Seasonal Production Patterns Research Articles

Changes in Patterns of Understory Leaf Phenology and Herbivory following Hurricane Damage

ABSTRACTHurricanes are important disturbance events in many forested ecosystems. They can have strong effects on both forest structure and animal populations, and yet few studies have considered the impacts on plant‐animal interactions. Reduction of canopy cover by severe winds increases light availability to understory plants, providing an opportunity for increased growth. An increase in light availability should cause an increase in annual production of leaves and a more even production throughout die year (i.e., less seasonally in production). This change will affect the availability of food resources to folivorous insects that feed primarily on young leaves; outbreaks of these insects could nullify the temporary advantage of increased understory light levels. On 21 September 1998, Hurricane Georges struck Puerto Rico, providing an excellent opportunity to determine the effect of the hurricane on leaf production and herbivory in the forest understory by comparing post‐hurricane data with data obtained from a previous study conducted at the same site. Eight species were analyzed at El Verde Field Station, a wet forest site in eastern Puerto Rico. For the eight species combined, there was an increase in number of leaves produced after the hurricane and a more even seasonal pattern of leaf production, as predicted. Levels of herbivory were much lower (2.03%) after the hurricane compared with pre hurricane conditions (16.05%), indicating that increased light availability to understory plants was not offset by increased herbivory. Lower levels of herbivory were possibly due to herbivore satiation, changes in leaf chemistry, changes in herbivore populations, changes in herbivore predator populations, or a combination of two or more of these factors.RESUMENLos huracanes son perturbaciones importantes en muchos ecosistemas forestales. Estos pueden tener fuertes efectos en la estructura de los bosques y en las poblaciones de animates, sin embargo pocos estudios han considerado su impacto en las interacciones planta–animal. La reducción de la cobertura del dosel, dada por fuertes vientos, aumenta la disponibilidad de luz para las plantas del sotobosque, dando una oportunidad de crecimiento para éstas. Un aumento en la disponibilidad de luz, podria causar un aumento en la producción anual de hojas al igual que una producción más continua a través del año. Este cambio afectaría la disponibilidad de alimento para insectos folívoros, que se alimentan principalmente de hojas jóvenes. Si el aumento en recursos se traduce en un gran aumento en las poblacionales de folívoros, esto podría anular la ventaja temporal dada por incrementos en niveles de luz. En 21 septiembre de 1998, el Huracán Georges azotó Puerto Rico, dando una oportunidad excelente para determinar el efecto de un huracán en la producción de hojas y herbivoría en el sotobosque, por medio de comparaciones con datos obtenidos antes del huracán. Ocho especies se analizaron en la Estación Biológica del Verde, en la parte Este de Puerto Rico. Para las ocho especies combinadas hubo un aumento en producción de hojas después del huracän, y un patrón de producción uniforme a lo largo del año. Los niveles de herbivoria fueron mucho menores (2.03%) después del huracán, comparados con las condiciones pre huracán (16.05%), indicando que el aumento en la disponibilidad de luz para las plantas del sotobosque no fue afectada por aumentos de herbivoria. Los bajos niveles de herbivoría pudieron darse posiblemente porque los herbívores fueron saciados, cambios en la química de las hojas, cambios en las poblaciones de herbívores, cambios en las poblaciones de depredadores de herbívores o por la combinatión de dos o más de estos factores.

Seasonal patterns of fine-root productivity and turnover in a tropical savanna of northern Australia

Fine roots and their turnover represent a dynamic aspect of below-ground biomass (BGB) and nutrient capital in forest ecosystems, and account for a significant fraction of net primary productivity (NPP) (Cuevas 1995, Vogt et al. 1990). On a weight basis, coarse roots contribute more to total ecosystem biomass than fine roots, but they account for only a small portion of annual root production (Eamus et al. 2002). Despite the fact that fine roots may compose less than 2% of total ecosystem biomass, they may contribute up to 40% of total ecosystem production (Vogt et al. 1990). Therefore, estimates of root production, like estimates of root biomass, should differentiate between coarse- and fine-root production.

