Talk, Adaptation of Forests and Forest Management to Changing Climate with Emphasis on Forest Health: A Review of Science, Policies, and Practices: 2008-09-25 - 2008-09-28
Abstract:
EXPERIMENTAL FROST AND DROUGHT AFFECT FINE ROOT DYNAMICS AND CARBON INPUT TO THE SOIL IN A SPRUCE FOREST Dirk Gaul*, Dietrich Hertel, Christoph Leuschner Plant Ecology, Albrecht-von-Haller Institute of Plant Sciences, University of Göttingen, Untere Karspüle 2, 37073 Göttingen, Germany Corresponding author: dgaul@gwdg.de 2nd author: dhertel@gwdg.de 3rd author: cleusch@gwdg.de Fine roots represent a small but functionally important element of ecosystem carbon cycling. Assuming that fine roots live and die within one year, fine root turnover is estimated to transfer about 30% of the global net primary production to the soil. However, the impacts of global change on fine root dynamics are very uncertain. Meteorologists predict temperature increases as well as stronger and more frequent summer droughts for many regions of Central Europe. However, climate change might also produce some unexpected effects. In that context, decreasing snow cover in winter may result in stronger soil frost at higher latitudes and in mountainous regions even though average winter air temperatures are increasing. In our study, we investigated the effects of experimental soil frost and soil drought on fine root production, mortality and decomposition of Norway spruce (Picea abies (L.) Karst.) in Southeast Germany. In order to simulate these extreme meteorological conditions, we applied a replicated snow removal experiment during winter 2005/06 and a replicated throughfall exclusion experiment during summer 2006. We used two different methods (minirhizotron observations and sequential soil coring) to monitor root production and mortality in the organic layer and the upper mineral soil of treatment and control plots. Fine root decomposition was investigated in a root-litterbag experiment. The results showed that fine root mortality was significantly increased by both, experimental frost and drought. However, enhanced fine root production at the treatment plots compensated for the root loss caused by these extreme meteorological conditions. As a consequence of increased fine root death, we estimated that experimental frost and drought led to an additional carbon input to the organic soil layer in the studied spruce stand of 21 and 26 g m-2, respectively. Our root-litterbag experiment indicated that fine root decomposition was significantly reduced during soil drought. We conclude that increased frequencies of freeze-thaw and drought-rewetting events in the frame of climate change will enhance the carbon sink strength of Norway spruce fine root systems. However, compensatory root production may draw on the carbohydrate reserves of the spruce trees, thereby possibly reducing their above-ground productivity. Key words: climate change, minirhizotron, fine root mortality, soil coring, throughfall exclusion