The growth and carbon allocation patterns of white clover (Trifolium repens L.) plants of contrasting branching structure

The growth, morphology and carbon allocation patterns of F1 progeny white clover (Trifolium repens L.) plants selected for either low ('LBF') or high ('HBF') frequency of stolon branching were compared in two controlled-environment experiments. Selections from within both a small-leaved ('Grasslands Tahora') and a large-leaved ('Grasslands Kopu') clover cultivar were compared, and plants were grown under a relatively lenient defoliation treatment (expt. 1) or under three levels of defoliation severity (expt. 2). Carbon allocation patterns were measured by 14CO2 pulse-chase labelling using fully unfolded leaves on the main (parent) stolon. LBF and HBF displayed consistent differences in the selected character though, within cultivars, the difference between selections was most pronounced for Kopu. The selections developed fundamentally different branching structures resulting from differences in branching frequency, with total branch weight per plant averaging 122 mg for LBF and 399 mg for HBF (mean of both experiments). More C moved from parent stolon leaves to branches in HBF than in LBF (mean 22.6% vs. 15.1% respectively of the 14C exported from source leaves). More C also moved to stolon tissue in HBF, but, counterbalancing this and the difference in allocation to branches, less moved to developing leaves and roots on the parent stolon itself compared to LBF. However, the total weight of developing leaves and roots per parent stolon was generally greater in HBF than in LBF, probably reflecting greater C import by these sinks from the higher number of branches present per plant in the former selection. HBF plants were consistently larger at harvest than LBF plants. There were no defoliation treatment X selection interactions in C allocation patterns in expt. 2. The implications of the results for plant performance in grazed pastures are discussed.