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Productivity and biogeochemistry of two contrasting floodplain forests.
Schilling, Erik*,1, Lockaby, Graeme1, 1 School of Forestry and Wildlife Sciences, Auburn, Alabama, USA
ABSTRACT- Nutrient circulation patterns were examined to provide insight into the nature and driving forces behind the variation in production observed within floodplain forests. Located in Georgia, USA, the Satilla River floodplain (SAT), an oligotrophic, blackwater river system, and the Altamaha River floodplain (ALT), a eutrophic, redwater river system, represent geochemical and biogeochemical contrasts typical of many Southeastern floodplain forests. Measurements of aboveground net primary production (ANPP), litterfall nutrient contents, and resorption proficiencies were made in 1999 and 2000 within plots covering a range of topographic positions across both floodplains. A greenhouse fertilization experiment was also used to examine seedling growth responses to N and P additions. For the ALT, ANPP (2-yr mean = 10.9 Mg ha-1 yr-1) exceeded the SAT by 2 Mg ha-1 yr-1. Litterfall production within the SAT and ALT averaged 5.3 and 5.7 Mg ha-1 yr-1, respectively. Slightly larger amounts of N circulated through litterfall on the SAT (40 kg ha-1 yr-1) compared to the ALT (37 kg ha-1 yr-1); however, P circulation in litterfall on the SAT (4.0 kg ha-1 yr-1) was more conservative than the ALT (8.0 kg ha-1 yr-1). The relationship between litterfall mass and litterfall P content, coupled with efficient P circulation, highly proficient P resorption, and growth responses to P fertilization suggest P limitation on the SAT. On the ALT, litterfall N/P ratios (<6.0), efficient N circulation, and proficient N resorption suggest N limitation. SAT base cation circulation patterns suggest low circulation and high efficiency of use for Ca and K compared to the ALT. Conversely, the ALT displayed low Mg circulation and high use efficiency. Relationships between productivity and nutrient circulation from these two systems appear to be strongly driven by differences in P availability and suggest that a broader array of nutrients limit productivity in oligotrophic compared to eutrophic floodplain forests.
Key words: floodplain, productivity, nitrogen , phosphorus