Land-use type affects N₂O production pathways in subtropical acidic soils

Area of Science:

• Environmental Science
• Soil Science
• Agricultural Science

Background:

• Land-use change, particularly from woodland to crop production, is a known driver of increased nitrous oxide (N₂O) emissions.
• Understanding the specific N₂O production pathways in different soil types and land-use systems is essential for developing effective mitigation strategies.
• Southeast China's subtropical acidic soils represent a significant agricultural region where N₂O emissions warrant detailed investigation.

Purpose of the Study:

• To investigate the impact of five distinct land-use types (shrub land, eucalyptus plantation, sweet potato farmland, citrus orchard, vegetable farmland) on N₂O emissions.
• To identify the dominant N₂O production pathways (autotrophic nitrification, heterotrophic nitrification, denitrification) under each land-use scenario.
• To correlate N₂O emission rates and pathway contributions with soil properties like nitrification rates, nitrate content, and C:N ratios.

Main Methods:

• Soil samples were collected from five different land-use types in southeast China.
• A stable isotope experiment using ¹⁵N-labeled ammonium nitrate was conducted to trace N₂O production pathways.
• Soils were incubated at 60% water holding capacity to simulate environmental conditions and measure N₂O emissions.

Main Results:

• Vegetable farmland (VE), citrus orchard (CO), and sweet potato farmland (SP) exhibited significantly higher average N₂O emission rates (5.30, 4.23, 3.36 µg N kg^-1 dry soil d^-1) compared to shrub land (SB) and eucalyptus plantation (ET) (0.98, 1.10 µg N kg^-1 dry soil d^-1).
• Heterotrophic nitrification dominated N₂O production in SB (51%) and ET (50%), while autotrophic nitrification was the primary pathway in SP (44%), CO (45%), and VE (66%).
• Denitrification was a significant N₂O source across all land uses, contributing 32-52%. N₂O emissions correlated positively with gross nitrification rates, nitrate content, and C:N ratios.

Conclusions:

• Land-use type significantly alters N₂O emission rates and the relative importance of nitrification and denitrification pathways in subtropical acidic soils.
• Agricultural land uses, particularly vegetable and citrus farming, are associated with higher N₂O emissions driven by autotrophic nitrification.
• Understanding these land-use specific pathways is crucial for developing targeted strategies to mitigate nitrous oxide emissions from agricultural soils.