Annual variation in leaf photosynthesis and leaf nutrient content of four Mediterranean seagrasses

We examine here the annual variation in leaf photosynthesis and nutrient status of four temperate seagrass species: Posidonia oceanica, Cymodocea nodosa, Zostera noltii, and Zostera marina. We also examine the relationship between leaf photosynthesis and seasonal plant growth and productivity. The four seagrass species examined co-occurred in a shallow protected cove on the NE Spanish Mediterranean coast. The results presented give evidence of large annual variation in the leaf physiological status of these four seagrasses, as well as the occurrence of significant differences in the seasonal pattern among species. We found two contrasting seasonal patterns characterized by optimal leaf photosynthesis in summer (represented by C. nodosa), and winter-autumn (represented by P. oceanica and Z. noltii). These contrasting patterns corresponded with a differential plant dependence on climate fluctuations (described by temperature and irradiance) vs. speciesspecific nutrient status (described by leaf nutrient content). As plant nutrient status results from speciesspecific differences in nutrient requirements, nutrient uptake efficiency, and internal nutrient economy, we conclude that the variation among species found in leaf nutrient content derives from species-specific responses to environmental forcing. Consequently, we can infer that an important fraction of the seasonal variability that seagrasses show may be related to species-specific responses. We also found significant differences among species in the coupling between leaf photosynthesis and plant growth and productivity. Both aspects, speciesspecific responses to environmental forcing and speciesspecific coupling between leaf photosynthesis and plant growth may result in differential seasonal patterns of growth and productivity among seagrass species.

Changes in Patterns of Understory Leaf Phenology and Herbivory following Hurricane Damage1

Hurricanes are important disturbance events in many forested ecosystems. They can have strong effects on both forest structure and animal populations, and yet few studies have considered the impacts on plant–animal interactions. Reduction of canopy cover by severe winds increases light availability to understory plants, providing an opportunity for increased growth. An increase in light availability should cause an increase in annual production of leaves and a more even production throughout the year (i.e., less seasonality in production). This change will affect the availability of food resources to folivorous insects that feed primarily on young leaves; outbreaks of these insects could nullify the temporary advantage of increased understory light levels. On 21 September 1998, Hurricane Georges struck Puerto Rico, providing an excellent opportunity to determine the effect of the hurricane on leaf production and herbivory in the forest understory by comparing post-hurricane data with data obtained from a previous study conducted at the same site. Eight species were analyzed at El Verde Field Station, a wet forest site in eastern Puerto Rico. For the eight species combined, there was an increase in number of leaves produced after the hurricane and a more even seasonal pattern of leaf production, as predicted. Levels of herbivory were much lower (2.03%) after the hurricane compared with pre hurricane conditions (16.05%), indicating that increased light availability to understory plants was not offset by increased herbivory. Lower levels of herbivory were possibly due to herbivore satiation, changes in leaf chemistry, changes in herbivore populations, changes in herbivore predator populations, or a combination of two or more of these factors.

Larval habitat diversity and ecology of anopheline larvae in Eritrea.

