Quantification of monoterpene emission sources of a conifer species in response to experimental drought. Issue 5 (30th August 2017) - Lüpke, Marvin
Abstract : We studied with the help of 13CO2 labelling and an advanced gas exchange measurement system (Tree DEMON) the strength of de novo and pool isoprenoid emissions of Scots pine during drought and rewetting. Both emission types showed a reduction, however, the de novo emissions were more strongly affected by drought and recovered slower during rewetting. The study also showed a strongly varying ratio of pool and de novo emissions for the individual isoprenoids. Furthermore an improved emission standardization algorithm was applied to correctly standardize the emission rates from de novo and pool emissions to determine the emission potential under different drought stress states. Abstract: Monoterpene (MT) emissions of conifer tree species, emitted from de novo synthesis and storage pools, play an important role in plant ecology and physiology. During drought stress both emission sources are affected differently and with conventional measuring techniques they are difficult to separate. We investigated 13 C labelled MT emission of eight 3-year-old Scots pine seedlings in a drought stress experiment using a dynamic gas exchange chamber system (Tree DEMON). Monoterpene, water vapour and CO2 gas exchange were measured for a 2-day normal watering, a 11-day treatment and a 3-day re-watering period. In each period all trees were 13 C labelled once for 5 h. Results showed the expected decrease of MT, water vapour and CO2 gas exchange with decreasing soil water content. However, during re-watering water vapour and CO2 gas exchange recovered fast to pre-drought levels, whereas MT increased to a lower level compared to the initial non-stressed phase. The 13 C labelling showed highly variable % 13 C values for different MTs, which ranged compound-specific from 0.5 to 95 % for unstressed trees. Overall, around 36 ± 5 % of the total emission rate originated from de novo synthesized MTs during the 2-day prior to stress period. During full drought, the de novo fraction was reduced to 3 %. For the re-watering phase de novo emissions recovered only partly to 20 %, while pool emissions reached pre-drought conditions. Thus, emissions of de novo synthesized MTs of Scots pine are down-regulated by soil drought rather than MT emissions from pools.