Effect of dry-wet cycles on carbon dioxide release from two different volcanic ash soils in a Japanese temperate forest

Abstract

In the present study, two volcanic ash soils (soil A and B) from a temperate broad-leaved forest in eastern Japan were aerobically incubated under repeated dry-wet cycles and continuously constant moisture conditions. The primary aims were to quantify the potential for enhancement of carbon dioxide (CO 2 ) release owing to increased water fluctuation and to examine differences in the responses of volcanic ash soils with different physicochemical properties. Soil B, rather than soil A, was a typical Andosol. During incubation at 20°C for 120 days with five dry-wet cycles, the CO 2 release rate was measured periodically. Abundance of the stable carbon isotope in CO 2 (δ 13 C-CO 2 ) was measured to capture changes in the origin of decomposed soil organic matter (SOM) owing to the dry-wet cycles. The CO 2 release rate under the dry-wet cycles was up to 49% higher than the values predicted from a parabolic relationship between CO 2 release and water content during incubation under the continuously constant moisture condition. The magnitude of CO 2 release enhancement was 2.7-fold higher in soil B relative to that in soil A. The δ 13 C-CO 2 value in the dry-wet cycles was enriched by 0.3-2.3‰ compared to that during incubation under the continuously constant moisture conditions, suggesting that the decomposition of well-metabolized and/or old SOM was enhanced by the dry-wet cycles. Thus, the present study suggests that Andosols, which have been believed to have a strong SOM stabilization ability, are vulnerable to dry-wet cycles. Then, increased water fluctuation in a future warmer world would have significant potential to stimulate CO 2 release from soils.

Comprehensive increase in CO2 release by drying-rewetting cycles among Japanese forests and pastureland soils and exploring predictors of increasing magnitude

“…Using two Luvisols from French long-term field experiment sites, Kpemoua et al (2023) also showed similar features of changes in CO 2 release associated with DWCs, indicating the need for further comparison of CO 2 release between DWCs and constant moisture conditions with the same mean water content. In contrast to these studies, Nagano et al (2019) found a 49% increase in CO 2 release rate associated with DWCs in an Andisol collected from a Japanese forest, and this increase was more than double that of another non-volcanic ash soil from the same forest. Therefore, there are substantial variations in trends of effects of DWCs in comparison with constant moisture conditions with the same mean water content during incubation, and knowledge gaps remain about environmental and soil predictors for variations in effect sizes.…”

“…We collected 10 soil samples from depths of 0-5 cm or 0-10 cm in six forests and a pastureland located in Niigata (six soils from four forests), Ibaraki (two soils from a forest) (Nagano et al, 2019), and Oita (two soils from a forest and a pastureland) (Wijesinghe et al, 2021) prefectures in Japan. Figure 1 and Table 1 present the locations and site characteristics, i.e., elevation, mean annual temperature (MAT), mean annual precipitation (MAP), potential evapotranspiration (PET), and net primary production (NPP).…”

“…Mason jars (1.0 L volume; Ball, Buffalo, NY, USA) with lids equipped with tube fitting systems for gas sample collection (Koarashi et al, 2012;Nagano et al, 2019) were used as incubation jars. Small vials (300 mL, SM sample glass vial; Sansyo, Tokyo, Japan) containing 5.31-10.63 g of soil sample depending on water content were placed in Mason jars.…”

“…Carbon dioxide (CO 2 ) release from soil is an ecosystem process that is sensitive to DWCs (Birch, 1958;Borken and Matzner, 2009;Lee et al, 2002;Nagano et al, 2019;Unger et al, 2010Unger et al, , 2012Zhang et al, 2020Zhang et al, , 2023) and has substantial feedback potential to the ongoing climate change due to its magnitude reaching as much as seven times greater than anthropogenic CO 2 emission on a global scale (Bond-Lamberty and Thomson, 2010;Friedlingstein et al, 2020). The effects of DWCs on soil CO 2 release were first shown by Birch (1958) as the marked increase in soil organic matter (SOM) decomposition and CO 2 release after the rapid rewetting of dried soil, and has since been the subject of intensive investigation (Borken and Matzner, 2009;Kpemoua et al, 2023;Lee et al, 2002Lee et al, , 2004Miller et al, 2005;Nagano et al, 2019;Unger et al, 2010Unger et al, , 2012Xiang et al, 2008), including meta-analyses (Kim et al, 2012;Jin et al, 2023;Zhang et al, 2020). However, it is still difficult to precisely quantify and predict the effects of DWCs on soil CO 2 release.…”

Stable C and N isotope abundances in water-extractable organic matter from air-dried soils as potential indices of microbially utilized organic matter

“…These soils were originally sampled to investigate the environmental distribution of radioactive cesium that was affected by the Fukushima nuclear accident (Atarashi-Andoh et al, 2021) and have been stored in air-dried conditions. The soils were heterogeneously affected by volcanic ash during their development, with various physiochemical and mineralogical properties and C dynamics within a single water catchment (Suzuki, 2002;Nagano et al, 2019). Assuming that WEOM from air-dried soils was derived from soil microbial bodies (Marumoto et al, 1977(Marumoto et al, , 1982Marumoto, 1984;Unger et al, 2010Unger et al, , 2012Kaiser et al, 2015), we expected that the enrichments of 13 C and 15 N in WEOM relative to the bulk soils would be correlated with the concentrations of organomineral complexes and short-range order minerals (non-crystalline oxyhydroxides of aluminum and iron, allophane, imogolite, and allophane-like constituents; Imaya et al, 2007), which likely control the SOM stability and thus their availability to soil microbes (Johnson et al, 1995;Baldock and Skjemstad, 2000;Asano and Wagai, 2014;Takahashi and Dahlgren, 2016;Rasmussen et al, 2018;Wagai et al, 2018).…”