Abstract: It is increasingly recognized that soil microbes have the ability to decompose old recalcitrant soil organic matter (SOM) by using fresh carbon as a source of energy, a phenomena called priming effect (PE). However, efforts to determine the consequences of this PE for soil carbon and nitrogen dynamics are in their early stage. Moreover, little is known about the microbial populations involved. Here we explore the consequences of PE for SOM dynamics and mineral nitrogen availability in a soil incubation experiment (161 days), combining the supply of dual-labeled (13C and 14C) cellulose and mineral nutrients. The microbial groups involved in PE were investigated using molecular fingerprinting techniques (FAMEs and B- and F-ARISA). We show that mean residence time of SOM pool controlled by the PE decreased from 3130 years in the subsoil, where the availability of fresh carbon is very low, to 17–39 years in the surface layer. This result suggests that the decomposition of this recalcitrant soil C pool is strictly dependent on the presence of fresh C and is not an energetically viable mean of accessing C for soil microbes. We also suggest that fungi are the predominant actors of cellulose decomposition and induced PE and they adjust their degradation activity to nutrient availability. The predominant role of fungi can be explained by their ability to grow as mycelium which allows them to explore soil space and mine large reserve of SOM. Finally, our results support the existence of a bank mechanism that regulates nutrient and carbon sequestration in soil: PE is low when nutrient availability is high, allowing sequestration of nutrients and carbon; in contrast, microbes release nutrients from SOM when nutrient availability is low. This bank mechanism may help to synchronize the availability of soluble nutrients to plant requirement and contribute to long-term SOM accumulation in ecosystems.

Abstract: Root exudates play a major role in the mobilization of sparingly soluble nutrients in the rhizosphere. Since the amount and composition of major metabolites in root exudates from one plant species have not yet been systematically compared under different nutrient deficiencies, relations between exudation patterns and the type of nutrient being deficient remain poorly understood. Comparing root exudates from axenically grown maize plants exposed to N, K, P, or Fe deficiency showed a higher release of glutamate, glucose, ribitol, and citrate from Fe-deficient plants, while P deficiency stimulated the release of c-aminobutyric acid and carbohydrates. Potassium-starved plants released less sugars, in particular glycerol, ribitol, fructose, and maltose, while under N deficiency lower amounts of amino acids were found in root exudates. Principal-component analysis revealed a clear separation in the variation of the root-exudate composition between Fe or P deficiency versus N or K deficiency in the first principal component, which explained 46% of the variation in the data. In addition, a negative correlation was found between the amounts of sugars, organic and amino acids released under deficiency of a certain nutrient and the diffusion coefficient of the respective nutrient in soils. We thus hypothesize that the release of dominant root exudates such as sugars, amino acids, and organic acids by roots may reflect an ancient strategy to cope with limiting nutrient supply.

Abstract: Concentrations of phosphorus and nitrogen in surface waters are being regulated in the United States and European Union. Human activity has raised the concentrations of these nutrients, leading to eutrophication of inland waters, which causes nuisance growth of algae and other aquatic plants. Control of phosphorus often has had the highest priority because of its presumed leading role in limiting development of aquatic plant biomass. Experimental evidence shows, however, that nitrogen is equally likely to limit growth of algae and aquatic plants in inland waters, and that additions of both nutrients cause substantially more algal growth than either added alone. A dual control strategy for N and P will reduce transport of anthropogenic nitrogen through drainage networks to aquatic ecosystems that may be nitrogen limited. Control of total phosphorus in effluents is feasible and is increasingly being required by regulations. The control strategy for nitrogen in effluents is more difficult, but could be made ...

Abstract: Understanding variation of plant nutrients is largely limited to nitrogen and to a lesser extent phosphorus. Here we analyse patterns of variation in 11 elements (nitrogen/phosphorus/potassium/calcium/magnesium/sulphur/silicon/iron/sodium/manganese/aluminium) in leaves of 1900 plant species across China. The concentrations of these elements show significant latitudinal and longitudinal trends, driven by significant influences of climate, soil and plant functional type. Precipitation explains more variation than temperature for all elements except phosphorus and aluminium, and the 11 elements differentiate in relation to climate, soil and functional type. Variability (assessed as the coefficient of variation) and environmental sensitivity (slope of responses to environmental gradients) are lowest for elements that are required in the highest concentrations, most abundant and most often limiting in nature (the Stability of Limiting Elements Hypothesis). Our findings can help initiate a more holistic approach to ecological plant nutrition and lay the groundwork for the eventual development of multiple element biogeochemical models.

