Tree-root systems and herbaceous species-characteristics under tree species introduced into grazing lands in subhumid Cameroon

The effect of tree species on the characteristics of the herbaceous stratum, during the first five years of a fallow, was evaluated in the North of Cameroon (average annual temperature 28.2 °C, total annual rainfall 1050 mm). Treatments included a natural grazed herbaceous fallow, a natural ungrazed herbaceous fallow and three planted tree fallows (Acacia polyacantha Willd. ssp. campylacantha (Hochst. ex A. Rich.), Senna siamea Lam. and Eucalyptus camaldulensis Dehnh.), which were protected against grazing. Because tree species influenced light interception in different ways, as well as having different root patterns, they had different effects on the herbaceous stratum in terms of species composition and biomass. The grazed herbaceous fallow maintained the greatest species richness. Protection against grazing or the introduction of tree species associated with the absence of grazing induced both a progressive evolution to a particular species composition. The ungrazed herbaceous fallow consisted mainly of Andropogon gayanus Kunth, which provided the greatest biomass (8 t dry matter ha^–1 at the end of the fallow period). E. camaldulensis provided little shade and the lowest fine root mass in the top layer allowing the growth of A. gayanus and thus a greater herbaceous biomass (3.5 t DM ha^–1) than that found under the other tree species. Under the heavy shade of A. polyacantha, the herbaceous stratum consisted mainly of annual Pennisetum spp. (2.2 t DM ha^–1) and showed the greatest N concentration (1.3%), probably due to N₂ fixation by the tree species. After the fourth year, despite the relatively open tree canopy, S. siamea, which showed the highest fine root mass, had a strong depressive effect on the herbaceous stratum. This revised version was published online in June 2006 with corrections to the Cover Date.     

Molluscicidal and antimicrobial activity of Solanum aculeastrum

The methanolic extract of the fresh root bark and berries of Solanum aculeastrum showed significant activity against host snails of schistosomiasis. The berries extract was more potent with 100% snail kill at 50 ppm. Fractionation increased activity with 100% mortality at 20 ppm. The aqueous and methanolic extracts of the berries showed moderate antimicrobial activity, increasing by fractionation.     

Light quality treatments enhance somatic seedling production in three southern pine species

Embryogenic cultures of loblolly pine (Pinus taeda L.), slash pine (Pinus elliottii Engelm.), longleaf pine (Pinus palustris Mill.) and slash pine x longleaf pine hybrids were initiated from immature seeds on an initiation medium containing 13.57 microM 2,4-dichlorophenoxyacetic acid and 2.22 microM benzylaminopurine. Embryogenic cultures proliferated and somatic embryos developed, matured and germinated following a modified protocol and media originally developed for radiata pine (Pinus radiata D. Don.) somatic seedling production. A discrete, light-sensitive pre-germination stage and a later germination (radicle emergence) stage were identified by the differential response of somatic embryos to light of different wavelengths. Different light quality treatments were applied during the pre-germination and germination steps, using cool white fluorescent bulbs or light-emitting diodes (LEDs), or both. In general, red wavelengths provided by LEDs during these steps resulted in higher frequencies of somatic embryo germination (up to 64%) and conversion (up to 50%), longer tap roots and more first-order lateral roots than the standard cool white fluorescent treatments or treatment with blue wavelengths from LEDs. In addition, exposure to red light allowed germination of somatic embryos of some clones that failed to produce germinants under fluorescent light. Germination and conversion were further enhanced by sequential application of cool white fluorescent light and red light, resulting in up to 100% germination and conversion in one experiment. Longleaf pine somatic embryos were especially responsive to the light quality treatments, resulting in the first report of somatic seedling production for this species.     

Extensive dispersal of Roanoke logperch (Percina rex) inferred from genetic marker data

The dispersal ecology of most stream fishes is poorly characterised, complicating conservation efforts for these species. We used microsatellite DNA marker data to characterise dispersal patterns and effective population size (N_e) for a population of Roanoke logperch Percina rex, an endangered darter (Percidae). Juveniles and candidate parents were sampled for 2 years at sites throughout the Roanoke River watershed. Dispersal was inferred via genetic assignment tests (ATs), pedigree reconstruction (PR) and estimation of lifetime dispersal distance under a genetic isolation‐by‐distance model. Estimates of N_e varied from 105 to 1218 individuals, depending on the estimation method. Based on PR, polygamy was frequent in parents of both sexes, with individuals spawning with an average of 2.4 mates. The sample contained 61 half‐sibling pairs, but only one parent–offspring pair and no full‐sib pairs, which limited our ability to discriminate natal dispersal of juveniles from breeding dispersal of their parents between spawning events. Nonetheless, all methods indicated extensive dispersal. The AT indicated unrestricted dispersal among sites ≤15 km apart, while siblings inferred by the PR were captured an average of 14 km and up to 55 km apart. Model‐based estimates of median lifetime dispersal distance (6–24 km, depending on assumptions) bracketed AT and PR estimates, indicating that widely dispersed individuals do, on average, contribute to gene flow. Extensive dispersal of P. rex suggests that darters and other small benthic stream fishes may be unexpectedly mobile. Monitoring and management activities for such populations should encompass entire watersheds to fully capture population dynamics.     

