Nutrient cycling in an excessively rainfed subtropical grassland at Cherrapunji

Cycling of six mineral elements (N, P, K, Na, Ca and Mg) was studied in a humid subtropical grassland at Cherrapunji, north-eastern India during 1988-1989. Elemental concentrations in the shoot of four dominant grass species,viz., Arundinella khaseana, Chrysopogon gryllus, Eragrostiella leioptera andEulalia trispicata were very low, and none of the species appears suitable for fodder use. Among different vegetation compartments, live root was the largest reservoir of all the nutrients (except Ca) followed by live shoot, dead shoot, litter and dead root. For Ca, live shoot was the major storage compartment. The total annual uptake (kg ha^-1) was 137.3, 10.4, 51.1, 5.5, 8.7 and 18.2 for N, P, K, Na, Ca and Mg, respectively. In an annual cycle 98% N, 77% P, 49% K, 109% Na, 87% Ca and 65% Mg returned to the soil through litter and belowground detritus. A major portion of N, P and Na was recycled through the belowground system, whereas nearly half of K, Ca and Mg was recycled through the shoot system. Precipitation acts as the source of N and P input, but at the same time causes loss of cations.     

Nutrient fluxes from upwelling and enhanced turbulence at the top of the pycnocline in Mono Lake, California

Time series measurements of temperature at 15 depths and profiles of temperature-gradient microstructure were obtained during a period with strong wind forcing and subsequent calm in Mono Lake, California. The wind forcing increased the amplitude of basin-scale internal waves and energy at all wave frequencies relative to the calm period. Rates of dissipation of turbulent kinetic energy, , were high ( > 10^–6 m² s^–3) at the top of the pycnocline at both an inshore and an offshore site on a day when winds reached 10 m s^–1 and on the following two days at an inshore site ( > 10^–7 m² s^–3). The enhanced turbulence occurred at the depth of a subsurface temperature maximum (z _TM) and coincidentally with elevated concentrations of NH₄, reduced concentrations of chlorophyll a and particulate carbon, and increased abundance of the macrozooplankter Artemia monica. The NH₄ at z _TM was more dispersed and of lower concentration inshore than offshore and indicated greater turbulent transport inshore. Over the course of 4 days, chlorophyll a concentrations increased in the upper mixed layer, and C:N and C:Chl ratios decreased. Offshore, the change in C:N ratio indicated a relaxation of moderate nutrient deficiency. We hypothesize that excretion by A. monica and turbulent transport of the NH₄ from the subsurface temperature maximum led to improved physiological status of phytoplankton in the upper mixed layer.     

Release rates and potential fates of nitrogen and phosphorus from sediments in a eutrophic reservoir

1. Nutrients released from lake sediments can influence water column nutrient concentrations and planktonic productivity. We examined sediment nutrient release [soluble reactive phosphorus (SRP) and ammonia (NH)] at two sites in a eutrophic reservoir (Acton Lake, OH, U.S.A.) that differed in physical mixing conditions (a thermally stratified and an unstratified site). 2. Sediment nutrient release rates were estimated with three methods: sediment core incubations, seasonal in situ hypolimnetic accumulation and a published regression model that predicted sediment phosphorous (P) release rate from sediment P concentration. All three methods were applied to the deeper stratified site in the reservoir; however, we used only sediment core incubations to estimate SRP and NH release rates at the shallow unstratified site because of the lack of thermal stratification. We also compared the total P concentration (TP_S) of sediments and the concentration of P in various sediment fractions at both sites. 3. Anoxic sediments at the stratified site released SRP at rates more than an order of magnitude greater than oxic sediments at the shallow unstratified site. However, P accumulated in the hypolimnion at much lower rates than predicted by sediment core incubations. In contrast, NH was released at similar rates at both sites and accumulated in the hypolimnion at close to the expected rate, indicating that P was ‘lost’ from the hypolimnion through biogeochemical pathways for P, such as precipitation with inorganic material or biological uptake and sedimentation. 4. TP_S was significantly greater at the deeper stratified site and organically bound P accounted for >50% of TP_S at both sites. 5. We examined the magnitude of SRP fluxes into the study reservoir in 1996 by comparing the mean summer daily SRP fluxes from anaerobic sediments, aerobic sediments, stream inflows and gizzard shad excretion. While the SRP release from anaerobic sediments was high, we hypothesise that little of this SRP gained access to the epilimnion in mid‐summer. SRP flux to the reservoir from aerobic sediments was less than from gizzard shad excretion and streams. Large interannual variability in thermocline stability, gizzard shad biomass and stream discharge volumes, will affect SRP loading rates from different sources in different years. Therefore, construction of P budgets for different years should account for interannual variation in these parameters.     

