Xiangrong Duan

Nonhydraulic signalling of soil drying in mycorrhizal maize

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 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.

Comparative dehydration tolerance of foliage of several ornamental crops

Cultivars of Dahlia, Pentas, Salvia and two Impatiens were subjected to severe soil drying, and their foliar water relations were measured when fewer than eight live leaves remained (defined as the lethal point). Salvia was the most dehydration tolerant of the four genera, as characterized by lethal leaf water potential, and showed the highest osmotic adjustment. Dahlia and the two Impatiens cultivars had similar water relations at the lethal point. Length of the drying period, which was varied by growing plants in three pot sizes, did not affect any leaf water relations parameter. The paper also provides a ranking of the foliar dehydration tolerance of 25 other ornamental plants, measured in additional experiments. Foliage of woody species tended to be more tolerant of dehydration than foliage of herbaceous species. # 2003 Elsevier Science B.V. All rights reserved.