Abstract: The effects of biochar properties on crop growth are little understood. Therefore, biochar was produced from eight feedstocks and pyrolyzed at four temperatures (300°C, 400°C, 500°C, 600°C) using slow pyrolysis. Corn was grown for 46 days in a greenhouse pot trial on a temperate and moderately fertile Alfisol amended with the biochar at application rates of 0.0%, 0.2%, 0.5%, 2.0%, and 7.0% (w/w) (equivalent to 0.0, 2.6, 6.5, 26, and 91 t biochar ha−1) and full recommended fertilization. Animal manure biochars increased biomass by up to 43% and corn stover biochar by up to 30%, while food waste biochar decreased biomass by up to 92% in relation to similarly fertilized controls (all P 0.05), and greater pH had only a weak positive relationship with growth at intermediate application rates. Greater nutrient contents (N, P, K, Mg) improved growth at low application rates of 0.2% and 0.5%, but Na reduced growth at high application rates of 2.0% and 7.0% in the studied fertile Alfisol.

Abstract: Despite the recent interest in the use of biochar in agriculture, its current use is still limited. In terms of market development, if biochar can be used as a soil amendment to improve soil quality and to increase crop production, this will increase its appeal (Day et al, 2004). In this regard, an obvious positive attribute of biochar is its nutrient value, supplied either directly by providing nutrients to plants or indirectly by improving soil quality, with consequent improvement in the efficiency of fertilizer use. As a measure of the direct nutrient value of biochars, it is not the total content but, rather, the availability of the nutrient that is an important consideration.The total content of nutrients is not an appropriate indicator of the availability of nutrients as only a fraction of the total content is immediately available or is readily converted to available forms for uptake by plants (Keeney, 1982).

Abstract: Nutrient resorption in plants influences nutrient availability and cycling and is a key process in biogeochemical models. Improved estimates of resorption parameters are needed for predicting long-term primary productivity and for improving such models. Currently, most models assume a value of 50% resorption for nitrogen (N) and phosphorus (P) and lack resorption data for other nutrients and for specific vegetation types. We provide global estimates of resorption efficiencies and nutrient concentrations for carbon (C), N, and P and the first global-scale estimates for essential nutrients such as potassium (K), calcium (Ca), and magnesium (Mg). We also examine leaf mass loss during senescence (LML) globally and for different plant types, thus defining a mass loss correction factor (MLCF) needed to quantify unbiased resorption values. We used a global meta-analysis of 86 studies and ∼1000 data points across climates for green and senesced leaves in six plant types: ferns, forbs, graminoids, conifers, and ev...

Abstract: The burgeoning population of world is expected to reach about 9-10 billion by the end of year 2050. Due to this rapidly increasing population, food productivity is de-creasing. Temperature induced stress is an important environmental factor that influ-ences the growth and development of plants. Both low and high temperatures affect plant growth and development at whole plant level, tissue and cell level and even at sub-cellular level. Temperature variation may affect morphology, anatomy, phenol-ogy and plant biochemistry at all levels of organization. Direct injuries due to high temperatures in plants include protein denaturation and aggregation, and increased fluidity of membrane lipids. Indirect or slower high temperature injuries include inactivation of enzymes in chloroplast and mitochondria, inhibition of protein syn-thesis, protein degradation and loss of membrane integrity. Low temperature stress during reproductive development induces flower abscission, pollen sterility, pollen tube distortion, ovule abortion and reduced fruit set, which ultimately lowers yield. A number of approaches are being used to alleviate the effect of temperature stress in crop plants. Proper plant nutrition is one of the good strategies to alleviate the temperature stress and in crop plants. Plant nutrients play a greater role in improv-ing the temperature stress tolerance. In this paper we discuss the possible effective techniques to alleviate the temperature stress and the role of some macronutrients (nitrogen, potassium, calcium and magnesium) micronutrients (boron, manganese, and selenium) and salicylic acid in detail as how these nutrients play their role in alleviation of temperature stress in crop plant.

