Global patterns of root turnover for terrestrial ecosystems

Authors: Gill R, RB Jackson

Root turnover is a critical component of ecosystem nutrient dynamics and carbon sequestration and is also an important sink for plant primary productivity. We tested global controls on root turnover across climatic gradients and for plant functional groups using a database of 190 published studies. Root turnover rates increased exponentially with mean annual temperature for fine roots of grasslands (r2=0.48) and forests (r2=0.17) and for total root biomass in shrublands (r2=0.55). Based on the best-fit exponential model, the Q10 for root turnover was 1.4 for forest small diameter roots (<5 mm), 1.6 for grassland fine roots, and 1.9 for shrublands. Surprisingly, after accounting for temperature, there was no such global relationship between precipitation and root turnover. The slowest average turnover rates were observed for entire tree root systems (10% annually), followed by 34% for shrubland total roots, 53% for grassland fine roots, 55% for wetland fine roots, and 56% for forest fine roots. Root turnover decreased from tropical to high-latitude systems for all plant functional groups. To test whether global relationships may be used to predict inter-annual variability in root turnover, we evaluated 14 years of published root turnover data from a shortgrass steppe site in northeastern Colorado, USA. At this site, there was no correlation between inter-annual variability in mean annual temperature and root turnover. Rather, turnover was positively correlated with the ratio of growing season precipitation and maximum monthly temperature (r2=0.61). We conclude that there are global patterns in rates of root turnover among plant groups and across climatic gradients but that these patterns may not always be used to successfully predict the relationship of root turnover to climate change at a particular site.
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