Photosynthate supply drives soil respiration of Fraxinus mandshurica seedlings in northeastern China: evidences from a shading and nitrogen addition experiment

Improved understanding of the link between photosynthesis and below-ground processes is needed to better understand ecosystem carbon (C) cycling and its feedback to climate change. We conducted a short-term shading and nitrogen (N) addition experiment from June to September 2013 to investigate the effect of photosynthate supply by Manchurian Ash (Fraxinus mandshurica) seedlings on soil respiration (SR). Shading significantly reduced SR in early and middle growing season, but not in late growing season, leading to a decrease in mean SR by 24 % in N-unfertilized treatments. N addition increased mean SR by 42 % in un-shaded treatment. The stimulation of SR was largely attributed to accelerated autotrophic respiration by increasing photosynthesis, leaf area index and belowground biomass. Shading reduced mean SR by 32 % in N addition treatment. The strengthened shading effect on SR resulted from N addition was because of more photosynthates supply at low soil temperature. Our findings highlight the predominance of photosynthates supply in regulating the responses of C cycling to global change.