap 1–2 m above ground. δ 13 C hd was compared with δ 13 C predicted by an environmentally driven, process‐based canopy photosynthesis model. Keeling plots of within‐canopy CO 2 were used to estimate δ 13 C R .• By including a lag of 3 d, there was good agreement in the timing and direction of variation in δ 13 C hd and predictions by the canopy photosynthesis model, suggesting that δ 13 C hd represents a photosynthesis‐weighted, integrative record of canopy photosynthesis and conductance.• Significant day‐to‐day variability in δ 13 C R was recorded at one of the two forests. At this site, δ 13 C R reflected variability in δ 13 C hd only on days with <2 mm rain. We conclude that the degree of coupling between canopy photosynthesis and ecosystem respiration varies between sites, and with environmental conditions at a single site.