Development and growth characteristics of Caucasian and white clover seedlings, compared with perennial ryegrass

Seedling competition for resources during establishment affects the potential success of individual species within a pasture. Germination, emergence and leaf expansion are key characteristics that contribute to the competitive ability of species. In this study, development and growth characteristics of Caucasian clover, white clover and perennial ryegrass (PRG) seedlings were quantified. A base temperature of <4°C and an optimum temperature of ～27°C were found for development in each species. Thermal time (Tt) requirements for 75% of final germination were lower for Caucasian clover (46°C d) and white clover (40°C d) than for PRG (76°C d), but Tt requirements for 50% of final emergence were similar (～110°C d). The phyllochron (°C d leaf^?1) for primary stem leaves was slower for Caucasian clover (109°C d) than for white clover (94°C d) and PRG (101°C d). Appearance of the first PRG tiller, which indicates the initiation of secondary leaf development, occurred after 373°C d, compared with 532°C d for the first white clover stolon. Caucasian clover crown shoots did not develop until >1180°C d. Consequently, white clover and PRG had more leaves (～15 plant^?1) and faster shoot relative growth rates (～0·062 mg mg^?1 d^?1) than Caucasian clover (5 leaves plant^?1, 0·049 mg mg^?1 d^?1).     

Impact of frost and plant age on compensatory growth in timothy and perennial ryegrass during winter

Two cultivars of each of two contrasting grass species, timothy ( Phleum pratense L.) and perennial ryegrass ( Lolium perenne L.), sown either in May or July, were sampled for dry matter (DM) weight of roots and herbage in late October (end of main growing season) and examined for regrowth when exposed to a frost treatment (−8 to −10°C in darkness for 48 h) in late January, early March and late April. The frost treatment caused compensatory root and herbage growth, and regrowth of roots in March and April was greater than regrowth of herbage. Early-sown plants had higher DM weights of roots and herbage than late-sown plants in October but had the lowest survival rate when exposed to the frost treatment in April. Compensatory growth of root and herbage in response to moderate frosts occurred in January and March in all cultivars, and in the most frost-resistant timothy cultivar in April. Concentration of total carbohydrates increased from October to March with the greatest increase in the most winter-hardy cultivar of each species, and then decreased in April. An indirect correlation between concentration of total carbohydrates and tolerance to moderate frost was indicated, and plant survival and ability for compensatory growth were also associated with differences in adaptation related to winter survival in the cultivars tested.