Beta Diversity of Arbuscular Mycorrhizal Communities Increases in Time after Crop Establishment of Peruvian Sacha Inchi (Plukenetia volubilis)

Abstract

(1) Background: Beta diversity, i.e., the variance in species compositions across communities, has been pointed out as a main factor for explaining ecosystem functioning. However, few studies have directly tested the effect of crop establishment on beta diversity. We studied beta diversity patterns of arbuscular mycorrhizal (AM) fungal communities associated to sacha inchi (Plukenetia volubilis) after crop establishment. (2) Methods: We molecularly characterized the AM fungal communities associated to roots of sacha inchi in plots after different times of crop establishment, from less than one year to older than three. We analyzed the patterns of alpha, beta, and phylogenetic diversity, and the sources of variation of AM fungal community composition. (3) Results: Beta diversity increased in the older plots, but no temporal effect in alpha or phylogenetic diversity was found. The AM fungal community composition was driven by environmental factors (altitude and soil conditions). A part of this variation could be attributed to differences between sampled locations (expressed as geographic coordinates). Crop age, in turn, affected the composition with no interactions with the environmental conditions or spatial location. (4) Conclusions: These results point out towards a certain recovery of the soil microbiota after sacha inchi establishment. This fact could be attributed to the low-impact management associated to this tropical crop.

Keywords: Plukenetia volubilis; T-RFLP; agroecosystem; arbuscular mycorrhizal fungi; community assembly.

Figure A1

Phylogenetic network showing the clustering of obtained arbuscular mycorrhizal fungal sequences through a monophyletic clade approach into 13 operational taxonomic units (OTUs).

Figure A2

Rarefaction analysis of the composition of operational taxonomic units (OTUs) of arbuscular mycorrhizal communities forming the gene library. Extrapolated value of the curve predicted a total of 16 OTUs when 1000 clones would be analyzed.

Figure A3

Sampling effort (number of detected arbuscular mycorrhizal fungal taxa per number of analyzed samples) calculated for each site and age using iNEXT R package considering incidence frequency counts. SC–Species coverage from 0 to 1.

Figure 1

Spatial location of the eight sampled sacha inchi production plots, located in four localities of the San Martín region in Peru. Red points represent plots with plantations less than one year old, and blue points represent those older than three years old.

Figure 2

Variation of beta diversity (Jaccard dissimilarity across sample pairs, y-axis) of AM fungal communities across crop ages (years, in x-axis) and localities (different color).

Figure 3

Ordination of the arbuscular mycorrhizal fungi community composition via redundancy analysis (RDA) (TRFLP database approach) in four localities in the San Martín region. The position of samples in the figure indicates their similarity (closer samples, more similar community composition) and correlation with shown variables (samples in the direction of arrows contains AM fungal taxa whose presence correlates with those variables). The pie chart shows a variance partitioning of the community composition by environmental factors (CaCO₃, base sum and altitude), plot spatial position, and crop age. In the figure, age, altitude, CaCO_3, and base sum soil content were used as constraints.

Figure 4

Ordination of the arbuscular mycorrhizal fungi community composition via redundancy analysis (RDA) (TRFLP peak profile approach) in four localities in the San Martín region. The pie chart shows a variance partition of the community composition explained by environmental factors (soil organic matter -OM- and P), plot spatial position, and crop age. In the figure, age, soil OM, and soil P content were used as constraints.