PHOTOSYNTHETICA

Photosynthetica X:X | DOI: 10.32615/ps.2026.037

Leaf photosynthesis is enhanced, not impaired, under severe potassium limitation in spinach despite arrested growth

K. NOMURA¹, Y. TANAKA², M. KOBAYASHI¹, M. SAITO¹, I. TADA¹, M. KITANO¹

¹ IoP Collaborative Creation Center, Kochi University, 200, Otsu, Monobe, Nankoku City, 783-8502 Kochi, Japan

² Faculty of Agriculture and Marine Science, Kochi University, 200, Otsu, Monobe, Nankoku City, 783-8502 Kochi, Japan

Potassium (K) deficiency has conventionally been reported to suppress leaf photosynthesis and growth. We show that in hydroponically grown spinach (Spinacia oleracea L.), severe K limitation maintained or increased the net photosynthetic rate per unit leaf area (P_N) at both ambient and saturating CO₂ concentrations with increased stomatal conductance, while whole-plant growth was severely restricted. Compared with K-sufficient controls, K-limited leaves had higher leaf mass per area, nitrogen and phosphorus concentrations, and SPAD values, whereas CO₂-saturated photosynthetic rates per unit dry mass remained near control levels. This indicates that the increase in area-based P_N reflects structural leaf densification, with the photosynthetic machinery remaining functional per unit mass. Sucrose concentrations tended to increase without hexose accumulation, and the carbohydrate-induced photosynthetic downregulation typical of nitrogen or phosphorus deficiency was absent. Shoot dry mass nonetheless fell by about 38%, revealing a marked decoupling between leaf photosynthesis and whole-plant growth under severe K limitation.

Additional key words: chlorophyll content; gas exchange; horticultural crop; leaf structural density; nonstructural carbohydrate; source-sink relations.

Received: August 15, 2026; Revised: October 15, 2026; Accepted: October 19, 2026; Prepublished online: November 2, 2026