No abstract

No abstract

Our objectives were to (1) verify that nonhydraulic signalling of soil drying can reduce leaf growth of maize, (2) determine if a mycorrhizal influence on such signalling can occur independently of a mycorrhizal effect on leaf phosphorus concentration, plant size or soil drying rate, and (3) determine if leaf phosphorus concentration can affect response to the signalling process. Maize (Zea mays L. 'Pioneer 3147') seedlings were grown in a glasshouse with root systems split between two pots. The 2 x 3 x 2 experimental design included two levels of mycorrhizal colonization (presence or absence of Glomus intraradices Schenck & Smith), three levels of phosphorus fertilization within each mycorrhizal treatment and two levels of water (both pots watered or one pot watered, one pot allowed to dry). Fully watered mycorrhizal and nonmycorrhizal control plants had similar total leaf lengths throughout the experiment, and similar final shoot dry weights, root dry weights and leaf length/root dry weight ratios. Leaf growth of mycorrhizal plants was not affected by partial soil drying, but final plant leaf length and shoot dry weight were reduced in half-dried nonmycorrhizal plants. At low P fertilization, effects of nonhydraulic signalling were not evident. At medium and high P fertilization, final total plant leaf length of nonmycorrhizal plants was reduced by 9% and 10%, respectively. These growth reductions preceded restriction of stomatal conductance by 7 d. This and the fact that leaf water potentials were unaffected by partial soil drying suggested that leaf growth reductions were nonhydraulically induced. Stomatal conductance of plants given low phosphorus was less influenced by nonhydraulic signalling of soil drying than plants given higher phosphorus. Soil drying was not affected by mycorrhizal colonization, and reductions in leaf growth were not related to soil drying rate (characterized by time required Abbreviations and symbols: ANOVA = analysis of variance; Cs = stomatal conductance(s); med = medium; P = probability; ~P~ = matric potential(s); ~o = water potential(s) Correspondence to: R.M. Aug6; FAX: 1 (615) 974 2765; Tel.: 1 (615) 974 2765 for soil matric potential to drop below control levels and by time roots were exposed to soil matric potential below typical leaf water potential). We conclude that mycorrhizal symbiosis acted independently of phosphorus nutrition, plant size or soil drying rate in eliminating leaf growth response to nonhydraulic root-to-shoot communication of soil drying.

No abstract

We propose that mycorrhizal colonization of roots alters nonhydraulic root to shoot communication of soil drying. Split-root rose (Rosa hybrida L. cv Samantha) plants-one side of the root system colonized by Glomus intraradices Schenck & Smith, the other side nonmycorrhizal-displayed different stomatal conductances upon partial drying, depending upon whether mycorrhizal or nonmycorrhizal roots were dried. No differences in leaf water status were observed among control plants and those whose mycorrhizal or nonmycorrhizal roots were dried.VA' mycorrhizal symbiosis can modify relationships between stomatal conductance and both soil water content (6) and shoot water content (5). In some cases, the mycorrhizal effect is a result of phosphorus deficiency in nonmycorrhizal controls (9,15 'Abbreviations: VA, vesicular-arbuscular; mycor. H20/nonmycordry, plants whose mycorrhizal roots were watered daily and whose nonmycorrhizal roots were allowed to dry after day 0; mycor-dryl nonmycor-H20, plants whose nonmycorrhizal roots were watered daily and whose mycorrhizal roots were allowed to dry after day 0; ', water potential; RWC, relative water content.