Higher Relative Growth Rate Research Articles

Effects of defoliation by Eucalyptus weevil, Gonipterus scutellatus, and chrysomelid beetles on growth of Eucalyptus globulus in southwestern Australia

Plantations of Eucalyptus globulus in southwestern Australia are defoliated by Eucalyptus weevil, Gonipterus scutellatus, and a complex of chrysomelid and scarab beetles, yet there is no information on the impact of beetle defoliation to tree growth in southwestern Australia. To address this shortcoming, we used insect exclusion trials, to compare growth of insecticide treated (and thus relatively undamaged) trees with untreated (and thus defoliated) trees to determine whether defoliation by G. scutellatus and other beetles reduced the growth and harvest volume of E. globulus trees. Our results showed some evidence of beetle defoliation reducing growth of E. globulus. Mean defoliation levels of the growing tip of untreated trees ranged from 18% to 33% across the duration of the study and were significantly greater than mean defoliation levels of 5–16% on insecticide treated trees. Seasonal peaks in defoliation of 30–80% to the growing tip of untreated trees were recorded between late spring and early autumn. The greatest impact of defoliation on tree growth was evident during the 2.5 year period of insect exclusion, when higher relative growth rates were recorded for insecticide treated trees, which were significantly different from relative growth rates of untreated trees at two of the four plantations. However, our results showed only a limited impact of beetle defoliation on the total volume at harvest. Initially small trees tended to suffer more severe defoliation than initially large trees. Effects of insect exclusion treatment on harvest volume were modified by the initial tree size and the relationship between the initial tree size and levels of defoliation.

Linkages of plant traits to soil properties and the functioning of temperate grassland

Summary 1. Global change is likely to alter plant community structure, with consequences for the structure and functioning of the below‐ground community and potential feedbacks to climate change. Understanding the mechanisms behind these plant–soil interactions and feedbacks to the Earth‐system is therefore crucial. One approach to understanding such mechanisms is to use plant traits as predictors of functioning. 2. We used a field‐based monoculture experiment involving nine grassland species that had been growing on the same base soil for 7 years to test whether leaf, litter and root traits associated with different plant growth strategies can be linked to an extensive range of soil properties relevant to carbon, nitrogen and phosphorus cycling. Soil properties included the biomass and structure of the soil microbial community, soil nutrients, soil microclimate and soil process rates. 3. Plant species with a high relative growth rate (RGR) were associated with high leaf and litter quality (e.g. low toughness, high nitrogen concentrations), an elevated biomass of bacteria relative to fungi in soil, high rates of soil nitrogen mineralization and concentrations of extractable inorganic nitrogen, and to some extent higher available phosphorus pools. 4. In contrast to current theory, species with a high RGR and litter quality were associated with soils with a lower rate of soil respiration and slow decomposition rates. This indicates that predicting processes that influence carbon cycling from plant traits may be more complex than predicting processes that influence nitrogen and phosphorus cycling. 5. Root traits did not show strong relationships to RGR, leaf or litter traits, but were strongly correlated with several soil properties, particularly the biomass of bacteria relative to fungi in soil and measures relating to soil carbon cycling. 6. Synthesis. Our results indicate that plant species from a single habitat can result in significant divergence in soil properties and functioning when grown in monoculture, and that many of these changes are strongly and predictably linked to variation in plant traits associated with different growth strategies. Traits therefore have the potential to be a powerful tool for understanding the mechanisms behind plant–soil interactions and ecosystem functioning, and for predicting how changes in plant species composition associated with global change will feedback to the Earth‐system.

Dense crowns of the hemiparasitic mistletoe Viscum album L. exhibit shrub-like growth and high dry matter turnover

