LAUSR

Abstract Exchanges of biogenic volatile organic compounds (BVOC) between plants and the atmosphere are likely to vary, in amount and composition, between different plant species but also for a single plant during its development. However, the effect of plant development stages, including senescence, on BVOC exchanges remains poorly investigated, especially in the case of crop plants. We investigated the BVOC exchange patterns for wheat plants, the most grown crop species worldwide, during seed maturation, senescence and after harvest. Fluxes were measured online, in situ, at the plant scale by combining automated chambers and a Proton Transfer - Reaction - Quadrupole ion guide - Time of Flight - Mass Spectrometer (PTR-Qi-Tof-MS). The high resolution and sensitivity of this method enabled the measurement of a large mass spectrum of compounds emitted at very small amounts, allowing a precise characterization of BVOC exchanges. We found that the overall BVOC emissions increased twofold during the senescence stage compared to the maturation stage. Methanol was found to be the most emitted compound (49 – 60% of the overall flux on a molar basis) followed by acetone (7.5 – 8.2% of the overall flux on a molar basis) during each developmental stage investigated. Acetaldehyde was another major emitted compound contributing mainly during late senescence to the overall flux (9.7%). When normalized for temperature and light conditions, most BVOC emissions increased during senescence, showing a clear effect of senescence on BVOC exchanges. Chamber emissions were comparable to whole ecosystem fluxes measured at the same site by eddy covariance the previous year. The OH reactivity of the emitted compounds was evaluated based on known reaction rate constants and was the largest during the first senescence stage, peaking at 12 s-1 in the chambers. The results of this study show the need for considering plant phenology when computing BVOC emissions from crops.