Hamer, U.; Rumpel, C. & Dignac, M. (2012): <b>Cutin and suberin biomarkers as tracers for the turnover of shoot and root derived organic matter along a chronosequence of Ecuadorian pasture soils</b>. <i>European Journal of Soil Science</i> <b>online</b>, 1-12.
Resource Description
Title:
Cutin and suberin biomarkers as tracers for the turnover of shoot and root derived organic matter along a chronosequence of Ecuadorian pasture soils
Forest-to-pasture conversion has been reported to increase soil organic matter (SOM) in mineral topsoils<br/>
in the tropical mountain rainforest region of south Ecuador, with subsequent decreases following pasture<br/>
abandonment. Until now the mechanisms behind these changes have not been fully understood. To elucidate<br/>
their varied preservation patterns, we analysed root- and shoot-derived organic matter and assessed their<br/>
contribution to the formation of SOM in topsoils (0?5 cm) on a chronosequence of pastures (Setaria sphacelata<br/>
(Schumach.); C4) established after slash and burn of the natural forest (diverse C3 plant species) and an<br/>
abandoned pasture site invaded by bracken fern (Pteridium arachnoideum (Kaulf.) Maxon.; C3). Cutin and<br/>
suberin biomarkers of the two plant species (grass and bracken) and of forest litter were identified after<br/>
saponification and their contribution to SOM was studied by compound-specific stable carbon isotope analyses.<br/>
Our results showed specific root and shoot biomarkers for the two plant species and for forest litter, which<br/>
often did not correspond to the classification of root-versus shoot-specific monomers reported in the literature.<br/>
This illustrates the importance of direct biomarker determination rather than using results from studies with<br/>
different plants. Shoot- as well as root-derived OM of forest and grass origin contributed to the stable SOM<br/>
pool with decadal turnover times. Forest-derived monomers contributed more to the stable SOM pool compared<br/>
with grass-derived monomers. ω-hydroxy carboxylic acids and α,ω-alkanedioic acids of forest origin may have<br/>
been stabilized in these tropical soils by bonding to soil minerals. Rapid degradation of grass-derived lipids<br/>
from the same compound classes suggests a saturation of the mineral binding capacity. In pasture soils, the<br/>
accumulation of SOM was mainly driven by large inputs of root OM. The accumulated SOM during pasture<br/>
use is, however, lost rapidly after abandonment.
