Abstract: The Midwest floods of 2008 added more than just water to the region's lakes, reservoirs, and rivers. Runoff from farms and towns carries a heavy load of silt, nutrients, and other pollutants. The nutrients trigger blooms of algae, which taint drinking water. Death and decay of the algae depletes oxygen, kills fish and bottom-dwelling animals, and thereby creates “dead zones” in the body of water. The syndrome of excessive nutrients, noxious algae, foul water, and dead zones—which ecologists call eutrophication—is depressingly familiar to those who depend on water from rich agricultural regions.

Abstract: Soil microbial communities under three agricultural management systems (conventionally tilled cropland, hayed pasture, and grazed pasture) and two fertilizer systems (inorganic fertilizer and poultry litter) were compared to that of a w150-y-old forest near Watkinsville, Georgia. Both 16S rRNA gene clone libraries and phospholipid fatty acid (PLFA) analyses indicated that the structure and composition of bacterial communities in the forest soil were significantly different than in the agricultural soils. Within the agricultural soils, the effect of fertilizer amendment on bacterial communities was more dramatic than either land use or season. Fertilizer amendment altered the abundance of more bacterial groups throughout the agricultural soils. In addition, the changes in the composition of bacterial groups were more pronounced in cropland than in pastures. There was much less seasonal variation between the soil libraries. Community-level differences were associated with differences in soil pH, mineralizable carbon and nitrogen, and extractable nutrients. Bacterial community diversity exhibited a complex relationship with the land use intensity in these agro-ecosystems. The pastures had the highest bacterial diversity and could be characterized as having an intermediate degree of intervention compared to low intervention in forest and high intervention in cropland. Changes in bacterial diversity could be attributed to the abundance of a few operational taxonomic units (OTUs). The microdiversity of abundant OTUs in both forest and cropland was consistent with an increase in abundance of many phenotypically similar species rather than a single species for each OTU. Soil microbial communities were significantly altered by long-term agricultural management systems, especially fertilizer amendment, and these results provide a basis for promoting conservation agricultural systems.

Abstract: In the 21st century, nutrient efficient plants will play a major role in increasing crop yields compared to the 20th century, mainly due to limited land and water resources available for crop production, higher cost of inorganic fertilizer inputs, declining trends in crop yields globally, and increasing environmental concerns. Furthermore, at least 60% of the world's arable lands have mineral deficiencies or elemental toxicity problems, and on such soils fertilizers and lime amendments are essential for achieving improved crop yields. Fertilizer inputs are increasing cost of production of farmers, and there is a major concern for environmental pollution due to excess fertilizer inputs. Higher demands for food and fiber by increasing world populations further enhance the importance of nutrient efficient cultivars that are also higher producers. Nutrient efficient plants are defined as those plants, which produce higher yields per unit of nutrient, applied or absorbed than other plants (standards) ...

Abstract: A 3 year field study was conducted with field corn from 2005 to 2007 to test the hypothesis that microbial inoc- ulants that increase plant growth and yield can enhance nutrient uptake, and thereby remove more nutrients, especially N, P, and K from the field as part of an integrated nutrient management system. The field trial evaluated microbial inoculants, which include a commercially available plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhiza fungi (AMF), and their combination across 2 tillage systems (no-till and conventional till) and 2 fertilization regimes (poultry lit- ter and ammonium nitrate). Data were collected on plant height, yield (dry mass of ears and silage), and nutrient content of corn grain and silage. In addition, nutrient content of soil was determined, and bioavailability of soil nutrient was meas- ured with plant root simulator probes. Results showed that inoculants promoted plant growth and yield. For example, grain yields (kgha -1 ) in 2007 for inoculants were 7717 for AMF, 7260 for PGPR+AMF, 7313 for PGPR, 5725 for the control group, and for fertilizer were 7470 for poultry litter and 6537 for NH4NO3. Nitrogen content per gram of grain tissues was significantly enhanced in 2006 by inoculant, fertilizer, and their interactions. Significantly higher amounts of N, P, and K were removed from the plots with inoculants, based on total nutrient content of grain per plot. These results supported the overall hypothesis and indicate that application of inoculants can lead to reduction in the build up of N, P, and K in agri- cultural soils. Further studies should be conducted to combine microbial inoculants with reduced rates of fertilizer.

