Potassium Fertilization Affects Metabolite Dynamics of Overwintering Annual Bluegrass.

While K is known to affect plant metabolic processes, the impact of K fertility on overwintering metabolite dynamics is poorly characterized, warranting experimentation. In a greenhouse, annual bluegrass [Poa annua var. reptans (Hauskn) Timm.] was seeded into 125 – 30 x 10 cm diam. sand filled columns. Nitrogen (0.5 g m²), K (0.5 g m²), and other plant essential nutrients (PENS) were applied weekly for 90 d. Following establishment, weekly application rates of N and PENS remained constant, yet 5 different K treatments (0, 0.25, 0.5, 2, 3 g m²) were imposed for 90 d. Columns were then moved to a refrigerated room, maintained under a photosynthetically active radiation flux of ~300 υmol m^-2 s^-1, and day/night air temperature incrementally decreased every 7d over 28 d (10/4°C, 4/-2°C, 2/-4°C, -2/-6°C). Next, plants were buried in 10 cm snow, kept under darkness at -4°C for 28 d, then maintained at 2°C (40 d) and 4°C (45 d) under periodic misting. Five replicates of each K level were harvested following establishment, fertilization, incremental cooling, snow cover, and misting periods. Tissues were analyzed for K content and a total of 20 different carbohydrates and tricarboxylic acid cycle intermediates (TCAI). The experiment was repeated twice and while absolute values of analytes varied across trials, ordinal treatment effects were consistent and are analyzed as such. Analyte content fluctuated greatly between sampling dates and was significantly affected by K fertilization in many cases. Most notably, the ratio of total TCAI to total carbohydrates as well as total TCAI content share a positive, linear correlation with K application rate across all sampling dates. Furthermore, K fertilization significantly affects proportional composition of the total TCAI pool. These results suggest that K fertilization profoundly affects the processing and fate of carbon skeletons under winter conditions.