| 英文摘要: | Essential services performed by Earth's ecosystems, such as decomposing detritus into nutrients, transforming plants into meat, creating and aerating fertile soil, arise from the combined actions of millions of organisms. Each of these organisms, from bacteria to butterflies to bison, best contribute to these services when they consume a healthy diet, which includes access to minerals, especially sodium. Sodium is a critical mineral for ecosystems because plants are generally low in sodium but the things that eat them, from fungi to grasshoppers, require it to grow and reproduce. Thus every plant eater must search out, harvest, and hang onto quantities of sodium, and will go to extremes eating carcasses, soil, and urine, to get that quota. Moreover, sodium is not uniformly distributed on the landscape. It falls as dilute ocean water near the coasts, it clings to clay soils but is leached from sandy soils, and it is distributed by the truckload to keep snowy roads free from ice. This project combines these two facts, that sodium is potentially one of the most important drivers of the health of plant consumers, and that sodium is geographically patchy, to predict the abundance and services of plant consumers across the North American continent. This research should lead to better prediction of such disparate phenomena as why grasshoppers are bigger crop pests in one county than another; why carbon is better stored in inland soils than those near the ocean; and why termite damage claims are centered along the Gulf Coast of the U.S. and up into the Mid-Atlantic states.
To evaluate this proposition, the project combines two methods. The first maps the distribution of sodium across and within North American ecosystems and focuses on the easily accessible and widespread grasslands, old fields, and roadsides, and the invertebrates that live in them. The goal in Year 1 is to explore the basic hypothesis that as soil supplies of sodium increase - due to deposition from the ocean, high clay content, or because they are salted every winter - plants will not be affected but the animals that eat them (and the predators that eat the plant consumers) will. Thus the first year will generate a map of the abundance and activity of invertebrates above and belowground, and the degree to which both track sodium supply (and other nutrients). Then, in Year 2 and 3, these correlations will be put to the test experimentally in 6 grasslands from the central and eastern U.S. At each grassland, 50 meter square plots will be fertilized with a dilute sodium concentrations mimicking the slightly salty rainfall of the island of Puerto Rico; smaller plots will receive sodium mimicking that deposited on a regular basis by every animal as urine. By carefully tracking where the sodium goes, and how it boosts the numbers and activity of invertebrates, the project will test how animal health and vigor across North America is influenced by sodium supply. By examining how pollinators, herbivores, and detritivores respond, the project will test the transformative idea that sodium is a catalyst for ecosystem services. |