An Experimental Comparison of Two Methods on Photosynthesis Driving Soil Respiration: Girdling and Defoliation

Previous studies with different experimental methods have demonstrated that photosynthesis significantly influences soil respiration (R(S)). To compare the experimental results of different methods, R(S) after girdling and defoliation was measured in five-year-old seedlings of Fraxinus mandshurica from June to September. Girdling and defoliation significantly reduced R(S) by 33% and 25% within 4 days, and 40% and 32% within the entire treatment period, respectively. The differential response of R(S) to girdling and defoliation was a result of the over-compensation for R(S) after girdling and redistribution of stored carbon after defoliation. No significant effect on RS was observed between girdling and defoliation treatment, while the soluble sugar content in fine roots was higher in defoliation than in girdling treatment, indicating that defoliation had less compensation effect for R(S) after interrupting photosynthates supply. We confirm the close coupling of R(S) with photosynthesis and recommend defoliation for further studies to estimate the effect of photosynthesis on R(S).