RESUMO
Human-induced climate change modifies plant species distribution, reorganizing ecologically suitable habitats for invasive species. In this study, we identified the environmental factors that are important for the spread of Calyptocarpus vialis, an emerging invasive weed in the northwestern Indian Himalayan Region (IHR), along with possible habitats of the weed under current climatic scenarios and potential range expansion under several representative concentration pathways (RCPs) using MaxEnt niche modeling. The prediction had a high AUC (area under the curve) value of 0.894 ± 0.010 and a remarkable correlation between the test and expected omission rates. BIO15 (precipitation seasonality; 38.8%) and BIO1 (annual mean temperature; 35.7%) had the greatest impact on the probable distribution of C. vialis, followed by elevation (11.7%) and landcover (6.3%). The findings show that, unlike the current situation, "high" and "very high" suitability areas would rise while less-suited habitats would disappear. All RCPs (2.6, 4.5, 6.0, and 8.5) indicate the expansion of C. vialis in "high" suitability areas, but RCP 4.5 predicts contraction, and RCPs 2.6, 6.0, and 8.5 predict expansion in "very high" probability areas. The current distribution of C. vialis is 21.59% of the total area of the state, with "medium" to "high" invasion suitability, but under the RCP 8.5 scenario, it might grow by 10% by 2070. The study also reveals that C. vialis may expand its niche at both lower and higher elevations. This study clarifies how bioclimatic and topographic factors affect the dispersion of invasive species in the biodiverse IHR. Policymakers and land-use managers can utilize the data to monitor C. vialis hotspots and develop scientifically sound management methods.
RESUMO
Calyptocarpus vialis (syn. Synedrella vialis; Asteraceae), a native of the tropical Americas, has acquired an invasive status in the eastern Asia and Africa and, of late, in India. It is an annual herbaceous weed that forms a dominant ground cover due to its prostrate expansion and interferes with the growth of other plant species. However, the reasons for this interference are largely unknown. Therefore, we examined the allelopathic interference of C. vialis via leachation and residue degradation on the emergence, growth, and development of three crop species (Brassica nigra, Triticum aestivum, and Avena sativa). In a laboratory bioassay, the leachates (0.5-4%) of C. vialis exhibited a dose-dependent inhibitory effect on various growth parameters of the test plants. Similarly, under screenhouse, C. vialis-amended soil (1-4%) affected the growth of test species in a dose-dependent manner. Further, the phytotoxicity of the residues of C. vialis was examined using rhizospheric soil (RS) and residue-amended soil (RAS). It was observed that RAS exerted the maximum allelopathic effect on the test species accompanied by significant changes in pH, electrical conductivity, and total water-soluble phenolic content, as compared with the control soil (CS) and RS. Liquid chromatography and mass spectroscopy analyses confirmed the presence of eleven allelochemicals as the major phytotoxins. The study demonstrated that C. vialis exerts strong phytotoxic effects on other plants through the release of potent allelochemicals, both via leachation and residue degradation.
