Invasion of Prosopis juliflora Figure 2. Plant species richness (mean + SE) under canopies of Prosopis pallida and nearby open areas in Chulucanas and Catacaos in its native Peru (upper panel); and under canopies of Prosopis juliflora and nearby open areas in its native range of Venezuela (middle panel), and non-native ranges of Delhi, Gujarat and Rajasthan in India, and Honolulu in Hawaii, USA two of its non-native ranges (lower panel). Asterisks above paired bars were derived from independent t tests except Rajasthan where Mann-Whitney U test (p,0.05) was used. doi:10.1371/journal.pone.0044966.g002 Effects of Congeners on Soil Chemistry The pH of P. cineraria soil was significantly lower than that of soil in the open (Figure 4A: FpH = 15.914; df = 2,27; p,0.0001, Tukey, p,0.0001) and P. juliflora soil (Tukey, p = 0.001) but that of P. juliflora soil did not differ from soil in open (Tukey, p = 0.525). As compared to soil in open, organic carbon and nitrogen were significantly higher in P. juliflora (Figure 4C; FOrganic carbon = 9.798; df = 2,27; p = 0.001, Tukey, p = 0.001; Figure 4E: FNitrogen = 19.897; df = 2,27; p,0.0001, Tukey, p = 0.001) and P. cineraria soils (organic carbon: Tukey, p = 0.005; nitrogen: Tukey’s test, p,0.0001) but did not differ significantly between the two congeners (organic carbon: Tukey, p = 0.775; nitrogen: Tukey, p = 0.109). Electrical conductiv- ity, exchangeable PO43–P and total phenolic content were signifi- cantly higher in soil from under P. juliflora than soil from under P. cineraria (Figure 4B: FElectrical conductivity = 9.105; df = 2,27, p = 0.001, Tukey, p = 0.006; Figure 4D: FPhosphorus = 26.574; df = 2,27, p,0.0001, Tukey, p,0.0001: Figure 4F: FPhenolics = 13.711; df = 2,25, p,0.0001, Tukey, p = 0.020) or from the open (electrical conductivity: Tukey, p = 0.001; exchangeable PO43–P: Tukey, p,0.0001; total phenolic content: Tukey, p,0.0001). These factors did not differ significantly between P. cineraria soil and soil from the open (electrical conductivity: Tukey, p = 0.847; exchangeable PO43–P: Tukey, p = 1.000; total phenolic content: Tukey, p = 0.084). Effects of Leaf Litter from Prosopis Congeners on Other Species Leaf litter from the Indian native P. cineraria increased the mortality of Dalbergia sissoo, but had no effect on any other native Indian species (Figure 5). In contrast, leaf litter from the invasive P. juliflora increased the mortality of all six native Indian species from 14–44%. The mean mortality of Indian species when exposed to litter from P. cineraria (565%) was not significantly different than that in the control (ANOVA, Ftreatment = 15.09; df = 2,15; P,0.001; Tukey P = 0.970), but much lower than the mean mortality (3364%) of plants treated with P. juliflora litter (Tukey P = 0.001). Effects of Leaf Leachate from Prosopis Congeners on Other Species As compared to control, leachate from the leaves of the native P. cineraria significantly enhanced the root growth of B. campestris at 150 (Figure 6 upper panel; t0 vs. 150 = 22.561; df = 1,10; p = 0.028;) and 300 mL/g soil concentrations (t0 vs. 300 = 22.955; df = 1,10; p = 0.014), and of B. juncea at 60 (Figure 6 middle panel; t0 vs. 60 = 23.506; df = 1,10; p = 0.006), 150 (t0 vs. 150 = 24.759, df = 1,6; p = 0.003), and 300 mL/g soil concentrations (t0 vs. 300 = 23.067; df = 1,6; p = 0.025). The root length of S. bicolor seedlings grown in P. cineraria leaf leachate amended soil was not significantly different from control at any tested concentration (Figure 6 lower panel; t0 vs. 60 = 1.475; df = 1,10; p = 0.171; t0 vs. 150 = 21.370, df = 1,10; p = 0.201; t0 vs. 300 = 0.496; df = 1,10; p = 0.631). In contrast, leachate from the leaves of the invasive P. juliflora significantly reduced the root growth of B. campestris as compared to control at the highest concentration (Figure 6 upper panel, t0 vs. 300 = 3.893, df = 1,10, p = 0.003) and of S. bicolor at 150 (Figure 6 lower panel, t0 vs. 150 = 3.006, df = 1,10, p = 0.013) and 300 mL/g soil concentrations (t0 vs. 300 = 6.226, df = 1,10, p,0.0001). Brassica juncea root growth increased in soil treated with 60 (Figure 5 middle panel; t0 vs. 60 = 22.477, df = 1,10; p = 0.033) and 150 mL/g soil concentrations (t0 vs. 150 = 23.693, df = 1,10, p = 0.004) of P. juliflora leachate and was not affected at highest concentration (t0 vs. 300 = 0.002, df = 1,10, p = 0.999). Root length of seedlings of all 3 species grown in soil amended with leaf leachate from P. juliflora was significantly lower than that of seedlings grown in P. cineraria leaf leachate-amended soil at similar concentrations i.e. 150 (Figure 6 upper panel; tB. campestris = 2.764; df = 1,10; p = 0.020; tS. bicolor = 3.116; df = 1,10, p = 0.011) and 300 mL/g soil (tB. campestris = 5.573; df = 1,10; p,0.001; tB. juncea = 2.936; df = 1,10; p = 0.015; tS. bicolor = 4.963; df = 1,10; p = 0.001), with the exception of B. juncea at 150 mL/g soil (tB. juncea = 1.151; df = 1,10; p = 0.277). However at 60 mL/g soil concentration, there was no significant difference in root growth of all 3 species grown in P. juliflora leaf leachate-amended soil compared to those in P. cineraria leaf leachate-amended soil. There was a significant interaction effect between leachate source and concentration on root growth for all 3 species (Figure 6). We also found significantly negative correlations between P. juliflora leachate concentration and root growth of B. campestris (r = 20.681, p,0.001) and S. bicolor (r = 20.476, p = 0.019), however no significant correlation was observed in case of B. juncea (r = 20.060, p = 0.779). In contrast, significant positive Figure 3. Plant species richness (mean + SE) beneath canopies of P. juliflora, its native congener P. cineraria, and from open areas. Differences in plant species richness beneath P. cineraria and P. juliflora canopies and open areas were tested using one way-ANOVA and post-hoc Tukey’s test (p,0.05). doi:10.1371/journal.pone.0044966.g003 PLOS ONE | www.plosone.org 7 September 2012 | Volume 7 | Issue 9 | e44966