Microbial activity and hydrolase activities during decomposition of root exudates released by an artificial root surface in Cd-contaminated soils

Abstract

The aim of this study was to assess the stimulatory effects of different low molecular weight organic compounds commonly present in root exudates on microbial activity and hydrolase activities, and the effects of high Cd concentrations in sandy soils collected from contaminated field plots on the stimulatory effects. Glucose, glutamic acid, citric acid, oxalic acid, or a mixture of all compounds were released by an artificial root surface in a simplified rhizosphere system. The effects were measured at !2 mm (rhizosphere soil layer) and O4 mm (bulk soil layer) distance from the root surface, 7 d after the root exudates release. Results showed that different root exudates were mineralized at different extent and had different stimulatory effects on microbial growth estimated by dsDNA content of soil, and on hydrolase activities, mostly localized in the rhizosphere soil layer. Mineralization of root exudates, microbial growth and stimulation of most of the measured hydrolase activities were drastically reduced by high Cd concentrations in soil. q

Using basalt flour and brown algae to improve biological properties of soil contaminated with cadmium

“…The tested metal also negatively influences ammonification bacteria and it takes the following place in the toxicity order: Ni > Pb > Cr (III) > Cd > Zn > Hg (Wyszkowska et al 2013b). Plants, to oppose the invasion of cadmium, activate mechanisms that give them a chance to detect cadmium as early as in root hairs (Irfan On the other hand, they do stay neutral for the diversity and microbiological activity of root secretions that accumulate in the rhizosphere: glucose, glutamate acid, citric acid, and oxalic acid (Renella et al 2006). The effects of four potentially alleviating substances with the use of EF factor were analyzed with the PCA method (Figure 2).…”

“…On the other hand, even if the number of microorganisms is not decreasing, their diversity is reduced (Wang et al 2007). Disruptions of the microbiological balance associated with cadmium deposition are a result of disturbances to the physiological functions of microbes, including protein denaturation and destruction of the cell membranes of microorganisms (Renella et al 2006).…”

Phenolic root exudate and tissue compounds vary widely among temperate forest tree species and have contrasting effects on soil microbial respiration

“…To analyze phenolic effects on microbial respiration, we added individual compounds from the identified biosynthetic classes to a forest soil and measured soil CO 2 emissions over a 5‐d period. This approach is similar to the experimental setup of other soil incubation studies that created an artificial and simplified rhizosphere to study the effect of single root exudates on soil microbial activity and SOM decomposition (Renella et al ., ; Keiluweit et al ., ), except that we added the chemicals as solids to an air‐dried soil at the start of the experiment due to their insolubility in water. Soil was collected from the first 0–15 cm mineral soil in the Arnot Forest (Central New York, USA).…”

Plant-borne flavonoids released into the rhizosphere: impact on soil bio-activities related to plant nutrition. A review

“…Roots can release extracellular enzymes into soil, or stimulate microbial growth and thus the synthesis of microbial enzymes through the release of root exudates, mucilages, and root remains (Dick 1994;Ladd 1985;Nannipieri 1994;Pinton et al 2001). Renella et al (2006a) reported that different root exudates were mineralized to different extents and had different stimulatory effects on microbial growth and on hydrolase activities, mostly localized in the rhizosphere soil. As a consequence of the plant effect, enzymatic activities of the rhizosphere are often higher than those of the bulk soil, but it is difficult to discriminate between plant and microbial sources of enzymes in soil Renella et al 2006aRenella et al , 2007a.…”