Naphthalene exerts substantial nontarget effects on soil nitrogen mineralization processes in a subalpine forest soil: A microcosm study

Unraveling the impact of human perturbation on nitrogen cycling in terrestrial ecosystems of lower Himalaya, Pakistan

Terrestrial ecosystems are under the enormous pressure of land use management regimes through human disturbances, resulting in the disruption of biogeochemical cycles and associated ecosystem services. Nitrogen (N) in soil ecosystems is of vital importance for primary productivity, hence estimating the extent of these human interventions on N-cycling processes becomes imperative from economic and environmental perspectives. This work investigated the impacts of variable anthropogenic activities on N cycling in three different terrestrial ecosystems (arable, grassland, and forest) in three regions of lower Himalaya, Pakistan. Potential nitrification (PNA) and denitrification (DEA) enzyme activities, relative distribution of inorganic N species (NH4, NO3), and the role of inherent edaphic factors were assessed. Results revealed high nitrification potentials and increased nitrous oxide (N2O) emissions in the incubated soil microcosms, in the order as arable > grassland > forest ecosystems. Notably, higher rates of both studied processes (~ 30-50%) and elevated soil mineral nitrogen pool were observed in arable ecosystems. Forest soils, assumed as pristine ecosystems relying mainly on natural N fixation, produced (de)nitrification rates relatively lower than grasslands, followed by arable soils which were moderately disturbed through long-term fertilization and intensive land-use regimes. Linear regression modeling revealed that the inorganic N species (particularly NO3), and inherent edaphic factors were the key determinants of high (de)nitrification rates, hence warn of accelerated N losses in these ecosystems. The study highlights that elevated PNA and DEA being proxies for the altered N cycling in the studied terrestrial ecosystems are of great ecological relevance in view of predicted N2O budget in the lower Himalaya.

Contrasting response strategies of microbial functional traits to polycyclic aromatic hydrocarbons contamination under aerobic and anaerobic conditions

PAHs (Polycyclic aromatic hydrocarbons) are widely distributed in soil ecosystems, but our knowledge regarding the impacts of PAHs effects on soil microbial functional traits is limited. In this study, we evaluated the response and regulating strategies of microbial functional traits that are associated with the typical C, N, P, S cycling processes in a pristine soil under aerobic and anaerobic conditions after the addition of PAHs. Results revealed that indigenous microorganisms had strong degradation potential and adaptability to PAHs especially under aerobic conditions, while anaerobic conditions favored the degradation of high molecular weight PAHs. PAHs exhibited contrasting effects on soil microbial functional traits under different aeration conditions. It would probably change microbial carbon source utilization preference, stimulate inorganic P solubilization and strengthen the functional interactions between soil microorganisms under aerobic conditions, while might cause the increase of H₂S and CH₄ emissions under anaerobic conditions. This research provides an effective theoretical support for the ecological risk assessment of soil PAHs pollution.

Non-target Effects of Naphthalene on the Soil Microbial Biomass and Bacterial Communities in the Subalpine Forests of Western China

Naphthalene is a biocide of soil fauna, particularly of soil arthropods, that has been widely applied to test the functional roles of soil fauna in soil processes. However, whether the use of naphthalene to expel soil fauna has a non-target effect on soil bacteria in subalpine forests remains unclear. We conducted a naphthalene treatment experiment to explore the effects of naphthalene on the soil bacterial community in subalpine forest soil. The results suggested that naphthalene treatment (at 100 g.m^-2 per month) significantly increased the abundances of total bacterial, gram-positive bacterial and gram-negative bacterial phospholipid fatty acids (PLFA) and did not change the microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) or MBC/MBN ratio. Moreover, a total of 1038 operational taxonomic units (OTUs) were detected by Illumina MiSeq sequencing analysis. Proteobacteria, Actinobacteria, and Acidobacteria Chloroflexi were the dominant phyla, and Bradyrhizobium was the most abundant genus. The naphthalene treatment did not affect soil bacterial diversity or community structure. Overall, these results demonstrated that the naphthalene treatment had non-target effects on the active bacterial community abundance but not the soil bacterial community structure. Thus, the non-target effects of naphthalene treatment should be considered before using it to expel soil fauna.