Candidate lignocellulosic biofuel species: Exotic vs. native grass biomass production in central Texas

Background/Question/Methods

Highly productive perennial bunchgrasses are among the most promising candidate species for developing low-input cropping systems for biomass energy production.  There is potential for developing multi-functional systems where senesced plants are left in the field to provide wildlife habitat.  Economically, species must maintain high biomass yields even after over-wintering.  We compared three candidate biofuel crops grown under the same, minimal input conditions in Central Texas.  Species included native C4 Panicum virgatum, exotic C4 Miscanthus × giganteus, and exotic C3 Arundo donax.  We formulated the following hypotheses: 1. the native species produces more biomass than either exotic species due to its adaptation to local climate and soils; 2. comparable C4 species produce more biomass than C3 species due to the higher photosynthetic efficiency of the C4 pathway under the high light intensity and high temperature conditions typical of Central Texas; 3. the relationship between biomass yields remains this same post-senescence, such that the highest yielding species at the end of the growing season retains its tissue most effectively over the winter.  A completely randomized design with four repetitions was established in Temple, Texas.  Plots (5×5m) were established from seedlings in April 2004. 

Results/Conclusions

Data from July 2007 do not support our hypotheses: the exotic C3 grass (A. donax) produced 13% and 54% more biomass than the native C4 grass (P. virgatum) and exotic C4 grass (M. × giganteus), respectively.  However, September 2007 data support our first hypothesis; the native C4 grass produced 30% more biomass (2512.7 ± 498 g^-1m^-2) than either the exotic C4 grass(1949.2 ± 487.4 g^-1m^-2) or the exotic C3 species (1905.7 ± 455.6 g^-1m^-2).  Our second hypothesis regarding the advantage of the C4 pathway was not supported by performance of the exotic C3 and C4 species, which produced biomass yields within 2% of each other.  In February 2008, the C4 grasses had retained 74% (P. virgatum) and 71% (M. × giganteus) of their September 2007 biomass, while the C3 species (A. donax) retained 95% of its September 2007 biomass, making February 2008 yields of A. donax (1819.5 ± 410.4 g^-1m^-2) and P. virgatum (1852.05 ± 534.1 g^-1m^-2) comparable. Based on these observations, we conclude that P. virgatum is capable of producing more biomass than M. × giganteus or A. donax under low nutrient, high light and temperature conditions typical of Central Texas. However, A. donax may be an important species in multi-functional systems designed to provide wintertime wildlife cover.