Changes in foliar ammonium concentrations in substrate-grown strawberry

Abstract

Strawberries (Fragaria x ananassa Duch. cv. Nyoho) grown in peat-based substrate often suffer interveinal chlorosis in their immature leaves 10-20 d after planting. Based on our previous results and observations from growing practice, we hypothesized that the cause of this phenomenon could be due to drastic changes in plant nitrogen (N) nutrition in strawberries just after planting into peat bags. To determine optimal sampling time, diurnal variations in foliar ammonium (NH4)-N concentration were evaluated under greenhouse conditions. Results showed a broadly similar pattern of diurnal variation, with the rates increasing to a maximum at midday and decreasing steadily during the second-half of the light period. However, foliar NH4-N concentration was higher under sunny than under cloudy or shaded light conditions. In the second part of this study, changes in foliar NH4-N and in nitrate (NO3)-N in petioles in relation to the occurrence of interveinal chlorosis were investigated. When the plants were supplied with 30 (control) or 50% Ohtsuka A' nutrient solution for two weeks after planting, foliar NH4-N concentrations increased earlier than petiole NO3-N concentrations, and reached their peak 8 and 10days after planting in 50% (1.90mol g(-1) FW) and 30% (1.78mol g(-1) FW) treatment respectively. Interveinal chlorosis was observed in immature leaves in 50% treatment about 10days after planting while there was no chlorotic symptom in control treatment. The absence of interveinal chlorosis in immature leaves in control plants, led to the conclusion that a high leaf NH4-N concentration and related accumulation of NH4-N play an important role in triggering interveinal chlorosis.