Ecobiological and Allelochemical Characterization of Selected Invasive Plants of Pothwar Region of Pakistan

Abstract

Pothwar region, Pakistan is a hot spot for biodiversity, but the vegetation is constantly under pressure of exotic invasive plants. Phytosociological studies help to understand extent of biological invasion. Multiple analyses of ecological parameters at different locations derive general explanations of impact on species diversity in plant communities. The current study assessed impact of selected invaders viz. Parthenium hysterophorus L., Lantana camara L., Xanthium strumarium L. and Broussonetia papyrifera (L.) L’Herit. ex Vent. invasion on native flora in Pothwar region of Pakistan. Paired plot experimental design with two categorical factors; invaded and non-invaded (control) under same habitat conditions was used for sampling. Differences in number of species (S), abundance (N), species richness (R), evenness (Jꞌ), Shannon index of diversity (Hꞌ) and Simpson index of dominance (λ) were calculated using PRIMER-7 software package. Ecological indices were compared between invaded and control plots by t-test series using IBM SPSS v. 21 software. Control plots harbored by an average of 0.9, 1.74, 1.28 and 1.3 more individuals per 10m2 respectively. The control category was diverse (Hꞌ=1.73, 2.56, 2.15, 2.00) than invaded category (Hꞌ=1.53, 1.56, 1.65, 1.82) for four studied invaders. Similarly, control plots showed higher value of Jꞌ and λ for all the studied sites. The higher value of species richness in control plots shows heterogeneous nature of communities and vice versa in invaded plots. The lower value of index of dominance in invaded plots shows less sample diversity than control ones. This decrease in number of species directly affects α- diversity in invaded plots. At multivariate scale, ordination (nMDS) and ANOSIM showed significant magnitude of differences between invaded and control plots in xvii all sites. The decrease in diversity indices in invaded over control sites indicated that plant communities become less productive due to invasion; hence a threat to plant diversity. Invasion impact was observed as Lantana camara > Xanthium strumarium > Parthenium hysterophorus > Broussonetia papyrifera. Results suggested appropriate control measures for studied invaders. Radish seed germination bioassay with methanol extracts harboring 0.05 gmL-1 of root, leaves, flowers and stem of selected invaders indicated L. camara leaves and X. strumarium fruits as most phytotoxic plant parts. Fractionation and bioassay guided isolation of allelochmicals from L. camara leaves against monocot (Phalaris minor Retz. & Avena fatua L.) and dicot (Rumex dentatus L. & Chenopodium album L.) weed test species provided evidence about herbicidal potential of test plant species. Among ethyl acetate, hexane, chloroform and aqueous methanolic extract fractions, ethyl acetate fraction was shown to be most inhibitory to selected weed test species. Through flash column chromatography using mobile phase of Hexane : Ethyl acetate (60:40), 31 fractions were collected in small vials and tested for inhibition activity against radish seeds. Fraction with highest inhibition activity was subjected to GC-MS analysis that shows compound as ‘Vitexin’. To the best of our knowledge Lantana camara leaves have not been previously reported to possess flavonoid compound ‘vitexin’ and tested against weeds of wheat crop. So this investigation has provided a clue about its herbicidal importance for further research.