Inter-annual variation of soil respiration and its spatial heterogeneity in a cool-temperate young larch plantation in northern Japan

To understand the magnitudes of temporal variation in soil respiration (Rs) and its spatial heterogeneity, and the effect of abiotic and biotic factors to cause the variation in a young plantation recovering after the clear-cutting of a mature forest, we analyzed 8 year Rs, microclimate, and vegetation data obtained in a young hybrid larch plantation with dense undergrowth of dwarf bamboo Sasa in northern Japan during snow-free periods from 2004 to 2014. Rs was measured by a multichannel automated chamber system and was resolved into two components, temperature sensitivity of respiration, Q10, and temperature-normalized basal respiration at 10°C, R10. Volumetric soil water content affects both seasonal and inter-annual variation of Rs by suppressing R10, whereas soil temperature affects only its seasonal variation. Vegetation recovery had significant effect on both temporal variation and spatial heterogeneity in Rs, although the tree and undergrowth Sasa had different contribution to these variations. Increase in the undergrowth Sasa PAI (plant area index) recovering after clear-cutting increased the Rs through the increase in Q10, whereas the spatial heterogeneity in Rs was increased by the increase in the tree PAI through the increase in R10. These results reveal that the soil water and vegetation has strong effect on the inter-annual variation of Rs and its spatial heterogeneity in the recovering young plantation, in spite of the strong exponential relationship of Rs with Ts in their seasonal variation. Although our results were obtained under the limited range in the inter-annual variation in seasonal mean Ts (< 2°C), this may not be the unique case only in our study site and gives us a caution when predicting Rs in future warmer environment.