Abstract: Drought is a major constraint for rice production in the rainfed lowlands in China. Silicon (Si) has been verified to play an important role in enhancing plant resistance to environmental stress. Two near-isogenic lines of rice (Oryza sativa L.), w-14 (drought susceptible) and w-20 (drought resistant), were selected to study the effects of exogenous Si application on the physiological traits and nutritional status of rice under drought stress. In wet conditions, Si supply had no effects on growth and physiological parameters of rice plants. Drought stress was found to reduce dry weight, root traits, water potential, photosynthetic parameters, basal quantum yield (Fv/F0), and maximum quantum efficiency of PSII photochemistry (Fv/Fm) in rice plants, while Si application significantly increased photosynthetic rate (Pr), transpiration rate (Tr), Fv/F0, and Fv/Fm of rice plants under drought stress. In addition, water stress increased K, Na, Ca, Mg, Fe content of rice plants, but Si treatment significantly reduced these nutrient level. These results suggested that silicon application was useful to increase drought resistance of rice through the enhancement of photochemical efficiency and adjustment of the mineral nutrient absorption in rice plants.

Abstract: Water, the most important component of life, is rapidly becoming a critically short commodity for humans and crop production. Limited water supply is one of the major abiotic factors that adversely affect agricultural crop production worldwide. Drought stress influences the normal physiology and growth of plants in many ways. It results in an increase of solute concentration outside the roots compared to the internal environment of the root and causes reverse osmosis. As a result, the cell membrane shrinks from the cell wall and may eventually lead to death of the cell. Water stress tends to shrink away from the interface with water-absorbing roots, creating a gap in the soil-plant-air continuum. As the plant continues to lose water via transpiration, water is drawn from root cells resulting in shrinkage of cell membranes and results in decreased integrity of the cell membrane and the living cell may be destroyed. Drought stress inhibits photosynthesis in plants by closing stomata and damaging the chlorophyll contents and photosynthetic apparatus. It disturbs the balance between the production of reactive oxygen species (ROS) and the antioxidant defence, causing accumulation of ROS which induces oxidative stress to proteins, membrane lipids and other cellular component. Mineral elements have numerous functions in plants including maintaining charge balance, electron carriers, structural components, enzyme activation, and providing osmoticum for turgor and growth .In this paper, an overview of some macronutrients (nitrogen, phosphorus, potassium, calcium and magnesium), micronutrients (Zinc, Boron, Copper) and silicon has been discussed in detail as how these nutrients play their role in decreasing the adverse effects of drought in crop plant.

Abstract: Agriculture is going through a profound revolution worldwide due to increasing world demand for food, higher costs of energy and other inputs, environmental pollution problems, and instability of cropping systems. In this context, knowledge of factors that affect root development is fundamental to improving nutrient cycling and uptake in soil–plant systems. Roots are important organs that supply water, nutrients, hormones, and mechanical support (anchorage) to crop plants and consequently affect economic yields. In addition, roots improve soil organic matter (OM) by contributing to soil pools of organic carbon (C), nitrogen (N), and microbial biomass. Root-derived soil C is retained and forms more stable soil aggregates than shoot-derived soil C. Although roots normally contribute only 10–20% of the total plant weight, a well-developed root system is essential for healthy plant growth and development. Root growth of plants is controlled genetically, but it is also influenced by environmental factors. Mineral nutrition is an important factor influencing the growth of plant roots, but detailed information on nutritional effects is limited, primarily because roots are half-hidden organs that are very difficult to separate from soil. As a result, it is difficult to measure the effect of biotic and abiotic factors on root growth under field conditions. Root growth is mainly measured in terms of root density, length, and weight. Root dry weight is often better related to crop yields than is root length or density. The response of root growth to chemical fertilization is similar to that of shoot growth; however, the magnitude of the response may differ. In nutrient-deficient soils, root weight often increases in a quadratic manner with the addition of chemical fertilizers. Increasing nutrient supplies in the soil may also decrease root length but increase root weight in a quadratic fashion. Roots with adequate nutrient supplies may also have more root hairs than nutrient-deficient roots. This may result in greater uptake of water and nutrients by roots well supplied with essential plant nutrients, compared with roots grown in nutrient-deficient soils. Under favorable conditions, a major part of the root system is usually found in the top 20 cm of soil. Maximum root growth is generally achieved at flowering in cereals and at pod-setting in legumes. Genotypic variations are often found in the response of root growth to nutrient applications, and the possibility of modifying root system response to soil properties offers exciting prospects for future improvements in crop yields. Rooting pattern in crop plants is under multi- or polygenic control, and breeding programs can be used to improve root system properties for environments where drought is a problem. The use of crop species and cultivars tolerant to biotic and abiotic stresses, as well as the use of appropriate cultural practices, can improve plant root system function under favorable and unfavorable environmental conditions.

