Linking soil aggregate properties to organic matter storage along a gradient of biological activity

Simon Stahr1, Markus Graf1, Friederike Lang1
1 Chair of Soil Ecology, Institute of Forest Sciences

P 4.26 in Below ground turnover of C and nutrients in forest soils

Poster Session 1 on Monday, 16:30-18:30

Our research is embedded in the priority program SPP 1685 of the German Research Foundation (DFG) which is about ecosystem nutrition and phosphorous availability in forest ecosystems. Our study sites represent five distinct statuses along a gradient of decreasing P-availability and biological activity as indicated by increasing thickness of the forest floor from mull to mor-like moder. It is known that P-distribution within aggregates depends highly on aggregate formation and properties; hence it is necessary to characterize the aggregates. Therefore we concentrate on the analysis of aggregate properties along that gradient as a first step of our sub-project. 

Our hypothesis is that with decreasing biological activity the amount of organic matter stored in small aggregates (< 2 mm) decreases as does the stability of the aggregates.

We test this hypothesis by the analysis of a) the release of organic matter from aggregates after sequential ultrasound disaggregation, b) aggregate turnover based on the size of oPOM as a proxy and c) the shape and size of aggregates with the image analysis sensor QICPIC (Sympatec).

First results contradict our hypothesis. Percentage of OM occluded within the aggregates did not decrease: but did increase with lower biological activity (Mull-site: 8 % of OC stored within the aggregates. Mor-like site: 54 % OC stored within the aggregates) while mineral associated organic matter decreases with decreasing biological activity. We found more stable aggregates on the sites influenced by podsolization and low biological activity.

We hope that we are able to explain these contradictions by the analyses on aggregate size and aggregate turnover which are being performed currently. Results will be presented.

Letzte Änderung 19.06.2014