Tree water relations can trigger monoterpene emissions from Scots pine stems during spring recovery

Abstract

Abstract. Tree canopies are known to emit large amounts of VOCs (volatile organic compounds) such as monoterpenes into the surrounding air. High VOC emission rates from boreal forests have been observed during the transition from winter to summer activity. The most important sources of these are considered to be the green foliage, understory vegetation and soil organisms, but emissions from the living stand woody compartments have so far not been quantified. We analyzed whether the non-foliar components could partially explain the springtime high emission rates. We measured the monoterpene emissions from Scots pine (Pinus sylvestris L.) stem and shoots during the dehardening phase of trees in field conditions in two consecutive springs. We observed a large, transient monoterpene burst from the stem, while the shoot monoterpene emissions remained low. The burst lasted about 12 h. Simultaneously, an unusual nighttime sap flow and a non-systematic diurnal pattern of tree diameter were detected. Hence, we suggest that the monoterpene burst was a consequence of the recovery of the stem from wintertime, and likely related to the refilling of embolized tracheids and/or phenological changes in the living cells of the stem. This indicates that the dominant processes and environmental drivers triggering the monoterpene emissions are different between the stem and the foliage.

Environmental control of growth variation in a boreal Scots pine stand – a data-driven approach

“…Our analyses also indicate that high GPP at the beginning of the growing season promotes radial growth supporting the findings of Schiestl-Aalto et al (2015), Chan et al (2015) and Babst et al (2014). The role of early carbon gain can be seen also in the negative correlation with NEE, whose negative values indicate carbon uptake as opposed to GPP.…”

“…This could reflect the fact that growth at the lower part of a stem is not critically limited by air humidity conditions and the level of water potential, which is always higher at the lower part of a stem than at shoots (Zimmermann 1983). Also this combination of conditions is normally favourable for photosynthetic production (Chan et al 2015).…”

“…Our results are, however, similar with those of Hordo et al (2011) who found that the temperature in current year March-April correlated positively with Scots pine radial growth in southern Finland and Estonia. Warm spring may also favour the recovery of xylem and phloem transport capacity after winter (Vanhatalo et al 2015) and for certain extend the growing season that reflects as larger accumulated growth at certain fixed time points.…”

“…If the growth were culminated by day length, the early onset would simply increase the annual ring width. On the other hand, Chan et al (2015) showed that a large amount of recently photosynthesized carbon increased daily growth in spring, so perhaps GPP in the early season stands out in the correlations since sugars have an important role both as a growth resource for cell differentiation and as a factor behind sufficient cell turgor together with water availability.…”

Variability of Ozone Deposition Velocity Over a Mixed Suburban Temperate Forest

“…Information about emission of storage or non-storage monoterpenes from the pine foliage, branches, stem or forest floor is, however, lacking at our site but BVOC measurements could have casted a light on the overly high O 3 fluxes, measured during spring 2007 or in other years with high O 3 dry deposition rates (e.g., 2010). Excessive springtime monoterpene emissions or standard emission rates were measured in Pinus stands as a consequence of drought stress (Bäck et al, 2005), springtime phase change in stem water transport capacity (Vanhatalo et al, 2015), bud break (Kim, 2001), general stress to the plant (Komenda and Koppmann, 2002) or disturbed tree-herbivore relations (Phillips and Croteau, 1999;Trowbridge et al, 2014). Emission of BVOCs from intact Scots pine branches can be very high in early spring, often much higher than the emission occurring later in the growing season (Tarvainen et al, 2005;Hakola et al, 2006).…”