Root phenology in a changing climate

Abstract

Plant phenology is one of the strongest indicators of ecological responses to climate change, and altered phenology can have pronounced effects on net primary production, species composition in local communities, greenhouse gas fluxes, and ecosystem processes. Although many studies have shown that aboveground plant phenology advances with warmer temperatures, demonstration of a comparable association for belowground phenology has been lacking because the factors that influence root phenology are poorly understood. Because roots can constitute a large fraction of plant biomass, and root phenology may not respond to warming in the same way as shoots, this represents an important knowledge gap in our understanding of how climate change will influence phenology and plant performance. We review studies of root phenology and provide suggestions to direct future research. Only 29% of examined studies approached root phenology quantitatively, strongly limiting interpretation of results across studies. Therefore, we suggest that researchers emphasize quantitative analyses in future phenological studies. We suggest that root initiation, peak growth, and root cessation may be under different controls. Root initiation and cessation may be more constrained by soil temperature and the timing of carbon availability, whereas the timing of peak root growth may represent trade-offs among competing plant sinks. Roots probably do not experience winter dormancy in the same way as shoots: 89% of the studies that examined winter phenology found evidence of growth during winter months. More research is needed to observe root phenology, and future studies should be careful to capture winter and early season phenology. This should be done quantitatively, with direct observations of root growth utilizing rhizotrons or minirhizotrons.

Unaltered phenology but increased production of ectomycorrhizal roots of Pinus elliottii under 4 years of nitrogen addition

“…). Root growth is endogenously regulated by the timing of C availability and tradeoffs among competing plant sinks (Comas et al ., ) and is exogenously influenced by climatic and edaphic variables (Abramoff & Finzi, ; Radville et al ., ,). A field experiment on root dynamics in a temperate steppe, for example, found that increased temperature and precipitation individually or interactively affected annual root production (Bai et al ., ).…”

“…C availability and tradeoffs among competing plant sinks) and exogenous factors (e.g. temperature, moisture, and nutrient availability) (Comas et al ., ; Du & Fang, ; Radville et al ., ,). Empirical studies of root initiation and cessation are rare, but these two phenophases may be controlled mostly by soil temperature and timing of C availability (Radville et al ., ), and peak root growth may represent tradeoffs among competing plant sinks (Comas et al ., ; Artacho & Bonomelli, ; Radville et al ., ).…”

“…temperature, moisture, and nutrient availability) (Comas et al ., ; Du & Fang, ; Radville et al ., ,). Empirical studies of root initiation and cessation are rare, but these two phenophases may be controlled mostly by soil temperature and timing of C availability (Radville et al ., ), and peak root growth may represent tradeoffs among competing plant sinks (Comas et al ., ; Artacho & Bonomelli, ; Radville et al ., ). Despite this improved understanding, few studies have examined the effects of increased N availability on root phenology and most of them focused only on peak root growth, rather than on the three root phenophases (Artacho & Bonomelli, ; McCormack et al ., ).…”

Fast Responses of Root Dynamics to Increased Snow Deposition and Summer Air Temperature in an Arctic Wetland

“…In the Arctic, the belowground plant biomass exceeds its aboveground counterpart (Mokany et al, 2006; Iversen et al, 2015; Wang et al, 2016a) and therefore represents an important component of soil nutrient cycling and net ecosystem C budget (Iversen et al, 2015). As concluded by Blume-Werry et al (2016) neither the knowledge from non-Arctic ecosystems, nor projections of aboveground to belowground production, reflect seasonal dynamics of root growth in arctic plant communities and limited data is available on root phenology in this region (Radville et al, 2016). …”

Contrasting root overwintering strategies of perennial wetland monocots

“…We conclude that in a northern temperate climate, the 37 overwintering strategies of roots of herbaceous monocots are binary: either avoidance or 38 tolerance of the long unfavourable season, similar to deciduous and evergreen leaves 39 among woody plants. Roots root phenology limits our understanding of the relationship between root turnover 61 strategies and environmental conditions (Radville et al 2016). 62…”