Abstract: Understanding the factors that drive soil carbon (C) accumulation is of fundamental importance given their potential to mitigate climate change. Much research has focused on the relationship between plant traits and C sequestration, but no studies to date have quantitatively considered traits of their mycorrhizal symbionts. Here, we use a modelling approach to assess the contribution of an important mycorrhizal fungal trait, organic nutrient uptake, to soil C accumulation. We show that organic nutrient uptake can significantly increase soil C storage, and that it has a greater effect under nutrient-limited conditions. The main mechanism behind this was an increase in plant C fixation and subsequent increased C inputs to soil through mycorrhizal fungi. Reduced decomposition due to increased nutrient limitation of saprotrophs also played a role. Our results indicate that direct uptake of nutrients from organic pools by mycorrhizal fungi could have a significant effect on ecosystem C cycling and storage.

Abstract: Root cortical aerenchyma (RCA) is induced by hypoxia, drought, and several nutrient deficiencies. Previous research showed that RCA formation reduces the respiration and nutrient content of root tissue. We used SimRoot, a functional-structural model, to provide quantitative support for the hypothesis that RCA formation is a useful adaptation to suboptimal availability of phosphorus, nitrogen, and potassium by reducing the metabolic costs of soil exploration in maize (Zea mays). RCA increased the growth of simulated 40-d-old maize plants up to 55%, 54%, or 72% on low nitrogen, phosphorus, or potassium soil, respectively, and reduced critical fertility levels by 13%, 12%, or 7%, respectively. The greater utility of RCA on low-potassium soils is associated with the fact that root growth in potassium-deficient plants was more carbon limited than in phosphorus- and nitrogen-deficient plants. In contrast to potassium-deficient plants, phosphorus- and nitrogen-deficient plants allocate more carbon to the root system as the deficiency develops. The utility of RCA also depended on other root phenes and environmental factors. On low-phosphorus soils (7.5 μm), the utility of RCA was 2.9 times greater in plants with increased lateral branching density than in plants with normal branching. On low-nitrate soils, the utility of RCA formation was 56% greater in coarser soils with high nitrate leaching. Large genetic variation in RCA formation and the utility of RCA for a range of stresses position RCA as an interesting crop-breeding target for enhanced soil resource acquisition.

Abstract: The availability of mineral nutrients in the soil dramatically fluctuates in both time and space. In order to optimize their nutrition, plants need efficient sensing systems that rapidly signal the local external concentrations of the individual nutrients. Until recently, the most upstream actors of the nutrient signalling pathways, i.e. the sensors/receptors that perceive the extracellular nutrients, were unknown. In Arabidopsis, increasing evidence suggests that, for nitrate, the main nitrogen source for most plant species, a major sensor is the NRT1.1 nitrate transporter, also contributing to nitrate uptake by the roots. Membrane proteins that fulfil a dual nutrient transport/signalling function have been described in yeast and animals, and are called 'transceptors'. This review aims to illustrate the nutrient transceptor concept in plants by presenting the current evidence indicating that NRT1.1 is a representative of this class of protein. The various facets, as well as the mechanisms of nitrate sensing by NRT1.1 are considered, and the possible occurrence of other nitrate transceptors is discussed.

