Solar radiation strongly influences the quantity of forest tree root exudates
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The quantity of root exudate carbon produced by Quercus crispula Blume was strongly influenced by the amount of solar radiation 1 day before collection.
We aimed to investigate seasonality in the quantity of root exudate produced, and the factors affecting exudate quantity, in mature Quercus crispula Blume trees throughout the growing season. We also aimed to understand the timespan of exudation, from production of photosynthate to release as exudate. We measured the amount of root exudate C produced by Q. crispula, as well as environmental factors including solar radiation and soil and air temperature throughout the growing season. The model best explaining the amount of exudate C, based on the lowest Akaike’s information criterion, was selected to determine the environmental factors that affect exudation. The quantity of exudates did not show clear seasonality, and instead varied widely among sampling dates. A regression model with daily solar radiation for 1 day before sample collection as the sole factor affecting the quantity of exudates was selected as the best model. Solar radiation, which fluctuated greatly among days, more strongly affected the quantity of exudates produced than factors that fluctuated seasonally, such as average temperature. Furthermore, most root exudates from Q. crispula are released within 1 day of being generated by photosynthesis, rather than over several days.
KeywordsBelowground C allocation Fine root Northern hardwood forest Quercus crispula Rhizodeposition Solar radiation
We would like to thank Chikae Iwaoka and Makoto Yasumatsu for supporting chemical analysis, Karibu Fukuzawa and the member of Forest Information Laboratory for their helpful suggestions. We also thank the staffs of Hokkaido forest research station, Field Science Education and Research Center, Kyoto University for helping with the experiments and for providing meteorological data. This study was supported by JSPS-KAKENHI (Nos. 26292085,16H04937and 17H03833).
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Conflict of interest
The authors declare that they have no conflict of interest.
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