State and change in carbon pools in the forests of tropical Africa

To improve estimates of the state and change in C pools due to changes in land use in tropical forests of Africa, we combined spatially explicit estimates of biomass C density, obtained by modelling in a geographical information system (GIS), with new data on the area of forests (woody formations with a minimum of 10% crown cover) reported at subnational units for 1980 and 1990 by the Food and Agriculture Organization (FAO). Estimates of the biomass C densities for grass/shrub savannas were also included using a simple model based on precipitation. The total C pool in above– and below–ground forests and grass/shrub savannas of Africa for 1980 was 50.8 Pg (10¹⁵g), with aboveground forest biomass accounting for 75% of the total, below–ground forest biomass for 21%, and grass/shrub savannas for 4%. Area weighted mean biomass C densities were about 180 Mg ha^–1 for lowland moist forests, 82 Mg ha^–1 for all forests, and 6 Mg ha^–1 for grass savannas. The total change in the aboveground forest C pool for the decade 1980–90 due to changes in land cover and use was estimated to be a decrease of 6.6 Pg C. Of this total, 43% was due to deforestation and 57% due to biomass reduction by other human activities. Six countries, mostly in central Africa, accounted for more than 73% of the total change in the C pool. The difference between state and change of C pool estimates made at the subnational scale and those made at the national scale proved to be insignificant across the region as a whole (2% for pools and – 1% for change in pool) but potentially important to individual countries (from + 36% to – 39% for pools and from + 43% to – 57% for change in pool). The differences between the two approaches may reflect a better match of the areas being deforested with the biomass C density of forests being cleared.     

Tyrosinase Autoactivation and the Problem of the Lag Period

Evidence is presented for the binding of the quinone oxidation product of the monohydric phenol substrate, 4-hydroxyanisole, to mushroom tyrosinase. Column chromatography and SDS-PAGE separation showed labelling of the enzyme when incubated with ¹⁴C ring-labelled 4-hydroxyanisole. It is proposed that covalent binding to the enzyme and other proteins is through reaction of accessible nucleophilic groups, including thiols and amino groups, with the anisylquinone. This reductive addition enables the indirect generation of the catecholic substrate, which acts as an electron donor for the bicupric active site of met-tyrosinase and explains the lag kinetics of tyrosinase oxidation of non-cyclizing substrates. The effects of diluting the enzyme or the addition of amino acids on the lag period was consistent with a mechanism involving indirect generation of the dihydric phenol, which acts as the met-enzyme-recruiting substrate.     

The typification of the names of New World Solatium species described by Linnaeus

Twenty-seven species of New World Solatium described by Linnaeus are lectotypified. All elements of the protologue are discussed and photographs of all lectotypes provided. Species that have been previously lectotypified are also discussed, and the lectotypifications verified.