Thursday, August 7, 2008 - 4:20 PM

COS 101-9: Response of Natal grass (Melinis repens), an invasive species in Florida, to varied temperature conditions

Roger C. Anderson, Illinois State University and Eric S. Menges, Archbold Biological Station.


Natal grass (C4 species) was introduced from South Africa into Florida where it is listed as a Category I invasive species.  In Florida, it grows and flowers year round.  We compared seed germination and vegetative growth under controlled conditions that simulated mid-March or mid-July temperatures and photoperiod in south-central Florida.  We predicted that (1) rate and percent of seed germination would be higher at warmer temperatures (July) than at cooler temperatures (March) and (2) plants would grow faster and produce more biomass at warmer temperatures than at cooler temperatures.  For the germination study, there were seven replicate Petri dishes each containing 25 seeds of natal grass for March and July temperature treatments.  For the study of the effect of temperature on growth of natal grass, seeds were germinated in growth chambers set for March or July conditions.  Seedlings were planted in plastic pots containing a 50/50 mixture of sand (1,750 cc) and placed in their respective growth chambers.  Plants were watered and fertilized as needed.  Above and below ground tissues were harvested at first flowering.  There were 18 replicate plants for the July treatment and 21 for the March treatment. 


Germination Experiment: There were significant (P<0.05) differences in germination (mean±SE) between treatments 24 hours after initiation of the experiment (first day) (27.4±3.8% and 3.4±1.0%, for July and March, respectively) and third day (4.0±1.9% and 16.5±3.5%, for July and March, respectively).  For both treatments, highest germination occurred on the second day (31.3±5.4% and 35.4±3.0%, for July and March, respectively).  Total germination was not significantly different between treatments (69% and 68%, for July and March, respectively).  Growth Experiment: At first flowering, mean oven dried biomass was significantly higher for plants grown under July conditions (18.7±1.4g) than for plants grown under March conditions (13.4±0.6g).  First flowering was reached in 71.7±1.9 days for plants grown under July conditions compared to 97.5±2.0 days for those grown under March conditions.  However, heat sums (degree-hours) accumulated by the two treatments at first flowering were not significantly different (46,620±1,256 and 45,543±911 degree-hours, for July and March, respectively).  These results and field observations indicate that Natal grass germinates and grows under a wide range of temperature conditions with rates of these processes being controlled by temperature when adequate moisture is available.