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824 Ergebnisse:

Altitudinal changes in leaf hydraulic conductance across five Rhododendron species in eastern Nepal
Tree Physiology (2016)
Haruhiko Taneda, Dhan Raj Kandel, Atsushi Ishida, Hiroshi Ikeda

This study investigated altitudinal changes in leaf-lamina hydraulic conductance (KL) and leaf morphological traits related to KL using five Rhododendron species growing at different altitudes (2500–4500 m above sea level) in Jaljale Himal region in eastern Nepal. Sun leaves were collected from the highest and the lowest altitude populations of each species, and KL was measured with a high pressure flow meter method. Leaf-lamina hydraulic conductance ranged from 7.7 to 19.3 mmol m−2 s−1 MPa−1 and was significantly positively correlated with altitude. The systematic increase with altitude was also found in KL, leaf nitrogen content and stomatal pore index. These relationships suggest that plants from higher-altitude habitats had a large CO2 supply to the intercellular space in a leaf and high CO2 assimilation capacity, which enables efficient photosynthesis at high altitude. The variation in KL was associated with the variation in several leaf morphological traits. High KL was found in leaves with small leaf area and round shape, both of which result in shorter major veins. These results suggest that the short major veins were important for efficient water transport in unlobed leaves of Rhododendron species. The extent of lignification in bundle sheaths and bundle sheath extension was associated with KL. Lignified compound primary walls inhibit water conduction along apoplastic routes. All species analyzed had heterobaric leaves, in which bundle sheath extensions developed from minor veins, but strongly lignified compound primary walls were found in Rhododendron species with low KL. It is still unclear why cell walls in bundle sheath at minor veins were markedly lignified in Rhododendron species growing at lower altitude. The lignified cell wall provides a high pathogenic resistance to infection and increases the mechanical strength of cell wall. The data imply that lignified bundle sheath may provide a trade-off between leaf hydraulic efficiency and leaf mechanical toughness or longevity.

Feeding patterns of two sympatric shark predators in coastal ecosystems of an oceanic island
Canadian Journal of Fisheries and Aquatic Sciences (2016)
Clément Trystram, Karyne Rogers, Marc Soria, Sébastien Jaquemet

Stomach contents and stable carbon and nitrogen isotope analyses (δ13C and δ15N) were used to investigate the trophic ecology of two apex predators, tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas), from Reunion Island to describe their dietary habits at both the population and individual levels. In this oceanic island, the tiger and bull sharks were more piscivorous and teutophagous than noted in previous research from other localities. The δ13C values suggested that bull sharks depended on more neritic organic matter sources than tiger sharks, confirming a coastal habitat preference for bull sharks. Moreover, the total length of the bull shark influenced δ13C values, with smaller individuals being more coastal than larger individuals. All indicators suggest that there is a higher degree of similarity between individual tiger sharks compared with the more heterogeneous bull shark population, which is composed of individuals who specialize on different prey. These results suggest tha...
Schlagworte: carbon , nitrogen , ecol , ocea , elem

N/P imbalance as a key driver for the invasion of oligothrophic dune systems by a woody legume
Oikos (2016)
Florian Ulm, Christine Hellmann, Cristina Cruz, Cristina Máguas

Oligotrophic ecosystems, previously considered to be more resilient to invasive plants, are now recognised to be highly vulnerable to invasions. In these systems, woody legumes show belowground ecosystem engineering characteristics that enable invasion, however, the underlying processes are not well understood. Using a Portuguese primary dune ecosystem as an oligotrophic model system, belowground biomass pools, turnover rates and stoichiometry of a native (Stauracanthus spectabilis) and an invasive legume (Acacia longifolia) were compared and related to changes in the foliage of the surrounding native (Corema album) vegetation. We hypothesized that the invasive legume requires less phosphorus per unit of biomass produced and exhibits an enhanced nutrient turnover compared to the native vegetation, which could drive invasion by inducing a systemic N/P imbalance. Compared with the native legumes, A. longifolia plants had larger canopies, higher SOM levels and lower tissue P concentrations. These attributes were strongly related to legume influence as measured by increased foliar N content and less depleted δ15N signatures in the surrounding C. album vegetation. Furthermore, greater root and rhizosphere mass and increased nutrient turnover in the rhizosphere of the invader were associated with depleted foliar P in C. album. Our results emphasize that while A. longifolia itself maintains an efficient phosphorus use in biomass production, at the same time it exerts a strong impact on the N/P balance of the native system. Moreover, this study highlights the engineering of a belowground structure of roots and rhizosphere as a crucial driver for invasion, due to its central role in nutrient turnover. These findings provide new evidence that, under nutrient-limited conditions, considering co-limitation and nutrient cycling in oligotrophic systems is essential to understand the engineering character of invasive woody legumes.
Schlagworte: nitrogen , soil , ecol , elem

