The soil matrix increases microbial C stabilization in temperate and tropical forest soils
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Microbial biomass represents a substantial source of labile C contributing to soil organic matter (SOM) maintenance. Microbial residues may associate with the soil matrix through a variety of mechanisms, reducing its bioavailability and increasing its persistence in soil. Our objective was to examine soil matrix effects on the stability of non-living microbial C inputs in two contrasting forest ecosystems by following microbial residues (Fungi, Actinobacteria, Gram-positive bacteria (Gm +), Gram-negative bacteria (Gm −)) into SOM fractions in a temperate forest in California (CA) and a tropical forest in Puerto Rico (PR) for 3 and 2 years, respectively. We isolated 3 SOM fractions: (i) free light fraction (FLF), (ii) occluded light fraction (OLF), and (iii) dense fraction (DF). Additionally, we characterized SOM fraction chemistry to infer quality and source of native fraction SOM. Our results showed greater stabilization as mineral-associated microbial C (i.e., as DF and OLF), compared with loose detrital C (i.e., FLF). There was no microbial group effect (i.e., differences in fraction C recovery among different microbial cell types). Our findings suggest that mineral association is more important for stabilizing non-living microbial C in soil than the cellular structure of the initial source of microbial inputs, with site specific edaphic factors as the major controllers of the amount of microbial residues stabilized.
KeywordsMicroorganisms Fungi Bacteria Carbon Soil organic matter Mineral protection Stabilization
This research was funded by The National Science Foundation’s Division of Environmental Biology, Ecosystem Science Cluster (Award No. 324002), The Kearney Foundation of Soil Science and the J. G. Boswell Endowed Chair in Soil Science. We are grateful for contributions from researchers J. Braun, L. Dane, E. Dubinsky, J. Fortney, D. Herman, J. Pett-Ridge and W. Silver, as well as the research staff of the UC Blodgett Forest Research Station and the Luquillo Experimental Forest.
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