Studies on the spatial distribution of anopheline mosquito larvae were conducted in 302 villages over two transmission seasons in Eritrea. Additional longitudinal studies were also conducted at eight villages over a 24-mo period to determine the seasonal variation in anopheline larval densities. Eight anopheline species were identified with Anopheles arabiensis predominating in most of the habitats. Other species collected included: An. cinereus, An. pretoriensis, An. d'thali, An. funestus, An. squamosus, An. adenensis, and An. demeilloni. An. arabiensis was found in five of the six aquatic habitats found positive for anopheline larvae during the survey. Anopheles larvae were sampled predominantly from stream edges and streambed pools, with samples from this habitat type representing 91.2% (n = 9481) of the total anopheline larval collection in the spatial distribution survey. Other important anopheline habitats included rain pools, ponds, dams, swamps, and drainage channels at communal water supply points. Anopheline larvae were abundant in habitats that were shallow, slow flowing and had clear water. The presence of vegetation, intensity of shade, and permanence of aquatic habitats were not significant determinants of larval distribution and abundance. Larval density was positively correlated with water temperature. Larval abundance increased during the wet season and decreased in the dry season but the timing of peak densities was variable among habitat types and zones. Anopheline larvae were collected all year round with the dry season larval production restricted mainly to artificial aquatic habitats such as drainage channels at communal water supply points. This study provides important information on seasonal patterns of anopheline larval production and larval habitat diversity on a countrywide scale that will be useful in guiding larval control operations in Eritrea.

Production regimes in four Eastern Boundary Current systems

High productivity (maxima ~3 g C m(sup -2)day(sup -1)) of the Eastern Boundary Currents (EBCs), i.e. the California, Peru-Humboldt, Canary and Benguela Currents, is driven by a combination of local forcing and large-scale circulation. The characteristics of the deep water brought to the surface by upwelling favorable winds depend on the large-scale circulation patterns. Here we use a new hydrographic and nutrient climatology together with satellite measurements ofthe wind vector, sea-surface temperature (SST), chlorophyll concentration, and primary production modeled from ocean color to quantify the meridional and seasonal patterns of upwelling dynamics and biological response. The unprecedented combination of data sets allows us to describe objectively the variability for small regions within each current and to characterize the governing factors for biological production. The temporal and spatial environmental variability was due in most regions to large-scale circulation, alone or in combination with offshore transport (local forcing). The observed meridional and seasonal patterns of biomass and primary production were most highlycorrelated to components representing large-scale circulation. The biomass sustained by a given nutrient concentration in the Atlantic EBCs was twice as large as that of the Pacific EBCs. This apparent greater efficiency may be due toavailability of iron, physical retention, or differences in planktonic community structure.

Seasonal egg production pattern of the Patagonian stock of Argentine hake (Merluccius hubbsi)

The reproductive biology of the Argentine hake, Merluccius hubbsi, inhabiting the Patagonian waters at south of 41°S was studied by using histological analysis of the ovaries. The samples were collected during the reproductive season from December 2000 to March 2001. Argentine hake is a batch spawner with indeterminate annual fecundity that spawns from the end of spring to summer with a main reproductive peak in January. Old females (>5 years) had a spawning season longer than young individuals. Spawning frequency, determined from the proportion of females with day 1 postovulatory follicles (POF), ranged between 0.10 and 0.15, being higher during the spawning peak. At these frequencies, a female hake would spawn on average 14 times between December and March. Batch fecundity (BF) was positively correlated with total length, total weight (without ovary) and age, ranging between 100,000 (32 cm TL) and 2,300,000 (87 cm TL) hydrated oocytes. Monthly egg production showed considerable variation during the spawning season with the main pulse of production in January (57% of the eggs spawned during the period). In spite of its low frequency, larger females showed the same level of contribution to the reproductive potential of the stock than young females. From December to February the number of eggs produced by unit-weight of hake did not change. In March the relative egg production decreased significantly coinciding with an increase of atresia.

Seasonal patterns of reserve and soluble carbohydrates in mature sugar maple (Acer saccharum)

Sugar maple (Acer saccharum Marsh.) trees exhibit seasonal patterns of production, accumulation, and utilization of nonstructural carbohydrates that are closely correlated with phenological events and (or) physiological processes. The simultaneous seasonal patterns of both reserve and soluble carbohydrates in the leaves, twigs, branches, and trunks of healthy mature sugar maple trees were characterized. The concentrations of starch and soluble sugars ( sucrose, glucose, fructose, xylose, raffinose, and stachyose) were determined. Starch, the major reserve carbohydrate in sugar maple, is low during the active photosynthetic growth season. Starch is accumulated in the xylem ray tissues in late summer and early fall. During the cold season, there is a close relationship between starch hydrolysis–accumulation and temperature. Soluble sugars increase when starch concentrations decrease during the cold months, and these sugars may play a role in cold tolerance. Patterns of change in the stem tissues are similar to those in the root tissues but with slight differences in the timing.Key words: starch, sucrose, glucose, fructose, raffinose, stachyose.

