Xylanase, invertase and protease at the soil-litter interface of a loamy sand

Organic residues are commonly added to soils, but little is known about C a nd N dynamics at the soil-litter interface (detritusphere). We investigated soil microbial processes in the detritusphere at the microscale by placing maize litter bags between two soil cores teach tube: 3.0 cm long, 5.6 cm d iameter) and incubating at 9 degrees C for 27 days. Subsequently, the soil cores were frozen with liquid nitrogen and cut with a microtome to yield sa mples at 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00, 3.00, 4.00, 5.00, 6.00 and 10.0 mm from the litter. Microbial biomass N, protease, xylanase a nd invertase activities for the maize straw were two orders of magnitude hi gher than the corresponding values of control soil. Microscale investigatio ns of controls (no litter addition) showed low spatial heterogeneity of pro tease and higher heterogeneity for xylanase, invertase and dissolved organi c substances within the first 10 mm of the soil cores. The detritusphere wa s characterised by high turnover of organic material visible as gradients i n xylanase, invertase and protease activities and the depletion of DOC at t he soil-litter interface. The scale of the soil-litter interface ranged fro m 1.1-1.3 mm, in which the gradients of the enzyme activities followed an e xponential function (y=c + exp (b(0) + b(1) x(1) + b(2) x(2))). The high lo cal release of substrates seems to be the major mechanism driving C and N t urnover within the 1-2 mm from the surface of litter. The transport (mass f low and diffusion) of dissolved organic compounds which provides energy for soil microorganisms is the cause of higher enzyme activities within the cl ose vicinity of the litter surface. (C) 1999 Elsevier Science Ltd. All righ ts reserved.