Contamination risk by heavy metals and enzymatic stoichiometry in agricultural soils under intense use of pesticides.

Soil contamination by heavy metals (HM) from pesticides poses a serious environmental threat, affecting sustainability and agricultural productivity. Soil enzymes are essential for biochemical reactions such as organic matter decomposition and nutrient cycling and are vital for maintaining soil health. However, the effects of HM on soil enzyme activity are not yet well understood. This study examined the impact of HM contamination on enzymatic stoichiometry in regions with intensive pesticide use. We selected flower cultivation areas with 5 years (CA1) and 10 years (CA2) of pesticide exposure and a native forest area (NFA) as a reference during the dry and rainy seasons. We measured Cd, Cu, Mn, Pb, and Zn levels and employed ecological risk indices to assess contamination levels. We also analyzed enzyme activities (arylsulfatase, ß-glucosidase, acid phosphatase, urease) and enzymatic stoichiometry. CA2 exhibited the highest concentrations of Cd, Cu, and Mn in both periods, while Zn was highest in both CA1 and CA2. CA2 had higher values for all indices, indicating significant contamination. Compared with NFA, arylsulfatase activity was lower in cultivated areas during both periods, suggesting decreased soil quality. We found negative correlations between Cu, Mn, Zn, and arylsulfatase, as well as a reduction in urease with Cd; these elements also increased microbial C limitation. Our findings show that continuous pesticide input increases HM levels and that enzyme activity and stoichiometry are effective bioindicator of soil contamination. This study underscores the urgent need for guidelines to protect soils from prolonged HM buildup.

Morphological pattern of colonization by mycorrhizal fungi and the microbial activity observed in Barbados cherry crops / Padrão morfológico de colonização por fungos micorrízicos arbusculares e atividade microbiana em cultivos de acerola

ABSTRACT: Our objective was to evaluate the morphological pattern of colonization by arbuscular mycorrhizal fungi (AMF) as well as to study the microbiological activity of the soil on family farms where Barbados cherry was cultivated. Soil and root samples were selected from four areas in the municipality of Maranguape-CE where Barbados cherry was grown, which were named according to the age of plants in the following manner: A1-3, A2-3, and A3-3 (3 years), and A4-2 (2 years). After sampling, the arbuscular mycorrhizal colonization, morphological colonization pattern, basal soil respiration (SBR), and density of mycorrhizal spores (DS) were analyzed. The Paris-type morphological pattern was predominant in the root system of Barbados cherry; the affinity of this pattern in the culture was clear. Time of installation and management of Barbados cherry orchards in family farming areas promoted reduction in SBR. P levels in the soil may have negatively influenced root colonization and density of mycorrhizal spores.

RESUMO: Objetivou-se avaliar o padrão morfológico de colonização por Fungos Micorrízicos Arbusculares (FMA), bem como a atividade microbiológica do solo sob cultivo da aceroleira em áreas de agricultores familiares. Para as coletas de solos e raízes foram selecionadas quatro áreas com aceroleira no município de Maranguape-CE, essas foram denominadas de acordo com a idade das plantas A1-3, A2-3 e A3-3 (3 anos) e A4-2 (2 anos). Após as coletas foi analisado a colonização micorrízica arbuscular, o padrão morfológico de colonização, a respiração basal do solo (RBS) e a densidade de esporos micorrízicos (DE). O padrão morfológico do tipo Paris foi predominante no sistema radicular da aceroleira, ficado claro a afinidade desse padrão na cultura. O tempo de instalação e o manejo do pomar da aceroleira nas áreas de agricultura familiar promoveu uma redução na RBS. Os teores de P no solo podem ter influenciado negativamente a colonização radicular e a densidade de esporos de fungos micorrízicos arbusculares.