Morphological and physiological plasticity of plant roots when nutrients are both spatially and temporally heterogeneous

Pu Mou1, Robert H. Jones2, Zengquan Tan1, Zhe Bao3, Hongmei Chen1
1 State Key Laboratory of Earth Surface Processes and Resource Ecology & Ministry of Education Key Laboratory for Biodiversity Science and Engineering, Beijing Normal University, Beijing 100875, China;
2 Eberly College of Art and Sciences, West Virginia University, Morgantown WV, USA;
3 Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
Background and Aims Roots express morphological and physiological plasticity that may be adaptations for efficient nutrient capture when soil nutrients are heterogeneous in space and time. In terms of nutrient capture per unit of carbon invested in roots, morphological plasticity should be more advantageous when nutrient patches are stable in time, and physiological plasticity when nutrients are variable in time.
Methods Here we examined both traits in two Pinus species, two Liquidambar species, two Solidago species, Ailanthus altissima and Callistephus chinesis, grown in pots where the same total level of nutrient addition was provided in a factorial experiment with different levels of spatial and temporal variability.
Results Total plant root growth, Root/Shoot ratios and morphological plasticity were less when nutrients were temporally variable instead of stable. Physiological plasticity was more variable than morphological across treatments and species and was not predictably greater when nutrient supply was pulsed instead of constant. Large variability, especially in physiological plasticity, was observed, and physiological plasticity was greater in non-woody than in woody species.
Conclusions Our results suggest that the two traits differ in environmental factors that control their expression, and that the nature of nutrient patchiness may have more direct impact on the evolution of morphological than physiological plasticity.
Keywords: Root nutrient foraging; Morphological plasticity; Physiological plasticity; Root/shoot ratio; Soil nutrient heterogeneity.
Published in Plant and Soil. 2013, 364: 373-384.