Seasonal Nutrient Dynamics Research Articles

Monsoonal influence on seasonal variations in nutrients and phytoplankton biomass in coastal waters of Hong Kong in the vicinity of the Pearl River estuary

Some estuarine ecosystems appear to be more resistant to eutrophication than others, but the mechanisms are not well understood. The Pearl River is the second largest river in China and little is known about the long-term nutrient enrichment processes in the Pearl River estuary and adjacent coastal waters of Hong Kong. Seasonal monsoons are a climatic feature of tropical and subtropical regions. However, monsoonal influences on seasonal dynamics of nutrients and phytoplankton biomass have been little studied. This is the first report of such a study using time series of water quality data at stations around Hong Kong from 1991 to 2000. There was a strong seasonality and spatial gradient in salinity, nutrients and phytoplankton biomass around Hong Kong waters. In winter, when the NE monsoon prevailed (winds were stronger), coastal waters and the eastern part of the Pearl River estuary were dominated by high salinities (> 30) low nutrients and low phytoplankton biomass. In summer, the coastal plume from the Pearl River estuary on the west moved across the southern waters of Hong Kong to the eastern waters of Hong Kong, as the SW monsoon (winds were weaker) dominated and the Pearl River discharge was maximal. Concentrations of nitrate were high (> 60 muM) during summer in the Pearl River estuary, decreased ( 64:1) in the southern waters of Hong Kong and was even higher than in the estuary. Low chl a relative to high N concentrations suggests that the eutrophication effect is not as severe as one would expect from N over enrichment. These results suggest an important role of P limitation in controlling phytoplankton biomass production. It appears that seasonal monsoons serve as a flushing mechanism in 2 ways: (1) monsoons reduce seasonal eutrophication effects by nutrient enrichment during summer; and (2) they prevent long-term (yr) accumulation of organic matter in the sediments due to nutrient enrichment in the region. In summer, when coastal upwelling resulting from the SW monsoon causes offshore movement of the coastal plume in the surface layer, the continental shelf oceanic waters moving shoreward at the bottom flush the coastal waters. In winter, coastal waters with low nutrients replace the entire coastal water of Hong Kong. Due to the monsoon-influenced processes and low phosphorus in the Pearl River estuary, the Pearl River estuary and adjacent coastal waters of Hong Kong appear to be more resilient to enrichment of N.

Seasonal and interannual dynamics of nutrients and phytoplankton pigments in the western Mediterranean Sea at the DYFAMED time-series station (1991–1999)

The phytoplankton dynamics in the western Mediterranean Sea has been studied at the DYFAMED (France JGOFS) time-series station from 1991 to 1999 by means of an analysis of monthly pigment profiles in the 0–200-m layer. The site (43125 0 N, 7152 0 E) is located in the central zone of the Ligurian Sea, NW-Mediterranean Sea, and is protected fromcoastal inputs by the presence of Ligurian current flowing along the coast. The seasonal hydrological regime varies from winter mixing (January–February) to strong thermal stratification in summer and fall. Nutrients are depleted in the surface layer during summer oligotrophic conditions and re-injected to the surface layer during winter mixing. The nitrate-to-phosphate ratio is about 20 in deep waters, which indicates a general tendency to P-limitation. Nevertheless our 9-year study indicates that N/P ratio in surface layer is always higher than 20 (up to 60) during oligotrophic period and generally lower than 20 during the rest of the year. This indicates a probable shift from N-limitation in winter to P-limitation in summer. Seasonal variations of phytoplankton dynamics have been characterized using the HPLC pigment approach, and related to hydrological conditions and distribution of nutrients. The 0–200 mintegrated chlorophyll a during the 9-year study is highly variable (from12 to 230 m g m � 2 ). The phytoplankton biomass is dominated by 19 0 -hexanoyloxyfucoxanthin-containing algae all the year round, but the relative abundance of the characteristic populations with respect to total biomass indicates a seasonal succession. The contribution of diatoms to biomass, as inferred from fucoxanthin, is maximal in January or February and is followed 1 month later by 19 0 -hexanoyloxyfucoxanthin-containing nanoflagellates. The ratio of zeaxanthin (associated to cyanobacteria) to chlorophyll a is highest at the beginning of the stratified period, just before maximal contribution of divinyl-chlorophyll a (prochlorophytes) to biomass. There was a general increase in total phytoplankton biomass during the 9-year study. This increase seems mainly due to small-sized phytoplankton as a specific response to the lengthening of the summer stratification period favoring the growth of species supporting the regenerated production. r 2002 Published by Elsevier Science Ltd.

