Unit Area Basis Research Articles

Phytoplankton Dynamics and Hypoxia in Lake Erie: A Hypothesis Concerning Benthic-pelagic Coupling in the Central Basin

Recent changes in the Lake Erie ecosystem suggest that reductions in phosphorus loads and invasion by dreissenid mussels, have enhanced light penetration, and altered phytoplankton distribution patterns in the lake. In this paper, we evaluate possible links between phytoplankton dynamics in Lake Erie, and seasonal development of hypoxia in the central basin by studying seasonal pattern of the vertical distribution of algae. On four occasions in 2002, the biomass of major algal assemblages was measured (epilimnion, metalimnion, hypolimnion, and benthos) at six sites in the central basin (n = 96). Pelagic chlorophyll concentrations in the central basin varied by several fold among the six sampling sites and three dates (range, 0.80 to 5.99 mg/m 3). The greatest values were measured in the metalimnion. Benthic chlorophyll concentrations in the central basin were large. Values were highest in June and decreased dramatically thereafter. Mean (± SD) concentrations for the benthic assemblages at two stations were 31.1 ± 18.9 mg/m 2, compared with values of 43.2 ± 9.2 mg/m 2 for the pelagic assemblage at the same two stations. The consistent presence of a benthic algal assemblage in the central basin, whose species make-up was dominated by planktonic diatoms, suggests that the benthic assemblage in the central basin is more aptly viewed as a meroplanktonic algal maximum (MAM); an algal assemblage that spends part of its life history associated with both the pelagic and benthic environments. On a unit area basis, this MAM layer supported biomass comparable to that for the entire water column, suggesting that the MAM figures prominently into the development of hypoxia.

Biological diversification in a complex region: a spatial analysis of faunistic diversity and biogeography of the Andes of Colombia

AbstractAim Understanding large‐scale patterns of beta diversity and endemism is essential for ecoregional conservation planning. We present a study of spatial patterns of faunal diversification and biogeographical relationships in the Andean region of Colombia. This region has a great geomorphological complexity, as it is formed by several mountain ranges with different geologic origins. We hypothesize that this complexity results in a high turnover in species composition among subregions.Location The Andean region of Colombia, including the Santa Marta and Macarena mountain ranges.Methods The region was divided into subregions, represented by the eastern and western slopes of each of the three Andean cordilleras, the Cauca and Magdalena valley bottoms, and the peripheral mountain ranges of Perijá, Macarena and Sierra Nevada de Santa Marta. Species lists for five animal taxa (rodents, bats, birds, frogs and butterflies) were compiled for each subregion and similarities in species composition were determined by cluster analysis. To explore biogeographical relationships, species were classified into one of four distributional categories: endemic, tropical Andean, Andean‐Central American and wide continental distribution.Results The highest species richness in the region was found in the Pacific and eastern versants of the Andes, and the lowest in the Cauca and Magdalena valley bottoms. Inter‐Andean slopes were intermediate in species richness. However, when species richness was calculated per unit area, the most diverse regions were the Santa Marta and Macarena ranges, the Cauca Valley watershed and the Pacific slope. Although each taxonomic group had a different branching pattern, dendrograms indicated five common subregional clusterings: (1) Perijá‐Sierra Nevada, (2) the Pacific slope, (3) the eastern Andean slope, (4) the Cauca and Magdalena valley bottoms, and (5) the inter‐Andean slopes. Clustering patterns of inter‐Andean slopes varied among taxa. In birds, bats and rodents, grouping was by opposite slopes of the same valley, whereas frogs were grouped by mountain ranges and butterflies by valleys and their respective slopes. Seventy‐five per cent of species in all taxa were found in less than five subregions. The fauna of the Magdalena and Cauca valley bottoms was composed mostly of lowland species with wide geographical distributions, whereas the cordilleran fauna was mostly restricted to the tropical Andes.Main conclusions The western and eastern versants of the Andes have the highest species richness, but are also the largest subregions. On a per unit area basis, the peripheral ranges (Santa Marta and Macarena) are the richest, followed by the western portion of the Andes (the Cauca Valley watershed and the Pacific versant). Clustering patterns in dendrograms suggest two major patterns of differentiation of the Andean fauna: one elevational (lowlands vs. highlands) and one horizontal (among ranges and/or slopes). Biogeographical affinities of the inter‐Andean valley bottoms are with the lowland faunas of tropical America. In contrast, Andean faunas diversified locally, resulting in the evolution of a large number of endemic species, particularly among the less vagile taxa. Three different main branches of Andean fauna can be recognized, one confined to the Pacific, another to the eastern (Amazonian‐Llanos) versant of the Andes, and the third one composed by the inter‐Andean slopes of the Cauca and Magdalena valleys. The identification of five main biogeographical units in the Andean region of Colombia has important implications for the conservation of the regional biota. Conservation initiatives that seek to preserve representative samples of the regional biodiversity should take into account the patterns of diversification described here, and the evolutionary processes that gave rise to these patterns.

