Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

First Advisor

Jim L. Chambers

Abstract

Root growth and its effects on water uptake and plant water relations of seedlings during the initial weeks after transplanting were studied. One-year old bare-root shortleaf pine seedlings were put into six different root zone environments defined by the factorial arrangement of two temperatures and three levels of soil water potential. Needle water potential and stomatal conductance were measured 28 days after planting. The next day, root system absorptive capacity was evaluated by forcing water at a constant hydrostatic pressure through detopped seedlings. The projected surface area of old and new roots was then measured. Also, the relative water content of each root system was determined. The experiments were repeated three times. Under the conditions of the study, about one-half of the variation in new root growth was accounted for by the root zone environment. The amount of root growth was affected by the interaction between root zone temperature and soil water potential. In the most favorable root environment, new roots made up about 20% of the mean total root system surface area after 29 days. Root relative water content had a minimum level associated with the presence of new roots; however, it was not highly correlated with the amount of root growth. The amount of new root surface area had a positive, linear relationship with absorptive capacity. Each 10 mm$\sp2$ of new root projected surface area improved absorptive capacity by about 5%. The amount of old root surface area did not influence absorptive capacity, probably because the experimental populations were restricted to a narrow range in initial root system size. The various measures of water status all improved with greater new root development. Under the conditions of these experiments, the water stress that was induced by transplanting was alleviated by the growth of approximately 500 to 550 mm$\sp2$ of new root projected surface area. Only among seedlings in the most favorable root zone environment did mean root growth exceed that amount.

Pages

136

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