Solar UV-A radiation and blue light enhance tree leaf litter decomposition in a temperate forest

Marta Pieristè,Titta K Kotilainen,Alan G Jones,Estelle Forey,Matthieu Chauvat,Michaël Aubert,T Matthew Robson

doi:10.1007/s00442-019-04478-x

Abstract

Sunlight can accelerate the decomposition process through an ensemble of direct and indirect processes known as photodegradation. Although photodegradation is widely studied in arid environments, there have been few studies in temperate regions. This experiment investigated how exposure to solar radiation, and specifically UV-B, UV-A, and blue light, affects leaf litter decomposition under a temperate forest canopy in France. For this purpose, we employed custom-made litterbags built using filters that attenuated different regions of the solar spectrum. Litter mass loss and carbon to nitrogen (C:N) ratio of three species: European ash (Fraxinus excelsior), European beech (Fagus sylvatica) and pedunculate oak (Quercus robur), differing in their leaf traits and decomposition rate, were analysed over a period of 7–10 months. Over the entire period, the effect of treatments attenuating blue light and solar UV radiation on leaf litter decomposition was similar to that of our dark treatment, where litter lost 20–30% less mass and had a lower C:N ratio than under the full-spectrum treatment. Moreover, decomposition was affected more by the filter treatment than mesh size, which controlled access by mesofauna. The effect of filter treatment differed among the three species and appeared to depend on litter quality (and especially C:N), producing the greatest effect in recalcitrant litter (F. sylvatica). Even under the reduced irradiance found in the understorey of a temperate forest, UV radiation and blue light remain important in accelerating surface litter decomposition.

Highlights

Photodegradation involves direct and indirect breakdown of organic matter mediated by sunlight which, alongside warm temperatures and high humidity, can accelerate the decomposition of plant litter (Brandt et al 2007; Gallo et al 2006, 2009; Almagro et al 2015; Ma et al 2017)
Oak litter decomposed much slower; only 50% mass was lost after 10 months, beech litter increased in mass during
The importance of photodegradation in arid and semiarid environments as a driver of carbon loss during decomposition is well known (Austin and Ballaré 2010; Austin et al 2016); this study allows us to extend that finding to temperate forest environments, albeit acknowledging that this study focused on decomposition of the top layer of surface leaf litter and not buried material

Summary

Introduction

Photodegradation involves direct (photochemical mineralization) and indirect (photofacilitation) breakdown of organic matter mediated by sunlight which, alongside warm temperatures and high humidity, can accelerate the decomposition of plant litter (Brandt et al 2007; Gallo et al 2006, 2009; Almagro et al 2015; Ma et al 2017). Solar radiation affects decomposition rate through direct effects on both the activity (Duguay and Klironomos 2000) and community composition of decomposer organisms (Pancotto et al 2003; Robson et al 2005). Because these multiple environmental factors interact to produce complex effects, the relative contribution of photodegradation to decomposition is difficult to quantify

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