Earthworm effects on soil biogeochemistry in temperate forests focusing on stable isotope tracing: a review

Abstract

Earthworms (Oligochaeta) are globally distributed soil-dwelling invertebrates that alter soil properties through feeding, casting, and burrowing behaviors. Soil physicochemical modification, which may directly influence the availability and dynamics of organic and inorganic nutrients in the soil, such as carbon and nitrogen, includes soil texture, porosity, and pH. Temperate forests produce year-round plant litter, the primary food source for earthworms, and litter processed by earthworms significantly contributes to soil organic material storage. In recent decades, studies on temperate forest ecosystems have attempted to elucidate and quantify the earthworm impact on soil organic material dynamics, mainly targeting carbon and nitrogen, using isotope analysis methods. This paper summarizes studies on the following topics: (1) effect of earthworm modification on soil property to understand these alterations’ interaction with carbon and nitrogen dynamics, and (2) isotope tracing method, used to elucidate the earthworm effect on carbon and nitrogen transformation and movements in temperate forests. The particular emphasis on the isotope method is based on its capability of time-adjusted quantification of organic materials in the ecosystem compartments. Also, isotopic labeling in biomass has a broad range of applications, such as tracing assimilated food sources, identifying trophic interactions in soil food webs, and addressing material dynamics in complex linkages between earthworms and their environment. In addition, we provide perspectives on other methodologies, such as chronology and population ecology, as feasible options to further assist the isotope tracing of earthworms’ impact on soil nutrient dynamics.

The Fate and Challenges of the Main Nutrients in Returned Straw: A Basic Review

“…In this review, we mainly focused on the qualitative description of the main destinations of straw nutrients, while quantifying their contribution has been lacking in the literature. Also, new material cycling techniques, such as molecular biology [98], gene microarray [99], and isotope tracing [100], are emerging and can provide insights on the distribution, existence patterns, and dynamic balance of different nutrients in returned straw ecosystems. Thus, examining the nutrient cycling pathways and stability mechanisms may become more feasible using these technologies.…”

Spatiotemporal Variations of Soil Reactive Nitrogen Oxide Fluxes across the Anthropogenic Landscape

“…In particular, the activities of AOA and AOB as part of the nitrification pathway have been linked to production of NO y . , Input of organic matter into soils differs between land-use types, determining the C/N ratios of dissolved organic matter (DOM) and, therefore, impacting the rates of N cycling processes . Woodland soils in particular are exposed to increased litter deposition, with the specific nature of the litter dependent upon the plant species present . As a result of decomposition of organic matter by heterotrophs, it is common for woodland soils to be relatively acidic compared to other land-use types, and excess H + protons may have consequences for pathways that lead to NO y emissions .…”

“…19 Grass-dominated soils tend to contain higher concentrations of DOM than agricultural soils but lower than woodland soils, primarily as a result of the diversity of vegetation. 18 Even more so than research on agricultural soils, reports on grass-dominated soils are focused on N 2 O emissions, and little attention is given to production of NO y gases from this landuse type. 20 In addition to higher levels of N deposition in urbanized areas, other biogeochemically active elements may be introduced to soils via anthropogenic means.…”

“…As a result of decomposition of organic matter by heterotrophs, it is common for woodland soils to be relatively acidic compared to other land-use types, and excess H + protons may have consequences for pathways that lead to NO y emissions . Grass-dominated soils tend to contain higher concentrations of DOM than agricultural soils but lower than woodland soils, primarily as a result of the diversity of vegetation . Even more so than research on agricultural soils, reports on grass-dominated soils are focused on N 2 O emissions, and little attention is given to production of NO y gases from this land-use type …”

“… 17 Woodland soils in particular are exposed to increased litter deposition, with the specific nature of the litter dependent upon the plant species present. 18 As a result of decomposition of organic matter by heterotrophs, it is common for woodland soils to be relatively acidic compared to other land-use types, and excess H + protons may have consequences for pathways that lead to NO y emissions. 19 Grass-dominated soils tend to contain higher concentrations of DOM than agricultural soils but lower than woodland soils, primarily as a result of the diversity of vegetation.…”