The contribution of photodegradation to litter decomposition in a temperate forest gap and understorey.

Qing‐Wei Wang,Thomas Matthew Robson,Chenggang Liu,Hiroko Kurokawa,Marta Pieristè,Tanaka Kenta

doi:10.1111/nph.17022

Abstract

Summary Litter decomposition determines carbon (C) backflow to the atmosphere and ecosystem nutrient cycling. Although sunlight provides the indispensable energy for terrestrial biogeochemical processes, the role of photodegradation in decomposition has been relatively neglected in productive mesic ecosystems.To quantify the effects of this variation, we conducted a factorial experiment in the understorey of a temperate deciduous forest and an adjacent gap, using spectral‐attenuation‐filter treatments.Exposure to the full spectrum of sunlight increased decay rates by nearly 120% and the effect of blue light contributed 75% of this increase. Scaled‐up to the whole forest ecosystem, this translates to 13% loss of leaf‐litter C through photodegradation over the year of our study for a scenario of 20% gap. Irrespective of the spectral composition, herbaceous and shrub litter lost mass faster than tree litter, with photodegradation contributing the most to surface litter decomposition in forest canopy gaps. Across species, the initial litter lignin and polyphenolic contents predicted photodegradation by blue light and ultraviolet B (UV‐B) radiation, respectively.We concluded that photodegradation, modulated by litter quality, is an important driver of decomposition, not just in arid areas, but also in mesic ecosystems such as temperate deciduous forests following gap opening.

Highlights

Litter decomposition, a critical step for carbon (C) and nutrient turnover, determines C balance in terrestrial ecosystems partially offsetting C input from primary production (Schlesinger & Bernhardt, 2013)
The closed canopy transmitted about 3.9%, 3.7% and 1.4% of above-canopy photosynthetically active radiation (PAR), UV-A and ultraviolet B (UV-B) radiation, respectively, over the whole study period (Figs 1d, S1)
Our study found that photodegradation plays a key role in driving surface litter decomposition in a temperate forest ecosystem

Summary

Introduction

A critical step for carbon (C) and nutrient turnover, determines C balance in terrestrial ecosystems partially offsetting C input from primary production (Schlesinger & Bernhardt, 2013). Climate (principally temperature and precipitation) and initial litter quality (directly affecting soil organisms), have been modelled extensively to predict litter decay rates (Gaxiola & Armesto, 2015). Empirical models can only explain up to 70% of the variation in decay rates in global terrestrial ecosystems (Parton et al, 2007). This implies that the models are importantly incomplete: other abiotic drivers or fundamental mechanisms in nature contribute to this process. Obtaining a more-complete picture of the drivers of litter decay is key to predicting how terrestrial C and nutrient cycles respond to climate changes

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Discussion

Conclusion