Comparison of two coniferous plantations in central Japan with respect to forest productivity, growth phenology and soil nitrogen dynamics

Japanese cypress ( Chamaecyparis obtusa Endl.) and Japanese cedar ( Cryptomeria japonica D. Don) are common species for plantation forestry in Japan. Cypress is conventionally planted on sites of low fertility whereas for cedar high fertility sites are used. Objectives of this study were to compare the productivities of cypress and cedar plantations grown on adjacent sites where common properties of soils, such as pH values and C and N contents, were similar, and to relate the N cycling at their site with productivities. The stem diameter of trees, aboveground litter production and fine root biomass were measured as indices of forest productivity. Parameters of N cycling included pools of total N and mineral N (ammonium + nitrate), annual N leaching, and potentially mineralizable N. The radial stem increment of the two tree species was similar. However, cedar site had higher total basal area and annual basal increment than cypress site reflecting higher tree density on the cedar site. Aboveground litter, fine root biomass, soil organic matter, and N turnover were higher on the cedar site than on the cypress site. However, litter production and fine root biomass per unit basal area was greater at the cypress site. Phenological pattern of stem growth and periodical litter production were similar for both species during the study period (1992–2000), but showed distinct annual variations caused by the fluctuation in the ambient temperature and precipitation. Mineral N content and the N mineralization potential were greater on the cedar site, indicating greater N availability and higher total tree productivity at the cedar site than those at the cypress site. When provided with more space in the canopy to expand more needles and in the soil to develop more fine roots to exploit sufficient resources, the individual cypress trees have the potential to grow faster. On fertile site and at lower tree density, thicker logs of cypress might be yielded.

Isoprene and other non-methane hydrocarbons from seaweeds: a source of reactive hydrocarbons to the atmosphere

Non-methane hydrocarbons (NMHCs) are produced naturally in the ocean and by terrestrial vegetation. Owing to its high reactivity and flux, isoprene (2-methyl-1,3-butadiene) is important in controlling the balance of atmospheric oxidants, and altering air quality on both local and global scales. Here we show, for the first time, that macroalgae (seaweeds) emit isoprene and a number of other non-methane hydrocarbons (NMHCs). We observed NMHC concentrations in rockpools containing macroalgae and estimated fluxes to the atmosphere over a full diurnal cycle. Emissions at our temperate coastal site (Mace Head, Ireland) in autumn are intermediate in magnitude between terrestrial and ocean fluxes (on a unit area basis), and may contribute significant concentrations to the local atmosphere. We also carried out a series of controlled laboratory experiments focusing on isoprene, in natural and artificial light, and under different temperature conditions involving red (Chondrus crispus, Asparagopsis armata), green (Ulva intestinalis, formerly known as Enteromorpha intestinalis) and brown (Laminaria digitata, Ascophyllum nodosum, Pelvetia canaliculata, Fucus vesiculosus, Fucus serratus, Halidrys siliquosa and Laminaria saccharina) macroalgae commonly found on the west coast of Ireland. We observed NMHC emissions from all the algae investigated and emissions were dominated by alkenes. Production is species-dependent, temperature-dependent and related to light availability. We discuss our observations in the context of what is known about the production of isoprene and ethene in higher plants.

