High Nutrient Supply Research Articles

RESPOSTA DA MAMONA A APLICAÇÃO DE DOSES EXCESSIVAS DE CALCÁRIO EM ARGISSOLO VERMELHO DISTROFÉRRICO

The castor oil plant has a strong fitness culture as summer or winter harvest in Central Brazil, but the tropical soils have high natural acidity and low nutrient supply, which limits the production potential. Liming is a technique devoted to the management of tropical soils, however, the excessive use of lime can compromise crop development. Aiming to evaluate the vegetative growth and nutrient content in the shoot of castor oil plant, depending on the application of excessive doses of lime, settled experiment in pots in a greenhouse. The substrate was composed of soil classified as typic dystrophic Argisoil (Rhodustults-PVd) corrected with different doses of lime (0, 1, 2, 4 and 8 t ha -1 ). We used the cultivar Savana, leaving two plants per pot. Were assessed, considering the shoot, the dry matter and calcium, magnesium, potassium, sulfur and boron. It was concluded that the excess of limestone is detrimental to plant growth and K absorption by castor oil plant.

How do evergreen and deciduous species respond to shade?—Tolerance and plasticity of subtropical tree and shrub species of South-East China

Different plant species make use of resource gradients such as light in different ways. First, plant species specialize in using different parts of the gradient, resulting in niche partitioning, Second, within the section of the gradient used by a species, plants respond to a different resource supply by plasticity. Our study addressed both of these strategies, with the main objective to relate mean responses and plasticity indices of seedlings of woody species to species characteristics such as leaf habit and to variation in branch lengths and local frequency of adult trees in forest communities.A greenhouse experiment with 36 deciduous and 35 evergreen subtropical tree and shrub species was carried out to test the influence of light and nutrient availability on trait expression and plasticity of the species. The greenhouse responses of seedlings were compared with adult individuals in the field, based on a set of 46 species that occurred also in the 27 permanent plots in a secondary subtropical broadleaved forest in Zhejiang Province (SE-China).In the greenhouse experiment, most variables showed significant differences between unshaded (250μEm−2s−1) and shaded (10μEm−2s−1) treatments as well as between high and low nutrient supply. Deciduous species were more plastic than evergreen species in their response to light. No significant correlations were detected in mean responses and plasticity between juvenile plants in the greenhouse and adult trees in the field. However, some trait values such as biomass and node density as well as plasticity of several traits were positively related to the species’ abundance in the field, suggesting that locally abundant species tend to be less “plastic” than locally rare species.

Gas exchange and growth responses to nutrient enrichment in invasive Glyceria maxima and native New Zealand Carex species

We compared photosynthetic gas exchange, the photosynthesis–leaf nitrogen (N) relationship, and growth response to nutrient enrichment in the invasive wetland grass Glyceria maxima (Hartman) Holmburg with two native New Zealand Carex sedges (C. virgata Boott and C. secta Boott), to explore the ecophysiological traits contributing to invasive behaviour. The photosynthesis–nitrogen relationship was uniform across all three species, and the maximum light-saturated rate of photosynthesis expressed on a leaf area basis (Amaxa) did not differ significantly between species. However, specific leaf area (SLA) in G. maxima (17±6m2kg−1) was 1.3 times that of the sedges, leading to 1.4 times higher maximum rates of photosynthesis (350–400nmolCO2g−1 dry masss−1) expressed on a leaf mass basis (Amaxm) when N supply was unlimited, compared to the sedges (<300nmolCO2g−1 dry masss−1). Analysis of Covariance (ANCOVA) revealed significant positive relationships between leaf N content and chlorophyll a:b ratios, stomatal conductance (gs), dark respiration rate (Rd), and the photosynthetic light saturation point (Ik) in G. maxima, but not in the sedges. ANCOVA also identified that, compared to G. maxima, the sedges had 2.4 times higher intrinsic water use efficiency (A/gs: range 20–70 cf. 8–30μmolCO2mol−1 H2O) and 1.6 times higher nitrogen use efficiency (NUE: 25–30 cf. 20–23gdry massg−1N) under excess N supply. Relative growth rates (RGR) were not significantly higher in G. maxima than the sedges, but correlations between leaf N, gas exchange parameters (Amaxa, Amaxm, Rd and gs) and RGR were all highly significant in G. maxima, whereas they were weak or absent in the sedges. Allocation of biomass (root:shoot ratio, leaf mass ratio, root mass ratio), plant N and P content, and allocation of N to leaves all showed significantly greater phenotypic plasticity and stronger correlation to final biomass in G. maxima than in the sedges. We therefore conclude that photosynthesis and growth rates are not intrinsically higher in this invader than in the native species with which it competes, but that its success under nutrient enrichment is a consequence of greater physiological responsiveness and growth plasticity, and stronger integration between gas exchange and growth, coupled with indifference to resource wastage (i.e. low WUE and NUE) at high nutrient supply. The poorer performance of G. maxima than the sedges under low nutrient supply supports the importance of nutrient management, especially N, as a strategy to minimise the invasive behaviour of fast-growing herbaceous species in wetlands.