Seasonal Nutrient Dynamics of Forested Floodplain Soil Influenced by Microtopography and Depth

Edaphic and hydrologic influences on floodplain soil nutrient dynamics must be characterized in order to more fully understand ecosystem functions of forested floodplains. The objective of this study was to characterize the impacts of microtopography and depth on soil microbial processes related to nutrient dynamics in a forested floodplain soil. Nutritional and biological parameters were measured seasonally for 2 yr at paired plots representing two microtopographic classes (swales and slopes) and three soil profile locations—surface organic material, root zone (RZ, 0–0.1 m), and sub‐root zone (SR, 0.2–0.3 m)—on the Coosawhatchie River floodplain, South Carolina. Litter decomposition dynamics followed trends previously described in the literature: N and P concentrations increased relative to C following litterfall, and the relative increase was greater in swales than on slopes. Mineral soil on the Coosawhatchie floodplain was rich in total P compared with other sites. Soil N pools fluctuated together with C, while P was redistributed by floodwater independently of major C and N pools. As a result, P accumulated more in swale soil. Carbon/N ratios in RZ soil were seasonally constant, averaging 14 in swales and 19 on slopes. Carbon/total P ratios were more variable, ranging from 77 to 118 in swales and 151 to 246 on slopes. Microtopographic differences (<1 m) profoundly influenced nutrient dynamics, particularly P, of surface organic material and soil on this floodplain.

Seasonal Biomass and Nutrient Dynamics of Zostera marina L. in Two Mediterranean Lagoons: Thau (France) and Venice (Italy)

Seasonal Biomass and Nutrient Dynamics of Zostera marina L. in Two Mediterranean Lagoons: Thau (France) and Venice (Italy)

Seasonal dynamics of biomass and nutrients in Hepatica nobilis

Seasonal allocation of biomass and nutrients (N, P, K, Ca and Mg) to different above- and below-ground parts was investigated in Hepatica nobilis. Below-ground biomass accounted for 43 to 62%, of which a major part consisted of roots. In May-June, the biomass of current leaves increased rapidly. Generally, the concentrations of nutrients in different parts did not differ very much during the season, and were generally on a low or intermediate level, compared to deciduous herbs. Phosphorus conc. in rhizome and roots decreased significantly in spring, indicating a translocation of stored P to growth of leaves and inflorescences. There was an indication of translocation of N, stored during the winter in rhizome and roots, to growth of new leaves. In spring, there was a significant uptake of Mg from soil. Both roots and rhizome were very poor in K throughout the year, whereas the leaves were important sinks for K. The results did not show evidence of major seasonal translocation of nutrients from above-ground to below-ground organs, presumably due to the rapid expansion of new leaves as the old leaves senesced in spring. The leaf phenology of Hepatica nobilis is discussed, as is the terminology of the leaf life-span of this species.

Seasonal dynamics of nutrients in leaves and xylem sap of coffee plants as related to different soil compartments

