Methylation procedures affect PLFA results more than selected extraction parameters

Evaluation of simplified ester-linked fatty acid analysis (ELFA) for phospholipid fatty acid (PLFA) analysis of bacterial population

Phospholipid fatty acid (PLFA) analysis is used for characterizing microbial communities based on their lipid profiles. This method avoids biases from PCR or culture, allowing data collection in a natural state. However, PLFA is labor-intensive due to lipid fractionation. Simplified ester-linked fatty acid analysis (ELFA), which skips lipid fractionation, offers an alternative. It utilizes base-catalyzed methylation to derivatize only lipids, not free fatty acids, and found glycolipid and neutral lipid fractions are scarcely present in most bacteria, allowing lipid fractionation to be skipped. ELFA method showed a high correlation to PLFA data (r = 0.99) and higher sensitivity than the PLFA method by 1.5-2.57-fold, mainly due to the higher recovery of lipids, which was 1.5-1.9 times higher than with PLFA. The theoretical limit of detection (LOD) and limit of quantification (LOQ) for the ELFA method indicated that 1.54-fold less sample was needed for analysis than with the PLFA method. Our analysis of three bacterial cultures and a simulated consortium revealed the effectiveness of the ELFA method by its simple procedure and enhanced sensitivity for detecting strain-specific markers, which were not detected in PLFA analysis. Overall, this method could be easily used for the population analysis of synthetic consortia.

Water limitation intensity shifts carbon allocation dynamics in Scots pine mesocosms

Background and aims

Tree species worldwide suffer from extended periods of water limitation. These conditions not only affect the growth and vitality of trees but also feed back on the cycling of carbon (C) at the plant-soil interface. However, the impact of progressing water loss from soils on the transfer of assimilated C belowground remains unresolved.

Methods

Using mesocosms, we assessed how increasing levels of water deficit affect the growth of Pinus sylvestris saplings and performed a 13C-CO2 pulse labelling experiment to trace the pathway of assimilated C into needles, fine roots, soil pore CO2, and phospholipid fatty acids of soil microbial groups.

Results

With increasing water limitation, trees partitioned more biomass belowground at the expense of aboveground growth. Moderate levels of water limitation barely affected the uptake of 13C label and the transit time of C from needles to the soil pore CO2. Comparatively, more severe water limitation increased the fraction of 13C label that trees allocated to fine roots and soil fungi while a lower fraction of 13CO2 was readily respired from the soil.

Conclusions

When soil water becomes largely unavailable, C cycling within trees becomes slower, and a fraction of C allocated belowground may accumulate in fine roots or be transferred to the soil and associated microorganisms without being metabolically used.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11104-023-06093-5.

Characteristics of organic pollutants and their effects on the microbial composition and activity in the industrial soils of Pearl River Delta, China

To investigate the interaction between organic pollutants and soil microorganisms, industrial soils were collected from Pearl River Delta region of China for determining semi-volatile organic pollutants, the community structure and activity of microorganisms. The results showed that polycyclic aromatic hydrocarbons (PAHs) (63.3-4956 μg kg^-1) and phthalate esters (PAEs) (272-65,837 μg kg^-1) were main organic pollutants in the research area soils. Chemical manufacturing industry and plastics manufacturing industry contributed greatly to PAH pollution and PAE pollution, respectively. Organic pollutants changed the biomass of microorganisms. In most industrial soils, the biomass of actinomycetes was the highest in the industrial soils, followed by G^- bacteria, G⁺ bacteria and fungi. The exception was that the biomass of fungi in the soil near chemical manufacturing industry was greater than that of G⁺ bacteria. The soil microbial biomass (including soil microbial biomass carbon, soil microbial biomass nitrogen, the biomass of actinomycetes, bacteria, and fungi) and soil enzyme activities (sucrase and urease) positively correlated with the organic pollutant residues, and the microbial species diversity and microbial species abundance decreased with organic pollutant residues increasing. Based on the correlation analysis, the urease activity, actinomycetes biomass, and fungi biomass were appropriate biological indicators for evaluating the stress of organic pollutants. Our research provides a new perspective for understanding the soil biological response in industrial soils.

Effects of Nitrogen Addition on Plant Properties and Microbiomes Under High Phosphorus Addition Level in the Alpine Steppe

Nitrogen (N) addition can increase the vegetative growth, improve the plant production, and restore the degraded terrestrial ecosystems. But, it simultaneously aggravates the soil phosphorus (P) limitation for plant growth, thus affecting its positive effects on ecosystems. However, how plants and soil microorganisms will change under conditions of high P content in soil is still unknown. In this study, we explored the effects of three levels of N addition (0, 7.5, and 15 g.N.m^-2.year^-1) on plants and microorganisms at the high P addition level (13.09 g.P.m^-2.year^-1) in the alpine steppe. We found that the soil microbial community composition had no significant difference between different N addition levels, and the soil AN and AP had a significant effect on the phospholipid fatty acid (PLFA) composition. The abundance of the core PLFAs (i.e., 16:1ω7c, 16:0, a17:1, i17:0, 18:1ω9c, and 18:1ω7c) also remained unchanged after N addition, and microbes at individual, population, and community levels were all correlated with SOM, AK, AN, and pH. Conversely, plant biomass and nutrient content showed linear trends with increasing N addition, especially the dominant functional groups. Specifically, the biomass and plant tissue N content of Gramineae, and the total N content of aboveground biomass were all improved by N addition. They were correlated with soil ammonium and AP. The structural equation modeling (SEM) demonstrated that N addition had a direct negative effect on soil microbial biomass, but an indirect positive effect on aboveground biomass via soil ammonium. These findings clarify the importance of N-amendment in regulating plants and microorganisms under high P conditions and provide a better understanding of the N-added effects in the alpine steppe.