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Leaf Toughness (leaf + toughness)
Selected AbstractsCan grazing response of herbaceous plants be predicted from simple vegetative traits?JOURNAL OF APPLIED ECOLOGY, Issue 3 2001Sandra Díaz Summary 1,Range management is based on the response of plant species and communities to grazing intensity. The identification of easily measured plant functional traits that consistently predict grazing response in a wide spectrum of rangelands would be a major advance. 2,Sets of species from temperate subhumid upland grasslands of Argentina and Israel, grazed by cattle, were analysed to find out whether: (i) plants with contrasting grazing responses differed in terms of easily measured vegetative and life-history traits; (ii) their grazing response could be predicted from those traits; (iii) these patterns differed between the two countries. Leaf mass, area, specific area (SLA) and toughness were measured on 83 Argentine and 19 Israeli species. Species were classified by grazing response (grazing-susceptible or grazing-resistant) and plant height (< or > 40 cm) as well as by life history (annual or perennial) and taxonomy (monocotyledon or dicotyledon). 3,Similar plant traits were associated with a specific response to grazing in both Argentina and Israel. Grazing-resistant species were shorter in height, and had smaller, more tender, leaves, with higher SLA than grazing-susceptible species. Grazing resistance was associated with both avoidance traits (small height and leaf size) and tolerance traits (high SLA). Leaf toughness did not contribute to grazing resistance and may be related to selection for canopy dominance. 4,Plant height was the best single predictor of grazing response, followed by leaf mass. The best prediction of species grazing response was achieved by combining plant height, life history and leaf mass. SLA was a comparatively poor predictor of grazing response. 5,The ranges of plant traits, and some correlation patterns between them, differed markedly between species sets from Argentina and Israel. However, the significant relationships between plant traits and grazing response were maintained. 6,The results of this exploratory study suggest that prediction of grazing responses on the basis of easily measured plant traits is feasible and consistent between similar grazing systems in different regions. The results challenge the precept that intense cattle grazing necessarily favours species with tough, unpalatable, leaves. [source] Litter decomposition in a Cerrado savannah stream is retarded by leaf toughness, low dissolved nutrients and a low density of shreddersFRESHWATER BIOLOGY, Issue 8 2007J. F. GONÇALVES JR Summary 1. To assess whether the reported slow breakdown of litter in tropical Cerrado streams is due to local environmental conditions or to the intrinsic leaf characteristics of local plant species, we compared the breakdown of leaves from Protium brasiliense, a riparian species of Cerrado (Brazilian savannah), in a local and a temperate stream. The experiment was carried out at the time of the highest litter fall in the two locations. An additional summer experiment was conducted in the temperate stream to provide for similar temperature conditions. 2. The breakdown rates (k) of P. brasiliense leaves in the tropical Cerrado stream ranged from 0.0001 to 0.0008 day,1 and are among the slowest reported. They were significantly (F = 20.12, P < 0.05) lower than in the temperate stream (0.0046,0.0055). The maximum ergosterol content in decomposing leaves in the tropical Cerrado stream was 106 ,g g,1, (1.9% of leaf mass) measured by day 75, which was lower than in the temperate stream where maximum ergosterol content of 522 ,g g,1 (9.5% of leaf mass) was achieved by day 30. The ATP content, as an indicator of total microbial biomass, was up to four times higher in the tropical Cerrado than in the temperate stream (194.0 versus 49.4 nmoles g,1). 3. Unlike in the temperate stream, leaves in the tropical Cerrado were not colonised by shredder invertebrates. However, in none of the experiments did leaves exposed (coarse mesh bags) and unexposed (fine mesh bags) to invertebrates differ in breakdown rates (F = 1.15, P > 0.05), indicating that invertebrates were unable to feed on decomposing P. brasiliense leaves. 4. We conclude that the slow breakdown of P. brasiliense leaves in the tropical Cerrado stream was because of the low nutrient content in the water, particularly nitrate (0.05 mgN L,1), which slows down fungal activity and to the low density of invertebrates capable of using these hard leaves as an energy source. [source] Consequences of simultaneous elevation of carbon dioxide and temperature for plant,herbivore interactions: a metaanalysisGLOBAL CHANGE BIOLOGY, Issue 1 2006E. L. ZVEREVA Abstract The effects of elevated carbon dioxide on plant,herbivore interactions have been summarized in a number of narrative reviews and metaanalyses, while accompanying elevation of temperature has not received sufficient attention. The goal of our study is to search, by means of metaanalysis, for a general pattern in responses of herbivores, and plant characteristics important for herbivores, to simultaneous experimental increase of carbon dioxide and