Priming of carbon and nitrogen mineralization in forest soils

Decomposition of soil organic matter (SOM) contributes significantly to the global carbon (C) cycle and climate feedbacks. SOM decomposition depends on soil microbial activities, and these activities are driven by the availability of C and other nutrients. Plant root exudates are known to alter decomposition of SOM, a phenomenon referred to as rhizosphere priming effects (RPE). In order to predict the effect of environmental changes such as elevated CO2 and increased N deposition on microbial SOM decomposition and release of CO2 to the atmosphere, we need a better understanding of the factors that regulate RPE. In this thesis, I present my results from priming experiments with and without plants. I studied the effect of root exudates on SOM decomposition by adding glucose to soil to simulate root exudation. I also performed experiments with living plants. The aim was to investigate how variations in C and N availability influence priming. I further aimed to determine how elevated CO2, N fertilization, and light intensity influence root exudation rates and priming. I also tested how priming influence gross N mineralization and protein depolymerization, and if this could be linked to the abundance of different microbial functional groups and extracellular enzyme activity.I found that the soil C:N ratio is a poor predictor of priming. Instead, my findings suggest that the C:N imbalance (soil C:N divided by microbial biomass C:N) could better predict priming. My findings suggest that C:N imbalances could induce priming by increasing the abundance of microbes able to decompose complex substrates such as lignin. My results further suggest that priming is a result of enhanced activity of extracellular oxidative enzymes, rather than a change in the concentration of enzymes. I also found that in addition to increasing N cycling rates, soil microbes could meet their increased N demand caused by C input through using the available N more efficiently. This suggests that plant C input might aggravate N limitation by promoting microbial N sequestration. My findings highlight that elevated CO2 and N deposition enhance plant C uptake, but they also increase the microbial respiration of SOM to an even greater extent. These findings suggest that in order to evaluate if elevated CO2 and N deposition increases terrestrial C sequestration, changes in the microbial decomposition of SOM also needs to be accounted for. Finally, my results demonstrated that physiological traits of different plant species, e.g. response to altered light intensity, also have important effects on RPE.In summary, my findings suggest that priming is of major importance not only for C cycling in forest soils, but also for N cycling. Stoichiometric imbalances in C and N, plant and microbial nutrient demands, and the microbial response to nutrient deficiency, are important factors regulating RPE. I also conclude that priming a result of stimulated activity of extracellular oxidative enzymes, rather than of increased concentration of such enzymes

MECHANISM DESIGN WITH GENERAL UTILITIES

This thesis studies mechanism design from an optimization perspective. Our main contribution is to characterize fundamental structural properties of optimization problems arising in mechanism design and to exploit them to design general frameworks and techniques for efficiently solving the underlying problems. Not only do our characterizations allow for efficient computation, they also reveal qualitative characteristics of optimal mechanisms which are important even from a non-computational standpoint. Furthermore, most of our techniques are widely applicable to optimization problems outside of mechanism design such as online algorithms or stochastic optimization. Our frameworks can be summarized as follows. When the input to an optimization problem (e.g., a mechanism design problem) comes from independent sources (e.g., independent agents), the complexity of the problem can be exponentially reduced by (i) decomposing the problem into smaller subproblems, each one involving one input source, (ii) simultaneously optimizing the subproblems subject to certain relaxation of coupling constraints, and (iii) combining the solutions of the subproblems in a certain way to obtain an (approximately) optimal solution for the original problem. We use our proposed framework to construct optimal or approximately optimal mechanisms for several settings previously considered in the literature and to improve upon the best previously known results. We also present applications of our techniques to non-mechanism design problems such as online stochastic generalized assignment problem which itself captures online and stochastic versions of various other problems such as resource allocation and job scheduling

Optimal Auctions vs. Anonymous Pricing

For selling a single item to agents with independent but non-identically distributed values, the revenue optimal auction is complex. With respect to it, Hartline and Roughgarden (2009) showed that the approximation factor of the second-price auction with an anonymous reserve is between two and four. We consider the more demanding problem of approximating the revenue of the ex ante relaxation of the auction problem by posting an anonymous price (while supplies last) and prove that their worst-case ratio is e. As a corollary, the upper-bound of anonymous pricing or anonymous reserves versus the optimal auction improves from four to $e$. We conclude that, up to an $e$ factor, discrimination and simultaneity are unimportant for driving revenue in single-item auctions.Comment: 19 pages, 6 figures, To appear in 56th Annual IEEE Symposium on Foundations of Computer Science (FOCS 2015