Abstract: Climate warming could increase rates of soil organic matter turnover and nutrient mineralization, particularly in northern high-latitude ecosystems. However, the effects of increasing nutrient availability on microbial processes in these ecosystems are poorly understood. To determine how soil microbes respond to nutrient enrichment, we measured microbial biomass, extracellular enzyme activities, soil respiration, and the community composition of active fungi in nitrogen (N) fertilized soils of a boreal forest in central Alaska. We predicted that N addition would suppress fungal activity relative to bacteria, but stimulate carbon (C)-degrading enzyme activities and soil respiration. Instead, we found no evidence for a suppression of fungal activity, although fungal sporocarp production declined significantly, and the relative abundance of two fungal taxa changed dramatically with N fertilization. Microbial biomass as measured by chloroform fumigation did not respond to fertilization, nor did the ratio of fungi : bacteria as measured by quantitative polymerase chain reaction. However, microbial biomass C : N ratios narrowed significantly from 16.0 ± 1.4 to 5.2 ± 0.3 with fertilization. N fertilization significantly increased the activity of a cellulose-degrading enzyme and suppressed the activities of protein- and chitin-degrading enzymes but had no effect on soil respiration rates or 14C signatures. These results indicate that N fertilization alters microbial community composition and allocation to extracellular enzyme production without affecting soil respiration. Thus, our results do not provide evidence for strong microbial feedbacks to the boreal C cycle under climate warming or N addition. However, organic N cycling may decline due to a reduction in the activity of enzymes that target nitrogenous compounds.

Abstract: The effects of a dry-rewetting event (D/RW) on soil microbial properties and nutrient release by leaching from two soils taken from adjacent grasslands with different histories of management intensity were studied. These were a low-productivity grassland, with no history of fertilizer application and a high-productivity grassland with a history of high fertilizer application, referred to as unimproved and improved grassland, respectively. The use of phospholipid fatty acid analysis (PLFA) revealed that the soil of the unimproved grassland had a significantly greater microbial biomass, and a greater abundance of fungi relative to bacteria than did the improved grassland. Soils from both grasslands were maintained at 55% water holding capacity (WHC) or dried to 10% WHC and rewetted to 55% WHC, and then sampled on days 1, 3, 9, 16, 30 and 50 after rewetting. The D/RW stress significantly reduced microbial biomass carbon (C), fungal PLFA and the ratio of fungal-to-bacterial PLFA in both soils. In contrast, D/RW increased microbial activity, but had no effect on total PLFA and bacterial PLFA in either soil. Microbial biomass nitrogen (N) was reduced significantly by D/RW in both soils, but especially in those of the improved grassland. In terms of nutrient leaching, the D/RW stress significantly increased concentrations of dissolved organic C and dissolved organic N in leachates taken from the improved soil only. This treatment increased the concentration of dissolved inorganic N in leachate of both soils, but this effect was most pronounced in the improved soil. Overall, our data show that D/RW stress leads to greater nutrient leaching from improved than from unimproved grassland soils, which have a greater microbial biomass and abundance of fungi relative to bacteria. This finding supports the notion that soils with more fungal-rich communities are better able to retain nutrients under D/RW than are their intensively managed counterparts with lower fungal to bacterial ratios, and that D/RW can enhance nutrient leaching with potential implications for water quality.

Abstract: Acquisition of nutrients by plants is primarily dependent on root growth and bioavailability of nutrients in the rooting medium. Most of the beneficial bacteria enhance root growth, but their effectiveness could be influenced by the nutrient status around the roots. In this study, two 1-aminocyclopropane-1-carboxylate (ACC)-deaminase containing plant-growth-promoting rhizobacteria (PGPR), Pseudomonas fluorescens and P. fluorescens biotype F were tested for their effect on growth, yield, and nutrient use efficiency of wheat under simultaneously varying levels of all the three major nutrients N, P, and K (at 0%, 25%, 50%, 75%, and 100% of recommended doses). Results of pot and field trials revealed that the efficacy of these strains for improving growth and yield of wheat reduced with the increasing rates of NPK added to the soil. In most of the cases, significant negative linear correlations were recorded between percentage increases in growth and yield parameters of wheat caused by inoculation and increasing levels of applied NPK fertilizers. It is highly likely that under low fertilizer application, the ACC-deaminase activity of PGPR might have caused reduction in the synthesis of stress (nutrient)-induced inhibitory levels of ethylene in the roots through ACC hydrolysis into NH3 and α-ketobutyrate. The results of this study imply that these Pseudomonads could be employed in combination with appropriate doses of fertilizers for better plant growth and savings of fertilizers.