Abstract: Nutrient leaching in highly weathered tropical soils often poses a challenge for crop production. We investigated the effects of applying 20 t ha biochar (BC) to a Colombian savanna Oxisol on soil hydrology and nutrient leaching in field experiments. Measurements were made over the third and fourth years after a single BC application. Nutrient contents in the soil solution were measured under one maize and one soybean crop each year that were routinely fertilized with mineral fertilizers. Leaching by unsaturated water flux was calculated using soil solution sampled with suction cup lysimeters and water flux estimates generated by the model HYDRUS 1-D. No significant difference ( > 0.05) was observed in surface-saturated hydraulic conductivity or soil water retention curves, resulting in no relevant changes in water percolation after BC additions in the studied soils. However, due to differences in soil solution concentrations, leaching of inorganic N, Ca, Mg, and K measured up to a depth of 0.6 m increased ( < 0.05), whereas P leaching decreased, and leaching of all nutrients (except P) at a depth of 1.2 m was significantly reduced with BC application. Changes in leaching at 2.0 m depth with BC additions were about one order of magnitude lower than at other depths, except for P. Biochar applications increased soil solution concentrations and downward movement of nutrients in the root zone and decreased leaching of Ca, Mg, and Sr at 1.2 m, possibly by a combination of retention and crop nutrient uptake.

Abstract: Summary 1. Nutrients are a critical resource for plant growth, but the elements limiting growth in tropical forests have rarely been determined. 2. We investigated the influence of nitrogen (N), phosphorus (P), potassium (K) and micronutrients on seedling biomass and nutrient allocation in a factorial nutrient fertilization experiment in lowland tropical forest at the Barro Colorado Nature Monument, Panama. We also measured 8 years of herbivory and growth for 1800 seedlings. We sought to determine the identity of limiting elements and possible nutrient interactions. 3. The five study species were Alseis blackiana, Desmopsis panamensis, Heisteria concinna, Sorocea affinis and Tetragastris panamensis. Plants grew in deeply shaded understorey with a mean canopy openness of 4.9% (±0.7%; 1 SE). 4. Tissue N concentration increased by 11% with N addition. Tissue P concentration increased by 16% with P addition. Tissue K increased by 4% with K addition. K addition reduced root-to-shoot biomass ratio. There was no significant effect of fertilization on specific leaf area or leaf area ratio. 5. The proportion of leaves damaged and the mean level of damage by herbivory increased with P and K addition and showed a significant P · Ki nteraction. 6. Across all species and years, relative growth rate of height increased with K addition and with N and P in combination. Relative growth rate of leaf count trended 8.5% higher with K addition (P =0 .076). 7. We also added micronutrients in a parallel experiment. There was no effect of micronutrient addition on any seedling parameter. 8. Synthesis. K addition affected seedlings by enhancing tissue nutrient concentration, increasing herbivory, reducing root-to-shoot biomass ratio and increasing height growth. Additional effects of N or P on tissue chemistry, herbivory and growth offer support for the multiple limiting resources hypothesis. Our results suggest that seedling growth is limited by nutrients, especially K, even under highly shaded conditions in this lowland tropical forest.

Abstract: Publisher Summary This chapter focuses on the various constraints faced by plants in adverse soil conditions such as acidity, poor aeration, alkalinity, and salinity. The low-external input high-efficiency involving adapted genotypes that efficiently uses the nutrients from soil reserves and fertilizer can lead to yields that are only 10–20% below the maximum. Two components that contribute to overall nutrient efficiency include uptake efficiency, which is the amount of nutrient absorbed, and utilization efficiency, which characterizes the efficiency with which the absorbed nutrients are utilized to produce yield. Both of them primarily depend on the nutrient supply by the soil and fertilizers. The main constraints to plant growth in flooded or submerged soils are the low oxygen availability, Fe and Mn toxicity and toxic metabolites of anaerobic decomposition. Adaptation to flooded soils includes aerenchyma formation to transport oxygen to the roots, efficient generation and use of energy and carbohydrate conservation. Plant growth in alkaline or calcareous soils is inhibited by low availability of Fe, Zn, Mn and B and tolerance to such soils is achieved by mobilization of Fe and Zn via exudation of chelating compounds such as organic acid anions in Strategy I plants and phytosiderophores in Strategy II plants. The main constraints to plant growth in saline soils are low osmotic potential and ion toxicity (Na, Cl, sulphate) as well as ion imbalances (low K/Na ratio). The salt tolerance mechanisms can be divided into salt exclusion (reduced uptake, increased efflux) and salt inclusion (compartmentation into the vacuole, release of salts via salt glands, and salt-tolerant enzymes).

