University of Kiel

About: University of Kiel is a education organization based out in Kiel, Germany. It is known for research contribution in the topics: Population & Transplantation. The organization has 27816 authors who have published 57114 publications receiving 2061802 citations. The organization is also known as: Christian Albrechts University & Christian-Albrechts-Universität zu Kiel.

Rhizosphere size and shape: Temporal dynamics and spatial stationarity

Abstract: The soil volume affected by roots – the rhizosphere – is one of the most important microbial hotspots determining the processes, dynamics and cycling of carbon (C), nutrients and water in terrestrial ecosystems. Rhizosphere visualization is necessary to understand, localize and quantify the ongoing processes and functions, but quantitative conclusions are very uncertain because of: 1) the continuum of the parameters between the root surface and root-free soil, i.e., there are no sharp borders, 2) differences in the distributions of various parameters (C, nutrients, pH, enzyme and microbial activities, gases, water etc.) across and along roots, 3) temporal changes of the parameters and processes with root growth as well as with water and C flows. In situ techniques: planar optodes, zymography, sensitive gels, 14C and neutron imaging as well as destructive approaches (thin layer slicing) have been used to analyze the rhizosphere extent and the gradients of various physico-chemical and biological characteristics: pH, CO2, O2, redox potential, enzyme activities, content of water, nutrients and excess elements, and organic compounds. A literature analysis allows the conclusion that: i) the rhizosphere extent for most of the parameters assessed by non-destructive visualization techniques is 0.5–4 mm but exceeds 4 mm for gases, nitrate, water and redox potential. ii) The rhizosphere extent of nutrients (N, P) is decoupled from the extent of the corresponding enzyme activities. iii) The imbalance between element flows to and uptake by roots may lead to accumulation of excess elements and formation of root carapaces (e.g. CaCO3 rhizoliths, Fe plaque) ranging up to a few cm. iv) All destructive approaches show a much (3–5 times) larger rhizosphere extent compared to visualization techniques. These conclusions are crucial for a mechanistic understanding of rhizosphere properties and functioning, estimation of the nutrient stocks available to roots, and for rhizosphere modelling considering root growth and architecture. Overall, roots function as ecosystem engineers and build their environment, serving as the main factors shaping rhizosphere extent. Sharp gradients are formed within a few days for nutrients and enzymes, but more time is necessary for the establishment of specific microbial communities. Despite the very strong dynamics of most parameters, their stationarity is reached within a few days because the release of C and enzymes or nutrient uptake are very quickly compensated by utilization by surrounding microorganisms or/and sorption and diffusion processes. We conclude that despite the dynamic nature of each property, the rhizosphere gradients, their extent and shape are quasi-stationary because of the opposite directions of their formation processes.

Decrepitation model for capacity loss during cycling of alloys in rechargeable electrochemical systems

Abstract: Mechanisms that are involved in the loss of capacity upon the cycling of electrochemical cells are discussed. The inherent instability of the electrochemical interface and the resultant geometrical changes are characteristic of electrodes in which the reactant is a pure element. On the other hand, decrepitation can play an important role in the case of polyphase electrodes in which significant changes in specific volume occur. A simple one-dimensional model is presented that shows the mechanism and the important parameters that are involved in particle fracture. It predicts that decrepitation will lead to a terminal particle size, as is found experimentally.

Policy: Five priorities for the UN Sustainable Development Goals.

Abstract: Restructure data-gathering and evaluation networks to address climate change, energy, food, health and water provision, say Yonglong Lu and colleagues