Litter decomposition in southern Appalachian black locust and pine–hardwood stands: litter quality and nitrogen dynamics

To compare litter decomposition and nitrogen (N) dynamics in 16-year-old black locust and pine-hardwood forest stands, weight loss, N concentration, and litter quality of the dominant species in each stand were monitored for 863 days, using litterbags. The species studied were Robiniapseudo-acacia L. (leaflets and rachises), Liriodendrontulipifera L., and Rubus spp. (leaves and stems) in the black locust stand and Kalmialatifolia L., Pinusrigida Mill., and L. tulipifera in the pine-hardwood stand. Between-stand comparison of L. tulipifera leaf litter indicated a significant stand effect on weight loss during the first 8 months but no significant stand effects on N concentration and net immobilization. Initial lignin content was highly correlated to percent weight remaining and net N immobilization after 331 and 863 days. All litter types exhibited an absolute increase in "lignin" that appeared to originate from the more soluble litter fraction. Robiniapseudo-acacia leaflets, P. rigida, K. latifolia, and Rubus stems decomposed slowly, but only the latter two species were in the net N immobilization phase at day 863. Rubus leaf litter decomposed rapidly, releasing 70% of its original N by day 331. The role of Rubus and other understory species in influencing organic matter and N accretion in these early successional systems is discussed. Robiniapseudo-acacia leaflets contained 81% of their original N at day 863. This retention of N, coupled with its greater potential to form recalcitrant material during decomposition, suggests a mechanism to explain the long-term effects of Robiniapseudo-acacia on N storage in the forest floor and soil.