Allocation to total nonstructural carbohydrates (TNC) has been proposed as a key plant trait that underlies perennial plant survival. TNC pools can constitute as much as 45% of root mass, but are highly variable among species and environments. We investigated some potential sources of interspecific variation in TNC including (1) phylogeny, (2) seed and plant size; and (3) growth vs. survival adaptive strategies. Related to (3), we investigated the popular hypothesis that there are necessary trade-offs between trait expressions favoring growth potential vs. storage, and that these define an axis along which species growth vs. survival (storage) adaptive strategies vary. To further explore this hypothesis, we quantified interrelations of whole-plant total non-structural carbohydrates (TNCWP), relative growth rate (RGR) and associated morphological and physiological traits for seedlings of 36 angiosperm and gymnosperm species that were grown in a common low light environment.
Results/Conclusions
Gymnosperms (n = 8) had lower TNCWP, RGR, specific leaf area and root mass fraction, and also greater leaf mass fraction and leaf production rates than angiosperms (n = 28). Across all species, variance in seed and seedling mass correlated positively with TNCWP and negatively with RGR. RGR and TNCWP were negatively correlated, but the relationship was weak and could be driven largely by covariation in plant size. In contrast, the residuals of the RGR vs. seedling mass regression correlated positively with TNCWP; i.e., when plant size effects on RGR are removed, RGR is positively related to TNCWP. Among physiological and morphological traits, across all species and within the angiosperm group, leaf area ratio correlated most strongly to RGR, root mass fraction was most strongly related to TNCWP. Leaf area ratio and root mass fraction were themselves negatively correlated indicating a possible necessary trade-off between leaves for productivity vs. roots for storage. However, lower leaf production rates, lower leaf light compensation points for photosynthesis and lower whole-plant respiration rates contributed to greater RGR independent of plant size and/or greater TNCWP. RGR, independent of size, was also positively related to seedling survival thus providing further support for the positive interrelations between growth-survival and carbon conservation traits in low light. In summary, under low light conditions, carbon conservation traits that increase growth independent of plant size also increase stored carbohydrates, which is contrary to the widely hypothesized trade-off between growth and survival adaptive strategies.