Variation in stand mortality related to successional composition

Forest ecologists have long recognized that there are large differences in the vital rates of early- and late-successional species: early-successional species typically grow faster than late-successional species, while late-successional species typically have lower rates of mortality than early-successional species. Numerous studies have shown that the differences in mortality are particularly evident when comparing per-capita rates in stands of early- and late-successional species. However, fewer studies have examined whether such differences in per-capita mortality are manifest as a difference in biomass turnover: do stands comprised late-successional species have lower rates of basal area mortality (mortality per unit basal area) than stands comprised of early-successional species? In this paper, the relationship between stand mortality and successional composition is examined using forest inventory data from the state of Michigan (USA). Mortality was quantified as the annual percentage of basal area lost to mortality, and successional composition was quantified using a continuous variable that reflects the successional status of each of the component tree species. Analysis by multivariate regression revealed that the difference in mortality between early- and late-successional stands is as great as 50%, and that the significance of this result is robust to collinearity between stand composition, stand age, and stand structure. This result suggests that successional composition could be used to better forecast changes in timber supply, habitat supply, and ecosystem function.

Mechanisms of cuticular uptake of xenobiotics into living plants: 1. Influence of xenobiotic dose on the uptake of three model compounds applied in the absence and presence of surfactants into Chenopodium album, Hedera helix and Stephanotis floribunda leaves

This study determined the uptake of three model compounds, applied in the presence and absence of surfactants, into the leaves of three plant species (Chenopodium album L, Hedera helix L and Stephanotis floribunda Brongn). The results with 2-deoxy-D-glucose, 2,4-dichlorophenoxyacetic acid and epoxiconazole in the presence ofsurfactants (the polyethylene glycol monododecyl ethers C12EO3, C12EO6, C12EO10 and a trisiloxane ethoxylate with mean EO of 7.5, all used at one equimolar concentration and therefore different percentage concentrations) illustrate that the initial dose (nmol mm(-2)) of xenobiotic applied to plant foliage is a strong positive determinant of uptake. This held true for all the xenobiotics studied over a wide concentration range in the presence of these surfactants. Uptake on a unit area basis (nmol mm(-2)) could be related to the initial dose of xenobiotic applied per unit area (ID) by an equation of the form: Uptake = a [ID]b at time t = 24h. ID is given by the mass of xenobiotic applied, M divided by the droplet spread area, A. Total mass uptake is then calculated from an equation of the form: Total Uptake = a [ID]b x A.

Isoprene and other non-methane hydrocarbons from seaweeds: a source of reactive hydrocarbons to the atmosphere

Non-methane hydrocarbons (NMHCs) are produced naturally in the ocean and by terrestrial vegetation. Owing to its high reactivity and flux, isoprene (2-methyl-1,3-butadiene) is important in controlling the balance of atmospheric oxidants, and altering air quality on both local and global scales. Here we show, for the first time, that macroalgae (seaweeds) emit isoprene and a number of other non-methane hydrocarbons (NMHCs). We observed NMHC concentrations in rockpools containing macroalgae and estimated fluxes to the atmosphere over a full diurnal cycle. Emissions at our temperate coastal site (Mace Head, Ireland) in autumn are intermediate in magnitude between terrestrial and ocean fluxes (on a unit area basis), and may contribute significant concentrations to the local atmosphere. We also carried out a series of controlled laboratory experiments focusing on isoprene, in natural and artificial light, and under different temperature conditions involving red ( Chondrus crispus, Asparagopsis armata), green ( Ulva intestinalis, formerly known as Enteromorpha intestinalis) and brown ( Laminaria digitata, Ascophyllum nodosum, Pelvetia canaliculata, Fucus vesiculosus, Fucus serratus, Halidrys siliquosa and Laminaria saccharina) macroalgae commonly found on the west coast of Ireland. We observed NMHC emissions from all the algae investigated and emissions were dominated by alkenes. Production is species-dependent, temperature-dependent and related to light availability. We discuss our observations in the context of what is known about the production of isoprene and ethene in higher plants.

