Developmental versus environmental control of early leaf phenology in juvenile Ohio buckeye (Aesculus glabra)

The spring phenology of juveniles of many canopy tree species in deciduous forests predates that of adult conspecifics. To determine whether the earlier phenology of seedlings of Aesculus glabra Willd. (Ohio buckeye) in Illinois, U.S.A., is developmentally or environmentally controlled, seedlings of five maternal parents were grown either in the understory or above a barn roof, simulating environmental conditions experienced at canopy height. Relative to canopy seedlings, understory seedlings had significantly earlier bud break (mean = 6 d), leaf expansion (8 d), leaf senescence (23 d), and leaf drop (18 d). Bud break and leaf expansion of canopy seedlings equalled that of canopy trees of Ohio buckeye, but senescence and leaf drop of canopy seedlings predated canopy trees by 45 and 67 d, respectively. Overall, results show evidence for environmental control over the spring phenology of juveniles. Thermal sums in spring accumulated more rapidly in the forest understory where nighttime temperatures were warmer than above the barn roof. Thus, the environmental control of spring phenology appears to be a non-stage-specific temperature cue that accumulates at different rates along the forest's vertical gradient. In contrast, senescence and leaf drop, while somewhat responsive to the environment, displayed strong developmental constraint.Key words: bud break, developmental constraint, leaf drop, leaf expansion, leaf senescence, thermal sums.

Buffered Phosphorus Fertilizer Improves Growth and Drought Tolerance of Woody Landscape Plants

The effects of alumina-buffered phosphorus (Al-P) were evaluated on growth and drought tolerance of woody plants and on seedling establishment of several tree species grown in containers with soilless media. Al-P reduced phosphorus leaching in all species. Vegetative growth of rhododendron (Rhododendron catawbiense Michx. cv. ‘English Roseum’), forsythia (Forsythia intermedia Zab. cv. ‘Spring Glory’), Ohio buckeye (Aesculus glabra Willd.), and bur oak (Quercus macrocarpa Michx.), measured as plant height, stem caliper, or biomass, was as fast or faster with Al-P as with Osmocote (17–6–10) or monoammonium phosphate fertilizer. Imposition of summer drought during the first growth season slightly reduced growth of rhododendron, with a stronger effect in the second year, while forsythia was more affected in the first season. Rhododendron plants fertilized with Al-P wilted more slowly than controls fertilized with Osmocote. Al-P fertilized forsythia plants grew faster than controls whether drought was imposed or not. Rhododendron plants produced more flower buds in the first year when fertilized with Al-P than with conventional phosphorus fertilizers. At the lower desorbing concentration, drought caused no reduction in percent of plants producing flower buds. A recharging treatment was tested at the beginning of the second season to replace P lost from the Al-P. Recharged Al-P reduced branching and flowering of rhododendron at the end of the second season, possibly as a result of damage from the recharging treatment.

Guignardia aesculi. [Descriptions of Fungi and Bacteria].

A description is provided for Guignardia aesculi. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Aesculus glabra, A. hippocastanum (main host) (Hippocastanaceae). Several other species of Aesculus and subspecies including A. ambigua, A. arnoldiana, A. bushii, A. carnea, A. discolor, A. dupontii, A. hybrida, A. mississippiensis, A. mutabilis, A. neglecta, A. octandra, A. pavia, A. splendens, A. turbinata and A. woerlitzensis have been reported to be susceptible (Neely & Himelick, 1963; 50, 2509). DISEASE: Leaf blotch or black rot of Aesculus hippocastanum (horse chestnut) and other Aesculus species (5, 706; 28, 38; 64, 4521). GEOGRAPHICAL DISTRIBUTION: Europe (Austria, Belgium, France, Germany, Italy, Netherlands, Portugal, Romania, Switzerland, U.K., Yugoslavia); North America (Canada: Manitoba, New Brunswick, Nova Scotia, Ontario, Quebec; U.S.A. : Eastern U.S.A). TRANSMISSION: Presumably by water-borne conidia during wet conditions. Ascomata are produced on leaves left to over winter outside and both conidia and ascospores discharged from over wintered leaves have been reported to infect leaves of seedlings and produce blotch symptoms (Hudson, 1987).