Non-progressive Non-immune Hydrops Fetalis Caused by a Novel Mutation in GUSB Gene

Mucopolysaccharidosis type VII or Sly syndrome is a rare autosomal recessive disorder caused by deficiency of β Glucuronidase enzyme, which is involved in degradation of glycosaminoglycans. The lack of β Glucuronidase in this lysosomal storage disorder is characterized by various manifestation such as non-immune hydrops fetalis, spinal deformity, organomegaly, multiplex dysostosis, intellectual disability, and eye involvement. It has been found to be caused by a mutation in GUSB gene on chromosome 7 q11. Here we reported an Iranian girl with Mucopolysaccharidosis type VII and a novel mutation (C. 542G>T, P.Arg181Leu) in GUSB gene

Microbial carbon use efficiency and priming of soil organic matter mineralization by glucose additions in boreal forest soils with different C:N ratios

Publisher Copyright: © 2022During the last decade it has been increasingly acknowledged that carbon (C) contained in root exudates can accelerate decomposition of soil organic matter (SOM), a phenomenon known as rhizosphere priming effect (RPE). However, the controlling factors and the role of different soil microorganisms in RPE are not yet well understood. There are some indications that the response of the soil microbial decomposers to labile C input in the rhizosphere depends on microbial demand of nutrients for growth and maintenance, especially that of C and nitrogen (N). To test this hypothesis, we assessed SOM decomposition induced by 13C-glucose additions during one week in forest soils with different C:N ratios (11.5–22.2). We estimated SOM respiration, the potential activity (concentration) of a range of extracellular enzymes, and incorporation of 13C and deuterium (D) in microbial phospholipid fatty acids (PLFAs). Glucose additions induced positive priming (a 12–52% increase in SOM respiration) in all soil types, but there was no linear relationship between priming and the soil C:N ratio. Instead, priming of SOM respiration was positively linked to the C:N imbalance, where a higher C:N imbalance implies stronger microbial N limitation. The total oxidative enzyme activity and the ratio between the activities of C and N acquiring enzymes were lower in soil with higher C:N ratios, but these findings could not be quantitatively linked to the observed priming rates. It appears as if glucose addition resulted in priming by stimulating the activity rather than the concentration of oxidative enzymes. Microbial incorporation of D and 13C into in PLFAs demonstrated that glucose additions stimulated both fungal and bacterial growth. The increased growth was mainly supported by glucose assimilation in fungi, while the increase in bacterial growth partly was a result of increased availability of C or N released from SOM. Taken together, the findings suggest that the soil C:N ratio is a poor predictor of priming and that priming is more dependent on the C:N imbalance, which reflects both microbial nutrient demand and nutrient provision.Peer reviewe

International collaboration formation in entrepreneurial food industry: evidence of an emerging economy

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Purpose International collaboration is a crucial requirement of entrepreneurship, particularly in developing emerging economies. This collaboration seems so necessary in the food industry as a major contributor to environmental, social and economic problems. This paper aims to identify, analyse the influential network relationship and prioritise the key success factors (KSFs) of international collaboration formation in the entrepreneurial food industry with a case study on Iran's emerging economy. Design/methodology/approach To identify a list of KSFs, a qualitative method, literature review, is initially used. A quantitative method, fuzzy-Delphi, then is employed to finalise the main KSFs based on the entrepreneurial food industry experts' opinion. To analyse the causal relationship, and prioritise the KSFs, a fuzzy decision-making trial and evaluation laboratory (DEMATEL)-analytic network process (ANP) methodology, i.e. FDANP, is applied. At the first stage, the cause–effect diagram of KSFs is extracted using fuzzy DEMATEL and then, the KSFs weights and priorities are evaluated using a fuzzy ANP. Findings The results illustrate that the characteristics of effective development workers are the leading dimension of a successful international collaboration that directly affects other dimensions. On the other hand, increased marketing and trading is the most important KSF that is directly related to international entrepreneurial collaboration team capabilities and professionalism. The leading and casual role of team members also plays a vital role in strategic and communication issues affecting the collaboration success, e.g. market research and new product development. Availability of financial resources and the ability of partners in continuous financing is also a crucial and required factor for a successful collaboration. Originality/value Using an extensive review of the literature to extract the KSFs of international entrepreneurial collaboration and finalising them using a fuzzy-Delphi method and examining the cause-effect relations between them, as well as prioritising the KSFs are the main contributions of this paper