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

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. Electronic supplementary material The online version of this article (10.1007/s00442-019-04478-x) contains supplementary material, which is available to authorized users.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…Since our last assessment [ 1 ], additional studies have provided more details about the significance of photodegradation in dry systems including an arid grassland [ 295 ], the Sonoran Desert [ 296 ], a semi-arid scrub system [ 297 ], and a semi-arid woodland ecosystem [ 298 , 299 ] (contributing towards SDG targets 15.1, 15.3). Other studies since our last assessment have shown that photodegradation is also associated with plant litter (dead plant material) decomposition in wetter ecosystems located in temperate and boreal forests [ 300 – 302 ]. Furthermore, solar radiation drives photodecomposition of litter in tropical [ 303 ] and subtropical monsoon forests [ 304 ].…”

“…Photodegradation has generally been neglected in carbon budgets from productive forested ecosystems where litter is exposed to a heterogeneous radiation environment due to vegetation cover. However, recent field studies have found evidence that photodegradation contributes to carbon loss in forests of tropical regions [ 303 ] as well as those at temperate mid- [ 300 ] and even high latitudes [ 302 ]. Some studies have suggested that photodegradation can partly explain the missing carbon loss in these systems, leading to underestimation of terrestrial emissions of the carbon [ 298 , 306 ].…”

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

“…3; Fig. S6, 7), because micro-and meso-fauna prefer darker environments (Lin et al, 2018;Pieristè et al, 2019. Hence, litter decomposition tends to be driven by microbial decomposition in the understorey and by photodegradation in the gaps of mesic ecosystems, with canopy openness being the key factor determining the balance between these two processes.…”

“…Litter materials were placed in an updated custom-made litterbox based on our previous design (Pieristè et al, 2019). The litterbox frame and central pillar were made of sterile plastic straws (21 cm long, 18 cm wide and 1.3 cm diameter, Bihin, Japan) which made a space in the Accepted Article litterbox to avoid litter touching the filters during decomposition.…”

“…The litterbox frame and central pillar were made of sterile plastic straws (21 cm long, 18 cm wide and 1.3 cm diameter, Bihin, Japan) which made a space in the Accepted Article litterbox to avoid litter touching the filters during decomposition. Considering the effects of mesh size on mass loss from our previous study (Pieristè et al, 2019), the litterbox bases were made of sterile 2 mm mesh of the polyethylene fiber, to avoid macrofaunal incursion while still allowing mesofauna access to the litter. Litterbox tops consisted of different filters: (i) Full-spectrum treatment, with a fully transparent polythene film (0.05 mm thick, 3904CF; Okura, Marugame, Japan), transmitting approximately 95% of the whole solar spectrum >280 nm; (ii) Tokyo, Japan).…”