Abstract: In woodland streams, the decomposition of allochthonous organic matter constitutes a fundamental ecosystem process, where aquatic hyphomycetes play a pivotal role. It is therefore greatly affected by water temperature and nutrient concentrations. The individual effects of these factors on the decomposition of litter have been studied previously. However, in the climate warming scenario predicted for this century, water temperature and nutrient concentrations are expected to increase simultaneously, and their combined effects on litter decomposition and associated biological activity remains unevaluated. In this study, we addressed the individual and combined effects of water temperature (three levels) and nutrient concentrations (two levels) on the decomposition of alder leaves and associated aquatic hyphomycetes in microcosms. Decomposition rates across treatments varied between 0.0041dayˉ¹ at 5°C and low nutrient level and 0.0100 dayˉ¹ at 15°C and high nutrient level. The stimulation of biological variables at high nutrients and temperatures indicates that nutrient enrichment of streams might have a higher stimulatory effect on fungal performance and decomposition rates under a warming scenario than at present. The stimulation of fungal biomass and sporulation with increasing temperature at both nutrient levels shows that increases in water temperature might enhance fungal growth and reproduction in both oligotrophic and eutrophic streams. The stimulation of fungal respiration and litter decomposition with increasing temperature at high nutrients indicates that stimulation of carbon mineralization will probably occur at eutrophied streams, while oligotrophic conditions seem to be 'protected' from warming. All biological variables were stimulated when both factors increased, as a result of synergistic interactions between factors. Increased water temperature and nutrient level also affected the structure of aquatic hyphomycete assemblages. It is plausible that if water quality of presently eutrophied streams is improved, the potential stimulatory effects of future increases in water temperature on aquatic biota and processes might be mitigated.

Abstract: A significant contributor to the rising rates of human obesity is an increase in energy intake. The ‘protein leverage hypothesis’ proposes that a dominant appetite for protein in conjunction with a decline in the ratio of protein to fat and carbohydrate in the diet drives excess energy intake and could therefore promote the development of obesity. Our aim was to test the ‘protein leverage hypothesis’ in lean humans by disguising the macronutrient composition of foods offered to subjects under ad libitum feeding conditions. Energy intakes and hunger ratings were measured for 22 lean subjects studied over three 4-day periods of in-house dietary manipulation. Subjects were restricted to fixed menus in random order comprising 28 foods designed to be similar in palatability, availability, variety and sensory quality and providing 10%, 15% or 25% energy as protein. Nutrient and energy intake was calculated as the product of the amount of each food eaten and its composition. Lowering the percent protein of the diet from 15% to 10% resulted in higher (+12±4.5%, p = 0.02) total energy intake, predominantly from savoury-flavoured foods available between meals. This increased energy intake was not sufficient to maintain protein intake constant, indicating that protein leverage is incomplete. Urinary urea on the 10% and 15% protein diets did not differ statistically, nor did they differ from habitual values prior to the study. In contrast, increasing protein from 15% to 25% did not alter energy intake. On the fourth day of the trial, however, there was a greater increase in the hunger score between 1–2 h after the 10% protein breakfast versus the 25% protein breakfast (1.6±0.4 vs 25%: 0.5±0.3, p = 0.005). In our study population a change in the nutritional environment that dilutes dietary protein with carbohydrate and fat promotes overconsumption, enhancing the risk for potential weight gain.

Abstract: Potassium is an essential element for plant growth and is an extremely dynamic ion in plant and soil system. As an ion, potassium is highly mobile in the plant system but only moderately mobile in the soil system. Just like humans require a balanced diet with appropriate amounts of carbohydrates, proteins, vitamins, minerals, fats and water, plants too require conditions of balanced nutrition. There is a pre-determined ratio of nutrients that is required by the plant system, depending on its life cycle, environment and its genotypic characteristics, to realize its maximum genetic potential. This ratio of elements is more critical than the actual concentration of the individual elements. Nutrient balancing in micronutrients is an important and yet more difficult than balancing between macronutrients. Synergistic and Antagonistic relationships between nutrients are responsible for efficient/inefficient uptake and utilization of potassium. This paper discusses the interrelationships between plant nutrients with a special reference to potassium and macronutrients like nitrogen and phosphorus, potassium and secondary nutrients like calcium, magnesium and sodium and finally potassium and micronutrients. The goal of this paper is to elucidate the complicated and still less understood relationships between essential nutrients so as to bridge the gap between potential yields and actual yields.

