Seasonal patterns of fine root dynamics and their contribution to net primary production in hinoki cypress (Chamaecyparis obtusa) and konara oak (Quercus serrata) forests

Ji Young An,Akira Osawa

doi:10.1007/s00468-020-02030-6

Abstract

Key messageFine root and litterfall are major contributor of NPP and fine root production may reflect forest productivity in a warm-temperate forest in Japan.Forest ecosystems play an important role as the major carbon sink on land, with fine root dynamics and litterfall representing major carbon fluxes. The objectives of this research were to estimate NPP including annual fine root production values, to investigate fine root dynamics and the relationships between above– and belowground organs in konara oak (Quercus serrata) and hinoki cypress (Chamaecyparis obtusa) forests. Litterfall was collected seasonally for 1 year from June 2013. The ingrowth core method and the sequential soil core method were applied with a root litterbag experiment to estimate fine root (< 2 mm) production (FRP), mortality (FRM), and decomposition (FRD) for 1 year (from 2013 to 2014), using the continuous inflow estimate method and the simplified decision matrix. The total NPP ranged from 8.2 to 13.9 (t ha− 1 yr− 1), and the sum of aboveground litterfall and FRP accounted for 60% of the total NPP on average, confirming the significance of above- and belowground litter for the forest NPP as a source of detritus for the decomposer system. In hinoki cypress stand, fine root biomass peaked in the end of winter while fine root necromass showed the highest peak in late summer. In konara oak stand, only very fine root (< 0.05 mm) biomass and necromass demonstrated significant seasonal patterns. The seasonal patterns of fine root production did not differ between forest types and root diameter classes. We found a possible relationship between above- and belowground production and fine root production tended to be high in productive forests. This study improves our understanding of different patterns of carbon dynamics between temperate broadleaved and coniferous forest ecosystems.

Highlights

Understanding patterns of carbon dynamics in terrestrial forest ecosystems is important in the matter of climate change, because carbon fluxes between forest ecosystems and the atmosphere are closely related to changing concentration of carbon dioxide in the atmosphere (Dixon et al 1994; Fang et al 2014; Xu et al 2014)
The aboveground net primary production (NPP) (ANPP) ranged from 6.7 to 11.0 t h a−1 yr−1, which accounted for an average of 81% of the total NPP
Litterfall and fine roots, which represent major carbon fluxes in forest ecosystems, contributed about 60% of the total NPP in hinoki cypress and konara oak stands in the Ryukoku Forest, confirming the significance of above- and belowground litter for forest NPP as inputs of detritus to the decomposer system

Summary

Introduction

Understanding patterns of carbon dynamics in terrestrial forest ecosystems is important in the matter of climate change, because carbon fluxes between forest ecosystems and the atmosphere are closely related to changing concentration of carbon dioxide in the atmosphere (Dixon et al 1994; Fang et al 2014; Xu et al 2014). Variations in belowground fine root productivity have not been fully quantified across forest types while aboveground productivity has been widely compared along with an understanding of responses to changing environmental conditions (Gower et al 2001; Xiao et al 2003; Girardin and Malhi 2010; Yuan and Chen 2010a, b). It is critical to identify temporal and spatial dynamics of fine roots for understanding how plants respond to changing environment and evaluating productivity of ecosystems. Despite the recognized important role of fine roots and increasing researches on root dynamics, patterns and amount of fine root production have not been fully identified yet, resulting in highly simplified descriptions of belowground processes in models (Ostle et al 2009; Iversen 2010). We can assume that seasonal patterns of fine root production vary between forest types because of internal (e.g., genotype of plant species and species composition of forests) and external (e.g., climatic conditions, soil properties, and nutrient availability) factors (Steele et al 1997; Pregitzer et al 2000; Tierney et al 2003; Majdi et al 2005; Brassard et al 2009)

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