Variation in growth rate and ecophysiology among 34 grassland and savanna species under contrasting N supply: a test of functional group differences

Abstract

Summary• We tested the hypothesis that biological trait-based plant functional groups provide sufficient differentiation of species to enable generalization about a variety of plant ecophysiological traits or responses to nitrogen (N).• Seedlings of 34 North American grassland and savanna species, representing 5 functional groups, were grown in a glasshouse in an infertile soil with or without N fertilization.• Forbs, C 3 and C 4 grasses, on average, had similar relative growth rates (RGR), followed in declining order by legumes and oaks, but RGR varied greatly among species within functional groups. All measured attributes differed significantly among functional groups, of these, only RGR and photosynthesis differed among functional groups in response to N. All groups, except the legumes, had significantly greater photosynthetic and respiration rates at elevated N supply. Principal components analyses and cluster analyses yielded groupings that corresponded only moderately well to the biologically based a priori functional groupings.• Variation in RGR among species and treatments was positively related to net CO 2 exchange (photosynthesis and respiration) and net assimilation rate, but unrelated to leaf area ratio. Photosynthetic and respiration rates were related to tissue %N among treatments and species. Our data indicate that RGR and related traits differ among the functional groups in significant ways, but in a complex pattern that does not yield simple generalizations about relative performance, controls on RGR, or response to resource supply rate. IntroductionThe potential utility of considering plant species within differing functional groups or types (hereafter used interchangeably) has been increasingly examined (Grime, 1979;Pearcy & Ehleringer, 1984;Garnier, 1992;Smith et al ., 1996;Lavorel et al ., 1997;Reich et al ., 1998b;Campbell et al ., 1999;Diaz et al ., 1999; Wand et al ., 1999;Craine et al ., 2002). If the use of functional types allows us to more easily characterize the attributes or responses of vegetation, it will enable higher order conceptual and more complex quantitative models at a range of scales. It is common sense to assume that functional groups will only be of use if the members of one group differ consistently on average from those of another group with respect to a single or set of target traits or responses. As yet, however, there is no definite set of rules that allows us to judge when functional types will be useful and when not.In this paper, we will refer to both traditional a priori groupings based largely on single biological traits of species and to posthoc classification schemes (e.g. plant functional types) that attempt to group plant species based on their responses to specific environmental factors (Lavorel et al ., 1997). The traditional a priori groupings are typically defined by discrete and measurable biological trait differences (e.g. whether a plant fixes nitrogen (N) or not; has perennial woody tissues or not; has a given photosynthetic pathway or not). Thus,...

Photosynthetic responses of four tropical tree species grown under gap and understorey conditions in a semi-deciduous forest

“…These functional groups help to predict the plant community response to environmental changes without requiring detailed information from each species (Lavorel et al 1997, Reich et al 2003. Group of species can be defined by life history, life form, taxonomy, physiological traits or some combination of these characteristics (Tilman 1997, Hooper 1998).…”

The ecological adaptability of four typical plants during the early successional stage of a tropical rainforest

“…Although differences were significantly enough among trait-based functional groups, it did not effectively discriminate herbaceous species (Reich et al 2003). Using mixtures of 14 calcareous grassland plant species drawn from three functional groups (nonleguminous forbs, grasses, and leguminous forbs), Hanley et al (2004) concluded that because of the idiosyncratic responses of individual species, the categorization of plants into broad functional groups was of limited use to understand the impacts of elevated atmospheric CO 2 on plant communities.…”

“…Smith et al (1993) coined the term "plant functional types", and Gitay and Noble (1997) defined it as "set of species showing similar responses to the environment and similar effects on ecosystem function". There have been some researches on plant functional groups (Wardle et al 1998;Gebauer et al 2002;Reich et al 2003;Hanley et al 2004;Chen et al 2005;Golluscio & Oesterheld 2007;Letts et al 2010;Kamiyama et al 2010). The usual groupings are defined by discrete and measurable biological trait differences (e.g., whether a plant fixes nitrogen or not, has perennial woody tissues or not, and has a given photosynthetic pathway or not) (Reich et al 2003).…”

“…There have been some researches on plant functional groups (Wardle et al 1998;Gebauer et al 2002;Reich et al 2003;Hanley et al 2004;Chen et al 2005;Golluscio & Oesterheld 2007;Letts et al 2010;Kamiyama et al 2010). The usual groupings are defined by discrete and measurable biological trait differences (e.g., whether a plant fixes nitrogen or not, has perennial woody tissues or not, and has a given photosynthetic pathway or not) (Reich et al 2003). Lavorel et al (1997) considered that classifications could not be expected to be universal, yet their development should aim at reaching greater generality by addressing mechanism.…”

Carbon sequestration: mathematical model of the Brazilian Atlantic Forest.

“…The classification of species into groups is particularly necessary in the BAF because many species are represented by only a few individuals (Swaine and Whitmore, 1988). Even if the classification implies a degree of simplification that diminishes information content, it allows general patterns and consequently helps to predict the plant community response to environmental changes without demanding precise information from each species (Reich et al, 2003;Souza et al, 2010).…”