Underwater Locomotion in the Desert Locust: Behavioural Choice When Confronted with an Aquatic Barrier

Laboratory studies have shown that adult desert locusts (Schistocerca gregaria) have a swim motor programme, and early field reports describe swimming by bands of hoppers if their route of march is obstructed by a channel of water. However, it is not known whether unconstrained adult locusts will enter water ‘voluntarily’. We found in the laboratory that not only will locusts readily enter water, but that they frequently submerge themselves completely under the water, and cross a water barrier by walking along the bottom. They can stay submerged for up to approximately 9 min, but there is no evidence for significant gas exchange with the water. So far as we are aware the demonstration of this capability for underwater locomotion is a novel finding in this well-studied insect.     

转基因植物中标记基因的消除

随着转基因植物的商业化,植物遗传转化技术将为农业生产带来一场新的革命,新的基因转化程序要求转基因为单拷贝,不带有标记基因,并在不同的转化体中表达一致,稳定遗传,本文讨论了转基因植物中有关标记基因及其安全性和标记基因消除的方法等问题。     

Uncertainty in Nutrient Spiraling: Sensitivity of Spiraling Indices to Small Errors in Measured Nutrient Concentration

Abstract Proper assessment of ecological data must consider uncertainty. However, reported estimation of uncertainty in calculated values of nutrient spiraling indices is rare. Interpretations based on single values of spiraling indices, may therefore be unwittingly flawed. We investigated the sources of analytical uncertainty in the nutrient concentrations used to calculate two spiraling indices, uptake length (S _w ) and uptake velocity (V _f ), and used Monte Carlo Simulation (MCS) to estimate the resultant uncertainty in index values. We also examined the effect of the level of nutrient enrichment on the magnitude of index uncertainty. Outcomes under high and low nutrient uptake capacity were compared by performing nutrient addition experiments in two streams with contrasting ambient nutrient concentrations. We found that small differences (or uncertainties) in the average plateau nutrient concentration resulted in large uncertainties in spiraling indices. The uncertainty resulted from a combination of small differences in nutrient concentrations between upstream and downstream stations (particularly for the low uptake case), the low nutrient concentration added into the stream, and the sample matrix and storage. The stream with low nutrient uptake capacity had larger relative uncertainties in S _w than when the nutrient uptake capacity was high. The presence of such errors demands that S _w and V _f values should be reported with uncertainty, rather than the normal practice of a single calculated value. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Elimination ofM. hyorhinis from murine neuroblastoma cell lines by in vivo passage

Summary Cell lines derived from a murine neuroblastoma, Clone N18, were cured of theirM. hyorhinis infection by in vivo passage. The major variable determining success of this method was found to be the incubation time in vivo. Infected cells maintained in vivo for 27 d or more and then placed in culture were free of mycoplasma whereas those maintained in vivo for 7 or 14 d were found to still be infected. This approach to eliminating mycoplasma infection may be successful using other tumor cell lines. This work was supported in part by Grants ES01530, GM24592, and GM26167 from the National Institutes of Health, Bethesda, MD.     

Elimination of foot-and-mouth disease in South America: lessons and challenges

Foot-and-mouth disease (FMD) is a highly transmissible and economically devastating disease of cloven-hoofed livestock. Although vaccines are available and have been instrumental in eliminating the disease from most of the South American animal population, viral circulation still persists in some countries and areas, posing a threat to the advances of the last 60 years by the official veterinary services with considerable support of the livestock sectors. The importance of the disease for the social and economic development of the American continent led to the establishment in 1951 of the Pan American Centre for Foot-and-Mouth Disease (PANAFTOSA), which has been providing technical cooperation to countries for the elimination of the disease. The first FMD national elimination programmes were established in South America around the 1960s and 1970s. To advance the regional elimination efforts in the 1980s, countries agreed on a Plan of Action 1988–2009 of the Hemispheric Program for the Eradication of Foot-and-Mouth Disease. The Plan of Action 1988–2009 did not reach the goal of elimination from the continent; and a new Plan of Action 2011–2020 was developed in 2010 based on the experience acquired by the countries and PANAFTOSA during the past 60 years. This plan is now being implemented; several challenges are still to be overcome to ensure the elimination of FMD from the Americas by 2020, however, the goal is achievable.     

