delta(18)O of water vapour, evapotranspiration and the sites of leaf water evaporation in a soybean canopy

作者：Welp Lisa R; Lee Xuhui^*; Kim Kyounghee; Griffis Timothy J; Billmark Kaycie A; Baker John M

来源：Plant, Cell and Environment, 2008, 31(9): 1214-1228.

DOI：10.1111/j.1365-3040.2008.01826.x

• canopy scale
• dew
• evaporative site
• non-steady state
• oxygen isotopes and tunable diode laser
• Peclet effect

Stable isotopes in water have the potential to diagnose changes in the earth's hydrological budget in response to climate change and land use change. However, there have been few measurements in the vapour phase. Here, we present high-frequency measurements of oxygen isotopic compositions of water vapour (delta(v)) and evapotranspiration (delta(ET)) above a soybean canopy using the tunable diode laser (TDL) technique for the entire 2006 growing season in Minnesota, USA. We observed a large variability in surface delta(v) from the daily to the seasonal timescales, largely explained by Rayleigh processes, but also influenced by vertical atmospheric mixing, local evapotranspiration (ET) and dew formation. We used delta(ET) measurements to calculate the isotopic composition at the sites of evaporative enrichment in leaves (delta(L,e)) and compared that with the commonly used steady-state prediction (delta(L,s)). There was generally a good agreement averaged over the season, but larger differences on individual days. We also found that vertical variability in relative humidity and temperature associated with canopy structure must be addressed in canopy-scale leaf water models. Finally, we explored this data set for direct evidence of the Peclet effect.

• 出版日期2008-9