Relationship of root biomass and soil respiration in a stand of deciduous broadleaved trees\u2014a case study in a maple tree

Jae-Seok Lee

doi:10.1186/s41610-018-0078-z

Abstract

BackgroundIn ecosystem carbon cycle studies, distinguishing between CO2 emitted by roots and by microbes remains very difficult because it is mixed before being released into the atmosphere. Currently, no method for quantifying root and microbial respiration is effective. Therefore, this study investigated the relationship between soil respiration and underground root biomass at varying distances from the tree and tested possibilities for measuring root and microbial respiration.MethodsSoil respiration was measured by the closed chamber method, in which acrylic collars were placed at regular intervals from the tree base. Measurements were made irregularly during one season, including high temperatures in summer and low temperatures in autumn; the soil’s temperature and moisture content were also collected. After measurements, roots of each plot were collected, and their dry matter biomass measured to analyze relationships between root biomass and soil respiration.ResultsApart from root biomass, which affects soil’s temperature and moisture, no other factors affecting soil respiration showed significant differences between measuring points. At each point, soil respiration showed clear seasonal variations and high exponential correlation with increasing soil temperatures. The root biomass decreased exponentially with increasing distance from the tree. The rate of soil respiration was also highly correlated exponentially with root biomass. Based on these results, the average rate of root respiration in the soil was estimated to be 34.4% (26.6~43.1%).ConclusionsIn this study, attempts were made to differentiate the root respiration rate by analyzing the distribution of root biomass and resulting changes in soil respiration. As distance from the tree increased, root biomass and soil respiration values were shown to strongly decrease exponentially. Root biomass increased logarithmically with increases in soil respiration. In addition, soil respiration and underground root biomass were logarithmically related; the calculated root-breathing rate was around 44%. This study method is applicable for determining root and microbial respiration in forest ecosystem carbon cycle research. However, more data should be collected on the distribution of root biomass and the correlated soil respiration.

Highlights

In ecosystem carbon cycle studies, distinguishing between CO2 emitted by roots and by microbes remains very difficult because it is mixed before being released into the atmosphere
The two components of soil respiration are controlled by the supply of different C sources, dead organic matter (OM) and plant photosynthates, which may respond differently to variations in soil temperature (Boone et al 1998)
Soil homogenization was performed between the measurement points to regularize the soil microbial respiration rate according to the distance to the trees

Summary

Introduction

In ecosystem carbon cycle studies, distinguishing between CO2 emitted by roots and by microbes remains very difficult because it is mixed before being released into the atmosphere. No method for quantifying root and microbial respiration is effective. This study investigated the relationship between soil respiration and underground root biomass at varying distances from the tree and tested possibilities for measuring root and microbial respiration. In forests, carbon absorbed into the ecosystem from the atmosphere is processed in several nutritional steps, and a large amount of carbon is returned to the atmosphere in the process. In estimating the net amount of carbon fixed in plants, quantifying carbon released from the underground parts is unproblematic because carbon from emission sources other than the plant can be distinguished. Carbon is released from the ground by microbial respiration processes in the soil. The two components of soil respiration are controlled by the supply of different C sources, dead organic matter (OM) and plant photosynthates, which may respond differently to variations in soil temperature (Boone et al 1998)

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