Abstract: Most water and essential soil nutrient uptake is carried out by fine roots in plants. It is therefore important to understand the global geographic patterns of fine-root nitrogen and phosphorus cycling. Here, by compiling plant root data from 211 studies in 51 countries, we show that live fine roots have low nitrogen (N) and phosphorus (P), but similar N:P ratios when compared with green leaves. The fine-root N:P ratio differs between biomes and declines exponentially with latitude in roots of all diameter classes. This is in contrast to previous reports of a linear latitudinal decline in green leaf N:P, but consistent with nonlinear declines in leaf litter N:P. Whereas the latitudinal N:P decline in both roots and leaves reflects collective influences of climate, soil age and weathering, differences in the shape of the response function may be a result of their different N and P use strategies. Through fine-root nutrient chemistry, it is possible to study ecosystem-scale biogeochemical cycling. Compiling data from 211 studies measuring nitrogen and phosphorus in plant roots, Yuanet al. find that tropical ecosystems are more phosphorous-limited than higher latitudes.

Abstract: Carbon storage and sequestration in tropical mountain forests and their dependence on elevation and temperature are not well understood. In an altitudinal transect study in the South Ecuadorian Andes, we tested the hypotheses that (i) aboveground net primary production (ANPP) decreases continuously with elevation due to decreasing temperatures, whereas (ii) belowground productivity (BNPP) remains constant or even increases with elevation due to a shift from light to nutrient limitation of tree growth. In five tropical mountain forests between 1050 and 3060 m a.s.l., we investigated all major above- and belowground biomass and productivity components, and the stocks of soil organic carbon (SOC). Leaf biomass, stemwood mass and total aboveground biomass (AGB) decreased by 50% to 70%, ANPP by about 70% between 1050 and 3060m, while stem wood production decreased 20-fold. Coarse and large root biomass increased slightly, fine root biomass fourfold, while fine root production (minirhizotron study) roughly doubled between 1050 and 3060 m. The total tree biomass (above- and belowground) decreased from about 320 to 175 Mg dry mass ha ―1 , total NPP from ca. 13.0 to 8.2 Mg ha ―1 yr ―1 . The belowground /aboveground ratio of biomass and productivity increased with elevation indicating a shift from light to nutrient limitation of tree growth. We propose that, with increasing elevation, an increasing nitrogen limitation combined with decreasing temperatures causes a large reduction in stand leaf area resulting in a substantial reduction of canopy carbon gain toward the alpine tree line. We conclude that the marked decrease in tree height, AGB and ANPP with elevation in these mountain forests is caused by both a belowground shift of C allocation and a reduction in C source strength, while a temperature-induced reduction in C sink strength (lowered meristematic activity) seems to be of secondary importance.

Abstract: Mangrove forests exchange materials with the coastal ocean through tidal inundation. In this study, we aim to provide an overview of the published data of carbon (C) and nutrient exchange of mangrove forests with the coastal ocean at different spatial scales to assess whether the exchange is correlated with environmental parameters. We collected data on C (dissolved and particulate organic C; DOC and POC) and nutrient exchange (dissolved and particulate nitrogen, N and phosphorus, P) and examined the role of latitude, temperature, precipitation, geomorphological setting, hydrology, dominant mangrove species and forest area in explaining the variability of the exchange. We identified that there are a range of methodologies used to determine material exchange of mangroves with the coastal zone, each methodology providing data on the exchange at different spatial scales. This variability of approaches has limited our understanding of the role of mangroves in the coastal zone. Regardless, we found that mangrove forests export C and nutrients to the coastal zone in the form of litter and POC. We found that precipitation is a major factor influencing the export of C in the form of litter; sites with low annual precipitation and high mean annual temperatures export more C as litter than sites with high precipitation and low temperature. Furthermore, export of POC is higher in zones with low mean annual minimum temperature. Identification of broad-scale trends in DOC and dissolved nutrients was more difficult, as the analysis was limited by scarcity of suitable studies and high variability in experimental approaches. However, tidal amplitude and the concentration of nutrients in the floodwater appears to be important in determining nutrient exchange. The strongest conclusion from our analysis is that mangrove forests are in general sources of C and nutrients in the form of litter and POC and that they are most likely to be exporting C subsidies in dry regions.

