Abstract:
Agrochemicals used for intensive crop production have detrimental effects on the
easily collected, trapped and visible organisms, but the effects of such management regimes
on the key players of agroecosystem productivity remain largely unknown. The degree to
which the millions of bacteria, fungi, small invertebrates and other invisible organisms that
underpin the land’s health are affected in general spatial and temporal scales is still
unappreciated. This thesis explores precisely the effect of management on multi-kingdom
biodiversity under different spatiotemporal resolutions. This exploration was developed using
New Zealand vineyards’ agroecosystems, and the DNA from its soils as a source of taxonomic
information. The vineyards, laid across two regions (Hawke’s Bay and Marlborough), operated
under either conventional or conservation (low-to-no agrochemical input) management
approaches. The sampling regimes varied depending on the specific hypotheses being
addressed, and the total number of experimental samples gather across years and seasons
was 1,962. Analyses of next-generation sequencing of genetic barcodes -16S, ITS2, 26S, and
COI- revealed that a) the effect size of weed-management techniques on fungal richness in
solely-experimental plots was 10% and nearly as strong as that of region of origin (13%) and
cultivar (18%), as determined by 26S phylotypes; b) herbicide rather than cultivation in the
same plots resulted in 14-20% greater fungal richness, but these numbers were highly
context-dependent; c) management approaches in commercial vineyards correlate with
significant differences in the numbers, types and abundances of phylotypes, and these
differences may vary from 1% up to 65% depending on the barcode, the region, the growing
season and the year; and d) importantly, the long-term impact and trends of management on
the biodiversity of agroecosystems does not always reflect what is measured in the short-term in nature and degree. While the data presented herein does not always show a large
effect of agrochemicals on soil biodiversity, the most critical findings are that not all taxa are
affected in the same way or to the same magnitude, that geographic locations impact the
degree to which management will affect biodiversity, that some organisms which are mostly affected are also related to the quality of the crop, and that long-term effects of agricultural
management are not always in line with what is found in snapshot data.