Size-related and seasonal patterns of egg collar production in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826

Polinices pulchellus held in the laboratory produced egg collars all year round. Egg collar production was greatest during July and August and only occurred in females >8–10 mm shell length. The largest individuals (14–16 mm shell length) had the highest fecundity and ceased egg-laying in late September, whilst 8–14 mm individuals laid egg collars until November. Small females (4–6 mm) grew rapidly during the warmer, summer months (April to August), became sexually mature and began laying egg collars in mid-September. Both the range of egg collar wet weights and the maximum wet weight of an individual egg collar increased with female size class. Temperature strongly affected the length of time between the laying of egg collars and the hatching of larvae (9–10 days at 19–20 °C and 14–15 days at 13–14 °C). A close relationship was also found between egg collar wet weight and the number of veliger larvae released.

Seasonal pattern of photosynthetic production in a subalpine evergreen herb, Pyrola incarnata.

The seasonal pattern of growth and matter production of Pyrola incarnata, an evergreen herb on the forest floor in subalpine deciduous forests, was analyzed to understand the ecological significance of evergreenness in a subalpine climate with a short growing season and low temperature. Net production was highest under favorable light conditions in spring after the disappearance of snow cover, and 68% of the annual net production was attained before the canopy tree foliage had fully expanded. Most of the photosynthetic production in this period was carried out with over-wintered leaves. This appears to be an advantage of evergreenness. New leaves and inflorescences had developed in the period. Positive net production was maintained under deteriorating light conditions during summer, when 32% of the annual net production occurred. This production was used mainly for growth of fruits and underground organs. The net production of P. incarnata during summer was much higher than that of a related species that inhabits warm-temperate regions, because of its higher photosynthetic activity rather than its lower respiratory losses. The storage of dry matter in leaves and underground organs was not conspicuous. Unlike the warm-temperate species and another subalpine species that inhabits higher altitudes, P. incarnata is not strongly dependent on its reserve matter for the development of new organs.

Root longevity and phenology differences between two co‐occurring savanna bunchgrasses with different leaf habits

Summary Aristida stricta and Schizachyrium scoparium are C4 perennial bunchgrass species native to Pinus palustris savannas in the south‐eastern USA. Species differences in growth rate, tissue nutrient content and distribution suggest that A. stricta is more stress‐tolerant (sensu Grime) than S. scoparium. In addition, A. stricta retains leaves all year, whereas S. scoparium is winter deciduous. Based on these observations, we wanted to determine (1) whether root longevity was higher for A. stricta as compared to S. scoparium; and (2) whether the leaf habits of these species had consequences for seasonal patterns of root production and death. Using in situ rhizotrons, we recorded root number and length of these species over the course of 2·5 years on flat, transparent 50 × 50 cm windows. Kaplan–Meier (product‐limit) analysis was used to produce survival functions and to estimate median lifespans for the right‐censored root longevity data. These survival functions were compared using log‐rank χ2 statistics, and a proportional hazards model was used to examine the effects of season and species on the survival of each cohort. Final demographic variables were analysed using anova. The median lifespan of A. stricta was 777 days whereas that of S. scoparium was 374 days. This significant difference in median lifespan was consistent between species for all cohorts in both years. Also, coincident with winter leaf senescence, root production nearly stopped for S. scoparium whereas A. stricta produced roots all year. This is probably due to the winter photosynthetic capacity of A. stricta. Root death did not exhibit any seasonal pattern in either species. A pulse of roots produced in apparent response to the 2000 drought was evident for S. scoparium but not for A. stricta. This cohort, however, rapidly died during the dormant season, probably due to the lack of winter photosynthesis in that species. Aristida stricta and S. scoparium exhibited root production, death and longevity patterns that were predicted on the basis of ecological and leaf habit differences between them. These findings suggest species‐specific differences in performance and element cycling in these nutrient‐poor soils.