Effects of N:P Ratio and Nutrient Level on the Competition between Invasive &lt;i&gt;Alternanthera philoxeroides&lt;/i&gt; and Native &lt;i&gt;Oenanthe javanica&lt;/i&gt;

This study examined the effects of N:P ratio and nutrient level on the competition between invasive Alternanthera philoxeroides and native Oenanthe javanica in terms of morphological and physiological traits and the relative dominance index (RDI). In the experiment, A. philoxeroides was grown in mixture with O. javanica at three N:P supply ratios (1,10,100) combined with three levels of nutrient supply. The results suggested that the morphological and physiological traits of invasive and native species were both significantly affected by N:P ratio and nutrient supply level. The total biomass of both species was maximal under the treatment of lowest N:P ratio and highest nutrient supply, and A. philoxeroides had higher total biomass than O. javanica in every treatment. A. philoxeroides had higher plasticity than O. javanica on total biomass, R/S, SLA, which had sensitive response to the changing nutrient conditions. Meanwhile, the RDI of A. philoxeroides under high nutrient supply was higher than that under low nutrient supply, which showed that high nutrient supply could promote the invasion of A. philoxeroides while P-limitation (high N:P ratio) may prevent the successful invasion of A. philoxeroides under the lower nutrient supply.

Effects of ultraviolet radiation and nutrients on the structure-function of phytoplankton in a high mountain lake

The combined effect of high solar ultraviolet radiation (UVR) and nutrient supply in a phytoplankton community of a high mountain lake is analyzed in a in situ experiment for 6 days with 2 × 2 factorial design. Interactive UVR × nutrient effects on structural and functional variables (algal biomass, chlorophyll a (chl a), primary production (PP), maximal electron transport rate (ETR(max)), and alkaline phosphatase activity (APA)), as well as stoichiometric ones (sestonic N per cell and N:P ratio) were found. Under non-nutrient enriched conditions, no deleterious effects of UVR on structural variables, PP, photosynthetic efficiency and ETR(max) were observed, whereas only particulate and total APA were affected by UVR. However, percentage excreted organic carbon (%EOC), dissolved APA and sestonic C and P per cell increased under UVR, leading to a decrease in algal C:P and N:P ratios. After nutrient enrichment, chl a, total algal biomass and PP were negatively affected by UVR whereas %EOC, ETR(max) and internal C, P and N content increased. We suggest that the mechanism of algal acclimation to UVR in this high UVR flux ecosystem seems to be related to the increase of internal algal P-content mediated by physiological mechanisms to save P and by a stimulatory UVR effect on dissolved extracellular APA. The mechanism involved in the unmasking effect of UVR after nutrient-enrichment may be the result of a greater sensitivity to UVR-induced cell damage, making the negative UVR effects more evident.

