Photodegradation alleviates the lignin bottleneck for carbon turnover in terrestrial ecosystems

Abstract

A mechanistic understanding of the controls on carbon storage and losses is essential for our capacity to predict and mitigate human impacts on the global carbon cycle. Plant litter decomposition is an important first step for carbon and nutrient turnover, and litter inputs and losses are essential in determining soil organic matter pools and the carbon balance in terrestrial ecosystems. Photodegradation, the photochemical mineralization of organic matter, has been recently identified as a mechanism for previously unexplained high rates of litter mass loss in arid lands; however, the global significance of this process as a control on carbon cycling in terrestrial ecosystems is not known. Here we show that, across a wide range of plant species, photodegradation enhanced subsequent biotic degradation of leaf litter. Moreover, we demonstrate that the mechanism for this enhancement involves increased accessibility to plant litter carbohydrates for microbial enzymes. Photodegradation of plant litter, driven by UV radiation, and especially visible (blue-green) light, reduced the structural and chemical bottleneck imposed by lignin in secondary cell walls. In leaf litter from woody species, specific interactions with UV radiation obscured facilitative effects of solar radiation on biotic decomposition. The generalized effect of sunlight exposure on subsequent microbial activity, mediated by increased accessibility to cell wall polysaccharides, suggests that photodegradation is quantitatively important in determining rates of mass loss, nutrient release, and the carbon balance in a broad range of terrestrial ecosystems.carbon cycle | plant litter decomposition | photodegradation | lignin |

Soil Respiration Components and their Temperature Sensitivity Under Chemical Fertilizer and Compost Application: The Role of Nitrogen Supply and Compost Substrate Quality

“…Consistently, the CC/MC, that is, ratios of carbohydrate to methoxyl C, also positively related to initial Rh. In contrast, lignin is relatively resistant against biodegradation, which can be undertaken only by a limited species of soil microbes (predominantly fungi) due to its recalcitrant polyphenolic structure (Austin et al, ). Therefore, it is traditionally believed to be not or rarely degraded in initial decomposition phases (Berg & Matzner, ).…”

Photodegradation accelerates ecosystem N cycling in a simulated California grassland

“…Studies on photodegradation historically examined the UV range only, but recent studies have found that blue-green (400-550 nm) range of photosynthetically active radiation is also involved (Brandt et al 2009, Austin and Ballare 2010, Day et al 2015, Austin et al 2016. Studies on photodegradation historically examined the UV range only, but recent studies have found that blue-green (400-550 nm) range of photosynthetically active radiation is also involved (Brandt et al 2009, Austin and Ballare 2010, Day et al 2015, Austin et al 2016.…”

“…The second is that photodegradation directly inhibits microbes, increasing microbial turnover from UV radiation damaging microbial cells (Kielbassa et al 1997, Johnson 2003, Zenoff et al 2006, Caldwell et al 2007, and reducing microbial activity , Hughes et al 2003, Uselman et al 2011, Lin et al 2015, Adair et al 2017. These mechanisms counteract, as direct degradation produces compounds that are more susceptible to subsequent microbial decomposition (Gallo et al 2009, Liu et al 2014, Wang et al 2015, Austin et al 2016. The mechanisms were incorporated into DayCent-UV, and the model was validated against observations from Long-Term Intersite Decomposition Experiment (LIDET) at three semi-arid sites in the western United States (Chen et al 2016).…”

Fall Rye Reduced Residual Soil Nitrate and Dryland Spring Wheat Grain Yield

“…Future research could investigate the role of photodegradation vs. biotic decomposition in semiarid agroecosystems to determine the magnitude of these processes in the regulation of litter decomposition. Research has indicated that the structural and chemical bottleneck induced by lignin content in litter can be "photoprimed" by UV radiation to enhance microbial decomposition processes (Austin et al, 2016). Further understanding these processes could assist in appropriately timing the fall rye kill date and improving the synchrony between cover crop N supply and crop N demand.…”