Calcium constrains plant control over forest ecosystem nitrogen cycling

Area of Science:

• Forest Ecology
• Biogeochemical Cycles
• Soil Science

Background:

• Forest ecosystem nitrogen (N) cycling is crucial for regulating reactive N and sequestering atmospheric carbon dioxide (CO2).
• Base cations, like calcium (Ca), are essential for maintaining soil fertility and nutrient cycling in forests.
• Acid rain and forest harvesting have led to the depletion of base cations in many global forest ecosystems.

Purpose of the Study:

• To investigate the role of calcium (Ca) in constraining forest ecosystem nitrogen (N) cycling.
• To evaluate the impact of Ca additions on soil N-cycling processes in the presence and absence of trees.
• To understand how Ca availability affects the capacity of forests to manage reactive N and sequester CO2.

Main Methods:

• Experimental addition of calcium (Ca) to forest soils.
• Evaluation of soil N-cycling responses, including inorganic N levels, N mineralization, microbial biomass N, and denitrification potential.
• Comparison of N-cycling responses in the presence and absence of plants (northern hardwood forest trees).

Main Results:

• In the presence of trees, Ca additions 'tightened' the ecosystem N cycle, reducing inorganic N, N mineralization, microbial biomass N, and denitrification.
• In the absence of trees, Ca additions significantly increased nitrification and inorganic N levels.
• These findings indicate that Ca availability fundamentally constrains the forest N cycle.

Conclusions:

• Forest tree capacity to absorb atmospheric N and CO2 is constrained by base cations, particularly calcium.
• Depletion of base cations due to acid rain and harvesting impairs the ability of forests to regulate N cycling.
• Maintaining adequate base cation levels is critical for forest ecosystem health and function in mitigating N pollution and climate change.