Decomposition rates of native and improved cultivars of grasses in the Northern Great Plains

Decomposition is a critical process that links the above- and below-ground portions of the nutrient cycle. A sturdy was initiated in North Dakota, USA , to evaluate the decomposition rate between three genetically improved gra ss species monocultures, Agropyron desertorum, Bromus inermis, and Pascopyr um smithii, and two native perennial grass species occurring in area rangel ands, Nassella viridula and Bouteloua gracilis. Standing litter of all five species was harvested in October 1996 and placed into litterbags. Litterba gs were placed along transects in early November 1996 and randomly selected bags were sampled in June, July, August, September, and October, 1997. Car bon (C), nitrogen (N) and lignin were determined on all samples including t he initial litter samples. The percent of dry matter decomposed across time ranged from 18.4% for B. gracilis to 26.8% for A. desertorum. The two nati ve species, occurring in undisturbed rangeland, had significantly lower rat es of decomposition than did the monocultures of the improved cultivars, in cluding the monoculture of the improved native, P. smithii. Most decomposit ion occurred prior to the June 1997 sampling date, and from June to October 1997 decomposition was approximately the same for all species (7 to 8%). T he N concentration of the initial samples had the strongest correlation (r = 0.78 P < 0.01) with decomposition rates. Lignin had a significant positiv e correlation (r = 0.49, P = 0.03) and the C: N ratio had a significant neg ative correlation (r = -0.67 P < 0.01) with decomposition. Traits, such as decomposition, that can affect ecosystem functioning need to be given great er emphasis in genetic selection of native and improved grass species.