Microhabitat effects on herbaceous nutrient concentrations at the community and species level in Mediterranean open woodlands: the role of species composition

The presence of a woody canopy in open oak woodlands affects not only the nutrition but also the species composition of the herbaceous community. Yet, the contribution of both effects (changes in nutrient concentrations and species composition) to total resources that are captured by the herbaceous community is not well understood. We assessed the mineral nutrition (N, P, K and Ca) of three herbaceous species and the herbaceous community as well as the species composition in contrasting microhabitats (beneath trees, beneath a leguminous shrub and in open spaces). Both trees and shrubs increased the nutrient concentrations of the herbaceous species that were studied, except for Taraxacum officinale. Their effects were less consistent when the entire community was considered and depended upon the nutrient being analysed. Species richness and N, P and K concentrations were positively associated, suggesting that more nutrients are captured by the herbaceous community as diversity increases. Our results suggest a close relationship between species composition and nutritional value at the community level that may explain the discrepancies observed between both levels of analysis (species vs. community). Thus, farm-level strategies based on the whole herbaceous community may overlook processes operating at the species level, which can be relevant to achieve sustainable management.     

Vertical root separation and light interception in a temperate tree-based intercropping system of Eastern Canada

We analysed the spatial distribution of fine roots and light availability in a tree-based intercrop system (TBI) composed of Quercus rubra L. (QUR), hybrid poplar (Populus deltoides × Populus nigra—HYP) and hay (CROP) in southern Québec (Canada) to evaluate interactions between trees and crop. Trees in the 8-year-old TBI system had superficial fine root profiles, which is common in tree species grown in conventional plantations and natural forests. More than 95 % of fine roots were found within the first 25 and 45 cm for QUR and HYP, respectively, and 35 cm for CROP. However, vertical separation between the fine root systems of QUR and CROP was evident, as QUR allocated less fine roots to the top 10 cm of soil, and more to depths between 10 and 30 cm, as opposed to CROP which had a greater proportion of fine roots in the top 10 cm. HYP fine roots showed no adaption when intercropped with hay. High tree fine root length density (FRLD) in the top soil layer was observed near the tree stems while hay FRLD was reduced by 45 %, suggesting strong competition for resources. Hay yield analysis revealed significant reduction near trees, particularly HYP. However, light did seem to be the main driver of intercrop yield, as it not only accounted for the effect of competition by roots (being correlated), but also had a singular effect.     

Observation of transient structural-transformation dynamics in a Cu2S nanorod

The study of first-order structural transformations has been of great interest to scientists in many disciplines. Expectations from phase-transition theory are that the system fluctuates between two equilibrium structures near the transition point and that the region of transition broadens in small crystals. We report the direct observation of structural fluctuations within a single nanocrystal using transmission electron microscopy. We observed trajectories of structural transformations in individual nanocrystals with atomic resolution, which reveal details of the fluctuation dynamics, including nucleation, phase propagation, and pinning of structural domains by defects. Such observations provide crucial insight for the understanding of microscopic pathways of phase transitions.     

Willows rapidly affect microclimatic conditions and forage yield in two temperate short-rotation agroforestry systems

Temperate short-rotation agroforestry systems are promising solutions for environmentally and economically sound production of crops and woody biomass. Accurate estimates of microclimatic conditions and tree-crop interactions in these systems are clearly needed to improve their adoption and management, especially in northeastern North America. The objective of this study was to determine the effects of a windbreak and an alley cropping system that were planted with strips of short-rotation willow on microclimate and forage crop yields. Microclimatic conditions (wind speed, air temperature, air relative humidity, light availability, soil moisture, snow depth) and forage yields were measured at different distances from the willow strips in these two agroforestry systems and in agricultural control plots between the third (2020) and fourth years (2021) after experiment establishment. Willow strips significantly reduced wind speed in both experiments, despite their relatively short stature (260 cm, June 2021). Wind speed reduction was greatest (50 and 58% in alley cropping and windbreak systems, respectively) close to the willow strips (5 m), intermediate at 20 m (22% in both systems), and negligible at 50 m (windbreak system). A significant increase in daytime air temperature that reached almost 1 °C was measured close to the willow strips in the agroforestry systems, compared to control plots. Higher soil moisture was measured close to the windbreak. In both agroforestry systems, snow depth was significantly greater near the willow strips. In both systems, forage yield close to the willow strips was not different from that at any other measured distances and in the control plots, which suggests that no competition for resources occurred between the willows and the forage crop during the study. In July 2021, forage yield within the windbreak (0–50 m from the willow strip) was 44% greater than that in the control plots. The alley cropping system had significant negative (-12%, June 2020) and positive (+?13%, September 2021) effects on forage yield, possibly as a result of temporal variation in climatic conditions. Results of this study stress the importance of better understanding of intra- and inter-annual forage crop variability within agroforestry systems.

