High Productivity Sites Research Articles

Seasonal changes in dissolved amino acids and sugars in basal culm internodes as physiological indicators of the C/N-balance of Phragmites australis at littoral sites of different trophic status

The nitrogen content of different internodes and the dissolved amino acids and sugars of the basal culm internodes of Phragmites australis (Cav.) Trin. ex Steud. were studied monthly in 1994 to estimate the carbon/nitrogen balance at eight sites and lakes. These stands had large differences in standing crop, with less than 400 g shoot dry weight m −2 in a mesotrophic lake and up to 1500 g dry weight m −2 in hypertrophic lakes. No significant differences were found between sites in the nitrate and ammonium concentration of the interstitial water because of very high variability in space and time. The relative nitrogen content (% of dry weight) of different leaves and culm internodes showed significant differences but only between the most different sites. The amount and composition of free amino acids and sugars of the basal culm internodes showed a clear association with the maximum standing crop of the sites. During the later shoot growth phase (July to September), plants of the high productivity sites exhibited a high content of dissolved amino acids in the basal culm internodes with asparagine as the main transport and storage compound, but a very low sugar content with sucrose as the main transport component in summer. At low productivity sites of mesotrophic to moderate eutrophic lakes, this relationship was inverse. The mean of the proportions of total sugars to total amino acids and asparagine to sucrose, respectively, were significantly correlated with the maximum standing crop of the eight sites. Alanine and serine were present in high concentration in early spring before outgrowth of the tiller without pressure induced ventilation of the subtending vertical rhizome parts. The results are discussed with respect to the indicatory value of the amino acid and sugar content of the basal shoot internodes to the productivity of the different stands and their limitation by the nitrogen availability of the plants.

Influence of red alder on soil nitrogen transformations in two conifer forests of contrasting productivity

We conducted laboratory studies to determine the effects of red alder ( Alnus rubra Bong.) on soil N transformations and N availability indices at two conifer forest sites of contrasting productivity. The inclusion of red alder in conifer forests significantly increased gross rates of N mineralization, N immobilization, nitrification and NO 3 − immobilization, and the effects of alder were generally similar for soils from low- and high-productivity sites. However, the addition of alder to the conifer stand at the high productivity site increased gross N mineralization and immobilization processes more than at the low productivity site. At both sites, gross N and NO 3 − production were enhanced by alder more than gross N immobilization processes, leading to higher rates of net N mineralization and nitrification. At the fertile site, most microbial N assimilation occurred from the NO 3 − pool, compared with less than half at the infertile site (none as NO 3 − in the less productive pure conifer stand). Heterotrophic nitrification (as indicated by a lack of C 2H 2 inhibition) accounted for 65–72% of the gross nitrification in all stands that exhibited nitrification (no nitrification was detected in the pure conifer stand at the infertile site). The inclusion of red alder had no effect on the proportion of total nitrification that was heterotrophic, despite the lower soil pH in mixed alder-conifer stands compared to conifer stands. Gross rates of N mineralization correlated well with both autotrophic and heterotrophic nitrification across all soils. Gross N mineralization may be a good index of NH 4 + availability to autotrophic nitrifiers, as well as the quality of organic N as a substrate for heterotrophic nitrification. Most estimates of microbial biomass and activity, N availability and N transformation rates were significantly correlated with each other. In general, gross N transformations were better correlated with other indices of N availability and microbial activity than estimates of net N transformations. Similar N cycling rates and microbial biomass N pool sizes in pure alder and adjacent alder-conifer stands at the fertile site suggest that continued inputs of N via symbiotic N-fixation by red alder in coniferous forest stands can lead to the elimination of N-limitation to forest ecosystem production.

The effects of fertilizers on early growth and foliar nutrient concentrations of three plantation eucalypts on high quality sites in Gippsland, southeastern Australia

Fertilizer trials of a standard design were established in experimental plantations of Eucalyptus regnans, Eucalyptus nitens and Eucalyptus globulus on sites of high potential productivity in Gippsland, southeastern Australia. The design involved factorial combinations of three rates of N (up to 400 kg ha −1 elemental) and four rates of P (up to 200 kg ha −1) with four additional treatments including K and trace elements. Treatments were complete after up to four applications at 2, 9, 14 and 26 months post-planting. P additions significantly increased foliar P concentrations and growth of E. regnans to 45 months but poor survival and competition from woody weeds limited growth responses to treatments. Foliar concentrations of N and P in E. nitens and E. globulus at age 1 year were significantly increased by N and P additions and were positively correlated with both early and later growth. Added P significantly decreased the foliar N to P ratios of all species at age 1 year, indicating that P additions, in particular, were required for good early growth. Combined additions of N and P significantly increased growth of E. nitens in the first year but growth responses to further additions of fertilizer were minimal. In contrast, growth of E. globulus increased in response to all fertilizer additions, leading to the greatest mean volumes at the highest combined rates of N and P. Relative gains in productivity were therefore greater in E. globulus (m.a.i. range at 71 months: 10–24 m 3 ha −1 year −1) than E. nitens (16–33 m 3 ha −1 year −1). There were no additional growth responses of any species to added K or trace elements. However, concentrations of K in E. regnans foliage at age 1 year were increased by K additions and were correlated with later growth. Low concentrations of Mg in E. nitens foliage suggest a probable response to Mg additions. General fertilizer prescriptions for the establishment phase of eucalypt plantations on sites of high quality are presented. Refinement of these prescriptions will rely on a better understanding of the nutritional requirements of individual species.