Light-modulation of bark photosynthesis in birch (Betula pendula Roth.)

Bark photosynthesis has been shown to be an effective mechanism for stem-internal refixation of respiratory CO . In young birch trees (Betula pendula Roth.) this function is clearly modulated by the prevailing light intensity regime. Although positive net photosynthesis was not found in intact birch twigs, apparent twig respiration was reduced upon illumination by 65 % in high-light grown birches and even more in shade grown trees (81 %). Compared on a unit area basis the bark chlorenchyma contained up to 55% of the chlorophyll of the concomitant leaves when grown under 100 % sunlight and even 66 % when trees were grown under low-light (20 % of full sunlight). Light penetration through the periderm of birch twigs and branches is age-dependent and ranges in control trees from roughly 24 % of the incident sunlight in recent-year twigs to 1-3 % in 5-year-old main stems. Peridermal light transmittance was also changed by the light intensity regime. An additional light-reducing peridermal layer present in control trees was not found in shade-grown birches. It was shown that CO -refixation is not limited to the light­ exposed outer parts of tree crowns. Our results show that also inner branches of trees are well adapted to function as a rather efficient system to prevent respiratory carbon loss.

Biomass production and nutritional levels of berseem ( Trifolium alexandrium) grown under elevated CO 2

There is little available information about the effect of elevated CO 2 on the growth and mineral nutrients of fodder crops. To investigate the changes in vegetative biomass and nutrient concentration of berseem ( Trifolium alexandrium L.), an important forage legume, was grown in ambient (360 μl l −1) as well as elevated (600 μl l −1) CO 2 conditions from germination onwards in open top chambers. Elevated CO 2 increased the leaf size, plant height and fresh and dry mass of shoots. There was more partitioning of photosynthates towards the growth of new branches than towards the growth of leaves. Leaf nitrogen, soluble proteins, calcium, iron and nitrate reductase (NR) activity decreased in elevated CO 2 while leaf carbon and phosphorus contents increased. The results suggest that berseem grown in elevated CO 2 throughout the crop season can produce more fodder in less time. The study concludes that elevated CO 2 may increase the fodder production by 30–35% but will adversely affect the nutritional quality of the forage due to reduction in nitrogen, protein, calcium and iron concentration in leaves on a unit dry weight basis. On a unit area basis, however, there will be an increase in total nutrient content, including nitrogen, due to increased fodder biomass in elevated CO 2.

Effect of age and season of harvesting on the growth, coppicing characteristics and biomass productivity of Leucaena leucocephala and Vitex negundo

Abstract Field trials to study the growth and biomass production of Leucaena leucocephala and Vitex negundo in relation to their age and season of harvesting were conducted on alkaline soils of North Indian plains under irrigated conditions. Both shrubs showed excellent regeneration and survival (>90%) of coppiced stumps. Increasing the harvest age from 10 months (in February) to 18 months (in October) did not result in statistically significant increase in biomass production of Leucaena . The yield on per plant and unit area basis was higher in coppiced stands than original stands of Leucaena and Vitex . The highest increase in biomass production of Leucaena was recorded between 18 and 20 months harvesting age. Harvesting in December was found the best for Leucaena . Vitex registered rapid growth during the period from summer untill the rainy season. The post-harvest conditions for coppice development, the period of rapid growth and the physiological stage at harvesting interacted significantly with the growth and biomass production of these shrubs.

