In the years shortly
before his death, Dean Martens' research efforts were directed to
investigations of land‑use effects on the cycling of C and N and related
impacts on potential climate change. The land‑use investigations focused
on grazing and associated growth and control of mesquite (Prosopis spp.)
in semiarid riparian woodlands, grasslands, and mountainous forage areas. The
growth of leguminous mesquite provides N inputs into N-limited semiarid soils, and
using plant and soil isotope signatures, Dean ascertained that although
mesquite litter is highly labile, limited rainfall in semiarid systems allowed
soil C and N to accumulate. In the past, moisture limitations in southwestern
ecosystems led researchers to believe that semiarid soils were not significant
consumers or producers of trace gases and as such, these regions were
traditionally overlooked in greenhouse gas inventories. Dean's work, however,
confirmed the presence of a large, previously unreported methane sink in
semiarid soils. While modeling the effects of soil moisture and temperature on
ecosystem/atmosphere exchange of carbon dioxide, Dean found that, unlike more
temperate systems, large differences in soil C content did not correlate with
variations in carbon dioxide production unless soil moisture was limiting. Taken
together, Dean's results suggested that soils of semiarid ecosystems could not
be discounted in potential mitigation of climate change. In addition, his work
confirmed the existence of a significant C sink in the San Pedro Riparian
National Conservation Area in southeastern