Understanding productivity, a key to Aedes aegypti surveillance.

The objective of this work was to define criteria that could be applied to achieve faster, more economical, and accurate assessment of vector populations for control of dengue viruses. During 1989-1990, 1,349 premises were surveyed in Townsville, Charters Towers and Mingela/Ravenswood, Queensland, Australia. In each locality, 1.9-8.4% of premises contained three or more containers with Aedes aegypti immature forms and were designated as key premises. Comparison of surveys in Townsville from 1989 to 1990 indicated that positive premises (i.e., those with at least one container with Ae. aegypti present) were 3.22 times more likely to remain positive than negative houses to become positive the following year. The Ae. aegypti population in Townsville was seen to be totally associated with garden receptacles, discarded household items, and trash but one well and one rainwater tank were responsible for 28% of all immature forms recorded in the 1,349 premises inspected. These breeding sites of high productivity were designated as key containers. At Charters Towers, Mingela, and Ravenswood, rainwater tanks were seen as the most important key container because although they constituted 13-29% of positive containers, they supported 60-63% of the immature forms. This study demonstrates that there is a certain degree of stability with regard to positive premises and that some of these, or some container types, contribute disproportionately to the Ae. aegypti population. Control programs could be made more efficient if efforts were concentrated on these sites of key vector productivity.

DRIS evaluation of teak ( Tectona grandis L.f.) mineral nutrition and effects of nutrition and site quality on teak growth in West Africa

The objective of the investigation was to study the site variables controlling teak yield ( Tectona grandis Linn.fil.) and to establish guidelines for the selection of high productivity sites in Benin, Côte d'Ivoire, Liberia, Nigeria and Togo. Depending on stand age, soil and region, between 70 and 90% of the variation in tree growth (site index, SI) could be explained by the supply of nitrogen, the root-available soil depth and precipitation. Diagnostic foliar analysis for a broad range of elements was carried out in all plantations with the exception of Nigeria. This showed that in 20% of the stands, various deficiency symptoms occur, and in an additional 40%, hidden demand of at least one nutrient is apparent. According to the Diagnosis and Recommendation Integrated System (DRIS), the most deficient nutrients besides N are Ca and P, while in 45% of all stands there is a relative Al excess. Recommendations for the evaluation and classification of site quality and the number of trees sampled for foliar analysis are given.

Productivity and cytogenetic characteristics of guayule. Screening of plants from the mapimi region

AbstractGuayule plants were screened in the region of Mapimi (Durango, Mexico) to evaluate physicochemical parameters for selection of increased productivity. The objective was to characterize rubber, and resin content, stem diameter, rubber molecular weight and cytology of these plants to identify and select high productivity sites. Samples were collected from nine locations within the Mapimi Region. Inflorescences containing young floral buds of the same plants were selected to determine ploidy level. Cytogenetic results showed the presence of di‐, tri‐ and tetraploids. Samples for rubber and resin analysis were cut from the branches. Genetic variation in molecular weight and molecular weight distributions for rubber was measured. Significant differences were found in resin content and stem diameter between the sampling sites, but differences were not significant for the rubber content between sites. A productivity parameter was defined and used to identify two locations where guayule genotypes exhibited the best characteristics for commercialization. This information may increase the industrial development and understanding of the polymerization bioprocess.

Effects of the Cessation of Grazing on the Grasslands and Grassy Woodlands of the Central Plateau, Tasmania

The response of grassy vegetation to exclusion from grazing was found to be related to a major productivity gradient in the central highlands of Tasmania. All sites showed a trend toward increased structural complexity, a decrease in bare ground and a decrease in species richness when grazing was excluded. However, the effect was much more pronounced at sites of high productivity. These findings support the theory that species richness is a function of both disturbance and the rate of competitive exclusion (site quality), and support suggestions that stock grazing is inappropriate above 1000 m on the Central Plateau.

Analysing yield stability of maize genotypes using a spatial model

The yield stability of some CIMMYT tropical maize (Zea mays L.) populations of early and intermediate maturity, measured by the performance of varieties derived from them, was determined. Results of the stability analyses, conducted over international environments from 1980 to 1983, indicated that selections from Mezcla Amarilla exhibited good stability in high yielding sites. Varieties derived from Antigua-Republica Dominicana tended to be more stable in unfavourable environments, whereas selections from Blanco Cristalino-1 and Blanco Dentado-2 were stable in both low and high production sites. The combination of enviromental factors in the specific test locations, namely Poza Rica (Mexico), Tocumen (Panama), Islamabad (Pakistan), and Ferkessedougou (Ivory Coast), allowed selection of varieties that are very stable in other regions of the world. The varieties formed on the basis of multilocational data do not seem to be any more stable than those formed using data from a single location.

