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Species richness in tropical forests is correlated with other dimensions of diversity, including the diversity of plant–herbivore interactions and the phytochemical diversity that influences those interactions. Understanding the complexity of plant chemistry and the importance of phytochemical diversity for plant–insect interactions and overall forest richness has been enhanced significantly by the application of metabolomics to natural systems. The present work used proton nuclear magnetic resonance spectroscopy (1H‐NMR) profiling of crude leaf extracts to study phytochemical similarity and diversity among Piper plants growing naturally in the Atlantic Rainforest of Brazil. Spectral profile similarity and chemical diversity were quantified to examine the relationship between metrics of phytochemical diversity, specialist and generalist herbivory, and understory plant richness. Herbivory increased with understory species richness, while generalist herbivory increased and specialist herbivory decreased with the diversity of Piper leaf material available. Specialist herbivory increased when conspecific host plants were more spectroscopically dissimilar. Spectral similarity was lower among individuals of common species, and they were also more spectrally diverse, indicating phytochemical diversity is beneficial to plants. Canopy openness and soil nutrients also influenced chemistry and herbivory. The complex relationships uncovered in this study add information to our growing understanding of the importance of phytochemical diversity for plant–insect interactions and tropical plant species richness. [ABSTRACT FROM AUTHOR]

Piper is one of two large genera in the Piperaceae, and with ca. 2600 species, is one of the largest plant genera in the world. Species delimitation and evaluation of genetic diversity among populations are important requisites for conservation and adequate exploitation of economically important species. DNA barcoding has been used as a powerful tool and a practical method for species characterization and delimitation. The present work aims to evaluate molecular markers for barcoding three Piper species native to Brazil: P. gaudichaudianum ("jaborandi" or "pariparoba"), P. malacophyllum ("pariparoba-murta") and P. regnellii ("caapeba" or "pariparoba"). A reference DNA barcode library was developed using sequences of three candidate regions: ITS2, trnH-psbA and rbcL. Transferability of the microsatellite (SSR) primers Psol 3, Psol 6 and Psol 10, designed originally for Piper solmsianum, to the three Piper species was also evaluated. The discriminatory power of the markers was based on the determination of inter- and intraspecific distances, phylogenetic reconstruction, and clustering analysis, as well as BLASTn comparison. Sequences of ITS2 enabled efficient species identification by means of the BLASTn procedure. Based on these sequences, intraspecific divergence was lower than interspecific variation. Maximum Parsimony analyses based on ITS2 sequences provided three resolved clades, each corresponding to one of the three analysed species. Sequences of trnH-psbA and rbcL had lower discriminatory value. Analyses combining sequences of these regions were less effective toward the attainment of resolved and strongly supported clades of all species. In summary, robustly supported clades of P. regnellii were obtained in most of the analyses, based either on isolated or combined sequences. The SSRs primers Psol 3, Psol 6 and Psol 10 were shown to be transferable to P. gaudichaudianum and P. regnellii, but not to P. malacophyllum. Preliminary cluster analyses based on the polymorphism of the amplified products suggested that Psol 3 has lower potential than Psol 6 and Psol 10 for discrimination of Piper species. [ABSTRACT FROM AUTHOR]

The growth and morphology of stromatolites have been previously linked to diverse microbial activities. However, the role of microbial metabolisms on carbonate formation during stromatolite growth remains controversial. Magnesium isotopes have been proposed to serve as a tracer of microbial carbonate formation, implying a potential biological isotope fractionation. To further elucidate whether Mg isotope fractionation is modified during microbial carbonate formation, this study reports Mg isotope compositions of Holocene stromatolites and pore waters from Lagoa Salgada, a coastal ephemeral lake in Brazil. The stromatolitic carbonates are composed of high-Mg calcites characterized by extremely positive inorganic δ13C values, up to +20‰, and variable δ26Mg values, ranging from −2.98‰ to −0.68‰. Multiple pieces of evidence consistently demonstrate changes in microbial metabolism resulting from ecosystem fluid chemistry evolution. However, the direction of Mg isotope fractionation associated with carbonate precipitation remained invariable despite the changes in microbial activity. Mineralogical features indicate that the stromatolitic carbonates formed via 2-D nucleation. An isotopic mass balance calculation based on the observed variations in δ26Mg values and Mg concentrations of associated pore waters argues for an Mg isotopic equilibrium fractionation factor of −2.60‰ associating with the carbonate formation at Lagoa Salgada, well-matching experimental values for abiotic calcite precipitation. Thus, the observed δ26Mg variability of stromatolitic carbonates is primarily controlled by the changes of physicochemical conditions in the ambient fluid. We infer that during the formation of stromatolites, a consortium of different microbial communities produces extracellular polymeric substances, which serve as a substrate for carbonate nucleation from ambient fluid without significantly affecting the fractionation of Mg-isotopes. Our findings shed light on the effects of microbial processes on carbonate formation during stromatolite growth and improve the current understanding of the Mg isotope record in microbial carbonates. [ABSTRACT FROM AUTHOR]