Abstract: Nutrient and hydrologic conditions strongly influence harmful planktonic and benthic cyanobacterial bloom (CHAB) dynamics in aquatic ecosystems ranging from streams and lakes to coastal ecosystems Urbanization, agricultural and industrial development have led to increased nitrogen (N) and phosphorus (P) discharge, which affect CHAB potentials of receiving waters The amounts, proportions and chemical composition of N and P sources can influence the composition, magnitude and duration of blooms This, in turn, has ramifications for food web dynamics (toxic or inedible CHABs), nutrient and oxygen cycling and nutrient budgets Some CHABs are capable of N2 fixation, a process that can influence N availability and budgets Certain invasive N2 fixing taxa (eg, Cylindrospermopsis, Lyngbya) also effectively compete for fixed N during spring, N–enriched runoff periods, while they use N2 fixation to supplant their N needs during N–deplete summer months Control of these taxa is strongly dependent on P supply However, additional factors, such as molar N:P supply ratios, organic matter availability, light attenuation, freshwater discharge, flushing rates (residence time) and water column stability play interactive roles in determining CHAB composition (ie N2 fixing vs non–N2 fixing taxa) and biomass Bloom potentials of nutrient–impacted waters are sensitive to water residence (or flushing) time, temperatures (preference for >15 °C), vertical mixing and turbidity These physical forcing features can control absolute growth rates of bloom taxa Human activities may affect “bottom up” physical–chemical modulators either directly, by controlling hydrologic, nutrient, sediment and toxic discharges, or indirectly, by influencing climate Control and management of cyanobacterial and other phytoplankton blooms invariably includes nutrient input constraints, most often focused on N and/or P While single nutrient input constraints may be effective in some water bodies, dual N and P input reductions are usually required for effective long–term control and management of blooms In some systems where hydrologic manipulations (ie, plentiful water supplies) are possible, reducing the water residence time by flushing and artificial mixing (along with nutrient input constraints) can be effective alternatives Blooms that are not readily consumed and transferred up the food web will form a relatively large proportion of sedimented organic matter This, in turn, will exacerbate sediment oxygen demand, and enhance the potential for oxygen depletion and release of nutrients back to the water column This scenario is particularly problematic in long–residence time (ie, months) systems, where blooms may exert a strong positive feedback on future events Implications of these scenarios and the confounding issues of climatic (hydrologic) variability, including droughts, tropical storms, hurricanes and floods, will be discussed in the context of developing effective CHAB control strategies along the freshwater–marine continuum

Abstract: Soils of the cerrado biome, mostly oxisols and deep sandy entisols, are acid, dystrophic and poor in available nutrients. These soils are not very different from soils that occur in the Amazon region. However, the open savanna physiognomies of cerrado with lower biomass of their different components are deficient in nutrients at the ecosystem level, unlike the Amazon forests which retain high nutrient reserves in their live biomass. Field crops are susceptible to aluminum and manganese toxicities, besides nutrient deficiencies, in cerrado soils and do not grow well in the absence of liming and fertilization. However, concepts of nutrient deficiencies and toxicities, well established for cultivated plants, should not be extended to native species in natural ecosystems, indiscriminately. Many native plants in the cerrado biome are resistant or tolerant to soil conditions deemed unfavorable for cultivated plants but their geographic distribution, frequency in native communities, growth and productivity are determined by water and nutrient availability and other edaphic conditions. Species growing on acid soils are aluminum tolerant or resistant, since their capacity to absorb essential nutrients, growth and reproduction is not affected by high aluminum levels in the soil. Many common species of the cerrado, instead of excluding aluminum, absorb and transport it to leaves and accumulate it in different tissues including leaves and seeds whereas others do not survive in the absence of exchangeable aluminum, even though no specific role of Al in plant metabolism is yet established.