     

Entorhinal cortex layer III input to the hippocampus is crucial for temporal association memory

Associating temporally discontinuous elements is crucial for the formation of episodic and working memories that depend on the hippocampal-entorhinal network. However, the neural circuits subserving these associations have remained unknown. The layer III inputs of the entorhinal cortex to the hippocampus may contribute to this process. To test this hypothesis, we generated a transgenic mouse in which these inputs are specifically inhibited. The mutant mice displayed significant impairments in spatial working-memory tasks and in the encoding phase of trace fear-conditioning. These results indicate a critical role of the entorhinal cortex layer III inputs to the hippocampus in temporal association memory.     

Agroforestry potential for adaptation to climate change: A soil-based perspective

Agricultural systems face several challenges that threaten their capacity to feed the world while maintaining a healthy and functional environment. Climate change, together with soil degradation, biodiversity loss, resource scarcity and invasive species, is a major threat to agricultural systems worldwide. In this context, new practices have been proposed to circumvent or minimize these threats. Yet, these mostly focus on the farm or plant level (e.g., breeding for stress-tolerant species), while frequently overlooking belowground components (e.g., soil organic carbon accrual). By interlinking above- and below-ground components, the likelihood of limiting the negative effects of current threats to agricultural systems can be maximized. This review explores current knowledge regarding agroforestry and its effects on belowground components as a key property in the reducing effects of climate change. We first review tree effects on key soil properties of agricultural systems. We synthesize evidence regarding agroforestry systems response to current environmental threats that are related to climate change. We continue by discussing how soil processes play a fundamental role in the capacity of agroforestry systems to cope with climate change. We conclude by proposing options on how resilience of agroforestry systems could be further enhanced.     

A dynamic model of protein digestion in the small intestine of pigs

A dynamic mathematical model of the digestion of proteins in the small intestine of pigs was developed. The model integrates current knowledge on the transit of digesta along the small intestine, endogenous secretions, digestion of proteins, and absorption of amino acids into a mechanistic representation of digestion. The main characteristics of the model are the following: the small intestine is divided into several segments of variable length but with equal digesta retention time; the rate of transfer of digesta between segments is based on the progression of myoelectric migration complexes; pancreatic and biliary secretions are poured into the first segment, whereas intestinal secretions enter all intestinal segments; protein hydrolysis is described by first-order equations; and an intestinal absorption capacity is used to estimate absorption of hydrolyzed protein. Simulation results are consistent with observed data, although more information is needed to represent reality more closely. The sensitivity analysis shows that parameters for protein hydrolysis largely determine protein digestibility. The absorption capacity of the small intestine limits the absorption of amino acids at the beginning of a meal and modulates the appearance of amino nitrogen in the portal vein. It also shows that amino acid absorption can be limiting to protein digestibility when large amounts of protein are eaten in a single daily meal. The model is useful in evaluating the dynamics of protein digestion and absorption of feedstuffs. The model can be used in evaluating protein digestion of different feedstuffs and feeding strategies.     

Intercropping hybrid poplar with soybean increases soil microbial biomass,mineral N supply and tree growth

We hypothesized that tree-based intercropping in southwestern Québec, Canada, would stimulate soil microbial activity and increase soil nutrient supply, thereby benefiting the growth of trees. Our experimental design comprised alternating rows of hybrid poplar (Populus nigra L. × P. maximowiczii A. Henry) and high-value hardwood species spaced 8 m apart, between which two alley treatments were applied 5–6 years after planting the trees. The first alley treatment consisted of a fertilized soybean (Glycine max (L.) Merr.) intercrop grown over two consecutive years, while the second consisted of repeatedly harrowing to minimize vegetation in the alley. Tree rows were mulched with a 1.5 m wide polythene mulch. Microbial respiration and biomass, and mineral N concentrations and mineralization rates were measured on five or six dates at 0, 2 and 5 m from hybrid poplar rows. On some of the sampling dates, we found significantly higher soil microbial biomass, mineral N concentrations and nitrification rates, and a significantly lower microbial metabolic quotient (qCO₂), in the soybean intercropping than in the harrowing treatment. Over the 2 year period, hybrid poplar biomass increment and N response efficiency (NRE) were significantly higher (51 and 47%, respectively) in the intercropping than in the harrowing treatment. Microbial biomass and mineral N supply were significantly lower beneath the polyethylene mulch than in the alleys, and we posit that this may stimulate the growth of tree roots into the alley. We conclude that soybean intercropping improves nutrient turnover and supply for hybrid poplar trees, thereby increasing the land equivalent ratio (LER).