Abstract: Forest ecosystems systematically produce more litterfall dry mass per unit of nitrogen in sites with less aboveground nitrogen circulation. This pattern is observed both within and among tropical, temperate deciduous, coniferous, Mediterranean, and fertilized ecosystems. The differences among sites are probably related to differences in soil nitrogen availability. Patterns of nitrogen use for root and wood production probably reinforce the litterfall results. An examination of phosphorus and calcium use efficiency for litterfall production yields more ambiguous results. The pattern for nitrogen circulation and nitrogen use efficiency in forests has important implications for ecosystem-level properties, including the development of low nitrogen availability in soil.

Abstract: Micronutrients and the nutrient status of soils :a global study , Micronutrients and the nutrient status of soils :a global study , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Abstract: The major constraints to nutrient uptake by vascular plants in mediterranean South Africa and Western Australia are: very infertile soils, relatively low temperatures when water availability is high, and hot, dry summers. These constraints are partly overcome through increased efficiency of uptake, tapping novel sources of nutrients, and prolonging water uptake. Absorptive area per unit “cost” may be enlarged directly through increased fineness of the root system and proliferation of long root hairs. This reaches its greatest development in the root clusters of the Proteaceae (proteoid roots), Restionaceae (“capillaroid” roots) and Cyperaceae (dauciform roots). Absorptive area is increased indirectly through fungal hyphae which extend from hairless rootlets into the soil. Two major groups can be recognised: general (VA mycorrhizas) and host-specific (ericoid, orchid and sheathing mycorrhizas). Mycorrhizas are the most widespread specialised modes of nutrition and are probably universal in such major taxa here asPodocarpus, Acacia, Fabaceae, Poaceae, Asteraceae, Rutaceae, terrestrial orchids, Ericales and Myrtaceae. General mycorrhizas are the least drought-adapted of mechanisms for maximising absorptive area. All have been implicated in enhancing P uptake through increasing access to inorganic P, solubilisation and shortening the diffusion path. However, selective uptake of other nutrients, especially N, by host-specific mycorrhizas may be equally important. Included under novel sources of nutrients are free N2 (utilised by N2-fixing nodules), small-animal prey (carnivorous leaves) and persistent leaf bases (aerial roots ofKingia australis). Both legume and non-legume N2-fixing species are well-represented in these two regions, with stands of individual species in southwestern Australia estimated to contribute 2–19 kg N/ha/yr to the ecosystem. Free nitrogen fixation requires additional nutrients, especially Mo and Co, but is enhanced following fires and by supplementary uptake mechanisms, especially VA mycorrhizas. Southwestern Australia is particularly rich in carnivorous species. Nitrogen, P, K and S are important nutrients absorbed, with digestion aided by enzymes provided by bacteria and the glands. Parasitic plants both tap novel sources of nutrients and capitalise on any efficient water and nutrient uptake mechanisms of the hosts. Root parasites are better represented than stem parasites in mediterranean South Africa and Western Australia. Phosphorus and K in particular are absorbed preferentially by the haustoria, but much remains to be known about their modes of operation. Maximum activity of all uptake mechanisms, except those attached to some deep-rooted plants, is restricted to winter-spring. Most new seasons’s rootlets and specialised roots are confined to the uppermost 15 cm of soil, especially in or near the decomposing litter zone. Nutrient uptake is further enhanced by the tendency for the rootlets to cluster, trapping water by capillary action and prolonging nutrient release. As an early product of decomposition, N tends to be available as NH4 (rather than NO3) and it is absorbed preferentially by almost all specialised modes of nutrition. Microorganisms are required in the formation and/or functioning of all these structures, except haustoria. Uptake mechanisms which are optional to the plant reach their peak contribution to the root system at soil nutrient levels well below those required for greatest plant growth, when they may be absent altogether. It is only over the narrow range of nutrient availability, where shoot content of a nutrient is greater in the presence of the mechanism than in its absence (other factors remaining constant), that specialised modes can be termed nutrient-uptake “strategies.” For all specialised modes of nutrition, the component genera are better represented in these two regions than in the surrounding more fertile, arid to subtropical regions of much greater area. Endemism of species with each mode exceeds that for the two floras overall (75%). This is taken as preliminary evidence that specialised modes of nutrition are best represented in nutrient-poor soils. While they serve to limit nutrient loss from the ecosystem, their proliferation is therefore not necessarily a response to increasing “leaks” in the system. A hierarchical scheme of the functional/structural relationships between the various mechanisms is presented, starting with the rootless, VA-mycorrhizal plant as the most primitive condition. Taxa with many of the specialised modes of nutrition at present in southwestern South Africa and Western Australia have been evident in the pollen record since the early Tertiary Period. The absence of ectomycorrhizal forests in mediterranean South Africa, in marked contrast to Western Australia, can be traced to differences in their paleohistory. In both regions, the combination of fluctuating, but essentially diminishing, nutrient and water availability that began with the first mediterranean climate < 5 million years ago resulted in decimation of the less-tolerant rainforest ancestors on the one hand, and remarkable rates of speciation of the pre-adapted sclerophyll nucleus on the other.

