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Title: New dual in-growth core isotopic technique to assess the root litter carbon input to the soil

item PANZACCHI, PIETRO - Free University Of Bozen-Bolzano
item GIOACCHINI, PAOLA - University Of Bologna, Italy
item Sauer, Thomas - Tom
item TONON, GUISTINO - Free University Of Bozen-Bolzano

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2016
Publication Date: 9/15/2016
Citation: Panzacchi, P., Gioacchini, P., Sauer, T.J., Tonon, G. 2016. New dual in-growth core isotopic technique to assess the root litter carbon input to the soil. Geoderma. 278:32-39. doi: 10.1016/j.geoderma.2016.05.010.

Interpretive Summary: Understanding root growth and decay is important for understanding the cylcing of soil organic matter and the amount of carbon plants store below ground. Methods to study root growth are difficult and complex. In this study, a technique called root in-growth cores (IGC) was tested for a young forest in Italy. Soil cores were removed in the forest and replaced with soil from a crop field that had no history of tree growth. Tree roots were allowed to grow into the new soil core for one year and then the soil was removed and the amount of roots measured. This method was compared with another technique based on measurements of several pools of carbon in the soil and forest components. There are advantages and disadvantages of the IGC method. First, it measures the carbon input from new roots, which is very hard to measure any other way. However, differences in soil properties between the original soil and the soil in the IGC may change the way the tree roots grow. In this study, the IGC technique provided reasonable results and values of root growth that were comparable to other studies. Precautions must be taken, however, by careful selection of the IGC soil and experimental conditions to ensure accurate results. This research is of interest to scientists and policymakers interested in climate change and methods to quantify carbon sequestration.

Technical Abstract: The root-derived carbon (C) input to the soil, whose quantification is often neglected because of methodological difficulties, is considered a crucial C flux for soil C dynamics and net ecosystem productivity (NEP) studies. In the present study, we compared two independent methods to quantify this C input to the soil in a young forest plantation in Northern Italy. Specifically, a mass balance approach applied to the soil C balance and an improved in-growth core (IGC) isotope technique accounting for both root- and non-root derived C inputs were tested and compared. No statistically significant difference between the results obtained by the two methods was found. Both estimates match with the results obtained by other authors for similar ecosystems confirming the importance of this C-flux that can account for more than 30% of net primary productivity (NPP). Finally, to properly apply the IGC isotopic technique, our results highlight, for the first time, the need to consider the changes in the isotopic signature, due to other factors other than root-derived C inputs. These include isotope discrimination that could take place during the decomposition of the original soil organic matter (SOM), the contamination due to dissolved organic carbon (DOC) leaching, or the carbon input via leaf litter. When this precaution is taken, the proposed IGC isotope technique seems to be a promising and reliable method to estimate root-derived C input to the soil in terrestrial ecosystems.