Potassium fertilization reduces silique canopy temperature variation in Brassica napus to enhance seed yield

Abstract

Abstract The seed yield of oilseed rape (Brassica napus), an important edible and industrial oil source, is derived mainly from the photosynthetic products of siliques. High temperatures in the pod-development stage threaten the oilseed rape production. Fertilization promotes the growth and yield of oilseed rape. However, it is unclear whether fertilization can alleviate the effect of the temperature on the yield. During 2017–2019 oilseed rape growing season, two oilseed rape cultivars with different K utilization efficiencies (KUtEs) were grown with four K fertilizer rates (0, 60, 120, and 180 kg\u202fha−1) to study the association between the application of the stress-resistance-related element K and silique canopy temperature of oilseed rape. Infrared imaging was used to determine the canopy temperature of the two cultivars at the silique development stage at different K application rates. Partial least squares path modeling (PLS-PM) was used to analyze the potential physiological mechanism of the increase in crop yield with K fertilization. The K fertilization reduced the canopy temperature, specifically, the canopy temperature variation (CTV), at the silique development stage (reduction of 1.3–3.0°C by 1 % increase in K amount). A reduction of 1°C in CTV increased the seed yield by approximately 417.6 kg\u202fha−1. Nevertheless, the cultivar with a low KUtE required almost twice the K amount, compared with the cultivar with a high KUtE, to achieve the same consequent CTV reduction, and produced a lower seed yield at the same K application rate. The reduction in CTV was induced by an increased stomatal function (transpiration rate), which was accelerated by the K application. PLS-PM showed that the K application promoted seed yield by reducing the CTV and increasing the photosynthetic rate and biomass. The photosynthetic rate and biomass were directly affected by the CTV. Overall, the K fertilization combined with the high KUtE cultivars could efficiently maintain a stable canopy temperature microenvironment to promote oil production.