Nutrient cycling in Pinus sylvestris stands in eastern Finland

Nutrient cycling within three Pinus sylvestris stands was studied in eastern Finland. The aim of the study was to determine annual fluxes and distribution of N, P, K, Ca, Mg, Zn, Fe, B, and Al in the research stands. Special emphasis was put on determining the importance of different fluxes, especially the internal cycle within the trees in satisfying the tree nutrient requirements for biomass production. The following nutrient fluxes were included, input; free precipitation and throughfall, output; percolation through soil profile, biological cycle; nutrient uptake from soil, retranslocation within trees, return to soil in litterfall, release by litter decomposition. The distribution of nutrients was determined in above- and belowground tree compartments, in ground and field vegetation, and in soil.The nitrogen use efficiencies were 181, 211 and 191 g of tree aboveground dry matter produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature stands, respectively. Field vegetation was more efficient in nitrogen use than trees. Stand belowground/aboveground and fine root/coarse root biomass ratios decreased with tree age. With only slightly higher fine root biomass, almost three times more nitrogen had to be taken-up from soil for biomass production in the mature stand than in the sapling stand.The annual input-output balances of most nutrients were positive; throughfall contained more nutrients than was lost in mineral soil leachate. The sulphate flux contributed to the leaching of cations, especially magnesium, from soil in the mature stand.Retranslocation supplied 17–42% of the annual N, P and K requirements for tree aboveground biomass production. Precipitation and throughfall were important in transferring K and Mg, and also N in the sapling stand. Litterfall was an important pathway for N, Ca, Mg and micro nutrients, especially in the oldest stands.     

树木细根养分内循环

养分内循环是树木减少养分损失,提高养分利用效率的重要途径。树木细根寿命短、周转快．每年大量凋落死亡,因此,近20多年来树木细根养分内循环的研究逐渐受到人们的重视。关于树木细根养分内循环目前的研究结论比较复杂。本文从细根在树木地下部分养分内循环中的重要地位、细根养分内循环对树木减少养分损失的重要性、细根中各养分元素内循环的研究现状以及细根养分内循环研究方法存在的问题等方面综合论述了国内外的进展情况,并对今后的研究趋势进行了展望。     

Elimination of mycoplasmas from cell cultures by a novel soft agar technique

Summary Mycoplasmal infection of cell cultures remains a significant threat to diagnostic and research procedures. In certain defined situations, curing of mycoplasmal infected cultures is a reasonable exercise. Four methods of curing were compared: treatment with BM-cycline, 5 bromouracil, use of specific antisera and treatment of infected cells suspended in soft agar with antibiotics. Antisera treatments were of low efficiency of curing: 50%. None of nine infected cell lines treated with 5-bromouracil were consistently cured of mycoplasmas. The use of BM-cycline was effective for some, but not all lines and required long periods of treatment, 12–21 days. 35 naturally or deliberately infected cultures were treated in soft agar a total of 119 times. This procedure which consisted of suspending infected cultures in soft agar containing appropriate antibiotics resulted in successful mycoplasmal elimination 118/119 times. This soft agar technique took 1–3 days. In separate studies, it was shown that certainMycoplasma fermentans strains were resisted to this and other curing methods. This may be due to their intracellular location. Such strains may be more amenable to antibiotics that penetrate mammalian cells. It is concluded that the soft agar technique is a rapid, efficient and reliable method to eliminate cell culture mycoplasmas. These studies were supported in part by grant 15748 from the National Institute of Allergy and Infectious Diseases and the W. W. Smith Charitable Trust.     

