Metabolomic responses of indigenous and nonindigenous plants to deer
exclosure fencing and deer herbivory in a suburban forest
Abstract
Trees and shrubs in suburban forest understories can be subject to
chronic herbivory from abundant white-tailed deer. An undocumented
consequence of this stress may be shifts in secondary metabolite
production associated with defense. We aimed to learn whether plants
protected from deer exhibited different metabolomic profiles compared to
those exposed to deer. We tested the indigenous species Nyssa
sylvatica and Lindera benzoin and the invasive, nonindigenous
species Rosa multiflora and Euonymus alatus within a
suburban forest understory in New Jersey, USA, in unfenced plots and
plots fenced for 5.3 years. We did untargeted metabolomics by sampling
leaves from three plants of each species per 6-7 fenced and unfenced
plots, conducting chloroform-methanol extractions followed by LC-MS/MS,
and conducting statistical analysis on Metaboanalyst. We also scored
each species for deer browse frequency over eight years, and compared
their heights and percent cover between unfenced and fenced plots. The
analysis identified 2,333 metabolites. The global metabolome diverged
significantly between fenced and unfenced plots pooled across species,
but for individual species only N. sylvatica exhibited a
significant fencing effect. Nyssa sylvatica was one of the most
browsed species and was the only one with both greater cover and height
in fenced plots, suggesting greater susceptibility to deer browsing. The
metabolites most responsible for the fenced/unfenced divergence also
were affected by the species-fencing combination, with increases in
certain species but decreases in others. The most significant
metabolites that were upregulated in fenced plants include some involved
in defense-related metabolic pathways, e.g. monoterpenoid biosynthesis.
Further study of more species in multiple sites is needed to learn how
common metabolomic responses to deer are among forest species, how the
intensity of deer pressure influences the responses, which types of
metabolites are most affected, and if there are ecological consequences
at the physiological, population, and/or community levels.