Sasha C. Reed
Colin Tucker
2016
<p><span>Arid and semiarid ecosystems (drylands) may dominate the trajectory of biosphere-to-atmosphere carbon (C) exchange, and understanding dryland CO</span><sub>2</sub><span> efflux is important for C cycling at the global-scale. However, unknowns remain regarding how temperature and moisture interact to regulate dryland soil respiration (</span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>), while ‘islands of fertility’ in drylands create spatially heterogeneous </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>. At a site in southeastern Utah, USA we added or removed litter (0–650 % of control) in plots associated with either shrubs or biological soil crust-dominated interspaces between vascular plants. We measured </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>, soil temperature (T</span><sub>s</sub><span>), and water content (θ) repeatedly from October 2013 to November 2014. </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>was highest following rain in late summer at T</span><sub>s</sub><span> ~30 °C, and lowest mid-summer at T</span><sub>s</sub><span> > 40 °C, resulting in apparent negative temperature sensitivity of </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>at high temperatures, and positive temperature sensitivity at low-moderate temperatures. We used Bayesian statistical methods to compare models capturing a range of hypothesized relationships between T</span><sub>s</sub><span>, θ, and </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>. The best model indicates that apparent negative temperature sensitivity of </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>at high T</span><sub>s</sub><span> reflects the control of water content, not high temperatures. Modeled Q</span><sub>10</sub><span> ranged from 2.7 to 1.4 between 5 and 45 °C. Litter addition had no effect on Q</span><sub>10</sub><span> or reference respiration (</span><i>R</i><span> </span><sub><i>ref</i><span> </span></sub><span> = </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>at 20 °C and optimum θ) beneath shrubs, and little effect on </span><i>R</i><span> </span><sub><i>ref</i><span> </span></sub><span>in interspaces, yet </span><i>R</i><span> </span><sub><i>ref</i><span> </span></sub><span>was 1.5 times higher beneath shrubs than in interspaces. Altogether, these results suggest reduced </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>often observed at high T</span><sub>s</sub><span> in drylands is dominated by the control of θ, and, on shorter-timescales, variable litter inputs exert minimal control over </span><i>R</i><span> </span><sub><i>s</i><span> </span></sub><span>.</span></p>
application/pdf
10.1007/s10533-016-0200-1
en
Springer
Low soil moisture during hot periods drives apparent negative temperature sensitivity of soil respiration in a dryland ecosystem: A multi-model comparison
article