Abstract: Responses of the benthic insect community of a southern Appalachian trout stream to inorganic sedimentation and nutrient enrichment were monitored over a period of eight months. Entry of pollutants from point sources established differentially polluted zones, allowing an assessment of impacts due to sedimentation alone and in association with elevated nutrient levels. Input of sediment resulted in a significant increase in bed load and decrease of pH at the substrate-water interface (P < 0.05). The zone receiving nutrient runoff from livestock pasture exhibited elevated levels of nitrate and phosphate, but available data indicated such concentrations to be quite low. Species richness, diversity, and total biomass of filter feeding Trichoptera and Diptera, predaceous Plecoptera, and certain Ephemeroptera were significantly reduced in the polluted zones. Inorganic sedimentation, operating indirectly through disruption of feeding and filling of interstitial spaces, was considered to be the primary factor affecting filter feeding taxa. Decomposition of compounds associated with materials in the bed load may depress pH and eliminate acid sensitive species of Plecoptera and Ephemeroptera. Such processes of acidification may be particularly important to Appalachian streams since the pH of regional surface waters is characteristically acidic prior to sedimentation. Accumulation of particles on body surfaces and respiratory structures, perhaps as a function of wax and mucous secretion or surface electrical properties, appears to be the major direct effect of inorganic sedimentation on stream insects. Growths of the filamentous bacterium Sphaerotilus natans were also frequently associated with silted individuals in the zone receiving nutrient addition. Distribution of the bacterium suggested that silted substrates, perhaps as related to the presence of iron compounds, are required for colonization in dilute nutrient solutions. The primary effect of Sphaerotilus colonies appears to be augmentation of particle accumulation through net formation by bacterial filaments. Data indicate that inorganic sedimentation and nutrient addition operate synergistically, eliminating a significantly greater number of taxa than exposure to one pollutant alone.

Abstract: Wildfire is an integral component of many temperate ecosystems. The impact of wildfire on the nutrient dynamics of an ecosystem is dependent on the proportion of biomass and nutrients aboveground, which is therefore susceptible to combustion. Mechanisms for postfire nutrient conservation are most strongly developed in nutrient-poor (oligotrophic) ecosystems, in which most of the nutrients are found aboveground, and least well developed in nutrient-rich (eutrophic) ecosystems, whose nutrients are predominantly belowground. (Accepted for publication 21 October 1981)

Abstract: B.- 1 Water in the Soil-Plant-Atmosphere Continuum.- 2 Water in Tissues and Cells.- 3 Water Uptake and Flow in Roots.- 4 Water Uptake by Organs Other Than Roots.- 5 Transport and Storage of Water.- 6 Resistance of Plant Surfaces to Water Loss: Transport Properties of Cutin, Suberin and Associated Lipids.- 7 Stomatal Responses, Water Loss and CO2 Assimilation Rates of Plants in Contrasting Environments.- 8 Mathematical Models of Plant Water Loss and Plant Water Relations.- 9 Physiological Responses to Moderate Water Stress.- 10 Desiccation-Tolerance.- 11 Frost-Drought and Its Ecological Significance.- 12 Water Relations in the Germination of Seeds.- 13 Environmental Aspects of the Germination of Spores.- 14 Physiological Responses to Flooding.- 15 Functional Significance of Different Pathways of CO2 Fixation in Photosynthesis.- 16 Modelling of Photosynthetic Response to Environmental Conditions.- 17 Regulation of Water Use in Relation to Carbon Gain in Higher Plants.- 18 Plant Life Forms and Their Carbon, Water and Nutrient Relations.- Author Index.- Taxonomic Index.

