Microbial mechanisms for improved soil phosphorus mobilization in monoculture conifer plantations by mixing with broadleaved trees.

Replanting broadleaved trees in monoculture conifer plantations has been shown to improve the ecological environment. However, not much is known about the distribution properties of soil phosphate-mobilizing bacteria (PMB) under different mixed plantings or how PMB affects biometabolism-driven phosphorus (P) bioavailability. The phoD and pqqC genes serve as molecular markers of PMB because they regulate the mobilization of organic (Po) and inorganic (Pi) P. Differences in soil bioavailable P concentration, phoD- and pqqC-harboring PMB communities, and their main regulators were analyzed using biologically-based P (BBP) and high-throughput sequencing approaches after combining coniferous trees (Pinus massoniana) and five individual broadleaved trees (Bretschneidera sinensis, Michelia maudiae, Cercidiphyllum japonicum, Manglietia conifera, and Camellia oleifera). The findings revealed that the contents of litter P, soil organic carbon (SOC), available Pi (CaCl2-P), and labile Po (Enzyme-P) were significantly higher in conifer-broadleaf mixed plantations than those in the monospecific Pinus massoniana plantations (PM), especially in the mixed stands with the introduction of Cercidiphyllum japonicum, Michelia maudiae, and Camellia oleifera. Conifer-broadleaf mixing had little effect on the abundance of phoD and pqqC genes but significantly altered species composition within the communities. Conifer-broadleaf mixing improved soil microbial habitat mainly by increasing the pH, increasing carbon source availability and nutrient content, decreasing exchangeable Fe3+ and Al3+ content, and decreasing the activation degrees of Fe and Al oxides in acidic soils. A small group of taxa (phoD: Bradyrhizobium, Tardiphaga, Nitratireductor, Mesorhizobium, Herbaspirillum, and Ralstonia; pqqC: Burkholderia, Variovorax, Bradyrhizobium, and Leptothrix) played a key role in the synthesis of P-related enzymes (e.g., alkaline phosphomonoesterase, ALP) and in lowering the levels of mineral-occluded (HCl-P) and chelated (Citrate-P) Pi. Overall, our findings highlight that mixing conifers and broadleaves could change the PMB communities that produce ALP and dissolve Pi to make P more bioavailable.

Mixing of pine and arbuscular mycorrhizal tree species changed soil organic carbon storage by affecting soil microbial characteristics.

Pure and mixed pine forests are found all over the world. The mycorrhizal type affects soil microbial activity and carbon sequestration capacity in pure forests. However, the effects of mycorrhizal type on microbial characteristics and carbon sequestration capacity in pine mixed forests remain untested. Further, making it difficult to predict carbon storage of the conversion from pure pine forests to mixed forests at larger scales. Herein, a meta-analysis showed that the contents of soil microbial biomass, mineral-associated organic carbon, and soil organic carbon in pine mixed forests with introduced arbuscular mycorrhizal tree species (PMAM) increased by 26.41 %, 58.55 %, and 27.41 %, respectively, compared to pure pine forests, whereas those of pine mixed forests without arbuscular mycorrhizal tree species (PMEcM) remained unchanged. Furthermore, the effect size of microbial biomass, mineral-associated organic carbon and organic carbon contents in subsoil of PMAM are 56.48 %, 78.49 % and 43.05 %, respectively, which are higher than those in topsoil. The improvement of carbon sinks throughout the PMAM soil profile is positively correlated with increases in microbial biomass and mineral-associated organic carbon in subsoil, according to regression analysis and structural equation modelling. In summary, these results highlight that the positive effects of introducing arbuscular mycorrhizal tree species rather than ectomycorrhizal tree species into pure pine forests on soil microbial biomass and carbon sequestration. The positive link between microbial biomass, mineral-associated organic carbon, and soil organic carbon suggests an underlying mechanism for how soil microorganisms store carbon in pine mixed forests. Nevertheless, our findings also imply that the soil carbon pool of PMAM may be vulnerable under climate change. Based on the above findings, we propose that incorporating mycorrhizal type of tree species and soil thickness into mixed forests management and biodiversity conservation.

Insight into ultrasensitive and high-stability flocculation-enhanced Raman spectroscopy for the in situ noninvasive probing of cupping effect substances.

The aggregation of nanoparticles is the key factor to form hot spots for the flocculation-enhanced Raman spectroscopy (FLERS) method. However, the structure of flocculation is still not clear. It is therefore necessary to explore and analyze the aggregation process of nanoparticles more carefully, so as to realize a better application of FLERS. Here, we report the application of in situ liquid cell transmission electron microscopy (TEM) combined with an in situ high-speed camera to analyze the particle behaviors. The results showed that flocculation can exist stably and the gap between the nanoparticles in the flocculation always remained at 7-9 nm, which ensured the high stability and sensitivity of the FLERS method. We successfully applied FLERS to the in situ noninvasive probing of cupping effect substances. The results indicated the scientific principle behind the traditional Chinese medicine method to some extent, which thus provides a new and effective method for the in situ dynamic monitoring of biological systems.

