Leaching of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in mor humus as affected by temperature and pH
2000
Andersson, S. | Nilsson, S.I. | Saetre, P.
We investigated how pH and microbial activity influence fluxes and composition of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in a laboratory leaching experiment with mor humus from a limed plot and an unlimed plot of Scots pine in northern Sweden. CaCO3 was applied at a rate of 5 t ha(-1) 23 yr before sampling. The limed (pH 5.4) and unlimed (pH 4.3) mor humus was incubated at +4 degrees C and +15 degrees C. The biological activity measured as CO2 evolution increased in the following order: unlimed +4 degrees C < limed +4 degrees C < unlimed + 15 degrees C < limed + 15 degrees C. During the first 36 d, leaching of DOC and DON increased as follows: unlimed +4 degrees C < unlimed + 15 degrees C < limed +4 degrees C < limed +15 degrees C, but later on DOC and DON leaching from the unlimed mor humus at + 15 degrees C increased markedly. The increase coincided with greater NH4+ leaching. A complementary leaching experiment indicated that Ca2+ ions have a moderating effect on DOC solubility and leaching. pH was more important than temperature for the leaching of DOC and DON at the beginning of the main experiment (d 1-d 36), but temperature was a more important factor after that. The leachates collected at the sixth leaching event were incubated for 24 h at +15 degrees C with [(3)H]-labeled thymidine and those from the limed treatment showed a higher incorporation of labeled thymidine per amount of DOC than those from the unlimed treatment, which might indicate more accessible substrates for microorganisms. There also was a relatively higher content of hydrophobic acids in the leachates from the limed than from the unlimed treatment, irrespective of temperature.
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