Abstract: The availability of essential nutrients, such as nitrogen (N) and phosphorus (P), can feedback on soil carbon (C) and the soil microbial biomass. Natural cycles can be supplemented by agricultural fertiliser addition, and we determined whether the stoichiometry and nutrient limitation of the microbial biomass could be affected by an unbalanced nutrient supply. Samples were taken from a long-term trial (in effect since 1968) with annual applications of 0, 15 and 30 kg P ha−1 with constant N and potassium. Soil and microbial biomass CNP contents were measured and nutrient limitation assessed by substrate-induced respiration. Linear regression and discriminant analyses were used to identify the variables explaining nutrient limitation. Soil and biomass CNP increased with increasing P fertiliser, and there was a significant, positive, correlation between microbial biomass P and biomass C, apart from at the highest level of P fertilisation when the microbial biomass was over-saturated with P. The molar ratios of C:N:P in the microbial biomass remained constant (homeostatic) despite large changes in the soil nutrient ratios. Microbial growth was generally limited by C and N, except in soil with no added P when C and P were the main limiting nutrients. C, N and P, however, did not explain all the growth limitation on the soils with no added P. Increased soil C and N were probably due to increased net primary production. Our results confirm that C:N:P ratios within the microbial biomass were constrained (i.e. homeostatic) under near optimum soil conditions. Soils with no added P were characterised by strong microbial P limitation and soils under high P by over-saturation of microorganisms with P. Relative changes in biomass C:P can be indicative of nutrient limitation within a site.

Abstract: Reduction in size and tissue nutrient concentration is widely considered to increase seedling drought resistance in dry and oligotrophic plantation sites. However, much evidence indicates that increase in size and tissue nutrient concentration improves seedling survival in Mediterranean forest plantations. This suggests that the ecophysiological processes and functional attributes relevant for early seedling survival in Mediterranean climate must be reconsidered. We propose a ecophysiological conceptual model for seedling survival in Mediterranean-climate plantations to provide a physiological explanation of the frequent positive relationship between outplanting performance and seedling size and nutrient concentration. The model considers the physiological processes outlined in the plantation establishment model of Burdett (Can J For Res 20:415–427, 1990), but incorporates other physiological processes that drive seedling survival, such as N remobilization, carbohydrate storage and plant hydraulics. The model considers that seedling survival in Mediterranean climates is linked to high growth capacity during the wet season. The model is for container plants and is based on three main principles, (1) Mediterranean climates are not dry the entire year but usually have two seasons of contrasting water availability; (2) summer drought is the main cause of seedling mortality; in this context, deep and large roots is a key trait for avoiding lethal water stress; (3) attainment of large root systems in the dry season is promoted when seedlings have high growth during the wet season. High growth is achieved when seedlings can divert large amount of resources to support new root and shoot growth. Functional traits that confer high photosynthesis, nutrient remobilization capacity, and non-structural carbohydrate storage promote high growth. Increases in seedling size and nutrient concentration strongly affect these physiological processes. Traits that confer high drought resistance are of low value during the wet season because hinder growth capacity. We provide specific evidence to support the model and finally we discuss its implications and the factors that may alter the frequent increase in performance with increase in seedling size and tissue nutrient concentration.

Abstract: In recent years, in developed countries and around the world, lifestyle-related diseases have become a serious problem. Numerous epidemiological studies and clinical trials have demonstrated that diet is one of the major factors that influence susceptibility to lifestyle-related diseases, especially the middle-senile state. Studies examining dietary habits have revealed the health benefits of seafood consumption. Seafood contains functional components that are not present in terrestrial organisms. These components include n-3-polyunsaturated fatty acids, such as eicosapentaenoic acid and docosahexsaenoic acid, which aid in the prevention of arteriosclerotic and thrombotic disease. In addition, seafood is a superior source of various nutrients, such as protein, amino acids, fiber, vitamins, and minerals. This review focuses on the components derived from seafood and examines the significant role they play in the maintenance and promotion of health.