Abstract: Zn, Se, and Fe levels in 65 Chinese rice samples were investigated, and the results indicated that these micronutrients contents of rice products from different location varied considerably. The mean contents of Zn, Se and Fe in these rice samples were 21.5 ± 1.8, 0.020 ± 0.012, and 12.4 ± 4.3 mg kg−1, respectively, which were too low to meet the micronutrient demands for the population feeding on the rice as staple. A field orthogonal experiment L9 (34) was conducted on rice cultivar Wuyunjing 7, to evaluate the effect of Zn, Se, and Fe foliar fertilization on the concentration of these micronutrients, yield, and protein and ash content of rice grain. The results indicated that Zn and Se were the main variables influencing the Zn, Se, and Fe content of rice, and the optimal combination of fertilization for enhancing these micronutrients was 0.90 kg ha−1 Zn, 0.015 kg ha−1 Se, and 0.90 kg ha−1 Fe. Under the optimal application condition, Zn, Se, and Fe content of rice could be significantly increased by 36...

Abstract: Nutrient profiling of foods, described as the science of ranking foods based on their nutrient content, is fast becoming the basis for regulating nutrition labels, health claims, and marketing and advertising to children. A number of nutrient profile models have now been developed by research scientists, regulatory agencies, and by the food industry. Whereas some of these models have focused on nutrients to limit, others have emphasized nutrients known to be beneficial to health, or some combination of both. Although nutrient profile models are often tailored to specific goals, the development process ought to follow the same science-driven rules. These include the selection of index nutrients and reference amounts, the development of an appropriate algorithm for calculating nutrient density, and the validation of the chosen nutrient profile model against healthy diets. It is extremely important that nutrient profiles be validated rather than merely compared to prevailing public opinion. Regulatory agencies should act only when they are satisfied that the scientific process has been followed, that the algorithms are transparent, and that the profile model has been validated with respect to objective measures of a healthy diet.

Abstract: Forest soil carbon (C) pools may act as sinks for, or sources of, atmospheric carbon dioxide, while nitrogen (N) fertilization may affect the net exchange of C in forest ecosystems. Since all major C and N processes in soil are driven by soil microorganisms, we evaluated the effects of N fertilization on biomass and bacterial and fungal activity in soils from three Norway spruce forests with different climatic and N availability conditions. N deposition and net N mineralization were higher at the sites in southern Sweden than at the site in northern Sweden. We also studied the extent to which N fertilization altered the nutrient(s) limiting bacterial growth in soil. We found that on average microbial biomass was reduced by ∼40% and microbial activity by ∼30% in fertilized plots. Bacterial growth rates were more negatively affected by fertilization than fungal growth rates, while fungal biomass (estimated using the phospholipid fatty acid (PLFA) 18:2ω6,9) decreased more than bacterial biomass as a consequence of fertilization. The microbial community structure (indicated by the PLFA pattern) was changed by fertilization, but not in the same way at the three sites. Soil bacteria were limited by a lack of carbon in all forests, with the carbon limitation becoming more evident in fertilized plots, especially in the forests that had previously been the most N-limited ones. This study thus showed that the effects of N fertilization differed depending on the conditions at the site prior to fertilization.

Abstract: Summary 1. The soil sink for carbon is important in regulating climate and soil fertility. The sink strength is dependent on the balance of soil carbon decomposition and formation. Variation in the rates of these processes to manipulations of resource availabilities under global change, such as elevated atmospheric carbon dioxide, is not explained by soil microbial theory. 2. To investigate disparate responses of soil carbon dynamics in field investigations, to altered carbon, nitrogen and phosphorus availability, we couple fractionation, isotope and mesocosm techniques to quantify soil carbon decomposition and formation under different resource regimes. These regimes involve addition of multiple levels of carbon, nitrogen and phosphorus, alone and in combination. 3. We hypothesize that: (i) there is no net effect of labile carbon input rate on soil carbon stocks because reductions in soil carbon decomposition are offset by reductions in soil carbon formation; (ii) with simultaneous nutrient addition soil carbon stocks will increase because nitrogen will inhibit further soil carbon decomposition, and mitigate reductions in soil carbon formation observed under elevated labile carbon availability alone; (iii) this increase in soil carbon stocks will be a product of greater formation and decreased decomposition of slower-cycling, mineral-associated, soil carbon, whereas less stable, particulate soil carbon will simply turnover faster (due to greater soil carbon decomposition and formation). 4. In contrast to our predictions formation of soil carbon is positively correlated with labile carbon input rates. In addition, nutrient amendment does not interact with carbon amendment to affect total soil carbon contents. However, there are significant interactive effects when the formation and decomposition responses of different soil carbon fractions are considered. For nitrogen alone, its effects on soil carbon fractions follow our hypotheses. However, phosphorus amendment increases decomposition of the soil carbon fraction that constitutes a longer-term sink. 5. Our results highlight the need for rhizodeposition, phosphorus and soil carbon fractions to be explicitly considered when interpreting potential soil organic carbon responses to altered resource availability. In the discussion, we make four recommendations for future investigations to improve our understanding of soil carbon responses to altered carbon, nitrogen and phosphorus availabilities.

