Morphological and Growth Responses of Lactuca sativa cv. Box Hill and L. sativa cv. Black Simpson to Phosphorus Starvation and Its Implication to Crop Production

Abstract

Phosphorus is a major plant nutrient yet it is one of the least available in the soil. In order to acquire inorganic phosphate (Pi), plants have developed several strategies for adaptation to low phosphorus. These include alterations in relative growth rates (RGR), root architecture, root-to-shoot ratio, and chlorophyll content. Lactuca sativa L., commonly known as lettuce, was used in the study. The study determined the effects of varying phosphorus concentrations (0 M 1 pMl mM, 1 M H2PO4) to the compensatory responses of the two varieties of Lactuca sativa L. (Black Simpson, Box Hill) and compared the two on how they differentially respond to phosphorus availability. RGR for leaves (RGRjeaves) was factorized into three components: Specific Leaf Area (SLA), Leaf Mass Fraction (LMF), and Unit Leaf Rate (ULR). All three increased significantly as the phosphorus concentration increased. RGR for plants (RGRpiant) exhibited a steady increase from 0 M to 1 mM H2PO4 concentrations. Plants grown in 1 M H2PO4 media showed a considerable gain of RGRpiant and represented the most favorable growth responses. Root-to-shoot ratio and primary root elongation increased significantly as the plants became more phosphorus-starved. In contrast, lateral root density was detected to have the least value in 0 M H2PO4 concentration media. Low phosphorus availability caused increased root hair proliferation as well. Chlorophyll a and b gained by 26% and 46% respectively in plants grown in 1 M H2PO4 as compared to those grown in 0 M H2PO4. Statistical analysis revealed that phosphorus availability is a significant factor in terms of affecting the morphological phosphorus-acquiring adaptations of the Lactuca sativa. There was also a significant difference in the responses of the two varieties.