Experimental test of phytoplankton competition for nutrients and light in poorly mixed water columns

A recent theory of the vertical distribution of phytoplankton considers how interacting niche construction processes such as resource depletion, behavior, and population dynamics contribute to spatial heterogeneity in the aquatic environment. In poorly mixed water columns with opposing resource gradients of nutrients and light, theory predicts that a species should aggregate at a single depth. This depth of aggregation, or biomass maximum, should change through time due to depletion of available resources. In addition, the depth of the aggregation should be deeper under low amounts of nutrient loading and shallower under higher amounts of nutrient loading. Theory predicts total biomass to exhibit a saturating relationship with nutrient supply. A surface biomass maximum limited by light and a deep biomass maximum limited by nutrients or co‐limited by nutrients and light is also predicted by theory. To test this theory, we used a motile phytoplankton species (Chlamydomonas reinhardtii) growing in cylindrical plankton towers. In our experiment, the resource environment was strongly modified by the movement, self‐shading, nutrient uptake, and growth of the phytoplankton. Supporting predictions, we routinely observed a single biomass maximum at the surface throughout the course of the experiment and at equilibrium under higher nutrient loading. However, at equilibrium, low nutrient loading led to a non‐distinct biomass maximum with the population distributed over most of the water column instead of the distinct subsurface peak predicted by theory. Also supporting predictions, total biomass across water columns was positively related to nutrient supply but saturating at high nutrient supply conditions. Further supporting predictions, we also found evidence of light limitation for a surface biomass maximum and nutrient limitation for the deep biomass when no surface maximum was present. In addition, the light level leaving the bottom of the water column declined through time as the phytoplankton grew and was negatively related to nutrient loading. Nutrients were strongly depleted where biomass was present by the end of the experiment. This experimental study shows that the vertical distribution of phytoplankton may be driven by intraspecific resource competition in space.

Resource availability mediates the importance of priority effects in plant community assembly and ecosystem function

Assembly history, including the order in which species arrive into a community, can influence long‐term community structure; however we know less about how timing of species arrival may alter assembly especially under varying resource conditions. To explore how the timing of species arrival interacts with resource availability to alter community assembly, we constructed experimental plant communities and manipulated the interval between plantings of groups of seedlings (0, 5, 10, 15 or 20 days) at low and high levels of soil nutrient supply. To see if community changes influenced ecosystem‐scale processes, we measured parameters across the plant–soil continuum (e.g. plant biomass and net ecosystem carbon dioxide exchange).We found that the timing of species arrival had a large impact on community assembly, but the size of the effect depended on soil fertility. As planting interval increased, plant communities diverged further from the control, but the divergence was stronger at high than at low nutrient supply. Our data suggest that at high nutrient supply, early‐planted species preempted light resources more quickly, thus preventing the successful establishment of later arriving species even at short planting intervals. Finally, we found that assembly related divergence in plant communities scaled to impact ecosystem‐level characteristics such as green leaf chemistry, but had little effect on total community biomass and net ecosystem exchange of CO2 and water vapor. Our data indicate that the effect of a stochastic factor, here the timing of species arrival on community composition, depends on the resource level under which the community assembles.

Response of Mallorca shelf ecosystems to an early Holocene humid phase

Benthic foraminiferal data as well as stable oxygen and carbon isotope records of different planktonic and benthic foraminifera from a shelf sediment core off southwest Mallorca document major sedimentological, hydrological and trophic changes during the Holocene. The Holocene relative sea-level rise resulted in the progradation of different sediment facies types characterized by specific benthic foraminiferal assemblages. This succession reflects the evolution from an unstable shelf ecosystem with high-energy conditions at the sea-floor in the earlier Holocene to a more stable shelf ecosystem in the middle and late Holocene. Between approximately 10.3 and 5.5 kyr BP, low δ13C values of the surface dweller Globigerinoides ruber (white) and high difference in δ13C values between the epifaunal Cibicides lobatulus and the infaunal Bulimina aculeata document enhanced input of nutrients in surface waters and high remineralization rates at the sea floor. The trophic change is associated with a change in sediment facies and can be attributed to higher precipitation and consequently, higher nutrient supply via riverine runoff from the island, mainly during the late summer/early fall season. This early Holocene humid interval is nearly contemporaneous to the formation of sapropel S1 in the eastern Mediterranean Sea and the African Humid Period. Highlights ► Isotope records and foraminiferal data from the western Mediterranean are presented. ► Benthic shelf ecosystem adaption is related to the Holocene sea-level rise. ► In the early–mid Holocene more humid conditions were established on Mallorca shelf. ► The humid interval is nearly contemporaneous to the sapropel S1 formation. ► Its end is synchronous to the end of the African Humid Period.