Abstract: The root:shoot ratio of grassland plants may be lower in high fertility sites than in low fertility sites as plants modify their root, rhizome and shoot morphologies (and masses) to suit prevail- ing nutrient availability. We conducted geographically diverse and regionally specific field sampling and measured above- and belowground plant biomasses in western Atlantic and Gulf of Mexico salt marshes to determine whether there is a similar morphological response in Spartina alterniflora, the dominant salt marsh plant. Coastal nutrient addition/enrichment, which is widespread and ongoing, may lower root and rhizome biomass, belowground production and organic accumulation in this spe- cies. Higher soil respiration and a lower Eh (redox potential) are expected additional soil property changes. The addition of P, more than of N, seems to reduce root and rhizome biomass accumulation. The cumulative effects of increased nutrient loadings on salt marshes may be to decrease soil eleva- tion and accelerate the conversion of emergent plant habitat to open water, particularly on the lower marsh. The recommendations for management practices intended to conserve coastal marshes include reducing nutrient loading to coastal zones, solving water quality problems with a multiple nutrient approach, and choosing monitoring metrics that are based on both above- and belowground plant biomass.

Abstract: The current best practice intensive culture of larval Atlantic cod includes feeding rotifers from onset of exogenous feeding until 25–30 days after hatching. These larvae grow considerably slower and develop higher frequencies of deformities than larvae reared in semi-extensive systems, using copepods as feed. The present study compares the micronutrient concentrations in rotifers with those of copepods, with the aim of identifying nutrients that may be limiting for normal growth and development of cod larvae. An additional criterion used is the nutrient requirements given for fish in general, by NRC (1993), as nutrient requirements of cod remains to be determined. Rotifers were fed on four different diets, consisting of baker’s yeast with cod liver oil (3.3 : 1 dry weight (DW)/v), baker’s yeast with Algamac 2000 TM (3.5 : 1 DW), baker’s yeast with live algae Chlorella (4.1 : 1 DW), and Culture Selco 3000 TM (CS). CS was a complete commercial diet for rotifers while the other diets are considered as based on raw ingredients. Compared with copepod nutrient levels, rotifers grown on yeast-based diets supplemented with either cod liver oil, Algamac 2000 or Chlorella were apparently sufficient for covering the requirements in cod larvae for all the B-vitamins, except thiamine. Rotifers cultured on the CS diet also had sufficient amounts of thiamine. Of the minerals, only calcium and magnesium were sufficient, using this criterion while iron was on the borderline. However, with reference to the requirements given for larger fish (NRC 1993), only thiamine, vitamin A, manganese, selenium and perhaps copper, appear too low in the rotifers cultured without extra micronutrient supplementation. The other nutrients were present at levels intermediate between copepod and fish requirement levels. This study suggests that it is necessary to develop enrichment techniques to produce rotifers with sufficient amounts of all micronutrients. Such techniques will also be important tools for determining which nutrients are present at levels below the actual requirements in cod larvae.