Can stable isotopes be used to infer site fidelity of nekton in open coastal areas?
Ecological Indicators (2016)
C. Vinagre, C. Madeira, M. Dias, L. Narciso, V. Mendonça

Stable isotope analysis has been applied to the investigation of movement in several species, including marine animals. However, its application to nekton living in open coastal areas is still very scarce. This study aims to test if stable isotope analysis can be used for this purpose over a much wider spatial scale than previously investigated. Stable isotope analysis was used to 1) investigate isotopic variation in shrimp and fish, in 11 sites, along a 160km coastal stretch, to 2) determine the site fidelity of the individuals within each species, and to 3) test the relation between the body size of the individuals within each species, at each site and the percentage of isotopic deviants. Site fidelity was the highest for the intertidal fish Gobius paganellus and Coryphoblennius galerita, with 60% and 64% of individuals considered residents, respectively, and lowest for the demersal fish Diplodus vulgaris and Diplodus sargus with 23% and 33% of resident individuals, respectively. The percentage of isotopic deviants was not correlated with length in any species. Site fidelity was considerably higher than that previously found for other open coastal areas and similar to more structured environments, like coastal ponds. It was hypothesized that the complex tri-dimensional structure of the rocky reefs that occur in this area, often encompassing channels and tide pools, offers conditions favourable to high site fidelity. This study shows that stable isotopes can be used to infer nekton movement in wide open coastal areas.
Schlagworte: carbon , nitrogen , ecol , elem

Emission characterization and δ13C values of parent PAHs and nitro-PAHs in size-segregated particulate matters from coal-fired power plants
Journal of Hazardous Materials (2016)
Ruwei Wang, Balal Yousaf, Ruoyu Sun, Hong Zhang, Jiamei Zhang, Guijian Liu

The objective of this study was to characterize parent polycyclic aromatic hydrocarbons (pPAHs) and their nitrated derivatives (NPAHs) in coarse (PM2.5–10), intermediate (PM1–2.5) and fine (PM1) particulate matters emitted from coal-fired power plants (CFPPs) in Huainan, China. The diagnostic ratios and the stable carbon isotopic approaches to characterize individual PAHs were applied in order to develop robust tools for tracing the origins of PAHs in different size-segregated particular matters (PMs) emitted CFPP coal combustion. The concentrations of PAH compounds in flue gas emissions varied greatly, depending on boiler types, operation and air pollution control device (APCD) conditions. Both pPAHs and NPAHs were strongly enriched in PM1–2.5 and PM1. In contrary to low molecular weight (LMW) PAHs, high molecular weight (HMW) PAHs were more enriched in finer PMs. The PAH diagnostic ratios in size-segregated PMs are small at most cases, highlighting their potential application in tracing CFPP emitted PAHs attached to different sizes of PMs. Yet, substantial uncertainty still exists to directly apply PAH diagnostic ratios as emission tracers. Although the stable carbon isotopic composition of PAH molecular was useful in differentiating coal combustion emissions from other sources such as biomass combustion and vehicular exhausts, it was not feasible to differentiate isotopic fractionation processes such as low-temperature carbonization, high-temperature carbonization, gasification and combustion.