Growth characteristics and crown parameters of the evergreen, hemiparasitic mistletoe Viscum album were studied using a growth model based on the regular dichotomous growth and conservancy of branching patterns. Data were collected from one final harvest of 13 individuals of three different subspecies growing on the hosts Betula pendula, Abies alba and Pinus sylvestris. Compared to Viscum album ssp. album growing on deciduous hosts, the two subspecies abietis and austriacum (syn. laxum) on evergreen hosts showed longer average leaf life spans, but leaves continuously increased in area over time up to an age of at least 4 years irrespective of host. Relative growth rates in plant dry matter (RGR; 0.53–0.61 g g −1 a −1) were in the same range as of deciduous shrubs in central Europe but clearly higher than in mature forest trees. However, this growth is hidden within the spherical crowns of mistletoes, as annual increase in crown volume is extraordinarily low, resulting in very high leaf area densities (LAD; 7.7–17.6 m 2 m −3), not found in any other woody species. Besides differences in leaf size and phenology, the three subspecies exhibit similar patterns of partitioning. As in other mistletoe species, significant parts of dry matter are regularly allocated into fruit production (10–15%). Regarding the generally lower net photosynthesis rates in mistletoes as compared to their hosts, it is questioned, whether photoautotrophic carbon gain of the leaves is sufficient to maintain the observed high relative growth rates.

Adaptability of four cassava (Manihot esculenta crantz) cultivars in swampy inland valley ecology

Cassava is a popular dry season crop grown to utilize residual soil moisture in inland valleys. Trials to evaluate growth rates of four cultivars (TMS 4(2) 1425, TMS 91/02324, TMS 91/02327 and Isunikankiyan) were conducted along the toposequence in a 4 x 4 Latin square design. Effects of toposequence position, site, year and their interactions as well as of cultivar were significant for Leaf area index (LAI), net assimilation rate (NAR), crop growth rate (CGR), tuberous root bulking rate (TRBR), relative growth rate (RGR) and root yield. LAI, NAR, CGR, TRBR and RGR correlated positively with yield. TMS 91/02324 and TMS 91/02327 with the highest growth indices produced the highest yields. The deep water table site at Alabata had the highest growth indices and yield in valley bottom and the lowest in the fringe, while the shallow water table site at Ibadan recorded higher yield and growth indices in the fringe than the other positions. The shallowest water table depths at Ibadan and Alabata were and below mound surface in valley bottom and fringe, respectively. Valley fringe at Ibadan and valley bottom at Alabata had similar water table depth and they produced the highest growth indices and yield. Shallow water table of below mound surface reduced LAI, TRBR, CGR, RGR and yield, but increased NAR. Drought stress and high radiation, temperature andevaporation reduced yield and growth indices, while well distributed rainfall increased them. Cassava cultivars with high root yields in swampy inland valley are early maturing and maintain high LAI, TRBR, CGR, RGR and NAR under excess soil moisture and drought stress. Keywords: Growth indices, Cassava cultivars, Root yield, Groundwater table depth, Inland valley ecology, Drought stress

Effects of temperature and irradiance on early development of Chondrus ocellatus Holm (Gigartinaceae, Rhodophyta)

Chondrus is a type of commercially produced red seaweed that widely used for food and carrageen extraction. Although the natural life history of the alga had been well understood, the factors influencing development of the tetraspore and carpospore remain poorly understood. In the perspective of seedling resources, the regulation of early development is crucial for the seedling nursing; therefore, it is necessary to understand the physiological influences during its early development. In this study, we studied the effects of temperature and irradiance on the early development of Chondrus ocellatus Holm under laboratory conditions. The released tetraspores and carpospores were cultivated at different temperatures (10-28 degrees C) and irradiances ( 10, 60 mu mol photons m(-2)s(-1)) with a photoperiod of 12L:12D. The results indicate that both tetraspores and carpospores are tolerant to temperatures of 10-25 degrees C, and have the highest relative growth rate at 20 degrees C. Irradiance variances influenced the growth of the discoid crusts, and the influence was more significant with increasing temperature; 60 mu mol photons m(-2)s(-1) was more suitable than 10 mu mol photons m(-2)s(-1). The optimum temperature and irradiance for the development of seedlings was 20 degrees C and 60 mu mol photons m(-2)s(-1), respectively.

Growth patterns of Chromolaena odorata in varied ecosystems at Kodayar in the Western Ghats, India

The growth and allocation patterns of biomass and nutrients (nitrogen, phosphorus and potassium) were studied in Chromolaena odorata populations grown in different human modified ecosystems including an Albizia plantation, a rubber plantation, community land and a naturally regenerating forest. The greater shoot length of C. odorata in the regenerating forest could be attributed to the competitive and shady environment created by the mature vegetation here. High relative growth rate, net assimilation rate and reproductive potential of C. odorata populations growing on the community land and in the rubber plantation may be due to the open habitat and frequent disturbances to these sites. In general, allocation of biomass and nutrients to the leaf and reproductive components was low in the regenerating forest. On the other hand, greater allocation to the root component in the regenerating forest may be a strategy for survival and regeneration after the disturbance. Low nutrient uptake and greater resource use efficiency in the regenerating forest could be a response to limited resource availability under the competitive micro-environment created by the fast growing tree species. C. odorata has an exploitative growth strategy and will persist in regenerating open habitats whereas it showed suppressed growth in the light – limited shaded environment.

