Above- and belowground litter stocks and decay at a multi-species afforestation site on arid, saline soil

Abstract

We evaluated the annual stocks and decay rates of leaf litter, green foliage, and fine roots at a multiple-species afforestation site using the litterbag technique over 3 years. During the course of each year the decomposition of all residue types exhibited a pattern of initially rapid loss of mass over winter followed by decomposition rates that were effectively zero for the rest of the year. Depending on the year of measurement and tree species, decay constants defined by the asymptotic function (k _a ) for foliar materials ranged between 3 and 16 year⁻¹, with 55–74 % of the initial mass remaining after 1 year of field exposure. The greatest amount of mass remaining was observed in the third year when topsoil salinity increased to a point (11–18 dS m⁻¹) that it inhibited decomposition, superseding the influences of species characteristics and soil moisture. For foliar materials, the remaining stable fraction was smaller in Elaeagnus angustifolia that also showed a slower decay rate than other species. Fine roots (at a depth of 30 cm) degraded faster in all species, with 33–38 % of the initial mass remaining. The decay rates were lowest for Ulmus pumila roots, which were characterized by relatively dense tissue. The greater production and decomposition of nitrogen-rich residue might explain the superior performance of E. angustifolia in improving saline soil productivity. Irrespective of species, the carbon returns through the relatively fast decomposition of fine roots benefit soil fertility, whereas large inputs of slowly decomposing foliar residues represent carbon sequestration in the aboveground litter pool.