ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 65 Number 3
Underground tissue biomass, carbon substrate contents and diazotrophic populations associated with forage grasses in Nigeria
The relationships between underground tissue biomass, carbon substrates and various diazotrophic bacterial groups associated with five Nigerian forage grasses on lateritic soils were studied. Biomass (kg m-2) was < 1.0 except for Pennisetum purpureum (1.65 ± 0.60). Sugars and organic acids were higher in rhizomes than roots, except in Andropogon tectorum where the reverse was noted; the root/rhizome ratios for these substrates varied between 31 and 87%. Organic acids were < 1.0 mg g-1 freshweight in all cases. Most Probable Number estimates of aerobes, microaerophiles and anaerobes showed the highest population in Panicum maximum and Andropogon tectorum. The range of counts (x 106 g-1 fresh wt) were 8.40-58.11 (aerobes), 6.15-16.75 (microaerophiles), 0—6.20 (Azospirillum) and 0.06-115 (anaerobes). The diazotrophic genera in decreasing frequency of occurrence were Enterobacter — Pseudomonas — Azospirillum —Klebsiella. Correlation matrices indicate that the root system biomass/diazotroph relationship was significant only with Azospirillum in P. maximum (P = 0.02; r = 0.861; n = 9). Microaerophiles as subsurface pellicle formers correlated with anaerobes in A. gayanus (P = 0.1; r = 0.904; n = 3) and with Azospirillum only in Hyparrhenia rufa (P = 0.001; r - 0.999; n = 3).
Keywords: Biomass; Carbon substrates; Diazotrophic populations; Forage grasses; Correlations