Tree species differentiation in growth, recruitment and allometry in relation to maximum height in a Bornean mixed dipterocarp forest

Summary 1 Maximum attainable height varies greatly between tree species in tropical rain forests and covaries with demographic and allometric traits. We examined these relationships in 27 abundant tree species in a mixed dipterocarp forest. These species were monitored over 3 years in two 1-ha plots in western Borneo. A 95-percentile upper height limit was used to represent maximum height, to avoid sample size differences among populations. 2 Average growth rate in trunk diameter was regressed against trunk diameter using a maximum likelihood model and assuming that growth rates were exponentially distributed around the average. Estimated average growth rate at small trunk diameters (up to 11 cm) was independent of maximum height among the 27 species, while the degree of growth reduction at larger diameters was larger for species with smaller maximum height. 3 The recruitment rate efficiency of saplings was negatively correlated with maximum height, regardless of the measure used to assess species abundance. In particular, sapling recruitment per unit basal area declined greatly with increasing maximum height, consistent with model predictions of the traits required for the stable coexistence of species at different heights within the canopy. 4 Allometric analyses showed that understorey species had shorter heights at the same trunk diameter, and deeper crowns at the same tree height, than canopy species. Therefore, understorey species showed adaptive morphology to deep shade. 5 The regressed size-dependent pattern of average growth rate and an assumption that the population was in a steady state readily explained the observed trunk diameter distributions for 21 species among 27 examined. These species, for which the projected size distribution hardly changed when the natural increase or decrease of the population was set at γ = ±0.005 year−1, had mortality rates of more than four times the value of γ.

Abaxial and Adaxial Stomatal Density, Stomatal Conductances and Water Status of Bean Primary Leaves as Affected by Paclobutrazol

The plant growth retardant, paclobutrazol at 8.5 or 17.0 μM concentrations effectively inhibited the stem elongation and primary leaf expansion of bean seedlings. Although the retardant reduced the relative water content in well-watered plants, the water and pressure potentials remained high in the primary leaves. K+, Na+, Mg2+ and Ca2+ contents in the primary leaves of the paclobutrazol-treated plants were not significantly different from those in the control. The stomatal density increased on both surfaces but the length of guard cells was not reduced significantly on the adaxial epidermes of the paclobutrazol-treated primary leaves. The inhibitory effect of paclobutrazol on the abaxial stomatal conductances became more pronounced with time during the light period but the adaxial surfaces displayed similar or slightly higher conductances than those of the control. The transpiration rate on a unit area basis did not change significantly or increased in the treated leaves thus the reduced water loss of paclobutrazol-treated plants was due to the reduced leaf area. Stomatal conductances of the adaxial surfaces responded more intensively to exogenous abscisic acid and the total leaf conductance decreased faster with increasing ABA concentration in the control than in the paclobutrazol-treated leaves. Paclobutrazol, an effective inhibitor of phytosterol biosynthesis, not only amplified the stomatal differentiation but increased the differences between the adaxial and abaxial stomatal conductances of the primary leaves.

A novel method of field release of Goniozus nephantidis (Muesebeck), an important primary parasitoid of Opisina arenosella Walker on coconut

Goniozus nephantidis (Muesebeck) is an important primary parasitoid of Opisina arenosella Walker in coconut eco-system. The method of release of G. nephantidis was standardized for the first time. It was found that 90-100 per cent of the parasitoids released at the trunk (1.2 m from the ground level) reached the crown of the palm irrespective of the height of the tree. The mean time taken by each batch of the parasitoids to reach the crown varied from 13 to 22 minutes. It was also found that the parasitoids preferred to crawl on the tree rather than flying. Hence it is suggested that G. nephantidis adults may be released at the trunk (1.2 m height from the ground level) of the coconut palm for the management of O. arenosella instead of releasing at the crown region of the palm or arbitrarily on unit area basis.

Determining the sources of suspended sediment in a forested catchment in southeastern Australia

Knowledge is scarce regarding the relative contributions from harvested areas and unsealed roads to sediments in forested catchments. We investigate the source composition of suspended sediment using sediment tracers and an improved multivariate mixing model. Sediment samples were collected during six rainfall events. Geochemical and radiometric tracer properties were corrected for particle size and organic content as well as conservativeness during erosion and sediment delivery. The mixing model incorporates variability of the tracer properties, using a Monte Carlo simulation technique. Mean sediment contribution from the undisturbed forest was 50–70%; harvested areas, gravel‐surfaced roads, and ungravelled roads contributed 5–15%, 6–14%, and 12–25%, respectively. The unsealed roads contribute 20 to 60 times more sediment than the undisturbed forest and about 10 times more sediment than the harvested areas on a per unit area basis. Harvested areas contribute 1 to 5 times greater sediment than the undisturbed forest. These results support other studies that identify unsealed roads as important sediment sources in forested catchments.

