Exposure to solar UV-B radiation accelerates mass and lignin loss of Larrea tridentata litter in the Sonoran Desert

Abstract

We assessed whether exposure to solar ultraviolet-B radiation (UV-B) affects the mass loss of Larrea tridentata (creosotebush) litter in the Sonoran Desert of central Arizona. We placed three types of litter (leaves, twigs, or a natural mixture of leaves, twigs, and seeds) in bags constructed of UV-B-transmitting or UV-Babsorbing filter material that allowed either 85% (near-ambient UV-B treatment) or 15% (reduced UV-B treatment) of the biologically effective solar UV-B to reach litter inside the bags. Bags were placed outdoors for 4-5 months during the winter at two sites: a balcony or on the soil surface of the desert. Mass loss of leaf litter was greater under near-ambient UV-B than reduced UV-B at both sites: 21 (near-ambient) vs. 18% (reduced) on the balcony, and 18 vs. 14% at the desert site. Mass loss of twig litter was also greater under near-ambient UV-B at the desert site. Mass loss of the natural mixture of litter was also greater when exposed to near-ambient UV-B on the balcony, and tended to be greater at the desert site. We estimate that about 14-22% of the total mass loss of leaf litter during our 4-5 month experiments was attributable to solar UV-B exposure. Leaf litter exposed to near-ambient UV-B had lower concentrations of lignin, and fats and lipids, and slightly higher concentrations of holocellulose. The greater mass loss of litter under near-ambient UV-B appeared mainly attributable to loss of lignin, although losses of fats and lipids were also appreciable. A primary reason for greater mass loss of litter under solar UV-B appeared to be photodegradation, particularly of lignin.

Dual role of lignin in plant litter decomposition in terrestrial ecosystems

“…The presence of lignin is therefore actually predicted to protect cellulose from photodegradation, a phenomenon that has been documented to some extent and attributed to the strong light absorption of lignin and its high capacity for autoxidation (27,32). Our results support the idea that lignin was the primary loss product due to photodegradation in our standard substrates, and they are consistent with observations indicating the disappearance of lignin in litter exposed to high natural UV-B radiation (20) and increased biotic lability of plant litter after solar radiation exposure (21,26).…”

“…Recent experimental evidence has shown that, in semiarid ecosystems, abiotic photodegradation can be a dominant control on decomposition of decaying plant material (18). Solar radiation causes mass loss from plant litter in low rainfall ecosystems (18)(19)(20)(21); photodegradation produces volatile carbon compounds (22)(23)(24) and alters the chemistry of the remaining material (21,25,26).…”

“…Litter decomposition experiments carried out in the field using various natural litter types have shown mixed results with respect to the relationships between initial litter chemistry and photodegradative losses (21,24). Some litter decomposition studies have demonstrated a modest decrease in lignin content during exposure to UV-B radiation (290-315 nm) (20,26,29), although others have shown no effect of UV radiation (290-400 nm) on litter lignin (19,30). Litter types used in these previous experiments varied in a number of characteristics other than lignin and cellulose concentrations, which makes it difficult to draw definitive conclusions about the roles of these polymers in the process of photodegradation.…”

The Effects of UV-A on Dry Rice Straw Decomposition under Controlled Laboratory Conditions

“…Because ultraviolet irradiation accelerates organic matter decomposition, different wavelengths of ultraviolet light have been tested in practice (Moorhead and Reynolds 1989;Schade et al 1999;Day et al 2007;Brandt et al 2010). Due to its long wavelengths and ability to penetrate the ozonosphere, UV-A radiation (315 to 400 nm) has an important effect on photodecomposition in the biosphere .…”

Straw Degradation Behaviors under Different Conditions of Relative Air Humidity and Ultraviolet-A Irradiation

“…Considerable research has shown that degradation is affected by experimental conditions (time, environment, and location) and material properties (type and composition) (Schade et al 1999;Brandt et al 2007;Day et al 2007;Kirschbaum et al 2011). In general, when crop residue is exposed to increased UV radiation under dry conditions, the photodegradation of biomass materials is primarily driven by UV irradiation through direct or indirect photolysis.…”