Genotypic Variation in Biomass and Physiological Traits of Switchgrass in Response to Nitrogen Treatments.

Nitrogen (N) is an important input for biomass production. The amount of nitrogen used can significantly alter the sustainability of bioenergy production systems. Therefore reducing the nitrogen use or increasing nitrogen use efficiency of bioenergy crop species is of vital importance. A study was conducted in summer 2009 to evaluate growth and physiological parameters and identify switchgrass traits that can contribute to increased nitrogen use efficiency (NUE). Thirteen genotypes were studied; three lowland (Carthage, Alamo, and Kanlow) and ten upland (Southlow, Cave-in-Rock, Forestburg, Blackwell, Nebraska 28, Shelter, Shawnee, Dacotah, Sunbrust, and WI Ecotype). Plants were grown in 12 L pots, with pure sand medium, and were supplied with Hoagland's nutrient solution. Three nitrogen treatments 100%N (control), 20%N and 0%N were imposed starting at 74 days after sowing. During the stress period, growth and physiological parameters measured included plant height tiller number, node number, photosynthesis, fluorescence, electron transport rate and stomatal conductance using LI-6400 portable photosynthesis measurement system. Principle component analysis was carried out to identify the genotypes with, and traits contributing to higher nitrogen use efficiency. Total biomass and biomass components of all genotypes were measured at final harvest. Results showed that genotypes differed significantly in response to nitrogen treatments.  A significant (P<0.05) genotype x nitrogen interaction was recorded for physiological, growth and biomass parameters. Genotypes that showed no decrease in biomass or increase in biomass under low N treatments had significantly higher root biomass than under control conditions. Kanlow among the lowland genotypes, and Cave-In-Rock and Blackwell among upland genotypes, exhibited significant increase in root biomass under low N compared to that under control conditions. Correlation analysis indicated plant height and root biomass as major indicators of NUE in switchgrass genotypes.