Invasão biológica por Cryptostegia madagascariensis Bojer ex Decne. em área de neossolo flúvico no semiárido paraibano

Abstract

The introduction of exotic species with invasive potential can generate several impacts to the natural ecosystem. Some studies in the Caatinga area with the invasive species Cryptostegia madagascariensis prove its negative effects on the diversity of native flora. The objective of this study was to evaluate the production and decomposition rate of litter produced by the invasive species Cryptostegia madagascariensis and native vegetation in a longitudinal gradient, as well as its effects on soil organisms (macrofauna and arbuscular mycorrhizal fungi) as a function of seasonality in a Entisols Fluvents in the semi-arid region of Paraíba. The research was carried out in the municipality of Pombal-PB. Two distinct and adjacent environments were selected. An environment of Caatinga vegetation with invasive C. madagascariensis (invaded environment) and an environment with Caatinga vegetation (native environment). For each environment, four 15 m long transects were delimited and the variables were analyzed according to the environments, the longitudinal gradient and seasonality. To quantify litter decomposition production and rate, a litter collector (n = 8) was distributed in each transect by environment and five litter bags (n = 20) were distributed around the collectors, containing 50 g of the material removed litter collectors. The evaluations for the production and decomposition rate of the litter were monitored every 60 days. Four soil samples by transect and period were also collected to assess the chemical attributes of the soil (n = 64), four samples to determine the water content in the soil (n = 64) and the soil temperature observed in the field. To assess the edaphic macrofauna, in each transect, two “Provid” traps were installed by distance and environment (n = 32), containing 200 mL of a preservative solution (20 mL of neutral detergent, 30 mL of 70% alcohol and 150 mL of water), which remained in the field for 72 h and the soil organisms were subsequently identified. The specimens of the edaphic macrofauna were quantified at Order level and gathered in functional groups. To identify arbuscular mycorrhizal fungi (AMF), in each transect and environment, four soil samples were collected every five meters in length (n = 128) and for analysis of the chemical attributes of the soil, four soil samples were collected by transect and environment (n=64). To identify the AMF, the method of spore extraction was used by means of wet sieving followed by centrifugation in a 40% sucrose gradient for one minute at 1000 rpm. Statistical analyzes were performed using free software R. The data were submitted to the Shapiro-Wilk test and the two-way ANOVA was used. For the production and decomposition rate of the litter, the averages were compared by the Tukey test (p <0.05), and the analysis of main components was used to evaluate the dissimilarities between environments and periods. As for edaphic biota, the Bonferroni test (p <0.05) was used for macrofauna and AMF species. For the edaphic macrofauna, non-metric multidimensional scaling analysis (NMDS) was applied to assess the dissimilarity between environments and distances. For the FMA community, principal component analysis was used to assess dissimilarities between environments, distances and periods. After analyzing the data, for the macrofauna and the AMF, abundance, absolute frequency, richness, Shannon's diversity index (H') and Simpson's dominance index (C') were calculated. The results showed a significant effect between the environments, distances and periods analyzed. The environment with invasive C. madagascariensis showed higher litter production, including in the period of water deficit, lower temperature and water content in the soil and higher levels of phosphorus and potassium in the litter. Regarding the chemical attributes of the soil, the environment with invasive C. madagascariensis showed alterations in the levels ofsodium, calcium and organic carbon of the soil. For the edaphic macrofauna, the environment with invasive C. madagascariensis showed a reduction in the diversity of Orders and functional groups. The environment with invasive C. madagascariensis also caused changes in the AMF community, causing an increase in the density and frequency of occurrence of specific AMF species, such as Claroideogomus etunicatum throughout the entire transect. On the other hand, it caused a reduction in the frequency of occurrence of the species of AMF Quatunica erythropus, Gigaspora albida and Gigaspora gigantea. It was concluded that the invader C. madagascariensis in Neossolo Flúvico in Caatinga area was able to promote its development in the environment. C. madagascariensis created a favorable habitat conditioning its invasion through greater litter production, favorable local microclimate, in addition to selecting certain Orders and functional groups of macrofauna and AMF species to decompose its plant residues and contribute to its invasion process in the new habitat.