Agriculture Reference
In-Depth Information
MBC (p < 0.001, R
2
= 0.72) but weaker relationships with MBN (p = 0.02,
R
2
= 0.40) and soil C (p = 0.02, R
2
= 0.40).
When soil physicochemical factors were used to constrain the ordina-
tion of all nine enzyme activities with RDA (Fig. 2), the model accounted
for 65% of the total variation (p < 0.001). Based on permutation tests, all
explanatory variables retained in the model were signifi cant (p < 0.05) in
constraining enzyme activities.
Increases in all enzyme activities along axis 1 (42% of total variation,
60% of fi tted variation) were positively correlated with MBC, which was
more highly associated with this axis than any other variable (Fig. 2a),
as indicated by the length and direction of its vector. Axis 2 (14% of the
total variation and 20% of the fi tted variation) largely differentiated C- vs.
N-cycling enzymes, with P- and S-cycling enzymes falling intermediate.
Activities of C-cycling enzymes β-glucosidase and α-galactosidase and
C/N-cycling enzyme β-glucosaminidase loaded positively on axis 2 and
were associated with soil inorganic N, especially NO
3
−
, and MBN. Activi-
ties of N-cycling enzymes aspartase and l-asparaginase loaded negatively
along axis 2 and were associated with soil C and N, soil C:N, and EOC
and EON.
Non-overlapping confi dence ellipses for most of the fi elds indicated
a unique suite of enzyme activities within each fi eld (Fig. 2b). Clusters
of fi elds refl ected the primary organic amendment used. Fields 1 and 2,
with the lowest soil C and N and receiving manure, had the lowest values
along axis 1 while fi eld 13, with the highest soil C and N and receiving
composted green waste, had the highest values. Other fi elds had similar,
positive values along axis 1 (except fi eld 7) but were strongly differenti-
ated by axis 2. Fields 10, 11, 12, and 13, in which composted green waste
was applied, had negative values along axis 2, such that increases in N-
cycling enzyme activities corresponded with indicators of higher SOM
pools. The remaining fi elds, in which manure or vetch was used (with the
exception of fi eld 8), had positive values along axis 2, such that increases
in C-cycling enzyme activities corresponded with higher inorganic N and
MBN. The pattern of sites and enzyme activities in the RDA resembled
that of an ordination by PCA (Supplemental Fig. 1).