Abstract: Soil samples of parabrown earth and chernozem, each having a different amount of microbial biomass, were used to investigate the contribution of microbial cells to the pool of mobile plant nutrients in soils. The quantities of nutrients mobilized in soils which had been dried or fumigated were closely related to the quantities available in freshly-killed biomass. For the percent of N mineralized from dead microbial biomass in arable soil during 28 days, a “kN-factor” (28 days) of 0.37 was suggested. In oven-dried (70°C) and air-dried (room temperature) soils, approximately 77 and 55% of the N mineralized after remoistening and incubating at 22°C for 4 weeks came from the freshly-killed biomass. The remaining 23 and 45% were derived from non-biomass organic N fractions of the soils. In fumigation experiments (CHCl3, 24 h), the amount of P released was closely related to the P content of the soil microbial biomass. The fluctuating amounts of K available after fumigation did not correspond to the amount of biomass killed. A scheme for the transformation of dead microbial biomass-C and -N in arable soil is suggested.

Abstract: Water and nutrient flow were measured on a complex upland-peatland watershed in north central Minnesota. Annual water budgets for upland and peatland components and for the total watershed were developed. Nutrient input and output budgets were developed for each component on a seasonal basis, using net precipitation inputs, and an annual nutrient budget was developed for the entire watershed, using gross precipitation and total outputs. Both components evapotranspire water near potential rates. The upland converts 34% of the water input to water yield, while the peatland (a bog in a lower topographic position) converts 55% of its water input to water yield. The upland annually retains some N, P, K, and Ca from net precipitation, but passes through Mg and supplies Na in excess of inputs. The peatland is a nutrient trap retaining 36-60% of all nutrient inputs annually. There are striking differences in the seasonal retention of nutrient forms between the upland and bog. The total watershed accumulates P and (apparently) N but loses more K, Ca, Mg, and Na than it receives in gross precipitation. Nutrient flow is interpreted for the design of nutrient-added technologies (fertilization and sewage treatment) and as a bench mark for nutrient-depleted technology (whole-tree harvesting).

Abstract: Summary (1) Plants of Impatiens parviflora were grown on a boulder-clay woodland soil at four levels of irradiance with and without addition of ammonium nitrate and calcium phosphate. (2) Addition of nitrogen and phosphorus fertilizer increased dry wt yield and relative growth rate at all four levels of irradiance, and there was a true interaction between the level of irradiance and nutrient supply. (3) At the three higher levels of irradiance the increased growth resulted from an increase in unit leaf rate and leaf weight ratio, but at the lowest level an increase in leaf weight ratio alone was found. (4) Evidence was obtained for lower rates of respiration in the leaves of plants grown with fertilizer at high irradiance. Mycorrhizas were absent from all fertilized plants, but were well developed in the unfertilized plants at high irradiance and absent from unfertilized plants at the lowest irradiance. (5) Plants grown at high irradiance with additional phosphate alone responded initially exactly like plants with additional nitrogen and phosphorus but grew poorly later; plants with additional ammonium nitrate alone showed no response initially, but grew about as fast as plants with additional nitrogen and phosphorus later on. (6) Plants grown one per small pot responded only to additional phosphate in the short term, but plants grown 10 per small pot responded only to additional nitrogen. (7) Emphasis is placed on the important effects of the differential mobilities of nitrate and phosphate ions in experiments on the limiting mineral nutrients in soils. (8) The results are discussed in relation to earlier work, and the penetration of deeper shade by herbs on soils of higher pH is tentatively related to a superior supply of nitrate.

Abstract: Ahstrnct The contribution of nine species of macrophytes to the phosphorus nutrition of their epiphytes and the rates of P &ease by Myriophyllum spicntunz L. were measured in situ on fully labeled (“‘I?) plants. The cpiphytcs derived only 3.4-9.0% of their P from the supporting macrophyte, indicating that previously suggested macrophyte-epiphytc nutrient interactions are of relatively minor importance. Although high diurnal P release rates (X = 3.24 pg*g-’ * h-‘) were observed for the Myriophyllum-epiphyte complex, Myriophyllum accounted for only 9.9% (0.32 pg*g-’ ah ‘) of the total I? released: The Myriophyllum-deriveclyZZum-derived P was, however, released in a highly available soh~blc form (minimum estimate: 60.3%). During the growing season, MyriophyZZum thus appears to be principally important as a physical support for an active microbial community rather than as a P source to its epiphyton and surrounding waters.

