Exploring the role of root anatomy in P-mediated control of colonization by arbuscular mycorrhizal fungi

Abstract

Alterations of root anatomy have been largely ignored as potential mechanisms for phosphorus-mediated control of arbuscular mycorrhizal colonization. However, at least three anatomical traits including the proportion of root length with a suberized hypodermis, the distribution of hypodermal passage cells, and the proportion of root volume as intercellular air space may influence the degree of colonization. In the present study, we determined whether these traits could be altered by variation in plant phosphorus (P) status. We grew 15 angiosperm species from 13 families, each at two P availabilities, and determined how P status influenced the three root traits. Of the three traits, only the distribution of passage cells was significantly affected by phosphorus status; high P plants possessed a reduced proportion of root length with passage cells. Therefore, in species with passage cells, change in the proportion of root length with passage cells may represent one mechanism for phosphorus-mediated control of mycorrhizal colonization. However, individual species responses to P treatment varied widely, and no single anatomical mechanism appeared to be responsible for the control of mycorrhizal colonization in all species.