Impacts of plant invasion on soil nutrient parameters along altitudinal gradient
Our study clearly indicate that invasion by L.vulgare altered the soil physicochemical properties consistently between the plots and among the sites along the altitudinal gradient. More specifically soil pH, TDS, SAL, WC, TOC, N and K values were higher in the invaded plots as compared to the uninvaded plots (Table 1). The results provide further empirical support to a recent study carried on L. vulgareinvasion, which reported that invasion significantly altered the overall soil properties to influence nutrient cycling and expedite its establishment and spread (Ahmad et al., 2019b). Particularly, the higher values of soil pH and WC in the invaded plots are in agreement with the findings of few other studies where invasion has led to the enhancement of the soil physicochemical properties (Manzoni et al., 2012; Simba et al., 2017; Ruwanza & Shackleton 2016). The possible reason for increased pH at invaded plots can be due to rapid uptake of nitrate ions from the rhizosphere by invasive plants (Ehrenfeld et al., 2001).The decrease in soil pH with increasing altitude can result from the fact that conifers tend to make soil pH acidic in character (FitzPatrick 1983). The increased WC in the L.vulgare invaded plots can be due to the excessive utilization of water for its growth and development. Similarly, the lower soil EC value in the invaded plots is in agreements with the results from several other studies (Osunkoya & Perrett 2011; Ahmad et al., 2019b). Our results revealed that TDS, TOC, N and K differed significantly between plots and among sites, which are in agreement with the findings of other studies where invasion has been reported to increase various nutrients such as carbon (Schaeffer et al., 2003; Pollierer et al., 2007), N and K (Niu et al., 2007) and C and N (Uddin & Robinson 2017). The increase in P at invaded plots could be due to microbial phosphatase activities and secretion of certain root exudates that displace P from humic metal complexes and enhance P concentration (Hinsinger 2001; Li et al., 2009). The low concentration of iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn)in the invaded plots, owing to rapid uptake and utilization by vigorously growing invasive plant species, could be the plausible explanation for their depletion in the invaded soils (Osunkoya & Perrett 2011; Ahmad et al., 2019b).