Dimethylsulfoniopropionate: its sources, role in the marine food web, and biological degradation to dimethylsulfide.

The massive quantities of phytoplankton in the North Atlantic and Antarctic oceans producing dimethylsulfoniopropionate (DMSP) as an osmoprotectant, much of which is degraded by marine bacteria to dimethylsulfide (DMS), ensures an important role for both compounds in the global sulfur cycle. The closest to a comprehensive review on this topic is a book of symposium proceedings edited by Kiene et al. (75); the more recent developments related specifically to DMSP degradation by microbial communities are found elsewhere (68). This article is more comprehensive, as it includes some of the earlier literature in describing the sources of DMSP, its release and linkage to the marine (primarily microbial) food web and subsequent degradation via cleavage to DMS and acrylic acid or demethylation and demethiolation to methanethiol. DMS production from DMSP has long been associated with marine algae according to the following reaction (20, 22): (1) DMSP is a tertiary sulfonium compound produced in high concentration by certain species of marine algae and plant halophytes for the regulation of their internal osmotic environment (1, 41, 47, 120), although its role in plants remains unclear. This alga-associated, i.e., particulate DMSP (DMSPp), when released into the marine environment as dissolved DMSP (DMSPd), can serve as a link between primary production and the microbial population, as it is readily degraded by chemoheterotrophic bacteria (59). DMSP turnover usually exceeds DMS production in natural waters (60) because DMSP is also demethylated to 3-methiolpropionate, which can be further demethylated to 3-mercaptopropionate or demethiolated, releasing methanethiol (72, 118). These reactions will be discussed in more detail below. The biogeochemical significance of DMSP cleavage was first suggested in 1972, when DMS was found to be universally present in seawater and emitted at a significant rate to the atmosphere (87). It was proposed that DMS, rather than H2S from coastal waters and mud flats, was the missing gaseous sulfur compound needed to enable the steady-state flow of sulfur between marine and terrestrial environments, making DMS emissions a key step in the global sulfur cycle (87). Atmospheric H2S, which arises primarily from dissimilatory sulfate reduction in organic matter-rich environments, could never be measured in sufficient quantity to be the vehicle for transferring large quantities of sulfur from sea to air to land. The total annual flux of biogenic DMS released to the atmosphere ranges from 28 to 45 Tg of S year−1, at least 10-fold higher than from all other sources (Table ​(Table1).1). Recent, more comprehensive calculations of global annual DMS flux from the oceans gave values that ranged from 13 to 37 Tg of S year−1 (57). This sea-to-air flux represents about 50% of the global biogenic sulfur flux to the atmosphere (3). However, anthropogenic sulfur emissions dominate the sulfur flux, representing 80 to 90% of the input to the global sulfur cycle (12, 23, 88). TABLE 1. Estimates of natural emissions of organosulfur compoundsa The magnitude of the marine DMS emissions is all the more remarkable considering that over half of the DMSP released is demethylated (68) and that a significant fraction of the DMS is oxidized by bacteria in the water column before it can be released to the atmosphere (13, 64). While most of the biogenic sulfur emissions (primarily DMS) come from the oceans, those coming from salt marshes and coastal wetlands are many times higher on a unit area basis (112). DMS flux per unit area from these marine wetlands is also much higher than from any known terrestrial soil (2). The biogeochemical cycling of DMSP and its biological degradation products are shown in Fig. ​Fig.11. FIG. 1. Scheme representing the mechanisms of DMSP and DMS cycling in the marine water column and atmosphere. DMSO, dimethyl sulfoxide; CCN, cloud-condensing nuclei; MMPA, 3-methiolpropionate; β-HP, β-hydroxypropionate; 3-MPA, 3-mercaptopropionate; ...