Interannual growth dynamics of vegetation in the Kuparuk River watershed, Alaska based on the Normalized Difference Vegetation Index

Interannual above-ground production patterns are characterized for three tundra ecosystems in the Kuparuk River watershed of Alaska using NOAA-AVHRR Normalized Difference Vegetation Index (NDVI) data. NDVI values integrated over each growing season (SINDVI) were used to represent seasonal production patterns between 1989 and 1996. Spatial differences in ecosystem production were expected to follow north-south climatic and soil gradients, while interannual differences in production were expected to vary with variations in seasonal precipitation and temperature. It was hypothesized that the increased vegetation growth in high latitudes between 1981 and 1991 previously reported would continue through the period of investigation for the study watershed. Zonal differences in vegetation production were confirmed but interannual variations did not covary with seasonal precipitation or temperature totals. A sharp reduction in the SINDVI in 1992 followed by a consistent increase up to 1996 led to a further hypothesis that the interannual variations in SINDVI were associated with variations in stratospheric optical depth. Using published stratospheric optical depth values derived from the SAGE and SAGE-II satellites, it is demonstrated that variations in these depths are likely the primary cause of SINDVI interannual variability.

Modeling controls of phytoplankton production in the southwest Pacific sector of the Southern Ocean

Abstract The Southern Ocean is the largest high-nutrient, low-chlorophyll region in the world's ocean and a potentially important site for the sequestration of carbon. We present a one-dimensional physical/biogeochemical model that integrates biogeochemical measurements obtained during the AESOPS (U.S. JGOFS) study in the southwest Pacific sector to elucidate the controls of primary productivity and export. The model is applied to a series of four stations along 170°W spanning the different biogeochemical subsystems in the Polar Frontal Zone, the Polar Front, and the Seasonal Ice Zone south of the Polar Front. Since horizontal fluxes of heat, freshwater and nutrients are found to be important but cannot be resolved explicitly in a one-dimensional model, we employ a restoration of temperature, salinity and nutrients. The surface fluxes of light and momentum are modified during ice-covered periods to account for the effects of sea ice. The biological model component includes the elemental cycles of nitrogen and silica. Diatoms are represented as a separate phytoplankton group, and small phytoplankton and zooplankton are tightly coupled. The effect of the low iron availability in the region is implicitly taken into account by using typical phytoplankton growth rates and a typical, high Si:N stoichiometry of 4 for the diatoms. The model captures the essential features of the distinct subsystems including the low-chlorophyll condition north of the Polar Front, the diatom blooms in the vicinity of the Polar Front and to its south, the differential drawdown of nitrate and silicic acid, and the seasonal patterns of biogenic silica, primary production and vertical particle flux. “Top-down” control of the small phytoplankton by efficient microzooplankton grazing and “bottom-up” control of diatoms by light and silicic acid are the main factors for the simulated behavior. A sensitivity analysis of the biological model component shows that the growth parameters for the two phytoplankton groups are most important in constraining primary productivity and overall model behavior. This implies that changes in growth rates induced by variations in iron supply as assumed over glacial–interglacial transitions can affect primary and export production substantially.

