How much invasive pine is changing soil properties in native Cerrado?

Background/Question/Methods

At least 20 Pinus species are considered to be invasive in at least one region of the southern hemisphere. In Brazil, several species of Pinus were introduced for commercial exploration and subsequently have spread into preserved areas. In our study area, in the Botanical Garden of Brasilia, Brasilia, Brazil some Pinus species were planted in a 8 ha stand near the public visitation area and currently there is evidence of invasion through spontaneous regeneration into adjacent native Cerrado vegetation. Previous studies have established that invasive pines can have a direct impact on the physical and chemical characteristics of the soil and the hypothesis tested in this study was that the litter layer produced by the pines in the natural area could alter the microbiological diversity of the Cerrado soil. We collected 21 soil samples, 10 in native Cerrado and 11 under the canopy of invading individuals of Pinus. In these samples, we determined the concentration of P, K, Ca, Mg, Al, Fe, Zn, Mn and Cu, along with soil organic matter and pH. These variables were correlated with functional diversity (calculated as the average well color development (AWCD) of 31 carbon sources using BIOLOG Ecoplates).

Results/Conclusions

Of the measured variables, only Al⁺³ had a significant difference between the samples collected under pine litter (1.14±0.16 cmol_c/dm³) and those in native Cerrado (0.90±0.26 cmol_c/dm³) (ANOVA, F_1,19=6.767, p=0.0175), and may increase the toxicity for cultivated plants, but it does not affect the native plants. A principal component analysis (PCA) with the variance/covariance matrix explained about 54,6% of variation on data, however didn't distinguished the bacterial community of native soil for the samples of soil with invasive pines. The redundancy analysis (RDA), combining the AWCD values against ambiental variables, the results show no direct relationships between the bacterial community and the soil variables (α=5%, R²=15.53%). In conclusion, the variability in the nutrients on soil and bacterial community is specific to each collection point, and occupation by Pinus does not alter neither the bacterial community nor the nutrients concentration.