The northwestern province of Costa Rica is a marginal coffee growing area. At the onset of the rainy season low redox potentials probably induce the mobilization of soil Mn resulting in enhanced plant uptake of Mn. To test this hypothesis we monitored from April to the end of June 1995 the mobile Mn in the soil and nutrient and Mn concentrations in leaves and xylem sap of coffee plants. Every 2 weeks we took aggregate and bulk soil samples. The aggregates were mechanically separated into interior and exterior, air-dried and all soil samples were extracted with 1 M NH4NO3. We also extracted the field moist soil with distilled water. In addition, the 3rd and the youngest pair of coffee leaves and xylem sap were sampled and analyzed. According to the results of leaf analyses the nutrient supply of the coffee plants in general seemed to be balanced. However, Mn concentrations of 223 mg kg-1 in the 3rd leaf pair at 18 April were above the optimum and the youngest leaves indicated Fe deficiency, but senescent leaves accumulated Fe and overcame the deficiency. Manganese concentrations in the xylem sap showed a pronounced maximum 2 weeks prior to a similar maximum of mobile Mn in the aggregate exterior. But in general the temporal variation of nutrient concentrations (especially Ca and Mg) in the plants are well correlated with the easily extractable nutrient concentrations in bulk soil. Probably due to its specific absorption and high rates of redistribution within the plant, K in the soil extracts did not correlate with plant concentrations. Element concentrations of youngest leaves could not be correlated with soil concentrations and are not considered to be an adequate tool for monitoring current nutrient uptake. Since plant element concentrations did not correlate with the aggregate interior, plants probably cannot use that nutrient source efficiently.

Cardamom, mandarin and nitrogen-fixing trees in agroforestry systems in India's Himalayan region. II. Soil nutrient dynamics

A study on seasonal soil nutrient dynamics was made in large cardamom (Amonum subulatum) and mandarin (Citrus reticulata) agroforestry systems in the Sikkim Himalaya, India. Alnus nepalensis was the N2-fixing associate in the large cardamom system, and Albizia stipulata in the mandarin agroforestry system. Sites without N2-fixing species in both agroforestry types comprised native non-symbiotic mixed tree species. Soil was acidic in the cardamom agroforestry and slightly acidic to neutral in the mandarin agroforestry system. Total-N in soils was the highest in the forest-cardamom stand and the lowest in the mandarin-based agroforestry systems. Soil ammonium-N and nitrate-N concentrations were highly seasonal, and the ratio of seasonal maximum and minimum varied up to six times. The C/N ratio was higher in cardamom agroforestry indicating lower N availability than in the mandarin agroforestry. Cardamom stand with Alnus showed a relatively narrower C/N ratio. N2-fixing species help in maintenance of soil organic matter levels with higher N-mineralization rate as land use change from natural-forest system to agroforestry systems with sparse tree populations. Ratios of inorganic-P/total-P were lower in cardamom agroforestry than the mandarin agroforestry. Seasonal fluctuation in Ca-PO4, Al-PO4 and Fe-PO4 contents regulated the availability of phosphates to some extent for plant uptake.

Seasonal dynamics of mineral nutrients and carbohydrates by walnut tree leaves

Abstract The dry weight accumulation per leaf as well as the concentration per gram of dry weight and the accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined in walnut tree leaves (Juglans regia L.) during a complete life cycle. Additionally, the dynamics of plant nutrient concentration in leaf petiole sap and carbohydrate accumulation in leaves were studied in relation to the main life cycle events of the walnut tree. Total N, P, K, Cu, and Zn concentrations decreased, whereas that of Ca, Mg, and Mn increased during the season. Iron concentration fluctuated around a mean value. Total N, P, K, Mg, and Cu concentrations detected in younger mature leaves were at the sufficient level, whereas Ca, Fe, Mn, and Zn concentrations were at higher levels as compared to those previously reported. All the detected nutrient accumulations increased abruptly during leaf ontogeny and leaf maturation until a maximum level was attained in the younger mature leaves. Similarly, sucrose, glucose, and fructose accumulation were observed at the same period. The rates of total N, P, Cu, and Zn accumulation were lower than the rates of the observed dry matter accumulation and nutrient concentration dilution. Potassium and Mn accumulation rates were almost equal, whereas those for Ca and Mg were higher as compared to the dry matter accumulation rate. The fast embryo growing phase resulted in a considerable decrease in dry weight, total N, P, K, Cu, Zn, and carbohydrate accumulation, and to a lesser degree in Ca, Mg, and Mn accumulation. Nutrient accumulation reduction in leaves by the influence of the growing fruits were estimated to be: total N 52%, K 48%, P 29.5%, Mg 16.3%, Ca 15%, Fe 51.2%, Cu 55.2%, Zn 37.3%, and Mn 5.4% of the maximum nutrient value of the younger mature leaves. Old leaves preserved nutrients before leaf fall as follows: total N 25.4%, P 45%, K 31%, Ca 74.8%, Mg 76.5%, Mn 89.2%, Fe and Zn 50%, and Cu 37%. Nutrient remobilization from the senescing old leaves before leaf fall were: total N 22.6%, P 25.5%, K 21%, Ca 10.2%, Mg 7%, Fe 3.2%, Mn 5.4%, Cu 8%, and Zn 13.3% of the maximum value in the younger mature leaves. In early spring, the absorption rates of N, P, and Ca were low while those of Mg, Fe, Mn, Cu, and Zn were high. During the fast growing pollen phase, the N, P, Fe, Mn, Cu, and Zn concentrations were reduced. Calcium concentration is supposed to be more affected by the rate of transpiration rather than during the growing of embryo. Calcium and Mg concentrations in the sap were negatively correlated. The detected K concentration level in the sap was as high as 33 to 50 times that of soluble N, 12 to 21 times to that of P, 5 times to that of Ca, and 10 to 20 times to that of Mg. The first maximum of starch accumulation in mature leaves was observed during the slow growing embryo phase and a second one after fruit ripening. Old senescing leaves showed an extensive carbohydrate depletion before leaf fall.