Controls on the diversity–productivity relationship in a marine ecosystem model

Species diversity influences the productivity of ecosystems across habitats, and may influence their susceptibility to environmental changes. More diverse communities are often found to be more productive because selection and complementarity effects allow more efficient use of available resources. However, which principles promote coexistence in pelagic model ecosystems is only beginning to be understood as are controls on the diversity–productivity relationship. Here we show that the diversity–productivity relationship of phytoplankton in a global self-assembling ocean ecosystem model depends on the simulated nutrient supply. Increasing productivity with increasing diversity can be found in regions with high nutrient supply. Using a simple idealized model we show that a more diverse community can be more productive if different phytoplankton types utilize complementary niches, here created by preferential zooplankton grazing, thereby increasing resource use. In our model context, total nutrient supply determines a maximum diversity sustained by the ecosystem. Systems with a low nutrient supply cannot sustain high productivity of more diverse communities and produce a neutral or even negative diversity–productivity relationship. Our model results suggest links between diversity, productivity and export production in marine pelagic ecosystems, with the potential for feedbacks of diversity on productivity in response to expected future environmental changes.

Productivity and nutrients use efficiency for cultivar of coffee plant

The optimization of the nutritional efficiency is of great importance to enlarge the productivity, to reduce the production cost and to increase the income of the rural producer. They were appraised four varieties of arabic coffee (Acaia IAC 474-19, Icatu Amarelo IAC 3282, Rubi MG 1192 and Catuai Vermelho IAC 99) as for the productivity of grains, to the agronomic efficiency and of absorption of nutrients. For so much, an experiment was carried out in field conditions whose treatments were distributed in factorial arrangement (4 x 3) x 4, constituted of four varieties, three levels of the fertilization (lower, normal and high) and four repetitions, arranged in randomized blocks. The plants that constituted the normal level received fertilization based in the march of accumulation of nutrients in Arabic coffee. The variety Icatu Amarelo IAC 3282 was the most productive in conditions field with restriction of nutrients, while the varieties Rubi MG 1192 and Catuai Vermelho IAC 99 were shown more productive with high supply of nutrients. With low doses of fertilizers and correctives (low level), the variety Icatu Amarelo IAC 3282 it tended to present the best agronomic efficiency as for all the studied nutrients, and Acaia IAC 474-19 it tended to present the worst ones.

Biopreservation of hamburgers by essential oil of Zataria multiflora

Hamburgers with high nutrient supply and a loosely-packed structure present favourable conditions for microbial growth. In this study, the chemical composition and antimicrobial activity of the essential oil of Zataria multiflora and its potential application as a natural preservative in reducing the indigenous microbial population of hamburgers were investigated. Carvacrol, thymol and linalool were found to be the most abundant constituents of the essential oil using GC-MS analysis. The essential oil exhibited strong antibacterial activity against Gram-positive and Gram-negative bacteria. Addition of Z. multiflora essential oil in concentrations higher than MIC values influenced the microbial population of hamburgers stored at 25°C, 4°C and –12°C. The significant results of this study are our observations that the use of Z. multiflora essential oil at 0.05% v/w increases the time needed for the natural microflora of hamburgers to reach concentrations able to produce a perceivable spoilage at refrigerator and room temperatures without any inverse effect on their sensory attributes. Freezing of essential oil-treated hamburgers may also reduce the risk of diseases associated with consumption of under-cooked hamburgers through significant microbial reduction by more than 3 log.