Soil organic carbon stocks in estuarine and marine mangrove ecosystems are driven by nutrient colimitation of P and N
Ecology and Evolution (2016)
Christian Weiss, Joanna Weiss, Jens Boy, Issi Iskandar, Robert Mikutta, Georg Guggenberger

Mangroves play an important role in carbon sequestration, but soil organic carbon (SOC) stocks differ between marine and estuarine mangroves, suggesting differing processes and drivers of SOC accumulation. Here, we compared undegraded and degraded marine and estuarine mangroves in a regional approach across the Indonesian archipelago for their SOC stocks and evaluated possible drivers imposed by nutrient limitations along the land-to-sea gradients. SOC stocks in natural marine mangroves (271–572 Mg ha−1 m−1) were much higher than under estuarine mangroves (100–315 Mg ha−1 m−1) with a further decrease caused by degradation to 80–132 Mg ha−1 m−1. Soils differed in C/N ratio (marine: 29–64; estuarine: 9–28), δ15N (marine: −0.6 to 0.7‰; estuarine: 2.5 to 7.2‰), and plant-available P (marine: 2.3–6.3 mg kg−1; estuarine: 0.16–1.8 mg kg−1). We found N and P supply of sea-oriented mangroves primarily met by dominating symbiotic N2 fixation from air and P import from sea, while mangroves on the landward gradient increasingly covered their demand in N and P from allochthonous sources and SOM recycling. Pioneer plants favored by degradation further increased nutrient recycling from soil resulting in smaller SOC stocks in the topsoil. These processes explained the differences in SOC stocks along the land-to-sea gradient in each mangrove type as well as the SOC stock differences observed between estuarine and marine mangrove ecosystems. This first large-scale evaluation of drivers of SOC stocks under mangroves thus suggests a continuum in mangrove functioning across scales and ecotypes and additionally provides viable proxies for carbon stock estimations in PES or REDD schemes.
Schlagworte: carbon , nitrogen , soil , ecol , elem

Common mycorrhizal networks amplify competition by preferential mineral nutrient allocation to large host plants
New Phytologist (2016)
Joanna Weremijewicz, Leonel da Silveira Lobo O'Reilly Sternberg, David P. Janos

Arbuscular mycorrhizal (AM) fungi interconnect plants in common mycorrhizal networks (CMNs) which can amplify competition among neighbors. Amplified competition might result from the fungi supplying mineral nutrients preferentially to hosts that abundantly provide fixed carbon, as suggested by research with organ-cultured roots. We examined whether CMNs supplied 15N preferentially to large, nonshaded, whole plants. We conducted an intraspecific target–neighbor pot experiment with Andropogon gerardii and several AM fungi in intact, severed or prevented CMNs. Neighbors were supplied 15N, and half of the target plants were shaded. Intact CMNs increased target dry weight (DW), intensified competition and increased size inequality. Shading decreased target weight, but shaded plants in intact CMNs had mycorrhizal colonization similar to that of sunlit plants. AM fungi in intact CMNs acquired 15N from the substrate of neighbors and preferentially allocated it to sunlit, large, target plants. Sunlit, intact CMN, target plants acquired as much as 27% of their nitrogen from the vicinity of their neighbors, but shaded targets did not. These results suggest that AM fungi in CMNs preferentially provide mineral nutrients to those conspecific host individuals best able to provide them with fixed carbon or representing the strongest sinks, thereby potentially amplifying asymmetric competition below ground.
Schlagworte: carbon , nitrogen , soil , elem

Nitrogen fixation by the reluctant diazotroph Cylindrospermopsis raciborskii (Cyanophyceae)
Journal of Phycology (2016)
Anusuya Willis, Ann W. Chuang, Michele A. Burford

Nitrogen fixation has been proposed as a mechanism that allows the diazotrophic cyanobacterium Cylindrospermopsis raciborskii to bloom in nitrogen-limited freshwater systems. However, it is unclear whether dinitrogen-fixation (N2-fixation) can supplement available dissolved inorganic nitrogen (DIN) for growth, or only provides minimum nitrogen (N) for cell maintenance under DIN deplete conditions. Additionally, the rate at which cells can switch between DIN use and N2-fixation is unknown. This study investigated N2-fixation under a range of nitrate concentrations. Cultures were grown with pre-treatments of nitrate replete (single dose 941 μmol NO3 ̅. L−1) and N-free conditions and then either received a single dose of 941 μmol NO3 ̅. L−1 (N941), 118 μmol. L−1 NO3 ̅ (N118) or 0 N. Heterocysts appeared from days 3 - 5 when treatments of high NO3 ̅ were transferred to N starvation media (N941:N0), and from day-5 in N941 transferred to N118 treatments. Conversely, transferring cells from N0 to N941 resulted in heterocysts being discarded from day-3 and day 5 for N0:N118. Heterocyst appearance correlated with a detectable rate of N2-fixation and up-regulation of nifH gene expression, the discard of heterocysts occurred after sequential reduction of nifH expression and N2-fixation. Nitrate uptake rates were not affected by pre-treatment, suggesting no regulation or saturation of this uptake pathway. These data demonstrate that for C. raciborskii, N2-fixation is regulated by the production or discard of heterocysts. In conclusion, this study has shown that N2-fixation only provides enough N to support relatively low growth under N-limited conditions, and does not supplement nitrate to increase growth rates.
Schlagworte: carbon , nitrogen , soil , ecol , elem

