Biolability of Fresh and Photodegraded Pyrogenic Dissolved Organic
Matter from Laboratory-Prepared Chars
Abstract
Pyrogenic dissolved organic matter (pyDOM) is known to be an important
biogeochemical constituent of aquatic ecosystems and the carbon cycle.
While our knowledge of pyDOM’s production, composition, and
photolability has been studied recently, we lack an understanding of
potential microbial mineralization and transformation of pyDOM in the
biogeosphere. Thus, leachates of oak charred at 400 and 650 °C, as well
as their photodegraded counterparts, were incubated with a
soil-extracted microbial consortium for up to 96 days. Over the
incubation, significantly more carbon was biomineralized from the lower
versus higher temperature char leachate (45% versus 37% lost,
respectively). Further, the photodegraded leachates were biomineralized
to significantly greater extents than their fresh non-photodegraded
counterparts. Kinetic modeling identified the mineralizable pyDOC
fractions to have half-lives of 9 to 13 days. Proton nuclear magnetic
resonance spectroscopy indicated that the majority of this loss could be
attributed to low molecular weight constituents of pyDOM (i.e., simple
alcohols and acids). Further, quantification of benzenepolycarboxylic
acid molecular markers indicated that condensed aromatic compounds in
pyDOM were biomineralized to much less extents (4.4 and 10.1% decrease
in yields of ΣBPCA-C over 66 days from Oak-400 and Oak-650 pyDOM,
respectively), but most of this loss could be attributed to
biomineralization of smaller condensed clusters (4 aromatic rings or
less). These results highlight the contrasting bioavailability of
different portions of pyDOM and the need to examine both to evaluate its
role in aquatic heterotrophy and its environmental fate in the
hydrogeosphere.