Seasonal dynamics of mineral nutrients by walnut tree reproductive organs

Abstract The dry weight accumulation per male and female flower as well as the concentration per gram of dry weight and the accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined in walnut tree (Juglans regia L.) catkins and female flowers at the stage of flower bud and during the flower development. Catkin emergence was accompanied by a very fast hydration of the tissues. After the catkin matured, the fresh and dry weights were reduced. The female flower development period was accompanied by the dry and fresh weight increase. Total N, P, K, Fe, Mn, Cu and Zn concentrations in catkin buds were detected at lower levels, Mg in equal levels, and Ca at higher levels as compared to the nutrient concentrations in young growing leaves. The estimated values of the ratio NCmfb/NCygl were: total N = 0.54, P = 0.83, K = 0.56, Ca = 1.5, Mg = 1.0, Fe = 0.46, Mn = 0.71, Cu = 0.85, and Zn = 0.60. Nutrient concentration in female flower buds was detected in almost equal levels with the exception of total N and Fe. The estimated values of the ratio: NCffb/NCygl were: total N = 0.57, P = 1.1, K = 1.17, Ca = 1.06, Mg = 0.9, Fe = 0.47, Mn = 1.0, Cu = 0.92, and Zn = 0.85. Total N, P, Mn, Cu, and Zn accumulations in the catkin were increased during the fast growing phase and decreased after catkin maturing. Potassium, Mg, and Fe accumulation continued to increase in the mature catkin. Calcium accumulation decreased at a very late mature catkin phase. Total N, P, and K accumulation rates during the catkin fast growing phase were higher than the dry weight accumulation rate. Calcium, Mg, Fe, Mn, Cu, and Zn accumulation rates at the same period were lower or equal to dry weight accumulation rates. In mature catkins, the total N, P, Mn, Cu, and Zn depletion rates were higher than the dry weight depletion rate. The continual increase of K, Ca, Mg, and Fe accumulation in mature catkin resulted in the increase of nutrients concentration also. Total N and P showed the highest remobilization values from mature catkin of 51.4% and 45%, respectively. Calcium, K, Mg, Cu, Mn, and Zn remobilization values estimated to be 22.1%, 7.5%, 3.2%, 45.3%, 33.4%, and 31.8%, respectively. Iron showed no remobilization at all. Nutrients remobilization from catkins as compared to the leaves had almost similar values for total N, Zn, and Cu, higher for P, Ca, and Mn, and lower for Mg, Fe, and K. Accumulation of all nutrients in female flowers increased after fertilization. The dry weight accumulation rate was higher than the nutrient accumulation rates.

