Effects of Vegetation Switch and Subsequent Change in Soil Invertebrate Composition on Soil Carbon Accumulation Patterns, Revealed by Radiocarbon Concentrations

Abstract

Vegetation types strongly affect soil organic carbon (SOC) accumulation in the terrestrial ecosystem through multiple factors such as litter quality and soil biodiversity. However, the roles of soil fauna in SOC accumulation remain unclear. The objectives of this study were to (1) examine how changes in litter types and soil animal communities affect SOC accumulation in continuously forested or vegetation-switched forest areas; and (2) discuss the role of soil animals in SOC accumulation in forest ecosystems. We focused on soils that have accumulated on top of a volcanic ash layer in the 268 yr since a volcanic eruption in 1739. The radiocarbon “bomb spike”' in the late 1950s and early 1960s provides a unique isotopic signature of soil carbon age. We investigated the combined effects of litter quality and soil invertebrate function on soil 14C accumulation patterns. To determine the effects of vegetation types on SOC accumulation, we selected 4 types of cool temperate forests, 2 of which had undergone a vegetation switch in about 1960 (conifer to broadleaved forest, CB; broadleaved forest to conifer, BC), and 2 that had continuous forests (conifer forest, CC; broadleaved forest, BB). The Δ14C values at depth intervals in CC were consistent with the expected bomb-14C profile. In contrast, Δ14C patterns in BB, BC, and CB differed from that of CC. Compared to CC, Δ14C values of the other sites showed relatively high 14C concentrations even in deeper soil layers, which suggests the bomb-induced 14C has been transported to a greater depth by soil animals. Current broadleaved forests (BB and CB) had higher biomass of litter-feeding invertebrates than in current coniferous forests (CC and BC). These results suggest that carbon from leaf litter was vertically translocated to deeper soil layers by the abundant soil invertebrates in broad-leaved forests. Disagreement with the expected soil profile in BC suggests that past vegetation (broadleaved forest) has affected the present SOC accumulation pattern.

Effect of vegetation switch on soil chemical properties

“…Nakai, and in the BC was hardly observed. As a basic reference for the present study, the results of Toyota et al (2010) are summarized in Table 1. Amounts of total soil C did not significantly differ among the four sites.…”

“…However, the amount of C in the O horizon was significantly lower in the current broadleaved sites (BB and CB) than in the current coniferous sites (CC and BC). Table 2 shows the biomass of soil macroinvertebrates at each site investigated by Toyota et al (2010). The total biomass of macroinvertebrates was significantly higher in the current broadleaved sites (BB and CB) than in the current coniferous sites (CC and BC).…”

“…It is interesting and important to examine the influence of bidirectional transformation (hereafter called ''vegetation switch'') on changes of soil properties in order to discuss and predict changes in soil environments after tree species changes by artificial plantations, natural disasters and climatic change or other courses in forest ecosystems. Toyota et al (2010) investigated C accumulation in the litter and soil, Á 14 C values at different soil depths, community composition of soil macroinvertebrates, and C and N stable isotope ratios of soil macroinvertebrates at vegetation switched sites. These sites consisted of a continuous broadleaved site (BB), a continuous coniferous site (CC), a coniferous site previously in broadleaved trees (BC), and a broadleaved site previously in coniferous trees (CB).…”

“…They classified three earthworm species, Metaphire hilgendorfi (Michaelsen, 1892), Amynthas yunoshimaensis (Hatai, 1930), and Amynthas vittatus (Goto and Hatai, 1898) as litter feeders (epigeic species), and one species, Eisenia japonica (Michaelsen, 1891), as a soil feeder (endogeic species) based on their C and N stable isotope ratios. Toyota et al (2010) hypothesized the following C movement in the soils at the broadleaved sites: (1) feeding of litter by the three epigeic earthworm species; (2) M. hilgendorfi drawing (bringing) C derived from the litter into the soil; and (3) movement of the C into deeper soil layers by the endogeic earthworm (E. japonica). Toyota et al (2010) reported that differences in the composition of the soil fauna as a result of vegetation switches brought change in the dynamics of soil C. However, they did not examine other soil nutrients, and consequently their study did not show the influence of the vegetation switch on general soil chemical properties.…”

“…Toyota et al (2010) hypothesized the following C movement in the soils at the broadleaved sites: (1) feeding of litter by the three epigeic earthworm species; (2) M. hilgendorfi drawing (bringing) C derived from the litter into the soil; and (3) movement of the C into deeper soil layers by the endogeic earthworm (E. japonica). Toyota et al (2010) reported that differences in the composition of the soil fauna as a result of vegetation switches brought change in the dynamics of soil C. However, they did not examine other soil nutrients, and consequently their study did not show the influence of the vegetation switch on general soil chemical properties. Therefore, in the present study we investigated chemical properties of soils that were collected at the same sites and time as those sampled by Toyota et al (2010), and discuss the effects of vegetation switch on soil chemical properties with reference to the results of Toyota et al (2010) on macroinvertebrate distribution and dynamics of soil C. We discuss the effects of vegetation switch from broadleaved to coniferous trees by comparing soils from the BC and BB, and BC and CC sites, and the switch from coniferous to broadleaved trees by comparing soils from the CB and CC, and CB and BB sites.…”