Interpretaciones de trabajos de fertilización con Solanaceae en Puerto Rico

Una metodología para realizar recomendaciones de fertilización se basa en relaciones entre niveles de fertilización y medidas correspondientes de rendimiento. El requisito nutricio nal del cultivo (RNC) es la totalidad del elemento que requiere el cuítivo durante el ciclo de producción para producir rendimientos económicos óptimos, y es equivalente al nivel de fertilización (cuando el suelo suple poca o ninguna cantidad del nutrimento) por encima del cual no existe un aumento significativo en rendimiento. Investigaciones realizadas con la familia Soianaceae: tomate (Lycopersicon esculentum), berenjena (Solatium melongena), y pimiento (Capsicum annuum) en Puerto Rico se utilizaron para calcular valores de RNC para nitrógeno (N), fósforo (P) y potasio (K). Los valores promedios obtenidos de cada nivel de fertilización fueron convertidos de unidad por área (ton/ha, kg/ha, cajas/acre) a rendimiento relativo (RR). Los valores de RR fueron grafícados contra niveles de aplicación de nutrimentos y se ajustaron diferentes modelos (lineal, cuadrática, iineai-meseta, cuadrático-meseta, exponencia! y Cate-Nelson) para determinar los vaiores de RNC. No se observó respuesta a la aplicación de K en suelos dominados por arcillas 2:1 (suelos 2:1). En suelos dominados por arcillas 1:1 (suelos 1:1) ninguna de las ecuaciones se ajustó adecuadamente a los datos porque había pocos datos experimentales y alta variabilidad entre los valores de rendimiento. Para P y N, los valores de RNC predichos variaron según el modelo utilizado. El mejor modelo se escogió basándose en los coeficientes de determinación y gráficos de residuales estandarizados, y corroborados con retornos económicos. En ¡os suelos 1:1, los valores de RNC predichos fueron 113 y 255 kg P205/ha y 150 y 207 kg N/ha para los modelos Cate-Nelson y cuadrático, respectivamente. En los suelos 2:1, los valores predichos fueron 50 y 148 kg P2Os/ha para los modelos Cate-Nelson y lineal-meseta, respectivamente, y 50 y 120 kg N/ha para los modelos Cate-Nelson y exponencial, respectivamente.

A combined rainfall simulator and tracer approach to assess the role of Best Management Practices in minimising sediment redistribution and loss in forests after harvesting

In this paper, we use the combined results from two contrasting methods to investigate the effectiveness of Best Management Practices (BMPs) on sediment erosion and redistribution in managed forestry environments in southeastern New South Wales (NSW), Australia. The first method employed a rainfall simulator at the skid track (snig track)—water bar (cross-bank)—general harvest area (GHA) spatial scale. This showed the majority of production and redistribution occurring from the skid tracks and coinciding with the period after initial disturbance. However, 5 years after harvesting, little redistribution between these elements was occurring. Furthermore, water bar structures were effective in trapping coarse sediment generated from skid tracks but markedly less so for fine <63 μm material. The second method involved constructing a tracer budget. This was based on measuring the 137Cs content in each of the landscape elements of an entire watershed, which also enclosed a 5-year forest coupe selected for the simulator experiments. The 137Cs budget effectively balanced with 61.1±4 and 59.2±4 MBq present prior to, and after, harvesting, respectively. Total recovery was 97±10%, which indicated no net loss of sediment from the study basin over the 6-year post-harvesting period within uncertainties. Of the total sediment redistribution, some 13±4% in losses occurred from the skid tracks and log landings, whilst net gains of 10±1% occurred in the GHA, filter strip and water bars. On a per unit area basis, the filter strip retained ∼8 times the 137Cs and associated sediment of the GHA; however, the greatest overall trapping of fine sediment occurred in the GHA. Combining these two approaches suggests that management of filter areas is paramount, although the GHA remains the primary sediment buffer for the system. Greater effort to disconnect flow paths, retain roughness and reduce overland flow volumes in order to increase sediment deposition should occur here.

