Spectral Composition of Sunlight Affects the Microbial Functional Structure of Beech Leaf Litter During the Initial Phase of Decomposition

Abstract

Aims This study tests whether different spectral regions of sunlight affect the microbial decomposer assemblage in surface leaf litter in a beech understorey over the first 6 months following leaf senescence. Methods We performed a litterbag experiment employing filters attenuating combinations of UV-B, UV-A, blue, and green light as well as the whole spectrum of sunlight. We measured changes in microbial biomass and community structure, litter mass loss and litter chemistry during the first 6 months of decomposition.Results Fungal and total microbial biomass were highest in the treatment excluding UV radiation, blue and green light. Exclusion of UV-B radiation decreased the fungal:bacterial biomass ratio and litter nitrogen content. Bacterial biomass was lower in the dark treatment compared to treatments receiving at least part of the solar spectrum. Our filter treatments affected microbial functional structure from the beginning of the experiment, whereas mass loss was only significantly affected after 6 months of decomposition and no effect was found on litter carbon content. Conclusions This study proves that sunlight, in a spectrally dependent manner, affects both microbial functional structure and biomass in temperate deciduous forests early in the decomposition process, with bacteria tending to dominate in sunlight and fungi in dark conditions. We found sunlight to be important in the decomposition in temperate forest understoreys despite the low irradiance characterizing these environments. However, long-term studies are required to estimate the relative contribution of sunlight among factors affecting the eventual incorporation of decomposing leaf litter into forest soils.

Assessment of Carbon Substrate Catabolism Pattern and Functional Metabolic Pathway for Microbiota of Limestone Caves

“…With regards to the difference observed in the AWCD patterns between sampling environments (i.e., outside and inside the cave), the microbial communities found outside of the cave were highly metabolically active, consuming and up taking carbon from the environment to fuel catabolic activity during cell growth. Previous studies have also reported that, in terrestrial environments, sunlight is the most influential factor for the production of simple organic carbon via photodegradation, resulting in a higher metabolic activity in microorganisms [ 35 , 36 ]. Similarly, in a study on permafrost, another extreme environment, the authors found that sunlight exposure can enhance the microbial respiration rate up to >40% compared with dark areas, mediated by dissolved organic carbon [ 37 ].…”

Assessment of Carbon Substrate Catabolism Pattern and Functional Metabolic Pathway for Microbiota of Limestone Caves

“…outside and inside the cave), the microbial communities found outside of the cave were highly metabolically active, consuming and up taking carbon from the environment to fuel catabolic activity during cell growth. Previous studies have also reported that, in terrestrial environments, sunlight is the most in uential factor for the production of simple organic carbon via photodegradation, resulting in a higher metabolic activity in microorganisms [33,34]. Similarly, in a study on permafrost, another extreme environment, the authors found that sunlight exposure can enhance microbial respiration rate up to > 40% compared to dark areas, mediated by dissolved organic carbon [35].…”

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

“…Herbaceous and shrub litter lost mass much faster than tree litter, irrespective of the filter treatment in the understorey (Fig. S6), attributable to their low toughness and low C and lignin content (Table S1), which are structural and persistent compounds affecting decomposability (Pieristè et al ., 2020a,b). In contrast, tougher litter from trees with a high content of recalcitrant compounds is more prone to photodegradation once exposed to sunlight in the gap (Fig.…”

“…However, the solar radiation reaching the forest floor varies greatly, as forests undergo succession, displaying spatially and temporally dynamic canopy and soil processes. In deciduous forest understoreys, seasonal canopy phenology causes large changes in light quality and irradiance through the year that potentially produce complex effects on litter decompostion (Pieristè et al ., 2019, 2020a,b). Canopy gap dynamics created by a variety of natural or human disturbances (Čada et al ., 2016), produce heterogeneous light environments in a forest that partially drive species diversity (Wang et al ., 2020).…”

“…lignin, nitrogen (N), polyphenols, and leaf mass area (LMA)), which may determine subsequent litter decomposition (Cornwell et al ., 2008). However, little is known about the role of the high irradiance in gaps on decomposition and also which spectral regions most drive decomposition processes (Ma et al ., 2017; Pieristè et al ., 2019, 2020a,b; Marinho et al ., 2020). It is also unclear whether photodegradation rates differ among plant growth forms, and if so, which initial litter traits best predict such changes.…”