Does water hyacinth ( Eichhornia crassipes) compensate for simulated defoliation? Implications for effective biocontrol

Biocontrol agents of water hyacinth ( Eichhornia crassipes), one of the most ubiquitous invasive aquatic species in the world, were introduced in the waterways of Florida, USA, more than 30 years ago but have not been as successful as expected. The high nutrient, high light, warm year-round temperatures and lack of natural predators provide an optimal growth environment for the plant. The current study was designed to test if a compensatory response by the water hyacinth plants to low levels of biomass removal was one of the reasons for the ineffectiveness of biocontrol agents in the successful control of water hyacinth. The plants were exposed to two levels of nutrient (high and low) and three levels (0%, 10% and 80%) of simulated herbivory treatment. The effect of the nutrient and repeated (i.e., chronic) defoliation treatments was determined after 6 weeks. Plants with 10% defoliation did not show any significant difference from control plants in biomass allocation or relative growth rate (RGR) in either nutrient concentration, while 80% defoliation caused a significant decrease in the final RGR under high and low nutrient treatments. High nutrient treatment resulted in higher RGR and allocation to asexual reproduction resulting in higher biomass accumulation compared to the low nutrient treatment, which had higher root growth and allocation to sexual reproduction. Results from this study indicate that water hyacinth can fully compensate for low levels of continuous defoliation regardless of the nutrient concentration, which has implications and important considerations for biocontrol strategies.

Fire Effects on Demography of the Invasive Shrub Brazilian Pepper (Schinus terebinthifolius) in Florida Pine Savannas

Fire is a common disturbance in savanna ecosystems that may either facilitate or impede non-native plant invasions. Although fire can create recruitment opportunities for non-native plants, it can also prevent their invasion if it exerts strong negative effects on their demographic processes. Some savannas may, therefore, be able to resist invasion provided the natural, frequent-fire regime remains intact. We examined the effects of fire on the demography of the invasive shrub Brazilian pepper, Schinus terebinthifolius Raddi., which is invading fire-prone slash pine savannas of southern Florida. We studied survivorship, growth, and reproduction of low-density populations of Brazilian pepper in a pine savanna within Everglades National Park to investigate whether fire might suppress Brazilian pepper in the early stages of invasion. We found a significant decrease in Brazilian pepper survivorship following fire, particularly among small individuals. We further found that fire reduced fecundity of surviving Brazilian pepper individuals for at least two years. However, resprouting individuals that survived fire had high relative growth rates the following year, which could facilitate population recovery during inter-fire periods. We used a simple population simulation to show that a low-density cohort of Brazilian pepper may be rapidly eliminated from pine savannas with fire-return intervals of four years or less, but individuals may persist for > 50 years with fire-return intervals of eight years or more. Our study suggests the need to maintain the historical frequent-fire regime in pine savannas in order to prevent their invasion by fire-intolerant shrubs such as Brazilian pepper.

Growth morphology of α-glycine crystals in solution environments: an extended interface structure analysis

Prediction of the morphology of organic crystals is a key first step in controlling crystal growth in chemical and pharmaceutical industries. Here, we predict the growth morphology and the relative growth rate of the morphologically important (010) and (011) faces of glycine crystals in aqueous solutions by fully accounting for the effects of solvent. Molecular dynamics simulations were used to obtain the relevant solvent-dependent properties such as the concentration of adsorbed growth units on the (010) and (011) faces and the amount of adsorbed growth units relative to the solute in the solution and are used along with molecular level crystallographic properties such as interplanar distance and crystallographic factor in newly developed “extended interface structure analysis” to determine the relative growth rates and morphology. We observe that the growth rate of the (011) face is 2.88 times greater than that of (010) face, consistent with experimental observations, in contrast to the much higher relative growth rates (4 to 7) predicted by attachment energy calculations in the literature in the absence of solvent. We show that the polar group present on the (011) face has stronger interactions with the solvent and reduces the growth rate, thereby underscoring the importance of the need to incorporate solvent effects in crystal growth analysis. Our prediction of the growth morphology is also consistent with experimental observations. Overall, the approach presented paves the way for exploring the effects of other solvents and impurities on the kinetics and the morphology of crystal growth.