Nutrient budgets and biogeochemistry in an experimental agricultural watershed in Southeastern China

During a two-year field study, an annual nutrient budget and cycles were developed for a small agricultural watershed. The study emphasized the integrated unit of the watershed in understanding the biogeochemistry. It was found that the total nutrient input was 39.1× 10⁴ kg nitrogen and 3.91×10⁴ kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7×10⁴ kg (676 kg/ha) nitrogen and 3.88×10⁴ kg (76 kg/ha) phosphorus. The total nutrient output from the watershed was 13.55×10⁴ kg nitrogen and 0.40×10⁴ kg phosphorus, while the largest output of nitrogen was denitrification, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutrient surplus within the watershed, a surplus which may become a potential source of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitrogen are key ways of nitrogen loss from the watershed. This suggests that careful management of fertilizer application will be important for the sustainable development of agriculture.The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutrients, benefiting the water, nutrient and sediment recycling in the terrestrial ecosystem and helping to reduce agricultural nonpoint pollution at its source. Therefore, this unique watershed system should be recommended due to its great potential relevance for sustainable agricultural development.     

Nutrient Sensing in Plant Meristems

Plants need nutrient to grow and plant cells need nutrient to divide. The meristems are the factories and cells that are left behind will expand and differentiate. However, meristems are not simple homogenous entities; cells in different parts of the meristem do different things. Positional cues operate that can fate cells into different tissue domains. However, founder/stem cells persist in specific locations within the meristem e.g. the quiescent centre of root apical meristem (RAM) and the lower half of the central zone of the shoot apical meristem (SAM). Given the complexity of meristems, do their cells simply respond to a diffusing gradient of photosynthate? This in turn begs the question, why do stem cell populations tend to have longer cell cycles than their immediate descendants given that like all other cells they are directly in the path of diffusing nutrient? In this review, we have examined the extent to which nutrient sensing might be operating in meristems. The scene is set for sugar sensing, the plant cell cycle, SAMs and RAMs. Special emphasis is given to the metabolic regulator, SnRK1 (SNF1-related protein kinase 1), hexokinase and the trehalose pathway in relation to sugar sensing. The unique plant cell cycle gene, cylin-dependent kinase B1;1 may have evolved to be particularly responsive to sugar signalling pathways. Also, the homeobox gene, STIMPY, emerges strongly as a link between sugar sensing, plant cell proliferation and development. Flowering can be influenced by sucrose and glucose levels and both meristem identity and organ identity genes could well be differentially sensitive to sucrose and glucose signals. We also describe how meristems deal with extra photosynthate as a result of exposure to elevated CO₂. What we review are numerous instances of how developmental processes can be affected by sugars/nutrients. However, given the scarcity of knowledge we are unable to provide uncontested links between nutrient sensing and specific activities in meristems.     

Thermal stratification, nutrient dynamics, and phytoplankton productivity during the onset of spring phytoplankton growth in Lake Baikal, Russia

Lake Baikal, Russian Siberia, was sampled in July 1990 during the period of spring mixing and initiation of thermal stratification. Vertical profiles of temperature, dissolved nutrients (nitrate and soluble reactive phosphorus), phytoplankton biomass, and primary productivity were determined in an eleven-station transect encompassing the entire 636 km length of the lake. Pronounced horizontal variability in hydrodynamic conditions was observed, with the southern region of the lake being strongly thermally stratified while the middle and north basins were largely isothermal through July. The extent of depletion of surface water nutrients, and the magnitude of phytoplankton biomass and productivity, were found to be strongly correlated with the degree of thermal stratification. Horizontal differences likely reflected the contribution of two important factors: variation in the timing of ice-out in different parts of the lake (driving large-scale patterns of thermal stratification and other limnological properties) and localized effects of river inflows that may contribute to the preliminary stabilization of the water column in the face of intense turbulent spring mixing (driving meso-scale patterns). Examination of the relationships between surface water inorganic N and P depletion suggested that during the spring and early summer, phytoplankton growth in unstratified portions of the lake was largely unconstrained by nutrient supplies. As summer progressed, the importance of co-limitation by both N and P became more apparent. Uptake and regeneration rates, measured directly using the stable isotope ¹⁵N, revealed that phytoplankton in stratified portions of the lake relied primarily on NH₄ as their N source. Rates of NH₄ regeneration were in approximate equilibrium with uptake; both processes were dominated by organisms <2 µm. This pattern is similar to that observed for oligotrophic marine systems. Our study underscores the importance of hydrodynamic conditions in influencing patterns of biological productivity and nutrient dynamics that occur in Lake Baikal during its brief growing season.     