Production potential and nitrogen use efficiency of inter specific and intra hirsutum cotton hybrids under graded levels of nitrogen and weed control methods

. . A field study was conducted during the winter seascn of 1997 and 1998 at Tamil Nadu Agricultural University, Coimbatore. Two hybrids (inter specific TCHB 213 and intra hirsutum Surya ) were evaluated for their production potential under 3 N levels (90. 120, and 150 kglha) and 4 weed control methods (Pendimethalin 1.0 kg 1 hand weeding, glyphosate 1.0 kg 1 hand weeding, hand weeding twice and unweeded control). The hybrids were grown following the recommended spacing of 90 cm x 60 cm for Surya and 120 cm x 60 cm for TCHB 213 . Among the hybrids, TCHB 213 gave better yield attributes and yield , on per plant basis. But Surya gave significantly more yreld than TCHB 21 3 on t unit area basis. The response to applied N was increasing at increasing rate up to the highest level (150 kglha) of N. But the N use efficiency decreased with increase in N level. Among the weed control treatments, hand weeding twice recorded significantly higher seed cotton yield and N use efficiency which was closely followed by glyphosate hand weeding.

Herbage and phytochemicals yield of mandukaparni (Centella asiatica) as influenced by time of harvest

Indian pennywort or mandukaparni [Centella asiatica (L.) Urban] containing four triterpenes; asiaticoside, madecassoside, asiatic acid and madecassic acid as principal bioactive phytochemicals, is an important medicinal crop and valued as brain tonic worldwide. An experiment was conducted during 201214 at Anand, Gujarat, to in- vestigate the effects of harvest time of main crop of mandukaparni as well as ratoon on herbage yield, and triterpenes content and yield. Significantly higher leaf area was found at the first harvesting of main crop at 6 months (21.9 cm2/leaf) and ratoon harvesting at 4 months (22.1 cm2/leaf), whereas leaves/node were found mark- edly higher at 4 months of first harvest (MFH) (11.3) and 2 months of ratoon harvest (MRH) (11). The first harvest- ing of the main crop at 5 months and ratoon harvesting at 4 months recorded markedly higher dry herbage yield (1,404 kg/ha), being higher by 54.8% over 4 MFH and 2 MRH. The highest triterpenes content were recorded at the first as well as ratoon harvesting at 4 months (2%) and increased by 42.8% over 4 MFH and 2 MRH. The triterpenes yield was markedly higher at the first harvesting of main crop at 5 months and ratoon harvesting at 4 months (26.7 kg/ha), which was 107% higher over 4 MFH and 2 MRH. Thus, mandukaparni should be harvested first at 5 months after planting and ratoon at 4 months interval for the production of maximum herbage and phytochemicals on unit area basis under commercial cultivation.

Leaf photosynthetic capacity and nitrogen content adjustment to canopy openness in tropical forest tree seedlings

Maximum assimilation rate under saturating light level, leaf nitrogen and chlorophyll content and specific leaf mass were measured in forest plants grown under a range of canopy openness. Seedlings from three tree species co-occurring in damar agroforest (Sumatra) were examined: Shorea javanica, Lansium domesticum and Cinnamomum porrectum. A shrub species, Piper hispidum, growing in a different location was also investigated. All species showed pronounced differences in maximum photosynthetic potential when grown under different canopy openness. All tree seedlings showed an increase in maximum assimilation rate (Amax) with canopy openness (CO) until a certain threshold was reached. This saturation threshold varied between species. A steady increase in the maximum assimilation rate over the entire range of canopy openness explored was found only for Piper. Correlation between leaf nitrogen content and Amax was usually highest when expressed on a per unit area basis. However the overall correlation was poor whether expressed per unit mass or per unit area when all species were pooled together questioning the universality of the relationship between both quantities. Potential photosynthetic nitrogen use efficiency, defined as the amount of CO2 uptake per unit leaf nitrogen under saturating light level, was highest in Cinnamomum, supposedly the most light-demanding species, and lowest in Lansium, the understorey specialist.