Can intercropping with the world's three major beverage plants help improve the water use of rubber trees?
Journal of Applied Ecology (2016)
Junen Wu, Wenjie Liu, Chunfeng Chen

1.The dramatic expansion of rubber plantations in mainland Southeast Asia and Southwest China has caused many eco-environmental problems, especially negative hydrological consequences. These problems have gradually worsened and pose formidable threats to rubber agriculture, especially in light of increasingly frequent extreme weather events. Although rubber-based agroforestry systems are regarded as the best solution for improving the sustainability of rubber agriculture and environmental conservation, plant water use and related interactions have rarely been examined in such systems. 2.We primarily used stable isotope (δD, δ18O, and δ13C) methods to test whether intercropping could improve the water use and extreme weather tolerance (extreme cold and drought in our study) of rubber trees in three types of promising agroforestry systems (i.e. rubber with tea, coffee, and cocoa) in Xishuangbanna, China. 3.We found that the rubber tree is a drought-avoidance plant with strong plasticity with respect to water uptake. This characteristic is reflected by its ability to cope with serious seasonal drought, allowing it to avoid interspecific competition for water. The rubber trees showed wasteful water behaviour unless they were intercropped with tea or coffee. However, these intercropped species exhibited drought-tolerance strategies and maintained lower water use efficiencies to strengthen their competitive capacity for surface soil water. The stable δ13C values of the intercrop leaves indicated that all the agroforestry systems have stable internal microclimatic environments or higher resistance. 4.Synthesis and applications. This study suggests that interspecific competition for water can enhance the water use efficiency of drought-avoidance plants (i.e. rubber trees) and lead to complementarity between the root distributions of plants in rubber agroforestry systems (i.e. rubber with tea, coffee, and cocoa). All agroforestry systems have higher resistance, but tea was the most suitable intercrop in terms of water use because the interspecific competition for water was moderate and the agroforestry system retained much more soil water and improved the water use efficiency of the rubber tree. Considering the root characteristics of the tea trees, we suggest that the crops selected for intercropping with rubber trees should have short lateral roots and a moderate amount of fine roots that overlap with the roots of the rubber trees in the shallow soil layer.
Schlagworte: carbon , nitrogen , soil , ecol , elem

Improved Discrimination for Brassica Vegetables Treated with Agricultural Fertilizers Using a Combined Chemometric Approach
Journal of Agricultural and Food Chemistry (2016)
Yuwei Yuan, Guixian Hu, Tianjin Chen, Ming Zhao, Yongzhi Zhang, Yong Li, Xiahong Xu, Shengzhi Shao, Jiahong Zhu, Qiang Wang, Karyne M. Rogers

Multielement and stable isotope (δ13C, δ15N, δ2H, δ18O, 207Pb/206Pb, and 208Pb/206Pb) analyses were combined to provide a new chemometric approach to improve the discrimination between organic and conventional Brassica vegetable production. Different combinations of organic and conventional fertilizer treatments were used to demonstrate this authentication approach using Brassica chinensis planted in experimental test pots. Stable isotope analyses (δ15N and δ13C) of B. chinensis using elemental analyzer–isotope ratio mass spectrometry easily distinguished organic and chemical fertilizer treatments. However, for low-level application fertilizer treatments, this dual isotope approach became indistinguishable over time. Using a chemometric approach (combined isotope and elemental approach), organic and chemical fertilizer mixes and low-level applications of synthetic and organic fertilizers were detectable in B. chinensis and their associated soils, improving the detection limit beyond the capacity of indivi...
Schlagworte: carbon , nitrogen , oxygen , food , soil , elem