Leaf decomposition of Mesosphaerum suaveolens affects the growth of Cactaceae species in the Brazilian Seasonally Dry Tropical Forest

Mesosphaerum suaveolens is a herbaceous plant native to the Caatinga, and has the ability to change the plant composition of surrounding areas, possibly through to the action of allelochemicals. In this study, the effect of M. suaveolens leaf decomposition on the germination and initial growth of two columnar cacti endemic to Brazil, Cereus jamacaru subsp. jamacaru and Pilosocereus gounellei subsp. gounellei, and the existence of autotoxicity were evaluated. The decomposing leaves of M. suaveolens negatively affected the germination and growth parameters of the two cacti, notably reducing the size and dry weight of cladodes. A reduction in photosynthetic pigment content was also observed. Furthermore, autotoxic effects were also observed. UPLC-MS of the soil revealed the presence of five diterpenes, three triterpenes, and one sugar. Considering that terpenoid compounds were the predominant components, our results suggest that they may be some of the allelochemicals used by M. suaveolens to reduce species competition. Thus, we demonstrate that M. suaveolens can negatively impact the growth and development not only of the two cacti studied, but also of the own species through autotoxicity. In areas with spontaneous presence of M. suaveolens, monitoring is recommended due to the negative impact of this plant.