Effects of flooding on photosynthesis and root respiration in Salt cedar (tamarix ramosissima), an invasive riparian shrub

The introduced shrub Tamarix ramosissima Lebed. invades riparian zones, but loses competitiveness under flooding. This was tested in Tamarix ramosissima by examining responses to flooding by soil type in a greenhouse setting. A field study examined responses of Tamarix ramosissima and other species to natural flooding. Leaf level photosynthesis rates, stomatal conductance, transpiration, and root alcohol dehydrogenase (ADH) activity were measured weekly to assess oxygen stress. In the field, stomatal conductance, leaf water potential, transpiration, canopy cover, and δ13C were measured as responses to soil water potential, soil moisture, Julian date, relative humidity, and water depth. In the greenhouse study, flooding affected Tamarix ramosissima initially. Photosynthesis rates within flooded plants ranged from 7.5 to 14 μmol CO2 m-2 s-1 during the first two weeks, but increased to 26.9 to 27 μmol CO2 m-2 s-1 by the fourth week. As flooding progressed, photosynthesis rates increased as plants became acclimated. Lower photosynthesis rates at the onset of flooding could account for the susceptibility of Tamarix ramosissima to flooding. Soil type had no effect on photosynthesis rates or on root ADH activity. Root ADH activity was higher in flooded plants compared to drained plants, indicating oxygen stress in flooded plants. The ability of Tamarix ramosissima to acclimate to flooding within four weeks indicated metabolic acclimation. In the field study, Tamarix ramosissima had lower stomatal conductance and leaf water potential compared to Populus deltoides Bartr. and Phragmites australis (Cav.) Trin. ex Steud at -1.4 MPa and 1.5 mol H2O m-2 s-1. Lower leaf water potential and stomatal conductance in the field can also account for loss of competitiveness of Tamarix ramosissima under flooding. Typha angustifolia L. had the highest canopy cover compared to Tamarix ramosissima, Melilotus officinalis (L.) Lam., Baccharis salicina Torr. & A. Gray, and Saccharum ravennae (L.) L. Differences in canopy cover indicated Typha angustifolia was more tolerant of flooding compared to Tamarix ramosissima. Nonetheless, T. ramosissima is more flooding tolerant than previously realized. Differences in physiological responses for Tamarix ramosissima could become important for ecological or management concerns with this species

The sources of sex differences in aging in annual fishes

Intersexual differences in life span (age at death) and aging (increase in mortality risk associated with functional deterioration) are widespread among animals, from nematodes to humans. Males often live shorter than females, but there is substantial unexplained variation among species and populations. Despite extensive research, it is poorly understood how life span differences between the sexes are modulated by an interplay among genetic, environmental and social factors. The goal of our study was to test how sex differences in life span and ageing are modulated by social and environmental factors, and by intrinsic differences between males and females. To disentangle the complex basis of sex differences in life span and aging, we combined comparative data from sex ratios in 367 natural populations of four species of African annual killifish with experimental results on sex differences in life span and aging from eight laboratory populations tested in treatments that varied social and environmental conditions. In the wild, females consistently outlived males. In captivity, sex-specific mortality depended on social conditions. In social-housed experimental groups, male-biased mortality persisted in two aggressive species, but ceased in two placid species. When social and physical contacts were prevented by housing all fish individually, male-biased mortality ceased in all four species. This outcome held across benign and challenging environmental conditions. Fitting demographic survival models revealed that increased baseline mortality was primarily responsible for a shorter male life span in social-housing conditions. The timing and rate of aging were not different between the sexes. No marker of functional aging we recorded in our study (lipofuscin accumulation, proliferative changes in kidney and liver) differed between males and females, despite their previously confirmed association with functional aging in Nothobranchius killifish. We show that sex differences in life span and aging in killifish are driven by a combination of social and environmental conditions, rather than differential functional aging. They are primarily linked to sexual selection but precipitated through multiple processes (predation, social interference). This demonstrates how sex-specific mortality varies among species even within an ecologically and evolutionary discrete lineage and explains how external factors mediate this difference

A new critical curve for a class of quasilinear elliptic systems

We study a class of systems of quasilinear differential inequalities associated to weakly coercive differential operators and power reaction terms. The main model cases are given by the $p$-Laplacian operator as well as the mean curvature operator in non parametric form. We prove that if the exponents lie under a certain curve, then the system has only the trivial solution. These results hold without any restriction provided the possible solutions are more regular. The underlying framework is the classical Euclidean case as well as the Carnot groups setting.Comment: 28 page

Propagation and blocking in periodically hostile environments

We study the persistence and propagation (or blocking) phenomena for a species in periodically hostile environments. The problem is described by a reaction-diffusion equation with zero Dirichlet boundary condition. We first derive the existence of a minimal nonnegative nontrivial stationary solution and study the large-time behavior of the solution of the initial boundary value problem. To the main goal, we then study a sequence of approximated problems in the whole space with reaction terms which are with very negative growth rates outside the domain under investigation. Finally, for a given unit vector, by using the information of the minimal speeds of approximated problems, we provide a simple geometric condition for the blocking of propagation and we derive the asymptotic behavior of the approximated pulsating travelling fronts. Moreover, for the case of constant diffusion matrix, we provide two conditions for which the limit of approximated minimal speeds is positive

Quasiperiodic solutions of elliptic equations on the entire space via center manifold and KAM theorems

We consider elliptic equations on the entire space of 2 or more dimensions. Using center manifold and KAM theorems, we show the existence of solutions which are quasiperiodic in one variable and decay in all the other variables.Non UBCUnreviewedAuthor affiliation: University of MinnesotaFacult