Trophobiosis between aphids (Aphididae, Hemiptera) and ants (Formicidae, Hymenoptera) is considered to provide an important source of nutrition for ants by aphid honeydew and aphids themselves used ...as prey. However, little is known about nutrient fluxes and the relative importance of trophobiosis for different ant species. Combining direct contact observations between ants and aphids with stable isotope analyses of distinct multitrophic sample sets (soil, plant, aphid, and ant), we aimed at disentangling the importance of trophobiosis in a Mediterranean food web and possible feedbacks on the functional diversity of ants in a species-rich organic Citrus plantation. We analyzed δ¹³C- and δ¹⁵N-values of sample sets for fertilized and natural soil, using the fertilizer as natural isotope label. The results showed trophic relationships between 18 host plant species, 22 aphid species, and 7 ant species. Direct observation revealed at least 40 different plant–aphid combinations and 25 aphid–ant combinations with a marked range of δ¹⁵N-values. However, the δ¹³C and δ¹⁵N isotope ratios still reflected the trophic levels. A significant correlation occurred between the isotope ratios of aphids and their host plants. However, no relationship was found between aphids and ants or between plants and ants revealing that many ant species do not exhibit a close relationship with their trophobiotic partners. Isotopic data allowed us to separate ant species into trophic functional groups and showed the relevance of other food resources. The applied fertilizer shifted the isotopic baseline for the whole trophic system. By combining the stable isotope analysis with the exact origin of the samples, we avoided a misleading interpretation of the high isotopic range of species. Thus, we emphasize the importance of considering a baseline in stable isotope food web studies.
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ABSTRACT
A canopy photosynthesis model was modified to assess the effect of photoinhibition on whole‐plant carbon gain. Photoinhibitory changes in maximum quantum yield of photosystem II (Fv/Fm) ...could be explained solely from a parameter (Lflux) calculated from the light micro‐environment of the leaves. This relationship between Fv/Fm and the intercepted cumulative light dose, integrated and equally weighted over several hours was incorporated into the model. The effect of photoinhibition on net photosynthesis was described through relationships between photoinhibition and the shaping parameters of the photosynthetic light‐response curve (quantum use efficiency, convexity, and maximum capacity). This new aspect of the model was then validated by comparing measured field data (diurnal courses of Fv/Fm) with simulation results. Sensitivity analyses revealed that the extent of photoinhibitory reduction of whole‐plant photosynthesis was strongly dependent on the structural parameters (LAI and leaf angle). Simulations for a Mediterranean evergreen oak, Quercus coccifera, under climatic conditions which cause mild photoinhibition revealed a daily loss of 7·5–8·5% of potential carbon gain in the upper sunlit canopy layers, a 3% loss in the bottom canopy, and an overall loss of 6·1%. Thus, this canopy photoinhibition model (CANO‐PI) allows the quantitative evaluation of photoinhibition effects on primary production.
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delta(15)N and total nitrogen content of above- and belowground tissues of 13 plant species from two successional stages (open pioneer community and ruderal grass stage) of a dry acidic grassland in ...Southern Germany were analysed, in order to evaluate whether resource use partitioning by niche separation and N input by N(2)-fixing legumes are potential determinants for species coexistence and successional changes. Within each stage, plants from plots with different legume cover were compared. Soil inorganic N content, total plant biomass and delta(15)N values of bulk plant material were significantly lower in the pioneer stage than in the ruderal grass community. The observed delta(15)N differences were rather species- than site-specific. Within both stages, there were also species-specific differences in isotopic composition between above- and belowground plant dry matter. Species-specific delta(15)N signatures may theoretically be explained by (i) isotopic fractionation during microbial-mediated soil N transformations; (ii) isotopic fractionation during plant N uptake or fractionation during plant-mycorrhiza transfer processes; (iii) differences in metabolic pathways and isotopic fractionation within the plant; or (iv) partitioning of available N resources (or pools) among plant groups or differential use of the same resources by different species, which seems to be the most probable route in the present case. A significant influence of N(2)-fixing legumes on the N balance of the surrounding plant community was not detectable. This was confirmed by the results of an independent in situ removal experiment, showing that after 3 years there were no measurable differences in the frequency distribution between plots with and without N(2)-fixing legumes.
