Phosphorus nutrition and mycorrhiza effects on grass leaf growth.: P status- and size-mediated effects on growth zone kinematics

This study tested whether leaf elongation rate (LER, mm h(-1)) and its components - average relative elemental growth rate (REGR(avg), mm mm(-1) h(-1)) and leaf growth zone length (L-LGZ, mm) - are related to phosphorus (P) concentration in the growth zone (P-LGZ, mg P g(-1) tissue water) of Lolium perenne L. cv. Condesa and whether such relationships are modified by the arbuscular mycorrhizal fungus (AMF) Glomus hoi. Mycorrhizal and non-mycorrhizal plants were grown at a range of P supply rates and analysed at either the same plant age or the same tiller size (defined by the length of the sheath of the youngest fully expanded leaf). Both improved P supply (up to 95%) and AMF (up to 21%) strongly increased LER. In tillers of even-aged plants, this was due to increased REGR(avg) and L-LGZ. In even-sized tillers, it was exclusively due to increased REGR(avg). REGR(avg) was strictly related to P-LGZ (r(2) = 0.95) and independent of tiller size. Conversely, L-LGZ strictly depended on tiller size (r(2) = 0.88) and not on P-LGZ. Hence, P status affected leaf growth directly only through effects on relative tissue expansion rates. Symbiosis with AMF did not modify these relationships. Thus, no evidence for P status-independent effects of AMF on LER was found.