Tournaisian (Mississippian) brachiopods from the Mobarak Formation, North Iran

ABSTRACTFollowing detailed stratigraphic work on the Mississippian marlstone and bioclastic limestone of the Mobarak Formation of the Alborz Mountains in North Iran, forty-eight of the most important brachiopod taxa are here systematically described and illustrated. The ranges of the taxa are given along the Abrendan and Simeh Kuh stratigraphic sections, located north of Damgham. The examined brachiopod species date the base of the Mobarak Formation to the Tournaisian, in absence of age-diagnostic foraminifers. Change in brachiopod settling preferences indicates a shift from high energy, shallow-water settings with high nutrient supply in the lower part of the formation to quieter, soft, but not soppy substrates, with lower nutrient supply in the middle part of the Mobarak Formation. Brachiopod occurrence is instead scanty at its top. The palaeobiogeographic affinity of the Tournaisian brachiopods from North Iran indicates a closer relationship to North America, Western Europe and the Russian Platform than to cold-water Australian faunas, confirming the affinity of the other biota of the Alborz Mountains. This can be explained by the occurrence of warm surface-current gyres widely distributing brachiopod larvae across the Palaeotethys Ocean, where North Iran as other peri-Gondwanan blocks acted as staging-posts.

Top-down and bottom-up regulation in a high nutrient–high herbivory coastal ecosystem

In this study, carried out in San Antonio Bay (Northern Argentinean Patagonia), we aimed to understand the relative importance of bottom-up and top-down controls on macroalgal blooms in a macrotidal system with high nutrient supply and high consumer abundance. Our results show that nutrients, pH, and O 2 concentrations were higher during low tide. A field experiment showed that the biomass accumulation rate of Ulva lactuca ranged from 6 to 12% d -1 and was reduced by herbivory by 60%. The biomass accumulation rate did not differ in thalli with different initial internal nutrient pools. There was a negative relationship between the percentage of algae consumed and the N content in algal tissues, suggesting compensatory feeding by herbivores. Herbivory reduced the biomass accumulation rate of U. lactuca when PO 4 3- or no nutrients were added, but not when NO 3 - was added. In the absence of herbivory, the addition of nutrients did not increase U. lactuca biomass accumulation rate. These results suggest that nutrients remain high enough for adequate time intervals to be assimilated by macroalgae and support blooms. Large water exchange during tidal changes, however, can diminish the potential negative effects of macroalgal accumulation (oxygen depletion, high ammonium concentrations) on herbivores such that herbivores can have a large impact on macroalgae. © Inter-Research 2011.

Succession in Stream Biofilms is an Environmentally Driven Gradient of Stress Tolerance

The century-long research on succession has bestowed us with a number of theories, but little agreement on what causes species replacements through time. The majority of studies has explored the temporal trends of individual species in plant and much less so in microbial communities, arguing that interspecific interactions, especially competition, play a key role in community organization throughout succession. In this experimental investigation of periphytic succession in re-circulating laboratory streams, we examined the density and the relative abundance of diatoms and soft algae for 35 days across gradients of low to high nutrient supply (nitrogen + phosphorus) and low to intermediate current velocity (10 vs. 30 cm·s(-1)). All algal species were classified into trophic groups and morphological guilds, both of which responded more strongly to nutrient than current velocity manipulations, as shown by regression analyses. We concluded that within the manipulated environmental ranges: (1) Succession was a gradient of stress tolerance, driven primarily by nutrient supply and secondarily, by current velocity. Nutrient supply had a qualitative effect in determining whether the contribution of species tolerant vs. sensitive to nutrient limitation would increase through time, while current velocity had a quantitative influence and affected only the rate of this increase. (2) The mechanism of algal succession at a functional level was a neutral coexistence, whereby the tolerant low profile guild maintained high density when overgrown by sensitive species, while sensitive species, constituting mostly the motile and high profile guilds, were neither facilitated nor inhibited by tolerant species but controlled by the environment. It is suggested that the mechanism of succession may depend on the level of biological organization with interspecific interactions giving way to neutral coexistence along the hierarchy from species to functional groups. Considering that the functional makeup is strictly environmentally defined, while species composition reflects local and regional species pools that may exhibit substantial geographic variability, succession is deterministic at a functional level but stochastic at a species level.

