Profiling of microbial PLFAs: implications for interspecific interactions due to intercropping which increase phosphorus uptake in phosphorus limited acidic soils.

摘要

Increased phosphorus (P) uptake during intercropping has been demonstrated previously between specific crop species, e.g. cereal-legumes, in P deficient alkaline or neutral soils. The evidence is less strong in P deficient acidic soils. To assess the interspecific effects of acidic soils on P uptake, and to determine the biochemical mechanisms involved, a field experiment with maize-based (Zea mays) intercropping was conducted with the legumes chickpea (Cicer arietinum) and soybean (Glycine max), as well as the cereal wheat (Triticum aestivum), respectively, in subtropical acidic soils of Southern China. The land equivalent ratio (LER) values (on an average of 1.20 and 1.07 for maize-chickpea and maize-soybean, respectively; and from 0.85 to 1.08 on average for maize-wheat after P fertilization) indicated that the interspecific stimulation of P uptake may be a general phenomenon i.e. controlled by soil P availability rather than crop species or soil type. Rhizosphere soil pH increased compared to that of non-rhizosphere even following the addition of the acidic calcium superphosphate (on an average of 0.16-0.56 pH units), suggesting rhizosphere acidification due to intercropping could not be the cause of increased P uptake in acid soils, unlike in alkaline or calcareous soils. The microbial phospholipids fatty acid (PLFA) profiles varied with both intercropping species and soil P status, indicating a selective enrichment of competent species (arbuscular mycorrhizal fungi, gram-negative bacteria, actinomycetes, and probably P solubilizing microorganisms) that may be responsible for increased P uptake during intercropping. The results suggest that root contact modified the microbial communities and the dominant microbial species in the intercropped rhizosphere, thereby contributing to increased P uptake during intercropping in acidic soils.