Jd. Derner et al., DOES GRAZING MEDIATE SOIL CARBON AND NITROGEN ACCUMULATION BENEATH C-4, PERENNIAL GRASSES ALONG AN ENVIRONMENTAL GRADIENT, Plant and soil, 191(2), 1997, pp. 147-156
An experiment was conducted to evaluate the influence of long-term (>2
5 yrs) grazing on soil organic carbon (SOC) and total soil nitrogen (N
) accumulation beneath individual plants of three perennial grasses al
ong an environmental gradient in the North American Great Plains. The
zone of maximum SOC and N accumulation was restricted vertically to th
e upper soil depth (0-5 cm) and horizontally within the basal area occ
upied by individual caespitose grasses, which contributed to fine-scal
e patterning of soil heterogeneity. Long-term grazing mediated SOC and
N accumulation in the tall-, mid-and shortgrass communities, but the
responses were community specific. SOC and N were lower beneath Schiza
chyrium scoparium plants in long-term grazed sites nf the tall- and mi
dgrass communities, but higher beneath Bouteloua gracilis plants in th
e long-term grazed site of the shortgrass community. SOC, but not N, w
as greater in soils beneath compared to between S. scoparium plants in
an abandoned field seeded in 1941, indicating that this caespitose gr
ass accumulated SOC more rapidly than N. SOC and N were greater in the
0-5 cm soil depth beneath a caespitose grass (S. scoparium) compared
to a rhizomatous grass (Panicum virgatum) in the tallgrass community,
with no significant accumulation of either SOC or N beneath P. virgatu
m plants. Grazing appears to indirectly mediate nutrient accumulation
beneath caespitose grasses along the environmental gradient by modifyi
ng the size class distribution of plants. Populations with a greater p
roportion of large plants have a greater potential for biomass incorpo
ration into soils and may more effectively capture redistributed organ
ic matter from between plant locations. Contrasting plant responses to
grazing at various locations along the environmental gradient conform
to the predictions of the generalized grazing model, as the selection
pressures of grazing and aridity may have also influenced the ability
of caespitose grasses to accumulate nutrients in soils beneath them b
y mediating grazing resistance, competitive ability and population str
ucture.