Smucker,A.J.M., C. Dell, Y. Kavedir, and D. Santos
Presented at the ASM at Snowbird (2000-08-02 to 2017-12-05 )
Greater quantities of new C were deposited on the outer one-third layers than the internal regions within soil macro-aggregates. Concentric layers of soil aggregates were removed by the soil aggregate erosion (SAE) method and C sources identified by their 13C signatures. Roots of contemporary plants contributed from 46 to 80% of the total C isolated from outer soil layers. Similar C gradients could not be detected within soil aggregates sampled from adjacent native forest ecosystems. Deposition of N to soil aggregate layers was evaluated by growing a rye cover crop whose shoots were labeled with 99 % atom excess 15N as (15NH4)2SO4 and spray-killed two weeks following labeling. Three months after rye death, soil aggregates contained atom excesses of 0.014 and 0.035% 15N deposited by decomposing rye roots or roots plus shoots. Total N in the exterior layers of aggregates was 1.6, 1.4, and 1.2 g N kg-1 in treatments containing in situ rye roots, rye shoots applied to the soil surface, and bare soils. Interior regions of all soil aggregates contained an average of 1.25 g N kg-1. Observed C and N gradients demonstrate the importance of measuring concentric layers when evaluating short-term changes in the C and N dynamics associated with soil aggregates.
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