Effects of N, P and K deficiencies on nutrient accumulation and quality parameters in hydroponic lettuce (Lactuca sativa L.) cultivation

Abstract

This study evaluated the chronological impacts of nitrogen (-N), phosphorus (-P), and potassium (-K)
deficiencies on lettuce (Lactuca sativa L.) grown hydroponically. Using a randomized complete block design
with three replicates, morphological, physiological, physicochemical, and tissue elemental dynamics were
assessed across early (Week 1) and chronic (Week 2) stress phases. Macronutrient starvation rapidly and
distinctly constrained shoot growth and vegetative development (P < 0.0001), while fully nourished controls
optimized plant height (30.63 cm) and shoot fresh mass (15.36 g). Individual omissions triggered immediate
root-zone adaptations: transient root elongation under -K (15.17 cm) and root thickening under -P. Leaf canopy
temperature was a sensitive physiological indicator; -K consistently elevated canopy temperatures (20.03 °C
to 19.16 °C) due to disrupted stomatal cooling. Root-zone solutions showed distinct acidification under -N (pH
6.39, Week 1) and alkalization under -K (pH 7.22). ICP spectrometry revealed strong microelement crosstalk
during chronic stress: controls maintained optimal molybdenum accumulation (10.75 ppb), whereas -N, -P, or -K
triggered complete shutdown of Mo transport, collapsing to 0.09 ppb under -K. This regulatory collapse indicates
molybdate transporter efficiency (MOT1) is tightly bound to primary nutrient availability and root energy status.
Monitoring non-destructive physiological vectors like early leaf temperature changes, combined with subtle
microelement signatures such as Mo dynamics, offers a precise diagnostic framework for early detection of
macronutrient starvation before irreversible visual stunting manifests.