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Title: Net primary productivity question Post by: ppk on May 6, 2011 You have been monitoring the net primary productivity (NPP) of a grassland area for several years. Over the years, NPP increased initially and then leveled off. You suspect that the availability of a nutrient is limiting productivity.
a. Design an experiment to determine whether there is a limiting nutrient. b. Given your design, what results would you expect if only one of the nutrients you test is limiting? c. What results would you expect if more than one of the nutrients are limiting? Would this affect your design in any way? d. What factor(s) other than nutrient limitation might cause NPP to level off? Title: Re: Net primary productivity question Post by: robertling on May 6, 2011 (a) To test whether a particular nutrient is limiting NPP, you could subdivide the area into a number of smaller plots. Treat some plots by adding more of the nutrient, and leave others untreated. Then measure the NPP produced on each type of plot. If the nutrient is limiting, you should find higher NPPs on treated plots than on untreated plots. You can repeat the experiment with a number of different nutrients.
(b) If your test plots are each set up to test addition of a single nutrient, you would expect to see an increase in growth only on the plot supplemented with the limiting nutrient. (c) If your test plots are each set up to test addition of a single nutrient, you would likely see no difference in growth across all plots if more than one nutrient is limiting. At this point you could start testing combinations of nutrients or other factors (see d below). (d) Among other things, plant growth can be limited by water availability, physical or chemical conditions related to the density of plants per unit area, and the presence or absence of symbiotic mycorrhizal fungi. |