1. Litter decomposition plays important roles in carbon and nutrient cycling. In dryland both microbial decomposition and abiotic degradation (by UV light or other forces) drive variation in decomposition rates, but whether and how litter traits and position determine the balance between these processes is poorly understood. 2. We investigated relationships between litter quality and their decomposition rates among diverse plant species in a desert ecosystem in vertically contrasting positions representing distinct decomposition environments driven by different relative contributions of abiotic and microbial degradation. Thereto, leaf litter samples from 17 desert species were sealed into litterbags and placed on the soil surface under strong solar exposure versus shade conditions, or buried in the soil at 10 cm depth, for a whole year. 3. Litter decomposition rates were 21 and 17 % higher in burial and light-exposed treatments, respectively, than those in shade. Leaf traits, i.e. specific leaf area (SLA), litter C:N ratio and lignin concentration could predict litter decomposition to some degree, but their predictive power was dependent on litter position. However, multiple linear regression showed that SLA, litter C and P significantly affected k values for leaf litter decomposition besides litter position, with SLA standing out as a strong determinant of litter decomposition rate as related either to solar radiation or the environment below the soil surface. Furthermore, the interspecific differences in litter decomposition rate decreased over time, implying that afterlife effects of leaf traits on decomposition were attenuated. 4. Synthesis. These findings suggest that abiotic photodegradation and soil burial mediated microbial decomposition could be responsible for higher than expected litter turnover in dryland. They point to a dual role of specific leaf area as a promotor of decomposition rates: via relative exposure of the leaf surface to abiotic factors such as UV light versus to soil moisture and microbes under soil burial.

Leaf litter decomposition in dryland under different three litter postionsThere are three excel sheets. 1. Initial traits and k values in litter decomposition model across 17 desert species 2. The fraction of mass loss during three incubation times for each of three treatments 3. Litter concentration during different incubation times for each of threee treatmentJEcol-2017-0346data.xlsx