Exposure to preindustrial, current and future atmospheric CO2 and temperature differentially affects growth and photosynthesis in Eucalyptus

To investigate if Eucalyptus species have responded to industrial-age climate change, and how they may respond to a future climate, we measured growth and physiology of fast- ( E. saligna ) and slow-growing ( E. sideroxylon ) seedlings exposed to preindustrial (290), current (400) or projected (650 μL L⁻¹) CO₂ concentration ([CO₂]) and to current or projected (current +4 °C) temperature. To evaluate maximum potential treatment responses, plants were grown with nonlimiting soil moisture. We found that: (1) E. sideroxylon responded more strongly to elevated [CO₂] than to elevated temperature, while E. saligna responded similarly to elevated [CO₂] and elevated temperature; (2) the transition from preindustrial to current [CO₂] did not enhance eucalypt plant growth under ambient temperature, despite enhancing photosynthesis; (3) the transition from current to future [CO₂] stimulated both photosynthesis and growth of eucalypts, independent of temperature; and (4) warming enhanced eucalypt growth, independent of future [CO₂], despite not affecting photosynthesis. These results suggest large potential carbon sequestration by eucalypts in a future world, and highlight the need to evaluate how future water availability may affect such responses.     

Limitation to Photosynthesis in Water-stressed Leaves: Stomata vs. Metabolism and the Role of ATP

Decreasing relative water content (RWC) of leaves progressivelydecreases stomatal conductance (g_s), slowing CO₂ assimilation(A) which eventually stops, after which CO₂ is evolved. In somestudies, photosynthetic potential (A_pot), measured under saturatingCO₂, is unaffected by a small loss of RWC but becomes progressivelymore inhibited, and less stimulated by elevated CO₂, below athreshold RWC (Type 1 response). In other studies, A_pot andthe stimulation of A by elevated CO₂ decreases progressivelyas RWC falls (Type 2 response). Decreased A_pot is caused byimpaired metabolism. Consequently, as RWC declines, the relativelimitation of A by g_s decreases, and metabolic limitation increases.Causes of decreased A_pot are considered. Limitation of ribulosebisphosphate (RuBP) synthesis is the likely cause of decreasedA_pot at low RWC, not inhibition or loss of photosynthetic carbonreduction cycle enzymes, including RuBP carboxylase/oxygenase(Rubisco). Limitation of RuBP synthesis is probably caused byinhibition of ATP synthesis, due to progressive inactivationor loss of Coupling Factor resulting from increasing ionic (Mg²⁺)concentration, not to reduced capacity for electron or protontransport, or inadequate trans-thylakoid proton gradient (pH).Inhibition of A_pot by accumulation of assimilates or inadequateinorganic phosphate is not considered significant. DecreasedATP content and imbalance with reductant status affect cellmetabolism substantially: possible consequences are discussedwith reference to accumulation of amino acids and alterationsin protein complement under water stress.     

Parental role division predicts avian preen wax cycles

Previous studies have shown that preen wax composition in some sandpipers shifts from the usual monoesters to diesters during the breeding season, possibly to reduce the ability of mammalian predators to find nests using olfactory cues. To investigate further the relationship between incubation and wax secretion, we examined seven sandpiper species with different incubation patterns (species in which both sexes incubate, in which only males incubate and in which only females incubate). During the breeding period, diester preen wax was secreted almost exclusively by the incubating sex in species with uniparental incubation, and by both sexes in species with biparental incubation. These findings suggest that diester preen waxes have a function that is directly related to incubation. Unexpectedly, in female-incubating Curlew Sandpiper Calidris ferruginea and Buff-breasted Sandpiper Tryngites subruficollis , some males also secreted diester preen waxes during the breeding period. This suggests that some males may in fact incubate, that these waxes may be a remnant from their evolutionary past when both sexes incubated, or that males need to be olfactorally cryptic because they are involved in the making of nest scrapes. The seasonal pattern of preen wax composition was also studied in captive male, female and female-mimicking male ('faeder') Ruff Philomachus pugnax . Captive female Ruff changed preen wax composition from monoesters to diesters in the spring despite the fact that no incubation took place. This suggests that circannual rhythms rather than actual incubation behaviour may trigger the shift to diester waxes. All captive male Ruff, including the faeders, continued to secrete monoesters, supporting the hypothesis that only the incubating sex secretes diesters.     

