A continental-scale analysis of tree cover in African savannas

Aim We present a continental‐scale analysis that explores the processes controlling woody community structure in tropical savannas. We analyse how biotic and abiotic factors interact to promote and modify tree cover, examine alternative ecological hypotheses and quantify disturbance effects using satellite estimates of tree cover. Location African savannas. Methods Tree cover is represented as a resource‐driven potential cover related to rainfall and soil characteristics perturbed by natural and human factors such as fire, cattle grazing, human population and cultivation. Within this framework our approach combines semi‐empirical modelling and information theory to identify the best models. Results Woody community structure across African savannas is best represented by a sigmoidal response of tree cover to mean annual precipitation (MAP), with a dependency on soil texture, which is modified by the separate effects of fire, domestic livestock, human population density and cultivation intensity. This model explains c. 66% of the variance in tree cover and appears consistent across the savanna regions of Africa. Main conclusions The analysis provides a new understanding of the importance and interaction of environmental and disturbance factors that create the broad spatial patterns of tree cover observed in African savannas. Woody cover increases with rainfall, but is modified by disturbances. These ‘perturbation’ effects depend on MAP regimes: in arid savannas (MAP < 400 mm) they are generally small (< 1% decrease in cover), while in semi‐arid and mesic savannas (400–1600 mm), perturbations result in an average 2% (400 mm) to 23% (1600 mm) decrease in cover; fire frequency and human population have more influence than cattle, and cultivation appears, on average, to lead to small increases in woody cover. Wet savannas (1600–2200 mm) are controlled by perturbations that inhibit canopy closure and reduce tree cover by, on average, 24–34%. Full understanding of the processes determining savanna structure requires consideration of resource limitation and disturbance dynamics.     

cDNA cloning and induction of tyrosine hydroxylase gene from the diamondback moth,Plutella xylostella

We cloned a full‐length tyrosine hydroxylase cDNA from the integument of the diamondback moth, Plutella xylostella. In the phylogenetic tree, tyrosine hydroxylase (PxTH) clustered with the other lepidopteran THs. Serine residues in the PxTH sequence, namely Ser²⁴, Ser³¹, Ser³⁵, Ser⁵³, and Ser⁶⁵, were predicted to be the target sites for phosphorylation based on PROSITE analysis. In particular, Ser³⁵ of PxTH is highly conserved across a broad phylogenetic range of animal taxa including rat and human. Western blot analysis using both PxTH‐Ab1 and PxTH‐Ab2 polyclonal antibodies verified the expression of PxTH in all life cycle stages of P. xylostella, namely the larval, pupal, and adult stages. To examine the possible immune function of PxTH in P. xylostella, PxTH gene expression was investigated by RT‐PCR and western blotting analysis after challenging P. xylostella with bacteria. PxTH expression was elevated 1 h post‐infection and was continued till 12 h of post‐infection relative to control larvae injected with sterile water. © 2010 Wiley Periodicals, Inc.     

Towards comparable assessment of the soil nutrient status across scales—Review and development of nutrient metrics

Nutrient availability influences virtually every aspect of an ecosystem, and is a critical modifier of ecosystem responses to global change. Although this crucial role of nutrient availability in regulating ecosystem structure and functioning has been widely acknowledged, nutrients are still often neglected in observational and experimental synthesis studies due to difficulties in comparing the nutrient status across sites. In the current study, we explain different nutrient‐related concepts and discuss the potential of soil‐, plant‐ and remote sensing‐based metrics to compare the nutrient status across space. Based on our review and additional analyses on a dataset of European, managed temperate and boreal forests (ICP [International Co‐operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests] Forests dataset), we conclude that the use of plant‐ and remote sensing‐based metrics that rely on tissue stoichiometry is limited due to their strong dependence on species identity. The potential use of other plant‐based metrics such as Ellenberg indicator values and plant‐functional traits is also discussed. We conclude from our analyses and review that soil‐based metrics have the highest potential for successful intersite comparison of the nutrient status. As an example, we used and adjusted a soil‐based metric, previously developed for conifer forests across Sweden, against the same ICP Forests data. We suggest that this adjusted and further adaptable metric, which included the organic carbon concentration in the upper 20 cm of the soil (including the organic fermentation‐humus [FH] layer), the C:N ratio and of the FH layer, can be used as a complementary tool along with other indicators of nutrient availability, to compare the background nutrient status across temperate and boreal forests dominated by spruce, pine or beech. Future collection and provision of harmonized soil data from observational and experimental sites is crucial for further testing and adjusting the metric.     

Ri-plasmid mediated transformation and regeneration of Ulmus procera (English Elm)

Infection of Ulmus procera (English elm) cloneSR4 internodal stem explants with Agrobacteriumtumefaciens C58 c1 pRiA4b resulted in callusdevelopment and extensive hairy root production. Shoots which regenerated from hairy roots, followingan extended culture period, were dwarf in stature,with reduced apical dominance and wrinkled leaves whencompared with wild type U. procera SR4. Shootswere rooted successfully and plants with extensiveroot systems have been transferred to soil. Thetransgenic status of regenerants was confirmed by PCRanalysis and DNA sequencing of pRiA4b TL- and TR- DNArolA (329 bp) and agropine synthase (490 bp)primed amplimers, which were 100% homologous to theexpected sequences. No vir D1 primed PCRproducts were obtained, indicating that the Agrobacterium was successfully removed. Thepotential of Ri plasmid mediated transformation forinducing altered elm xylem structure, restrictedspread of the Dutch elm disease fungus and inphytoremediation is discussed.