Eco-physiological responses of nitrogen-fixing cyanobacteria to light

The eco-physiological responses of three nitrogen-fixing cyanobacteria (N-fixing cyanobacteria), Aphanizomenon gracile, Anabaena minderi, and Ana. torques-reginae, to light were assessed under nutrient saturation. The N-fixing cyanobacteria were isolated into monocultures from a natural bloom in a shallow colored lake and their growth irradiance parameters and pigment composition were assessed. The different ecological traits related to light use (μmax, α, I k) suggest that these N-fixing cyanobacteria are well adapted to low light conditions at sufficient nutrients, yet interspecific differences were observed. Aphanizomenon gracile and Anabaena minderi had high relative growth rates at low irradiances (ca. 70% of those in high light), low half saturation constant for light-limited growth (I k < 9.09 μmol photon m−2 s−1) and high efficiency (α < 0.11 day−1 μmol photon−1 m2 s). Conversely, Ana. torques-reginae showed poorer light competitiveness: low relative growth rates at low irradiances (ca. 40% of those in high light), low α (0.009 day−1 μmol photon−1 m2 s) and higher I k (35.5 μmol photon m−2 s−1). Final densities in Aphanizomenon gracile and Anabaena minderi reached bloom densities at irradiances above 30 μmol photon m−2 s−1 with different hierarchy depending on irradiance, whereas Ana. torques-reginae never achieved bloom densities. All species had very low densities at irradiances ≤17 μmol photon m−2 s−1, thus no N-fixing blooms would be expected at these irradiances. Also, under prolonged darkness and at lowest irradiance (0 and 3 μmol photon m−2 s−1) akinetes were degraded, suggesting that in ecosystems with permanently dark sediments, the prevalence of N-fixing cyanobacteria should not be favored. All species displayed peaks of phycocyanin, but no phycoeritrin, probably due to the prevailing red light in the ecosystem from which they were isolated.

Seawater Stress Differentially Affects Germination, Growth, Photosynthesis, and Ion Concentration in Genotypes of Jerusalem Artichoke (Helianthus tuberosus L.)

Two Jerusalem artichoke (Helianthus tuberosus L.) genotypes, NY-1 and NY-7, were subjected to different seawater concentrations (0, 10, 20, 30, 40, and 50%) for various periods of time to determine the effects on seedling growth, ion content, and photosynthetic productivity in a greenhouse. Under different seawater concentrations, sprouting rates varied greatly among the genotypes. The differences in relative growth rate (RGR), leaf chlorophyll content, total leaf area (TLA), plant dry weight (PDW), photosynthetic rate (A), stomatal conductance (g s), and efficiency of the light harvesting of photosystem II (F v ′ /F m ′ ) were significant between NY-1 and NY-7 after 12 days of stress at 40 and 50% seawater. Seawater treatments resulted in the reduction of almost all the growth parameters and coincident increases of Na+ and Ca2+ concentrations in plant tissues. Our results indicate that there is great variability for seawater tolerance among H. tuberosus varieties, and that greater photosynthesis capacity, higher RGR, and relatively higher tissue Na+ accumulation at high seawater concentrations appears to be associated with seawater tolerance in H. tuberosus varieties.

