Growth of Cymbopogon citratus inoculated with mycorrhizal fungi under different levels of lead

Abstract

Cymbopogon citratus Stapf is an important aromatic plant used by industries of fragrances and aroma. Although, the effects of arbuscular mycorrhizal fungi (AMF) inoculation on the metabolism of these plants, in environments with presence of heavy metals such as lead (Pb) are little known. Thereat, this work aims at assessing the effect of the Rhizophagus clarus an AMF and Pb addition in soil on Pb, phosphorous (P) and nitrogen (N) uptake by C. citratus as well as its effects on the plant growth and microbial soil quality. The statistical design was completely randomized in a 5×2 factorial: 5 levels of Pb(NO3)2 (lead nitrate) 0, 50, 100, 500 and 1000mgPbkg−1 and 2 levels of AMF inoculation (with and without AMF) with 5 replications for each treatment, amounting to 50 experimental units. The spore density and the AMF root colonization were determined in addition to the microbial biomass C (MB-C), basal soil respiration (BSR) and metabolic quotient (qCO2) of the soil. The plant dry matter, number of tillers, chlorophyll and stomatal indexes of leaves, P and N shoot content, and plant Pb content were also determined. The spore density, AMF root colonization, MB-C and BSR were significantly higher when C. citratus was inoculated with AMF, except for the levels of 500 and 1000mgkg−1 Pb(NO3)2 applied to the soil. Plant dry matter was significantly decreased with Pb applied to the soil and without Pb addition, AMF inoculation increased plant growth. Addition of Pb in the soil increased Pb content in the plant and the AMF inoculation and Pb×AMF interaction showed significant effects on the plant Pb content. The Pb content in roots was significantly increased with addition of Pb(NO3)2 to the soil, but reduced about 50% with AMF inoculation, even with high levels of Pb. The P and N content in shoot were significantly increased with the AMF inoculation, mainly under low levels of Pb. It is concluded that Pb addition in the soil decreased MB-C. The AMF inoculation increased plant growth and reduced the accumulation of Pb in roots and increased the P and N content in plant shoot, but under high Pb levels, AMF inoculation increased Pb in shoots.