Seasonal dynamics of mineral nutrients by walnut tree fruits

Abstract Walnut (Juglans regia L.) tree fruit showed after the endocarp lignification a fast growing stage during which fresh and dry weights increased abruptly. From the beginning of fruit ripening and during the fast sperm growing stage, fresh weight started to decrease while dry weight continued to increase with a reduced growth rate. Dry weights increased in sperm and decreased in exocarp‐mesocarp tissues during the fast sperm growing stage. The material exit from pericarp tissues was completed in the ripe fruit. By contrast, fresh weight continued to decrease in the tissue. Patterns of nutrient accumulation per fruit increased continuously during the fruit growth period. The observed reductions of nutrient accumulations for total nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in the fruit individuals during the very late fruit stage after fruit ripening, and in conjunction with the pericarp tissues senescence, are suppo...

Seasonal nutrient dynamics in white pine and white spruce in response to environmental manipulation.

Seasonal retranslocation in white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) was examined in response to silvicultural treatments (scarification, annual fertilization application, and annual control of competing vegetation with herbicide) that changed both environmental conditions and the growth rate of the trees. Four years after plantation establishment and initial treatment, nutrient accumulation in current-year needles of white pine and retranslocation from 1-year-old needles were increased following the vegetation control treatment, which increased resource availability (nutrients, water and light) and, hence, growth rate. Nutrient accumulation also increased in current-year white spruce needles following the same treatment, whereas retranslocation decreased in 1-year-old white spruce needles. Correlations of retranslocation (N, P and K) with growth rate (shoot biomass increment) showed a strong positive relationship for white pine and a negative relationship for white spruce. Retranslocation of K was correlated with foliar and soil K concentrations; the availability of this nutrient was also significantly reduced by vegetation control. A general theory for the control of nutrient retranslocation in conifers, which is not based exclusively on either sink strength or soil nutrient availability, is proposed. We conclude that retranslocation response is species specific and related to the potential phenotypic growth response to changing environmental conditions and to short-term imbalance in the supply versus the demand for nutrients.

Nutrition of Breeding Female Ruddy Ducks: The Role of Nutrient Reserves

We determined fat, protein, and mineral content of somatic tissue, and estimated amounts of these nutrients committed to eggs by Ruddy Ducks (Oxyurajamaicensis) nesting in southern Manitoba in 1988. Seasonal nutrient dynamics differed between breeding and nonbreeding females. Nonbreeders had less fat and protein reserves than did breeders early in the nesting season, but these then increased and subsequently declined, whereas nutrient reserves of breeders declined linearly with date from the outset of our study. Onset of breeding was related to a nutrient reserve threshold (early RFG [rapid follicle growth] ducks had 22.7 g more fat and 5.1 g more protein than did non-RFG ducks). Adults showed greater propensity to initiate breeding (73% of breeding population) than did yearlings (68% of nonbreeding population), and we relate this to greater fat and protein reserves of adults. Adult breeders had more fat and protein reserves than did yearlings at every stage in the breeding cycle but no age-related differences in use of fat, protein or mineral reserves for clutch formation were found. When controlling for date effects, fat reserves declined (b = -0.49) as fat was committed to eggs. Early nesters initiated and ended egg laying with significantly more fat compared to late nesters, although rate of fat use was not different. Protein and mineral reserves were used for clutch formation by early nesters (b = -0.24 and -0.08, respectively), but not by late nesters. Among females nearing end of laying, number of developing follicles was related to mineral, but not fat or protein reserves, indicating that mineral reserves were a proximate factor constraining clutch size. Our findings confirm that, for Ruddy Ducks, somatic tissues are important sources of nutrients for clutch formation, and that clutch size is directly related to mineral reserves. Of importance to lifetime reproduction, and thus fitness, is our finding that minimum levels ofnutrient reserves appear critical for initiation of breeding by female Ruddy Ducks.

