Linking changes in insect abundance with plant productivity in response to increased precipitation, nitrogen deposition and CO2 in the Mojave Desert.
Newingham, Beth*,1, deSoyza, Amrita2, Smith, Stanley1, 1 University of Nevada, Las Vegas, Las Vegas, NV, USA2 University of Nevada, Reno, Reno, NV, USA
ABSTRACT- Global change factors including altered precipitation, nitrogen deposition and elevated CO2 can affect plant productivity; therefore, changes in plant productivity will likely affect insect communities. We examined the effects of increased summer precipitation and nitrogen at the Mojave Global Change Facility (MGCF) and elevated CO2 at the Nevada Desert FACE Facility (NDFF) on insect abundance in the Mojave Desert to link these changes with perennial plant productivity. At the MGCF, we have applied 3 treatments each year for the past 4 years: 25 mm of water in June, July and August in irrigated plots, 40 kg N ha-1 yr-1 in nitrogen plots, and irrigation and nitrogen combined. At the NDFF, ambient and elevated CO2 levels have been 360 and 550 umol mol-1 CO2, respectively, since 1997. Insects were sampled at both sites in June, August and September by placing sticky traps in the open, in the canopy of the evergreen shrub Larrea tridentata, the drought deciduous shrub Lycium pallidum, and the C4 grass Pleuraphis rigida. At both sites insect abundance was higher in the canopy of Larrea than in Lycium, Pleuraphis or in the open. At MGCF prior to irrigation in 2004, irrigated, 40N, and irrigated + 40N treatments had no effect on insect abundance. In contrast, after irrigation insect abundance was 52% higher in 40N plots, 111% higher in irrigated plots, and 194% higher in irrigated + 40N plots than in control plots. At NDFF, elevated CO2 had no effect on insect abundance throughout the summer. These changes in insect abundance were partially explained by changes in plant productivity. For example, irrigation increased productivity of Larrea and Pleuraphis, but not Lycium. However, 40N and irrigated + 40N treatments did not affect plant productivity although these treatments increased insect abundance. Elevated CO2 had no effect on plant productivity, at least in summer months, which corroborated the lack of an elevated CO2 effect on insect abundance. Our results suggest that increased summer precipitation and nitrogen deposition are two primary factors influencing both perennial plant productivity and insect communities.
Key words: global change, insects, plant productivity, deserts
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