Managing Agroecosystems for Soil Microbial Carbon Use Efficiency: Ecological Unknowns, Potential Outcomes, and a Path Forward

Agricultural systems are increasingly managed for improving soil carbon (C) accumulation. However, there are limits to C returns in agricultural systems that constrain soil C accumulation capacity. Increasing the efficiency of how soil microbes process C is gaining interest as an important management strategy for increasing soil C and is a key feature of soil C dynamics in many new microbial-explicit models. A higher microbial C use efficiency (CUE) may increase C storage while reducing C system losses and is a fundamental trait affecting community assembly dynamics and nutrient cycling. However, the numerous ecological unknowns influencing CUE limit our ability to effectively manage CUE in agricultural soils for greater soil C storage. In this perspective, we consider three complex drivers of agroecosystem CUE that need to be resolved to develop effective C sequestration management practices in the future: (1) the environment as an individual trait moderator versus a filter, (2) microbial community competitive and faciliatory interactions, and (3) spatiotemporal dynamics through the soil profile and across the microbial lifecycle. We highlight ways that amendments, crop rotations, and tillage practices might affect microbial CUE conditions and the variable outcomes of these practices. We argue that to resolve some of the unknowns of CUE dynamics, we need to include more mechanistic, trait-based approaches that capitalize on advanced methods and innovative field research designs within an agroecosystem-specific context. By identifying the management-level determinants of CUE expression, we will be better positioned to optimize CUE to increase soil C storage in agricultural systems

Unifying soil organic matter formation and persistence frameworks: the MEMS model

Soil organic matter (SOM) dynamics in ecosystem-scale biogeochemical models have traditionally been simulated as immeasurable fluxes between conceptually defined pools. This greatly limits how empirical data can be used to improve model performance and reduce the uncertainty associated with their predictions of carbon (C) cycling. Recent advances in our understanding of the biogeochemical processes that govern SOM formation and persistence demand a new mathematical model with a structure built around key mechanisms and biogeochemically relevant pools. Here, we present one approach that aims to address this need. Our new model (MEMS v1.0) is developed from the Microbial Efficiency-Matrix Stabilization framework, which emphasizes the importance of linking the chemistry of organic matter inputs with efficiency of microbial processing and ultimately with the soil mineral matrix, when studying SOM formation and stabilization. Building on this framework, MEMS v1.0 is also capable of simulating the concept of C saturation and represents decomposition processes and mechanisms of physico-chemical stabilization to define SOM formation into four primary fractions. After describing the model in detail, we optimize four key parameters identified through a variance-based sensitivity analysis. Optimization employed soil fractionation data from 154 sites with diverse environmental conditions, directly equating mineral-associated organic matter and particulate organic matter fractions with corresponding model pools. Finally, model performance was evaluated using total topsoil (0–20&thinsp;cm) C data from 8192 forest and grassland sites across Europe. Despite the relative simplicity of the model, it was able to accurately capture general trends in soil C stocks across extensive gradients of temperature, precipitation, annual C inputs and soil texture. The novel approach that MEMS v1.0 takes to simulate SOM dynamics has the potential to improve our forecasts of how soils respond to management and environmental perturbation. Ensuring these forecasts are accurate is key to effectively informing policy that can address the sustainability of ecosystem services and help mitigate climate change.</p

Gaming with eutrophication: Contribution to integrating water quantity and quality management at catchment level

