Comparative defoliation tolerance of temperate perennial grasses

Abstract

The defoliation tolerance of cultivars of four temperate perennial pasture grasses, perennial ryegrass (Lolium perenne, cv. Yatsyn1), phalaris (Phalaris aquatica cv. Australian), tall fescue (Festuca arundinaceae cv. Demeter) and cocksfoot (Dactylis glomerata cv. Porto), was determined under controlled conditions over a period of 12 weeks. Undefoliated plants were compared with defoliated plants, where only half of one leaf was left intact at the initial defoliation, and leaf regrowth was harvested every 3-4 d. The growth responses measured were plant tiller number, dry weight, relative leaf regrowth rate, root:shoot ratio, sheath:stem ratio and specific leaf weight. All species showed morphological adaptations that potentially increased their ability to tolerate defoliation (e.g. increased allocation to shoot at the expense of roots and lower specific leaf weights) but cocksfoot was found to be the most defoliation-tolerant and perennial ryegrass the least. The adaptation that favoured cocksfoot most strongly was high sheath:stem ratio, which, it is proposed, allowed it to maintain photosynthesis and a level of carbon supply sufficient to support regrowth throughout the experiment. The strategy of perennial ryegrass which favours leaf growth and leads to rapid leaf turnover rates made it particularly susceptible to defoliation under the conditions of this experiment. This highlights the likely importance of defoliation-avoidance responses in explaining the wellknown grazing resistance of this species. Phalaris and tall fescue showed responses that were intermediate between the other two species. The importance of defoliation-avoidance mechanisms and implications for grazing management are discussed.

Defoliation frequency effects on winter forage production and nutritive value of different entries of Agropyron cristatum (L.) Gaertn

“…Indeed, it has been reported that multiple grass defoliations reduced grass root weight, root area, root length, and weight of total nonstructural carbohydrates in roots more than single defoliations did (Engle et al, 1998). Moreover, when defoliation combined with other stresses (low temperatures in this case), enlarged the priority for leaf regrowth at the expense of roots (Fulkerson and Donaghy, 2001;Cullen et al, 2006). It seems that all these factors contributed to a reduced root DM at the end of the first harvest year.…”

Defoliation frequency effects on winter forage production and nutritive value of different entries ofDactylis glomerataL.

“…This means that following defoliation plants initially replace the removed leaf area and then invest energy into shoot and root growth. in defoliated plants of D. glomerata, low root: shoot ratios (Cullen et al 2005) and an increase in tiller number per plant (Cullen et al 2006) indicate a strong priority for shoot growth and a competitive growth strategy (Grime 1981). Accordingly, D. glomerata can be characterised as a defoliation-tolerant species that has higher regrowth rates than other grass species following defoliation (Cullen et al 2006).…”

“…in defoliated plants of D. glomerata, low root: shoot ratios (Cullen et al 2005) and an increase in tiller number per plant (Cullen et al 2006) indicate a strong priority for shoot growth and a competitive growth strategy (Grime 1981). Accordingly, D. glomerata can be characterised as a defoliation-tolerant species that has higher regrowth rates than other grass species following defoliation (Cullen et al 2006). Thus the increased DM production under frequent defoliation during the first year could have been attributed to this regrowth habit of D. glomerata.…”

“…The 4-or 6-week intervals of the current study, combined with the low temperatures of winter, may have been insufficient for the development of four to five leaves, and as a consequence root regrowth would not have recommenced. Moreover, when defoliation combined with other stresses (low temperatures in this case), it potentially increased the priority for leaf regrowth at the expense of roots (Fulkerson & Donaghy 2001;Cullen et al 2006). it is possible that all these factors contributed to a reduced root DM at the end of the first harvest year, and it follows that any factor that retards root growth has a carry-over effect on other components of plant growth due to restricted uptake of water and nutrients (Clement et al 1978).…”

Modelling pastoral farm agro‐ecosystems: A review

“…These act to influence how much the animal eats through metabolic and rumen fill feedback mechanisms, the extent of fibre degradation, protein turnover and greenhouse gas production. Representation of these processes is vital due to their effect on plant defoliation and subsequent regrowth of pasture species (Cullen et al 2006), the effect of plant composition on nutrient return to soils and thus environmental outcomes (Kebreab et al 2002), the prediction of animal performance from plants with different nutrient characteristics (Casler 2001), and the identification of the most suitable supplements for specific pastures (Doyle et al 2005). Nevertheless, thorough testing of mechanistic rumen-feeding decision models are needed to ensure they predict accurately levels of intake, animal performance, ruminal concentrations of nutrients, end products of fermentation, nutrients excreted in urine and faeces, and greenhouse gases emissions.…”