Derivation of a dynamic model of the kinetics of nitrogen uptake throughout the growth of lettuce : calibration and validation

A kinetic model of nitrogen (N) uptake throughout growth was developed for lettuce cultivated in nutrient solution under varying natural light conditions. The model couples nitrogen uptake with dry matter accumulation using a two-compartment mechanistic approach, incorporating structural and non-structural pools. Maximum nitrogen uptake rates are assumed to decline with shoot dry weight, to allow for the effects of plant age. The model was parameterized using data from the literature, and calibrated for differences in light intensity using an optimization algorithm utilizing data from three experiments in different growing seasons. The calibrated model was validated against the data from two independent experiments conducted under different light conditions. Results showed that the model made good predictions of nitrogen uptake by plants from seedlings to maturity under fluctuating light levels in a glasshouse. Plants grown at a higher light intensity showed larger maximum nitrogen uptake rates, but the effect of light intensity declined towards plant maturity

Hydraulic conductivity, xylem cavitation, and water potential for succulent leaves of agave deserti and agave tequilana

Journal ArticleAxial hydraulic conductivity (Kh) was measured for fresh, dehydrated, and rehydrated leaves of the Crassulacean acid metabolism (CAM) leaf succulents, Agave deserti and Agave tequilana. Dehydration of leaves at 35(o)C for several hours caused Kh to decrease, with a 50% decrease occurring at a leaf water potential of -2.37 MPa for A. deserti and at -1.72 MPa for A. tequilana

Advection, diffusion and delivery over a network

Many biological, geophysical and technological systems involve the transport of resource over a network. In this paper we present an algorithm for calculating the exact concentration of resource at any point in space or time, given that the resource in the network is lost or delivered out of the network at a given rate, while being subject to advection and diffusion. We consider the implications of advection, diffusion and delivery for simple models of glucose delivery through a vascular network, and conclude that in certain circumstances, increasing the volume of blood and the number of glucose transporters can actually decrease the total rate of glucose delivery. We also consider the case of empirically determined fungal networks, and analyze the distribution of resource that emerges as such networks grow over time. Fungal growth involves the expansion of fluid filled vessels, which necessarily involves the movement of fluid. In three empirically determined fungal networks we found that the minimum currents consistent with the observed growth would effectively transport resource throughout the network over the time-scale of growth. This suggests that in foraging fungi, the active transport mechanisms observed in the growing tips may not be required for long range transport.Comment: 54 pages including appendix, 10 figure

Hydraulic architecture of palms

Journal ArticleThe water transport and storage system of palms is adapted to maintain the primary stem xylem functional over the life of the shoot, and in spite of severe drought. However, our structural information far exceeds our knowledge of vascular function, and these functional considerations bring more questions than answers. The tendency to generalize from limited data on a few species begs the question of how the hydraulic parameters discussed vary between palms with different growth forms and ecologies

Not by transmission alone: the role of invention in cultural evolution

Innovation—the combination of invention and social learning—can empower species to invade new niches via cultural adaptation. Social learning has typically been regarded as the fundamental driver for the emergence of traditions and thus culture. Consequently, invention has been relatively understudied outside the human lineage—despite being the source of new traditions. This neglect leaves basic questions unanswered: what factors promote the creation of new ideas and practices? What affects their spread or loss? We critically review the existing literature, focusing on four levels of investigation: traits (what sorts of behaviours are easiest to invent?), individuals (what factors make some individuals more likely to be inventors?), ecological contexts (what aspects of the environment make invention or transmission more likely?), and populations (what features of relationships and societies promote the rise and spread of new inventions?). We aim to inspire new research by highlighting theoretical and empirical gaps in the study of innovation, focusing primarily on inventions in non-humans. Understanding the role of invention and innovation in the history of life requires a well-developed theoretical framework (which embraces cognitive processes) and a taxonomically broad, cross-species dataset that explicitly investigates inventions and their transmission. We outline such an agenda here. This article is part of the theme issue ‘Foundations of cultural evolution’

Patient- and Hospital-level Predictors of 30-day Readmission after Acute Coronary Syndrome: A Systematic Review

Background: Readmissions following acute myocardial infarction (AMI) are costly and may be partly due to poor care. A previous systematic review examined the literature through 2007. Since then, health policy has changed and additional articles examining predictors of readmission have appeared. We sought to conduct a systematic review of the literature after 2007 regarding socio-demographic, clinical, psychosocial, and hospital level predictors of 30-day readmissions after acute coronary syndrome. Methods: A systematic search of the literature using Pubmed, OVID, ISI web of science, CINAHL, ACP and the Cochrane Library was conducted, including a quality assessment using Downs and Black criteria. Articles reporting on 30-day readmission rate and examining at least one patient-level predictor of readmission at 30 days were included; articles examining interventions to reduce readmissions were excluded. Results: Twenty-two studies were included in this review from which more than 60 predictors of 30-day readmission were identified. Age, co-morbidity, COPD, diabetes, hypertension and having had a previous AMI were all consistently associated with higher risk of readmission. However, no studies reported psychosocial factors as predictors of readmission at 30 days. Conclusion: Studies of readmission should adjust for age and co-morbidity, consistent predictors of readmission at 30-days. Patients with these risk factors for readmission should be targeted for more-intensive follow-up after discharge. Psychosocial predictors of readmission remains a relatively unexplored area of research