N-transfer through aspen litter and feather moss layers after fertilization with ammonium nitrate and urea

When fertilizer is broadcast in boreal forest stands, the applied nutrients must pass through a thick layer of either feather moss or leaf litter which covers the forest floor. In a growth chamber experiment we tested the transfer of N through living feather moss or aspen litter when fertilized with urea ((NH2)2CO) or NH4NO3 at a rate of 100 kg ha−1 and under different watering regimes. When these organic substrates were frequently watered to excess they allowed the highest transfer of nutrients through, although 72% of the applied fertilizer was captured in the substrates. In a field experiment we also fertilized moss and aspen litter with urea ((NH2)2CO) or NH4NO3 at a more operationally relevant rate of 330 kg ha−1. We captured the NO3− or NH4+ by ion exchange resin at the substrate–mineral soil interface. In contrast to the growth chamber experiment, this fertilizer rate killed the moss and there was no detectable increase in nutrient levels in the aspen litter or feather moss layers. Instead, the urea was more likely transferred into the mineral soil; mineral soil of the urea treatment had 1.6 times as much extractable N compared to the NH4NO3 treatment. This difference between the growth chamber and field studies was attributed to observed fertilizer- damage to the living moss and possibly damage to the litter microflora due to the higher rate of fertilization in the field. In addition, the early and substantial rainfall after fertilization in the field experiment produced conditions for rapid leaching of N through the organic layers into the mineral soil. In the field, only 8% of the urea-N that was applied was captured by the ion exchange resin, while 34% was captured in for the NH4NO3 fertilization. Thus, the conditions for rapid leaching in the field moved much of the N in the form of urea through the organic layers and into the mineral soil before it was hydrolyzed

A Slow Neutron Polarimeter for the Measurement of Parity-Odd Neutron Rotary Power

We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutronoptical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable ofmeasuring a neutron rotary power of dϕ/dz = 1 × 10−7 rad/m

A Slow Neutron Polarimeter for the Measurement of Parity-Odd Neutron Rotary Power

We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10−7 rad/m

Light and tree size influence belowground development in yellow birch and sugar maple

The effects of light and tree size on the root architecture and mycorrhiza of yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh) growing in the understory of deciduous forests in southern Qu

The motion of trees in the wind : a data synthesis

Interactions between wind and trees control energy exchanges between the atmosphere and forest canopies. This energy exchange can lead to the widespread damage of trees, and wind is a key disturbance agent in many of the world’s forests. However, most research on this topic has focused on conifer plantations, where risk management is economically important, rather than broadleaf forests, which dominate the forest carbon cycle. This study brings together tree motion time-series data to systematically evaluate the factors influencing tree responses to wind loading, including data from both broadleaf and coniferous trees in forests and open environments. Wefoundthatthetwomostdescriptive features of tree motion were (a) the fundamental frequency, which is a measure of the speed at which a tree sways and is strongly related to tree height, and (b) the slope of the power spectrum, which is related to the efficiency of energy transfer from wind to trees. Intriguingly, the slope of the power spectrum was found to remain constant from medium to high wind speeds for all trees in this study. This suggests that, contrary to some predictions, damping or amplification mechanisms do not change dramatically at high wind speeds, and therefore wind damage risk is related, relatively simply, to wind speed. Conifers from forests were distinct from broadleaves in terms of their response to wind loading. Specifically, the fundamental frequency of forest conifers was related to their size according to the cantilever beam model (i.e. vertically distributed mass), whereas broadleaves were better approximated by the simple pendulum model (i.e. dominated by the crown). Forest conifers also had a steeper slope of the power spectrum. We interpret these finding as being strongly related to tree architecture; i.e. conifers generally have a simple shape due to their apical dominance, whereas broadleaves exhibit a much wider range of architectures with more dominant crowns

Mountain maple and balsam fir early response to partial and clear-cut harvesting under aspen stands of northern Quebec

This study is a component of the Sylviculture et am

Nutritional Systems Biology Modeling: From Molecular Mechanisms to Physiology

The use of computational modeling and simulation has increased in many biological fields, but despite their potential these techniques are only marginally applied in nutritional sciences. Nevertheless, recent applications of modeling have been instrumental in answering important nutritional questions from the cellular up to the physiological levels. Capturing the complexity of today's important nutritional research questions poses a challenge for modeling to become truly integrative in the consideration and interpretation of experimental data at widely differing scales of space and time. In this review, we discuss a selection of available modeling approaches and applications relevant for nutrition. We then put these models into perspective by categorizing them according to their space and time domain. Through this categorization process, we identified a dearth of models that consider processes occurring between the microscopic and macroscopic scale. We propose a “middle-out” strategy to develop the required full-scale, multilevel computational models. Exhaustive and accurate phenotyping, the use of the virtual patient concept, and the development of biomarkers from “-omics” signatures are identified as key elements of a successful systems biology modeling approach in nutrition research—one that integrates physiological mechanisms and data at multiple space and time scales

Using Root Carbohydrates Reserves as an Indicator of Vulnerability to Defoliation in Trembling Aspen

Tent caterpillar (Malacosoma disstria [H¸bner]) and large aspen tortrix (Choristoneura conflictana [Walker]) are native defoliators of trembling aspen (Populus tremuloides Michx.) in the boreal forests of North America. Defoliation events can be sporadic and localized but there can be large scale outbreaks covering hundreds of square kilometers. Large outbreaks are thought to occur in 10-year cycles and can last several years. Generally it is thought that defoliation events have short-term effects on aspen productivity but do not result in significant mortality, as aspen reflushes after these spring defoliation events. However, in combination with other stressors such as drought, it has been observed that aspen clones can be weakened and are more susceptible to stem dieback or even clone mortality. Over a period of 8 years we determined seasonal carbohydrate reserves of different tissues in aspen clones. Non-structural carbohydrate reserves were determined in twig, stem and root samples from 9 different clones. During the collection period some of the aspen clones were defoliated in 2000 and/or 2007. After defoliation, tissue carbohydrate reserves in stems and twigs recovered by the end of the same summer. In contrast, in roots, carbohydrates reserves (particularly starch) were still depressed the second summer after defoliation, relative to clones that were not defoliated. After only one defoliation event starch reserves in the roots were close to zero, suggesting that repeated defoliations could have significant impacts on the survival of aspen clones. The research indicates that root reserves are severely impacted by defoliation and that clones with already low carbohydrate reserves are likely at a higher risk of dieback and mortality and could function as a valuable indicator to assess risks of clonal dieback in aspen