The Metropolitan Region of Sao Paulo (MRSP) hosts 18 million inhabitants. A complex system of 23 interconnected reservoirs was built to ensure its water supply. Half of the potable water produced for MRSP's population (35 m3/s) is imported from a neighbour catchment, the other half is produced within the Alto Tietê catchment, where 99% of the population lives. Perimeters of land use restriction were defined to contain uncontrolled urbanization, as domestic effluents were causing increasing eutrophication of some of these reservoirs. In the 90's catchment committees and sub committees were created to promote discussion between stakeholders and develop catchment plans. The committees are very well structured "on paper". However, they are not very well organised and face a lack of experience. The objective of this work was to design tools that would strengthen their discussion capacities. The specific objective of the AguAloca process was to integrate the quality issue and its relation to catchment management as a whole in these discussions. The work was developed in the Alto Tietê Cabeceiras sub-catchment, one of the 5 sub catchments of the Alto-Tietê. It contains 5 interconnected dams, and presents competitive uses such as water supply, industry, effluent dilution and irrigated agriculture. A RPG was designed following a companion modelling approach (Etienne et al., 2003). It contains a friendly game-board, a set of individual and collective rules and a computerized biophysical model. The biophysical model is used to simulate water allocation and quality processes at catchment level. It articulates 3 modules. A simplified nutrient discharge model permits the estimation of land use nutrient exportation. An arc-node model simulates water flows and associated nutrient charges from one point of the hydrographical network to another. The Vollenweider model is used for simulating specific reservoir dynamics. The RPG allows players to make individual and collective decisions related to water allocation and the management of its quality. Impacts of these decisions are then simulated using the biophysical model. Specific indicators of the game are then updated and may influence player's behaviour (actions) in following rounds. To introduce discussions on the management of water quality at a catchment level, an issue that is rarely explicitly dealt with, four game sessions were implemented involving representatives of basin committees and water and sanitation engineers. During the game session, the participants took advantage of the water quality output of the biophysical model to test management alternatives such as rural sewage collection or effluent dilution. The biophysical model accelerated calculations of flows and eutrophication rates that were then returned to the game board with explicit indicators of quantity and quality. Players could easily test decisions impacting on qualitative water processes and visualize the simulation results directly on the game board that was representing a friendly, virtual and simplified catchment. The Agualoca game proved its ability to turn complex water processes understandable for a non totally initiated public. This experience contributed to a better understanding of multiple-use water management and also of joint management of water quality and quantity. (Résumé d'auteur

Influence of the 6^1S_0-6^3P_1 Resonance on Continuous Lyman-alpha Generation in Mercury

Continuous coherent radiation in the vacuum-ultraviolet at 122 nm (Lyman-alpha) can be generated using sum-frequency mixing of three fundamental laser beams in mercury vapour. One of the fundamental beams is at 254 nm wavelength, which is close to the 6^1S_0-6^3P_1 resonance in mercury. Experiments have been performed to investigate the effect of this one-photon resonance on phasematching, absorption and the nonlinear yield. The efficiency of continuous Lyman-alpha generation has been improved by a factor of 4.5.Comment: 8 pages, 7 figure

