Photodegradation alleviates the lignin bottleneck for carbon turnover in terrestrial ecosystems

BALLARÉ, CARLOS L.; MÉNDEZ, M. SOLEDAD; AUSTIN, AMY T.

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

NATL ACAD SCIENCES

Lugar: Washington DC, USA; Año: 2016 vol. 113 p. 4392 - 4397

0027-8424

A mechanistic understanding of the controls on carbon storage andlosses is essential for our capacity to predict and mitigate humanimpacts on the global carbon cycle. Plant litter decomposition is animportant first step for carbon and nutrient turnover, and litter inputsand losses are essential in determining soil organic matter pools andthe carbon balance in terrestrial ecosystems. Photodegradation, thephotochemical mineralization of organic matter, has been recentlyidentified as a mechanism for previously unexplained high rates oflitter mass loss in arid lands; however, the global significance of thisprocess as a control on carbon cycling in terrestrial ecosystems is notknown. Here we show that, across a wide range of plant species,photodegradation enhanced subsequent biotic degradation of leaflitter. Moreover, we demonstrate that the mechanism for thisenhancement involves increased accessibility to plant litter carbohydratesfor microbial enzymes. Photodegradation of plant litter, drivenby UV radiation, and especially visible (blue?green) light, reduced thestructural and chemical bottleneck imposed by lignin in secondary cellwalls. In leaf litter from woody species, specific interactions with UVradiation obscured facilitative effects of solar radiation on biotic decomposition. The generalized effect of sunlight exposure on subsequentmicrobial activity, mediated by increased accessibility to cellwall polysaccharides, suggests that photodegradation is quantitativelyimportant in determining rates of mass loss, nutrient release,and the carbon balance in a broad range of terrestrial ecosystems.