Primary production and nitrogen allocation of field grown sugar maples in relation to nitrogen availability |
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Authors: | J Mar Lennon John D Aber Jerry M Melillo |
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Institution: | (1) Department of Forestry, University of Wisconsin-Madison, Madison, WI 53796, USA;(2) Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA |
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Abstract: | Above ground net primary production (NPP), nitrogen (N) allocation, and retranslocation from senescing leaves were measured in 7 sugar-maple dominated sites having annual net N mineralization rates ranging from 26 to 94 kg · ha–1 · yr–1. The following responses were observed: (1) Green sun leaves on richer sites had higher N mass per unit leaf area than sun leaves on poorer sites; (2) Total canopy N varied much less than annual net mineralization, ranging from 81 to 111 kg · ha–1; (3) This was due to the existence of a large and relatively constant pool of N which was retranslocated from senescing leaves for use the following year (54 to 80 kg · ha–1); (4) The percentage of canopy N retranslocated by sugar maple was also relatively constant, but was slightly higher on the richer sites. Percent N in leaf litter did not change across the gradient; (5) Above ground NPP increased linearly in relation to N allocated above ground. Therefore, N use efficiency, expressed as above ground NPP divided by N allocated above ground was constant; (6) N use efficiency expressed as (NPP above ground/total N availability) was a curvilinear function of N availability; and (7) This pattern reflected a decreasing apparent allocation of N below ground with decreasing N availability. |
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Keywords: | Retranslocation in situ incubation canopy nitrogen nitrogen use efficiency stagnation canopy structure buried polyethylene bags |
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