Ecological phytochemistry of Cerrado (Brazilian savanna) plants

The Cerrado (the Brazilian savanna) is one of the vegetation formations of great biodiversity in Brazil and it has experienced strong deforestation and fragmentation. The Cerrado must contain at least 12,000 higher plant species.We discuss the ecological relevance of phytochemical studies carried out on plants from the Cerrado, including examples of phytotoxicity, antifungal, insecticidal and antibacterial activities. The results have been classified according to activity and plant family. The most active compounds have been highlighted and other activities are discussed. A large number of complex biochemical interactions occur in this system. However, only a small fraction of the species has been studied from the phytochemical viewpoint to identify the metabolites responsible for these interactions

Pequi leaves incorporated into the soil reduce the initial growth of cultivated, invasive and native species

Estudos têm identificado potencial fitotóxico de tecidos vegetais de diversas espécies do Cerrado. Entretanto, a maior parte destes estudos foi conduzida em substrato inerte, ou fazendo uso de quantidades exageradas de material vegetal. Neste estudo investigamos o potencial fitotóxico de folhas de pequi adicionadas a substrato solo em quantidades compatíveis ao volume de liteira produzida por esta espécie no campo. Folhas de pequi foram trituradas e incorporadas a latossolo vermelho em proporções entre 0,75 e 3% (p/p), sendo o controle constituído por solo sem folhas. Estas misturas foram adicionadas a vasos plásticos irrigados diariamente. Sementes germinadas das espécies cultivadas sorgo e gergelim, da invasora braquiária, e da nativa ipê-roxo foram dispostas nos vasos e crescidas por cinco a sete dias a 30°C, com fotoperíodo de 12 h. Plântulas de todas as espécies apresentaram redução dose-dependente no crescimento, sendo o crescimento radicular mais afetado que o aéreo. Sinais de necrose foram observados nas raízes de sorgo, gergelim e braquária. Os efeitos fitotóxicos gerados por uma quantidade relativamente baixa de tecido vegetal, em substrato solo, e em razoável número de espécies de diferentes grupos funcionais sugerem que a liteira desta espécie possa exercer real potencial alelopático em condições de campo.Studies have identified the phytotoxicity of many native species of the Cerrado; however, most of them were conducted either in inert substrates, or using exaggerate proportions of plant material. We investigated the phytotoxicity of pequi leaves added to substrate soil in quantities compatible with the litter produced by this species. Pequi leaves were triturated and added to red latosol in concentrations of 0.75%, 1.5% and 3%; the control was constituted of leafless soil. These mixtures were added to pots and irrigated daily to keep them moist. Germinated seeds of the cultivated sorghum and sesame, of the invasive brachiaria and of the native purple ipê, were disposed in the pots to grow for five to seven days at 30°C within a photoperiod of 12 h. Seedlings of all the species presented a reduction in their initial growth in a dose-dependent way. In general, the root growth was more affected by the treatments than the shoot growth; moreover, signs of necrosis were observed in the roots of the sorghum, sesame and brachiaria. The phytotoxic effects generated by relatively small quantities of leaves, in a reasonable range of species within a soil substrate, suggest potential allelopathy of pequi leaves under natural conditions

TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS

CONTEXT: TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2σ. AIMS: Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope. METHODS: We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series. RESULTS: We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of Mb = 20.4−2.5+2.6 M⊕ (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of Rb = 3.490−0.064+0.070 R⊕ (∼1.9%). Our mass and radius measurements imply a mean density of ρb = 2.65−0.35+0.37 g cm−3 (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41−0.20+0.34 M⊕ and a thickness of 1.05−0.29+0.30 R⊕. CONCLUSIONS: Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b