Observations of Spring Hard Freeze Injury to C&sub&4&/sub& Perennial Grasses Native to the Great Plains, USA

摘要

The native prairies of the Great Plains USA are dominated by perennial C_( 4 ) grasses like switchgrass ( Panicum virgatum ) and big bluestem ( Andropogon gerardii ). Spring hard freeze injury to C _( 4 ) perennial grasses is rare but information is lacking in the literature. Our objective was to document effects of spring hard freeze damage to C _( 4 ) perennial grasses native to the Great Plains USA. On 2 May at 24:00 pm, air temperature near Mead, Nebraska was below freezing and remained below freezing until 8:00 am on 3 May, with a minimum air temperature of -2.8°C. Based on 50-year of weather data for this site, a minimum threshold temperature of 0°C on or after 3 May occurred 16 times, but a minimum threshold temperature of -2.8°C on or after 3 May occurred only twice. Grass tillers were visually evaluated to determine extent of freeze damage. The terminal 3- to 5-cm of the leaf lamina w as blackened 4-d after freezing and had complete browning, rolling, and desiccation 14-d after freezing. Tiller survival was not negatively affected by the freezing temperatures in May 2004. As the growing season progressed, all agronomic and livestock responses were within normal ranges for these C _( 4 ) grasses. This is the first field report of multiple C _( 4 ) prairie grass species responses to a spring hard freeze following significant spring growth. Plant recovery to this late-spring hard freeze demonstrates the ecological resilience of these C _( 4 ) prairie grasses. These rare spring hard freezes had short-term impacts on C _( 4 ) grasses but did not negatively impact agronomic performance for forage or bioenergy later in the growing season.