Assessment of Nutrient Limitation in Floodplain Forests with Two Different Techniques

We assessed nitrogen and phosphorus limitation in a floodplain forest in southern Georgia in USA using two commonly used methods: nitrogen to phosphorus (N:P) ratios in litterfall and fertilized ingrowth cores. We measured nitrogen (N) and phosphorus (P) concentrations in litterfall to determine N:P mass ratios. We also installed ingrowth cores within each site containing native soil amended with nitrogen (N), phosphorus (P), or nitrogen and phosphorus (N + P) fertilizers or without added fertilizer (C). Litter N:P ratios ranged from 16 to 22, suggesting P limitation. However, fertilized ingrowth cores indicated N limitation because fine-root length density was greater in cores fertilized with N or N + P than in those fertilized with P or without added fertilizer. We feel that these two methods of assessing nutrient limitation should be corroborated with fertilization trials prior to use on a wider basis

The role of floods in particulate organic matter dynamics of a southern

Abstract. We investigated the effect of a flood on particulate organic matter (POM) dynamics in the floodplain and active channel of the Little Tennessee River in western North Carolina. We measured litterfall, leaf breakdown, and floodplain litter (before and after the flood) at 12 sites. Annual litterfall (256-562 g m Ϫ2 y Ϫ1 ) was typical of a temperate deciduous forest but lower than lowland floodplain forests in the eastern US. Leaf breakdown rates of 4 tree species (Acer rubrum, Carpinus caroliniana, Juglans nigra, and Platanus occidentalis) ranged from 0.001 to 0.010/d. We separated the 12 sites into 2 groups (inundated and non-inundated) based on the degree of flooding after a flood on 8 January 1998 and determined POM exchange between the active channel and floodplain. Significant transport of leaves from the floodplain to the river occurred at inundated sites, but transport of herbaceous or woody material did not occur. The flood increased leaf breakdown rates of all 4 tree species. Our measurements of litterfall, leaf breakdown, and floodplain litter standing crop suggest that leaves entrained from the floodplain of Little Tennessee River during floods are a source of POM to the active channel. However, flood input of leaves to the river were a small source of POM compared to direct leaffall