Abstract: Nutrient balance studies of mature ecosystems have shown that in many cases leaching losses are greater than atmospheric inputs. If the systems are not degrading, this means that the net losses must be compensated for by weathering of parent material. In contrast to ecosystems with rates of nutrient leaching that are higher than rates of atmospheric input, leaching of nutrients from an Amazonian rain forest ecosystem was less than or equal to input from the atmosphere every year between 1975 and 1980. If this forest is not aggrading this means that weathering of parent materials does not play an important role in the nutrient economy of the ecosystem. The forest apparently maintains itself on nutrients derived from the atmosphere.

Abstract: Details of the vertical distribution of oceanic phytoplankton species are investigated by means of four stations occupied during June 1977 and August 1978 near 28°N, 155°W. Two distinct, recurring floral associations, separated by a region of rapid transition near or below 100 m, are identified. The associations are apparently related to the "nutrient limited" and "light limited" physiological regimes described previously. Inverse abundance relationships of congeners within the deeper association are compatible with the hypothesis of disequilibrium competitive interactions and community regulation. Among species of the shallow association congeners are positively associated and predation is postulated to be the important regulating mechanism. See full-text article at JSTOR

Abstract: SUMMARY The hypothesis was tested that the amount of external hyphae of a vesicular-arbuscular mycorrhizal (VAM) fungus extending from roots out into soil is not always proportional to the extent of colonization of the root cortex. Growth enhancement and amount of external hyphae were compared for eight isolates of five Glomus spp. that differed in their geographic origin and capacity to enhance growth of Troyer citrange, but were similar in their capacity to extensively colonize Troyer citrange roots. In general, isolates from California increased growth in a P-deficient (9-8 mg kg-1) California soil more than did non-native isolates from Florida soils. The difference between the capacity of California and Florida isolates to enhance growth was not a function of the degree to which they colonized the roots since all had colonized over 95 % of the root length by the time of harvest. Differences in growth enhancement did appear, however, to be a function of the amount of external hyphae that had developed as estimated by the weight of soil they had bound into aggregates. This study suggests that isolates of VA mycorrhizal fungi may differ in their capacity to develop an external hyphal system independent of their capacity to colonize the root cortex, and that we cannot assume that high levels of colonization will necessarily mean the fungus has also developed the mycelium in the soil necessary to transport nutrients responsible for plant growth enhancement.

Abstract: Summary The effect of barley plants on the rate of decomposition of soil organic matter over a 6-week period was studied using soil that had been previously labelled by incubation with 14C-labelled ryegrass for 1 year. The plants reduced the loss of 14CO2, from soil by 70 per cent over 42 days. About half of the reduction was accounted for by the uptake of labelled C by the plant roots, very little 14C label being associated with the shoot. Chemical fractionation of the root showed that the 14C was chemically incorporated into cell wall materials such as cellulose and holocellulose. The reduction in organic matter decomposition in the presence of plants has been explained by earlier workers in terms ofa reduction in microbial activity as a result of a soil moisture deficit caused by plant transpiration. This explanation does not account for all the reduction in decomposition noted in the present experiments. Control soil (without a plant, but amended with glucose or yeast extract to simulate the effect of root exudates) showed a small positive priming effect, the release of 14CO2, being increased. Thus the mechanism by which plants conserve organic matter is complex and cannot be explained merely by analogy to an increased level of nutrients available for microbial metabolism.

