|dc.description.abstract||This study involved three key experiments to examined the effect of Nil endophtye and novel endophyte strains (AR1, AR37, Wild-Type (WT) and NEA2) of perennial ryegrass on dry-matter (DM) production, botanical compositon, alkaloid profiles and possible effects on soil-pasture ecosystems interactions.
A field trial measured DM production and composition of perennial ryegrass pastures sown with a diversity treatment of with or without additional prairie grass, herb (chicory) and legume (white clover). In the same trial, alkaloid and endophyte concentrations were examined in dissected vegetative grass tillers to ascertain how alkaloids may potentially leave the plant and affect soil-pasture ecosystems. Finally, a pot trial comparing the addition of live or dead perennial ryegrass plant material was used to examine the effect of endophyte strain on the growth of associated pasture species.
There was no effect of endophyte or diversity treatment on the total or seasonal herbage DM production of the field trial, with a non-significant 18,540 kg DM/ha and 18,090 kg DM/ha total yield for the diverse and monoculture treatments respectively over the 16 months of the trial. There was a significant endophyte x diversity interaction in spring 2011 when monocultures of Nil and AR37 (5638 and 4963 kg DM/ha respectively) yielded significantly higher than that of their equivalent diverse pastures (4099 and 4323 kg DM/ha). It is unclear the reasoning for this interaction.
The different seasons showed significant differences in the proportion of white clover in the diverse swards with the highest in summer, and the lowest in winter (25% and 11% respectively as a porportion of the total sward DM). There were minimal effects of endophyte on botanical composition, with no significant differences for monocultures. The proportion of prairie grass present in summer 2010/11 was significantly higher in WT diverse plots than other endophytes and spring 2011 showed higher chicory present in WT and NEA2 diverse plots over AR37.
Endophyte concentration differed for the different disected parts of the grass tillers and different endophyte strains. The highest concentrations of endophyte was in the stem with 317 copies per ng of gDNA. The leaves ranged from the youngest first leaf with 59 copies, increasing with leaf age to 268 copies in the remnant leaf. This is consistent with other findings of the endophyte being located mainly at the base of the plant and having hyphae carried up as the leaf expands.
NEA2 had lower endophyte concentration with roughly 50% less copies of endophyte gDNA/ng than the next closest treatment (AR1), approximately 66% less than WT, and 68% less than AR37. NEA2 had significantly less peramine than WT or AR1 for all tiller parts.
The pot trial live and dead plant material thatches differed in alkaloids. Peramine and Janthitrems were higher in the live than the dead plant material. Lolitrem B concentrations for NEA2 were similar in the live and dead plant material (1.55 and 1.34 ppm respectively), but higher in WT endophyte in the dead compared to the live plant material (4.43 vs 1.04 ppm). Ergovaline was low (<0.01 ppm) for NEA2 live and dead, but higher for WT live compared to dead plant material (0.30 vs 0.13 ppm). Despite differences in alkaloids between live and dead thatch, there was little effect of endophyte on shoot or root DM production. For the species tested, there was no evidence of endophyte exudates from thatch affecting growth of prairie grass or Nil endophyte ryegrass companion pasture species. White clover had an endophyte effect on the root: shoot ratio with AR37 and the no thatch control resulting in a higher root: shoot ratio.
The addtion of thatch and thatch type affected plant growth. Addition of live plant material increased shoot production over dead plant material addition for the ryegrass and prairie grass, but not for white clover. This result is likely from the differing nutirent application from the plant thatch material. The higher added nitrogen content from the live thatches (averaged 2.2% for live and 1% of plant material for dead) has increased growth of the grasses, but had minimal effects on white clover. Overall, the effects of endophyte were minor compared to the effects of either the live or dead plant material. It could have been of interest to collect back any remaining plant thatch material that was applied to the pots and have the samples bulk tested to identify the changes in alkaloids or endophyte content over the time of the pot trial. There was no expression of any alkaloids in any of the indicator plants.
It had been hypothesised that the decomposing plant material may indirectly affect associated pasture plants in the sward through negatively impacting beneficial soil microbes and functions, or it was proposed there could be a direct allelopathic impact of the chemicals present. It is concluded that leaching from live and dead decaying plant leaf material of E+ plants is not a major mechanism by which endophytes shape pasture plant communities.
No allelopathic impact of alkaloids was observed. There may be more unanswered questions for water soluble type endophyte alkaloids which may have a greater potential the transfer from the plant. Questions are raised around endophytes which also express alkaloid chemicals in their roots and protect from certain root feeding insects.||en