Phytomasse- und Nährstoffdynamik sowie floristische Veränderungen von Knickfuchsschwanz-Flutrasen (Ranunculo-Alopecuretum geniculati Tx. 37) unter extensiver Nutzung

In Schleswig-Holstein, the change of fen vegetation on peaty soils in the last decades is characterized by the development of Calthion vegetation types into species-poor Ranunculo-Alopecuretum geniculati caused by intensive agricultural use. Within the scope of the projekt, “Ecosystem Research in the Vicinity of Bornhoeveder chain of lakes”, the seasonal dynamics of phytomass and nutrients of extensively used Ranunculo-Alopecuretum stands were observed with respect to the possibility of regeneration to species-rich wet meadows. Floristic observations revealed that throughout a period of five years with annual haymaking without fertilization, no characteristic species of wet meadows have established themselves. This indicates that the environmental conditions have not effectively changed yet. The high production of above-ground stand phytomass indicates yet a good availability of nutrients, especially of nitrogen. The dynamics of nitrogen yield in the above-ground phytomass showed that in order to achieve an efficient impoverishment of soil nutrients, it is necessary to cut the vegetation at least twice a year. Additionally, this management practice interferes positively with the structure of the plant composition. The success of restoration moreover depends on the biotic potential (recent vegetation, neighbouring vegetation, seed bank). In the investigated vegetation types the seed bank contains no characteristic species of wet meadows. Therefor apart from suitable management practices, a successful restoration of species-poor Ranunculo-Alopecuretum requires much more time.

Nitrogen fertilization effects on foliar nutrient dynamics and autumnal resorption in maidenhair tree (Gingko bilobaL.)

Abstract We quantified seasonal foliar nutrient dynamics and autumnal N and P resorption of individuals of the deciduous gymnosperm Gingko biloba (maidenhair tree) growing in compacted, urban soils over two years following a single fertilization with 150 kg/ha/yr of N (and no P). Mean foliar nutrient concentrations were more similar to those reported for angiosperm trees than for other gymnosperms. During the autumn following fertilization, 46% and 48 of foliar N and P were resorbed, respectively; during the second year both increased significantly, to 68% of foliar N and 74% of foliar P. Absolute N resorption was also greater during the second year, whereas absolute P resorption did not differ significantly between years. During the second year, the level of N resorption rates was similar to that reported for Larix laricina (larch or tamarack), a needle‐leafed, deciduous gymnosperm, and greater than those reported for broad‐leafed deciduous angiosperms. The level of 1992 P resorption was similar to those...

PRIMARY PRODUCTION AND NUTRIENTS IN A HONG KONG SHRUBLAND

Secondary shrubland is widespread in southern China. This study is a pioneer one of this plant community's distribution and seasonal dynamics of phytomass and nutrients, production of dry matter and nutrients, cycling and use of nutrients. These were studied for a period of two years in the shrubland at sites in Hong Kong's New Territories. Above-ground phytomass, including standing dead matter and litter, averaged 2 239 g/m2 and below-ground phytomass averaged 1 408 g/m2. Foliage production of the evergreen shrub Rhodomyrtus tomentosa, the dominant species, was continuous and gradual. The foliage phytomass depended upon a balance of production of new foliage and senescence and abscission. The phytomass of reproductive structures of R. tomentosa tended to increase regularly from April to July and exhibited a sudden decline after September. A study of the nutrient distribution showed that the distribution patterns of phytomass and nutrient resources are significantly different. For foliage and reproductive structures, the distribution ratios of nutrients were larger than those of phytomass. It is inverse for standing dead matter and stems and branches. The seasonal pattern of N, P and K contents in the foliage and reproductive structures of R. tomentosa paralleled that of the phytomass. R. tomentosa contained a relatively large amount of nutrients in the leaves throughout the year. Mean net primary production (NPP) of the shrubland was 972 g/m2/yr. The mean above-ground dry matter production was 757g/m2/yr which made up 77.9 per cent of the total NPP. The mean production of N, P and K in the shrubland were, respectively, 6 726, 464 and 4 282 mg/m2/yr. Litterfall occurred throughout year, but there was a marked seasonal pattern in the rates of litter production. Climatic factors have an important influence on litter fall seasonality. High litter production is associated with a period of dry weather or a typhoon. The mean return of dry matter by litter fall for two years was 477 g/m2/yr; the N, P and K returns were respectively 2 815,164 and 892 mg/m2/yr. This study showed that 45.1 per cent of the N requirement in NAPP and 51.3 per cent of the P requirement in NAPP came from internal cycling of the plants. Four definitions of nutrient-use efficiency are discussed and compared. An assessment of nutrient-use efficiency through the litter fall mass and concentration data indicated that efficiency for the use of nutrients in the shrubland was greater than the value for an efficient nutrient economy in tropical forest. A conservative utilization of phytomass resources based on reduced nutrient losses is stressed. It is suggested that the foliage, branchlets, bark and reproductive structures from shrubs and trees are not removed.