Nutrient retention by the Kis-Balaton Water Protection System

Water quality of Lake Balaton, particularly that of its south-western basin (the Keszthely-Bay), has been deteriorating faster and faster. The greatest transporter of inorganic nutrients to the Bay is the Zala River.The lower valley of the river was part of the lake until about 200 years ago. Later, a large part of the area was turned to a wetland, while the smaller part dried up.To retain the nutrients from Keszthely-Bay, the former marshland is now being reconstructed: the so-called Kis-Balaton Water Protection System (KBWPS). The first part of the System, the Hidvégi-Pond, has been operating since the middle of 1985. The second stage, the Fenéki-Pond, to be finished by the end of this century, is now under construction. The main purpose of the KBWPS is to gain enough time to build up the technology necessary for an adequate protection of Lake Balaton.From the beginning of the operation of the Hidvégi-Pond a multidisciplinary research program has been carried out to monitor the hydrological, hydraulical, ecological, and biological processes in the reservoir. This program focused on nitrogen and phosphorus loadings and retention. Input and output loads were estimated from daily measurements. The mechanisms of retention were studied in special projects.With the exception of TN, nutrient retention increased from year to year. In 1990, 96% of PO₄-P, 87% NO₃-N, and 58% of TP were retained.This efficiency exceeds expectations. Retention of TN is the lowest (about 20%), due to N₂-fixation by blue-green algae. However, the second stage needs to be implemented, since there is an additional external load from the watershed of the lower valley, and nutrient release takes place during decomposition of the organic matter which leaves the Hidvégi-Pond.     

Nutrient transport in mycorrhizas: structure,physiology and consequences for efficiency of the symbiosis

Nutrient transport in mycorrhizas occurs across specialized interfaces which are the result of corrdinated development of the organisms. The structural modifications give rise to large areas of either inter- or intra-cellular interface in which wall synthesis is frequently modified and in which altered distribution of membrane bound ATPases is important, particularly with respect to mechanisms that may be involved in bidirectional transfer of nutrients. Except in orchid mycorrhizas, net movement of organic carbon from plant to fungus occurs, complemented by mineral nutrient movement in the opposite direction. The general consensus is that sustained transfer at rates that will maintain the growth and development of the organisms requires increases in the rates at which nutrients are lost from the organisms; possible mechanisms for this are discussed. The transfer processes are essential in determining both plant and fungal productivity and an approach to calculating the efficiency of the symbiosis in terms of the expenditure of carbon (or of phosphorus) is discussed.     

Nutrient uptake and allocation at steady-state nutrition

Ingestad, T. and Ågren, G. I. 1988. Nutrient uptake and allocation at steady-state nutrition. - Physiol. Plant. 72: 450–459. Net nutrient uptake and translocation rates are discussed for conditions of steady-state nutrition and growth. Under these conditions, the relative uptake rate is equal to the relative growth rate, for whole plants as well as for plant parts, since the root/shoot ratio and internal concentrations remain stable. The nutrient productivity and the minimum internal concentration are parameters characteristic for the plant and the nutrient. A conceptual, mathematical model, based on these two fundamental parameters is used for calculation and prediction of the net nutrient uptake rate, which is required to maintain steady-state nutrition at a specified internal nutrient concentration or relative growth rate. When uptake rate is expressed on the basis of the root growth rate, there is, up to optimum, a strong linear relationship between uptake rate and the internal concentration of the limiting nutrient. More complicated and less consistent relationships are obtained when uptake rate is related to root biomass. The limiting factor for suboptimum uptake is the amount of nutrients becoming available at the root surface. When replenishment is efficient, e.g. with vigorous stirring, the concentration requirement at the root surface appears to be extremely low, even at optimum. In the suboptimum range of nutrition, the effect of nutrient status on root growth rate is a critical factor with a strong feed-back on nutrition, growth and allocation. At supraoptimum conditions, the uptake mechanism is interpreted as a protection against too high uptake rates and internal concentrations at high external concentration. In birch (Betula pendula Roth.), the allocation of nitrogen to the shoots is high compared to that of potassium and also to that of phosphorus at low nitrogen or phosphorus status. With decreasing stress, phosphorus allocation becomes more and more similar to nitrogen allocation. The formulation of a mathematical model for calculation of allocation of biomass and nutrients requires more exact information on the quantitative dependence of the growth-regulating processes on nutrition.