『Abstract
Two shrub species (Piliostigma reticulatum (D.C.) Hochst
(Caesalpinioideae) and Guiera senagalensis J.F. Gmel (Combretaceae)
are commonly found in farmers' fields at varying densities in
semi-arid Senegal and throughout the Sahel where soils have chronically
low phosphorus (P) availability. It seems plausible that shrub
litter and the rhizospheres could influence P fractions and other
chemical soil properties that affect crop productivity. Thus,
a study was done at two sites, on the distribution of inorganic
and organic soil P pools, organic C levels, and pH in soil beneath
and outside the canopies of P. reticulatum and G. senegalensis
(0-30 cm depth). Both sites had low total P ranging from 64 mg
P kg-1 to 135 mg P kg-1, and low extractable
PO4 (resin Pi) (1-6 mg P kg-1)
with P fractions dominated by NaOH-P. Organic P (Po) made up about
50％ of total P, and most of the organic P (＞60％) was found in
the NaOH-P fractions. The labile , particularly bicarb-Po was
higher in soil beneath shrub canopies (8.4 mg P kg-1),
than outside the canopy (6.2 mg P kg-1). Similarly,
C, N and P to a lesser extent, were more concentrated beneath
shrub canopies. P. reticulatum soil was dominated by the
NaOH-Po fraction, whereas G. senegalensis had higher bicarb-Po
at one of the study sites. An index of biologically available
organic P (Bicarb-Po) / (Bicar-Po+Bicarb-Pi+Resin Pi) was ＞60％
and indicates that biological processes represent an important
part of P cycling processes represent an important part of P cycling
in these shrub ecosystems. The differential ability of shrubs
in modifying soil chemical properties under their canopies has
major implications for biogeochemical cycling of nutrients and
C in sandy soils of semi arid Sahelian ecosystems.
Keywords: Canopy soil; P fractions; Sahel; Semi-arid; Shrubs;
Total C』
Abbreviations
Introduction
Materials and methods
Study sites and sampling design
Laboratory analyses
Soil P fractionation
Interpretation of P fractions
Statistical analyses
Results
Soil organic C, N, P and pH
Soil P fractions
Discussion
Soil chemical properties
Soil P fractions
Conclusions and perspectives
Acknowledgements
References
※リンの連続分別法は、Hedley et al.（1982）とTiessen and Moir（1993）とCross and Schlesinger（2001）による。