Effects of Paclobutrazol and its method of application on the growth and transpiration of Acacia Mangium Seedlings

Ten-week-old potted A. mangium seedlings were subjected to a growth retardant, paclobutrazol (PP333), at concentrations of 0, 0.5, 1, 4 and 12 gil. Four methods of application were tested namely S, soil drenching at week 0; F1, foliar spray (potting soil protected from chemical) at week 0; F2, foliar spray (potting soil protected from chemical) at week 0 and 6; and S+F, soil and foliar spray (potting soil exposed to chemical spray) at week O. Plants were harvested after 12 weeks for various growth measurements. Height and leaf area increments, transpiration and stomatal conductance were monitored at weekly intervals. Paclobutrazol was found to be effective in reducing root and shoot growth, transpiration and stomatal conductance of the seedlings. Treated plants had higher root to shoot ratios. The effects of the chemical increased with increasing concentration and frequency of application for the foliar spray. The chemical was most effective when applied through the soil either l7y drenching (S) or soil and foliar spray (S+F)

Increase in size and nitrogen concentration enhances seedling survival in Mediterranean plantations:insights from an ecophysiological conceptual model of plant survival

Reduction in size and tissue nutrient concentration is widely considered to increase seedling drought resistance in dry and oligotrophic plantation sites. However, much evidence indicates that increase in size and tissue nutrient concentration improves seedling survival in Mediterranean forest plantations. This suggests that the ecophysiological processes and functional attributes relevant for early seedling survival in Mediterranean climate must be reconsidered. We propose a ecophysiological conceptual model for seedling survival in Mediterranean-climate plantations to provide a physiological explanation of the frequent positive relationship between outplanting performance and seedling size and nutrient concentration. The model considers the physiological processes outlined in the plantation establishment model of Burdett (Can J For Res 20:415-427, 1990), but incorporates other physiological processes that drive seedling survival, such as N remobilization, carbohydrate storage and plant hydraulics. The model considers that seedling survival in Mediterranean climates is linked to high growth capacity during the wet season. The model is for container plants and is based on three main principles, (1) Mediterranean climates are not dry the entire year but usually have two seasons of contrasting water availability; (2) summer drought is the main cause of seedling mortality; in this context, deep and large roots is a key trait for avoiding lethal water stress; (3) attainment of large root systems in the dry season is promoted when seedlings have high growth during the wet season. High growth is achieved when seedlings can divert large amount of resources to support new root and shoot growth. Functional traits that confer high photosynthesis, nutrient remobilization capacity, and non-structural carbohydrate storage promote high growth. Increases in seedling size and nutrient concentration strongly affect these physiological processes. Traits that confer high drought resistance are of low value during the wet season because hinder growth capacity. We provide specific evidence to support the model and finally we discuss its implications and the factors that may alter the frequent increase in performance with increase in seedling size and tissue nutrient concentration