Phosphorus

About: Phosphorus is a research topic. Over the lifetime, 53120 publications have been published within this topic receiving 939731 citations. The topic is also known as: element 15 & P.

Phosphorus Limitation of Coastal Ecosystem Processes

Abstract: Primary production in coastal wetlands is conventionally thought to be limited by nitrogen. Although the plant community in a pristine salt marsh was found to be limited primarily by nitrogen availability, the bacterial community in the soil was limited by phosphorus. Hence, in coastal wetlands, and possibly in many ecosystems, individual trophic groups may respond differently to nitrogen and phosphorus loading. Phosphorus limitation of the growth of nitrogen-transforming bacteria will affect carbon fixation, storage, and release mediated by plants, a result that has important implications for ecosystem management.

Agricultural Phosphorus and Eutrophication

Abstract: Sharpley, A.N., T. Daniel, T. Sims, J. Lemunyon, R. Stevens, and R. Parry. 1999. Agricultural Phosphorus and Eutrophication. U.S. Department of Agriculture, Agricultural Research Service, ARS–149, 42 pp. Inputs of phosphorus (P) are essential for profitable crop and animal agriculture. However, P export in watershed runoff can accelerate the eutrophication of receiving fresh waters. The rapid growth and intensification of crop and animal farming in many areas has created regional imbalances in P inputs in feed and fertilizer and P output in farm produce. In many of these areas, soil P has built up to levels in excess of crop needs and now has the potential to enrich surface runoff with P. The overall goal of efforts to reduce P losses from agriculture to water should be to increase P use efficiency, balance P inputs in feed and fertilizer into a watershed with P output in crop and animal produce, and manage the level of P in the soil. Reducing P loss in agricultural runoff may be brought about by source and transport control strategies. This includes refining feed rations, using feed additives to increase P absorption by animals, moving manure from surplus to deficit areas, finding alternative uses for manure, and targeting conservation practices, such as reduced tillage, buffer strips, and cover crops, to critical areas of P export from a watershed. In these critical areas high P soils coincide with parts of the landscape where surface runoff and erosion potential are high.

P limitation of heterotrophic bacteria and phytoplankton in the northwest Mediterranean

Abstract: Surface-water microbial populations were investigated in the northwest Mediterranean for possible indicators of phosphate deficiency and limitation. Low phosphorus availability was suggested by short turnover time (min. observed 0.68 h), high-alkaline phosphatase activity (V,,,,, = 28 nM hydrolyzed h-l), subsaturation of phosphate uptake (2.6-9% of V,,,), and high-pulse uptake capacity of added orthophosphate. Based on high pulse uptake capacity and subsaturated uptake in both the >l-pm and in the 0.2-l-pm size fractions, P deficiency is suggested for both phytoplankton and heterotrophic bacteria. P limitation of heterotrophic bacteria was also supported by fast positive responses after phosphate addition in both thymidine incorporation in whole-water samples and increased bacterial cell numbers in predator-free water. No effects were found after addition of carbon or nitrogen sources alone. Combined with other published evidence, we suggest that the growth rates of not only phytoplankton, but also of heterotrophic bacteria, are P limited in this environment in summer. The finding has important implications for the dynamics of accumulation of dissolved organic carbon in the photic zone and thus for the carbon cycle of oceans. The generally oligotrophic state of the Mediterranean Sea has traditionally been explained as a consequence of its antiestuarine circulation; the net evaporation from the Mediterranean produces an inflow of low-nutrient surface water through the Gibraltar and an eastward surface current in the Mediterranean (Redfield et al. 1963). If one combines an assumption of nitrogen-limited growth in the inflowing Atlantic water with the usual assumption of a faster recycling of phosphorus than of nitrogen, one might expect a strong nitrogen limitation in the upper photic zone during Mediterranean summer stratification. Contrary to such an expectation, accumulated experimental data seem to indicate that parts of the Mediterranean are characterized by a nitrate : phosphate ratio below Redfield (Krom et al. 1991). This seems to be particularly prominent in the eastern parts of the Mediterranean (Krom et al. 1991) and in the Adriatic Sea (Vukadin and Stojanski 1976). In an investigation of orthophosphate uptake in surface water from Villefranche Bay on the French Mediterranean coast, Dolan et al. (1995) found relatively short turnover times (down to 1.6 h). Estimates of bioavailable orthophosphate concentrations in this area (Thingstad et al. 1995) are also very low (0.8 nM), indicating, but not proving, that P may be the limiting nutrient also in this part of the western Mediterranean. The underlying biogeochemical mechanisms behind such an apparent shift toward P deficiency seem still to be unknown,