PARENT SESSION
Oral Session # 68: Soil Ecology I: Communities, Respiration, and Nutrient Cycling.
Presiding: C Rumbaitis-del Rio
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 106.
Nitrogen retention and hydrological loss in intact soil cores during a 24-week lab incubation.
Zhu, Weixing*,1, Zhang, Tao1, 1 Binghamton University, Binghamton, New York, USA
ABSTRACT- Forests have been found retaining N inputs from human activities in many parts of the world. Studies in the past decade suggest that soil is the largest N-sink, through possible mechanisms of microbial immobilization, organic matter accumulation, and abiotic retention. We tested N retention in intact soil cores collected from forest patches along an urban-rural gradient in the New York City metropolitan area. We hypothesized that higher nitrification found in urban soils would lead to higher N-loss and less N-retention. We also tested the hypothesis that leaf litter with different C-to-N ratios would retain N differently, by adding sugar maple and red oak litters to respective soil cores. Cores were leached weekly with a 2-cm simulated rain containing 2 mg/L NH4-N and NO3-N. Inorganic-N export increased linearly during the first 12 weeks and soils quickly shifted from net N-sinks to net N-sources. By the end of the 12th week, mean NH4-N in leachate reached 4.4 mg/L and mean NO3-N 23.9 mg/L. Urban soils had much higher NO3 export than the rural soils. We found, however, no litter effort on N retention. From weeks 13 to 20, we added 100 mg/L labile carbon to 60% of the soil cores, and in the last 4 weeks, created temporarily hydrological retention on these C-amended cores. We found neither carbon addition, nor hydrological retention, had affected N-export. The cumulative net N-exports in this 24-week lab incubation spanned from 0.5 to 15.1 g m-2 and were positively correlated to the previous field measurements of net N mineralization and nitrification rates. The large hydrological loss of inorganic-N from these intact soil cores suggests that retention mechanisms based on short-term soil studies need to be examined carefully in the context of a functional ecosystem containing live plants and plant-soil interactions.
Key words: soil, leaching, nitrogen retention, incubation