Phosphorus mobilizing consortium Mammoth P enhances plant growth

Global agricultural productivity may be constrained by the finite and limited supply of phosphorus (P), adding to the challenges in meeting the projected needs of a growing human population in the coming decades. In addition, when P fertilizers are added to soils, they can become bound to soils resulting in low fertilizer efficiency. However, P-mobilizing bacteria could potentially liberate soil-bound P, resulting in a higher plant P uptake and increased yield. Bacteria can mobilize P through several mechanisms, suggesting that consortia of P-bacteria may be more effective than single species. Species diversity can have a synergistic, or non-additive, effect on ecosystem functioning (&quot;the whole is more than the sum of its parts&quot;) but rarely is the microbial community structure intentionally managed to improve plant nutrient uptake. We investigated whether inoculation of soils with a four-species bacterial community developed to mobilize soil P could increase plant productivity. In wheat and turf trials, we found that Mammoth P was able to deliver yields equivalent to those achieved using conventional fertilizer applications. Herbs and fruits showed that the combination of fertilizer with Mammoth P significantly increased productivity -in some cases productivity doubled. Metabolites produced by the Mammoth P consortium led to increased yields in some cases, suggesting that microbial products (produced in the absence of plants) played a role in enhancing plant productivity. Results from these trials indicate substantial potential of Mammoth P to enhance P supply to plants, improving P fertilizer use-efficiency and increasing agricultural productivity. 19 Agricultural productivity may be constrained in the 21 st Century by the finite supply of global a 20 phosphorus (P), adding to the challenges in meeting the projected needs of a growing human population 21 in the coming decades. In addition, when P fertilizers are added to soils, they can become bound to soils 22 resulting in low fertilizer efficiency. However, bacteria have the ability to mobilize soil bound P through 23 several mechanisms potentially resulting in a higher plant P uptake and increased yield. Furthermore, 24 species diversity can have a synergistic effect on ecosystem functioning (&quot;the whole is more than the sum 25 of its parts&quot;) suggesting that bacterial communities, or consortia, may be more effective than single 26 species. However, in agriculture management practices, rarely is the soil microbial community structure 27 effectively manipulated to improve plant nutrient uptake. We investigated whether inoculation of soils 28 with a bacterial consortium developed to mobilize soil P named Mammoth P could increase plant 29 productivity. In turf, herbs and fruits, we showed that the combination of conventional inorganic fertilizer 30 combined with Mammoth P increased productivity up to twofold compared to the fertilizer treatments 31 without the Mammoth P inoculant. In wheat trials, we found that Mammoth P by itself was able to deliver 32 yields equivalent to those achieved with conventional inorganic fertilizer applications. The metabolites 33 produced by the consortium in Mammoth P likely played a role in enhancing plant productivity. Results 34 from this study indicate the substantial potential of Mammoth P to enhance P supply to plants, improving 35 P fertilizer use-efficiency and increasing agricultural productivity. 3

Decreased mass specific respiration under experimental warming is robust to the microbial biomass method employed

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Ecology Letters 12 (2009): E15-E18, doi:10.1111/j.1461-0248.2009.01332.x.Hartley et al. question whether reduction in Rmass, under experimental warming, arises because of the biomass method. We show the method they treat as independent yields the same result. We describe why the substrate-depletion hypothesis cannot alone explain observed responses, and urge caution in the interpretation of the seasonal data.This research was supported by the Office of Science (BER), U.S. Department of Energy, the Andrew W. Mellon Foundation and U.S. National Science Foundation grants to the Coweeta LTER program

A three-dimensional view of structural changes caused by deactivation of fluid catalytic cracking catalysts

Since its commercial introduction three-quarters of a century ago, fluid catalytic cracking has been one of the most important conversion processes in the petroleum industry. In this process, porous composites composed of zeolite and clay crack the heavy fractions in crude oil into transportation fuel and petrochemical feedstocks. Yet, over time the catalytic activity of these composite particles decreases. Here, we report on ptychographic tomography, diffraction, and fluorescence tomography, as well as electron microscopy measurements, which elucidate the structural changes that lead to catalyst deactivation. In combination, these measurements reveal zeolite amorphization and distinct structural changes on the particle exterior as the driving forces behind catalyst deactivation. Amorphization of zeolites, in particular, close to the particle exterior, results in a reduction of catalytic capacity. A concretion of the outermost particle layer into a dense amorphous silica–alumina shell further reduces the mass transport to the active sites within the composite

Linear stability analysis of retrieval state in associative memory neural networks of spiking neurons

We study associative memory neural networks of the Hodgkin-Huxley type of spiking neurons in which multiple periodic spatio-temporal patterns of spike timing are memorized as limit-cycle-type attractors. In encoding the spatio-temporal patterns, we assume the spike-timing-dependent synaptic plasticity with the asymmetric time window. Analysis for periodic solution of retrieval state reveals that if the area of the negative part of the time window is equivalent to the positive part, then crosstalk among encoded patterns vanishes. Phase transition due to the loss of the stability of periodic solution is observed when we assume fast alpha-function for direct interaction among neurons. In order to evaluate the critical point of this phase transition, we employ Floquet theory in which the stability problem of the infinite number of spiking neurons interacting with alpha-function is reduced into the eigenvalue problem with the finite size of matrix. Numerical integration of the single-body dynamics yields the explicit value of the matrix, which enables us to determine the critical point of the phase transition with a high degree of precision.Comment: Accepted for publication in Phys. Rev.