Scaling from leaf to ecosystem: influence of phenology on seasonal CO2 exchange in a winter oilseed rape crop

  • Oral Presentation
  • Climate Change and Sustainable Land Use
  • 11 Jun 2018 15:45
  • FS-G01, UCD Agriculture and food science Centre
  • View all IPSAM abstracts

Macdara O'Neill*
School of Biology and Environmental Science, Belfield, Dublin 4
Teagasc Crops Research Centre, Oakpark, Co. Carlow

Orlaith Ní Chonchubhair
Teagasc Environmental Research Centre, Johnstown Castle, Co. Wexford

Gary Lanigan
Teagasc Environmental Research Centre, Johnstown Castle, Co. Wexford

Bruce Osborne
School of Biology and Environmental Science, Belfield, Dublin 4
UCD Earth Institute, Belfield, Dublin 4

*Presenting Author

Although winter oilseed rape (WOSR) is the second most important oilseed crop in the world, there is limited information on how its cultivation will affect carbon budgets at European and Irish arable sites. We quantified net ecosystem CO2 exchange (NEE) over a WOSR field using the eddy covariance (EC) technique for a six-month period in 2016. Micrometeorological variables, leaf photosynthesis, soil respiration and yield were also quantified to identify the main factors governing carbon exchange for this site. We obtained an NEE flux of -530 ± 111 g C m-2 indicating the crop to be a large sink for atmospheric CO2, with gross primary production (GPP) exceeding total ecosystem respiration 86% of days during the integration period. Cumulative NEE values were greatest in April (-181 ± 26 g C m-2) coinciding with expansion in leaf area plus crop height and in May (-154 ± 28 g C m-2) during higher pod growth rates. Gross primary production (GPP) on a canopy scale increased linearly with photosynthetically active radiation (PAR) >1400 µmol m-2 s-1 whilst leaf photosynthesis saturated at PAR levels of ~966 ± 33 µmol m-2 s-1. This indicates that radiation absorbed by leaves/pods beneath the canopy apex significantly contributes to seasonal carbon uptake. Moreover, the highest mean GPP of 7.2 g C m-2 d-1 occurred briefly at post-anthesis (30th May – 11th June 2016) as both pods and upper canopy leaves received higher levels of incident radiation. Our analysis indicates that the canopy structure of WOSR maximises radiation interception and the amount of CO2 converted to phytomass, contributing to an enhanced GPP/NEE, at each phenological stage of crop growth. Management practices such as the timing of nitrogen fertilisation and pre-harvest responses to water deficits could also modulate NEE through an alteration in leaf photosynthetic capacity and through variations in the duration of vegetative growth.