Climatic Resiliency of Pastures in the Eastern United States

Organização: Centro de Estudos Florestais e Centro de Ecologia Aplicada Prof. Baeta Neves
Data: 2 de abril de 2014 :: 12h30 - 13h30
Local: Sala PF 1.6 (Antigo Auditório de Florestal)

Orador: Rebecca McCully, Department of Plant and Soil Sciences, University of Kentucky, E.U.A.


Tall fescue pastures cover extensive acreage in the eastern half of the United States and contribute to important ecosystem services, including the provisioning of forage for grazing livestock. Tall fescue’s ability to effectively compete with other plant species and persist under heavy grazing and environmental stress is thought to be enhanced by it forming a symbiosis with the fungal endophyte, Neotyphodium coenophialum. This symbiotic fungal endophyte produces alkaloids known to be toxic to insects (e.g. lolines) and mammals (ergots), the latter of which, unfortunately, can cause the syndrome known as ‘fescue toxicosis’ in grazing animals. The ability of tall fescue to persist and thrive under a warmer and wetter environment, as is predicted to occur as a result of climate change for much of this region, is largely unknown at present, but is likely to be depend on its’ symbiotic relationship with N. coenophialum. To evaluate this supposition we experimentally increased temperature (+3oC, day and night, year-round) and growing season precipitation (+30% of the long-term mean) from 2009 – 2013 in a mixed species sward, that included tall fescue that was 40% endophyte-infected and was managed as a hay pasture (harvested three times a year). Because tall fescue is a cool season grass (C3 physiology) and the warming treatment was expected to increase the intensity and duration of seasonal dry periods normally experienced at the site, we anticipated that warming would decrease tall fescue abundance, especially in the summer and fall, and that this environmental stress would increase the level of endophyte infection within the tall fescue community over time. We also hypothesized that warming would stimulate alkaloid concentrations in endophyte-infected individuals and that the addition of precipitation would ameliorate some of these effects of warming on the plant and its’ symbiotic partner. Consistent with our hypotheses, warming significantly reduced the dominance and biomass production of tall fescue (by half, on average, for both parameters), but this effect was only apparent in the summer and fall harvests and was not ameliorated by the increased precipitation treatment. However, the addition of more precipitation alone increased the relative abundance and biomass of tall fescue over ambient control levels (by ~10%), illustrating that water regularly limits tall fescue production at this site. Although the warming treatment increased environmental stress on tall fescue, we measured only a slight increase in the frequency of endophyte infection within the tall fescue community in those plots (+10% over non-heated treatments, but not significantly different). However, endophyte-infected individuals in the warmed plots had consistently 30-40% higher concentrations of ergovaline and ergovalinine than endophyte-infected individuals in non-heated plots. Warming also increased concentrations of measured loline alkaloids in endophyte-infected material, but was only significant when combined with increased precipitation. These results suggest that future warming will increase the environmental stress experienced by tall fescue, most likely reducing its’ contribution to forage production in pastures of the southeastern U.S. Over time, hotter conditions may increase the prevalence of the fescue-Neotyphodium symbiosis in the landscape, and warming will produce an immediate and dramatic increase in ergot alkaloid concentrations in endophyte-infected individuals, with effects on insect-active alkaloids more dependent on water availability. Although tall fescue dominance in pastures may be reduced in a future warmer environment, substantially increased ergot alkaloid concentrations in endophyte-infected material, coupled with a trend for more infected individuals, strongly suggest that climate change will increase the susceptibility of livestock grazing endophyte-infected stands of tall fescue to fescue toxicosis.