Primary Production and Nutrient Content in Two Salt Marsh

Seasonal variation patterns of aboveground and belowground biomass, net primary production, and nutrient accumulation were assessed in Atriplex portulacoides L. and Limoniastrum monopetalum (L.) Boiss. in Castro Marim salt marsh, Portugal. Sampling was conducted for five periods during 2001–2002 (autumn, winter, spring, summer, and autumn). This study indicates that both species have a clear seasonal variation pattern for both aboveground and belowground biomass. Mean live biomass was 2516 g m22 yr21 for L. monopetalum and 598 g m22 yr21 for A. portulacoides. Peak living biomass, in spring for both species, was three times greater in the former, 3502 g m22 yr21, than in the latter, 1077 g m22 yr21. For both the Smalley (Groenendijk 1984) and Weigert and Evans (1964) methods, productivity of L. monopetalum (2917 and 3635 g m22 yr21, respectively) was greater than that of A. portulacoides (1002 and 1615 g m22 yr21, respectively). Belowground biomass of L. monopetalum was 1.7 times greater than that of A. portulacoides. In spite of this, the root:shoot ratio for A. portulacoides was greater throughout the year. This shows that A. portulacoides allocates more biomass to roots and L. monopetalum to aerial components. Leaf area index was similar for both species, but specific leaf area of A. portulacoides was twice that of L. monopetalum. The greatest nutrient contents were found in leaves. Leaf nitrogen content was maximum in summer for both species (14.6 mg g21 for A. portulacoides and 15.5 mg g21 for L. monopetalum). Leaf phosphorus concentration was minimum in summer (1.1 mg g21 in A. portulacoides and 1.2 mg g21 in L. monopetalum). Leaf potassium contents in A. portulacoides were around three times greater than in L. monopetalum. Leaf calcium contents in L. monopetalum were three times greater than in A. portulacoides. There was a pronounced seasonal variation of calcium content in the former, while in the latter no clear variation was registered. Both species exhibited a decrease in magnesium leaf contents in the summer period. Manganese content in L. monopetalum leaves was tenfold that in A. portulacoides. Seasonal patterns of nutrient contents in A. portulacoides and L. monopetalum suggest that availability of these elements was not a limiting factor to biomass production

Malaria was a weak selective force in ancient Europeans

Malaria, caused by Plasmodium parasites, is thought to be one of the strongest selective forces that has shaped the genome of modern humans and was endemic in Europe until recent times. Due to its eradication around mid-twentieth century, the potential selective history of malaria in European populations is largely unknown. Here, we screen 224 ancient European genomes from the Upper Palaeolithic to the post-Roman period for 22 malaria-resistant alleles in twelve genes described in the literature. None of the most specific mutations for malaria resistance, like those at G6PD, HBB or Duffy blood group, have been detected among the available samples, while many other malaria-resistant alleles existed well before the advent of agriculture. We detected statistically significant differences between ancient and modern populations for the ATP2B4, FCGR2B and ABO genes and we found evidence of selection at IL-10 and ATP2B4 genes. However it is unclear whether malaria is the causative agent, because these genes are also involved in other immunological challenges. These results suggest that the selective force represented by malaria was relatively weak in Europe, a fact that could be associated to a recent historical introduction of the severe malaria pathogen.This research was supported by a grant to C.L.-F. from FEDER and Ministry of Economy and Competitiveness (BFU2015–64699-P) of Spain and by a grant 2014 SGR 464 (GRBIO) from the Departament d’Economia i Coneixement de la Generalitat de Catalunya (Spain) to S.C. We are grateful to Joshua Schraiber and Agnar Helgason for helpful comments and suggestions

Coffee agroforestry systems in Central America: I. A review of quantitative information on physiological and ecological processes

Coffee is widely grown across Central America at altitudes between 600 and 2500 m, mostly in association with trees that provide shade and other services. Research on coffee agroforestry systems has identified many environmental factors, management strategies and plant characteristics that affect growth, yield and environmental impact of the system. Much of this literature only presents qualitative estimates of the importance of the different growth determining factors, or highly site-specific estimates. Quantitative information is required to allow statistical analysis or the construction of process-based models of the system. Here, we review the available quantitative information for the latter purpose, with emphasis on the data needs for modelling agroforestry systems common in Central America. Process-based models require environmental data—weather, soil—and data on the physiological characteristics of the coffee plants and trees. Our review showed that the current literature is insufficient to allow full parameterisation of a process-based model for any coffee-tree combination. Information on weather, coffee and trees is highly limited, but soil information seems more adequate. A regional network of replicated multi-factorial experiments, focusing on the interactive effects of different environmental factors, may help address the main knowledge gaps