Agriculture Reference
In-Depth Information
13.3.4 RELATIVE INFLUENCE OF SOIL PHYSICOCHEMICAL
FACTORS AND FAMES ON ENZYME ACTIVITIES
Canonical variation partitioning showed the relative influence of soil phys-
icochemical factors and microbial community composition on potential
enzyme activities by quantifying both the unique and shared proportion of
variability accounted for by each set of explanatory factors (Table 4). Soil
physicochemical factors and the relative abundance of indicator FAMEs
together explained 64.9% of the total variation in soil potential enzyme
activities, compared to 37.7% for soil factors alone (p < 0.001). Indicator
FAMEs uniquely explained only 6.1% of the variation (p < 0.001). The re-
maining variation, which cannot be attributed uniquely to either explana-
tory dataset, totaled 27.2%.
13.4 DISCUSSION
This research approach provides insight into how microbial community
function and composition respond to the variation that exists across organic
farm fields where farmers are growing the same crop in a single landscape.
The two hypotheses were supported in the following ways. First, distinct
profiles of soil potential enzyme activities indicated unique potential met-
abolic capacities across the fields, such that C-cycling enzyme activity
increased with inorganic N availability while N-cycling enzyme activity
increased with C availability. Second, although FAMEs suggested that mi-
crobial community composition was less variable across fields than poten-
tial enzyme activities, there were slight community differences that were
related to the use of compost vs. manure as the primary organic amend-
ment. Overall, however, the general similarity among fields for particular
taxonomic indicators, such as saprophytic fungi, is consistent with another
nearby study in this intensively managed landscape (Young-Mathews et
al., 2010). These patterns suggest that differences in organic agroecosys-
tem management have strongly influenced soil nutrients and potential en-
zyme activity, but without a major effect on soil microbial communities
