The influence ofRhizobium leguminosarumbiovar.trifoliion the growth and neighbour relationships ofTrifolium repensand three grasses

摘要

Trifolium repenswas sampled from 10 areas dominated by each ofDactylis glomerata,Holcus lanatus, andLolium perennein each of three different-aged pastures. Cell extracts of nodule isolates ofRhizobium leguminosarumbiovar.trifoliiwere compared using polyacrylamide gel electrophoresis. Each pasture contained a range ofRhizobiumstrains as defined by the protein profiles. No single strain was common toTrifoliumsampled from the same grass species neighbourhood. The diversity ofRhizobiumstrains encountered was negatively correlated (rensp;=ensp;minus;0.67;nensp;=ensp;9) with pasture age; old pastures showed a decrease in strain diversity. In addition, in the oldest pasture (45-year-old), tillers of the associated grasses were also sampled. In a glasshouse, ramets from eachTrifoliumclone and each of the three grass species were grown in all possible combinations with each of the threeRhizobiumstrains, plusTrifoliummonocultures and an uninoculated control. AllTrifoliumclones gave increased yield in mixture withLoliumcompared with yields withDactylisandHolcus.Trifoliumfrom theHolcuspatches, in most cases, had higher yield thanTrifoliumfrom other grass patches.Rhizobiuminoculation did not consistently increaseTrifoliumyield; it actually caused a decrease in yield when in mixture withLolium. A significantRhizobiumtimes;Trifoliuminteraction indicated a variable performance of eachTrifoliumgenotype with differentRhizobiumstrains. The identity of theTrifoliumclone had a significant effect on the yield ofHolcusandLolium, but notDactylis. Total mixture yields were highest whenTrifoliumfrom aLoliumpatch was part of the mixture. These results are discussed in the context of the hypothesis thatTrifoliumndash;grass coexistence is significantly influenced byRhizobiumstrain differences.