Home About us Contact
|
Home About us Contact | ||
|
|
||
Plant Parameters (plant + parameter)
Selected AbstractsThe role of leaf inclination, leaf orientation and plant canopy architecture in soil particle detachment by raindropsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2005Kirsten Foot Abstract A laboratory investigation of the effect of plant architecture on soil particle detachment by rainfall is described. The effects of leaf inclination, leaf orientation, effective canopy area, leaf area index, leaf subcatchment area, lowest canopy area, largest canopy area, canopy overlap area and an alternative leaf area index are examined using artificial plants. Detachment from a 30 cm diameter splash cup filled with sand (150 µm,1 mm particle size) was measured under three types of plant (small leaved, broad leaved and long narrow leaved) for a 10 minute simulated rainstorm of 75 mm/h intensity. There were no significant differences in soil particle detachment between the three plant types or between detachment under the plants and detachment of bare soil. No significant relationships were obtained between detachment and any of the plant parameters. Soil particle detachment by leaf drips can offset any protective effects of the canopy so that detachment does not differ significantly from that on bare soil. Plant architecture significantly affected the distance from the plant stem at which detachment was concentrated even though the canopy diameters of the plants were similar. There would appear to be no advantages in a detailed description of plant architecture and its effects in process-based models of soil erosion. Parameters such as plant height and plant canopy area are sufficient descriptors for modelling plant effects. Copyright © 2005 John Wiley & Sons, Ltd. [source] The importance of plant root characteristics in controlling concentrated flow erosion ratesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2003G. Gyssels Abstract While it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross-sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley & Sons, Ltd. [source] Synergistic effect of insect herbivory and plant parasitism on the performance of the invasive tree Schinus terebinthifoliusENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2009Veronica Manrique Abstract Schinus terebinthifolius Raddi (Anacardiaceae) is an introduced tree from South America that has invaded many ecosystems throughout central and south Florida, USA. Exploratory surveys in the plant's native range identified several potential biocontrol agents, including the leaflet rolling moth, Episimus unguiculus Clarke (Lepidoptera: Tortricidae). The larval stages of E. unguiculus tie together the plant leaflets while feeding and can completely defoliate small plants. The native love vine, Cassytha filiformis L. (Lauraceae), has been found parasitizing S. terebinthifolius in Florida. Natural processes such as plant parasitism may be one of the components of an integrated approach for S. terebinthifolius management in Florida. Thus, the objective of this study was to evaluate the combined effects of insect herbivory and plant parasitism on the performance of S. terebinthifolius. A factorial design experiment was conducted in the greenhouse to determine the effect of C. filiformis parasitism and E. unguiculus feeding damage on the growth and biomass of S. terebinthifolius. Results showed that plant parameters, including leaflet biomass, growth rate, and flower production, were negatively affected by plant parasitism and insect herbivory. Moreover, the decrease in S. terebinthifolius performance was greater when these two factors were combined, indicative of a synergistic relationship. In addition, the combined effect of C. filiformis and E. unguiculus suppressed plant performance for at least 2 months after the moths were removed. Therefore, increased control of S. terebinthifolius stands may be achieved in those areas where C. filiformis is present in Florida (e.g., pinelands, hammock forests) if the biocontrol agent E. unguiculus is approved for release. [source] Manipulation of flooding and arbuscular mycorrhiza formation influences growth and nutrition of two semiaquatic grass speciesFUNCTIONAL ECOLOGY, Issue 6 2000S. P. Miller Abstract 1Two semiaquatic grasses, Panicum hemitomon Schultes and Leersia hexandra Schwartz, were grown for 12 weeks in sterilized soil in experimental mesocosms, with and without the addition of arbuscular mycorrhizal (AM) fungal inoculum (as nonsterilized soil), under the following rooting-zone flood regimes: waterlogged (W), free-draining (D), beginning W and ending D (W,D), and beginning D and ending W (D,W). The purpose of the experiment was to determine whether these controlled water regimes affected both colonization of wetland grasses by AM fungi and the effects of the colonization on various plant parameters. 2Water regime, addition of inoculum, and their interaction were highly significant effects on total and proportion of root length colonized by AM fungi. Trends were very similar for the two grass species. Colonization was less and plants smaller in the W and W,D than in the D and D,W treatments. The viability of mycorrhiza at the end of the experiment, as measured by vital staining techniques, was not affected by changes in water level. 3Colonized plants in all water level treatments showed an improvement in phosphorus (P) nutrition over noncolonized plants. Colonized grasses of both species gained consistently more P per plant and had greater tissue P concentrations, with the greatest P concentration in the most heavily colonized plants (from the D and D,W treatments). 