Morphological and Physiological Changes of Hydroponic Lettuce Grown in Varying Potassium Concentrations and an Adaptive Lighting Control System

Abstract

We investigated the growth dynamics of hydroponic lettuce (Lactuca sativa) driven by the influence that potassium (K+) has on crop growth. This study aimed to determine whether increased K+ concentrations under different daily light integrals (DLIs) in a hydroponic system will boost growth of greenhouse lettuce. This study was conducted within a controlled glass greenhouse environment with varying DLIs achieved by integrating an adaptive lighting control system over a 16-hour photoperiod. We used three K+ treatments of 200, 400, or 600 mg⋅L−1 K+ and six DLI lighting treatments of 11.1, 12.9, 14.6, 15.9, 16.9, and 17 mol⋅m−2⋅d−1. We found that increasing K+ did not increase shoot dry weight, leaf area, or specific leaf area with increasing DLIs. Although K+ and DLI had an interacting effect on the root dry weight fraction, leaf chlorophyll content, and quantum yield of photosystem II, the K+ treatments did not increase or decrease with increasing DLIs. The influencing factor was DLI, which led to increases in shoot dry weight and leaf area, whereas a decrease in specific leaf area was observed with increasing DLIs. Ultimately, adding supplemental concentrations of K+ did not enhance lettuce growth, nor did these effects show any increase with increasing DLIs.