Growth of marandu palisadegrass subjected to strategies of intermittent stocking

Grazing strategies alter sward leaf area patterns of growth, affecting herbage accumulation and utilisation. The objective of this experiment was to evaluate the growth of marandu palisadegrass (Brachiaria brizantha cv. Marandu) swards subjected to strategies of intermittent stocking. The experiment was carried out in Piracicaba, São Paulo, Brazil, from October/2004 to September/2005. Swards were grazed at 95 and 100% canopy light interception (LI) to post-grazing heights of 10 and 15 cm, following a 2 × 2 factorial arrangement with four replications in a randomised complete block design. The response variables evaluated were: crop growth rate, relative growth rate, net assimilation rate, leaf area ratio and leaf weight ratio. In early and late spring, the highest crop growth rate was recorded for treatment 95/15 (11.2 and 10.1 g m-2 day-1, respectively), along with high values of net assimilation rate (4.4 and 6.9 g m-2 day-1, respectively), leaf area ratio (0.0095 and 0.0103 m-2 g-1, respectively) and leaf weight ratio (0.56 and 0.56 g g-1, respectively). To compensate reductions in net assimilation rate plants made some morphological and physiological adjustments increasing leaf area and leaf weight ratio. Relative growth rate and net assimilation rate were 26 and 50% higher, respectively, on swards grazed at 95% than at 100% LI. In early spring treatments 100/10 and 95/15 resulted in the highest relative growth rate (0.086 and 0.059 g m-2 day-1, respectively). Treatment 95/15 resulted in the most favourable pattern of growth (crop growth rate, relative growth rate, net assimilation rate), particularly during the transition period between winter and spring.

Elevated CO 2 accelerates net assimilation rate and enhance growth of dominant shrub species in a sand dune in central Inner Mongolia

It has been reported that elevated CO 2 can enhance plant growth and water use, and that desert plants in particular will show the strongest response to rising atmospheric CO 2 due to the strong water stress on these plants. In this study experiments were conducted to understand the responses of seedlings from four species, which are dominant in different successional stages in the semi-arid sandy grassland of central Inner Mongolia, to rising temperature and elevated CO 2. Seedlings of the four species were grown for 8 weeks at two air temperatures and two CO 2 concentration regimes in growth chambers. It was found that for the two Artemisia species and Hedysarum laeve elevated CO 2 level resulted in increased relative growth rates (RGR) (6–12%), height increments (24–106%), net assimilation rates (20–45%) and water use efficiencies (WUE) (43–105%), and decreased transpiration (16–55%). For Caragana korshinskii, the elevated CO 2 significantly increased the ratio of below ground to above ground biomass (16–23%), height increment (31–65%) and WUE (79–84%). At elevated CO 2 level and the higher temperature, the two Artemisia species showed decreased RGR and height increments, while for, C. korshinskii and H. laeve increased RGR and height increments were observed. For A. sphaerocephala the higher temperature also resulted in increased WUE, but decreased WUE for the other three species. Obvious differences were observed between the two Artemisia species and C. korshinskii, with the Artemisia species characterized by higher RGR, lower ratio of below ground to above ground biomass and lower WUE. These findings should be applicable to similar shrub species located in other arid and semi-arid environments.

HYDROPONIC CUCUMBER PRODUCTION USING A NEW RECYCLABLE GROWTH SUBSTRATE AND IRRIGATION SYSTEM

In the Canadian vegetable greenhouse industry, the traditional soilless substrate used in hydroponic production systems is costly to recycle and is undesirable as landfill. After more than five years of research and development, SRI Inc. in collaboration with the University of Guelph (UoG) has developed a system that incorporates a synthetic growth substrate with an internal irrigation system. This product is known as the Enviro-Grow System (EGS) and can be recycled at the end of its lifecycle using conventional recycling technologies (similar to recycling a plastic bottle). During spring 2008, we conducted a large scale cucumber production experiment comparing the EGS vs. conventional rockwool (RW). Plant development and yield were evaluated at a commercial hydroponic greenhouse facility located in the Niagara Region of Ontario, Canada. Each substrate treatment (the EGS and RW) contained 2,310 linear meters of substrate and 6,720 cucumber (Cucumis sativus 'Camaro') plants for comparison. Irrigation scheduling for both substrate treatments were determined by solar radiation accumulation and plant demand. Plants grown using the EGS exhibited a significantly higher relative growth rate (RGR) than plants grown in RW. This resulted in an earlier harvest date (by one day). No difference in yield was found between plants grown in the EGS vs. plants grown in RW.