temperature (ECET) in comparison with both ambient conditions and responses to elevated CO2 (EC) and temperature (ET) applied separately. Our database includes 42 papers describing studies of 31 plant species and seven herbivore species. Nitrogen concentration and C/N ratio in plants decreased under both EC and ECET treatments, whereas ET had no significant effect. Concentrations of nonstructural carbohydrates and phenolics increased in EC, decreased in ET and did not change in ECET treatments, whereas terpenes did not respond to EC but increased in both ET and ECET; leaf toughness increased in both EC and ECET. Responses of defensive secondary compounds to treatments differed between woody and green tissues as well as between gymnosperm and angiosperm plants. Insect herbivore performance was adversely affected by EC, favoured by ET, and not modified by ECET. Our analysis allowed to distinguish three types of relationships between CO2 and temperature elevation: (1) responses to EC do not depend on temperature (nitrogen, C/N, leaf toughness, phenolics in angiosperm leaves), (2) responses to EC are mitigated by ET (sugars and starch, terpenes in needles of gymnosperms, insect performance) and (3) effects emerge only under ECET (nitrogen in gymnosperms, and phenolics and terpenes in woody tissues). This result indicates that conclusions of CO2 elevation studies cannot be directly extrapolated to a more realistic climate change scenario. The predicted negative effects of CO2 elevation on herbivores are likely to be mitigated by temperature increase. [source] Leaf Quality of Some Tropical and Temperate Tree Species as Food Resource for Stream ShreddersINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2010Manuel A. S. Graça Abstract We tested the hypotheses that (1) plant defenses against consumers increase in the tropics, and that these differences in quality are perceived by detritivores; and (2) microbial conditioning of leaf litter is important for the feeding ecology of shredders from both geographical regions. We compared quality parameters of 8 tree species from Portugal and 8 from Venezuela. The tropical leaves were tougher, but did not differ from temperate leaves in terms of N, C: N, and polyphenols. In multiple-choice experiments, shredders from Portugal (Sericostoma vittatum and Chaetopteryx lusitanica) and from Venezuela (Nectopsyche argentata and Phylloicus priapulus) discriminated among conditioned leaves, preferentially consuming softer leaves. In another set of experiments, all shredders preferentially fed on conditioned rather than unconditioned leaves, grew faster when fed conditioned than unconditioned leaves and fed more on temperate than tropical leaves. We conclude that leaf litter from the tropics is a low-quality resource compared to leaves in temperate systems, because of differences in toughness, and that tropical shredders benefit from microbial colonization, as previously demonstrated for temperate systems. We suggest that leaf toughness could be one explanation for the reported paucity of shredders in some tropical streams. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Below-ground herbivory and root toughness: a potential model system using lignin-modified tobaccoPHYSIOLOGICAL ENTOMOLOGY, Issue 2 2010SCOTT N. JOHNSON Plants exploit an array of defences against insect herbivores based on chemical and biomechanical properties. There is increasing evidence that plant toughness comprises a particularly effective defence against herbivory, yet studies to date have focussed exclusively on leaf toughness and folivore behaviour. The relationship between root mechanical properties and the chewing behaviour of a root-feeding insect, the Agriotes spp. wireworm (Coleoptera: Elateridae L.), feeding on tobacco (Nicoiana tabacum) is investigated. Root toughness is manipulated using introduced transgenes for the down-regulation of key enzymes in the lignin biosynthesis pathway: cinnamoyl-CoA reductase (CCR line) and caffeate O -methyltransferase and cinnamyl alcohol dehydrogenase (CO line). Two biomechanical analyses (i.e. conventional cutting and notched tensile) are conducted to quantify root toughness on both lines. Roots from the CO line are significantly tougher than those of the CCR line in terms of fracture toughness and fracture energy, although not for cutting energy or stiffness. Bioassays that compel wireworms to chew through roots demonstrate that only 30% can penetrate roots of the CO line compared with 90% on the CCR line. It takes wireworms over twice as long to penetrate roots from the CO line (8 h) compared with CCR roots (3.5 h). There is a statistically significant positive relationship between penetration time and fracture toughness evaluated with tensile tests, although not with cutting energy from cutting tests. Using this exploratory model system, it is concluded that root toughness derived from tensile tests is a practical indicator of the ability of root-feeding insects to penetrate roots. [source] Seven-Year Results of Thinning and Burning Restoration Treatments on Old Ponderosa Pines at the Gus Pearson Natural AreaRESTORATION ECOLOGY, Issue 2 2004Kimberly F. Wallin AbstractWe examined the 7-year effects of three restoration treatments on leaf physiology and