Juvenile–mature genetic correlations in Pinus radiata D. Don. under different nutrient × water regimes in Spain

Individual and family heritabilities and juve- nile-mature genetic correlations were estimated for growth and biomass traits recorded in treatment with optimal and limiting water and/or nutrient availability to study how the different growth environments affected genetic parameter estimates. Thirty open-pollinated families, randomly selected among the 58 families used in field progeny tests in Galicia, were cultivated for 30 weeks in a climatic chamber under controlled conditions. Two water regimes (high and low water supply) combined with two nutrient regimes (high and low nutrient supply) were applied by subirrigation. Several growth, branching and dry mass traits were assessed 30 weeks after sowing and compared with field performance (height, diameter and volume) of 4-year-old progeny tests established at three different sites in Galicia (NW Spain). Both the irrigation and the fertil- ization treatments had a strong effect in all the assessed traits except irrigation for the number of branches. Herit- abilities for growth and biomass traits were moderate to high (0.13-0.77) in individual treatments. However, when analyzing all treatments together, the impact of the family 9 treatment interactions led to a reduction (0.20-0.35) in the heritability estimates. The results indi- cated that the genotype 9 water and genotype 9 nutrient interactions may be important and could not be ignored in the Galician radiata pine breeding program. Climatic chamber-field correlations were different between different traits measured at climatic chamber experiments and the three field tests. The correlations were larger with the well- watered treatments, suggesting that further development of early testing methods for radiata pine in Galicia should include treatments with no limiting water availability.

Distinctive types of leaf tissue damage influence nutrient supply to growing tissues within seagrass shoots

Herbivory is now recognized as an important structuring agent in seagrass meadows but the attack pattern and tissue damage of consumers are highly variable. Nutritional preferences of herbivores and/or easy access to resources may cause differences in biomass loss among tissues that damage the plant in functionally distinctive ways. The two main Mediterranean herbivores, the fish Sarpa salpa (L.) and the sea urchin Paracentrotus lividus (Lmk.), remove higher amounts of intermediate and external shoot leaves, respectively. To test whether this selective feeding can have different consequences on the allocation patterns of nutrient within plants, we simulated the effect of both herbivores by clipping external and intermediate leaves (plus unclipped controls) of Posidonia oceanica (L.) and we measured plant tolerance in terms of shoot growth and leaf nutrient supply to new tissue using isotopic markers. As expected, control treatments displayed high carbon and nutrient supply from external leaves (83% of the total 15N and 84% of the total 13C incorporated by the shoot). When subjected to clipping, the remaining leaves enhanced carbon and nitrogen supply compared with the control by 16% of N and 36% of C—in the intermediate clipping—and by over 100% of N and 200% of C—in the external clipping—to compensate for the nutrient lost. However, only in the case of fish herbivory (intermediate clipping), enhanced supply alone was able to fully compensate for the nutrient losses. In contrast, this mechanism is not completely effective when external leaves are clipped (urchin herbivory). Yet, the consequences of this nutrient loss under sea urchin herbivory are not apparent from the nutrient content of the new tissue, suggesting that there are other sources of nitrogen income (uptake or reallocation from rhizomes). Our study does not only confirm the tolerance of P. oceanica to herbivory, but also constitutes the first evidence of leaf-specific, compensatory nutrient supply in seagrasses.

Improving the aeration of critical fine-grained landfill top cover material by vegetation to increase the microbial methane oxidation efficiency

The natural methane oxidation potential of methanotrophic bacteria in landfill top covers is a sustainable and inexpensive method to reduce methane emissions to the atmosphere. Basically, the activity of methanotrophic bacteria is limited by the availability of oxygen in the soil. A column study was carried out to determine whether and to what extent vegetation can improve soil aeration and maintain the methane oxidation process. Tested soils were clayey silt and mature compost. The first soil is critical in light of surface crusting due to vertical erosion of an integral part of fine-grained material, blocking pores required for the gas exchange. The second soil, mature compost, is known for its good methane oxidation characteristics, due to high air-filled porosity, favorable water retention capacity and high nutrient supply. The assortment of plants consisted of a grass mixture, Canadian goldenrod and a mixture of leguminous plants. The compost offered an excellent methane oxidation potential of 100% up to a CH 4-input of 5.6 l CH 4 m −2 h −1. Whereas the oxidation potential was strongly diminished in the bare control column filled with clayey silt even at low CH 4-loads. By contrast the planted clayey silt showed an increased methane oxidation potential compared to the bare column. The spreading root system forms secondary macro-pores, and hence amplifies the air diffusivity and sustain the oxygen supply to the methanotrophic bacteria. Water is produced during methane oxidation, causing leachate. Vegetation reduces the leachate by evapotranspiration. Furthermore, leguminous plants support the enrichment of soil with nitrogen compounds and thus improving the methane oxidation process. In conclusion, vegetation is relevant for the increase of oxygen diffusion into the soil and subsequently enhances effective methane oxidation in landfill cover soils.