Growth and photosynthesis of four invasive aquatic plant species in Europe

Summary Crassula helmsii, Hydrocotyle ranunculoides, Ludwigia grandiflora and Myriophyllum aquaticum are four well known invasive aquatic plants in European waters. In this study, plant growth at different nutrient availabilities, regeneration capacity and photosynthesis were investigated. Results show high relative growth rates (RGR) of the species of up to 0.132 ± 0.008 g g−1 dry weight (dw) day−1 (H. ranunculoides) and a significant increase in RGR with increasing nutrient availability. All species show a high regeneration capacity and the ability to form new shoots from single nodes, even though it differs between the species. Ludwigia grandiflora and M. aquaticum also show regeneration from single leaves. Species differed in maximal amounts, and in temperature and light optima of net assimilation rates: H. ranunculoides leaves reach maximum photosynthetic rates of up to 3500 μmol CO2 × h−1 g−1 dw, L. grandiflora (leaves) up to 2200 μmol CO2 × h−1 g−1 dw, M. aquaticum (shoots) 400 μmol CO2 × h−1 g−1 dw and C. helmsii (shoots) up to 200 μmol CO2 × h−1 g−1 dw. Hydrocotyle ranunculoides, L. grandiflora and M. aquaticum preferred high light intensity and high temperatures, whilst C. helmsii was negatively affected by intense sunlight. Summarising, it can be assumed that at least H. ranunculoides, L. grandiflora and M. aquaticum can grow well under current and likely future central European climate conditions.

Dissecting iron deficiency‐induced proton extrusion in Arabidopsis roots

Here, we have analysed the H(+)-ATPase-mediated extrusion of protons across the plasma membrane (PM) of rhizodermic cells, a process that is inducible by iron (Fe) deficiency and thought to serve in the mobilization of sparingly soluble Fe sources. The induction and function of Fe-responsive PM H(+)-ATPases in Arabidopsis roots was investigated by gene expression analysis and by using mutants defective in the expression or function of one of the isogenes. In addition, the expression of the most responsive isogenes was investigated in natural Arabidopsis accessions that have been selected for their in vivo proton extrusion activity. Our data suggest that the rhizosphere acidification in response to Fe deficiency is chiefly mediated by AHA2, while AHA1 functions as a housekeeping isoform. The aha7 knock-out mutant plants showed a reduced frequency of root hairs, suggesting an involvement of AHA7 in the differentiation of rhizodermic cells. Acidification capacity varied among Arabidopsis accessions and was associated with a high induction of AHA2 and IRT1, a high relative growth rate and a shoot-root ratio that was unaffected by the external Fe supply. An effective regulation of the Fe-responsive genes and a stable shoot-root ratio may represent important characteristics for the Fe uptake efficiency.

Environmental change controls postglacial forest dynamics through interspecific differences in life‐history traits

A key goal of functional ecology is identifying relationships between species traits and environmental conditions. Here, the nature and significance of these relationships to community composition on long ecological timescales is investigated using paleoecological and paleoenvironmental data from coastal British Columbia, Canada. RLQ and fourth-corner analyses, two three-table statistical techniques, are used to link traits of the region's dominant woody plants to environmental conditions over the last 15 000 calendar years (cal yr) through a fossil pollen record derived from lake sediments. Both RLQ and fourth-corner analyses revealed highly significant correlations between plant traits and temporal changes in environmental conditions. Axis 1 of the RLQ explained 92% of the total covariance between plant species traits and paleoenvironmental variables and was correlated most strongly with temperature and relative growth rate. In general, climate change during the cold period following deglaciation favored species such as Alnus sinuata and Pinus contorta that exhibit a "fast" life-history strategy (e.g., high relative growth rate, short life span, low shade tolerance), whereas the relative climatic stability of the last 8000 cal yr favored species such as Tsuga heterophylla that exhibit a "slow" life-history strategy (e.g., low relative growth rate, long life span, high shade tolerance). Fourth-corner analyses revealed significant correlations between all paleoenvironmental variables (i.e., temperature, precipitation, summer insolation, vegetation density) and most plant traits (relative growth rate, minimum seed-bearing age, seed mass, height, life span, and shade, drought, and waterlogging tolerances). The strongest correlation was between paleotemperature and height, reflecting the positive effect of temperature on plant growth and development and the overarching competitive advantage that height confers. This research demonstrates that environmental conditions interact significantly with life-history and stress tolerance traits over long ecological timescales to determine forest composition. Climate is the ultimate control on postglacial forest composition and species abundances, but long-term community assembly is also constrained through interspecific differences in plant traits.

