Early Stage Fine-Root Decomposition and Its Relationship with Root Order and Soil Depth in a Larix gmelinii Plantation

Tao Sun,Yuanyuan Li,Qingkui Wang,Lili Zhang,Zhengwen Wang,Zhijie Wu,Lili Dong,Hongguang Zhang

doi:10.3390/f7100234

Tao Sun, Yuanyuan Li + Show 6 more

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https://doi.org/10.3390/f7100234

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Abstract

Characterization of decomposition dynamics of fine roots is essential for understanding vegetation–soil feedbacks and predicting ecosystem responses to future climate scenarios, given their more rapid turnover rates. Using a branch-order classification, we separated the fine root systems of Larix gmelinii into two classes: first- and second-order roots combined into one (lower-order); third- and fourth-order roots combined into another (higher-order). In a field experiment, we conducted a litterbag study to investigate fine root decomposition and its relationship with root order class and soil depth over 17 months. Despite their lower C:N ratio and smaller diameter, lower-order roots decomposed more slowly compared with higher-order roots over this period. This pattern also seems to hold true at each different depths (10, 20 and 30 cm) in the soil profile. Our data suggest that the slow decomposition rate of lower-order roots may result from their poor carbon quality. Moreover, we found that the decomposition rates of both lower-order and higher-order roots decreased linearly from 10 cm to 30 cm, which implied that a substantially larger fraction of fine root mass would be stabilized as soil organic carbon in the deeper rather than the upper soil layers.

Highlights

Up to more than 50% of terrestrial net primary production is returned to the soil via the decomposition of plant tissues [1]
Initial concentrations of acid-hydrolyzable fraction and total non-structural carbohydrate (TNC) were much lower in first- and second-order roots compared with third- and fourth-order roots (p < 0.0001)
This pattern holds true across three different soil depths in a soil profile

Summary

Introduction

Up to more than 50% of terrestrial net primary production is returned to the soil via the decomposition of plant tissues [1]. Despite the fact that the dominant input of plant material into soil may be driven from the turnover of fine roots [5,6,7,8], understanding of the factors that control fine root decomposition remains limited. In global data sets of a large range of species, Silver and Miya [9] found fine root chemistry ( C:N ratio and Ca concentration) to be the factor most closely linked to root decomposition rates. Other studies suggested that the initial C:N ratio, N concentration, or Ca concentration explained no variation in fine root decomposition rates in many ecosystems [10,11,12,13,14]. Our inability to determine generalized drivers of Forests 2016, 7, 234; doi:10.3390/f7100234 www.mdpi.com/journal/forests

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