Partitioning the Components of Relative Growth Rate: How Important Is Plant Size Variation?

Abstract

Plant growth plays a key role in the functioning of the terrestrial biosphere, and there have been substantial efforts to understand why growth varies among species. To this end, a large number of experimental analyses have been undertaken; however, the emergent patterns between growth rate and its components are often contradictory. We believe that these conflicting results are a consequence of the way growth is measured. Growth is typically characterized by relative growth rate (RGR); however, RGR often declines as organisms get larger, making it difficult to compare species of different sizes. To overcome this problem, we advocate using nonlinear mixed-effects models so that RGR can be calculated at a standard size, and we present easily implemented methods for doing this. We then present new methods for analyzing the traditional components of RGR that explicitly allow for the fact that is log (RGR) the sum of its components. These methods provide an exact decomposition of the variance in . Finally, we use simple analytical log (RGR) and simulation approaches to explore the effect of size variation on growth and its components and show that the relative importance of the components of RGR is influenced by the extent to which analyses standardize for plant size.

Corrigendum to: New handbook for standardised measurement of plant functional traits worldwide

“…References on theory, significance and large datasets: Evans (1972); Grime and Hunt (1975); Kitajima (1994); Cornelissen et al (1996); Walters and Reich (1999); Poorter and Nagel (2000); Poorter and Garnier (2007); Rees et al (2010).…”

“…More on methods: Evans (1972); Causton and Venus (1981); Hunt (1982); Poorter and Lewis (1986); Poorter and Welschen (1993); Cornelissen et al (1996); Rees et al (2010).…”

Environmental tolerances of rare and common mangroves along light and salinity gradients

“…RGR was compared among treatments only for individuals that survived the entire experimental period. We adopted this protocol because, for most organisms, RGR changes as individuals grow; typically it declines with size/age (Rees et al 2010;Paine et al 2012). Therefore, using all individuals regardless of the size/age at death to compute a mean weekly RGR might have introduced a bias into the treatment comparisons.…”

C4 photosynthesis boosts growth by altering physiology, allocation and size

“…advantage associated with C 4 photosynthesis (reviewed elsewhere 1,6,7 ). We hypothesize 8 that this inconsistency arises from the large variation in growth rates among ecologically 9 diverse species, coupled with low statistical power arising from small sample sizes.…”