Abstract: Phytoplankton biomass (chlorophyll a) and primary production rates in Baffin Bay during summer 1978 were comparable to levels reported for other open water arctic and subarctic regions. Values were moderately high ( mg Chl∙m−2; 227 mg C-fixed∙m−2∙d−1) considering the low mixed-layer nutrient (nitrogen) concentrations, low ambient temperatures ( euphotic zone = −0.2 °C), and variable and moderately low daily solar radiation ( MW∙m−2). Biomass maxima were consistently found at or near the bottom of the euphotic zone, and were 6 times higher than surface values on the average. Nitrate and ammonium were assimilated in approximately equal proportions despite the relatively greater abundance of nitrate in the euphotic zone, particularly below the mixed layer. Average C:N assimilation ratios were slightly lower (5:1) than the chemical composition ratio of the particulate matter (7:1). High phosphate assimilation rates reflected the abundance of this nutrient in the euphotic zone and resulted in low C:P (22:1) an...

Abstract: The dynamics of desert ecosystems control levels of resources that are essential to the survival of desert biotas. Because precipitation is both low and relatively unpredictable in arid regions, the climates, topographies, and soils, of these areas present formidable constraints to resource availability in space and time. And for the same reason, the processes of production, consumption, decomposition, and nutrient-cycling in deserts are also highly irregular and difficult to predict with accuracy. For example, global models relating actual evapotranspiration to primary production and decomposition apply poorly in arid regions.Surprisingly great amounts of carbon are stored in desert soils, particularly in caliche deposits which represent a major ‘sink’ of carbon from the atmosphere. In Arizona desert soils, inorganic carbon exceeds organic carbon by a factor of > 10. Direct use of organic carbon is made principally by organisms that break down desert litter and simultaneously cause relatively high rates of nitrogen mineralization. While nitrogen is traditionally considered deficient in arid environments, its flux is considerable because of high rates of gain by fixation and loss by denitrification and volatilization. Nitrogen accumulates in ‘islands of fertility’ beneath desert shrubs where it becomes relatively available because of (i) its high concentration in plant litter, and (ii) reduced activity of any aromatic modifiers that retard decomposition.It is misleading in deserts to relate nutrient availability to yearly averages, as nutrients may become highly available following pulses of ‘effective’ precipitation. Moreover, mineralization and subsequent availability to plants of phosphorous, the ‘master element’ in nutrient cycling, are moderately independent of nitrogen mineralization and can proceed rapidly. Clearly, the case for nutrient deficiency in deserts may be overstated.Consumption of primary production has varying effects on rates of resource availability in desert ecosystems. Generally weak regulation of primary production is predicted for consumers of green vegetation, except occasionally during early drought. Carnivores should exert variable controls over their prey, while pollinators, seed-eaters, and detritivores—most of which are strongly soil-associated—should have the greatest impacts on primary production and nutrient cycling.

Abstract: Whole-tree harvesting of a northern hardwood stand in New Hampshire removed an average of 111 dry metric tons/ha of biomass, representing 96% of the aboveground total. Nutrient removal in harvested trees averaged 344, 242, 128, and 19 kg/ha for Ca, N, K, and P, respectively. The nutrients removed were between 2 and 3% of estimated total soil capital for Ca and N, and about 1% of total soil capital for K and P. Of estimated available nutrient capital, the removals were 30% for Ca and 85% for K. The harvest was carried out on the lower 40% of a 16-ha watershed. Concentrations of NO/sub 3/, Ca, and K in soil solution and streamflow of the harvested watershed increased for 1 1/2 to 2 years. Streamflow concentrations increased by a maximum of 3, 1, and 0.2 mg/liter for NO/sub 3/, Ca, and K, respectively. Increased loss of N and Ca by leaching to streams is estimated at more than 40 kg/ha. NO/sub 3/ in soil solution increased from background levels of 1 mg/liter to a maximum of 95 mg/liter. Ca increased from background levels of 2 mg/liter to a maximum of 19 mg/liter. Concentrations of both ions returned to background levelsmore » by the third growing season after harvest. The increases in nutrient ions in streams and soil solution are thought to result from increased mineralization and nitrification immediately after harvest. The harvested area has regenerated rapidly with pioneer and commercial species, perhaps partly because of the enriched soil solution. Nutrient removals and leaching losses by themselves do not seem to deplete total nutrient capital significantly. However, the impacts of whole-tree harvesting upon the processes, mechanisms, and rates by which nutrients are made available for future stnads are still of concern. 25 references.« less

