Herbivore trampling as an alternative pathway for explaining differences in nitrogen mineralization in moist...

Area of Science:

• Ecology
• Soil Science
• Biogeochemistry

Background:

• Large herbivores influence nitrogen cycling in grasslands, with effects varying by soil fertility.
• Recent findings indicate herbivores can reduce nitrogen mineralization in some fertile soils, prompting further investigation.

Purpose of the Study:

• To test the hypothesis that large herbivores affect nitrogen mineralization based on soil texture.
• To elucidate the mechanisms behind herbivore impacts on nitrogen mineralization in different soil types.

Main Methods:

• A 37-year field experiment on a salt marsh comparing herbivore-grazed and hand-mown treatments.
• Analysis of nitrogen mineralization rates, soil physical properties (compaction, water-filled porosity, redox potential), and soil macrofauna abundance.
• Investigation of decomposition activity in clay and sandy soil types.

Main Results:

• Herbivore presence decreased nitrogen mineralization in clay soil but not in sandy soil.
• Differences were attributed to herbivore-induced soil physical changes, not biomass removal.
• Clay soils showed increased water-filled porosity, negative redox potentials, reduced macrofauna, and lower decomposition under grazing.

Conclusions:

• Soil texture is a critical factor in understanding herbivore effects on nitrogen mineralization.
• Herbivore impacts are mediated by soil compaction, leading to anoxia and reduced decomposition in clay soils.
• Soil moisture and macrofauna dynamics are essential components of herbivore-ecosystem interactions.