Quantification of octacalcium phosphate, authigenic apatite and detrital apatite in coastal sediments using differential dissolution and standard addition

Knowledge of calcium phosphate (Ca-P) solubility is crucial for understanding temporal and spatial variations of phosphorus (P) concentrations in water bodies and sedimentary reservoirs. In situ relationships between liquid-and solid-phase levels cannot be fully explained by dissolved analytes alone and need to be verified by determining particular sediment P species. Lack of quantification methods for these species limits the knowledge of the P cycle. To address this issue, we (i) optimized a specifically developed conversion-extraction (CONVEX) method for P species quantification using standard additions, and (ii) simultaneously determined solubilities of Ca-P standards by measuring their pH-dependent contents in the sediment matrix. Ca-P minerals including various carbonate fluorapatite (CFAP) specimens from different localities, fluorapatite (FAP), fish bone apatite, synthetic hydroxylapatite (HAP) and octacalcium phosphate (OCP) were characterized by XRD, Raman, FTIR and elemental analysis. Sediment samples were incubated with and without these reference minerals and then sequentially extracted to quantify Ca-P species by their differential dissolution at pH values between 3 and 8. The quantification of solid-phase phosphates at varying pH revealed solubilities in the following order: OCP> HAP> CFAP (4.5% CO3)> CFAP (3.4% CO3)> CFAP (2.2% CO3)> FAP. Thus, CFAP was less soluble in sediment than HAP, and CFAP solubility increased with carbonate content. Unspiked sediment analyses together with standard addition analyses indicated consistent differential dissolution of natural sediment species vs. added reference species and therefore verified the applicability of the CONVEX method in separately determining the most prevalent Ca-P minerals. We found surprisingly high OCP contents in the coastal sediments analyzed, which supports the hypothesis of apatite formation by an OCP precursor mechanism

Authigenic apatite and octacalcium phosphate formation due to adsorption–precipitation switching across estuarine salinity gradients

Mechanisms governing phosphorus (P) speciation in coastal sediments remain largely unknown due to the diversity of coastal environments and poor analytical specificity for P phases. We investigated P speciation across salinity gradients comprising diverse ecosystems in a P-enriched estuary. To determine P load effects on P speciation we compared the high P site with a low P site. Octacalcium phosphate (OCP), authigenic apatite (carbonate fluorapatite, CFAP) and detrital apatite (fluorapatite) were quantitated in addition to Al/Fe-bound P (Al/Fe-P) and Ca-bound P (Ca-P). Gradients in sediment pH strongly affected P fractions across ecosystems and independent of the site-specific total P status. We found a pronounced switch from adsorbed Al/Fe-P to mineral Ca-P with decreasing acidity from land to sea. This switch occurred at near-neutral sediment pH and has possibly been enhanced by redox-driven phosphate desorption from iron oxyhydroxides. The seaward decline in Al/Fe-P was counterbalanced by the precipitation of Ca-P. Correspondingly, two location-dependent accumulation mechanisms occurred at the high P site due to the switch, leading to elevated Al/Fe-P at pH 6.6 (seaward; precipitation). Enhanced Ca-P precipitation by increased P loads was also evident from disproportional accumulation of metastable Ca-P (Ca-Pmeta) at the high P site. Here, sediments contained on average 6-fold higher Ca-Pmeta levels compared with the low P site, although these sediments contained only 2-fold more total Ca-P than the low P sediments. Phosphorus species distributions indicated that these elevated Ca-Pmeta levels resulted from transformation of fertilizer-derived Al/Fe-P to OCP and CFAP in nearshore areas. Formation of CFAP as well as its precursor, OCP, results in P retention in coastal zones and can thus lead to substantial inorganic P accumulation in response to anthropogenic P input

Ideas and perspectives : Tracing terrestrial ecosystem water fluxes using hydrogen and oxygen stable isotopes – challenges and opportunities from an interdisciplinary perspective

The authors thank Marialaura Bancheri, Michele Bottazzi, Roman Cibulka, Massimo Esposito, Alba Gallo, Cesar D. Jimenez-Rodriguez, Angelika Kuebert, Ruth Magh, Stefania Mambelli, Alessia Nannoni, Paolo Nasta, Vladimir Rosko, Andrea Rücker, Noelia Saavedra Berlanga, Martin Šanda, and Anna Scaini for their contributions during the discussion at the workshop “Isotope-based studies of water partitioning and plant–soil interactions in forested and agricultural environments”. The authors also thank “Villa Montepaldi” and the University of Florence for the access to the workshop location, and the municipality of San Casciano in Val di Pesa for logistical support. The authors thank the Department of Innovation, Research and University of the Autonomous Province of Bozen/Bolzano for covering the Open Access publication costs. Last, but not least, the authors wish to thank Matthias Sprenger, Stephen Good, and J. Renée Brooks, as well as the Editor David R. Bowling, whose constructive reviews greatly improved this manuscript.Peer reviewedPublisher PD

