Growth of Lippia alba (Mill.) N. E. Brown inoculated with arbuscular mycorrhizal fungi with different levels of humic substances and phosphorus in the soil

Inoculation with arbuscular mycorrhizal fungi (AMF) and the addition of humic substances (HSs) might contribute to the growth and development of Lippia alba (Mill.) N. E. Brown. The objective of this study was to evaluate the effect of the AMF Rhizophagus clarus (Nicolson T.H. & Schenck N.C.), with low and high (20 and 200 mg dm(-3) of soil, respectively) additions of phosphorus (P) and with or without HSs in the soil, on the growth and uptake of P and nitrogen (N) by L. alba, and microbial soil quality. The experiment was designed in a completely randomized factorial of 2 x2 x2 (with and without AMF, levels of P, and with or without HSs in the soil), with six replications, totaling 48 experimental units. Development of the plant was evaluated by measuring shoot dry matter (SDM), root dry matter (RDM), total dry matter (TDM), chlorophyll index (CI), N content in the shoots, and P in the plant. In addition, spore density and root colonization by AMF, as well as basal soil respiration (BSR), and the microbial biomass carbon (MB-C) and metabolic quotient (qCO(2)) of the soil were measured. The RDM and TDM, CI, N, and P content in the plant, the spore density and root colonization by AMF, and MB-C and qCO(2) were significantly increased with the inoculation of AMF. The addition of P to the soil significantly increased the SDM (up to 74%) and TDM (up to 29%). Plant inoculation with AMF and the addition of HSs and P to the soil increased plant P content (up to 60%) and N in the shoot (up to 74%) compared with that of the control (uninoculated, without HSs and P). The increase in plant uptake of P and N after inoculation with AMF and addition of HSs and P to the soil stimulated growth of L. alba. It was concluded that inoculation with AMF, with the addition of HSs and P, increased growth and the content of N and P of L. alba.