Laboratory analysis of the effects of elevated atmospheric carbon dioxide on respiration in biological soil crusts

摘要

Metabolic activity of Biological Soil Crusts (BSCs) is principally dependent on moisture availability, but also on temperature and light conditions. Less understood is how BSCs respond to elevated atmospheric CO_2. This paper reports laboratory experimental results of elevated atmospheric CO_2 on carbon fluxes for cyanobacterial BSCs. The study uses newly designed dynamic gas exchange chambers in which the internal atmosphere was controlled. CO_2 flux was monitored during controlled experiments in two phases under simulated rainfall events (2 & 5 mm plus control with no wetting) each lasting 3 days with a dry period in between. Phase 1 subjected crusts to 392 ppm CO_2 (representing ambient level) in dry air; in phase 2, the CO_2 concentration was 801 ppm. Both phases exhibited significant efflux (respiration) of CO_2 immediately after wetting, followed by substantial influx (sequestration) of CO_2. Samples subject to 2 mm wetting sequestered an order of magnitude more C under elevated CO_2 than at ambient CO_2; for samples subject to 5 mm wetting, this increase was threefold. The findings highlight the role of BSCs in future carbon budgets by enabling greater sequestration into dryland soils even under enhanced atmospheric CO_2 concentrations, following both light and heavy rainfall events.