Dissolved and colloidal phosphorus fluxes in forest ecosystems—an almost blind spot in ecosystem research

Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “Ecosystem Nutrition: Forest Strategies for limited Phosphorus Resources” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L^?1, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m^?2 a^?1, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.     

Adsorption controls mobilization of colloids and leaching of dissolved phosphorus

Loss of phosphorus (P) from agriculture contributes to the eutrophication of surface waters. We have assessed the magnitude and controls of P leaching and the risk of colloid‐facilitated transport of P from sandy soils in Münster. Concentrations of soluble reactive P in drainage water and groundwater were monitored from 0.9 to 35 m depth. Total P concentrations, P saturation, and P sorption isotherms of soil samples were determined. Concentrations of dispersible soil P and colloidal P in drainage water and groundwater were investigated. The concentrations of soluble reactive P in drainage water and groundwater were close to background concentrations (< 20 µg P l^?1). Median concentrations in excess of 100 µg P l^?1 were found down to 5.6 m depth at one of four research sites and in the lower part of the aquifer. Experimentally determined equilibrium concentrations and the degree of P saturation were good predictors of P concentrations of drainage water. Large concentrations of dispersible P were released from soil with large concentrations of oxalate‐extractable P and addition of P induced further dispersion. Colloidal P was transported in a P‐rich subsoil when there was a large flow of water and after nitrate had been flushed from the soil profile and total solute concentrations were small. We conclude that the concentration of soluble reactive P in drainage water is controlled by rapid adsorption in the sandy soils. Subsurface transport of dissolved P contributes substantially to the loss of P from the soils we investigated. Accumulation of P in soils increases the risk of colloid‐facilitated leaching of P.     

Evidence for a cultivar and a chronology from patterned wetlands in central veracruz, Mexico

The patterning found in certain wetlands of lowland Mesoamerica has added an important element to the subsistence system that may be attributed to pre-Hispanic inhabitants of the region. The form of the remains, largely expressed in terms of surface vegetation, suggests agriculture on planting platforms, separated by canals. The physical and chemical aspects of the stratigraphy have clarified depositional environments but have not indicated agricultural horizons. Maize phytoliths at about 1 meter below the surface in two Central Veracruzan wetlands do confirm the practice of agriculture. Associated ceramics indicate wetlands agriculture was practiced by A.D. 500 and perhaps earlier.     

Effects of dietary water content on meal size, daily food intake, digestion and growth in turbot, Scophthalmus maximus (L.)

When fed once daily with wet squid, turbot (30–50 g) accustomed to dry pellets require many days to increase intake to meet their feed requirement (≈ 10 mg dry matter g⁻¹ bw meal⁻¹). Adaptation takes 1–2 days if several daily feedings are given. With dried squid, they ingest about 20% of the wet squid bulk because the stomach contents expand when moisturised. In contrast, turbot eat enough wet squid to fill most of the available stomach volume (≈ 7.6 mL 100 g⁻¹ bw). When presented in gelatine capsules, food water content is masked and does not affect the volume ingested. Moistening the contents shortens the delay before gastric emptying starts to one-third (0.6 h) compared with dry food (1.9 h). Daily dry-matter intake increased when dry contents were moistened but only if two or more meals were offered per day. Turbot adapt their digestion to supply water for dry diets but this may add extra metabolic costs. When offered 20 mg dry matter g bw⁻¹ day⁻¹, divided into four equal meals, turbot grew faster and more efficiently with moist than with dry squid. Protein, energy and dry-matter digestibilities were also enhanced. The increased daily protein absorption did not increase ammonia release, indicating that the extra protein was used for somatic growth.     

