Rising atmospheric CO2 concentrations are expected to increase plant productivity, particularly in arid ecosystems, but this response may be limited in the Mojave Desert by low nutrient availability. Therefore, plants may invest additional fixed carbon into means of nutrient acquisition, such as root activity or arbuscular mycorrhizal fungi (AMF). I investigated responses of root respiration and AMF to elevated CO2 in a greenhouse and at the Mojave Desert at the Nevada Desert FACE Facility (NDFF). I also conducted a supplemental study of seasonal AMF dynamics. Root respiration of Ambrosia dumosa and Larrea tridentata, two dominant Mojave Desert shrubs, was not affected by elevated CO2. Root system sizes of these species at the NDFF were also not significantly different between CO2 treatments; thus, root respiration was not greater when extrapolated to a plot-level scale. Similarly, AMF root colonization, extraradical hyphal (ERH) length, and glomalin related soil protein (GRSP) concentrations were not significantly different in the elevated CO2 plots. These results suggest that the demonstrated increases in Mojave Desert shrub productivity with elevated CO2 are not constrained by belowground resources. Increased activity of the carbon limited microbial community with elevated CO2 shown by other studies may be the result of greater litter inputs or root exudation. This increase in activity has enhanced nutrient cycling and reduced limitations, perhaps to a level where increased root activity or reliance on AMF is unnecessary under elevated CO2. Results from our supplemental seasonal study of AMF dynamics showed a general decrease in AMF presence from February to November without a significant difference in soil moisture among sample collections. As nutrient demands were reduced after flowering and fruiting of plants, allocation of resources to AMF also declined. However, the seasonality of GRSP concentrations was microsite specific and restricted to soils beneath L. tridentata canopies. I hypothesize that the high initial GRSP concentrations in this microsite were residual from the unusually wet previous year, but information on how AMF variables respond to soil moisture would provide more insight to the observed pattern in GRSP.SRL of very fine roots was significantly different among sampling dates for both species; however, CO2 x sampling date was not a significant interaction (Table 8B). Unlike root respiration rates, SRL differences among sampling dates do not anbsp;...
|Title||:||Seasonal Belowground Plant Responses to Elevated Carbon Dioxide in the Mojave Desert: Root Respiration and Arbuscular Mycorrhizal Fungi Dynamics|
|Author||:||Naomi M. Clark|
|Publisher||:||ProQuest - 2007|