Seasonality of ecosystem respiration and gross primary production as derived from FLUXNET measurements

Differences in the seasonal pattern of assimilatory and respiratory processes are responsible for divergences in seasonal net carbon exchange among ecosystems. Using FLUXNET data ( http://www.eosdis.ornl.gov/FLUXNET) we have analyzed seasonal patterns of gross primary productivity ( F GPP), and ecosystem respiration ( F RE) of boreal and temperate, deciduous and coniferous forests, Mediterranean evergreen systems, a rainforest, temperate grasslands, and C 3 and C 4 crops. Based on generalized seasonal patterns classifications of ecosystems into vegetation functional types can be evaluated for use in global productivity and climate change models. The results of this study contribute to our understanding of respiratory costs of assimilated carbon in various ecosystems. Seasonal variability of F GPP and F RE of the investigated sites increased in the order tropical< Mediterranean< temperate coniferous < temperate deciduous < boreal forests . Together with the boreal forest sites, the managed grasslands and crops show the largest seasonal variability. In the temperate coniferous forests, seasonal patterns of F GPP and F RE are in phase, in the temperate deciduous and boreal coniferous forests F RE was delayed compared to F GPP, resulting in the greatest imbalance between respiratory and assimilatory fluxes early in the growing season. F GPP adjusted for the length of the carbon uptake period decreased at the sampling sites across functional types in the order C 4 crops, temperate and boreal deciduous forests (7.5–8.3 g C m −2 per day )> temperate conifers, C 3 grassland and crops (5.7–6.9 g C m −2 per day )> boreal conifers (4.6 g C m −2 per day). Annual F GPP and net ecosystem productivity ( F NEP) decreased across climate zones in the order tropical>temperate>boreal. However, the decrease in F NEP with latitude was greater than the decrease in F GPP, indicating a larger contribution of respiratory (especially heterotrophic) processes in boreal systems.

The annual patterns of photosynthesis in two large, freshwater, ultra-oligotrophic Antarctic lakes

The phytoplankton productivity and biomass of two large, freshwater Antarctic lakes (Vestfold Hills, eastern Antarctica) were investigated over a 12-month period. Crooked Lake was sampled at one site, while Lake Druzhby, a complex lake with two shallow and one deep basin, was subject to a more detailed investigation. Concentrations of chlorophyll a were usually below 1 µg l–1, indicating ultra-oligotrophic conditions. Despite periodic low nutrient levels, low temperatures (range 0.4–2.8°C) and periodic poor light climate, some degree of photosynthesis was measurable throughout the year, including the dark winter phase. Snow cover had a pronounced impact on the light climate of the water column and inhibited photosynthesis. Mean rates of carbon fixation in the 0- to 15-m water column varied between 0 and 38.47 µg C l–1 day–1 in Crooked Lake and 0.24 and 37.68 µg C l–1 day–1 in Lake Druzhby. There were significant differences in the seasonal patterns of primary production between the basins of Lake Druzhby. The shallow basins had highest productivity in August, whereas the deep basin had highest rates in summer. Chlorophyll specific rates of photosynthesis or assimilation numbers [µg C (chl. a)–1 h–1] varied between 0.05 and 44.9, and photosynthetic efficiency [µg C (chl. a)–1 h–1 µmol m–2 s–1] between 0.02 and 5.19. The data suggest that the phytoplankton of these lakes is adapted to low irradiance levels, low temperatures and nutrient limitation.

Forage Production and Nutritive Value of Selected Pigeonpea Ecotypes in the Southern Great Plains