insect-resistance characteristics of pre-settlement age ponderosa pines (Pinus ponderosa Dougl. ex Laws.) at the Gus Pearson Natural Area (GPNA) in northern Arizona. Restoration treatments were: (1) thinned in 1993 to approximate pre-Euro-American settlement stand structure, (2) thinned plus prescribed burned in 1994 and 1998, and (3) untreated control. Tree physiological and insect-resistance characteristics were measured in year 2000, 7 years after thinning, using the same procedures as an earlier study performed in 1996. Consistent with the 1996 results, pre-dawn water potential in 2000 was consistently lower in the control than both thinned treatments. Both thinned treatments continued to have increased foliar nitrogen concentration in leaves 7 years after treatment. However lower leaf nitrogen concentration in the thinned and burned compared with the thinned treatment suggests lower nitrogen availability to trees in repeatedly burned plots. Analysis of leaf gas exchange characteristics and carbon isotope content (,13C) suggests continued stimulation of photosynthesis by both thinning treatments. Differences among treatments in resin volume, a measure of bark beetle resistance, depended on season of measurement. Trees in both thinning treatments continued to have increased leaf toughness, a measure of resistance to insect folivores. Our results show that many beneficial effects of restoration treatments on carbon, water, and nitrogen relations and insect-resistance characteristics of pre-settlement ponderosa pines continue to be expressed 7 years after treatment at the GPNA. [source] Colonization Strategies of Two Liana Species in a Tropical Dry Forest CanopyBIOTROPICA, Issue 3 2007Gerardo Avalos ABSTRACT Lianas impose intense resource competition for light in the upper forest canopy by displaying dense foliage on top of tree crowns. Using repeated access with a construction crane, we studied the patterns of canopy colonization of the lianas Combretum fruticosum and Bonamia trichantha in a Neotropical dry forest in Panama. Combretum fruticosum flushed leaves just before the rainy season, and its standing leaf area quickly reached a peak in the early rainy season (May,June). In contrast, B. trichantha built up foliage area continuously throughout the rainy season and reached a peak in the late rainy season (November). Both species displayed the majority of leaves in full sun on the canopy surface, but C. fruticosum displayed a greater proportion of leaves (26%) in more shaded microsites than B. trichantha (12%). Self-shading within patches of liana leaves within the uppermost 40,50 cm of the canopy reduced light levels measured with photodiodes placed directly on leaves to 4,9 percent of light levels received by sun leaves. Many leaves of C. fruticosum acclimated to shade within a month following the strongly synchronized leaf flushing and persisted in deep shade. In contrast, B. trichantha produced short-lived leaves opportunistically in the sunniest locations. Species differences in degree of shade acclimation were also evident in terms of structural (leaf mass per area, and leaf toughness) and physiological characters (nitrogen content, leaf life span, and light compensation point). Contrasting leaf phenologies reflect differences in light exploitation and canopy colonization strategies of these two liana species. RESUMEN Las lianas imponen una competencia intensa por la luz en el dosel superior al desplegar un denso follaje encima de las copas de los árboles. Usando acceso repetido al dosel a través de una grúa de construcción, estudiamos los patrones de colonización del dosel de las lianas Combretum fruticosum y Bonamia trichantha en un bosque neotropical seco en Panamá. Combretum fruticosum produjo hojas nuevas justo antes de la estación lluviosa, y su área foliar total alcanzó rápidamente un pico a inicios de la estación lluviosa (mayo-junio). En contraste, B. trichantha construyó su área foliar de forma continua a través de la estación lluviosa alcanzando un pico al final de esta (noviembre). Ambas especies desplegaron la mayoría de sus hojas bajo alta irradiación en la superficie del dosel, aunque C. fruticosum desplegó una mayor proporción de follaje (26%) en micrositios más sombreados que B. trichantha (12%). El auto sombreo dentro de los parches de hojas de lianas dentro de los primeros 40-50 cm del dosel superior redujo el nivel de radiación medido con fotodiodos colocados directamente sobre las hojas a 4-9% de la luz recibida por las hojas de sol. Muchas hojas de C. fruticosum se aclimataron a la sombra luego de un mes después de la producción inicial de hojas altamente sincronizada y persistieron en sombra profunda. En contraste, B. trichantha produjo hojas de corta longevidad de forma oportunística bajo las condiciones de mayor irradiación. Las diferencias entre especies en el grado de aclimatación a la sombra fueron evidentes en términos de caracteres estructurales (masa foliar por unidad de área, y dureza foliar) y fisiológicos (contenido de nitrógeno, longevidad foliar, y punto de compensación lumínica). Estas fenologías foliares tan contrastantes reflejan diferencias en las estrategias de explotación de luz y colonización del dosel por parte de estas dos lianas. [source] | ||||||||||