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

Abstract

 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 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.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021

“…The role of photodegradation in litter decomposition is well established [ 84 , 112 ]. There is now more evidence that photodegradation plays a key role in moist and temperate systems, such as in temperate forests [ 117 ], as well as in dryland systems [ 118 , 119 ]. How much plant litter gets exposed to solar radiation, including the UV component, varies among ecosystems.…”

“…How much plant litter gets exposed to solar radiation, including the UV component, varies among ecosystems. In dryland ecosystems, litter is left on the ground in the dry season but burial can reduce exposure [ 119 ], while in temperate forests litter becomes exposed when gaps form in the canopy [ 117 ]. Fire also reduces vegetation cover and temporarily increases exposure to solar radiation [ 120 ].…”

Linking the Spectra of Decomposing Litter to Ecosystem Processes: Tandem Close-Range Hyperspectral Imagery and Decomposition Metrics

“…In addition to decay under real-world conditions likely being mediated by a wider consortium of decomposers, plant litter is exposed to ultraviolet (UV) radiation, which causes the direct (photochemical mineralization) and indirect (photofacilitation) breakdown of organic matter [30]. In contrast to microbial decomposition, photodegradation produces a "bleached" appearance and the loss of color [31]. As microbial and photodegradation are concurrent processes, incorporating UV radiation into the methodological design is essential for understanding the diversity of decaying leaf spectra.…”

Meta-Analysis Of Ecological Studies Attenuating Solar Radiation Illustrates The Importance Of Blue Light Over Ultraviolet Radiation In Driving Photodegradation Of Litter In Terrestrial Ecosystems

“…Photodegradation has a role in litter decomposition in terrestrial ecosystems, not only in arid and semiarid environments at low latitudes (Almagro et al 2015; Day et al, 2007), as originally thought, but also at higher latitudes (Jones et al, 2016;Zaller et al, 2009) and in mesic environments (Brandt et al, 2010). Recently, forests have been added to the list of ecosystems where photodegradation affects biogeochemical cycling, extending the reach of this process to dynamic radiation environments where gap opening and forest management practices, as well as seasonal phenology, cause large uctuations in received solar radiation (Méndez et al, 2019;Pieristè et al, 2019Wang et al, 2021).…”