Kuzyakov, Yakov
Department of Soil Science of Temperate Ecosystems and Department of Agricultural Soil Science, University of Goettingen, Germany
Soils are the most heterogeneous parts of the biosphere, with an extremely high differentiation of properties and processes within nano- to macroscales. The spatial and temporal heterogeneity of input of labile organics by plants creates microbial hotspots over short periods of time – the hot moments. We define microbial hotspots as small soil volumes with much faster process rates compared to the average soil conditions. Such hotspots are found in the rhizosphere, detritusphere, biopores (including drilosphere) and on aggregate surfaces. Hot moments are short-term events or sequences of events inducing accelerated process rates as compared to the average rates. Thus, hotspots and hot moments are defined by dynamic characteristics, i.e. by process rates.
Localization and size of hotspots, their spatial distribution, transport of labile C to and from hotspots, lifetime and process intensities will be presented with a special focus on process rates and microbial activities. The fraction of active microorganisms in hotspots is 2-20 times higher than in the bulk soil, and their specific activities (i.e. respiration, microbial growth, mineralization potential, enzyme activities, RNA/DNA ratio) may be much higher. The duration of hot moments in the rhizosphere (hours to few days) is limited and is controlled by the length of the input of labile organics. In the detritusphere, however, the duration of hot moments is regulated by decomposition rates of litter (weeks to months). The faster turnover and lower C use efficiency in hotspots counterbalances the high C inputs, leading to the absence of strong increases in C stocks. Consequently, the intensification of fluxes is much stronger than the increase of pools. Maintenance of stoichiometric ratios by accelerated microbial growth in hotspots requires additional nutrients (e.g. N and P) from soil organic matter, i.e. priming effects. Consequently, priming effects are localized in microbial hotspots and are consequences of hot moments.
Martinoia, Enrico
Department of Plant and Molecular Biology, University Zurich, Switzerland
Every living organism needs essential heavy metals such as iron and zinc. However, if plants grow on soils containing high concentrations of these metals or of non-essential, toxic metals and metalloids such as cadmium or arsenic they may accumulate them at concentrations toxic for their growth as well as for animals and humans feeding these plants. For plants, one of the major steps to survive in heavy metal contaminated soils consists in depositing heavy metals safely into the large central vacuole. To be efficiently stored in this metabolic nearly inactive compartment, complexing agents such as carboxylates, nicotianamine or phytochelatins have also to be transported concomitantly with heavy metals into the vacuole in order to avoid that they can be transported back to the cytosol. Our laboratory is interested since many years in heavy metal resistance and especially in the role of the vacuole in heavy metal detoxification. On one side this knowledge will provide us with basic knowledge how plants deal with abiotic stresses, on an other side this knowledge can be exploited to learn which strategies should be applied in plant breeding and which are the most promising approaches allowing to produce plants that can clean up the environment and that accumulate less toxic metals in the edible parts. In the first part of my talk I will show how we succeeded to identify two vacuolar ABC transporters acting as the long-sought phytochelatine transporters. These transporters play a central role in providing resistance to plants against arsenic, mercury and cadmium. In the second part I will discuss how we identified the corresponding transporter in rice. Due to the complex anatomy this transporter plays mainly a role in nodes, which are the crossroads for the delivery of inorganic nutrients to the different parts of this crop. Absence of this transporter results in an increased arsenic content in grains. Finally I will discuss two biotechnological approaches. The first one was carried out with poplar. The goal was to produce plants that can be used for phytoremediation/phytostabilisation. The second approach deals with arsenic in rice fields. This is extremely important in India and Bangladesh, where rice is a staple food. Paddy fields of these countries contain very high amounts of arsenic due to irrigation with arsenic-containing water in former times. Rice growing on these soils takes up high arsenic concentrations which is transferred to grains and enters in the food chain. This has a toxic effect for the population. Therefore we have the goal to produce rice plants that accumulate much less heavy metals in rice grains.
