Vertical root distribution and biomass allocation along proglacial chronosequences in Central Switzerland

Konrad Greinwald,Lea Adina Dieckmann,Carlotta Schipplick,Anne Hartmann,Michael Scherer-Lorenzen,Tobias Gebauer

doi:10.1080/15230430.2020.1859720

Abstract

ABSTRACT Investigating changes in belowground functional plant traits is an important step toward a better understanding of vegetation dynamics during primary succession. However, in alpine glacier forelands, we still lack an accurate assessment of plant rooting patterns. In this study, we established two proglacial chronosequences with contrasting bedrocks to investigate changes in rooting patterns and biomass allocation with terrain age. We extracted soil cores up to 1 m depth and measured root traits every 10 cm of each drilled core. Furthermore, we sampled aboveground biomass determining the contributions of functional groups to total aboveground biomass. We found that root traits associated with the root economics spectrum varied significantly along the chronosequences. Vertical root distribution coefficients revealed that early successional communities had more evenly distributed root systems compared to late successional communities. Biomass allocation showed diverging patterns. We found evidence for both the isometric allocation and optimal partitioning hypotheses. In addition, we observed a significant correlation between rooting parameters and plant community composition, suggesting that the dominance of distinct plant functional groups was one important factor explaining the observed rooting patterns. Our results shed light on the often neglected belowground compartments during plant succession and contribute to a better understanding of hillslope functioning.

Highlights

Since the late Pleistocene, glaciers in alpine regions have been shrinking dramatically (e.g., Boxleitner et al 2019)
In the top 20 cm of the soil pro files, fine root mass density (FRMD) and fine root length density (FRLD) were considerably higher on old moraines (2.21 g cm−3, 16.48 cm cm−3) than on young moraines (0.14 g cm−3, 1.58 cm cm−3)
The presented data set is of interest for a broader understanding of functional root traits in alpine communities and provides comprehen sive information on the hidden half of successionrelated vegetation dynamics

Summary

Introduction

Since the late Pleistocene, glaciers in alpine regions have been shrinking dramatically (e.g., Boxleitner et al 2019). Former glacier positions can be identified by moraines representing distinct ages of substrate exposure (e.g., Egli, Fitze, and Mirabella 2001; Musso et al 2019; Maier et al 2020). This space-for-time substitution, called a chronosequence approach, enables scientists to test hypotheses related to terrain age. Retreating glaciers expose young soils that have little biological legacy (Matthews 1992; Prach and Walker 2020) Such barren surfaces represent a very inhospitable habitat for early colonizers (Caccianiga et al 2006)

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