Effects of Elevated CO2 Concentration and Nitrogen Addition on Soil Respiration in a Cd-Contaminated Experimental Forest Microcosm

Abstract

Forests near rapidly industrialized and urbanized regions are often exposed to elevated CO2, increased N deposition, and heavy metal pollution. To date, the effects of elevated CO2 and/or increased N deposition on soil respiration (Rs) under heavy metal contamination are unclear. In this study, we firstly investigated Rs in Cd-contaminated model forests with CO2 enrichment and N addition in subtropical China. Results showed that Rs in all treatments exhibited similar clear seasonal patterns, with soil temperature being a dominant control. Cadmium addition significantly decreased cumulative soil CO2 efflux by 19% compared to the control. The inhibition of Rs caused by Cd addition was increased by N addition (decreased by 34%) was partially offset by elevated CO2 (decreased by 15%), and was not significantly altered by the combined N addition and rising CO2. Soil pH, microbial biomass carbon, carbon-degrading hydrolytic enzymes, and fine root biomass were also significantly altered by the treatments. A structural equation model revealed that the responses of Rs to Cd stress, elevated CO2, and N addition were mainly mediated by soil carbon-degrading hydrolytic enzymes and fine root biomass. Overall, our findings indicate that N deposition may exacerbate the negative effect of Cd on Rs in Cd-contaminated forests and benefit soil carbon sequestration in the future at increasing atmospheric CO2 levels.

Determination of Poultry Manure and Plant Residues Effects on Zn Bioavailable Fraction in Contaminated Soil via DGT Technique

“…The presence of DOC, particularly humic acids, may be the main factor contributing to the increased C E -Zn and DTPAextractable Zn (except for C E -Zn in sorghum residues-amended soil) through decreased pH and formation soluble organo-Zn. Increases of metal bioavailability as a result of decreased pH can occur in different ways, including the acidic groups contained in DOC such as hydroxyl functional groups and carboxyl (Adeleke et al 2017), and the production of CO 2 from root respiration and microbial activity, thereby increasing exchangeable metal form (Yao et al 2020). The increase in exchangeable form of Zn may be linked to decreased oxide fractions of Zn which is likely due to the excretion of Zn 2+ /OHto balance the internal charge variation as a result of increased H + in the soil solution.…”

Determination of Poultry Manure and Plant Residues Effects on Zn Bioavailable Fraction in Contaminated Soil Via DGT Technique

“…The presence of DOC, particularly humic acids, may be the main factor contributing to the increased CE-Zn and DTPA-extractable Zn (except for CE-Zn in sorghum residues-amended soil) through decreased pH and formation soluble organo-Zn. Increases of metal bioavailability as a result of decreased pH can occur in different ways, including the acidic groups contained in DOC such as hydroxyl functional groups and carboxyl (Adeleke et al 2017), and the production of CO2 from root respiration and microbial activity, decrease pH, thereby increasing exchangeable metal form (Yao et al 2020). The increase in exchangeable form of Zn may be linked to decreased oxide fractions of Zn which is likely due to the excretion of Zn 2+ /OHto balance the internal charge variation as a result of increased H + in the soil solution.…”

Microbial responses towards biochar application in potentially toxic element (PTE) contaminated soil: a critical review on effects and potential mechanisms

“…The inferior microbial activity may lead to the loss of C storage of topsoil, and hence increase soil C emission (Zahorec et al 2022). Some researchers believed that microbial growth would occur only when bioavailable PTEs were reduced to a threshold concentration (Yao et al 2020). Microbial enzyme deletion may affect soil fertility due to the repression of SOM turnover.…”