Stocker cattle production in portions of southern Great Plains depends on wheat (Triticum aestivum L.) and warm-season perennial grasses. Nutrient supply is limited in both quantity and quality from late July through November. To determine if pigeonpea [Cajanus Cajan (L.) Millsp.] could fill this deficit, a field study was conducted from 1996 to 1998, Seasonal forage production patterns, yield, and quality of three pigeonpea ecotypes (ICP8151, ICPX910007, and PBNA) were evaluated. Pigeonpeas produced 5 Mg ha -1 dry matter by 26 August, with N concentration >20 g kg -1 and digestible dry matter (DDM) > 500 g kg -1 .Ecotype ICPX910007 accumulated greatest dry matter in 136 d (16 Mg ha -1 ), followed by ICP8151 (13 Mg ha -1 ) and PBNA (9.5 Mg ha -1 ). Mean N concentration for PBNA was 28.6 g kg -1 as compared with 23.3 and 23.0 g kg -1 for ICP8151 and ICP910007, respectively. Digestible dry matter of PBNA was 614 g kg -1 , followed by 576 and 572 for ICP8151 and ICP910007, respectively. Leaf dry matter yield averaged across sampling dates and years for all ecotypes ranged from 2360 to 2600 kg ha -1 . Leaf quality was similar to that of alfalfa for all ecotypes. Environmental conditions such as cooler spring and summer temperatures and excess rainfall (1997) or extreme drought (1988) reduced yield of all ecotypes. Pigeonpea can provide high-quality forage that could be used as a primary or supplementary forage for grazing livestock at a time when other forages are less productive.

Contrasting seasonal patterns of fine root production for blue oaks (Quercus douglasii) and annual grasses in california oak woodland

In a blue oak woodland in NE California, we used root ingrowth cores to study seasonal patterns of fine root (< 2 mm diameter) production (FRP) for annual grasses and blue oaks (Quercus douglasiiHook and Arn.). At each of three sites (River, Upland and Hilltop) there were three studies: a short-term seasonal study, a long-term cumulative study and a core nutrient enrichment study. In the short-term study, ingrowth cores were installed and harvested in 3-month intervals. Grass and oak FRP dominated in different seasons. Grass FRP was greater in fall (Oct–Dec, 26.0 g m−2 month−1(gmm)) and winter (Jan–Mar, 18.1 gmm), lower in spring (Apr–Jun, 2.9 gmm) and negligible in summer (July–Sep). In contrast, oak FRP was greater in spring (6.1 gmm) with lower, but significant summer growth (2.9 gmm). Grass FRP declined steadily with soil depth (0–40 cm) in all seasons. Oak FRP changed little with soil depth, except in the summer, when production was greatest at lower soil depths. In the long-term study, ingrowth cores were installed and harvested after 3, 6, 9 and 12 months. Oak annual FRP was greater in the long-term study than in the short-term study at the River and Upland sites. Thus production in the short-term study may be an underestimate, due to disturbance effects. Nutrient enrichment of cores with N-P-K increased grass FRP, but surprisingly, decreased oak FRP, suggesting that annual grasses may have competitive advantages in nutrient enriched soil.

Seasonal variability of the effect of coral reefs on seawater CO2 and air—sea CO2 exchange

There are complex physical and biological processes controlling the exchange of carbon dioxide (CO2) between the ocean and atmosphere. In coral reef ecosystems, the balance of biological processes such as calcium carbonate (CaCO3) formation and organic carbon production can either lead to CO2 being retained in the oceanic environment (i.e., oceanic sink of CO2) or returned to the atmosphere through gas exchange (oceanic source of CO2). What remains uncertain is the fate of CO2 in reefs subject to seasonal change and the annual balance of air—sea CO2 flux in such systems. Here it is shown that the Bermuda coral reef acts as a sourc of CO2 to seawater overlying the reef. The magnitude of this source of CO2 varies seasonally in response to changes in the reef community between coral‐ and macroalga‐dominated states, reflecting changes in the net balance between calcification and organic carbon production. With knowledge of the calcification rate (~5.6 to 10.6 g CaCO3 m−2 d−1) and observed modification in seawater fCO2 by reef metabolism, rates (—0.6 to 3.3 g C m−2 d−1) and seasonal patterns of macroalgal productivity were estimated. Whether the Bermuda coral reef system acts as an oceanic sink or source of CO2 to the atmosphere not only depends on this seasonal variation, but, more importantly, depends on the pre‐existing air‐sea CO2 disequilibrium of open ocean waters surrounding the reef system. The Bermuda coral reef system serves as a useful model for understanding the fate of CO2 in other reefs, particularly those reefs changing because of environmental stress.

