Testing the growth-differentiation balance hypothesis: dynamic responses of willows to nutrient availability.
Here, the growth-differentiation balance hypothesis (GDBH) was tested by quantifying temporal variation in the relative growth rate (RGR), net assimilation rate (NAR), and phenylpropanoid concentrations of two willow species (Salix sericea and Salix eriocephala) across five fertility levels. Initially, RGR increased and total phenylpropanoids declined (although every individual phenolic did not) as fertility increased, but NAR was unaffected. Subsequently, NAR and phenylpropanoids declined in the low fertility treatment, generating a quadratic response of secondary metabolism across the nutrient gradient. As above- and below-ground growth rates equilibrated, NAR and phenylpropanoids increased in the low fertility treatment, re-establishing a negative linear effect of fertility on secondary metabolism. A transient quadratic response of secondary metabolism is predicted when GDBH is integrated with models of optimal phenotypic plasticity, occurring when low NAR imposes carbon constraints on secondary metabolism in low nutrient environments. Once plants acclimate to nutrient limitation, the equilibrium allocation state is predicted to be a negative correlation between growth and secondary metabolism. Although both willow species generally responded according to GDBH, the complexity observed suggests that prediction of the effects of nutrient availability on secondary metabolism (and other plastic responses) in specific cases requires a priori knowledge of the physiological status of the plant and soil nutrient availability.
Glynn
Carolyn
C
Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, SE-750 07 Uppsala, Sweden.
Herms
Daniel A
DA
Department of Entomology and.
Orians
Colin M
CM
Department of Biology, Tufts University, Medford, MA 02155, USA.
Hansen
Robert C
RC
Department of Food, Agricultural, and Biological Engineering, The Ohio State University/Ohio Agricultural Research and Development Center, 1680 Madison Ave., Wooster, OH 44691, USA.
Larsson
Stig
S
Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, SE-750 07 Uppsala, Sweden.
D018533:Biomass; D005308:Fertilizers; D010636:Phenols / Q000378:metabolism*; D010666:Phenylpropionates / Q000378:metabolism*; D018515:Plant Leaves / Q000254:growth & development* / Q000378:metabolism; D011897:Random Allocation; D032108:Salix / Q000254:growth & development* / Q000378:metabolism; D013634:Tannins / Q000378:metabolism*
D005308:Fertilizers; D010636:Phenols; D010666:Phenylpropionates; D013634:Tannins