Controlling the Shrinkage of 3D Hot Spot Droplets as a Microreactor for Quantitative SERS Detection of Anticancer Drugs in Serum Using a Handheld Raman Spectrometer.

Quantitative measurement is one of the ultimate targets for surface-enhanced Raman spectroscopy (SERS), but it suffers from difficulties in controlling the uniformity of hot spots and placing the target molecules in the hot spot space. Here, a convenient approach of three-phase equilibrium controlling the shrinkage of three-dimensional (3D) hot spot droplets has been demonstrated for the quantitative detection of the anticancer drug 5-fluorouracil (5-FU) in serum using a handheld Raman spectrometer. Droplet shrinkage, triggered by the shaking of aqueous nanoparticle (NP) colloids with immiscible oil chloroform (CHCl3) after the addition of negative ions and acetone, not only brings the nanoparticles in close proximity but can also act as a microreactor to enhance the spatial enrichment capability of the analyte in plasmonic sites and thereby realize simultaneously controlling 3D hot spots and placing target molecules in hot spots. Moreover, the shrinking process of Ag colloid droplets has been investigated using a high-speed camera, an in situ transmission electron microscope (in situ TEM), and a dark-field microscope (DFM), demonstrating the high stability and uniformity of nanoparticles in droplets. The shrunk Ag NP droplets exhibit excellent SERS sensitivity and reproducibility for the quantitative analysis of 5-FU over a large range of 50-1000 ppb. Hence, it is promising for quantitative analysis of complex systems and long-term monitoring of bioreactions.

General Surface-Enhanced Raman Spectroscopy Method for Actively Capturing Target Molecules in Small Gaps.

Over the past decade, many efforts have been devoted to designing and fabricating substrates for surface-enhanced Raman spectroscopy (SERS) with abundant hot spots to improve the sensitivity of detection. However, there have been many difficulties involved in causing molecules to enter hot spots actively or effectively. Here, we report a general SERS method for actively capturing target molecules in small gaps (hot spots) by constructing a nanocapillary pumping model. The ubiquity of hot spots and the inevitability of molecules entering them lights up all the hot spots and makes them effective. This general method can realize the highly sensitive detection of different types of molecules, including organic pollutants, drugs, poisons, toxins, pesticide residues, dyes, antibiotics, amino acids, antitumor drugs, explosives, and plasticizers. Additionally, in the dynamic detection process, an efficient and stable signal can be maintained for 1-2 min, which increases the practicality and operability of this method. Moreover, a dynamic detection process like this corresponds to the processes of material transformation in some organisms, so the method can be used to monitor transformation processes such as the death of a single cell caused by photothermal stimulation. Our method provides a novel pathway for generating hot spots that actively attract target molecules, and it can achieve general ultratrace detection of diverse substances and be applied to the study of cell behaviors in biological systems.

Effects of nitrogen deposition and phosphorus addition on arbuscular mycorrhizal fungi of Chinese fir (Cunninghamia lanceolata).

Nitrogen (N) deposition is a key factor that affects terrestrial biogeochemical cycles with a growing trend, especially in the southeast region of China, where shortage of available phosphorus (P) is particularly acute and P has become a major factor limiting plant growth and productivity. Arbuscular mycorrhizal fungi (AMF) establish a mutualistic symbiosis with plants, and play an important role in enhancing plant stress resistance. However, the response of AMF to the combined effects of N deposition and P additions is poorly understood. Thus, in this study, a field experiment was conducted in 10-year Chinese fir forests to estimate the effects of simulated nitrogen (N) deposition (low-N, 30 kg ha-1 year-1 and high-N, 60 kg ha-1 year-1) and phosphorus (P) addition treatments (low-P, 20 mg kg-1 and high-P, 40 mg kg-1) on AMF since April 2017, which was reflected in AMF root colonization rates and spore density of rhizosphere soil. Our results showed that N deposition significantly decreased AMF root colonization rates and spore density. In N-free plots, P addition significantly decreased AMF root colonization rates, but did not significantly alter spore density. In low-N plots, colonization rates significantly decreased under low P addition, but significantly increased under high P addition, and spore density exhibited a significant decline under high P additions. In high-N plots, colonization rates and spore density significantly increased under P additions. Interactive effects of simulated N deposition and P addition on both colonization rates and spore density were significant. Moderate N deposition or P addition can weaken the symbiotic relationship between plants and AMF, significantly reducing AMF colonization rates and inhibiting spore production. However, a moderate addition of P greatly enhances spore yield. In the case of interactive effects, the AMF colonization rates and spore density are affected by the relative content of N and P in the soil.