Abstract: [1] Most vegetation is limited in productivity by nutrient availability, but the magnitude of limitation globally is not known. Nutrient limitation is directly relevant not only to ecology and agriculture, but also to the global carbon cycle by regulating how much atmospheric CO2the terrestrial biosphere can sequester. We attempt to identify total nutrient limitation in terrestrial plant productivity globally using ecophysiological theory and new developments in remote sensing for evapotranspiration and plant productivity. Our map of nutrient limitation qualitatively reproduces known regional nutrient gradients (e.g., across Amazonia), highlights differences in nutrient addition to croplands (e.g., between “developed” and “developing” countries), identifies the role of nutrients on the distribution of major biomes (e.g., tree line migration in boreal North America), and compares similarly to a ground-based test along the Long Substrate Age Gradient in Hawaii, U.S.A. (e.g., foliar and soil nutrients, litter decomposition). Nonetheless, challenges in representing light and water use efficiencies, disturbance, and comparison to ground data with multiple interacting nutrients provide avenues for further progress on refining such a global map. Global average reduction in terrestrial plant productivity was within 16–28%, depending on treatment of disturbance; these values can be compared to global carbon cycle model estimates of carbon uptake reduction with nutrient cycle inclusion.

Abstract: Use of industrial and wastewater for irrigation is on the rise in India and other developing countries because of scarcity of good-quality irrigation water Wastewaters contain plant nutrients that favour crop growth but leave a burden of heavy metals which can enter the food chain and is a cause of great concern The present study was undertaken on the long-term impact of irrigation with treated sewage water for growing vegetables and the potential health risk associated with consumption of such vegetable Treated sewage water (TSW), groundwater (GW), soil and plant samples were collected from peri urban vegetable growing areas of Northern India (Varanasi) and analysed to assess the long-term effect of irrigation with TSW on Cd, Cr, Ni and Pb build-up in soils and its subsequent transfer into commonly grown vegetable crops Results indicate that TSW was richer in essential plant nutrients but contained Cd, Cr and Ni in amounts well above the permissible limits for its use as irrigation water Long-term application of TSW resulted in significant build-up of total and DTPA extractable Cd, Cr, Ni and Pb over GW irrigated sites TSW also resulted in slight lowering in pH, increase in organic carbon (16 g kg − 1) and cation exchange capacity (52 cmol kg − 1) The tissue metal concentration and relative efficiency of transfer of heavy metals from soil to plant (transfer factor) for various groups of vegetables were worked out Radish, turnip and spinach were grouped as hyper accumulator of heavy metals whereas brinjal and cauliflower accumulated less heavy metals Health risk assessment by consumption of vegetables grown with TSW indicated that all the vegetables were safe for human consumption However, significant accumulation of these heavy metals in soil and plant needs to be monitored

Abstract: The relationship between plant nutrient content and insect herbivore populations and community structure has long interested ecologists. Insect herbivores require multiple nutrients, but ecologists have focused mostly on nitrogen (an estimate of plant protein content), and more recently phosphorus (P); other nutrients have received little attention. Here we document nutrient variation in grass and forb samples from grassland habitats in central Nebraska using an elemental approach; in total we measured foliar concentrations of 12 elements (N and P, plus S, B, Ca, Mg, Na, K, Zn, Fe, Mn, and Cu). We detected significant variability among sites for N, P, Mg, Na, K, and Cu. We next used a model selection approach to explore how this nutritional variation and plant biomass correlate with grasshopper densities (collectively and at the feeding-guild level), and principal component analysis to explore nutrient correlations with grasshopper community species composition. When all grasshoppers were pooled, densities varied among sites, but only P was associated with abundance of the elements shown to vary between sites. Different responses occurred at the feeding-guild level. For grass specialists, densities were associated with N, plus P, Mg, and Na. For forb specialists, N and P were often associated with density, but associations with Na and K were also observed. Finally, mixed-feeder abundance was strongly associated with biomass, and to a lesser extent P, Mg, Na, and Cu. At the community level, B, Ca, Zn, and Cu, plus biomass, explained .30% of species composition variation. Our results confirm the positive association of N and P with insect herbivore populations, while suggesting a potential role for Mg, Na, and K. They also demonstrate the importance of exploring effects at the feeding-guild level. We hope our data motivate ecologists to think beyond N and P when considering plant nutrient effects on insect herbivores, and make a call for studies to examine functional responses of insect herbivores to dietary manipulation of Mg, Na, and K. Finally, our results demonstrate correlations between variation in nutrients and species assemblages, but factors not linked to plant nutrient quality or biomass likely explain most of the observed variation.

