Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.). 1. Response of Leaf Extension to Temperature during the Transition from Vegetative to Reproductive Growth

Abstract

The potential for leaf extension of plants of Lolium perenne cv S24 growing in small artificial communities under natural conditions was measured as the plants progressed from the vegetative to the reproductive state In two consecutive years, 1975 and 1976, ‘simulated swards’ were sown in autumn and overwintered in an open, unheated glasshouse Individual swards from the batch sown in 1975 were brought in to a growth room on two occasions in spring 1976 to measure their potential for leaf extension at a range of temperatures (5–20 °C) Individual swards from the batch sown in autumn 1976 were brought in to the growth room on 15 occasions between November 1976 and May 1977 and their potential for leaf extension was measured at a single temperature of 15 °C Frequent dissections were made in both years to describe changes in the developing apex. The potential for leaf extension at 15 °C decreased from c 17 mm day⁻¹ in November to c 10 mm day⁻¹ in mid-winter. In January, the potential rapidly increased threefold to reach 30mm day⁻¹ by mid February The increase began coincident with the earliest stages of floral initiation and was completed by the time of double-ridge formation Spring-grown vegetative plants, however, showed potential rates of < 20 mm day⁻¹ at 15 °C The results are discussed in relation to reproductive development and to changes in the carbohydrate strategy of the plants in early spring