Nutrient limitation of bacterial production in clear water Amazonian ecosystems

The aim of this research was to determine the main limiting nutrient ( carbon, nitrogen or phosphorus) to bacterial production in different clear water Amazonian ecosystems during the high water period, when there is influence of the flooded land, mainly as sources of organic matter. Five stations were sampled in three clear water ecosystems: Trombetas River, Lake Batata and Carana Stream. We estimated in each station the nutrient concentration, bacterial production and bacterial abundance. The experiment was set up with GF/ F filtered water from all stations together with additions of glucose ( 400 muM C), KNO3 ( 15 muM N) and KH2PO4 ( 5 muM P) in accordance with each treatment ( C, N, P, CN, CP, NP, CNP and no amends). Bacterial production was estimated after 24 h of incubation. We observed that the values of bacterial production after additions of phosphate alone ( P treatment) were 2- to 6- fold greater than the values measured in control flasks. Additions of nitrate ( N treatment) and glucose alone ( C treatment) had no effect on the bacterial production in four out of five ecosystems studied. However, additions of glucose with phosphate ( CP treatment) strongly stimulated bacterial production in all ecosystems studied, including treatments with phosphate addition only. We conclude that phosphorus is the main limiting nutrient to bacterioplankton production in these clear water Amazonian ecosystems during the high water period. In addition, we conclude that, together with phosphorus, additions of glucose stimulated the bacterial production mainly due to the low quality of the carbon pool present in these ecosystems.