Abstract: Philosophical differences exist in the interpretation and recommendations made from soil test values acquired by different organizations that provide advice to farmers on fertilizer use. It was the objective of this sfudy to evaluate the economic and agronomic impacts of these varied philosophies with particular reference to concepts of cation ratio, nutrient maintenance, and nutrient sufficiency level. Field experiments were conducted during 1973-1980 on four major soils of Nebraska comparing yields of corn (Zea mays L.) grown with fertilizer treatments as recommended by five soil testing laboratories operating in the state. The 29 field comparisons revealed no real yield differences despite wide variation in number, rate, and cost of nutrients applied. Since soil test levels are increasing or at least holding steady with the “nutrient sufficiency” approach to soil testing, we find no economic or agronomic basis for the “balance” or “maintenance” concepts on these representative soils of the western Corn Belt. Not to be overlooked are environmental implications nor the waste of energy and resources from any approach responsible for excessive fertilizer use. It is recognized that reserves of available nutrients in the deep subsoils and underlying soil-forming materials in this region have a substantial bearing on soil test calibration and that different calibrations may exist with less favorable subsoil rooting conditions. OIL fertility research and associated laboratory S studies over the past 30 years have established the efficacy of soil testing as a means for predicting the nutrient needs of crops to be grown. The procedure is generally recognized as the best available for diagnosing soil nutrient limitations before a crop is planted so that correction can be made in that year by appropriate fertilization. Although generally accepted as a viable practice, real philosophical differences exist on interpreting the tests. This results in radically different fertilizer recommendations being given to farmers with attendant erosion in credibility of soil testing. Three major concepts are in use by the various organizations doing soil testing, viz., maintenance, cation saturation ratio, and sufficiency level. The maintenance concept implies that whatever the soil test level, a quantity of nutrient should be added to replace the amount expected to be removed by the crop. This “conservation” of a soil’s nutrient supplying capacity has strong appeal but discounts the economic aspect to the farmer in those situations where the soil’s delivery capacity of a given nutrient may be adequate for top yields for some years to come. Focus is primarily on NPK rather than the 13 soil-derived nutrients, all of which should receive equal consideration if the approach were truly to represent the maintenance concept. The cation ratio concept probably originated from New Jersey work that projected an ideal soil as one with the following distribution of exchangeable cations: 65% Ca, 10% Mg, 5% K, and 20% H, therewith Ca:Mg of 6.5:1, Ca:K of 13:l and Mg:K of 2:l (2, 3). I Contribution-of the Nebraska Agric. Exp. Stn., Lincoln, NE. Professor, and district extension agronomists, respectively,

Abstract: Nitrogen and phosphorus were identified as nutrients limiting the growth of plants in an herbaceous community on serpentine soil. Potassium, sulfur and calcium additions had little or no effect. Nutrients were added, alone and in combination, to plots in the field and to greenhouse pots of serpentine soil containing the annual grasses, Bromus mollis and Vulpia microstachys. The absence of any effect due to added calcium indicates that calcium deficiency is not a universal explanation of the low primary production on serpentine soils. INTRODUCTION Wherever they are found, serpentine soils support a vegetation that differs from that on surrounding nonserpentine soils in productivity, floristic composition and often physiognomy. It is now clear that a considerable degree of variability in physical and chemical properties is found among soils classified as serpentine. Thus the phenomenon cannot be ascribed to a single cause but rather a family of causes that vary in importance from site to site. Most notable among these are low levels of the major nutrients, nitrogen, phosphorus and potassium, low levels of calcium combined with high magnesium, and high concentrations of the potentially toxic elements, nickel, chromium and cobalt (Proctor and Woodell, 1975). Serpentine outcrops are common in the California Coastal Mountains as part of the Franciscan formation (Page, 1966). Among these is an outcrop supporting an herbaceous plant community contained within the Jasper Ridge Biological Preserve. The low productivity and floristic uniqueness of this grassland has been well-documented by McNaughton (1968). The consequences of its low productivity for foliage canopy development and potential light competition were studied by Turitzin (1978). No one, however, has reported on the causes of its low productivity. The present study was undertaken to analyze nutrient limitations to plant growth on this serpentine soil. MATERIALS AND METHODS The Jasper Ridge Biological Preserve occupies half of a low-lying ridge on the eastern side of the Santa Cruz Mountains in San Mateo Co., Calif. The crest of the ridge, which reaches an elevation of 189 m, supports an extensive area of annual grassland. A serpentine outcrop, obliquely bisecting the ridge, is occupied by a mixture of annuals and herbaceous perennials. The climate is of the Mediterranean type with warm, dry summers and cool, wet winters. Plants are active from October until May. Nutrient limitations to productivity in the field were studied on experimental plots arranged in a randomized complete blocks design (Sokal and Rohlf, 1969). Treatments were applied to nine 0.25m2 square plots arranged in 1 x 2.5 m blocks that included an untreated control plot. Blocks were replicated six times. Nutrient supplements were applied on 12 January and 12 March 1975. On each occasion nitrogen, phosphorus or potassium, or various combinations were added as solutions of reagent grade NH4NO3 (28.6g m2),. NaH2PO4 * H20 (19.4g m-2) and K2S04 (18.5g m2). Calcium applied as powdered agricultural grade gypsum (calcium sulfate, 1OOg m-2) was added in January only. Aboveground biomass contained within a 0.09 m2 quadrat was harvested from the center of each plot during late April. 'Present address: University Honors Program and School of Life and Health Sciences, University of Delaware, Newark 1971 1.

