Effects of Light Intensity and Growth Rate on Tipburn Development and Leaf Calcium Concentration in Butterhead Lettuce

Abstract

Tipburn is a severe problem in producing butterhead lettuce under artificial lighting and develops as a consequence of decreased calcium concentrations in leaves. Here, we investigated the effects of light intensity on tipburn development and calcium concentration in leaves by comparing their growth rates. Butterhead lettuce was grown in a plant factory under artificial light at photosynthetic photon flux (PPF) densities of 150, 200, 250, and 300 μmol·m−2·s−1. Fresh and dry weights of shoots, relative growth rate, the number of leaves, and the number of tipburned leaves significantly increased with light intensity. Associations existed between growth and tipburn occurrence. Calcium absorption rate per plant also increased with light intensity in association with increased water absorption rate. Consequently, calcium concentrations in the entire plant and outer leaves increased with light intensity. In contrast, calcium concentration in the inner enclosed leaves did not increase with light intensity. This pattern can be attributed to the higher mass flow of calcium to outer leaves than to inner leaves, driven by transpiration, under high light intensities. Thus, a lack of calcium in the inner leaves resulting from rapid growth may contribute to the frequent tipburn development.