hide
Free keywords:
-
Abstract:
Microbial degradation of carbon derived from black shale and slate has been shown in vitro. However, in natural settings
where other labile carbon sources are likely to exist, this has not been previously demonstrated. We investigated the uptake of
ancient carbon derived from slate weathering and from recently photosynthesised organic matter by different groups of microorganisms.
Therefore we isolated microbial biomarkers (phospholipid fatty acids, PLFAs) from black slates collected at a
chronosequence of waste piles which differed in age and vegetation cover. We quantified the amount of PLFAs and performed
stable isotope and radiocarbon measurements on individual or grouped PLFAs to quantify the fraction of slate derived carbon.
We used black slate from a pile heaped in the 1950s with either uncovered black slate material (bare site) or material
slightly colonized by small plants (greened site) and from a forested leaching pile (forested site) used for alum-mining in
the 19th century.
Colonization by plants influenced the amount and composition of the microbial community. Greater amounts of PLFAs
(5410 ng PLFA/g dw) were extracted from slate sampled at the forested site as opposed to the bare site (960 ng PLFAs/g dw)
or the greened (annual grasses and mosses) rock waste pile (1050 ng PLFAs/g dw). We found the highest proportion of
PLFAs representing Gram-negative bacteria on the forested site and the highest proportion of PLFAs representing Grampositive
bacteria on the bare site. The fungal PLFA was most abundant at the greened site. Sites with less plant colonization
(bare and greened site) tended to have more depleted d13C values compared to the forested site. Radiocarbon measurements
on PLFAs indicated that fungi and Gram-positive bacteria were best adapted to black slate carbon uptake. In the fungal
PLFA (combined bare and greened waste pile sample) and in PLFAs of Gram-positive bacteria (greened site) we measured
39.7% and 28.9% ancient carbon uptake, respectively. Our results prove that black slate degradation followed by carbon
uptake takes place in situ. Results imply that plant colonization might additionally affect this process. Slight colonization with
few plants increased slate derived carbon uptake in PLFAs of Gram-positive bacteria. Evidently, Gram-positive bacteria represented
by specific PLFAs from the greened site held more ancient carbon than from the bare site. In contrast, no black slate
derived carbon was used by microorganisms at the forested site with 2–3 times greater carbon content. Results suggest that the
use of ancient slate derived carbon dominates mainly in early stages of microbial colonization of surfaces and that with increasing ecosystem development recycling of plant derived carbon dominates.