A review of pastoral research carried out on the West Coast of the South Island: 1960-2000

The pastoral research carried out on the West Coast of the South Island between 1960 and 2000 could be divided into three categories; nutrient requirements for pasture, pasture establishment and growth and animal performance. Because of the varied fertility of the soil types present, research on nutrient requirement was the largest category. In the 1960's, requirements for pasture establishment and early growth on pakihi (podzol) soils of lime, phosphorus (P), elemental sulphur (S), potassium (K), copper (Cu) and molybdenum were identified. This work was extended to determine P, S and K maintenance requirements of pakihi, recent alluvial and brown terrace soils in the 1970's and 1980's. Elemental S was shown to be the most cost effective S fertiliser under annual rainfall greater than 2000 mm and the tetraphenyl boron (TBK) test was calibrated to measure the supply of nonexchangeable K on recent soils. A series of trials were carried out to determine pasture yield responses to fertiliser nitrogen (N) on recent soils in the early 1970's. Later work in the mid 1980's showed that measurement of accumulated soil and air temperature from early spring did not improve the accuracy in prediction of pasture yield responses to N. On the poorly drained, acid and infertile pakihi soils, the interactions between seed coating and lime were measured and the yield advantages of Maku Lotus and Yorkshire fog as alternative pasture species to ryegrass and white clover demonstrated. Rate of pasture growth trials determined the seasonal pattern of pasture production on a range of sites from 1970 to 1995. On recent soils that could not be moled, gravel moling and hump and hollowing substantially increased pasture production during a spring with high rainfall (2000 mm). In the early 1980's, dairy grazing trials showed that lengthening the grazing rotation during autumn increased winter and spring pasture production. For sheep, preferential grazing of thin ewes from weaning to mating increased overall ovulation rate. The density of sheep dung patches was shown to increase with winter stocking intensity on a pakihi soil. Surveys of dairy farm practice established an association between effectiveness of magnesium (Mg) supplementation of dairy cows and reducing the incidence of metabolic disorders. Many dose response trials established the requirement by dairy calves for selenium (Se), cobalt (Co) and Cu on different West Coast soils. Close contact between West Coast scientists, advisors and farmers ensured that local research information was efficiently communicated with a resulting high level of farmer adoption. Keywords: animal management, fertility, lime, nitrogen, pasture establishment, phosphorus, potassium, soils, South Island, sulphur, trace elements, West Coast

Phytoplankton biomass, production and potential export in the North Water

Abstract The seasonal patterns of phytoplankton biomass and production were determined in the North Water, located between Greenland and Ellesmere Island (Canadian Arctic), in August 1997, April–July 1998, and August–September 1999. The patterns differed among the four defined regions of this large polynya, i.e. North (>77.5°N), East (>75°W), West ( 5 μm) fraction dominated the biomass and production during the bloom. During July, August, and September, biomass and production decreased over the whole region, with the highest biomass, dominated by large cells, occurring in the North. The annual particulate and dissolved phytoplankton production were the highest ever reported for the high Arctic, reaching maximum values of 254 and 123 g C m−2 yr−1, respectively, in the East. Rates in the North and West were considerably lower than in the East (ca. two- and three-fold, respectively). The f-ratios (i.e. ratio of new to total production), derived from the size structure of phytoplankton, were high north of 76°N (0.4–0.7). Regionally, this indicated a high potential export of particulate organic carbon (EPOC) from the phytoplankton community to other trophic compartments and/or downwards in the East (155 g C m−2 yr−1), with lower values in the North and West (i.e. 77 and 42 g C m−2 yr−1, respectively). The seasonal and spatial patterns of EPOC were consistent with independent estimates of potential carbon export. Phytoplankton biomass and production were generally dominated by the large size fraction, whereas EPOC seemed to be dominated by the large size fraction early in the season and by the small size fraction (