Implications of future climate and atmospheric CO2 content for regional biogeochemistry,biogeography and ecosystem services across East Africa

We model future changes in land biogeochemistry and biogeography across East Africa. East Africa is one of few tropical regions where general circulation model (GCM) future climate projections exhibit a robust response of strong future warming and general annual‐mean rainfall increases. Eighteen future climate projections from nine GCMs participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment were used as input to the LPJ dynamic global vegetation model (DGVM), which predicted vegetation patterns and carbon storage in agreement with satellite observations and forest inventory data under the present‐day climate. All simulations showed future increases in tropical woody vegetation over the region at the expense of grasslands. Regional increases in net primary productivity (NPP) (18–36%) and total carbon storage (3–13%) by 2080–2099 compared with the present‐day were common to all simulations. Despite decreases in soil carbon after 2050, seven out of nine simulations continued to show an annual net land carbon sink in the final decades of the 21st century because vegetation biomass continued to increase. The seasonal cycles of rainfall and soil moisture show future increases in wet season rainfall across the GCMs with generally little change in dry season rainfall. Based on the simulated present‐day climate and its future trends, the GCMs can be grouped into four broad categories. Overall, our model results suggest that East Africa, a populous and economically poor region, is likely to experience some ecosystem service benefits through increased precipitation, river runoff and fresh water availability. Resulting enhancements in NPP may lead to improved crop yields in some areas. Our results stand in partial contradiction to other studies that suggest possible negative consequences for agriculture, biodiversity and other ecosystem services caused by temperature increases.     

Challenges to estimating carbon emissions from tropical deforestation

An accurate estimate of carbon fluxes associated with tropical deforestation from the last two decades is needed to balance the global carbon budget. Several studies have already estimated carbon emissions from tropical deforestation, but the estimates vary greatly and are difficult to compare due to differences in data sources, assumptions, and methodologies. In this paper, we review the different estimates and datasets, and the various challenges associated with comparing them and with accurately estimating carbon emissions from deforestation. We performed a simulation study over legal Amazonia to illustrate some of these major issues. Our analysis demonstrates the importance of considering land-cover dynamics following deforestation, including the fluxes from reclearing of secondary vegetation, the decay of product and slash pools, and the fluxes from regrowing forest. It also suggests that accurate carbon-flux estimates will need to consider historical land-cover changes for at least the previous 20 years. However, this result is highly sensitive to estimates of the partitioning of cleared carbon into instantaneous burning vs. long-timescale slash pools. We also show that carbon flux estimates based on 'committed flux' calculations, as used by a few studies, are not comparable with the 'annual balance' calculation method used by other studies.     

Mechanisms of Sodium and Rubidium Uptake by Excised Barley Roots

Accumulation of sodium and rubidium by excised barley roots was investigated. The concentration isotherm yielded one absorption shoulder. Nevertheless, it is suggested that two mechanisms take part in the uptake of sodium and rubidium: One non-metabolic mechanism with an apparent participation at low external salt concentrations (< 1 mM) and at high concentrations (> 20 mM). Such a mechanism is almost unaffected by low temperature conditions and by metabolic inhibitors. Rubidium possesses a high affinity toward this non-metabolic system. The second mechanism is sensitive to metabolic inhibitors and to low temperature conditions. It dominates at intermediate external concentrations (1–20 mM). Sodium possesses high affinity towards this mechanism. The two mechanisms operate in a parallel manner beyond a diffusion barrier (= plasmamembrane) surrounding the cells. It is assumed that both the metabolic and the non-metabolic mechanisms operate in the entire concentration spectrum, but their relative contribution to the total uptake varies at different ranges.     

Relationships between Motor Cell Ultrastructure and Leaf Movements in Samanea saman

We examined the fine structure of motor cells in the secondary pulvinus of Samanea saman (Jacq.) Merrill, to aid in analyzing the cellular basis for K⁺ and Cl^? driven, turgor regulated circadian leaflet movements. Pulvini that were (a) open (horizontal) in the light, (b) closed (vertical) in the dark, or (c) at an intermediate angle after 96-h incubation in H₂O in darkness, were cut into cross sections, sub-divided into quadrants, and prepared for electron microscopy by standard methods. The walls of many cells are ridged, appearing scalloped in cross section, the plasmalemma following the wall contours. Plasmodesmata localized in pit fields are most numerous in the inner cortex of the extensor (abaxial), and least numerous in the outer cortex of the flexor (adaxial) (3.9 and 0.7, respectively, per μm² wall area). Vacuole size, number of vacuoles per cell, and the condition of the electron dense precipitate within the vacuole also vary with cell location, multivacuolation being most pronounced in the outer cortex of the extensor. Chloroplasts are dimorphic: those in cells close to the vascular tissue are very large, circular in cross section, and contain huge starch deposits at all times, while those in the remainder of the cortex are smaller, usually oblong, and contain large starch deposits at the beginning of the dark period, but are devoid of starch at the beginning of the light period. However, both types of chloroplasts in excised pulvini incubated in H²O in darkness for 96 h still contain starch deposits, indicating that (1) light may promote starch degradation, or (2) starch degradation and resynthesis may be rhythmic.     

Cofactor Binding and Oxygen Equilibria in Haemoglobin

THE oxygen affinity of haemoglobin is profoundly affected by the presence of low concentrations of organic phosphates, in particular 2,3-diphosphoglycerate (DPG)^1–5. This phenomenon, which has now been widely recognized as a physiologically vital control mechanism^6–10, can be explained qualitatively by our observations² that deoxyhaemoglobin has a single strong binding site for the cofactor, which in consequence stabilizes it in relation to the oxygenated state. The binding site is associated with the β chains¹¹ and it has been identified as the cavity at the conjunction of the N-termini of these chains^5,12–18, lying therefore on the dyad axis of the tetramer.     

The regeneration ecology of Kunzea ericoides (A. Rich.) J. Thompson at Coranderrk Reserve,Healesville

The spatial structure, age structure and population dynamics of the shrub Kunzea ericoides (A. Rich.) J. Thompson were investigated at Coranderrk Reserve, near Healesville, Victoria, Australia. The shrub is known to be invasive in many areas and, although indigenous to the reserve, has greatly increased its population size and distribution within the reserve in the past 30 years. Dendrochronology showed a constant relationship between age and stem diameter for K. ericoides in the reserve. The spatial structure of the variable stem diameter was investigated by the use of spatial correlograms and results suggested that K. ericoides is spreading via the formation of discrete clumps and gap-phase regeneration. The two main populations in the reserve recruited continuously in time but patchily in space. A simple statistical model for size–frequency data showed that K. ericoides is expanding faster in some areas of the reserve than others. The trend of expansion of K. ericoides may be irreversible. Intensive management of Coranderrk Reserve will be required if K. ericoides is to be controlled and the conservation value of the reserve maintained.