Distribution and Spread of the Great European Spruce Bark Beetle, Dendroctonus micans, in Britain--1982 to 1989

The great European spruce bark beetle (Dendroctonus micans),which had for many years been seen as a potential threat toBritain's spruce plantations, was first discovered in Britainduring August 1982, breeding in Sitka spruce. Surveys in spruceplantations were initiated to determine the distribution ofthe beetle, a necessary background for development of controlstrategies. This paper reports the development and evolutionof survey techniques from 1982 to 1989, as well as the spreadof the D.micans populations during this time. Details of controlstrategies and legislation to contain the outbreak are alsogiven, along with conclusions concerning the natural dispersalof D.micans. Received 23 July 1990.     

Crop response of drought-tolerant and conventional maize hybrids in a semiarid environment

In the High Plains, corn (Zea mays L.) is an important commodity for livestock feed. However, limited water resources and drought conditions continue to hinder corn production. Drought-tolerant (DT) corn hybrids could help maintain high yields under water-limited conditions, though consistent response of such hybrids is unverified. In this two-year study, the effects of three irrigation treatments were investigated for a DT and conventional maize hybrid, Pioneer AQUAMax P0876HR and Pioneer 33Y75, respectively. In 2013, the drier of the 2 years, irrigation amounts and crop water use (ET_c) were greater for the conventional hybrid, but grain water use efficiency (WUE) and harvest index were significantly greater for the DT hybrid. In 2014, grain yields and WUE were not significantly different between hybrids. However, irrigation amounts, ET_c and biomass yields were greater for the conventional hybrid. Results from both years indicate that the DT hybrid required less water to maximize grain yield as compared to the conventional hybrid. Producing relatively high yields with reduced amounts of water may provide a means for producers to continue corn production in a semiarid environment with declining water supplies.     

Distribution of aluminum in black spruce saplings growing on two New Brunswick forest soils with contrasting acid sulfate sorption

Two adjacent soils with contrasting sulfate sorption were examined in terms of (i) water-soluble and ion-exchangeable Al, Fe, Ca, Mg, K, Mn and Zn, (ii), water- and bicarbonate-extractable sulfate, (iii) Truog-extractable P, (iv) dithionite-extractable Al, Mn and Fe and (v) treatment response to irrigation with simulated acid precipitation. The biomass of 8 year old black spruce saplings growing on the soils, and the distributions of Al, Fe, Ca, Mg, K, Mn, P and Zn within these plants, were also examined. The soils were well to moderately-well drained, with the mineral soil exposed by site preparation prior to planting. The exposed soil underneath individual saplings was treated with acid sulfate solutions (75 mm containing 2 to 50 mg L^?1 H₂SO₄) applied during each of three consecutive growing seasons. The results indicate that Al, much like Fe, Ca, Mn and Zn, accumulated with time in the foliage, but K, Mg and P were highest in young plant tissues. Much of Al and Fe taken up remained in the fine roots. Aluminum uptake increased with the amount of dithionite-extractable Al (free Al oxide) in the soil. Growth of the black spruce saplings was not visibly affected by readily accessed Al in each soil, or by acid irrigation.Instead, growth was restricted by factors other than soil Al and acid irrigation in spite of (i) low soil pH, (ii) high levels of exchangeable Al, and (iii) high levels of Al in fine roots. Sulfate retention across and within the two soils was positively correlated with free Al oxide. The two soils responded to acid irrigation by accelerated silicate weathering and enhanced ion leaching. Sulfate sorption reduced these effects.     

Estimating the component of soil respiration not dependent on living plant roots: Comparison of the indirect y-intercept regression approach and direct bare plot approach

Distinguishing between root and non-root derived CO₂ efflux is important when determining rates of soil organic matter turnover, however, in practice they remain difficult to separate. Our aim was to evaluate two methods for determining the component of below-ground respiration not dependent on plant roots (i.e., basal soil respiration; R_b). The first approach estimated R_b indirectly from the y-intercept of linear regressions between below-ground respiration (BGR) and root biomass. The second approach involved direct measurements of soil respiration from bare plots. To compare the contrasting approaches, BGR and crop biomass measurements were collected throughout the year in a range of agricultural systems. We found that both methods were very closely correlated with each other. Values of R_b determined by the intercept approach, however, were slightly higher than those determined by measurement of bare plots. Both approaches showed a seasonal trend with estimates of R_b lowest in winter months at 0.02 t C ha⁻¹ month⁻¹ for the y-intercept approach and 0.11 t C ha⁻¹ month⁻¹ for the bare plots approach, even after the data had been corrected for the influence of soil temperature. Highest rates of R_b occurred from the height to the end of the crop growing season (0.8-1.5 t C ha⁻¹ month⁻¹). The annual CO₂ efflux due to R_b was estimated to be 8.1 t C ha⁻¹ y⁻¹ from the y-intercept approach and 6.8 t C ha⁻¹ y⁻¹ from bare plots. Annual BGR was 12.1 t C ha⁻¹ y⁻¹. We conclude that both methods provide similar estimates of R_b, however, logistically the bare plots approach is much easier to undertake than the y-intercept approach.