Stem CO2 efflux and its contribution to ecosystem CO2 efflux decrease with drought in a Mediterranean forest stand

Abstract

Keywords:Water deficit Respiration acclimation Carbohydrate Carbon balance Forest decline Net ecosystem exchangeThe rate of metabolic processes demanding energy in tree stems changes in relation with prevailing climatic conditions. Tree water availability can affect stem respiration through impacts on growth, phloem transport or maintenance of diverse cellular processes, but little is known on this topic. Here we monitored seasonal changes in stem CO2 efflux(F s ), radial growth, sap flow and non-structural carbohydrates in trees of Quercus ilex in a Mediterranean forest stand subjected since 2003 to either partial (33%) throughfall exclusion (£) or unchanged throughfall (C). F s increased exponentially during the day by an effect of temperature, although sap flow attenuated the increase in F s during the day time. Over the year, F s also increased exponentially with increasing temperatures, but F s computed at a standard temperature of 15 °C (F s 15 ) varied by almost 4-fold among dates. F s 15 was the highest after periods of stem growth and decreased as tree water availability decreased, similarly in Cand E treatments. The decline in F s 15 was not linked to a depletion of soluble sugars, which increased when water stress was higher. The proportion of ecosystem respiration attributed to the stems was highest following stem growth (23.3%) and lowest during the peak of drought (6.5%). High within-year variability in F s 15 makes unadvisable to pool annual data of F s vs. temperature to model F s at short time scales (hours to months) in Mediterranean-type forest ecosystems. We demonstrate that water availability is an important factor governing stem C0 2 efflux and suggest that trees in Mediterranean environments acclimate to seasonal drought by reducing stem respiration. Stem respiratory rates do not seem to change after a long-term increase in drought intensity, however.

Transporte y reciclaje de CO2 en el interior del árbol: factores que complican la estimación de la respiración leñosa a través de la emisión radial de CO2

“…B) The rise of temperature during the day is higher than the decrease during the evening; thus, during the day, the difference between the temperature recorded at the time of measuring radial CO 2 efflux and that recorded, for example, 3 hours before, is higher than during the night. Theoretical data based on previous works reporting similar trends in Pinus taeda L. (Maier and Clinton 2006) and Quercus ilex (Rodríguez-Calcerrada et al 2014a). …”

“…Atendiendo a la Ley de Henry, el CO 2 disuelto en la savia se encuentra en equilibrio con el CO 2 en fase gaseosa -medible con microelectrodos o sensores no dispersivos de infrarrojo (NDIR) -y puede ser estimado una vez conocido el pH y la temperatura de la savia, aplicando las ecuaciones expuestas en McGuire y Teskey (2002). En especies con flujos de savia elevados, por ejemplo especies riparias, el impacto podría ser mayor que en aquellas con menores flujos de savia, por ejemplo, especies Mediterráneas adaptadas a la sequía como Quercus ilex L. (Rodríguez-Calcerrada et al 2014a). Es posible estimar la magnitud del flujo axial de CO 2 a partir de la concentración de CO 2 interna y el flujo, temperatura y pH de la savia.…”

“…Este fundamento ha sido y es la base para estudiar diversos aspectos ecológicos forestales relacionados con la respiración leñosa, como su importancia en la adaptación del árbol al medio (Ryan et al 1995), la variación con los tratamientos selvícolas (Lavigne 1987), la influencia de factores climáticos (Rodríguez-Calcerrada et al 2014a) y la separación de costes de mantenimiento y crecimiento (Ryan 1990). También a partir de medidas puntuales se llega a modelizar la respiración de troncos y raíces a grandes escalas espaciales, por ejemplo a las escalas de rodal, bosque o región, empleando ecuaciones de extrapolación (upscaling) que incluyen la superficie total o más comúnmente el volumen de albura del árbol por unidad de superficie de terreno (Rodríguez-Calcerrada et al 2014a). El éxito de este enfoque (medir la emisión de CO 2 para estimar la respiración) se basó en tres ventajas que ofrece en comparación con otros métodos: escasa perturbación en el árbol, posibilidad de muestrear zonas amplias simultáneamente, y relativa sencillez en la adquisición de datos.…”

Xylem and soil CO2 fluxes in a Quercus pyrenaica Willd. coppice: root respiration increases with clonal size

“…Nevertheless, this is the first time that [CO 2 * ] was measured in the Mediterranean region during summer drought (note that the study of Cerasoli et al (2009) was performed during autumn). Summer drought in Mediterranean climates restrains respiratory processes at the ecosystem (Reichstein et al 2002;Guidolotti et al 2013;Rambal et al 2014), soil (Rey et al 2002;Tang and Baldocchi 2005), stem, and foliage levels (Maseyk et al 2008;Rodríguez-Calcerrada et al 2014) and may be the cause of the comparatively low [CO 2 * ] and F T measured in this study. Moreover, lower root water content caused by limited soil water availability would enhance F S-root to the detriment of F T due to reduced resistance to radial CO 2 diffusion ]-drought experiment existent to date after 9 days without watering, with a sharp increase in [CO 2 * ] once watering resumed , as was seen in this species after first autumn rain.…”

Post-harvest respiration of Pinus radiata logs under different temperature and storage conditions

“…Most studies focus on the respiration rate of living stems (Ryan et al 1994;Damesin et al 2002;Guidolotti et al 2013;Rodriguez-Calcerrada et al 2014) or coarse wood litter (Progar et al 2000;Chambers et al 2001). For both living stems and coarse wood litter, respiration rate increases as temperatures rise within a day or throughout the year, although discrepancies exist because of genetic, developmental and other environmental factors, such as shelter, which affects moisture content, and heterotrophic community composition (Progar et al 2000;Rodriguez-Calcerrada et al 2014). Therefore, it is expected that the respiration rates of harvested radiata pine logs also respond to temperature, storage condition and time.…”