CONSEQUENCES OF NITROGEN ADDITIONS FOR SOIL PROCESSES AND SOLUTION LOSSES FROM WET TROPICAL FORESTS

摘要: Wet tropical forests growing on highly weathered soil, depleted in rock- derived nutrients, yet rich nitrogen (N), may respond quite differently to anthropogenic N inputs than those younger soils low N. We evaluated the effects of first- time and long-term additions pattern regulation hydrologic losses from wet located at extreme ends a soil age fertility gradient Hawaiian Islands. In contrast our expectations that N-limited forest 300-year-old would initially retain inputs, both forests, regardless or fertility, responded first-time with immediate significantly elevated nitrate (NO3 ) solution losses. However, patterns NO3 loss differed markedly between sites largely reflected differences hydrological processes due age. young soils, previously unfertilized resulted significant microbial immobilization ammonium (NH4) small as NH4, whereas added appeared be free move solution. Nitrogen N-fertilized (13 years) increased rates nitrification, were similar total during period. Poor development, therefore hydraulic resistance, was critical factor determining NO3-retention capacity soils. contrast, N-rich 4.1-million-year-old but more delayed lower The old, developed offered greater resistance leaching High anion exchange (AEC) subsurface clay horizon old also delay Our findings suggest responses tropics will vary function age, nutrient status, form added, chemical physical mechanisms important biological ones controlling While re- tention determined by strength biotic demand (and ability plants microbes these inputs) relative other pathways retention (cation exchange) (denitrification), properties flow paths dominant controls residence routing water nutrients. Nitrate adsorption serve an abiotic mechanism delaying onset large receiving inputs.