Background/Question/Methods Previous studies have demonstrated that plant roots nutrient foraging plasticity morphologically and physiologically varies among plant species. Negative correlation between morphological and physiological plasticity has been hypothesized. Our results also suggested that physiological plasticity may be critically important in plant nutrient uptake under the condition of pulse nutrient release. To test the hypothesis and further examine the impact of temporal heterogeneity of soil nutrients on root foraging plasticity, we conducted a series of greenhouse experiments on three herbaceous species: Solidago altissima, S. canadensis and Callistephus chinensis, and five woody species: Pinus taeda, P. massoniana, Liquidambar styraciflua, L. formosana and Alanthus altissima under four spatiotemporal treatments (quarter/even fertilization with continue/pulse manners) of soil nutrient. Plants were grown in 19-liter pots (one plant per pot) that the treatments were applied after the seedlings established. As the plant reached harvestable size, each pot was injected 20 ml 5 atom% ¹⁵NH₄¹⁵N O₃ solution (0.58 M N) twice (18-hr apart) into a soil column of six different patches according to the treatments. 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 to achieve ¹⁵N uptake rates. Physiological plasticity and morphological plasticity of the plant and their relationship were evaluated with conventional statistics and Jackknife method.   

Results/Conclusions The results of this study demonstrated that 1) pulse fertilization generally reduced the degree of morphological plasticity expressed by either lower RFRMD (Relative Fine Roots Mass Difference) or higher variances, but may increase physiological plasticity in root nutrient foraging; 2) the herbaceous species showed less clear pattern than the woody species in nutrient foraging plasticity regarding to the experimental treatments; 3) the impacts of growing conditions (rich vs. poor patches) of fine roots on their physiological plasticity were mixed among species. The data suggested that: 1) stronger physiological nutrient uptake rates under pulse fertilization treatments may compensate the less stronger morphological plasticity; 2) two solidago species revealed much similer traits than two other closely related but geologically remote species pairs (pines and sweetgums); 3) there may be other variables than nutrient availability affect root nutrient foraging plasticity in our experiments.