LAUSR

Many belowground processes, such as soil respiration and soil-atmosphere VOC exchange are closely linked to soil microbiological processes. However, little is known about how changes in plant species cover, i.e. after plant invasion, alter these soil processes. In particular, the response of soil volatile organic compound emission (VOCs) to plant invasion is not well understood. We analyzed soil VOC emissions and soil respiration of a Mediterranean cork oak (Quercus suber) ecosystem, comparing soil VOC emissions from a non-invaded Q. suber woodland to one invaded by the shrub Cistus ladanifer. Soil VOC emissions were determined under controlled conditions using online proton-transfer time-of-flight mass-spectrometry. Net soil VOC emissions were measured exposing soils with and without litter to different temperature and soil moisture conditions. Soil VOC emissions were sensitive to C. ladanifer invasion. Highest net emission rates were determined for oxygenated VOCs (acetaldehyde, acetone, methanol, acetic acid) and high temperatures enhanced total VOC emissions. Invasion affected the relative contribution of various VOCs. Methanol and acetaldehyde were emitted exclusively from litter and were associated to the non-invaded sites. In contrast, acetone emissions increased in response to shrub presence. Interestingly, low soil moisture enhanced the effect of shrub invasion on VOC emissions. Our results indicate that shrub invasion substantially influences important belowground processes in cork oak ecosystems, in particular soil VOC emissions. High soil moisture is suggested to diminish the invasion effect by a moisture induced increase of microbial decomposition rates of soil VOCs.