Abstract: The slow alteration of the surface of charred biomass (biochar) over time may contribute to an improved nutrient retention and thus fertility of tropical soils. Here, we investigated soils from temperate climates and investigated whether a technical steam activation of biochar could accelerate its positive effects on nutrient retention and uptake by plants relative to nonactivated biochar. To this aim, we performed microcosm experiments with sandy or silty soil, mixed with 2.0, 7.5 and 15.0 g ⁄ kg soil of fine (<2 mm) or coarse-sized (2–10 mm) biochar from beech wood (Fagus sp.). After initial fertilizer (NPK), ashes and excess nutrients were leached with water, and the microcosms were planted for 142 days with Italian Ryegrass (Lolium multiflorum ssp. italicum). Thereafter, leachate, soil and plant samples were analysed for their nutrient contents. The results showed that biochar additions of £15 g ⁄ kg soil left elevated contents of available P and N in the surface soil but reduced their uptake into the plants. As a result, total biomass production was unchanged. Different particle size and application amounts influenced these findings only marginally. Nitrate leaching was enhanced in the sandy soil (+41% for nitrate, but reduced in the silty soil )17%) and P was immobilized. Hence, the fertility of the temperate soils under study was only marginally affected by pure biochar amendments. Steam activation, however, almost doubled the positive effects of biochars in all instances, thus being an interesting option for future biochar applications.

Abstract: Mitigating nutrient losses from anthropogenic nonpoint sources is today of particular importance for improving the water quality of numerous freshwater lakes worldwide. Several empirical relationships between land use and in-lake water quality variables have been developed, but they are often weak, which can in part be attributed to lack of detailed information about land use activities or point sources. We examined a comprehensive data set comprising land use data, point-source information, and in-lake water quality for 414 Danish lakes. By excluding point-source-influenced lakes (n = 210), the strength in relationship (R2) between in-lake total nitrogen (TN) and total phosphorus (TP) concentrations and the proportion of agricultural land use in the watershed increased markedly, from 10–12% to 39–42% for deep lakes and from 10–12% to 21–23% for shallow lakes, with the highest increase for TN. Relationships between TP and agricultural land use were even stronger for lakes with rivers in their watershed (5...

Abstract: There is a perception that anthropogenically-driven changes in nutrient supply to coastal waters influences the abundance, frequency and toxicity of harmful algal blooms (HABs) through a change in the form or ratio of nutrient that limits phytoplankton growth. If nutrient concentrations are not limiting for growth, then ratios do not influence floristic composition. At non-limiting concentrations, evidence that alteration of nitrogen: phosphorus (N:P) ratios has stimulated HABs is limited, and primarily based on hypothesised relationships in relatively few locations (in particular: Tolo Harbour Hong Kong and Dutch Coastal Waters). In all cases, an unequivocal causal link between an increase in HABs (frequency, magnitude or duration) and change in N or P as the limiting nutrient is difficult to establish. The silicon (Si) limitation hypothesis is generally supported by experimental evidence and field data on the nuisance flagellate Phaeocystis. We found little evidence that high N:Si ratios preferentially promote harmful dinoflagellates over benign species. Laboratory studies demonstrate that nutrient ratios can influence toxin production, but genus and species specific differences and environmental control make extrapolation of these data to the field difficult. Studies of the role of dissolved and particulate organic nutrients in the growth of HAB species, while limited, demonstrate the potential for organic nutrients (especially organic N) to support the growth of a range of HAB species. There is a clear need for better understanding of the role of mixotrophy in the formation of HABs and for studies of HAB and non-HAB species in competition for environmentally realistic concentrations of organic nutrients.

