Lesson 32 Mineral Cycling - Alaska Geobotany Center
Lesson 32 Mineral Cycling - Alaska Geobotany Center
Lesson 32 Mineral Cycling - Alaska Geobotany Center
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Summary of effects of nitrogen saturation in<br />
forested ecosystems<br />
• Even though Clean Air Bill intended to<br />
improve air quality, total N deposited in NE<br />
US will remain high for many years,<br />
exceeding forest outputs, resulting in N<br />
saturation, i.e. a net export of N from the<br />
system into streams and the atmosphere.<br />
• Diagram is a summary of forest nitrogen<br />
biogeochemistry trends along a gradient of<br />
increasing N saturation.<br />
• Foliar N content increases across the full<br />
gradient.<br />
• N-mineralization and NPP increase and then<br />
decline.<br />
• Ca:Al and Mg:N ratios decline along the full<br />
gradient.<br />
Increasing N saturation<br />
HFHW: Harvard forest hardwood<br />
HFP: Harvard forest pine<br />
BBW: Bear Brook stand<br />
Ascutney: Mount Ascutney transect<br />
Transect: 161 spruce-fir stands across NE US.<br />
• Nitrification and N-leaching increase from 0<br />
to high values along the gradient.<br />
• Consequences include increased emission<br />
of N 2 O, stream eutrophication, declining tree<br />
vigor, and potential loss of frost hardiness in<br />
conifers.
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