Nonlinear plant-plant interactions modulate impact of extreme drought and recovery on a Mediterranean ecosystem.

Interaction effects of different stressors, such as extreme drought and plant invasion, can have detrimental effects on ecosystem functioning and recovery after drought. With ongoing climate change and increasing plant invasion, there is an urgent need to predict the short- and long-term interaction impacts of these stressors on ecosystems. We established a combined precipitation exclusion and shrub invasion (Cistus ladanifer) experiment in a Mediterranean cork oak (Quercus suber) ecosystem with four treatments: (1) Q. suber control; (2) Q. suber with rain exclusion; (3) Q. suber invaded by shrubs; and (4) Q. suber with rain exclusion and shrub invasion. As key parameter, we continuously measured ecosystem water fluxes. In an average precipitation year, the interaction effects of both stressors were neutral. However, the combination of imposed drought and shrub invasion led to amplifying interaction effects during an extreme drought by strongly reducing tree transpiration. Contrarily, the imposed drought reduced the competitiveness of the shrubs in the following recovery period, which buffered the negative effects of shrub invasion on Q. suber. Our results demonstrate the highly dynamic and nonlinear effects of interacting stressors on ecosystems and urges for further investigations on biotic interactions in a context of climate change pressures.

Esterification of p-Coumaric Acid Improves the Control over Melanoma Cell Growth.

Previous studies reported that p-coumaric acid modulates melanoma growth. Because the esterification of p-coumaric acid (p-CA) enhanced its activity as an antimelanogenic agent, we aimed to determine the antitumor potential of two derivatives, the ethyl and butyl esters, against the murine B16-F10 and the human SK-MEL-25 melanoma cells. Cell viability was determined in vitro by the lactate dehydrogenase release and violet crystal absorption assays. The cell proliferation rate and cell cycle behavior were determined by the colony formation assay and flow cytometry analysis. Although p-CA, at the concentration of 1 mM, failed to exert a significant antitumor activity, the ethyl and butyl ester derivatives caused substantial tumor cell death at doses < 1 mM. Despite a reduction in their direct cytotoxicity at minor doses, both products controlled the melanoma growth by arresting the cell cycle at the G0/G1 (B16-F10) or S/G2 (SK-MEL-25). Furthermore, the in vivo experiments showed that the butyl ester derivative suppressed the lung B16-F10 burden, compared to the p-CA-treated mice. Thus, the esterification of p-coumaric acid improved the control over the proliferation of murine and human melanoma cells and can be considered an approach for designing novel anticancer agents.