Tree species effects on the release of dissolved organic carbon and nitrogen from decomposing logs
O 2.1 in Biodiversität: Verbreitung, Funktion und Erhaltung
11.10.2012, 09:30-09:45, H8
There still is a lack of knowledge concerning the contribution of dissolved organic matter (DOM) to the mass loss of decomposing logs. Moreover, the nitrogen turnover in logs exposed to decomposition is still poorly understood. The project is guided by the following hypotheses:
- quality and release of DOM is tree species specific
- quality of DOM changes with decomposition stages
- decomposing logs act as a sink for dissolved mineral N
Our study is part of the BeLongDead-initiative within the DFG Biodiversity Exploratories. Since 2009 logs of 13 different tree species were exposed to decomposition at sites (Hainich, Schorfheide and Schwäbische Alb) under natural environmental conditions. We collect runoff samples from the logs since April 2011 in intervals of 2 - 6 weeks, depending on precipitation. At the Schorfheide and Schwäbische Alb we sample beech, oak and spruce logs and at the Hainich Exploratory all 13 tree species. After filtration (0.45µm) we determine the concentration of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate and ammonia, pH and the electrical conductivity. The net release of DOC and DON is calculated by subtracting the throughfall fluxes from the runoff fluxes at each log.
The concentrations of DOC in runoff from logs ranged from 5-548 mg/L and generally exceed those in throughfall by far. Highest concentrations were found underneath oak trees and lowest under lime trees. The amount of precipitation in the sampling period did not correlate with the concentration of DOC in log runoff. Tree species also influenced the quality of DOC: The humification index calculated from the emission spectra at 280nm ranged from 4,25 for maple up to 8,44 for oak trees.
The first data show a rather low mass loss of the logs by DOM (0.02 - 0.06 % per year) in the initial phase of decomposition. The N budget of the logs indicated a negative flux for dissolved mineral nitrogen for the first sampling period.
Based on the first results we conclude that tree species has a strong influence on DOC and N dynamics of decomposing logs.
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