Response of Cocoa Trees (Theobroma cacao) to a 13-month Dessication Period in Sulawesi, Indonesia

In South-east Asia, ENSO-related droughts represent irregularly occuring hazards for agroforestry systems containing cocoa which are predicted to increase in severity with expected climate warming. To characterize the drought response of mature cocoa tree, we conducted the Sulawesi Throughfall Displacement Experiment in a shaded (Gliricidia sepium) cocoa agroforestry system in Central Sulawesi, Indonesia. Three large sub-canopy roofs were installed to reduce throughfall by about 80% over a 13-month period to test the hypotheses that (i) cocoa trees are sensitive to drought due to their shallow fine root system, and (ii)bean yield is more sensitive to drought than leaf or stem growth. As 83% of fine root (diameter 2mm) was located in the upper 40 cm of the soil, the cocoa tree examined had a very shallow root system. Cocoa and Gliricidia differed in their vertical rooting patterns, thereby reducing competition for water. Despite being exposed for several mnths to soil water contents close to the conventional wilting point, cocoa trees showed no significant decreases in leaf biomass, stem and branch wood production or fine root biomass. Possible causes are active osmotic adjusment in roots, mitigation of drought stress by shading from Gliricidia or other factors. By contrast, production of cocoa bean

The physiological responses of cacao to the environment and the implications for climate change resilience. A review

Cacao (Theobroma cacao L.) is a tropical perennial crop which is of great economic importance to the confectionary industry and to the economies of many countries of the humid tropics where it is grown. Some recent studies have suggested climate change could severely impact cacao production in West Africa. It is essential to incorporate our understanding of the physiology and genetic variation within cacao germplasm when discussing the implications of climate change on cacao productivity and developing strategies for climate resilience in cacao production. Here we review the current research on the physiological responses of cacao to various climate factors. Our main findings are 1) water limitation causes significant yield reduction in cacao but genotypic variation in sensitivity is evident, 2) in the field cacao experiences higher temperatures than is often reported in the literature, 3) the complexity of the cacao/ shade tree interaction can lead to contradictory results, 4) elevated CO2 may alleviate some negative effects of climate change 5) implementation of mitigation strategies can help reduce environmental stress, 6) significant gaps in the research need addressing to accelerate the development of climate resilience. Harnessing the significant genetic variation apparent within cacao germplasm is essential to develop modern varieties capable of high yields in non-optimal conditions. Mitigation strategies will also be essential but to use shading to best effect shade tree selection is crucial to avoid resource competition. Cacao is often described as being sensitive to climate change but genetic variation, adaptive responses, appropriate mitigation strategies and interactive climate effects should all be considered when predicting the future of cacao production. Incorporating these physiological responses to various environmental conditions and developing a deeper understanding of the processes underlying these responses will help to accelerate the development of a more resource use efficient tree ensuring sustainable production into the future

Soil CO₂ efflux in an old-growth southern conifer forest (<i>Agathis australis</i>) &ndash; magnitude, components and controls

Total soil CO₂ efflux and its component fluxes, autotrophic and heterotrophic respiration, were measured in a native forest in northern Aotearoa–New Zealand. The forest is dominated by <i>Agathis australis</i> (kauri) and is on an acidic, clay rich soil. Soil CO₂ efflux, volumetric soil water content and soil temperature were measured bi-weekly to monthly at 72 sampling points over 18 months. Trenching and regression analysis was used to partition total soil CO₂ efflux into heterotrophic and autotrophic respiration. The effect of tree structure was investigated by calculating an index of local contribution (<i>I</i>_c, based on tree size and distance to the measurement location) followed by correlation analysis between <i>I</i>_c and total soil CO₂ efflux, root biomass, litterfall and soil characteristics. The measured mean total soil CO₂ efflux was 3.47 µmol m⁻² s⁻¹. Autotrophic respiration accounted for 25 % (trenching) or 28 % (regression analysis) of total soil CO₂ efflux. Using uni- and bivariate models showed that soil temperature was a poor predictor of the temporal variation in total soil CO₂ efflux (&lt;  20 %). In contrast, a stronger temperature sensitivity was found for heterotrophic respiration (around 47 %). We found significant positive relationships between kauri tree size (<i>I</i>_c) and total soil CO₂ efflux, root biomass and mineral soil CN ratio within 5&ndash;6 m of the sampling points. Using multiple regression analysis revealed that 97 % of the spatial variability in total soil CO₂ efflux in this kauri-dominated stand was explained by root biomass and soil temperature. Our findings suggest that biotic factors such as tree structure should be investigated in soil carbon related studies