Abstract: Nutrient loss following whole-tree harvesting of aspen (Populus tremuloides Michx) was assessed on coarse-loamy Typic Fragiochrepts in northeastern Minnesota We used a methodology that could be applied to other systems to roughly estimate the impact of harvesting on nutrient capital Ceramic cups collected soil solution through the frost-free season at 130 cm on sites harvested 1, 2, and 5 years before and on undisturbed sites (total = 24) Nutrients in vegetation, soil, and forest floor were also determined An evapotranspiration model predicted the flux of water moving through the soil Soil solution concentrations peaked in midsummer Nitrogen concentrations in solution were below detection limits, and P concentrations were not related to harvesting Potassium in soil solution decreased, and Ca and Mg increased on harvested sites compared to undisturbed sites After adjusting for leaching flux, only Ca showed a statistically significant loss associated with harvest in the first 5 years after the harvest (60 kg/ha) Over a 60-year rotation, precipitation and normal weathering will replace N, P, and K lost by product removal and deep leaching, will replace about one-half the Mg, but will not replace Ca Because of their initial abundance in the soil, Ca and Mg will probably not become nutritionally deficient, but their loss may lead to accelerated soil acidification and associated secondary effects

Abstract: Ecosystem analysis has established nutrient cycling as an important area of ecology involving biological, chemical, and geological interactions. Studying the flow of elements through ecosystems provides us with a tool for understanding the functioning of ecosystems. For example, if an ecosystem component has a rapid flux of elements through it, or if it stores large amounts of an element, that component is clearly important in ecosystem function. Nutrient cycling strongly influences ecosystem productivity since nutrient flows are closely linked with transfers of carbon and water. In addition nutrient cycling may also affect succession and evolution in forest ecosystems. Various distinct processes are involved in nutrient cycling, such as decomposition, weathering, uptake, leaching, and so on. Each is a precursor to another and the flow of nutrients follows a set of interconnected steps. Although the basic nutrient cycling processes are common to all ecosystems, the rates of the processes vary from one forest ecosystem to another. This variation plays an important role in forest succession and evolution. For example, long-term foliage retention by conifers may allow a species to exist where only a marginal nutrient supply is available from the soil. Nitrogen-fixing species, on the other hand, can occupy sites where nitrogen availability is low because they can provide their own nitrogen. An understanding of nutrient cycling is thus essential for the rational management of forest ecosystems. Nitrogen is recognized as the most limiting element for forest growth in the Pacific Northwest, particularly in Douglas-fir (Pseudotsuga menziesii) ecosystems (Gessel and Walker 1956; Gessel et al. 1969). For this reason this chapter focuses largely on nitrogen cycling. Cycling of other elements such as potassium and calcium are compared with that of nitrogen, where contrasting behavior may provide insight into nutrient-cycling processes. The objectives of this chapter are to (1) briefly describe the important nutrient cycling processes; (2) contrast nutrient cycles in different forest eco-

