Detrital controls on soil organic matter dynamics and soil solution chemistry: An experimental approach.
Lajtha, Kate*,1, Crow, Susan1, Yano, Yuriko2, Kaushal, Sujay3, Sulzman, Elizabeth1, Spears, Julie1, 1 Oregon State University, Corvallis, OR2 Ecosystems Center, Woods Hole, MA3 Institute of Ecosystem Studies, Millbrook, NY
ABSTRACT- We established a long-term field study in an old growth coniferous forest at the H.J. Andrews Experimental Forest, OR, to address how detrital quality and quantity control soil organic matter (SOM) accumulation and stabilization. The Detritus Input and Removal Treatments (DIRT) plots consist of treatments that double needle litter, double woody debris inputs, exclude litter inputs, or remove root inputs via trenching. The effect of adding woody debris was to increase DOC concentrations in O-horizon leachate and at 30 cm, but not at 100 cm compared to control plots, suggesting increased rates of DOC retention with added woody debris. DOC concentrations decreased through the soil profile in all plots to a greater degree than did DON, and nitrate showed very little decrease with depth. These trends are most likely due to preferential sorption of high C:N hydrophobic DOM in upper horizons; %hydrophobic DOM decreased significantly with depth, and hydrophilic DOM had a much lower and narrower C:N ratio. Although laboratory extracts of different litter types showed differences in DOM chemistry, %hydrophobic DOM did not differ among detrital treatments in the field, suggesting microbial equalization of DOM leachate in the field. This was supported by the fact that laboratory leachates had a higher %hydrophilic DOM content that DOM from lysimeters, suggesting microbial consumption of labile hydrophilic DOM. We expected to see very little N leaching from any of the plots due to the high C:N ratio of the forest floor and mineral soil, as well as the very low N deposition input. However, DIN losses were significantly elevated in the two treatments without roots, suggesting that the simple forest floor C:N ratio theory is inadequate, and that labile, available carbon introduced belowground by root turnover, root exudates, and/or mycorrhizal turnover is more critical to N immobilization than is bulk SOM.
Key words: DOC, SOM, DON
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