University of Hohenheim

About: University of Hohenheim is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Population & Soil water. The organization has 8585 authors who have published 16406 publications receiving 567377 citations.

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

Abstract: Organic residues are commonly added to soils, but little is known about C and 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 (each tube: 3.0 cm long, 5.6 cm diameter) and incubating at 9°C for 27 days. Subsequently, the soil cores were frozen with liquid nitrogen and cut with a microtome to yield samples 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 and invertase activities for the maize straw were two orders of magnitude higher than the corresponding values of control soil. Microscale investigations of controls (no litter addition) showed low spatial heterogeneity of protease and higher heterogeneity for xylanase, invertase and dissolved organic substances within the first 10 mm of the soil cores. The detritusphere was characterised by high turnover of organic material visible as gradients in xylanase, invertase and protease activities and the depletion of DOC at the soil–litter interface. The scale of the soil–litter interface ranged from 1.1–1.3 mm, in which the gradients of the enzyme activities followed an exponential function ( y=c +exp ( b 0 + b 1 x 1 + b 2 x 2 )). The high local release of substrates seems to be the major mechanism driving C and N turnover within the 1–2 mm from the surface of litter. The transport (mass flow and diffusion) of dissolved organic compounds which provides energy for soil microorganisms is the cause of higher enzyme activities within the close vicinity of the litter surface.

Stimulation of microbial extracellular enzyme activities by elevated CO2 depends on soil aggregate size

Abstract: Increased belowground carbon (C) transfer by plant roots at elevated CO 2 may change properties of the microbial community in the rhizosphere. Previous investigations that focused on total soil organic C or total microbial C showed contrasting results: small increase, small decrease or no changes. We evaluated the effect of 5 years of elevated CO 2 (550 ppm) on four extracellular enzymes: β-glucosidase, chitinase, phosphatase, and sulfatase. We expected microorganisms to be differently localized in aggregates of various sizes and, therefore analyzed microbial biomass (C mic by SIR) and enzyme activities in three aggregate-size classes: large macro- (> 2 mm), small macro- (0.25-2 mm), and microaggregates (< 0.25 mm). To estimate the potential enzyme production, we activated microorganisms by substrate (glucose and nutrients) amendment. Although C total and C mic as well as the activities of β-glucosidase, phosphatase, and sulfatase were unaffected in bulk soil and in aggregate-size classes by elevated CO 2 , significant changes were observed in potential enzyme production after substrate amendment. After adding glucose, enzyme activities under elevated CO 2 were 1.2-1.9-fold higher than under ambient CO 2 . This indicates the increased activity of microorganisms, which leads to accelerated C turnover in soil under elevated CO 2 . Significantly higher chitinase activity in bulk soil and in large macroaggregates under elevated CO 2 revealed an increased contribution of fungi to turnover processes. At the same time, less chitinase activity in microaggregates underlined microaggregate stability and the difficulties for fungal hyphae penetrating them. We conclude that quantitative and qualitative changes of C input by plants into the soil at elevated CO 2 affect microbial community functioning, but not its total content. Future studies should therefore focus more on the changes of functions and activities, but less on the pools.

Organic phosphorus in the terrestrial environment: a perspective on the state of the art and future priorities

Abstract: Background: The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (Po) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction. Scope: We asked a group of experts to consider the global issues associated with Po in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the Po cycle, and to set priorities for Po research. Conclusions: We identified seven key opportunities for Po research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of Po in natural and managed systems; the role of microorganisms in controlling Po cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the Po research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems.