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

Abstract

In arid and semi-arid areas, organic matter decomposition is stimulated by ultraviolet radiation. In this paper, the association between straw decomposition and UV-A exposure was evaluated. Oven-dried rice straw samples were chronically exposed to UV-A radiation and examined periodically for up to 90 days at room temperature. Scanning electron microscopy (SEM) showed that noticeable disintegration of the fiber structure occurred on the irradiated sample surface in comparison to the control. At the end of the UV-A treatment period, straw mass had decreased by 5%, and dissolved organic carbon (DOC) increased by 18%. The content of cellulose, hemicellulose, and lignin of the irradiated straw decreased by 29.3%, 14.4% and 49.3%, respectively. The marked loss of nitrogen and potassium in the exposed straw were also observed. Thermogravimetric analysis (TGA) showed that treatment with UV-A radiation tended to decrease the mass loss rate and the thermal degradation temperature of the straw biomass from 220 °C to 208 °C. Infrared spectrometric analysis (ATR-FTIR) showed that functional groups, e.g., C-OH and C-O-C, were disrupted obviously due to UV-A exposure. These results suggest that ultraviolet-A irradiation facilitates straw decomposition by direct photochemical degradation.

Ultraviolet radiation accelerates photodegradation under controlled conditions but slows the decomposition of senescent leaves from forest stands in southern Finland

“…While the exclusion of solar UV radiation enhanced mass loss from leaf litter decomposing in the forest stands, the presence of UV-A radiation in the controlled environment tended to accelerate photodegradation. An increase in mass loss due to photodegradation in controlled environments has also been reported for rice and wheat straws exposed to enhanced UV-A [51] and UV-B radiation [52]. The effect of UV radiation did not transfer to decomposition under equivalent filters in forest stands, a distinction that would be consistent with any effect of sunlight photoinhibition on decomposers predominating over photochemical mineralization during the initial 6 months of decomposition following leaf fall.…”

Reviews and syntheses: VOC emissions from soil cover in boreal and temperate natural ecosystems of the Northern Hemisphere

“…Bosco et al (2016) found additive effects of ultraviolet (UV) radiation and soil water on litter mass loss. Recent laboratory experiments have shown that the photodegradation of plant litter driven by UV radiation is important in influencing mass loss, nutrient release and the carbon balance in a broad range of terrestrial ecosystems (Austin et al, 2016;Li et al, 2016). It can be assumed that the loss of litter mass under the action of solar radiation (light and/or its thermal component) is at least partially related to the emission of VOCs, but at present it is difficult to draw definite conclusions in this regard due to the limited number of studies of this phenomenon.…”

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

“…The supernatant was separated from a 0.50-mm film filter after standing for 20 min. The liquid was analyzed by an elemental analyzer (Multi N/C 3100 Analyzer, Analytik-Jena Group, Jena, Germany) (Song et al 2011;Li et al 2016). The contents of potassium (K) and phosphorus (P) were recorded by flame photometric analysis and spectrophotometry, respectively (Song et al 2012).…”

“…As a result, environmental microorganisms went into an apoptotic phase after day 100, and the straw decomposition rate gradually decreased until it was stable. Li et al (2016) exposed dry rice straw to increased UV-A irradiation and found that long-term radiation decreased the straw mass by 5%. The mass loss of 39.1% provides strong evidence that degradation was accelerated both by photodegradation and biodegradation.…”

“…Due to the high activity of hydroxyl free radicals, hydroxyl radicals react with carbonaceous compounds and abstract hydrogen atoms bonded to them (Bailey 1985;Kolar 1997;Malešič et al 2005). Cellulose and hemicellulose are degraded by free radicals and active oxygen after the degradation of partial lignin (Gould 1982;King et al 2012;Li et al 2016).…”