Biomass allocation and seasonal non-structural carbohydrate dynamics do not explain the success of tall forbs in short alpine grassland

Erika Hiltbrunner,Jonas Arnaiz,Christian Körner

doi:10.1007/s00442-021-04950-7

Abstract

The majority of alpine plants are of small stature. Through their small size alpine plants are decoupled from the free atmospheric circulation and accumulate solar heat. However, a few alpine species do not follow that “rule” and protrude with their aboveground structures from the microclimatic shelter of the main canopy boundary layer. We aim at explaining the phenomenon of being tall by exploring the biomass production and carbon relations of four pairs of small and tall phylogenetically related taxa in alpine grassland. We compared species and stature-specific biomass allocation, shifts in non-structural carbohydrate (NSC) concentrations in different tissues throughout the season, and we used 13C labels to track carbon transfer from leaves to belowground structures. Small and tall herbs did not differ in their above- to belowground biomass allocation. The NSC composition (starch, fructan, simple sugars) and allocation did not show a stature-specific pattern, except for higher concentrations of simple sugars in tall species during their extended shoot growth. In relative terms, tall species had higher NSC pools in rhizomes, whereas small species had higher NSC pools in roots. Our findings do not place tall alpine forbs in an exceptional category in terms of biomass allocation and carbohydrate storage. The tall versus small stature of the examined herbs does not seem to be associated with specific adjustments in carbon relations. 13C pulse labelling revealed early C autonomy in young, unfolding leaves of the tall species, which are thus independent of the carbon reserves in the massive belowground organs.

Highlights

In the temperate zone, life conditions of alpine plants are characterised by long, cold winters with a protective snow cover, and a relatively short growing season (2.5–3.5 months)
The actual climate alpine plants commonly experience during the growing season is not well represented by air temperature measured at a weather station (Körner and Larcher 1988; Scherrer et al 2011; Körner and Hiltbrunner 2018)
The 13C pulse labelling in tall species showed that the allocation of newly assimilated C to belowground organs has a high priority already from early developmental stages on, and independently of the already massive non-structural carbohydrate (NSC) stores

Summary

Introduction

Life conditions of alpine plants are characterised by long, cold winters with a protective snow cover, and a relatively short growing season (2.5–3.5 months). The actual climate alpine plants commonly experience during the growing season is not well represented by air temperature measured at a weather station (Körner and Larcher 1988; Scherrer et al 2011; Körner and Hiltbrunner 2018). Owing to their small stature and dense canopies, most alpine plants operate within an aerodynamic. Some of these tall herbs are confined to sheltered gullies or nutrient-rich, ruderal locations (e.g., Rumex alpinus), but others are not. We explore this question with a focus on growth and carbon relations. It is well established that biomass allocation into storage organs has a strong influence on plant growth, potentially outweighing the role of per-unitleaf area C assimilation (functional growth analysis; Briggs et al 1920; Körner 1991; van der Werf et al 1993; Poorter et al 2000)

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Conclusion