Nitrogen Addition Decreases Rhizodeposition by Chinese Fir (Cunninghamia lanceolata (Lamb.) Hook) Seedlings and Its Distribution in Soil Aggregates

Abstract

Rhizodeposition-derived carbon plays an important role in plant nutrient acquisition and soil carbon sequestration. However, how nitrogen deposition affects the distribution of rhizodeposition-derived carbon into aggregate classes (macrogagregates, microaggregates, and silt and clay) is unclear. We conducted a nitrogen addition experiment on Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) seedlings with continuously labeled 13CO2 for 120 days. Plant growth and the distribution of rhizodeposition-derived carbon into aggregate classes were assessed. Results showed that nitrogen additionconsiderably increased the ratio of aboveground to belowground biomass, but not aboveground and belowground biomass. Compared with the control, nitrogen addition resulted in a significantdecreaseby 52% inrhizodeposition-derived carbon in bulk soil.We found that more rhizodeposition-derived carbon was incorporated into macroaggregate, followed by microaggregate, and silt and clay regardless of nitrogen addition. The rhizodeposition-derived carbon was significantly decreased by 40% in macroaggregate, 60% in microaggregate, and 61% in silt and clay after nitrogen addition. Nitrogen addition and aggregate classes had no interactive effect on the rhizodeposition-derived carbon. Our results suggest that nitrogen deposition decreases the rhizodeposition of Chinese fir and its distributionin aggregate classes.