Tillering and partitioning of dry matter and nutrients in Lolium perenne growing with neighbours of different species: effects of nutrient supply and defoliation.

The hypotheses that performance of Lolium perenne L. (ryegrass) differs when plants grow with conspecific or heteraspecific neighbours, and that nutrient supply and severity of defoliation modifies the effect, were tested in a target: neighbour pot experiment. Target L. perenne plants were grown with neighbours of five grass species (L. perenne, Poa pratensis L., P. trivialis L., Festuca ovina L. and F. rubra L.) and Trifolium repens L. (white clover), at three nutrient levels (high, medium and low) and three defoliation severities (no defoliation or cut every 2 wk to 4 cm or 8 cm) over a 12 wk experimental period. Performance of L. perenne plants differed depending on the species of neighbour. Tiller numbers and dry weights of clippings of L. perenne, at both individual cuts and the total accumulated over all seven cuts, were greater with P. pratensis, F. ovina or T. repens as neighbours than in a monoculture. The differences were generally confined to medium and high nutrient levels. The pattern of clippings depended on species association: clippings were similar at successive cuts except in mixtures with P pratensis, F. ovina and T. repens, where they increased until the 4-5th cuts. The total accumulated dry matter (DM) and nutrients of L. perenne and the percentage contribution of DM to the pot total were also greater in these mixtures. Individual linear regressions of tiller numbers and accumulated N for each species combination best described the relationships between L. perenne and its neighbour. Neighbouring species had no significant effect on the relative losses of dry weight of nutrients in clippings of L. perenne when expressed as a proportion of the total accumulated, but partitioning of DM to L. perenne roots (root weight ratio) was greater in associations with Poa species than in a monoculture. It was concluded that the species of neighbour affected the accumulation and partitioning of dry matter and nutrients in L. perenne and that nutrient supply, but not defoliation, modified the responses. The results are discussed in relation to species interactions in grazed swards.