Invasion of Prosopis juliflora Figure 4. Chemical properties – pH (A), electrical conductivity (B), organic carbon (C), PO43–Phosphorus (D), total organic nitrogen (E) and total phenolic content (F) of soil from the rhizosphere of Prosopis juliflora, Prosopis cineraria and soil from adjacent open area in Punjab, India. Error bars represent +1SE of mean. Different letters above bars indicate significant differences (one way ANOVA, post-ANOVA Tukey’s test; p,0.05). doi:10.1371/journal.pone.0044966.g004 correlations between P. cineraria leachate concentration and root growth of B. campestris (r = 0.594, p = 0.002) and B. juncea (r = 0.589, p = 0.002) were observed, however no significant correlation was observed in case of S. bicolor (r = 0.084, p = 0.695). Effect of Microbes in Litter of Prosopis Congeners on Other Species Bacteria and fungi isolated from the leaves of P. julifora and P. cineraria, when applied directly to other species, killed almost all B. juncea and C. dolichostachya seedlings precluding statistical analysis, but there were no discernible patterns in mortality for isolates from the two congeners. Fungal isolates from P. juliflora, applied as a group, killed 97% of B. juncea and 98% of C. dolichostachya seedlings (data not shown). Bacterial isolates from P. juliflora, applied as a group, killed 100% of B. juncea and 94% of C. dolichostachya. Fungal isolates from P. cineraria, applied as a group, killed 98% of B. juncea and 100% of C. dolichostachya (data not shown). Bacterial isolates from P. cineraria, applied as a group, killed 94% of B. juncea and 99% of C. dolichostachya. Chemical Characteristics of Soil Amended with Leaf Leachates of Two Congeners Both treatments, P. juliflora leaf leachate and P. cineraria leaf leachate, resulted in a significant decrease in pH and an increase in EC, OC, PO43–P, and total organic N of soil with the effect of former treatment being significantly higher than latter (Table S1). Prosopis cineraria leaf leachate treated soil did not differ significantly for PO43–P from untreated soil (Table S1). Effects of Leaf Leachate and Leaf Litter on Soil Phenolic Content Soil amended with leaf leachate of P. juliflora had 12.4 times higher values of total phenolics (5.95660.054 mg/100 g soil) than soil amended with P. cineraria (0.47960.019 mg/100 g soil) and 60.2 times higher concentrations than unamended soil (0.09960.004 mg/100 g soil; F = 9734.99; df = 2,15; p,0.015; Figure 7A). The total phenolic content of soil amended with leaf litter from P. juliflora was significantly higher than soil amended with P. cineraria litter and unamended soil, from 0 d to 14 d of incubation (Figure 7B, Table S2). L-tryptophan Recovery from Leaf Leachate Amended Soil L-tryptophan concentrations in the leachates of leaves of P. juliflora (4.9260.05 mg/ml leaf leachate) was 73.1% greater than that of P. cineraria (1.3260.014 mg/ml leaf leachate) (t = 70.509, df = 4, p,0.0001). Over 40% (0.7960.006 mg/g soil) of the originally added 1.968 mg/g soil of L-tryptophan from P. juliflora leachate, was recovered from soil immediately after application, but we could not detect L-tryptophan in soil amended with P. cineraria leachates. Discussion Prosopis juliflora is among the most invasive species in hot semiarid and arid regions of the world, and our results indicate that this invader has substantially stronger impacts on native diversity in two non-native ranges than in its native range of Venezuela where P. juliflora had facilitative effects and in the native range of Peru where P. pallida (often misidentified as P. juliflora [5]) had overall neutral effects. Despite the widely documented and very strong impacts of invasive species on natives [36,37], to our knowledge only two other studies have quantified the impact of an invasive species on the productivity or diversity of its neighbors in the field in both its native and non-native ranges. Inderjit et al. [38] found that the canopies of Ageratina adenophora, a widespread and aggressive subtropical invader, had facilitative effects on other species in its native Mexico but highly inhibitory effects in its non- Figure 5. Mortality (mean + SE) of different species - Acacia nilotica, Brassica campestris, Brassica juncea, Chloris dolichostachya, Dalbergia sissoo and Prosopis cineraria - when grown in soil amended with leaf litter of Prosopis juliflora (black box), P. cineraria (gray box) or without litter (white box). Different letters above bars indicate significant differences (one way ANOVA, post-ANOVA Tukey’s test; p,0.05). doi:10.1371/journal.pone.0044966.g005 PLOS ONE | www.plosone.org 9 September 2012 | Volume 7 | Issue 9 | e44966