Subsurface Nitrogen and Carbon Cycling Responses to Drought and Re-wetting at the Biosphere 2 Tropical Rainforest

Abstract:

Subsurface gas concentrations reflect dynamic and spatially heterogeneous soil processes such as nitrogen and carbon cycling, stress response, and VOC signaling. Recent advances in soil probe technology allow for subsurface gases to be quantitatively transported to sensitive, high-precision above-ground analyzers for fast (minutes) and spatially-resolved (cm) measurements.

Here we present isotopically-resolved soil N₂O, CH₄, and CO₂ measurements over a drought and rewetting period during the Water, Atmosphere and Life Dynamics (WALD) experiment at the Tropical Rainforest at Biosphere2. The resulting data reveals the value of spatial, temporal, and chemical resolution afforded by subsurface measurements coupled to trace gas analyzers. The observed trends in soil trace gases during WALD reflect an initial response to drought stress followed by rapid recovery after rainfall. Spatially-resolved rhizosphere and non-rhizosphere gas dynamics were tracked to reveal differences in N and C cycling in these regions. Depth-resolved probe measurements show a gradient in N₂O production in response to rewetting. After rewetting, an isotopically-resolved N₂O Birch Effect was observed on hour timescales, followed by “hot moments” of N₂O production. N₂O, CO₂, and CH₄ all exhibit characteristically different responses to rainfall. The resulting data provides a unique view into the response of tropical subsurface biogeochemical cycling to drought and recovery.