Abstract: Food security could only be attained with increasing crop productivity. One of the major crop productivity constraints is the unavailability of crop nutrients. Both macro and micro nutrient deficiencies have been reported in most of the soils, which could be provided through various nutrient management practices. Different nutrient application measures were studied for their impact on crop yield and yield-related parameters in a series of experiments, conducted at agricultural research farm, NWFP Agricultural University Peshawar, Pakistan from 2004 through 2007. FYM application was observed to improve crop growth and yield of different wheat cultivars. Nutrient seed priming resulted in better early growth of maize. At field level, nutrient seed priming improved performance of wheat. Similarly for maize crop, nutrient seed priming resulted in more number of cobs plot -1 , grains cob -1 , 1000-grain weight and biological yield of maize crop even at lower soil application. Soil application of P improved yield and yield components. Better results were obtained from combined use of priming and soil P application. Foliar application of macro and micro nutrients also produced better crop yield and yield components. Similarly, foliar application of micro nutrients (zinc and boron) improved yield over two years. Our results show that all of these crop nutrients management practices has a positive impact on crop performance and call for an integrated approach of crop nutrient management. Such integrated approach must be evaluated at farm level for their economic impact. Adoption of integrated crop nutrient management techniques could be more economical and environmental friendly to achieve higher yields and thus food security.

Abstract: The effects of 16 different combinations of nutrient load and agitation on yield, nutrient uptake and proximate chemical composition of the seaweed Ulva lactuca cultured in tanks were evaluated. Intensive fishpond outflow passed through seaweed tanks at four nutrient loading levels and four water agitation combinations of water exchange, bottom aeration and frequently changing water levels (an accelerated tide regime). Specific results from these outdoor experiments were examined further under controlled conditions in laboratory experiments. Agitation treatments affected the performance of U. lactuca only under TAN (\({\text{NH}}_{3} + {\text{NH}}^{ + }_{4} \)) load levels below 4 g N m−2 day−1; biofiltration of TAN was the parameter most affected. Biomass yields at each of the four nutrient loading levels were not significantly different between the agitation treatments. Protein content increased significantly with increasing nutrient loading. The agitation treatments had a slight effect on seaweed protein content only at the lowest nutrient loading levels. There were no significant differences in dissolved oxygen concentration, pH, and temperature among the agitation treatments at all nutrient loading levels. Under laboratory conditions, growth rates, protein content, and photosynthetic and biomass yield of the seaweed were affected by water velocity under low nutrient concentrations. It is concluded that the effect of air agitation under the conditions of these experiments was not directly related to photosynthesis, excess dissolved oxygen, or carbon limitation, but to the diffusion of macro nutrients from the water to the seaweed. Therefore, once nutrient concentrations are high enough (above about 4 μM of TAN with the other nutrients in their corresponding proportions), aeration per se is not essential for effective growth and biofiltration by seaweeds.

Abstract: Magnesium is an essential nutrient, which activates more enzymes than any other mineral element and, thus, plays an important role in biogeochemical cycles. With three stable isotopes naturally abundant (24Mg, 78.992%; 25Mg, 10.003%; 26Mg, 11.005%), magnesium stable isotope fractionation may provide insights into these cycles. Here, we detail for the first time the magnesium stable-isotope distribution in a higher plant, wheat (Triticum aestivum L.), during its growth cycle. Wheat plants were grown in a limiting nutrient supply hydroponically, some being left to mature through senescence and others detopped at maturity for collection of exudates. Measurements of the magnesium isotopic composition of chlorophylls, seeds, shoots, roots, leaves, exudates, and the limiting nutrient solution over time show that the plant appears to establish an isotopic equilibrium with the nutrient available to it and that the plant (in particular, the seeds and exudates) becomes enriched in the heavy isotopes of magnesium in a mass-dependent relationship as the plant reaches maturity. The preference of the plants for heavy magnesium isotopes suggests that a difference might exist in the bioavailable magnesium of agricultural and natural soils due to the periodic removal of heavy magnesium isotopes by harvest.

