A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

SEASONAL CHANGES IN LEAF LITTER NUTRIENT CONCENTRATIONS, AND POSSIBLEIMPLICATIONS FOR NUTRIENT CYCLING AND PLANT GROWTHFlávio J. Luizão, Heraldo Vasconcelos, Claudio YanoE-mail: fluizao@inpa.gov.brSeveral studies in central Amazonia have shown litter production to be seasonal, with higherlitterfall during the dry season, when decomposition is slower. That leads to a temporaryaccumulation and growth of the litter layer on forest floor. However, it is not known the behavior ofbehavior of mineral nutrients in litter along the year. The present study aim to assess if litterconcentrations change considerably between seasons, and to suggest possible implications ofsuch changes. Two set of data from central Amazonia were used: (1) a 1-year series, gathered in1999-2000 at ZF-3 INPA-Smithsonian Institute Reserves; and (2) a 3-year data set from ZF-2 INPAReserve, collected from 1979 to 1982. Nutrient concentrations were determined monthly for theZF-2 samples and each 2-3 months for the ZF-3 samples. Concentrations of most nutrients werehigher in the dry season than in the wet season. For the 3-years period (1979-82), concentrationsof dry season were: N=19-22 g kg -1 ; P=0.36 g kg -1 ; K=1.5-2.0 g kg -1 ; Ca=3.8-4.9 g kg -1 ; S=2.1-2.3 gkg -1 ; Na=1105-1619 mg kg -1 ; B=44-64 mg kg -1 . In the wet season, these concentrations were: N=14-16 g kg -1 ; P=0.28 g kg -1 ; S=1.1 g kg -1 ; K=0.9-1.5 g kg -1 ; Ca=3.2-3.4 g kg -1 ; Na=922-943 mg kg -1 ;B= 28-37 g kg -1 . Within the same season, nutrients wich are more leachable, such as K and,especially, Na had their lowest concentrations in the first months (December-Febrruary) of the wetseason. Thus, higher nutrient concentrations coincided with higher litter production, and theopposite was also true. The lower concentrations in the wet season is likely a result of strongerleaching by rain water percolating forest canopy (internal precipitation) and washing mature, presenescentleaves. Alternatively, or additionally, it may be a result of strong nutrient retranslocationfrom mature leaves, which would allow a subsequent nutrient allocation to the young leaves,woody parts, or in the root system of the trees. That would imply in either crown, root or trunkgrowth, or all of them, during the wet season.