Jökull - 01.12.2007, Page 45

Rates of carbon ingrowth and nutrient release from young Icelandic basalts
understand what drives the variations in the contents
of mineral P in Icelandic soils, because mineral P is a
critical factor in the development of soils and functio-
ning of terrestrial ecosystems, particularly in a rocky
environment.
Figure 6. Comparison of organic C and P fractions
in soils derived from four lava flows in Iceland. n=1,
2, 2 and 3 for 1783, 1554, 1300 and 934 AD flows,
respectively. – Samanburður á lífrænu kolefni og
fosfór í jarðvegi á Skaftáreldahrauni, Hekluhraunum
frá 1554 og 1300 og Eldgjárhrauni.
A concurrent examination of organic C and P con-
tents in soils derived from various lava flows can re-
veal the role of biomass production and weathering of
substrates in soil formation. Both elements increased
in soil organic matter as a function of time, but thro-
ugh two different pathways. The ingrowth of organic
C in soil profiles is through the sequestration of atmo-
spheric CO2 by photosynthesis. The increase of or-
ganic P, in contrast, is through the transformation of P
stored in rock minerals and from airborne sources into
organicmolecules via plant root uptake and biological
use of P as an essential nutrient. Thus, C ingrowth is
from the atmosphere while P ingrowth is mostly from
the lithosphere. Despite their different ingrowth pa-
thways, organic C and P showed similar patterns of
accumulation in the soil over time (Figure 6). Results
from our study demonstrated that the ingrowth of or-
ganic P in the soil was primarily facilitated by the in-
creasing plant and microbial activities, which would
increase organic P to a greater extent than other frac-
tion of soil P. Our results also demonstrated the inter-
play of the biogenic activities responsible for the ac-
cumulation of C and P that differ in biogeochemical
pathways in the sub-arctic ecosystem in Iceland.
In summary, our study showed basalt-derived An-
dosols in southern Iceland exhibited a number of geo-
chemical changes over the last millennium. Biologi-
cal activities in the soil have been increasing in the soil
over time as evidenced by the increases in both orga-
nic C and P. In addition, changes in the concentrations
of organic and occluded P demonstrated that weathe-
ring of parent rock is continuously occurring in this
ecosystem. Our results suggest that biological acti-
vity and weathering of parent rock occur concurrently
in southern Iceland, each process acting to facilitate
and accelerate the other. These processes will gradu-
ally change the storage capacity for C in the soils and
alter the cycling patterns of essential nutrients, such
as C and P, in these fragile but important ecosystems.
Acknowledgements
We thank Andrew Wolf, Lenore Tedesco, Kathy
Licht, Jeff Swope, Leda Casey, Nick Kauffman and
other members of the Iceland field project for their
help in the field. Support for this research came
from Undergraduate Research Opportunity Program
(UROP) and the U.S. National Science Foundation
(BCS–9911526 to GF and CS).
JÖKULL No. 57 43