The effect of long-term CO₂ enrichment on carbon and nitrogen content of roots and soil of natural pastureland
Al-Traboulsi, Manal | Wilsey, Brian | Potvin, Catherine
Increasing levels of atmospheric CO₂ may change C and N dynamics in pasture ecosystems. The present study was conducted to examine the impact of four years of CO₂ enrichment on soil and root composition and soil N transformation in natural pastureland. Plots of open-top growth chambers were continuously injected with ambient CO₂ (350 µL L–¹) and elevated CO₂ (625 µL L–¹). Soil cores exposed to ambient and elevated CO₂ treatment were incubated and collected each year. Net N-mineralization rates in soil (NH₄⁺-N plus NO₃ˉ–-N), in addition to total C and N content (%) of soil and root tissues were measured. Results revealed that elevated CO₂ caused a significant reduction in soil NO₃ (P < 0.05), however, no significant CO₂ effect was found on total soil C and N content (%). Roots of plants grown under elevated CO₂ treatment had higher C/N ratios. Changes in root C/N ratios were driven by changes in root N concentrations as total root N content (%) was significantly reduced by 30% (P < 0.05). Overall, findings suggest that the effects of CO₂ enrichment was more noticeable on N content (%) than C content (%) of soil and roots; elevated CO₂ significantly affected soil N-mineralization and total N content (%) in roots, however, no substantial change was found in C inputs in CO₂-enriched soil.
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