Temporal dynamics of fine roots under long-term exposure to elevated CO_2 in the Mojave Desert

摘要

Deserts are considered 'below-ground dominated', yet little is known about the impact of rising CO_2 in combination with natural weather cycles on long-term dynamics of root bio-mass. This study quantifies the temporal dynamics of fine-root production, loss and standing crop in an intact desert ecosystem exposed to 10 yrof elevated CO_2. We used monthly minirhizotron observations from 4yr (2003 2007) for two dominant shrub species and along community transects at the Nevada Desert free-air CO_2 enrichment Facility. Data were synthesized within a Bayesian framework that included effects of CO_2 concentration, cover type, phenological period, antecedent soil water and biological inertia (i.e. the influence of prior root production and loss). ElevatedCO_2 treatment interacted with antecedent soil moisture and had significantly greater effects on fine-root dynamics during certain phenological periods. With respect to biological inertia, plants under elevated CO_2 tended to initiate fine-root growth sooner and sustain growth longer, with the net effect of increasing the magnitude of production and mortality cycles. Elevated CO_2 interacts with past environmental (e.g. antecedent soil water) and biological (e.g. biological inertia) factors to affect fine-root dynamics, and such interactions are expected to be important for predicting future soil carbon pools.