What was done
Working in the Mojave Desert at the Free-Air Carbon Enrichment facility near Mercury, Nevada, USA, where various shrubs and perennial grasses grow, the authors examined the effects of atmospheric CO2 enrichment (to 550 ppm throughout each growing season since April 1997) on soil nitrogen (N) dynamics via measurements of foliage C and N contents and isotope composition, and by measuring resin-available N and rates of soil respiration in the field in conjunction with assessments of potential C evolution and net N mineralization derived from long-term soil incubations.

What was learned
Billings and Schaeffer say their data indicate that "effects of elevated CO2 on soil C and N dynamics are variable and complex, with many competing processes," noting that "changes in soil microbial activity with elevated CO2 ... could affect both mineralizing and immobilizing microbial processes." Nevertheless, the bulk of their observations suggest that "elevated CO2 may increase root and/or soil microbial activity," which more often than not "can result in periodic increases in resin-available N, particularly when soil moisture is available," and they say that these several interrelated phenomena "may translate into more plant available N at these times."

What it means
In the simplest of terms, the two researchers conclude that "if increases in plant-available N are maintained, particularly when soil moisture is available, arid ecosystems may be able to sustain any increases in productivity induced by elevated CO2 [our italics]," and a quick perusal of the materials filed under Deserts in our Subject Index will reveal that such CO2-induced plant productivity increases can be substantial.