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Below-ground Interactions (below-ground + interaction)
Selected AbstractsEffect of arbuscular mycorrhizal (AM) colonization on terpene emission and content of Artemisia annua L.PLANT BIOLOGY, Issue 1 2008F. Rapparini Abstract Plant roots interact with a wide variety of rhizospheric microorganisms, including bacteria and the symbiontic arbuscular mycorrhizal (AM) fungi. The mycorrhizal symbiosis represents a series of complex feedbacks between plant and fungus regulated by their physiology and nutrition. Despite the widespread distribution and ecological significance of AM symbiosis, little is known about the potential of AM fungi to affect plant VOC metabolism. The purpose of this study was to investigate whether colonization of plant roots by AM fungi and associated soil microorganisms affects VOC emission and content of Artemisia annua L. plants (Asteraceae). Two inoculum types were evaluated: one consisted of only an arbuscular mycorrhizal (AM) fungus species (Glomus spp.), and the other was a mixture of different Glomus species and associated soil bacteria. Inoculated plants were compared with non-inoculated plants and with plants supplemented with extra phosphorus (P) to obtain plants of the same size as mycorrhizal plants, thus excluding potentially-confounding mycorrhizal effects on shoot growth. VOC emissions of Artemisia annua plants were analyzed by leaf cuvette sampling followed by off-line measurements with pre-concentration and gas chromatography mass spectrometry (GC-MS). Measurements of CO2 and H2O exchanges were conducted simultaneously. Several volatile monoterpenes were identified and characterized from leaf emissions of Artemisia annua L. by GC-MS analysis. The main components identified belong to different monoterpene structures: ,-pinene, ,-pinene, camphor, 1,8-cineole, limonene, and artemisia ketone. A good correlation between monoterpene leaf concentration and leaf emission was found. Leaf extracts included also several sesquiterpenes. Total terpene content and emission was not affected by AM inoculation with or without bacteria, while emission of limonene and artemisia ketone was stimulated by this treatment. No differences were found among treatments for single monoterpene content, while accumulation of specific sesquiterpenes in leaves was altered in mycorrhizal plants compared to control plants. Growth conditions seemed to have mainly contributed to the outcome of the symbiosis and influenced the magnitude of the plant response. These results highlight the importance of considering the below-ground interaction between plant and soil for estimating VOC emission rates and their ecological role at multitrophic levels. [source] Factors affecting the evolution of development strategies in parasitoid wasps: the importance of functional constraints and incorporating complexityENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 1 2005Jeffrey A. Harvey Abstract Parasitoid wasps have long been considered as model organisms for examining optimal resource allocation to different fitness functions, such as body size and development time. Unlike insect predators, which may need to consume many prey items to attain maturity, parasitoids generally rely on a limited amount of resources that are obtained from a single source (the host). This review discusses a range of ecophysiological constraints that affect host quality and concomitantly the evolution of development strategies in parasitoids. Two macroevolutionary differences in host usage strategies (idiobiosis, koinobiosis) are initially described. Over many years, particular attention has been paid in examining a range of quantitative host attributes such as size, age, or stage, as these affect idiobiont and koinobiont parasitoid development. Parasitoids and their hosts, however, constitute only a small part of an ecological community. Consequently, host quality may be affected by a broad range of factors that may operate over variable spatial and temporal scales. Intimate factors include aggressive competition with other parasitoids and pathogens for access to host resources, whereas less intimate factors include the effects of toxic plant compounds (allelochemicals) on parasitoid performance as mediated through primary and/or secondary hosts. It is suggested that future experiments should increase the levels of trophic complexity as these influence the evolution of life history and development strategies in parasitoids. This includes integration of a suite of direct and indirect mechanisms, including biological processes occurring in different ecological realms, such as above-ground and below-ground interactions. [source] Below-ground carbon flux and partitioning: global patterns and response to temperatureFUNCTIONAL ECOLOGY, Issue 6 2008C. M. Litton Summary 1The fraction of gross primary production (GPP) that is total below-ground carbon flux (TBCF) and the fraction of TBCF that is below-ground net primary production (BNPP) represent globally significant C fluxes that are fundamental in regulating ecosystem C balance. However, global estimates of the partitioning of GPP to TBCF and of TBCF to BNPP, as well as the absolute size of these fluxes, remain highly uncertain. 2Efforts to model below-ground processes are hindered by methodological difficulties for estimating below-ground C cycling, the complexity of below-ground interactions, and an incomplete understanding of the response of GPP, TBCF and BNPP to climate change. Due to a paucity of available data, many terrestrial ecosystem models and ecosystem-level studies of whole stand C use efficiency rely on assumptions that: (i) C allocation patterns across large geographic, climatic and taxonomic scales are fixed; and (ii) c. 50% of TBCF is BNPP. 3Here, we examine available information on GPP, TBCF, BNPP, TBCF : GPP and BNPP : TBCF from a diverse global data base of forest ecosystems to understand patterns in below-ground C flux and partitioning, and their response to mean annual temperature (MAT). 4MAT and mean annual precipitation (MAP) covaried strongly across the global forest data base (37 mm increase in MAP for every 1 °C increase in MAT). In all analyses, however, MAT was the most important variable explaining observed patterns in below-ground C processes. 5GPP, TBCF and BNPP all increased linearly across the global scale range of MAT. TBCF : GPP increased significantly with MAT for temperate and tropical ecosystems (> 5 °C), but variability was high across the data set. BNPP : TBCF varied from 0·26 to 0·53 across the entire MAT gradient (,5 to 30 °C), with a much narrower range of 0·42 to 0·53 for temperate and tropical ecosystems (5 to 30 °C). 6Variability in the data sets was moderate and clear exceptions to the general patterns exist that likely relate to other factors important for determining below-ground C flux and partitioning, in particular water availability and nutrient supply. Still, our results highlight global patterns in below-ground C flux and partitioning in forests in response to MAT that in part confirm previously held assumptions. [source] The effect of pea cultivar and water stress on root and shoot competition between vegetative plants of maize and peaJOURNAL OF APPLIED ECOLOGY, Issue 1 2001Tzehaye Semere Summary 1Improvements in intercrop yields may be achieved through an understanding of yield advantages due to above-ground or below-ground interactions. 2Forage maize and two morphologically contrasting cultivars of pea (leafy cv. Bohatyr and semi-leafless cv. Grafila) were grown alone and in additive mixtures, under two contrasting levels of soil moisture (± water stress). 3The mechanism of competition between maize and pea was studied by separating the effects of root competition and shoot competition, using soil and aerial partitions. Plants were grown in rectangular tanks in a glasshouse. 4Leafy pea cv. Bohatyr was as competitive as maize, both below-ground and above-ground, whereas semi-leafless pea cv. Grafila was less competitive than maize or pea cv. Bohatyr. The greater competitive ability of the leafy pea, both above- and below-ground, was probably due to its greater growth rate, associated with its greater leaf area. 5The competitive ability of maize, relative to peas, was considerably reduced by water stress. Both the root and shoot competitive abilities of pea were greater under water stress, compared with those of maize. 6Relative yield total (RYT) values were significantly greater when maize and pea were subjected to shoot competition only (RYT = 1·76) than when subjected to root competition (RYT = 1·17) or when subjected to both shoot and root competition (RYT = 1·13). This reflects the fact that the effects of root competition were greater than those of shoot competition. 7Root competition decreased the shoot dry weights, plant height and leaf area of both maize and pea, whereas shoot competition had no significant effect on these attributes, indicating that soil resources, i.e. mineral nutrients and water, were more limiting than light. [source] | ||||||||||