Abstract: Organic and inorganic fertilizers are used primarily to increase nutrient availability to plants. Monitoring balanced versus unbalanced fertilization effects on soil microbes could improve our understanding of soil biochemical processes and thus help us to develop sound management strategies. The objective of this study was to investigate the effects of long-term fertilization regimes on soil microbial community functional diversity, metabolic activity, and metabolic quotient and to find out the main factors that influence these parameters. A long-term fertilization experiment established in a sandy loam soil at northern China has received continuous fertilization treatments for more than 20 years, including control, mineral fertilizers of NK, PK, NP, and NPK, organic amendment (OA), and half organic amendment plus half mineral fertilizer (1/2 OM). Top soil samples (0–15 cm) from four individual plots per treatment were collected for the analysis of chemical properties and microbial parameters. Microbial biomass C was analyzed using the fumigation–extraction method. Invertase activity and basal respiration were determined based on incubation method. Then, the microbial metabolic quotient was calculated as the ratio of basal respiration to microbial biomass C. To this end, microbial functional diversity was evaluated using the community level physiological profile method by Biolog Eco-microplate. Higher microbial biomass C, invertase activity, and basal respiration, but lower microbial metabolic quotient, were observed in P-fertilized soils, and OA had significantly greater (P < 0.05) impacts on the biomass, activity, and quotient compared with mineral fertilizers. Both the sole-carbon-source utilization activity and the functional diversity of soil microbial community were significantly increased (P < 0.05) by balanced fertilization (NPK, OA, or 1/2 OM), and species richness of community and relative abundance of the most common species in the K-deficient (NP) treatment were also significantly increased (P < 0.05). Principal component analysis and redundancy analysis showed that both organic and mineral fertilizers could affect microbial parameters by increasing soil organic C contents, and P was the key factor to increase soil microbial diversity and soil fertility. Long-term balanced fertilization greatly increased soil microbial biomass, functional diversity, and invertase activity and played an important role in decreasing soil microbial metabolic quotient, while P could be considered as the key factor to control soil microbial diversity as well as soil fertility. With regard to the different effects of OA and mineral fertilizer on soil organic C contents and root exudates, combined application of mineral and organic fertilizers is recommended in the region.

Abstract: A sediment-type photomicrobial fuel cell (PFC), based on the synergistic interaction between microalgae (Chlorella vulgaris) and electrochemically active bacteria, was developed to remove carbon and nutrients from wastewater, and produce electricity and algal biomass simultaneously. Under illumination, a stable power density of 68 ± 5 mW m−2 and a biomass of 0.56 ± 0.02 g L−1 were generated at an initial algae concentration of 3.5 g L−1. Accordingly, the removal efficiency of organic carbon, nitrogen and phosphorus was 99.6%, 87.6% and 69.8%, respectively. Mass balance analysis suggested the main removal mechanism of nitrogen and phosphorus was the algae biomass uptake (75% and 93%, respectively), while the nitrification and denitrification process contributed to a part of nitrogen removal (22%). In addition, the effect of illumination period on the performance of PFC was investigated. Except notable fluctuation of power generation, carbon and nutrients removal was not significantly affected after changing the light/dark photoperiod from 24 h/0 h to 10 h/14 h. This work represents the first successful attempt to develop an effective bacteria–algae coupled system, capable for extracting energy and removing carbon, nitrogen and phosphorus from wastewater in one-step.

Abstract: This study was conducted to isolate plant growth promoting rhizobacteria (PGPR) from wheat rhizosphere and to evaluate their potential use for improving growth, yield and nutrient uptake of wheat. Eight PGPR strains were isolated and studied for their morphological and cultural characteristics, phosphate solubilization and indole acetic acid (IAA) production. All isolates produced IAA ranging from 5.5–31.0 μg/ml, while four isolates were P-solubilizers. On the basis of morphological characteristics, IAA production and P solubilization, strains WPR-32, WPR-42, and WPR-51 were identified as PGPR and selected for further study. Efficiency of these three PGPR isolates and their mixtures (combinations) at two N levels (N at the rate of 50 and 100 kg ha−1) was evaluated in wheat under greenhouse conditions. Application of PGPR significantly increased plant height, shoot fresh weight and shoot dry weight by 25, 45, and 86%, respectively, while increase in root length, root fresh and dry weight was 27, 1...