The Right-Skewed Distribution of Fine-Root Size in Three Temperate Forests in Northeastern China.

Cunguo Wang,Wei Guo,Junni Wang,Zhenzhen Geng,Ivano Brunner,Mai-He Li,Xiuyun Yang,Shijie Han,Zhijie Chen

doi:10.3389/fpls.2021.772463

Abstract

Trees can build fine-root systems with high variation in root size (e.g., fine-root diameter) and root number (e.g., branching pattern) to optimize belowground resource acquisition in forest ecosystems. Compared with leaves, which are visible above ground, information about the distribution and inequality of fine-root size and about key associations between fine-root size and number is still limited. We collected 27,573 first-order fine-roots growing out of 3,848 second-order fine-roots, covering 51 tree species in three temperate forests (Changbai Mountain, CBS; Xianrendong, XRD; and Maoershan, MES) in Northeastern China. We investigated the distribution and inequality of fine-root length, diameter and area (fine-root size), and their trade-off with fine-root branching intensity and ratio (fine-root number). Our results showed a strong right-skewed distribution in first-order fine-root size across various tree species. Unimodal frequency distributions were observed in all three of the sampled forests for first-order fine-root length and area and in CBS and XRD for first-order fine-root diameter, whereas a marked bimodal frequency distribution of first-order fine-root diameter appeared in MES. Moreover, XRD had the highest and MES had the lowest inequality values (Gini coefficients) in first-order fine-root diameter. First-order fine-root size showed a consistently linear decline with increasing root number. Our findings suggest a common right-skewed distribution with unimodality or bimodality of fine-root size and a generalized trade-off between fine-root size and number across the temperate tree species. Our results will greatly improve our thorough understanding of the belowground resource acquisition strategies of temperate trees and forests.

Highlights

Fine roots play a critical role in resource absorption because they are metabolic hotspots associated with symbiotic mycorrhizal fungi (Zadworny and Eissenstat, 2011; McCormack et al, 2020; Kong et al, 2021)
The positive skewness indicated that the distributions of first- and second-order fine-root size were rightskewed for almost all species, with a systematic right-hand tail of the distributions (Supplementary Table 2 and Supplementary Figures 1–3)
Based on a large dataset of 27,573 individual first-order fine roots from three temperate forest ecosystems in Northeastern China, we explored the size distribution pattern of fine roots and their relationships with fine-root number

Summary

Introduction

Fine roots play a critical role in resource absorption because they are metabolic hotspots associated with symbiotic mycorrhizal fungi (Zadworny and Eissenstat, 2011; McCormack et al, 2020; Kong et al, 2021). Their size (e.g., the diameter of first-order roots) profoundly influences a variety of eco-physiological processes such as lifespan, mortality and decomposition Variation in the length and diameter of fine roots within a root system can be considered a strategy to reduce ecological niche overlap (e.g., root lifespan overlap) and competition between individual roots, resulting in the exploration of a greater volume of soil (Pagès et al, 1993; Pregitzer et al, 2002)

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