Rhizosphere activity in an old-growth forest reacts rapidly to changes in soil moisture and shapes whole-tree carbon allocation
Jobin Joseph, Decai Gao, Bernhard Backes, Corinne Bloch, Ivano Brunner, Gerd Gleixner, Matthias Haeni, Henrik Hartmann, Günter Hoch, Christian Hug, Ansgar Kahmen, Marco M. Lehmann, Mai–He Li, Jörg Luster, Martina Peter, Christian Poll, Andreas Rigling, Kaisa Rissanen, Nadine K. Ruehr, Matthias Saurer, Marcus Schaub, Leonie Schönbeck, B. Stern, Frank M. Thomas, Roland A. Werner, Willy Werner, Thomas Wohlgemuth, Frank Hagedorn, Arthur Geßler
Abstract
pulse labeling to naturally dry control and long-term irrigated trees and tracked the fate of the label in above- and belowground C pools and fluxes. Allocation of new assimilates belowground was ca. 53% lower under nonirrigated conditions. A short rainfall event, which led to a temporary increase in the soil water content (SWC) in the topsoil, strongly increased the amounts of C transported belowground in the nonirrigated plots to values comparable to those in the irrigated plots. This switch in allocation patterns was congruent with a tipping point at around 15% SWC in the response of the respiratory activity of soil microbes. These results indicate that the metabolic sink activity in the rhizosphere and its modulation by soil moisture can drive C allocation within adult trees and ecosystems. Even a subtle increase in soil moisture can lead to a rapid recovery of belowground functions that in turn affects the direction of C transport in trees.