Chiara Bertora1, Elena Rizhiya1, Petra C.M. Van Vliet2, and Jan W. van Groenigen1. (1) "Alterra, Soil Sciences Center", Po Box 47, Po Box 47, Wageningen, 6700AA, NETHERLANDS, (2) Dept. of Soil Quality, Wageningen UR, P.O. Box 8005, 6700 EC, Wageningen, Netherlands
The crucial role of earthworms in stabilizing soil organic
matter and thereby stimulating carbon sequestration is widely acknowledged in
the literature. However, there is a separate body of literature reporting
elevated emissions of the greenhouse gas (GHG) nitrous oxide (N2O)
from earthworm-worked soil, earthworm casts, and earthworms themselves. As
these last results are mainly derived from natural ecosystems, we quantified
the effects of earthworms on N2O and carbon dioxide (CO2)
emissions from a 3-year old pasture on a sandy soil in the Netherlands. In
a first experiment, the effect of an anecic species (Aporrectodea longa) on emissions
after grassland renewal was quantified for three different moisture contents.
None of the moisture treatments showed a significant effect of A. longa on CO2 emissions. At the highest soil
moisture content (70% Water-filled pore space) presence of A. longa resulted in significantly higher N2O
emissions during the first two weeks, representing a difference of
approximately 450 g N2O-N ha-1. However, after three
weeks patterns reversed and N2O emissions became significantly lower
in the presence of A. longa for the remainder of the
2 month experiment. Potential denitrification and N2O
emission at the end of the experiment showed significant differences with
respect to earthworm presence. In a second experiment, both the effect of an
additional epigeic earthworm (Lumbricus rubellus) and of soil compaction were quantified, showing intricate interactions between
earthworm species, compaction and GHG emissions. We conclude that the effects
of earthworms on net GHG emissions from soils are not always exclusively
beneficial and need to be studied further. Finally, we discuss the role of earthworms
in the often-observed trade-off between C sequestration and N2O
emission after introduction of minimum tillage.