4The effect of flooding on the mycorrhizal association depended largely on the extent to which the association was already established when the flooding occurred. Flooding reduced the initiation of colonization either directly or indirectly, but once the fungi were established in the roots they were able to maintain and expand with the growing root system. [source] Neotyphodium endophyte infection affects the performance of tall fescue in temperate region AndisolsGRASSLAND SCIENCE, Issue 1 2006M. Hasinur Rahman Abstract A pot experiment was conducted for 75 days to observe the effect of Neotyphodium coenophialum endophyte on three tall fescue (Festuca arundinacea Schreb.) ecotypes grown in two Andisols viz. Black Andisol and Red Andisol. Black Andisol with a naturally low content of P was high in other nutrients such as N, K, while Red Andisol, with a naturally high content of P, was low in other nutrients. Tiller number, plant height, chlorophyll content, shoot dry weight and agronomic efficiency of water use (WUEag) showed higher values in endophyte-infected (E+) plants than noninfected (E,) plants. Plants growing in Black Andisol performed better than those in Red Andisol. Among the three tall fescue ecotypes, one of them (ecotype Showa) had the best performance regardless of soils and endophyte infection. When considering the effect of endophyte infection in different soil conditions, higher WUEag was observed in endophyte-infected plants grown in Black Andisol. Endophyte infection significantly enhanced all plant parameters in Black Andisol but they were reduced in Red Andisol. Our results indicate that infected plants grew better in soil that was naturally low in P whereas uninfected plants had increased vegetative growth in soil that was naturally high in P. In nutrient poor soil with comparatively high P content (Red Andisol) the cost of endophyte infection may override its benefit. The presence of endophyte had a variable impact on plant performance and the effect of endophyte varied with ecotype of grass it infected into. [source] Stochastic stability of a neural-net robot controller subject to signal-dependent noise in the learning ruleINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 6 2010Abraham K. Ishihara Abstract We consider a neural network-based controller for a rigid serial link manipulator with uncertain plant parameters. We assume that the training signal to the network is corrupted by signal-dependent noise. A radial basis function network is utilized in the feedforward control to approximate the unknown inverse dynamics. The weights are adaptively adjusted according to a gradient descent plus a regulation term (Narendra's e -modification). We prove a theorem that extends the Yoshizawa D-boundedness results to the stochastic setting. As in the deterministic setting, this result is particularly useful for neural network robot control when there exists bounded torque disturbances and neural net approximation errors over a known compact set. Using this result, we establish bounds on the feedback gains and learning rate parameters that guarantee the origin of the closed-loop system is semi-globally, uniformly bounded in expected value. Copyright © 2009 John Wiley & Sons, Ltd. [source] Near optimal LQR performance for uncertain first order systemsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2004L. Luo Abstract In adaptive control, the objective is to provide stability and acceptable performance in the face of significant plant uncertainty. However, often there are large transients in the plant output and the control signal can become excessively large. Here, we consider the first order case with the plant parameters restricted to a compact set; we show how to design a (linear time-varying) adaptive controller which provides near optimal LQR performance. This controller is periodic with each period split into two parts: during the Estimation Phase, an estimate of the optimal control signal is formed; during the Control Phase, a suitably scaled estimate of this signal is applied to the system. We demonstrate the technique with a simulation and discuss the benefits and limitations of the approach. Copyright © 2004 John Wiley & Sons, Ltd. [source] Quantitative variability of cyanogenesis in Cathariostachys madagascariensis,the main food plant of bamboo lemurs in Southeastern MadagascarAMERICAN JOURNAL OF PRIMATOLOGY, Issue 4 2009Daniel J. Ballhorn Abstract Giant bamboo (Cathariostachys madagascariensis) is a major food plant for three sympatric species of bamboo-eating lemurs (Hapalemur aureus, H. griseus, and Prolemur simus) in the rain forests of southeastern Madagascar. This plant species is strongly cyanogenic. However, quantitative data on cyanide concentration in C. madagascariensis are scarce. Previous studies reported 15,mg cyanide per 100,g fresh shoot material (corresponding to approx. 57,µmol cyanide per gram dry weight). However, we found mean concentrations (±SE) ranging from 139.3±19.32 in ground shoots to 217.7±16.80,µmol cyanide per gram dry weight in branch shoots. Thus, cyanogenesis of C. madagascariensis was up to four times higher than reported before. In contrast to the strongly cyanogenic shoots no cyanide could be detected in differently aged leaves of C. madagascariensis confirming earlier studies. Within individual shoots fine-scaled analysis revealed a characteristic ontogenetic pattern of cyanide accumulation. Highest concentrations were found in youngest parts near the apical meristem, whereas concentrations decreased in older shoot parts. Beyond the general intra-individual variability of cyanogenic features analyses indicated site-specific variability of both, the ontogenetic pattern of cyanide concentration as well as the total amount of cyanide accumulated in shoots. Additionally, analyses of soluble proteins,one important nutritive measure affecting food plant quality,demonstrated a converse quantitative relation of protein concentrations in leaves to cyanide concentration in shoots at the site-specific level. We, thus, suggest integrative analyses on quantitative variation of cyanogenesis together with nutritive plant parameters in future studies. This approach would allow obtaining more detailed insights into spatial variability of giant bamboo's overall browse quality and its impact on lemur herbivores. Am. J. Primatol. 71:305,315, 2009. © 2009 Wiley-Liss, Inc. [source] | |||||||||||||