Topography-driven differences in soil N transformation constrain N availability in karst ecosystems.

Area of Science:

• Soil Science
• Ecology
• Biogeochemistry

Background:

• Karst ecosystems exhibit complex topography and variable vegetation, impacting nutrient cycling.
• Understanding nitrogen (N) availability and its drivers is crucial for effective vegetation restoration in these fragile environments.

Purpose of the Study:

• To identify characteristics and driving factors of soil nitrogen availability across a topographic gradient in a karst region.
• To guide vegetation restoration strategies by elucidating the role of topography in N cycling.

Main Methods:

• Collected soil and plant leaf samples along a topographic gradient (ridge, upper slope, middle slope, foot slope) in southwest China.
• Measured indicators of soil N availability, N transformation rates (mineralization, nitrification), and extracellular enzyme activities.
• Analyzed soil properties (organic matter, calcium, structure) and microbial community structure (abundance, ratios).

Main Results:

• Soil and foliar N content, along with N:P ratios, decreased significantly on steeper slopes compared to ridges.
• N-limitation of microbial growth was indicated by enzyme analyses, with vector angles decreasing with slope.
• Soil mineralization and nitrification rates declined with increasing slope, while N immobilization and adsorption increased.
• Deteriorated soil structure, reduced organic matter and calcium, altered microbial communities, and shifts in microbial ratios were key drivers.

Conclusions:

• Topography critically controls soil N availability in karst regions by regulating N transformation processes.
• Reduced N supply capacity on steeper slopes is linked to changes in soil properties and microbial communities.
• Topography must be considered a key factor influencing the functions and services of karst ecosystems.