Seasonal nutrient dynamics in an Amazonian floodplain lake

Seasonal nutrient dynamics in an Amazonian floodplain lake

Seasonal Dynamics of Phytomass and Nutrients in Chalk Grassland

Effects of extra N input on above- and below-ground phytomass and on the concentration of N and P in chalk grassland during one growing season were studied, with special attention to the effects on the grass Brachypodium pinnatum compared with other species. N fertilization in spring resulted in a significantly increased peak standing crop. This higher production could be almost completely accounted for by the increase in above-ground dry weight of Brachypodium. The total below-ground phytomass, ca. 2-3 times higher than the above-ground peak standing crop, was not influenced by extra N input. Concentrations of N and P in the below-ground parts decrease in spring, caused by translocation to the developing shoots, and increase again from August to December as a result of withdrawal from the dying shoots. Brachypodium proves to have a highly efficient system of nutrient withdrawal into its well-developed rhizome system. Almost all of the extra N is found in Brachypodium only. As a consequence only dry weight of this species doubled. Phytomass production increases in Brachypodium after extra N application because

Seasonal Nutrient Dynamics, Nutrient Resorption, and Mycorrhizal Infection Intensity of Two Perennial Forest Herbs

Seasonal Nutrient Dynamics, Nutrient Resorption, and Mycorrhizal Infection Intensity of Two Perennial Forest Herbs

Evaluation of seasonal nutrient dynamics in the oosterschelde (SW Netherlands)

A large set of data obtained from several monitoring programmes covering more than 3 years of registration of environmental parameters in the Oosterschelde estuary were used to evaluate seasonal trends in dissolved nutritive compounds. The deviations from conservative behaviour were calculated. It is concluded that specific estuarine processes rule the distributions of nitrogen compounds within the estuary and that these processes are largely dependent on the input of organic material from the sea. Levels of silica are almost completely governed by fresh water discharges throughout the year, except for the Keeten-Krammer area in spring. Phosphorus concentrations are steady throughout the year with minor influences of exchange with sediment in spring and summer and an influence of the North Sea in spring.

Seasonal Nutrient Dynamics of Solidago altissima (Compositae)

ABRAHAMSON, W. G. AND K. D. MCCREA (Dept. Biology, Bucknell University, Lewisburg, PA 17837). Seasonal nutrient dynamics of Solidago altissima (Compositae). Bull. Torrey Bot. Club 112:414-420, 1985.-The pattern of biomass distribution, and the concentrations of N, P, K, Ca, and Mg were determined by standard methods in goldenrod ramets throughout the annual growing-dormancy cycle. In spring, N, P, K, and Mg were translocated to new rhizomes over a month before ramets emerged and, with the exception of Mg, the concentrations of these elements rapidly declined in above-ground organs after ramet emergence. Although there was a continuous uptake of all five elements from soil reserves during the growing season, there was little autumn retranslocation of nutrients from above-ground to below-ground organs. The mineral element allocation patterns were stable during the growing season except for the principal trade-off between the major sinks of leaves and inflorescences for N, P, K, and Mg and between stems and inflorescences for Ca. The data show that S. altissima is efficient in its use of nutrients, thus reducing the amounts of nutrients required from soil reserves. This, in part, may explain the broad site tolerance of tall goldenrod.