Horvat, Milena, Kocman, David
Jožef Stefan Institute, Jamova cesta 39, Lubiana, Slovenia
Mercury is a contaminant of a global relevance, which is evidenced from a new global mercury treaty “Minamata Convention”, adopted in 2013. The main objectives of this convention are to protect human and ecosystem health from adverse effects of this toxic metal by reducing the emissions to air and releases to aquatic environment. Several articles within this convention address these issues including the reduction of emissions from stationary sources; limit the use of mercury in products and processes; closure of the primary mercury mining; permanent and safe storage of surplus liquid mercury and appropriate handling of wastes containing high concentrations of mercury. Remediation of mercury-contaminated sites are also addressed by the convention. Due to the unique chemical and physical properties, mercury cycles between environmental compartments (soil, water, air, and biosphere) and can reach places far away from sources of emissions. Global mercury emission inventories include anthropogenic emissions, contributing via current use or presence of mercury in a variety of products and processes, as well as natural source emissions. These inventories neglect the contribution of areas contaminated with mercury from historical accumulation, which surround mines or production plants associated with mercury production or use. Although recent studies have shown that releases of mercury from these historical sites can be significant, a database of the global distribution of mercury-contaminated sites does not exist, nor are there means of scaling up such releases to estimate fluxes on a regional and global basis. Therefore, an effort was made to estimate the contribution of mercury releases from contaminated sites to the global mercury budget. A geo-referenced database was built, comprising over 3000 mercury contaminated sites associated with mercury mining, precious metal processing, non-ferrous metal production and various polluted industrial sites. In the assessment, mercury releases from these sites to both the atmosphere as well as the hydrosphere were considered based on data available for selected case studies, their number, the reported extent of contamination and geographical location. Annual average global emissions of mercury from identified contaminated sites account for about 3-5 % of the global mercury released to the aquatic environment and up to 5 % to the atmosphere. Although these estimates are associated with large uncertainties, our current understanding of mercury releases from contaminated sites indicates that these releases can also be of paramount importance on the global perspective. This is especially important, as it is known that these sites represent a long-term source of releases if not managed properly. Therefore, it is important to re-focus resources in making decisions regarding mitigation and remediation strategies of mercury-contaminated sites on a global level.
Cakmak, Ismail
Sabanci University, Faculty of Engineering and Natural Sciences, 34956 Istanbul, Turkey
Despite significant achievements in reducing global hunger problem, micronutrient malnutrition (“hidden hunger”) still represents a major health problem in the world. Around 2 billion people are affected from micronutrient deficiencies such as zinc, iodine and iron deficiencies. Inadequate dietary intake of micronutrients is the particular reason of the problem, especially in the developing countries where extensive amounts of cereals are consumed with very low concentrations of micronutrients. High prevalence of micronutrient deficiencies is commonly associated with the regions where soils contain low amounts of micronutrients. Most of the cereal cultivated soils globally have diverse of chemical and physical problems (such as high pH and low amounts of organic matter and water) which limit chemical solubility and root uptake of micronutrients. Under such adverse soil and climatic conditions, the new genotypes developed by classical plant breeding or genetic engineering for high macronutrients in grain may not be able to fully exploit their genetic capacity to absorb and accumulate sufficient amounts of micronutrients in their grains. Therefore, treatment of plants with micronutrients seems to be an essential agronomic practice to ensure and maintain sufficiently high micronutrients in grains for human nutrition. The field studies conducted in the past 7-8 years under the HarvestZinc project (www.harvestzinc.org) on different cereal species demonstrated that the plant nutrition-based (i.e., agronomic) approach is a quick and cost-effective solution. A targeted foliar spray of micronutrients, such as right after anthesis, either individually or as a cocktail of micronutrients was found to be highly effective in increasing grain micronutrients. Maintenance of high pool of zinc, iodine and selenium in the leaf tissue during the reproductive growth stage through foliar spray seems to be a critical issue in achieving desirable concentrations of micronutrient in grains for human nutrition. The increases were found not only in whole grain but also in endosperm part or polished rice. It is also important to highlight that application of plant mineral nutrition approaches on genotypes with high genetic capacity for root uptake and seed translocation of micronutrients will further maximize accumulation of micronutrients in grain. The foods made from cereal grains biofortified agronomically with micronutrients, such as bread and cookies, had also sufficiently high micronutrients indicating higher stability of the micronutrients in the end-products. Consuming agronomically-biofortified foods is expected to result in significant contribution to human nutrition with high biological impacts.