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

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.