A cross-biome comparison of daily light use efficiency for gross primary production

Vegetation light use efficiency is a key physiological parameter at the canopy scale, and at the daily time step is a component of remote sensing algorithms for scaling gross primary production (GPP) and net primary production (NPP) over regional to global domains. For the purposes of calibrating and validating the light use efficiency ( ε _g) algorithms, the components of ε _g– absorbed photosynthetically active radiation (APAR) and ecosystem GPP – must be measured in a variety of environments. Micrometeorological and mass flux measurements at eddy covariance flux towers can be used to estimate APAR and GPP, and the emerging network of flux tower sites offers the opportunity to investigate spatial and temporal patterns in ε _g at the daily time step. In this study, we examined the relationship of daily GPP to APAR, and relationships of ε _g to climatic variables, at four micrometeorological flux tower sites – an agricultural field, a tallgrass prairie, a deciduous forest, and a boreal forest. The relationship of GPP to APAR was close to linear at the tallgrass prairie site but more nearly hyperbolic at the other sites. The sites differed in the mean and range of daily ε _g, with higher values associated with the agricultural field than the boreal forest. ε_g decreased with increasing APAR at all sites, a function of mid‐day saturation of GPP and higher ε _g under overcast conditions. ε _g was generally not well correlated with vapor pressure deficit or maximum daily temperature. At the agricultural site, a ε _g decline towards the end of the growing season was associated with a decrease in foliar nitrogen concentration. At the tallgrass prairie site, a decline in ε _g in August was associated with soil drought. These results support inclusion of parameters for cloudiness and the phenological status of the vegetation, as well as use of biome‐specific parameterization, in operational ε _g algorithms.     

Regeneration of Hydra from Reaggregated Cells

Separated cells of hydra reaggregate and develop into normal animals. The regeneration of serially grafted aggregates derived from different parts of hydra tissue demonstrates that the polarity of morphogenesis in hydra is the result of the cellular composition of the tissue, not cellular orientation.     

Age determination of Acacia tortilis (Forsk.) Hayne from northern Kenya

Age determination on the basis of ring count holds great potential for the study of dry woodland ecosystem dynamics. Discs from stems of Acacia tortilis from Marsabit District, northern Kenya, were collected for dendrochronological analysis. Problems in the identification of growth rings are summarized. Regression analysis is used to develop age–ring count and ring count–size relationships. The time seedlings spend in a browse‐suppressed state is also estimated. It is concluded that there is insufficient evidence for the development of statistically valid age–size relationships. Problems that current techniques have yet to overcome are identified. Future studies are recommended using cambial injury techniques, particular emphasis being placed on the potential effects of browsing on cambial activity.     

A Fatigue-Based Model of Disuse Osteoporosis

A theoretical model has been developed for predicting the extent of bone adaptation as a function of exercise level. The model works by estimating the amount of fatigue damage which will occur for a given cyclic strain. This allowed us to predict that there would be a difference in the strengths of bones taken from sedentary individuals compared to those from more active individuals. The predicted difference, expressed as the ratio of the fatigue strengths of the two bones, was 1.53.

Experimental tests were carried out using bones from chickens, comparing those kept in battery cages (who are unable to engage in any strenuous activity) with those kept in normal free-range conditions. A finite element model was used to ensure that the in vitro fatigue tests were conducted at strain levels within the physiological range. Significant differences in both static and fatigue strength were found for the radius and tibia bones. These differences could be accurately predicted by the theoretical model, after a slight difference in weight between the two groups was allowed for. Additional evidence for these predictions can also be found in the literature. This work supports the concept that bone adaptation is driven by the need to optimise fatigue damage accumulation.