Comparative Litter Quality and Recalcitrance Among Native Grasses and the Invasive, Non-indigenous KR Bluestem (Bothriochloa ischaemum)

Abstract

AbstractKR Bluestem (Bothriochloa ischaemum) is a non-indigenous, invasive, C4 grass that was introduced throughout the Midwestern and Southwestern U.S. short- to midgrass prairies with the aim of improving degraded rangelands. The aggressive nature of KR bluestem has led to dramatic alterations of natural and managed ecosystems. Comparative studies of decomposition often show that non-indigenous, invasive plant species have higher rates of nutrient cycling than indigenous species; however, KR bluestem appears to deviate from this trend. Large amounts of litter are observed in KR-dominated grasslands as compared to intact native grasslands, suggesting that the species has a relatively lower decomposition rate and may slow nutrient cycling in these systems. Indeed, as a result of lower decomposition, KR-dominated sites generally have higher fuel loads. We employed a two-way factorial design to assess differences in decomposition between KR Bluestem and three native, perennial grasses in two habitat types, KR-dominated grasslands or intact native grassland. Dried above ground litter for each species was divided into leaves and culms. For each species, replicate fiberglass mesh bags were filled with one gram of leaves plus one gram of culms. The bags measured 10.16 cm x 15.24 cm. Bags were placed in the field in one of three replicate sites of either KR-dominated or intact, native grassland and collected approximately every three months. Litter was analyzed for dry weight biomass, nitrogen, carbon, and lignin. Analysis by ANCOVA demonstrated statistically significant differences in litter quality among the four species, suggesting that KR Bluestem litter is more recalcitrant to decomposition. We found no significant differences in rates of decomposition between the two habitats. Trends in the data suggest that nutrient cycling is slower in KR Bluestem due to higher lignin and C:N and low total nitrogen content.