Nitrogen-mediated effects of elevated CO₂ on intra-aggregate soil pore structure

Area of Science:

• Soil Science
• Ecology
• Biogeochemistry

Background:

• Soil pore structure critically influences water retention, affected by plant and microbial dynamics.
• Interactions between nitrogen (N) availability and elevated atmospheric CO2 (eCO2) on soil biota are known, but their impact on soil structure and water retention is unclear.

Purpose of the Study:

• To investigate how factorial additions of N and eCO2 affect soil pore structure and water retention in a long-term experiment.
• To understand the role of biotic factors in mediating these structural changes.

Main Methods:

• Analysis of soil aggregate fractal properties using 3D microtomographic imagery.
• Long-term field experiment with factorial N and eCO2 treatments on a sandy loam soil with Paspalum notatum.

Main Results:

• N fertilization increased intra-aggregate porosity and pore space in larger aggregates, an effect amplified by eCO2, leading to higher water retention near the wilting point.
• eCO2 alone reduced pore space in larger aggregates, decreasing water retention.
• Observed structural changes were linked to organic matter dynamics.

Conclusions:

• Rising atmospheric CO2 concentrations may induce N-dependent changes in soil pore structure, impacting global water balance, carbon storage, and rhizosphere functions.
• Understanding these soil structural shifts is crucial for predicting ecosystem responses to climate change.