Sponges play a key role in (re)cycling of dissolved organic matter (DOM) and inorganic nutrients in coral reef ecosystems. Macroalgae and corals release different quantities of DOM and at different bioavailabilities to sponges and their microbiome. Given the current coral- to algal-dominance shift on coral reefs, we assessed the differential processing of macroalgal- and coral-DOM by three high and three low microbial abundance (HMA and LMA) encrusting sponge species. We followed the assimilation of naturally sourced 13C- and 15N-enriched macroalgal- and coral-DOM into bulk tissue and into host- versus bacteria-specific phospholipid fatty acids (PLFAs). Additionally, we compared sponge-processing of the two natural DOM sources with 13C- and 15N-enriched laboratory-made diatom-DOM. All investigated sponges utilized all DOM sources, with higher assimilation rates in LMA compared to HMA sponges. No difference was found in carbon assimilation of coral- versus macroalgal-DOM into bulk tissue and host- versus bacteria-specific PLFAs, but macroalgal nitrogen was assimilated into bulk tissue up to eight times faster compared to the other sources, indicating its higher bioavailability to the sponges. Additionally, LMA sponges released significantly more inorganic nitrogen after feeding on macroalgal-DOM. Therefore, we hypothesize that, depending on the abundance and composition of the sponge community, sponges could catalyze reef eutrophication through increased turnover of nitrogen under coral-to-algal regime shifts.

The use of 2H and 18O isotopic analyses combined with chemometrics as a traceability tool for the geographical origin of bell peppers de Rijke, E.; Schoorl, J.C.; Cerli, C.; Vonhof, H.B.; Verdegaal, S.J.A.; Vivó Truyols, G.I.; Lopatka, M.; Dekter, R.; Bakker, D.; Sjerps, M.J.; Ebskamp, M.; de Koster, C.G. Published in: Food Chemistry DOI:10.1016/j.foodchem.2016.01.134 Link to publicationCitation for published version (APA): de Rijke, E., Schoorl, J. C., Cerli, C., Vonhof, H. B., Verdegaal, S. J. A., Vivó-Truyols, G., ... de Koster, C. G. (2016). The use of 2H and 18O isotopic analyses combined with chemometrics as a traceability tool for the geographical origin of bell peppers. Food Chemistry, 204, 122-128. DOI: 10.1016/j.foodchem.2016 General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Keywords:Isotope ratio mass spectrometry Gas chromatography Geographic origin Food products authenticity Linear discriminant analysis Likelihood ratio Bell peppers Capsicum annuum a b s t r a c t Two approaches were investigated to discriminate between bell peppers of different geographic origins. Firstly, d 18 O fruit water and corresponding source water were analyzed and correlated to the regional GNIP (Global Network of Isotopes in Precipitation) values. The water and GNIP data showed good correlation with the pepper data, with constant isotope fractionation of about À4. Secondly, compoundspecific stable hydrogen isotope data was used for classification. Using n-alkane fingerprinting data, both linear discriminant analysis (LDA) and a likelihood-based classification, using the kernel-density smoothed data, were developed to discriminate between peppers from different origins. Both methods were evaluated using the d 2 H values and n-alkanes relative composition as variables. Misclassification rates were calculated using a Monte-Carlo 5-fold cross-validation procedure. Comparable overall classification performance was achieved, however, the two methods showed sensitivity to different samples. The combined values of d 2 H IRMS, and complimentary information regarding the relative abundance of four main alkanes in bell pepper fruit water, has proven effective for geographic origin discrimination. Evaluation of the rarity of observing particular ranges for these characteristics coul...

Sponge-microbe symbioses underpin the ecological success of sponges in many aquatic benthic ecosystems worldwide. These symbioses are often described as mutually beneficial, but identifying positive symbiotic interactions and quantifying the contribution of partners to physiological processes is challenging. For example, our understanding of the relative contribution of sponge cells and their microbial symbionts to the uptake and exchange of dissolved organic matter (DOM)—a major component of sponge diet—is limited. Here, we combined host-symbiont cell separation with pulse-chase isotopic labelling in order to trace the uptake of 13C- and 15Nenriched DOM into sponge cells and microbial symbionts of the encrusting Caribbean sponges Haliclona vansoesti and Scopalina ruetzleri, which are low microbial abundance (LMA) species. Sponge cells were responsible for >99% of DOM assimilation during the pulse-chase experiment for both sponge species, while the contribution of symbiotic microbes to total DOM uptake was negligible (<1%). Nitrogen derived from DOM was translocated from sponge cells to microbial cells over time, indicating processing of host nitrogenous wastes by microbial endosymbionts. Thus, host cells drive DOM uptake in these species, while microbial symbionts may aid in the recycling of host-waste products. Our findings highlight the ability of sponges to derive nutrition by internalizing dissolved compounds from their environment and retaining nutrients via host-microbe interactions.

Climate change affects the occurrence of high‐discharge (HD) events and associated nutrient exports in catchment stream water. Information on colloidal events‐based losses of important nutrients, such as organic C(Corg), N, P, and S, remain relatively scarce. We hypothesized that contributions of colloidal exported N, S, and P due to differing hydrological mechanisms vary between HD events in late winter and spring. We examined one combined snowmelt and rainfall event (March 2018) with one rainfall event (May 2018) for temporal Corg, N, P, and S dynamics. The catchment exports of colloids and their subset nanoparticles were analyzed by asymmetric‐flow field flow fractionation (P) and a filtration cascade (N and S). The Corg source in both events was assessed by δ13C composition of the stream water in relation to that of the soil. In winter, <6% of stream water P was transported by colloids (>0.1 μm), but this was 29–64% in spring and was associated with Corg, Fe, and Al. Colloidal N and particulate S (>1 μm) were higher during both events, but the majority of losses were dissolved (<0.1 μm). The δ13C values of dissolved organic matter (13CDOM) showed that in winter, most Corg was exported from the hydrologically connected hillslopes by water flowing through mineral horizons, due to snowmelt. During and after the rainfall events, export from organic horizons dominated the nutrient losses as particulates, including colloids. These events highlight the need for a better quantification of often underreported particulate, colloid, and nanoparticle contributions to weather‐driven nutrient losses from catchments.

Increased anthropogenic nitrogen (N) inputs can alter the N cycle and affect forest ecosystem functions. The impact of increased N deposition depends among others on the ultimate fate of N in plant and soil N pools. Short-term studies (3-18 months) have shown that the organic soil layer was the dominant sink for N. However, longer time scales are needed to investigate the long-term fate of N. Therefore, the soils of four experimental forest sites across Europe were re-sampled * 2 decades after labelling with 15 N. The sites covered a wide range of ambient N deposition varying from 13 to 58 kg N ha-1 year-1. To investigate the effects of different N loads on 15 N recovery, ambient N levels were experimentally increased or decreased. We hypothesized that: (1) the mineral soil would become the dominant 15 N sink after 2 decades, (2) long-term increased N deposition would lead to lower 15 N recovery levels in the soil and (3) variables related to C dynamics would have the largest impact on 15 N recovery in the soil. The results show that large amounts of the added 15 N remain in the soil after 2 decades and at 2 out of 4 sites the 15 N recovery levels are higher in the mineral soil than in the organic soil. The results show no clear responses of the isotopic signature to the changes in N deposition. Several environmental drivers are identified as