Deposition of the Bear Gulch Limestone: a Carboniferous Plattenkalk from central Montana

ABSTRACTThe Carboniferous Bear Gulch Limestone of the central Montana Big Snowy Trough is a lithographic limestone analogous to the plattenkalk carbonates of the Mesozoic European/Middle Eastern Tethyan belt. It contains an excellently preserved chitinous and phosphatic marine fauna.Petrographic and field studies synthesized with palaeontological data provide insights into depositional history. Tectonic activity initiated development of small en echelon basins. Rims of these basins were sites of high primary productivity. Photosynthesis by subtidal cyanobacterial mats and algae caused in situ precipitation of micrite. Cyanobacteria and algae also provided a food source for benthic and nektonic organisms, which provided food for predators. Respiration in turn provided carbon dioxide for continued photosynthesis. Thus a balanced ecosystem evolved.Productivity in the water column used up available oxygen, resulting in dysaerobic to anaerobic conditions in the bottom waters and sediments. This plus high sedimentation rates of carbonate ooze transported downslope, aided in preservation of whole‐body fossils.There are no likely modern analogues known for the Bear Gulch Limestone. However, comparisons with Mesozoic plattenkalke demonstrate that it is most closely analogous to those deposited in shallow water back‐reef areas of the Tethyan carbonate platform, rather than to those deposited in the deeper water shelf‐edge environment. This is in agreement with the water depth of roughly 40 m estimated for the Bear Gulch Limestone.

Environmental and successional relationships of the forest communities of the Porcupine River drainage, interior Alaska

The structure and function of taiga ecosystems over a 3 600 000 ha area of northeastern interior Alaska was shown to be consistent with a hypothesis relating vegetative structure and dynamics to site nutrient status and soil temperature. Ordination of modal community descriptions and correlation of the ordination values with environmental parameters indicated that controls of vegetative structure and function found for the Fairbanks area, where the hypothesis was developed, can be applied to the interior Alaska taiga. High productivity sites were associated with warmer soil temperatures, smaller accumulation of soil organic layers, and lower C:N ratios. Lower productivity sites were associated with the opposite trends. Black spruce (Piceamariana (Mill.) B.S.P.) generally dominated the less productive sites, while white spruce (Piceaglauca (Moench) Voss) and hardwoods occupied the more productive sites. The successional trends described for other areas of interior Alaska appear to be valid for this remote study area.

Above- and Below-ground Growth of Forest Stands: a Carbon Budget Model

The utilization and allocation of carbon by a forest stand are examined through a simple dynamic, mechanistic model which incorporates radiation interception, photosynthesis, respiration, assimilate partitioning, litterfall, root mortality and turnover. Qualitative mathematical analysis of the balance between carbon gains and losses provides an intuitive insight into the determinants of above- and below-ground growth. The patterns of dry matter accumulation produced by the model are compared with observed trends in stand development. Reported differences between biomass distribution on sites of high and low productivity are reproduced by adjusting the coefficients of assimilate partitioning.

Above- and below-ground net production in 40-year-old Douglas-fir stands on low and high productivity sites

Above- and below-ground net primary production was estimated for 40-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stands growing on sites with apparently large differences in productivity potential. Aboveground net production was estimated from direct measurements of tree growth; belowground productivity was derived from data obtained by sorting live and dead roots from soil cores used in combination with measurements of root growth on observation windows.Aboveground net production was 13.7 t•ha−1 on the high productivity site and 7.3 t•ha−1 on the low productivity site. Belowground dry matter production on the high productivity site was 4.1 t•ha−1 compared with 8.1 t•ha−1 for the poorer site. On the more productive site, 8% of total stand dry matter production was in fine roots in contrast to over 36% on the poorer site. The difference in total net production (aboveground plus belowground) between the two sites was small (2.4 t•ha−1). Apparent differences in aboveground productivity may, to a large extent, result from the need for a greater investment in the fine roots on harsher sites.

Petroleum Source Beds on Continental Slopes and Rises

Continental slopes commonly are sites of high marine organic productivity and frequently contain reducing bottom conditions, quiet water, and intermediate sedimentation rates, all of which favor deposition of organic-rich sediments. These deposits typically have high percentages of aquatic organic matter with high petroleum yields as contrasted to relatively organic-lean shelf deposits which contain primarily low-yield terrestrial organic matter. Conversion of organic matter in potential source beds to oil and gas requires a combination of temperature and time. These variables are controlled primarily by the geothermal gradient, the rate of burial, and the age of the source interval. Most divergent margins need between 2 and 4 km of overburden for oil generation and from 3 to 7 km for gas generation. Typically cooler and younger convergent margins and deltaic margins must have even greater burial depth to achieve the same results. Continental margins, including present slopes and rises, can contain oil and gas source beds when minimum requirements of organic content, kerogen type, and thermal maturity are met. Migration and accumulation are most efficient, however, where reservoir sequences prograde over source beds in areas of structural complexity. Preservation of trapped petroleum requires effective seals and minimal structural readjustment after accumulation. All these conditions can be found on present slopes and rises, although they are not common, and must be considered as part of any economic evaluation of these largely untested deep-water realms.