Population and Environmental Correlates of Maize Yields in Mesoamerica: a Test of Boserup’s Hypothesis in the Milpa

Using a sample of 40 sources reporting milpa and mucuna-intercropped maize yields in Mesoamerica, we test Boserup’s (1965) prediction that fallow is reduced as a result of growing population density. We further examine direct and indirect effects of population density on yield. We find only mixed support for Boserupian intensification. Fallow periods decrease slightly with increasing population density in this sample, but the relationship is weak. Controlling for other covariates, fallow-unadjusted maize yields first rise then fall with population density. Fallow-adjusted maize yields peak at 390 kg/ha/yr for low population densities (8 persons / km2) and decline to around 280 kg/ha/yr for the highest population densities observed in our dataset. Fallow practices do not appear to mediate the relationship between population density and yield. The multi-level modeling methods we adopt allow for data clustering, accurate estimates of group-level variation, and they generate conditional predictions, all features essential to the comparative study of prehistoric and contemporary agricultural yields

Arabidopsis Class I and Class II TCP Transcription Factors Regulate Jasmonic Acid Metabolism and Leaf Development Antagonistically

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR1 (TCP) transcription factors control developmental processes in plants. The 24 TCP transcription factors encoded in the Arabidopsis (Arabidopsis thaliana) genome are divided into two classes, class I and class II TCPs, which are proposed to act antagonistically. We performed a detailed phenotypic analysis of the class I tcp20 mutant, showing an increase in leaf pavement cell sizes in 10-d-old seedlings. Subsequently, a glucocorticoid receptor induction assay was performed, aiming to identify potential target genes of the TCP20 protein during leaf development. The LIPOXYGENASE2 (LOX2) and class I TCP9 genes were identified as TCP20 targets, and binding of TCP20 to their regulatory sequences could be confirmed by chromatin immunoprecipitation analyses. LOX2 encodes for a jasmonate biosynthesis gene, which is also targeted by class II TCP proteins that are under the control of the microRNA JAGGED AND WAVY (JAW), although in an antagonistic manner. Mutation of TCP9, the second identified TCP20 target, resulted in increased pavement cell sizes during early leaf developmental stages. Analysis of senescence in the single tcp9 and tcp20 mutants and the tcp9tcp20 double mutants showed an earlier onset of this process in comparison with wild-type control plants in the double mutant only. Both the cell size and senescence phenotypes are opposite to the known class II TCP mutant phenotype in JAW plants. Altogether, these results point to an antagonistic function of class I and class II TCP proteins in the control of leaf development via the jasmonate signaling pathway.159415111523European Union FP6 AGRO-Nomics project [LSHG-CT-2006-037704]Dutch Ministry of Economic Affairs, Agriculture, and Innovation in the framework of the Instellingsplan/Ondernemingsplan programEuropean Union Marie Curie Intra-European Fellowship Grant [PIEF-GA-2009-236623]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Bijzonder Onderzoeksfonds Methusalem Project of Ghent University [BOF08/01M00408]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)European Union FP6 AGRO-Nomics project [LSHG-CT-2006-037704]European Union Marie Curie Intra-European Fellowship Grant [PIEF-GA-2009-236623]Bijzonder Onderzoeksfonds Methusalem Project of Ghent University [BOF08/01M00408