Decomposition Rates of Native and Improved Cultivars of Grasses in the Northern Great Plains

Abstract

Decomposition is a critical process that links the above- and below-ground portions of the nutrient cycle. A study was initiated in North Dakota, USA, to evaluate the decomposition rate between three genetically improved grass species monocultures, Agropyron desertorum, Bromus inermis, and Pascopyrum smithii, and two native perennial grass species occurring in area rangelands, Nassella viridula and Bouteloua gracilis. Standing litter of all five species was harvested in October 1996 and placed into litterbags. Litterbags were placed along transects in early November 1996 and randomly selected bags were sampled in June, July, August, September, and October, 1997. Carbon (C), nitrogen (N) and lignin were determined on all samples including the 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 native species, occurring in undisturbed rangeland, had significantly lower rates of decomposition than did the monocultures of the improved cultivars, including the monoculture of the improved native, P. smithii. Most decomposition 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% ). The N concentration of the initial samples had the strongest correlation ( r = 0.78 P < 0.01) with decomposition rates. Lignin had a significant positive correlation ( r = 0.49, P = 0.03) and the C:N ratio had a significant negative correlation ( r = -0.67 P < 0.01) with decomposition. Traits, such as decomposition, that can affect ecosystem functioning need to be given greater emphasis in genetic selection of native and improved grass species.