The effect of potassium on photosynthetic acclimation in cucumber during CO2 enrichment

Abstract

Long-term CO2 enrichment (1,000 μmol mol-1) leads to photosynthetic acclimation in cucumber. Here, through hydroponic experiments in an open-top climate chamber system, we investigated key photosynthetic parameters of cucumbers using potassium stimulation (120 or 240 mg L-1). Short-term CO2 enrichment (less than 25 days) significantly increased the net photosynthetic rate in cucumber. However, long-term CO2 enrichment (43 d) led to photosynthetic acclimation and decrease in stomatal conductance. The increase in potassium alleviated the decrease in photosynthetic rate and stomatal conductance, which reduced photosynthetic acclimation. In addition, 13C isotope tracing showed that under CO2 enrichment, plants with higher potassium concentrations showed higher sink/source and flow/source ratios of photosynthetic assimilative C (δ13C) abundance. Moreover, the abnormal accumulation of soluble carbohydrates and starch resulted in photosynthetic acclimation in cucumber. Increasing potassium significantly reduced the accumulation of soluble carbohydrates and promoted the transport of soluble carbohydrates to the sink, which alleviated photosynthetic acclimation.

Keywords

• co2 enrichment; cucumber; final product negative feedback; photosynthetic acclimation; potassium.