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N2 (C2 H2 )ASE ACTIVITY BY ALNUS INCANA SSP. RUGOSA (BETULACEAE) IN THE NORTHERN HARDWOOD FOREST.
Patricia D Younger1, Lawrence A Kapustka1
1Department of Botany, Miami University, Oxford, Ohio, 45056.
American Journal of Botany
|August 25, 2018
Summary
Nitrogen fixation rates, measured by nitrogenase (N2 (C2 H2 )ase) activity, were significantly higher in alder stands compared to mixed alder-aspen stands. This difference is attributed to factors like nitrogen feedback inhibition and allelochemic interference.
Area of Science:
- Plant Ecology
- Biogeochemistry
- Nitrogen Cycling
Background:
- Nitrogenase (N2 (C2 H2 )ase) activity is crucial for biological nitrogen fixation in symbiotic plant-microbe associations.
- Understanding factors influencing nitrogenase activity in different forest ecosystems is vital for assessing nitrogen input and nutrient cycling.
Purpose of the Study:
- To compare field nitrogenase activity and nitrogen influx between pure alder and mixed alder-aspen stands.
- To investigate the influence of plant size and environmental factors on nitrogen fixation rates.
- To explore potential reasons for observed differences in nitrogen fixation between the two stand types.
Main Methods:
- Field assays of intact nodules were conducted to measure nitrogenase (N2 (C2 H2 )ase) activity.
- Assays were performed diurnally and seasonally across different nodule sizes and plant size classes.
- Nitrogen influx was calculated based on measured nitrogenase activity and nodule biomass.
Main Results:
- Alder stands exhibited significantly higher seasonal mean nitrogen influx (26.70 μg N g-1 hr-1) compared to alder-aspen stands (14.63 μg N g-1 hr-1).
- Smaller shrub size classes showed significantly higher nitrogenase activity than medium or large classes.
- Seasonal N influx was substantially greater in alder stands (4.69 kg ha-1) versus alder-aspen stands (0.84 kg ha-1).
Conclusions:
- Pure alder stands support higher rates of biological nitrogen fixation than mixed alder-aspen stands.
- Nitrogen feedback inhibition and allelochemic interference from aspen are proposed as key factors limiting nitrogen fixation in mixed stands.
- Plant size and nodule characteristics play a significant role in modulating nitrogenase activity and overall nitrogen input.
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