Sammendrag
Soil organic matter (OM) is a source of fertility for food provisioning and a means for climate mitigation. A high
pedodiversity observed over very short distances due to both past and present land use, such as in Western Africa
(Northern Togo), makes this a crucial issue. In particular, some small spots covered by sacred forests (forˆets
sacr ́ees) of high cultural value in this area are extremely biodiverse, calcareous and high in OM in contrast with
the non-calcareous, poor OM, overgrazed woody savannah and agricultural surroundings. The objectives of our
work were to understand this pedodiversity and the process of CaCO3 formation in the soil under the highly
biodiverse forest using morphological, micromorphological, chemical and mineralogical soil analyses. The re-
sults show a high degree of weathering of the gneiss parent material, presence of plinthite gravels, dominance of
1:1 clays, formation of swelling clays in the imperfectly drained soils, and low OM content. The presence of
palygorskite, although in traces, suggests drier intervals and is consistent in this context with the extreme wet
and dry climate conditions in the region. In the OM rich soils under forest, bio-calcification takes place in the
form of CaCO3 needles, micrite hypocoatings around biopores and calcified cells. Oribatid excrements are
associated with calcite and organic matter in the sacred forest soil, indicating that litter recycling has played an
important role in the formation of calcite. We hypothesize that the high biological activity releasing CO2, for-
mation of HCO3
– and precipitation of CaCO3 due to the Ca2+ released by the recycled organic matter and
weathering of plagioclases, lead to different forms of secondary calcium carbonate in the sacred forest soils. The
high oxalate content of the vegetation in the sacred forest suggests that calcium carbonate formation, possibly via
the oxalate-carbonate pathway, may also have played a role in calcite precipitation in these in organic matter
rich soils. The parent material of these soils is not calcareous, meaning that these are not lithogenic carbonates,
thus making them an important carbon sink. The soil characteristics indicate a high potential for development of
the soils of the area in both agricultural yields and in potential carbon sequestration relevant to global change
policies.
Vis fullstendig beskrivelse
