Journal
NEW PHYTOLOGIST
Volume 166, Issue 1, Pages 217-230Publisher
BLACKWELL PUBLISHING LTD
DOI: 10.1111/j.1469-8137.2005.01332.x
Keywords
carbon dioxide (CO2); grassland; climate change; N cycle; nitrogen-use efficiency; N productivity; competition
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The aim of this study was to evaluate whether the responsiveness of mixed C-3 grass species to elevated CO2 is related more to nitrogen uptake or to N-use efficiency. Nitrogen uptake and whole-plant N-use efficiency were investigated with two binary mixtures: Lolium perenne was mixed either with Festuca arundinacea or with Holcus lanatus. The swards were grown on sand with or without CO2 doubling, and subjected to two cutting frequencies. A C-20 alcohol was used as a marker to determine species proportion in the total root mass of the mixtures. The mean residence time of N was calculated from that of N-15-labelled fertilizer. Lolium perenne took up significantly more N per unit root mass than its grass competitors, but its N-use efficiency was lower. Elevated CO2 significantly reduced the N uptake of the three grass species. A trade-off between N capture and use was found, as N-use efficiency and N-uptake rate were negatively correlated. A high N-use efficiency, and conversely low N uptake appeared to favour the responsiveness to elevated CO2 of the infrequently cut grasses.
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