Eutrophication of lakes. Some lakes also demonstrate the reverse process (meiotrophication), becoming less nutrient rich with time. The main difference between natural and anthropogenic eutrophication is that the natural process is very slow, occurring on geological time scales. Eutrophication is a common phenomenon in coastal waters. In contrast to freshwater systems, nitrogen is more commonly the key limiting nutrient of marine waters; thus, nitrogen levels have greater importance to understanding eutrophication problems in salt water. Estuaries tend to be naturally eutrophic because land-derived nutrients are concentrated where run-off enters a confined channel. Upwelling in coastal systems also promotes increased productivity by
Plant to plant communication via mycorrhizal networks help plants in mycorrhizal networks defend themselves against attack by pathogens or herbivores, and transferred nutrients can affect growth and nutrition. Results of studies which demonstrate these modes of communication have led the authors to hypothesize mechanisms by which the transfer of these nutrients can affect the fitness of the connected plants. Plants and fungi form mutualistic symbiotic relationships called mycorrhizae, which take several forms, such as arbuscular mycorrhizae (AM) and ectomycorrhizae (ECM), and are widespread in nature. Host plants provide photosynthetically derived carbohydrates to the mycorrhizal fungi, which use them in metabolism, either for energy or to increase the