Growth responses of the perennial legume Sesbania sesban to NH 4 and NO 3 nutrition and effects on root nodulation

Preference for NH 4 + or NO 3 − nutrition by the perennial legume Sesbania sesban (L.) Merr. was assessed by supplying plants with NH 4 + and NO 3 − alone or mixed at equal concentrations (0.5 mM) in hydroponic culture. In addition, growth responses of S. sesban to NH 4 + and NO 3 − nutrition and the effects on root nodulation and nutrient and mineral composition of the plant tissues were evaluated in a hydroponic setup at a range of external concentration of NH 4 + and NO 3 − (0, 0.1, 0.2, 0.5, 2 and 5 mM). Seedlings of S. sesban grew equally well when supplied with either NH 4 + or NO 3 − alone or mixed and had high relative growth rates (RGRs) ranging between 0.19 and 0.21 d −1. When larger plants of S. sesban were supplied with NH 4 + or NO 3 − alone, the RGRs and shoot elongation rates were not affected by the external concentration of inorganic N. At external N concentrations up to 0.5 mM nodulation occurred and contributed to the N nutrition through fixation of gaseous N 2 from the atmosphere. For both NH 4 + and NO 3 −-fed plants the N concentration in the plant tissues, particularly water-extractable NO 3 −, increased at high supply concentrations, and concentrations of mineral cations generally decreased. It is concluded that S. sesban can grow without an external inorganic N supply by fixing atmospheric N 2 gas via root nodules. Also, S. sesban grows well on both NH 4 + and NO 3 − as the external N source and the plant can tolerate relatively high concentrations of NH 4 +. This wide ecological amplitude concerning N nutrition makes S. sesban very useful as a N 2-fixing fallow crop in N deficient areas and also a candidate species for use in constructed wetland systems for the treatment of NH 4 + rich waters.

Deltamethrin‐induced feeding plasticity in pyrethroid‐susceptible and ‐resistant strains of the maize weevil, Sitophilus zeamais

AbstractPhenotypic plasticity contributes to the adaptative evolution of populations exposed to new or altered environments. Feeding plasticity is a component of phenotypic plasticity not usually considered in insect strains adapted to insecticide‐altered environments, but which may either accentuate or mitigate insecticide resistance. This is a concern in the pyrethroid‐resistant strains of the maize weevil Sitophilus zeamais Motsch. (Col., Curculionidae), and the reason for this study. A pyrethroid‐susceptible and two pyrethroid‐resistant strains of maize weevil were subjected to free‐choice and no‐choice tests with maize grains sprayed with increasing doses of the pyrethroid, deltamethrin. The insects from the pyrethroid‐resistant strains exhibited higher feeding avoidance with increased deltamethrin doses than insects from the susceptible strain when subjected to free‐choice tests. The strains of maize weevil physiologically resistant to pyrethroids were also behaviourally resistant to deltamethrin – an additional management concern. The resistant strains avoid deltamethrin‐sprayed grains and are less nutritionally affected by this compound, with divergent responses from the susceptible strain with increased doses of deltamethrin. Furthermore, the higher relative growth rate and consequently higher efficiency of food conversion observed in the insecticide‐resistant strains were significant even without insecticide exposure, indicating that these traits are stimulus‐independent and may persist even without further insecticide selection, potentially limiting the options available for their management.

Influence of major genes for crested-head, frizzle-feather and naked-neck on body weights and growth patterns of indigenous chickens reared intensively in Kenya

The influence of major genes for crested-head (Cr), frizzle-feather (Fr) and naked-neck (Na) on body weights and growth patterns of indigenous chickens reared intensively was investigated and compared with normal-feather (na) gene. Birds were individually weighed at hatch and every two weeks up to 30 weeks of age. Growth patterns were modelled using the Gompertz-Laird function. The genes influenced body weights and growth patterns at various ages. The Cr gene had significant (P < 0.05) negative effects on body weights (between 52.2 g and 112.3 g) from 18 weeks onwards and low absolute growth rate from 10 to 22 weeks than na, but higher initial specific growth and maturation rates than the Na gene. The Fr gene had significant negative effects on body weights (between 28.2 g and 75.1 g) from 8 to 16 weeks than na, but a higher relative growth rate than Cr from 12 to 16 weeks. The Na gene had significant negative effects on body weights (between 24.7 g and 134.6 g) from 8 weeks onwards than na. It was concluded that Frfr and Nana genotypes are not ideal for cool environments in Kenya and indigenous chicken genotypes have varied growth potentials and patterns that can be improved to increase production.