Morphological and physiological plasticity of root nutrient foraging in Solidago altissimas and Callistephus chinensis

Background/Question/Methods Nutrient foraging of plant roots in spatiotemporally heterogeneous soil environment is enhanced by morphological and physiological plasticity. It has been hypothesized that morphological and physiological plasticity would be negatively correlated. To test the hypothesis and examine the impact of temporal heterogeneity of soil nutrients on root foraging plasticity, we conducted a greenhouse experiment on two herbaceous species: Solidago altissimas L. and Callistephus chinensis (Linn.) Nees under four spatiotemporal treatments of soil nutrient. Plants were grown in 19-liter pots (one plant per pot) that the treatments were applied after the seedlings establishment. As the plant reached harvestable size, each pot was injected 20 ml 5 atom % double labeled ¹⁵N ammonium-nitrate solution (0.58 M N with red food dye) twice (18-hr apart) into a soil column of six types of patches according to the fertilization method.  Plants were harvested 18-hr after the second injection. Leaves, stems, and roots were partitioned before they were oven-dried, samples of the plant parts were analyzed for ¹⁵N concentration to achieve ¹⁵N uptake per unit root. Physiological plasticity and morphological plasticity of the plant and their relationship were evaluated with conventional statistics and Jackknife method.

Results/Conclusions

This study partially supported our hypotheses that 1) both morphological and physiological plasticity in root nutrient foraging were negatively correlated; 2) the physiological plasticity is much more expressed as plants growing in temporally or spatiotemporally heterogeneous soil nutrient environment; 3) under the condition of pulse release of soil nutrients (here N), nutrient uptake due to physiological plasticity is much more than that due to morphological plasticity. The data revealed that: 1) both species had significant, but different degrees of morphological and physiological plasticity; 2) the morphological and physiological plasticity of the two species showed somewhat negative relationships; 3) plants grown in the temporal heterogeneous treatments demonstrated stronger physiological plasticity; and 4) very high percentages of ¹⁵N uptake in both species were attributed to physiological plasticity.     

This study indicated that soil resource heterogeneous can greatly influence below ground carbohydrate allocation pattern that affect plant resource uptake, and further plant growth, as well as its competitive ability.