Abstract: The invasion of non-native plants can alter the diversity and activity of soil microorganisms and nutrient cycling within forests. We used field studies to analyze the impact of a successful invasive groundcover, Alliaria petiolata, on fungal diversity, soil nutrient availability, and pH in five northeastern US forests. We also used laboratory and greenhouse experiments to test three mechanisms by which A. petiolata may alter soil processes: (1) the release of volatile, cyanogenic glucosides from plant tissue; (2) the exudation of plant secondary compounds from roots; and (3) the decomposition of litter. Fungal community composition was significantly different between invaded and uninvaded soils at one site. Compared to uninvaded plots, plots invaded by A. petiolata were consistently and significantly higher in N, P, Ca and Mg availability, and soil pH. In the laboratory, the release of volatile compounds from the leaves of A. petiolata did not significantly alter soil N availability. Similarly, in the greenhouse, the colonization of native soils by A. petiolata roots did not alter soil nutrient cycling, implying that the exudation of secondary compounds has little effect on soil processes. In a leaf litter decomposition experiment, however, green rosette leaves of A. petiolata significantly increased the rate of decomposition of native tree species. The accelerated decomposition of leaf litter from native trees in the presence of A. petiolata rosette leaves shows that the death of these high-nutrient-content leaves stimulates decomposition to a greater extent than any negative effect that secondary compounds may have on the activity of the microbes decomposing the native litter. The results presented here, integrated with recent related studies, suggest that this invasive plant may change soil nutrient availability in such a way as to create a positive feedback between site occupancy and continued proliferation.

Abstract: Multi-year nitrogen (N) and phosphorus (P) budgets were developed for the Patuxent River estuary, a seasonally stratified and moderately eutrophic tributary of Chesapeake Bay Major inputs (point, diffuse, septic, and direct atmospheric) were measured for 13 years during which, large reductions in P and then lesser reductions in N-loading occurred due to wastewater treatment plant improvements Internal nutrient losses (denitrification and long-term burial of particulate N and P) were measured in tidal marshes and sub-tidal sediments throughout the estuary as were nutrient storage in the water column, sediments, and biota Nutrient transport between the oligohaline and mesohaline zones and between the Patuxent and Chesapeake Bay was estimated using a salt and water balance model Several major nutrient recycling terms were directly and indirectly evaluated and compared to new N and P inputs on seasonal and annual time-scales Major findings included: (1) average terrestrial and atmospheric inputs of N and P were very close to the sum of internal losses plus export, suggesting that dominant processes are captured in these budgets; (2) both N and P export were a small fraction (13% and 28%, respectively) of inputs, about half of that expected for N based on water residence times, and almost all exported N and P were in organic forms; (3) the tidal marsh-oligohaline estuary, which by area com- prised ~27% of the full estuarine system, removed about 46% and 74% of total annual upland N and P inputs, respectively; (4) recycled N and P were much larger sources of inorganic nutrients than new inputs during warm seasons and were similar in magnitude even during cold seasons; (5) there was clear evidence that major estuarine processes responded rapidly to inter-annual nutrient input variations; (6) historical nutrient input data and nutrient budget data from drought periods indicated that diffuse nutrient sources were dominant and that N loads need to be reduced by about 50% to restore water quality conditions to pre-eutrophic levels

Abstract: Ongoing global warming will increase the frequency of soil freeze-thaw cycles (FTCs) in cool-temperate and other high-latitude regions. The spatial relevance of seasonally frozen ground amounts to c. 55% of the total land area of the northern hemisphere. Evidence suggests that FTCs contribute to nutrient dynamics. Knowledge of their effects on plant communities is scarce, although plants may be the decisive factor in controlling ecosystem functions such as nutrient retention. Here, the effects are analysed of five additional FTCs in winter for the above- and below-ground productivity of experimental grassland communities and soil enzymatic activity over the following growing season. Freeze-thaw cycles increased the above-ground productivity but reduced root length over the whole subsequent growing season. In summer, no changes in soil enzymatic activities representing the carbon, nitrogen and phosphorus cycles were observed in the FTC-manipulated plots, except for an increased cellobiohydrolase activity. Changes in productivity resulting in an increased shoot-to-root ratio and shifts in timing are capable of altering ecosystem stability and ecosystem services, such as productivity and nutrient retention.

