Scientific Theme: Advanced Modeling and Observing Systems

Complementary Research: Innovative Research Program
Research Plan. We will collect organic and mineral soils from a range of sites across the United States. We will
focus on sites within the NSF-funded Long-Term Ecological Research network so that follow-up studies will be
possible and NSF funds can accessed. The goal is to collect a diverse array of soil types (30-50 soils) so we can
examine correlations between mVOC production and soil/site characteristics. After an equilibration period, root-free
soils will be incubated in gas-tight containers for 24-48 h with headspace samples analyzed for VOCs using protontransfer-reaction
mass spectrometry (PTR-MS). Headspace samples will also be analyzed for CO2 concentrations
with an infrared gas analyzer so we can compare net CO2 and net VOC production rates. We will collect relevant
site information and measure basic soil physico-chemical characteristics for each soil. In addition, we will use the
quantitative PCR approach described in Fierer et al. [2005] to quantify the abundances of bacterial and fungal
groups in each soil sample. By analyzing a relatively large number of samples, we can determine if VOC
―fingerprints‖ (the types and quantities of VOCs released) are unique to each soil type and we can assess
relationships between specific soil characteristics and mVOC production. We will use multivariate statistical
methods (non-metric multi-dimensional scaling and ANOSIM procedures, [Fierer and Jackson, 2006]) to look for
correlations between VOC fingerprints and soil/site characteristics.
Once the cross-site study has established linkages between microbial VOC production and soil/site characteristics
we will test our hypothesis that VOC production is strongly correlated with microbial community composition. By
simply screening the collected soils, we cannot distinguish the effects of microbial community composition from
other factors (soil organic carbon characteristics, texture, and nutrient status) that may also influence mVOC
production. To determine the strength of the relationship between community composition and mVOC fingerprints,
we will experimentally manipulate the microbial communities in five soils that have distinct VOC fingerprints by
autoclaving each soil and re-introducing microbes with five different soil inocula, one from each of the five soil
types. After an equilibration period, VOC production will be measured using the techniques described above. If
VOC fingerprints correspond to microbial community composition, we should observe a strong effect of inoculum
on VOC fingerprints from a given soil type. If VOC production is unrelated to microbial community composition,
but is instead driven by intrinsic abiotic soil properties, we will see no apparent inoculum effect. The linkages
between microbial community composition and VOC fingerprints will be further examined by adding known
organic substrates (e.g. cellulose, proteins, sugars) to each of the five soils and measuring VOC production over
time. If substrate characteristics are less important than community composition in controlling mVOC production,
soils receiving the same substrate should yield distinct VOC fingerprints.
Expected outcome and impact. This work is just the first step towards understanding microbial VOC production and
its consequences. This work will allow us to parameterize the relative importance of soil VOC production and assess
how VOC production varies across a wide range of soil types. We expect that the proposed work will yield valuable
data sets than can be leveraged to obtain extramural funding in the future. If we find that microbial VOC production
is an important source of VOCs, more detailed experiments and field studies will follow. If we find that VOC
analysis can be used to infer microbial community composition, this work may to lead to the development of new
methods for rapidly assessing soil biological characteristics.
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