Temporal dynamics of fine roots under long‐term exposure to elevated CO₂ in the Mojave Desert

Abstract

SummaryDeserts 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 biomass. This study quantifies the temporal dynamics of fine-root production, loss and standing crop in an intact desert ecosystem exposed to 10 yr of elevated CO 2 .We used monthly minirhizotron observations from 4 yr (2003)(2004)(2005)(2006)(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).Elevated CO 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.

Water availability drives fine root dynamics in a Eucalyptus woodland under elevated atmospheric CO2 concentration

“…June 2014 and February 2016, respectively). As with many water‐limited ecosystems, FRP ig is strongly affected by precipitation events (Day et al., 2013), although fine root responses to changing moisture conditions may occur with a time lag (Sonderegger et al., 2013). The greater FRP ig under eCO 2 seen during autumn 2014 may be attributed to a faster response to the precipitation events experienced during this period (Figure 1).…”

“…Most FACE experiments showing sustained stimulation of fine root production and biomass have been conducted in aggrading forest, with comparatively greater phosphorous availability; and involving younger trees which are thought to be more responsive to eCO 2 (Norby & Zak, 2011). The few experiments involving mature trees or shrubs have reported transient or no stimulation of either fine root biomass or production, with periodic responses associated with particular climatic events such as droughts (Sonderegger, Ogle, Dave Evans, Ferguson, & Nowak, 2013) or natural disturbances (Day et al., 2013). Indeed, the limited empirical evidence on how fine roots will respond to eCO 2 in mature forest systems precludes reliable incorporation of key ecosystem processes driven by fine roots into Earth system models (Norby et al., 2016).…”

The effects of 11 yr ofCO2enrichment on roots in aFlorida scrub‐oak ecosystem

“…Periodic rain events in this system apparently act as an environmental signal eliciting CO 2 responses. Elevated CO 2 had greater effects on fine root dynamics during certain phenological events influenced by soil moisture (Sonderegger et al ., ). Similar pulse drivers occur in savanna ecosystems (Chen et al ., ; February & Higgins, ; Tomlinson et al ., ).…”

“…Second, belowground biomass is temporally dynamic and undergoes natural cycles that are affected by ecosystem disturbances in systems with strong disturbance regimes. Similar responses have been observed in desert plants, with CO 2 effects dependent on soil moisture (Ferguson & Nowak, ; Sonderegger et al ., ). The change in root biomass over time means that one‐time sampling will not give an accurate representation of root parameters over the long term.…”

Introduction to a Virtual Special Issue: modeling the hidden half – the root of our problem

“…Also, for plants growing under elevated CO 2 , Sonderegger et al. ( ) showed positive feedback effects of roots on shoot growth by means of increased ability to break dormancy and initiate growth, allowing for earlier access to resources during springtime. Similarly, both Smithwick et al.…”