Switchgrass (Panicum virgatum), a candidate perennial bioenergy crop, has a wide geographic range and a number of cultivars have been developed as bioenergy feedstocks. Cultivars differ in a number of morphological and physiological traits that may affect performance. However it is not known if these trait differences are expressed in mixtures and can be used to manage productivity in response to climate variation. We compared the productivity of monocultures and mixtures of four cultivars of P. virgatum in a common garden experiment and assessed if performance of mixtures and monocultures differed and if this was related to traits. Four cultivars – Alamo, Dakota, Trailblazer and Cave-in-Rock – were planted in monocultures, all bi-cultures, and a four-cultivar polyculture in a common garden at the WK Kellogg Biological Station in southwest Michigan in June 2016. A single ramet was planted in each corner of a 0.5m2 plot; 8 replicates of each treatment. Plots were watered weekly for 4 weeks following planting and weeded occasionally the first year. In 2017, the plots were not weeded to assess capacity to reduce weed competitors; tiller height and leaf nitrogen content were measure bi-weekly over the summer and above-ground biomass of weeds and cultivars determined in the fall.
Results/Conclusions
Dakota produced the least and Cave-in-Rock the most biomass in monoculture. While there was a positive relationship between the number of cultivars planted and biomass, biomass of the Cave-in-Rock monocultures was equivalent to that of all mixtures. A mixed-model ANOVA detected a significant effect of cultivar identity, but not neighbor identity on biomass production; however bi-cultures with Dakota produced less biomass than monocultures of the other cultivars. Dakota made up less than 10% of the biomass in all mixtures, suggesting that differences in biomass among treatments was correlated with the number of high performing ramets planted. Treatment differences in biomass production were reflected in the capacity to reduce weeds; the lowest performing monocultures (Dakota and Trailblazer) had the most weeds, the polyculture and bi-cultures with Alamo and Dakota were intermediate, and the monoculture of the Cave-in-Rock lowest weed biomass. Plant height appeared to be an important trait determining differences in biomass in monocultures and mixtures. While there was no evidence that trait complementarity affected performance in mixtures, initial evidence suggests that cultivar performance differs in wet vs. dry years so these effects may develop over time.