Namib Desert primary productivity is driven by cryptic microbial community N-fixation.

Area of Science:

• Dryland Ecology
• Biogeochemistry
• Microbial Ecology

Background:

• Drylands typically exhibit low carbon exchange.
• Rainfall events create temporary carbon sinks in drylands.
• Nitrogen availability limits carbon uptake during these wet anomalies.

Purpose of the Study:

• Investigate the source of nitrogen supporting plant productivity in the Namib Desert after rainfall.
• Determine the role of hypolithic communities in the desert's nitrogen budget.
• Assess the contribution of hypolithic nitrogen fixation to primary productivity.

Main Methods:

• Measured stable nitrogen isotope (δ15N) values in hypolithic biomass, soil, and surface/subsurface soils over three years.
• Compared hypolithic biomass and soil organic matter characteristics.
• Analyzed data across dune and gravel plain biotopes.

Main Results:

• Hypolithic communities exhibited significantly higher biomass compared to soil organic matter.
• Hypolithic biomass showed lower δ15N values than soil organic matter.
• Observed δ15N values in hypoliths approached theoretical values for nitrogen fixation.

Conclusions:

• Photoautotrophic hypolithic communities are the primary source of nitrogen for plant productivity following rain events in the Namib Desert.
• These communities are foundational to the desert's carbon sink capacity.
• Hypolithic nitrogen fixation likely plays a significant role in other arid ecosystems globally.