Seasonal Changes in Nonstructural Carbohydrate Levels and Innovation Number of Kentucky Bluegrass Turf Growing in Three Plant-Climate Areas

Controlled environment studies have shown temperature to be one of the most important factors controlling nonstructural carbohydrate levels and density of Kentucky bluegrass (Poa pratensis L.) turf. Little information is available showing similar responses to temperature on a seasonal basis in the field. The objective of this experiment was to determine how nonstructural carbohydrate levels and density of Kentucky bluegrass turf differ among climatic areas and from season to season within an area. Total nonstructural carbohydrates (TNC) and innovation development were studied in five Kentucky bluegrass cultivars grown in the field in three distinct climate areas of California. These are a maritime climate of coastal southern California, a southern California interior valley thermal belt, and a temperate mountain valley. The respective soils of these areas are San Emigdio sandy loam classified as coarse-loamy, mixed (calcareous), thermic Typic Xerofluvents; Arlington fine sandy loam classified as coarse-loamy, mixed, thermic Haplic Durixeralf; and Havala sandy loam classified as fine-loamy, mixed, thermic Typic Arglxerolls. Results showed that changes in TNC levels and numbers of innovations followed seasonal patterns which were closely associated with the prevailing temperatures of each specific location. Consistently high summer temperatures reduced TNC stores but moderate temperatures did not affect them. Brief periods of exceptionally high temperature also reduced TNC levels. Accumulation of TNC occurred at each location at the time when temperatures were well below optimum for growth at that location. In the cold winter location, TNC levels decreased during the winter months. Flushes of growth occurring in spring depleted TNC. Density, the number of innovations per unit area, decreased throughout the summer at the high temperature location but increased through the cool winter. In the location of moderate summer and winter temperatures the number of innovations remained high and showed less seasonal fluctuation. Temperature, rather than day length, appeared to be the primary factor affecting innovation development.