Open AccessSeasonal variability in net ecosystem carbon dioxide exchange over a young Switchgrass stand
Author(s) -
Wagle Pradeep,
Kakani Vijaya Gopal
Publication year - 2014
Publication title -
gcb bioenergy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.378
H-Index - 63
eISSN - 1757-1707
pISSN - 1757-1693
DOI - 10.1111/gcbb.12049
Subject(s) - eddy covariance , environmental science , ecosystem , ecosystem respiration , vapour pressure deficit , photosynthesis , biomass (ecology) , panicum virgatum , growing season , atmospheric sciences , carbon dioxide , photosynthetically active radiation , agronomy , carbon sink , primary production , zoology , botany , ecology , biofuel , biology , bioenergy , transpiration , geology
Understanding carbon dynamics of switchgrass ecosystems is crucial as switchgrass ( Panicum virgatum L.) acreage is expanding for cellulosic biofuels. We used eddy covariance system and examined seasonal changes in net ecosystem CO 2 exchange ( NEE ) and its components – gross ecosystem photosynthesis ( GEP ) and ecosystem respiration ( ER ) – in response to controlling factors during the second (2011) and third (2012) years of stand establishment in the southern Great Plains of the United States (Chickasha, OK). Larger vapor pressure deficit ( VPD > 3 kPa) limited photosynthesis and caused asymmetrical diurnal NEE cycles (substantially higher NEE in the morning hours than in the afternoon at equal light levels). Consequently, rectangular hyperbolic light–response curve ( NEE partitioning algorithm) consistently failed to provide good fits at high VPD . Modified rectangular hyperbolic light– VPD response model accounted for the limitation of VPD on photosynthesis and improved the model performance significantly. The maximum monthly average NEE reached up to −33.02 ± 1.96 μmol CO 2 m −2 s −1 and the highest daily integrated NEE was −35.89 g CO 2 m −2 during peak growth. Although large differences in cumulative seasonal GEP and ER were observed between two seasons, total seasonal ER accounted for about 75% of GEP regardless of the growing season lengths and differences in aboveground biomass production. It suggests that net ecosystem carbon uptake increases with increasing GEP . The ecosystem was a net sink of CO 2 during 5–6 months and total seasonal uptakes were −1128 ± 130 and −1796 ± 217 g CO 2 m −2 in 2011 and 2012, respectively. In conclusion, our findings suggest that the annual carbon status of a switchgrass ecosystem can be a small sink to small source in this region if carbon loss from biomass harvesting is considered. However, year‐round measurements over several years are required to assess a long‐term source‐sink status of the ecosystem.