Differential Variation in Non-structural Carbohydrates in Root Branch Orders of Fraxinus mandshurica Rupr. Seedlings Across Different Drought Intensities and Soil Substrates.

Li Ji,Lijie Zhang,Zhimin Lu,Jun Wang,Yuchun Yang,Yue Liu

doi:10.3389/fpls.2021.692715

Abstract

Non-structural carbohydrates (NSCs) facilitate plant adaptation to drought stress, characterize tree growth and survival ability, and buffer against external disturbances. Previous studies have focused on the distribution and dynamics of NSCs among different plant organs under drought conditions. However, discussion about the NSC levels of fine roots in different root branch orders is limited, especially the relationship between fine root trait variation and NSC content. The objective of the study was to shed light on the synergistic variation in fine root traits and NSC content in different root branch orders under different drought and soil substrate conditions. The 2-year-old Fraxinus mandshurica Rupr. potted seedlings were planted in three different soil substrates (humus, loam, and sandy–loam soil) and subjected to four drought intensities (CK, mild drought, moderate drought, and severe drought) for 2 months. With increasing drought intensity, the biomass of fine roots decreased significantly. Under the same drought intensity, seedlings in sandy–loam soil had higher root biomass, and the coefficient of variation of 5th-order roots (37.4, 44.5, and 53% in humus, loam, and sandy–loam soil, respectively) was higher than that of lower-order roots. All branch order roots of seedlings in humus soil had the largest specific root length (SRL) and specific root surface area (SRA), in addition to the lowest diameter. With increasing drought intensity, the SRL and average diameter (AD) of all root branch orders increased and decreased, respectively. The fine roots in humus soil had a higher soluble sugar (SS) content and lower starch (ST) content compared to the loam and sandy–loam soil. Additionally, the SS and ST contents of fine roots showed decreasing and increasing tendencies with increasing drought intensities, respectively. SS and ST explained the highest degree of the total variation in fine root traits, which were 32 and 32.1%, respectively. With increasing root order, the explanation of the variation in root traits by ST decreased (only 6.8% for 5th-order roots). The observed response in terms of morphological traits of different fine root branch orders of F. mandshurica seedlings to resource fluctuations ensures the maintenance of a low cost-benefit ratio in the root system development.

Highlights

In recent decades, forest decline and death caused by high temperatures and extreme droughts have occurred on a large scale worldwide (Allen et al, 2010; Choat et al, 2012; Zhang et al, 2015; Martínez-Vilalta et al, 2016)
The average diameter (AD) of all root branch orders was less affected by drought intensity (Figures 2G–I and Supplementary Table 2)
Our results highlighted several key findings related to Non-structural carbohydrates (NSCs) and fine root traits of F. mandshurica seedlings under different soil substrates and drought intensities

Summary

Introduction

Forest decline and death caused by high temperatures and extreme droughts have occurred on a large scale worldwide (Allen et al, 2010; Choat et al, 2012; Zhang et al, 2015; Martínez-Vilalta et al, 2016). The different responses of NSCs among different plant tissues or organs under drought stress have been discussed deeply (Martínez-Vilalta et al, 2016; Furze et al, 2019; Deng et al, 2020; He et al, 2020; Zhang et al, 2020). Understanding the variation in the composition and level of fine root NSCs under drought conditions is of great significance for better recognition of the carbon balance and dynamics of plant survival and growth (Hartmann and Trumbore, 2016)

Objectives

Methods

Results

Conclusion