Abstract: Phytoplankton is widely recognized as being regulated mainly by resources (nutrients and light) and predation by higher trophic levels. In reservoirs, these controls also can be modulated by hydrology, for example through the influence of flow pulses generated by the operation of the dam. In this study, we tested the influence of light, nutrients, and zooplankton grazing pressure, and also hydrology (as water residence time) on the phytoplankton biomass in eight tropical hydroelectric reservoirs, which differ in size, morphometry, location, trophic state, and water residence time. Our hypothesis was that, as these reservoirs are used for hydroelectric purposes, the control that would otherwise be exerted on phytoplankton biomass primarily by resource availability and grazing will also be modulated by hydrology. Low phytoplankton biomass (range of system medians = 12–299 μg C l−1) occurred in most systems, except for one highly eutrophic reservoir (median = 1331 μg C l−1). Our data showed that phosphorus was more often likely to be the limiting nutrient in these systems, as assessed through nutrient limitation indexes (nitrogen and phosphorus), based on concentrations and ratios. For most reservoirs, excluding the eutrophic system with high cyanobacteria biomass, seasonal water residence time was the variable that best explained phytoplankton variation among the several environmental variables analyzed in this study (P < 0.0001; adjusted r 2 = 0.38). Hydrology was an important and additional factor modulating phytoplankton in these tropical reservoirs, directly removing phytoplankton populations and their potential zooplankton grazers by washout, and also affecting nutrient availability.

Abstract: The majority of studies on rhizospheric interactions between microbial communities and vegetation focus on pathogens, mycorrhizal symbiosis, and/or carbon transformations. Although the biogeochemical transformations of nitrogen (N), sulfur (S) and iron (Fe) have profound effects on plants, these effects have received far less attention. Firstly, all three elements are plant nutrients, and microbial activity significantly changes their mobility and availability. Secondly, microbial oxidation with oxygen supplied by radial oxygen loss (ROL) from roots in wetlands causes acidification, while reduction using alternative electron acceptors leads to generation of alkalinity, affecting pH in the rhizosphere and hence plant composition. Thirdly, reduced species of all three elements may become phytotoxic. In addition, Fe cycling is tightly linked to that of S and phosphorus (P). As water level fluctuations are very common in wetlands, rapid changes in the availability of oxygen and alternative terminal electron acceptors will result in strong changes in the prevalent microbial redox reactions, with significant effects on plant growth. Depending on geological and hydrological settings, these interacting microbial transformations change the conditions and resource availability for plants, which are strong drivers of vegetation development and composition by changing relative competitive strengths. Conversely, microbial composition is strongly driven by vegetation composition. Therefore, the combination of micro- and macroecological knowledge is essential to understand the biogeochemical and biological key factors driving heterogeneity and total (i.e., micro-macro) community composition at different spatial and temporal scales. As N and S inputs have drastically increased due to anthropogenic forcing and Fe inputs have decreased at a global scale, this combined approach has become even more urgent.

Abstract: Tropical regions are facing increasing atmospheric inputs of nutrients, which will have unknown consequences for the structure and functioning of these systems. Here, we show that Neotropical montane rainforests respond rapidly to moderate additions of N (50 kg ha−1 yr−1) and P (10 kg ha−1 yr−1). Monitoring of nutrient fluxes demonstrated that the majority of added nutrients remained in the system, in either soil or vegetation. N and P additions led to not only an increase in foliar N and P concentrations, but also altered soil microbial biomass, standing fine root biomass, stem growth, and litterfall. The different effects suggest that trees are primarily limited by P, whereas some processes—notably aboveground productivity—are limited by both N and P. Highly variable and partly contrasting responses of different tree species suggest marked changes in species composition and diversity of these forests by nutrient inputs in the long term. The unexpectedly fast response of the ecosystem to moderate nutrient additions suggests high vulnerability of tropical montane forests to the expected increase in nutrient inputs.

Abstract: The purpose of this study was to assess the quality of cassava cultivars, in terms of cyanogenic potential and composition of macro- and micronutrients, sampled from different locations in rural Mozambique. Total cyanide concentrations in fresh cassava tissues were measured using portable cyanide testing kits, and elemental nutrients were later analyzed from dried plant tissue. Variation in cyanogenic potential and nutrient composition occurred both among cultivars and across locations. The majority of cultivars contained >100 ppm total cyanide, fresh weight, and are therefore considered to be dangerously poisonous unless adequately processed before consumption. Leaf cyanogenic and nutrient content varied with plant water status, estimated using carbon isotope discrimination (δ13C). The colonization of roots of all cultivars by arbuscular mycorrhizal fungi was also quantified and found to be high, indicating that mycorrhizas could play a key role in plant nutrient acquisition in these low-input farming sy...