Abstract: Transpiration-driven 'mass-flow' of soil-water can increase nutrient flow to the root surface. Here it was investigated whether transpiration could be partially regulated by nutrient status. Seeds of Ehrharta calycina from nine sites across a rainfall gradient were supplied with slow-release fertilizer dibbled into the sand surrounding the roots and directly available through interception, mass-flow and diffusion (dubbed 'interception'), or sequestered behind a 40-microm mesh and not directly accessible by the roots, but from which nutrients could move by diffusion or mass-flow (dubbed 'mass-flow'). Although mass-flow plants were significantly smaller than interception plants as a consequence of nutrient limitation, they transpired 60% faster, had 90% higher photosynthesis relative to transpiration (A/E), and 40% higher tissue P, Ca and Na concentrations than plants allowed to intercept nutrients directly. Tissue N and K concentrations were similar for interception and mass-flow plants. Transpiration was thus higher in the nutrient-constrained 'mass-flow' plants, increasing the transport of nutrients to the roots by mass-flow. Transpiration may have been regulated by N availability, resulting in similar tissue concentration between treatments. It is concluded that, although transpiration is a necessary consequence of photosynthetic CO(2) uptake in C(3) plants, plants can respond to nutrient limitation by varying transpiration-driven mass-flow of nutrients.

Abstract: Arctic soils hold large amounts of nutrients in the weatherable minerals and the soil organic matter, which slowly decompose. The decomposition processes release nutrients to the plant-available nutrient pool as well as greenhouse gases to the atmosphere. Changes in climatic conditions, for example, changes in the distribution of snow, water balance and the length of the growing season, are likely to affect the complex interactions between plants, abiotic and biotic soil processes as well as the composition of soil micro- and macro-fauna and thereby the overall decomposition rates. These interactions, in turn, will influence soil-plant functioning and vegetation composition in the short as well as in the long term. In this chapter, we report on soils and. plant communities and their distribution patterns in the valley Zackenbergdalen and focus on the detailed investigations within five dominating plant communities. These five communities are located along an ecological gradient in the landscape and are closely related to differences in water availability. They are therefore indirectly formed as a result of the distribution of landforms, redistribution of snow and drainage conditions. Each of the plant communities is closely related to specific nutrient levels and degree of soil development including soil element accumulation and translocation, for example, organic carbon. Results presented here show that different parts of the landscape have responded quite differently to the same overall climate changes the last 10 years and thus, most likely in the future too. Fens represent the wettest sites holding large reactive buried carbon stocks. A warmer climate will cause a permafrost degradation, which most likely will result in anoxic decomposition and increasing methane emissions. However, the net gas emissions at fen sites are sensitive to long-term changes in the water table level. Indeed, increasing maximum active layer depth at fen sites has been recorded together with a decreasing water level at Zackenberg. This is in line with the first signs of increasing extension of grasslands at the expense of fens. In contrast, the most exposed and dry areas have less soil carbon, and decomposition processes are periodically water limited. Here, an increase in air temperatures may increase active layer depth more than at fen sites, but water availability will be critical in determining nutrient cycling and plant production. Field manipulation experiments of increasing temperature, water supply and nutrient addition show that soil-plant interactions are sensitive to these variables. However, additional plant-specific investigations are needed before net effects of climate changes on different landscape and plant communities can be integrated in a landscape context and used to assess the net ecosystem effect of future climate scenarios.

Abstract: Potential enzyme activities in soil and water samples are measured by addition of an excess amount of suitable substrate and subsequent determination of product release. If the approach is reversed and an excess of enzyme is added, substrate availability becomes rate-limiting and the maximum release of product indicates the availability of a given substrate in a sample. This approach has been used in a range of studies using phosphatase enzyme additions to soil, manure and sediment extracts, soil suspensions, and lake and sea water ( n = 41). Significantly fewer studies have used enzymes from the carbon, nitrogen and sulfur cycles ( n = 14). In this review, the methodological aspects of enzyme additions are discussed using examples from studies in which enzymes from the phosphorus cycle were used. A meta-analysis performed for various soil extracts and water samples revealed that the majority of studies (75th percentile) indicate availability of organic phosphorus to enzymatic hydrolysis of up to 60%, with crude phytase preparations showing the lowest substrate specificity and greatest release of phosphorus. Compared to addition of enzymes from the phosphorus cycle, lower substrate degradation was generally achieved by addition of enzymes from the carbon, nitrogen and sulfur cycles to soil suspensions and soil organic matter extracts. Enzyme additions can be a valuable tool in process research, provided all the necessary controls are included and assay conditions optimized to ensure that the reaction reaches completion. Recommendations for the development of a standard protocol are made.