The response of fine root morphological and physiological traits to added nitrogen in Schrenk's spruce (Picea schrenkiana) of the Tianshan mountains, China.

Lu Gong,Jingjing Zhao

doi:10.7717/peerj.8194

Abstract

Fine roots are essential for water and nutrient uptake in plants, but little is known about the variation in fine root traits and the underlying mechanisms that drive it. Understanding the responses of fine root function traits to changing environmental conditions and the role of fine root traits as drivers of forest ecosystem processes are critical for informing physiological and ecological theory as well as ecosystem management. We measured morphological and physiological traits of fine roots from six soil layers and three diameter classes in Schrenk’s spruce (Picea shrenkiana) forests of the Tianshan mountains, China. We found significant effects of nitrogen addition on these morphological and physiological traits, which varied by soil layer and root diameter. Specifically, specific root length (SRL) was higher in medium N addition group (N2) than in control group (N0). Specific root area (SRA) was higher in the control group (N0) than fertilized groups (N1, N2 and N3). Root tissue density (RTD) was higher in low N addition group (N1) than in the other group. Root dry matter content had no significant difference among four treatment groups. SRL, SRA, and RTD of fine roots in different diameter classes were all significantly different between high N addition (N3) and the control (N0) groups. The physiological characteristics of fine roots showed that soluble sugar (SS), fine root vitality (FRV), and tissue water content (TWC) in different soil layers were higher in the control group than in the fertilized groups. While soluble protein (SP), malondialdehyde (MDA) and free proline (FP) were lower in the control group (N0) than in the fertilized groups. In addition, SS, FRV, SP, TWC, FP, and MDA in all N addition treatments groups were significantly different from the control group. Fine root morphological traits were closely related to physiological traits, and added nitrogen inputs change these correlations. Our study confirms that nitrogen addition has specific effects on the morphological and physiological traits of fine roots of Schrenk’s spruce, and the effects of N addition vary according to the amount added.

Highlights

Plant roots perform indispensable functions, including nutrient and water acquisition, and influence a broad spectrum of ecological processes
Effects of added nitrogen on root morphological traits for different diameter classes and soil depths The morphological traits of roots in different soil layers and different diameter classes varied in their response to N addition (Fig. 1)
Considering fine roots from the same soil layer but different N addition treatments, specific root length (SRL) and Root tissue density (RTD) were significantly greater in N2 and N1 than in N3 (Figs. 1A and 1E)

Summary

Introduction

Plant roots perform indispensable functions, including nutrient and water acquisition, and influence a broad spectrum of ecological processes Root morphological changes are often the result of internal physiological changes, while morphological changes in turn can lead to changes in physiological indicators (Hishi, 2007; Makita et al, 2011). Changes in both types of traits are complementary, working in combination to resist environmental stress. Fine root functional traits are responsive to environmental conditions, which may affect below-ground nutrient cycling allocations in temperate and subtropical forest ecosystems (Kou et al, 2015; Dorr et al, 2010; Freschet et al, 2017). The study of root morphological and physiological traits may offer vital insights into patterns of carbon allocation and nitrogen cycling in forest ecosystems

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