Identification of C3 and C4 plants was done visually and confirmed with del13
inspection. Isotopic identification proved conclusive as variation within C3 and C4
plants was 1.2 ‰, and 0.5‰ respectively and difference between the two groups was ~
17‰. With this confirmation of photosynthetic pathway, we attempted to discern the
connection between C3 and C4 plants and carbon and nitrogen abundance. We found
less significance between photosynthetic pathway than between plant type - forbs vs.
grasses, where forbs had a significantly lower C:N.
There is strong evidence that C:N of our soil is less than that of plants, with very minimal
data falling outside this trend. This relationship of soils having a lower C:N has been
found by others and explained by atmospheric loss through microbial decomposition and
other well accepted explanations (Simpson 1983).
It has been proposed by others that percent carbon should decrease, and percent nitrogen
should increase resulting in an increasing C:N with depth (Hedges, 1997). Our dataset is
insufficiently small - four segments, to draw conclusions on profile behavior, but a facile
relationship of decreasing carbon and nitrogen percentages can be seen, and C:N varied
inconsistently yet fell within ranges proposed for soils. Higher resolution and deeper
sampling could elucidate whether or not a relationship does exist between carbon,
nitrogen and depth at this site.
The grasshopper had a lower carbon percentage - approximately 75% lower than plant
material, and a nitrogen percentage significantly higher (ten fold or greater), producing a
significantly lower C:N value. It is generally accepted that grasses and forbs are
predominately cellulose and hemicellulose – nitrogen free polymers, and the major
biopolymer of grasshoppers is chitin, a polysaccharide with N-H functional groups.
FTIR spectra show evidence of amines and amides within the grasshopper, corroborating
the presence of chitin and protein. Plant FTIR analysis led us to believe we have
abundant cellulose and cellulose like oxidation products, and little lignin.
Isotopic analysis of the grasshopper found a δ13C value in between that of C3 and C4
plants, which in combination with literature and field observation lead us to believe this
insect to be a “generalist” forager – that is to not have a preference between the C3 and
C4 plants at our site.
The soil shows a 13C enrichment in between those of our C3 and C4 plants, however is
closer in value to the minority C3 plants. We attribute this to fractionation through
decomposition and to the fact that we are studying an ecosystem in transition, in which
we do not know which grass was dominant two years ago. Keeping in mind that the δ13C
signal of soils might be from litter/exudates more than ten years old, we attempted to see
if there was a change in signal with depth, however no relationship could be established.
Detecting organic material with FTIR in the soil was difficult due to mineral and water
overshadowing, however we were able to attribute some peaks to aliphatic compounds
and saw no evidence of aromatic compounds, which makes sense when you consider that
the contributing material – grasses, and forbs, showed the same patterns.
We found that combining mass and infrared spectrometries does well in providing
simplistic insight into the cycling of carbon and nitrogen through the atmospheric, plant,
insect, and soil pools of an ecosystem. Obviously, these pools do not cover all aspects
and have holes between them, however we believe that much can be acquired by
combining mass spectrometry and FTIR if you measures to allocate sources and sinks
within an ecosystem.