Decomposition and nutrient release patterns of the leaf biomass of the wild sunflower (Tithonia diversifolia): a comparative study with four leguminous agroforestry species

The selection and use of appropriate plant materials to maintain a sufficiently high nutrient supply to meet crop needs remains a major challenge of nutrient management under low input systems. Therefore, research on plant biomass quality as it relates to decomposition and nutrient release has become imperative. This research was conducted at the Agroforestry Research Station of the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana to determine the decomposition and nutrient release patterns of Tithonia diversifolia, a rarely used non-traditional species but of research interest in soil fertility improvement practices in Ghana. The decomposition and nutrient release patterns of T. diversifolia was compared with Sennaspectabilis, Gliricidia sepium, Leucaena leucocephala and Acacia auriculiformis which are commonly used in biomass transfer systems. Results of the study confirmed significantly high N, P, K concentrations in T. diversifolia comparable to levels recorded for the four leguminous species. In addition, T. diversifolia recorded the highest percent decomposition and nutrient release rates which differed significantly (P < 0.05) from rates of the four leguminous species. It was apparent from the study that decomposition and nutrient release rates of species are related to quality of leaf material. Phosphorus and Mg concentration in particular were most influential in decomposition and nutrient release based on significant results. For this reason, it would be imperative to consider the concentrations of P and Mg among other factors in selecting high quality plant materials for green manuring.

How do nutrient conditions and species identity influence the impact of mesograzers in eelgrass-epiphyte systems?

Coastal eutrophication is thought to cause excessive growth of epiphytes in eelgrass beds, threatening the health and survival of these ecologically and economically valuable ecosystems worldwide. Mesograzers, small crustacean and gastropod grazers, have the potential to prevent seagrass loss by grazing preferentially and efficiently on epiphytes. We tested the impact of three mesograzers on epiphyte biomass and eelgrass productivity under threefold enriched nutrient concentrations in experimental indoor mesocosm systems under summer conditions. We compared the results with earlier identical experiments that were performed under ambient nutrient supply. The isopod Idotea baltica, the periwinkle Littorina littorea, and the small gastropod Rissoa membranacea significantly reduced epiphyte load under high nutrient supply with Rissoa being the most efficient grazer, but only high densities of Littorina and Rissoa had a significant positive effect on eelgrass productivity. Although all mesograzers increased epiphyte ingestion with higher nutrient load, most likely as a functional response to the quantitatively and qualitatively better food supply, the promotion of eelgrass growth by Idotea and Rissoa was diminished compared to the study performed under ambient nutrient supply. Littorina maintained the level of its positive impact on eelgrass productivity regardless of nutrient concentrations.

Effect of nutrient supply on photosynthesis and pigmentation to short-term stress (UV radiation) in Gracilaria conferta (Rhodophyta)

The effects of increased photosynthetic active radiation (PAR), UV radiation (UVR), and nutrient supply on photosynthetic activity, pigment content, C:N ratio and biomass yield were studied in tank cultivated Gracilaria conferta (Rhodophyta). Electron transport rate (ETR) and biliprotein content were higher under high nutrient supply (HNS), obtained from fishpond effluents, compared to low nutrient supply (LNS), in contrast to mycosporine-like amino acids (MAAs) dynamic. The high MAA content in LNS-algae could be explained by higher UVR penetration in the thallus and by the competition for the use of nutrients with other processes. Effective quantum yield decreased after short-term exposure to high irradiance whereas full recovery in shade was produced only under slightly heat shock. UVA radiation provoked an additional decrease in photosynthesis under high water temperature. UVB radiation reversed UVA’s negative effect mainly with HNS. Results support that nutrient-sufficiency help G. conferta to resist environmental changes as short-term temperature increase.