Day-length effects on carbon stores for respiration of perennial ryegrass.

• The mechanism controlling the use of stored carbon in respiration is poorly understood. Here, we explore if the reliance on stores as respiratory substrate depends on day length. • Lolium perenne (perennial ryegrass) was grown in continuous light (275 μmol photons m(-2) s(-1) ) or in a 16 : 8 h day : night regime (425 μmol m(-2) s(-1) during the photoperiod), with the same daily photosynthetic photon flux density (PPFD).

Observing 13C labelling kinetics in CO2 respired by a temperate grassland ecosystem.

* The kinetic characteristics of the main sources of ecosystem respiration are quite unknown, partly because of methodological constraints. Here, we present a new open-top chamber (OTC) apparatus for continuous 13C/12C labelling and measurement of ecosystem CO2 fluxes, and report the tracer kinetics of nighttime respiration of a temperate grassland. * The apparatus includes four dynamic flow-through OTCs, a unit mixing CO2-free air with 13C-depleted CO2, and a CO2 analyser and an online isotope ratio mass spectrometer.