Abstract: [1] Using in situ data from 88 cruises from 1987 to 2009 in the East China Sea, downstream nutrient flux (the product of velocity and nutrient concentration) and nutrient transport (integration of flux over a section) by Kuroshio were examined. The presence of a maximum nutrient flux core in the middle layer was confirmed. Seasonal variation in the nutrient flux was not significant and was much smaller than interannual variations. The change in the Kuroshio speed and current structure were major causes for interannual variations in the nutrient flux. The downstream nitrate transport by the Kuroshio in the East China Sea had a mean value of 170.8 kmol s−1 and a standard deviation of 41.6 kmol s−1. The mean seasonal nitrate transport ranged between about 161 and 177 kmol s−1 and the absolute interannual variation from about 100 to 280 kmol s−1. The phosphate flux and phosphate transport can be approximately estimated by the ratio (13.64) of nitrate concentration to phosphate concentration. The nitrate concentration in the middle and bottom layers across the Kuroshio in the East China Sea was found to increase significantly over the 23 year period, and especially after 2004 but not at ratios with oxygen that suggest increased remineralization of organic matter. The nutrient transport, however, did not increase significantly because increases in the surface layer were offset by decreases in the middle and bottom layers caused by reduction in velocity in the density ranges of 26.0 to 27.2 σθ below the Kuroshio.

Abstract: Tree species can affect the decomposition process through the quality of their leaf fall and through the species-specific conditions that they generate in their environment. We compared the relative importance of these effects in a 2-year experiment. Litterbags containing leaf litter of the winter-deciduous Quercus canariensis, the evergreen Q. suber and mixed litter were incubated beneath distinct plant covers. We measured litter carbon loss, 9 macro- and micronutrients and 18 soil chemical, physical and biological parameters of the incubation environment. Tree species affected decay dynamics through their litter quality and, to a lesser extent, through the induced environmental conditions. The deciduous litter showed a faster initial decomposition but left a larger fraction of slow decomposable biomass compared with the perennial litter; in contrast the deciduous environment impeded early decomposition while promoting further carbon loss in the latter decay stages. The interaction of these effects led to a negative litter‐environment interaction contradicting the home-field advantage hypothesis. Leaf litter N, Ca and Mn as well as soil N, P and soil moisture were the best predictors for decomposition rates. Litter N and Ca exerted counteractive effects in early versus late decay stages; Mn was the best predictor for the decomposition limit value, that is, the fraction of slowly decomposable biomass at the later stage of decomposition; P and soil moisture showed a constant and positive relation with carbon loss. The deciduous oak litter had a higher initial nutrient content and released its nutrients faster and in a higher proportion than the perennial oak litter, significantly increasing soil fertility beneath its canopy. Our findings provide further insights into the factors that control the early and late stages of the decomposition process and reveal potential mechanisms underlying tree species influence on litter decay rate, carbon accumulation and nutrient cycling.

Abstract: [1] From September 2009 to August 2010, intensive monthly sampling of nutrients was conducted at two stations at the mouth of the Changjiang (Yangtze River). Particulate organic carbon (POC), particulate nitrogen (PN), and their stable isotope values (δ13C and δ15N) were also measured in selected samples of all months. Most nutrients (nitrate, phosphate, ammonia, and nitrite) as well as POC, PN, and δ13C displayed peak values when the highest or lowest Changjiang monthly discharges occurred, suggesting the Changjiang discharges strongly influence the seasonal variations of these chemicals. The sharply increases in concentrations of ammonia and nitrite in winter probably suggest nitrification was greatly depressed during this cold period. Using five interpolation methods, the annual discharge fluxes of nutrients, POC, and PN from the Changjiang to the East China Sea shelf were calculated. Combining this nutrient data with data from previous studies, the seasonal Mann-Kendall test, in which the influence of seasonal variation was considered, suggests concentrations of nitrate and phosphate in the Changjiang have significantly increased during recent decades at rates of 2.2μM yr−1 and 0.03 μM yr−1, respectively; no significant trend for silicate was noted. Decreased POC annual fluxes along with sharply decreased suspended particulate matter yields were also seen in recent years (1993–2010). However, no distinct changes of δ13C, δ15N, and the POC/PN ratio, which describe the particulate organic matter properties, were observed during this period.