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Defoliation Treatments (defoliation + treatment)
Selected AbstractsLinking above-ground and below-ground effects in autotrophic microcosms: effects of shading and defoliation on plant and soil propertiesOIKOS, Issue 3 2000Juha Mikola Although factors affecting plant growth and plant carbon/nutrient balance , e.g., light availability and defoliation by herbivores , may also propagate changes in below-ground food webs, few studies have aimed at linking the above-ground and below-ground effects. We established a 29-week laboratory experiment (,one growing season) using autotrophic microcosms to study the effects of light and defoliation on plant growth, plant carbon/nutrient balance, soil inorganic N content, and microbial activity and biomass in soil. Each microcosm contained three substrate layers , mineral soil, humus and plant litter , and one Nothofagus solandri var. cliffortioides seedling. The experiment constituted of the presence or absence of two treatments in a full factorial design: shading (50% decrease in light) and artificial defoliation (approximately 50% decrease in leaf area in the beginning of the growing season). At the end of the experiment a range of above-ground and below-ground properties were measured. The shading treatment reduced root and shoot mass, root/shoot ratio and leaf production of the seedlings, while the defoliation treatment significantly decreased leaf mass only. Leaf C and N content were not affected by either treatment. Shading increased NO 3,N concentration and decreased microbial biomass in humus, while defoliation did not significantly affect inorganic N or microbes in humus. The results show that plant responses to above-ground treatments have effects which propagate below ground, and that rather straightforward mechanisms may link above-ground and below-ground effects. The shading treatment, which reduced overall seedling growth and thus below-ground N use and C allocation, also led to changes in humus N content and microbial biomass, whereas defoliation, which did not affect overall growth, did not influence these below-ground properties. The study also shows the carbon/nutrient balance of N. solandri var. cliffortioides seedlings to be highly invariant to both shading and defoliation. [source] Repeated grazing of a salt marsh grass by moulting greylag geese Anser anser, does sequential harvesting optimise biomass or protein gain?JOURNAL OF AVIAN BIOLOGY, Issue 1 2003Anthony D. Fox The effects of simulated goose grazing on common saltmarsh-grass Puccinellia maritima plants were tested on a Danish salt marsh during the flightless moulting period of greylag geese Anser anser (3,21 June 1998). Plants in an area exclosed from the influence of grazing and the nutrient effects of goose faeces were subject to removal of youngest lamina at 3-, 6-, 9- and 18-day intervals during this period. Average biomass and protein accumulation between harvests was highest at defoliation intervals of 9 days or more. Field observations from two separate study areas demonstrated geese returned to regraze the Puccinellia sward after 6,8 days and oesophageal contents from feeding geese showed selection for lamina lengths consistent with the results of clipping every 6 days. Geese therefore regrazed Puccinellia patches at shorter intervals than expected were they to maximise their intake of biomass or protein at each visit. However, total cumulative lamina elongation, equivalent to the long term gain during the entire moult period, showed no significant difference between the three most intensive defoliation treatments, which were significantly greater than those of plants defoliated at 18 day intervals. Highest overall lamina protein levels were maintained at 6- and 9-day defoliation intervals. This suggests geese regrazed Puccinellia patches at a rate that maximised their number of harvests during the flightless period, but maintained highest protein levels and overall biomass in the sward. This suggests, in line with earlier studies, that moulting greylag geese combine dietary selection, reduced nitrogen excretion and regrazing patterns to meet protein demands during regrowth of flight feathers. [source] Shading delays bud break in Brachsyegia spiciformisAFRICAN JOURNAL OF ECOLOGY, Issue 4 2008R. A. Richer Abstract Whole tree manipulation experiments were performed in the common southern African tree species, Brachystegia spiciformis to test a novel hypothesis that decreasing Total nonstructural carbohydrates (TNC) in the stem could cause bud break in Brachystegia spiciformis. The experimental treatments included fertilization, canopy defoliation, shading and stem heating to decrease stem carbohydrates. None of the treatments significantly decreased mean stem TNC. Likewise the heating, fertilization and defoliation treatments did not significantly affect the date of bud break. However, shading significantly delayed bud break. This delay in bud break could not be attributed to changes in leaf level photosynthetic traits, stem water content, leaf predawn water potential or delayed leaf fall. These results question widely accepted hypotheses about the mechanisms controlling bud break and suggest a carbohydrate homeostatic mechanism. Résumé Des expérimentations de manipulations d'arbres très complètes ont été réalisées sur l'espèce très commune en Afrique du Sud Brachystegia spiciformis pour tester une nouvelle hypothèse selon laquelle une diminution des TNC, les hydrates de carbone nonstructuraux, dans le tronc pourrait causer l'éclosion des bourgeons chez cette espèce. Les traitements expérimentaux comprenaient une fertilisation, le défeuillage de la canopée, la mise à l'ombre ou le chauffage des troncs pour diminuer les hydrates de carbone. Aucun de ces traitements n'a diminué significativement les TNC dans les troncs. Le chauffage, la fertilisation ou le défeuillage n'ont pas non plus affecté la date de l'éclatement des bourgeons. Le fait d'être à l'ombre a, par contre, significativement retardé l'éclosion des bourgeons. Ce retard ne pouvait pas être attribué aux changements du taux de photosynthèse des feuilles, à la teneur en eau des troncs, au potentiel aqueux des feuilles avant l'aube, ni au retard de la chute des feuilles. Ces résultats remettent en question les hypothèses largement acceptées au sujet des mécanismes qui contrôlent l'éclosion des bourgeons et suggèrent l'existence d'un mécanisme homéostatique lié aux hydrates de carbone. [source] Flooding and grazing promote germination and seedling establishment in the perennial grass Paspalum dilatatumAUSTRAL ECOLOGY, Issue 3 2009PATRICIA S. CORNAGLIA Abstract Seed germination and seedling emergence are key processes for population recruitment. Flooding and grazing are disturbances forming gaps that may strongly influence recruitment patterns in space and time, but their combined effects and action mechanisms have rarely been addressed. In this study we analysed the effects of microhabitat conditions associated with winter flooding and spring-summer defoliation on seed germination and seedling establishment of Paspalum dilatatum, a dominant perennial C4 grass in native grasslands of the Flooding Pampa, Argentina. The dynamics of seedling emergence from natural seed banks and buried seeds was studied in a factorial experiment with flooding and defoliation treatments applied to soil monoliths (mesocosms) collected from natural grassland. Additional laboratory experiments were applied to investigate seed germination under different combinations of temperature, light quality and simulated flooding. Seed germination and seedling emergence of P. dilatatum were promoted by flooding and high intensity defoliation. Gaps generated by flooding were maintained by high intensity defoliation exercising a synergistic effect on survival seedlings. Flooding resulted in the breaking of seed dormancy and higher germination rates associated with alternating temperature and the activation of the phytochrome system. Our results indicate that microhabitat conditions associated with the disturbances forming gaps, such as flooding and heavy grazing, synergistically promote the recruitment process of this dominant grass species. [source] | ||||||||||