Responses of ponderosa pine growth and volatile terpene concentrations to manipulation of soil water and sunlight availability
1997
Johnson, R.H. | Young, B.L. | Alstad, D.N.
A field manipulation of resources that may control the balance of growth versus differentiation (secondary metabolism and storage) in ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) was performed by supplementing 10 mature trees with water, limiting water to 10 trees, and maintaining 10 controls. Within all trees, two or three branches were covered with shade cloth bags (60% light reduction). Within 4 months, watering increased sun-exposed needle mass and volatile terpene levels by approximately 35% above controls. Sampling at 12 months indicated a continuation of this trend. By 16 months of age, water-limited sun needles exhibited increased terpenes that approximated the levels of watered trees. The subsequent needle year class (1992) was produced under 14 months of combined water and shade treatment. Masses of 4-month-old 1992 needles were greatest among watered trees; however, shading interacted to constrain watering effects to the same levels of control and water-limited trees. Volatile terpenes of the 4-month sun needles were highest among watered trees and intermediate among water-limited trees. Shading reduced all measures of needle terpenes, starch, and resin canal number but increased nitrogen content. No predictable trade-offs were observed between needle growth and differentiation processes. Scale insect densities on 4-month-old needles grown during the second year of treatment were not affected by either water or light availability.
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