Tree diversity enhances tree transpiration in a Panamanian forest plantation

1. Tree plantations play an important role in meeting the growing demand for wood, but there is concern about their high rates of water use. Recent approaches to reforestation in the tropics involve the establishment of multispecies plantations, but few studies have compared water use in mixed vs. monospecific stands. 2. We hypothesized that tree species diversity enhances stand transpiration. Tree water use rates were estimated in monocultures (n = 5), two-species mixtures (n = 3), three-species mixtures (n = 3) and five-species mixtures (n = 4). Sap flux densities were monitored with thermal dissipation probes in 60 trees for 1 year in a 7-year-old native tree plantation in Panama. We also estimated changes in the amount of wood produced per unit water transpired (i.e. water use efficiency, WUEwood). 3. Annual stand transpiration rates in two-/three-species mixtures (464 +/- 271 mm year) 1) and five-species mixtures (900 +/- 76 mm year) 1) were 14% and 56% higher than those of monocultures (398 +/- 293 mm year) 1), respectively. Trees growing in mixtures had larger diameters, conductive sapwood and basal area than those in monocultures, which partly explained the enhanced stand transpiration in mixtures. 4. The five-species mixtures maintained equally high stand transpiration rates during wet (2 64 +/- 0 30 mm day) 1) and dry seasons (2 51 +/- 0 21 mm day) 1), whereas monocultures and two-species mixtures had significantly lower transpiration rates during the dry season, because of the presence of dry season deciduous species. 5. The WUEwood of the five-species mixtures (2.1 g DM kg(-1) H2O) was about half that of either monocultures, two-or three-species mixtures. 6. The comparably high stand transpiration rates in the five-species plots may arise from enhanced vegetation-atmosphere-energy exchange through higher canopy roughness and/or complementary use of soil water. 7. Synthesis and applications. Stand transpiration increased linearly with tree species richness and basal area in monocultures, two-and three-species mixtures, but the ratio of stand transpiration to basal area was larger for five-species mixtures. In conclusion, species selection and consideration of species richness and composition is crucial in the design of plantations to maximize wood production while conserving water resources

Partitioning of soil water among canopy trees during a soil desiccation period in a temperate mixed forest

Complementary resource use is considered an important mechanism in the study of biodiversity effects. Here we explore how species identity, species mixture and tree size influence the vertical partitioning of soil water among canopy trees during a soil desiccation period. In the Hainich Forest, Germany, the species &lt;i&gt;Fagus sylvatica&lt;/i&gt;, &lt;i&gt;Tilia&lt;/i&gt; sp. and &lt;i&gt;Fraxinus excelsior&lt;/i&gt; were studied in single- and three-species mixed clusters, each consisting of three co-dominant trees situated within a larger mixed forest stand. Vertical soil water uptake depth was assessed by analyzing the hydrogen stable isotope composition (deuterium, δD) of water from depth intervals throughout the soil profile and in tree xylem water. For single species clusters, a mixing model suggested that &lt;i&gt;Fagus&lt;/i&gt; distinctively drew water from soil depths of 0.3–0.5 m, &lt;i&gt;Tilia&lt;/i&gt; from 0.3–0.5 m and 0.5–0.7 m and &lt;i&gt;Fraxinus&lt;/i&gt; mainly used water from 0.5–0.7 m. In mixed clusters, the uptake patterns of &lt;i&gt;Fagus&lt;/i&gt; and &lt;i&gt;Tilia&lt;/i&gt; were similar to those of the single-species clusters (mainly uptake form 0.3–0.5 m), but &lt;i&gt;Fraxinus&lt;/i&gt; showed a different uptake pattern. &lt;i&gt;Fraxinus&lt;/i&gt; in mixture had a somewhat homogenously distributed uptake over the soil depths 0.2–0.7 m. For single species clusters, there was no correlation between main soil water uptake depth and tree diameter, irrespective of variations in tree size. In contrast, for mixed clusters there was a significant decrease in the main uptake depth with increasing tree size (&lt;i&gt;P&lt;/i&gt;&lt;0.001, &lt;i&gt;R&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt;&lt;sub&gt;adj&lt;/sub&gt; = 0.73), irrespective of species mix. In consequence, soil water partitioning was strongest where species were mixed &lt;i&gt;and&lt;/i&gt; tree size varied. We further analyzed whether single and mixed-species clusters differed in the level of water uptake, e.g. due to complementarity, but our soil water budgeting did not indicate any such differences. A possible explanation might be that the volume of water used is predominantly governed by properties at the stand level, such as aerodynamic roughness, rather than by processes acting at the meter scale between neighbouring trees. With respect to application, we assume that the upcoming close-to-nature forestry approach for the area, which fosters mixed stands of heterogonous diameters, may result in enhanced complementarity in soil water uptake among canopy trees