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With one volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of the plant sciences. The present volume includes reviews ...on genetics, cell biology, physiology, comparative morphology, systematics, ecology, and vegetation science.
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FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We studied competitive interactions among three species (Corynephorus canescens, Hieracium pilosella and Carex arenaria) of different early successional stages on sand dunes. Our study focused on the ...influence of competition and water availability on biomass allocation patterns and the plasticity of root responses. Plants were grown for one growing season in a simple additive (target-neighbour) design under low or ambient water supply. Overall competition intensity (e.g., above- and below-ground), as well as root competition alone, were compared using control plants grown without competitors. Our results show high competition intensity leading to an average target plant biomass reduction of 56% relative to controls. Competition was mostly below-ground. With increasing water availability, the competitive effect of H. pilosella on both of the other species decreased significantly. All other tested species combinations were not influenced by water availability. Soil moisture seemed to be a key factor determining the plasticity of root responses. Under limited water availability, strong competitors caused a significant decrease of response ratio (lnRR) based on root: shoot ratios for H. pilosella and C. arenaria and a decrease in lnRR based on specific root length (SRL) for C. arenaria. Under sufficient water supply, however, there was no significant effect of competition on root: shoot ratios for any of the species and only C. arenaria in competition with C. canescens showed a lower lnRR based on SRL. These water-related, species-specific changes of root morphology and allocation patterns may point to an adaptive response to competition.
Four herbaceous plant species of a sand dune area and several herb species of an open early-successional patch were investigated for the occurrence of a simple relationship between aboveground ...biomass and plant cover. Without exception linear regressions of aboveground biomass on plant cover were found with slope factors depending on the growth form of the species. These results suggest that (early) growth of herbaceous plants in low and (temporarily) open vegetation is not affected by possible constraints caused by a decreasing ratio of plant cover to aboveground biomass. The obtained linear relationships could be used for rapid non-destructive determination of aboveground biomass by image-analysis of cover data.
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7.
Progress in Botany Esser, K; Beyschlag, W; Lüttge, U ...
2006, 2008-10-31, 2007-11-22, 2009-12-02, 2011-12-02, Volume:
70
eBook
With one volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of the plant sciences.The present volume includes reviews on ...genetics, cell biology, physiology, comparative morphology, systematics, ecology, and vegetation science.
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FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
With one volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of the plant sciences.The present volume includes reviews on ...genetics, cell biology, physiology, comparative morphology, systematics, ecology, and vegetation science.
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FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
9.
Progress in Botany Lüttge, Ulrich; Beyschlag, Wolfram; Murata, Jin
2007
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With one volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of the plant sciences. The present volume includes reviews ...on genetics, cell biology, physiology, comparative morphology, systematics, ecology, and vegetation science.
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Pressure infiltration of water into a leaf via the stomatal pores can be used to quickly determine whether all stomata are open, or as recently described for several mesophytic and xerophytic ...species, whether there is a non-homogeneous distribution of stomatal opening (stomatal patchiness) on the leaf surface. Information about this phenomenon is important since the commonly used algorithms for calculation of leaf conductance from water vapor exchange measurements imply homogeneously open stomata, which in the occurrence of stomatal patchiness will lead to erroneous results. Infiltration experiments in a growth chamber with leaves of the Mediterranean evergreen shrub Arbutus unedo, carried out under simulated Mediterranean summer day conditions, where the species typically exhibits a strong midday stomatal closure, revealed a temporary occurrence of stomatal patchiness during the phase of stomatal closure in the late morning and during the stomatal reopening in the afternoon. Leaves were, however, found to be fully (i.e. homogeneously) infiltratable in the morning and in the evening. At midday during maximum stomatal closure, leaves were almost non-infiltratable. During the day, the infiltrated amount of water was found to be linearly correlated with porometer measurements of leaf conductance of the same leaves, carried out with the attached leaves immediately before infiltration.
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