Yearling adjustments for pelvic area of test station bulls

Yearling bulls (n = 3,071) located at 18 stations in Missouri, Nebraska, Virginia, and Wisconsin were measured for pelvic area, in addition to standard performance traits. Linear adjustments for age and weight were determined using covariate regression analyses. Only bulls that were 300 to 452 d of age, 325 to 640 kg, and were in consignments offering more than nine bulls per breed were included in the analyses. Because the subsets of Angus, Polled Hereford, and Simmental bulls had large numbers of observations (817, 271, and 449, respectively), individual adjustment coefficients were determined for each breed. Angus, Polled Hereford, and Simmental bulls had pelvic area adjustment regressions on age of .20, .32, and .20 cm2/d, respectively, and regressions on body weight of .15, .22, and .18 cm2/kg, respectively. Homogeneous linear responses of all breeds (11 breeds including Angus, Polled Hereford, and Simmental) were combined to form all-breed coefficients for age and weight adjustments, which were .21 cm2/d and .15 cm2/kg, respectively. Weight or age adjustments can be used to compare contemporaries for relative pelvic area differences, but both should not be used on the same bull. Although many factors contribute to dystocia, high priority should be given to identifying sires of replacement heifers of low to moderate birth weight genotype and above average pelvic area genotype.     

Sorption of copper (II) and sulphate to different biochars before and after composting with farmyard manure

Biochar application has been suggested for reducing toxic levels of metals in contaminated soils and enhancing nutrient retention in agro‐ecosystems. We studied sorption of copper (Cu(II)) and sulphate‐sulphur (SO₄‐S) to charcoal, gasification coke and flash‐pyrolysis biochar in order to relate sorption to char properties. Furthermore, we investigated the effect of composting of charcoal and gasification coke on sorptive properties. Langmuir sorption affinity coefficients for Cu(II) for non‐composted biochars increased in the order flash‐pyrolysis char < charcoal < gasification coke. The sorption capacity for Cu(II) of the chars decreased in the order gasification coke (629 mg kg^?1) > flash‐pyrolysis char (196 mg kg^?1) > charcoal (56 mg kg^?1). Composting significantly increased the sorption affinity coefficient approximately by a factor of 5 for charcoal (up to 1.1 l mg^?1) and by a factor of 3–4 for gasification coke (up to 3.2 l mg^?1). Whereas Cu(II) sorption to gasification coke (composted or not) was largely irreversible, sorption to flash‐pyrolysis char and charcoal showed higher reversibility. Relationships between Cu(II) sorption and biochar properties such as cation exchange capacity, specific surface area or aromaticity suggest that sorption was largely determined by complexation with organic matter. Sorption of SO₄‐S was negligible by non‐composted and composted biochars. Composted gasification coke might be suited to reducing toxic Cu(II) concentrations in contaminated soils. Composted charcoal can potentially improve Cu(II) retention in a plant available form in acidic, sandy soils with small organic matter contents. Transient effects of biochars on soil pH can over‐ride the influence of sorption to biochars on concentrations of trace elements in soil solution and their availability to plants.     

Hebeloma crustuliniforme facilitates ammonium and nitrate assimilation in trembling aspen (Populus tremuloides) seedlings

This study examined the role of ectomycorrhizal associations in nitrogen assimilation of Populus tremuloides seedlings. Seedlings were inoculated with Hebeloma crustuliniforme and compared with non-inoculated plants. Nitrogen-metabolizing enzymatic properties were also determined in H. crustuliniforme grown in sterile culture. The seedlings and fungal cultures were subjected to nitrogen treatments (including NO??, NH?? and a combination of NO???+?NH??) for 2 months to examine the effects on growth, nitrogen-assimilating enzyme activities and xylem sap concentrations of NH?? and NO??. Seedlings were also provided for 3 days with 1?N-labeled NH?? and NO??, and leaf and root 1?N content relative to total nitrogen was measured. Both NO?? and NH?? were effective in supporting seedling growth when either form was provided separately. When NO?? and NH?? were provided together, seedling growth decreased while enzymatic assimilation of NH?? increased. Additionally, nitrogen assimilation in inoculated seedlings was less affected by the form of nitrogen compared with non-inoculated plants. Fungal ability to enzymatically respond to and assimilate NH?? combined with aspen's enzymatic responsiveness to NO?? was likely the reason for efficient assimilation of both nitrogen forms by mycorrhizal plants.