Abstract: The effect of a 1976 nitrogen, phosphorus, and nitrogen-phosphorus-potassium fertilization at Eagle Creek, Alaska, on photosynthetic rates was investigated in 1978 in eight vascular and three nonvascular plant species. While NPK fertilization increased the growth rate of shoots of most vascular plant species, this treatment depressed photosynthetic rates in all vascular species. Therefore, it appears that nutrient limitation of growth is a direct limitation and not mediated through nutrient effect on carbon uptake rates and levels of available photosynthate. The reason for the reduction in photosynthetic rates with fertilization is not known. It is speculated that increases in growth with fertilization causes a dilution of other nutrients or factors, the effect of which is to depress photosynthesis. Moss photosynthesis is stimulated with fertilization, High NPK fertilizer levels stimulate photosynthesis more than low NPK fertilizer levels. This may indicate basic differences in the ecology or physiology of the two growth forms. It is not yet known if the growth of mosses in this area is stimulated by NPK fertilization.

Abstract: Nutrient deficiency diseases are public health problems in developing nations. Our objective was to design a rice-fortification method using materials approved for use in foods to retain significant quantities of added nutrients during the common practice of boiling rice in excess water and draining it. We accomplished this by applying nutrients to rice in edible polymer coatings. Various starches and cellulosic polymers were evaluated with respect to flexibility, strength, stickiness and nutrient retention. Combining hydroxypropyl methylcellulose and methylcellulose (3:1) gave the best results. Nutrient retentions for 1g of coated rice cooked in 100 ml water and drained were: Vitamin A, 70%; iron, 100%; niacin, 18%; thiamin, 18%, riboflavin, 21%.

Abstract: (1) Different combinations of nitrogen, phosphorus and potassium were added to two nutrient-poor, rabbit-grazed dune swards at Holkham, Norfolk. The plant communities included a wide range of annual species with some perennial species, bryophytes and lichens. The complete (+NPK) mixture was also applied at higher concentrations to establish the effect of differing rates of application. (2) Because of intense rabbit grazing in the area, perennial grasses did not dominate the sward, and only very few unpalatable perennials were favoured by nutrient addition. (3) Annual species generally declined in frequency when fertilizer was added, as did the cover of bryophytes and lichens, with a reduction in species diversity. This was most marked with treatments containing nitrogen. The reaction to phosphate and potassium treatments differed according to species. (4) The relatively diverse plant communities at Holkham apparently owe their existence both to low nutrient status and to relatively high rabbit grazing intensity. The importance of differential response to nutrients by species, and of local variation in soil nutrient supply is considered in relation to niche separation.

Abstract: The purpose of this study was to examine the growth response of Bouteloua gracilis, with and without the vescular-arbuscular mycorrhiza (VAM), Glomus fasciculatus, to varying levels of phosphorus and nitrogen (as NH +4 ) and to determine whether nitrogen and phosphorus levels influence VAM establishment. Bouteloua gracilis was grown in 225 g of soil in a factorial experiment combining four levels of ammonium nitrogen (4, 30, 60, and 126 μg/g), four levels of phosphorus (3, 7, 12, and 22 μg/g), and with VAM spores or no spores. Bouteloua gracilis showed enhanced growth with increased nutrients over the entire range of experimental amendments. Shoot nitrogen concentration for all plants ranged from an average of 0.73% at the low amendment level to 1.61% at the high level, whereas shoot total averages ranged from 2.43 mg at the low amendment to 16.4 mg at the high amendment. Mean shoot phosphorus concentrations ranged from 0.109% at the low amendment level to 0.150% at the high amendment, while totals averaged 5.29 mg at the low amendment and 11.8 mg at the high amendment level. Infected plants were consistently smaller than uninfected plants. This reduction was significant at high nitrogen-low phosphorus, where percent infection was highest (71%). At low nitrogen levels, moderate infection (17%) was established at all phosphorus levels. No infection occurred when both nitrogen and phosphorus levels were high. The lack of a positive nutrient or biomass response to VAM establishment is contrary to most published reports, but is similar to a lack of response shown with certain grasses and other plants. It is possible that the parasitic nature of the response to infection represents the early phase of infection.

Abstract: In most arable soils the nitrate availability depends mainly on the quantity of nitrate present in the rooting zone at the beginning of the growing season. Easily mineralizable organic N and the release of non-exehangeable NH4 from clay minerals may in addition control the nitrogen availability during a season.