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Oxygen isotope content of CO 2 in nocturnal ecosystem respiration: 2. Short‐term dynamics of foliar and soil component fluxes in an old‐growth ponderosa pine forest
Author(s) -
Bowling D. R.,
McDowell N. G.,
Welker J. M.,
Bond B. J.,
Law B. E.,
Ehleringer J. R.
Publication year - 2003
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2003gb002082
Subject(s) - ecosystem respiration , xylem , environmental science , soil respiration , ecosystem , respiration , soil water , water content , precipitation , forest ecology , environmental chemistry , transpiration , atmospheric sciences , chemistry , hydrology (agriculture) , soil science , ecology , botany , eddy covariance , photosynthesis , geology , biology , biochemistry , geotechnical engineering , physics , meteorology
The oxygen isotope contents (δ 18 O) of soil, xylem, and leaf water and ecosystem respiration were studied in a ponderosa pine forest during summer 2001. Our goal was to assess whether δ 18 O of CO 2 could be used to quantify the relative contributions of soil and foliar respiration to total nocturnal ecosystem respiration. The δ 18 O in leaf and soil water showed enrichment over a 2‐week sampling period as the weather became hot and dry (leaves 0.9 to 15.0‰, and soil −10.4 to −3.1‰), while δ 18 O of xylem water remained constant (−12.9‰). Water in the soil was enriched in 18 O near the soil surface (−6.4‰ at 5 cm depth) relative to greater depths (−11.1‰ at 20 cm). The δ 18 O of ecosystem respiration became gradually enriched over the 2‐week sampling period (from 24.2 initially to 32.9‰ at the end, VSMOW scale). Soil respiration contributed 80 ± 12 percent to the total respiratory flux, close to estimates from scaled‐up chamber data (77% [ Law et al. , 2001a]). Quantitative application of the isotopic approach to determine respiratory proportions required direct measurement of δ 18 O of soil and xylem water, air and soil temperature, and humidity. Better estimates of the isotopic signatures of component fluxes could be achieved with additional measurements and more detailed modeling. Results demonstrate that (1) there is variability in δ 18 O of precipitation inputs to ecosystems, (2) immediately following a precipitation event, δ 18 O of ecosystem respiration may reflect δ 18 O of precipitation, (3) periods of hot dry weather can substantially enrich ecosystem water pools and subsequently alter the isotope content of CO 2 in ecosystem respiration, and (4) stable oxygen isotopes in CO 2 can be used to quantify the foliar and soil components of ecosystem respiration.