Soil enzyme kinetics and thermodynamics in response to long-term vegetation succession

Phytoremediation of Oil-Contaminated Soil by Tagetes erecta L. Combined with Biochar and Microbial Agent

Crude oil pollution of soil is an important issue that has serious effects on both the environment and human health. Phytoremediation is a promising approach to cleaning up oil-contaminated soil. In order to facilitate phytoremediation effects for oil-contaminated soil, this study set up a pot experiment to explore the co-application potentiality of Tagetes erecta L. with two other methods: microbial agent and biochar. Results showed that the greatest total petroleum hydrocarbon (TPH) biodegradation (76.60%) occurred in the soil treated with T. erecta, a microbial agent, and biochar; the highest biomass and root activity also occurred in this treatment.GC-MS analysis showed that petroleum hydrocarbon components in the range from C10 to C40 all reduced in different treatments, and intermediate-chain alkanes were preferred by our bioremediation methods. Compared with the treatments with biochar, the chlorophyll fluorescence parameter NPQ_Lss and plant antioxidant enzyme activities significantly decreased in the treatments applied with the microbial agent, while soil enzyme activities, especially oxidoreductase activities, significantly increased. Although the correlation between biochar and most plant growth and soil enzyme activity indicators was not significant in this study, the interaction effect analysis found a synergistic effect between microbial agents and biochar. Overall, this study suggests the co-addition of microbial agents and biochar as an excellent method to improve the phytoremediation effects of oil-contaminated soil and enhances our understanding of the inner mechanism.

Long-term phosphorus addition alters soil enzyme kinetics with limited impact on their temperature sensitivity in an alpine meadow

The soil enzymes excreted by soil microorganisms and plant roots are essential for decomposing organic matter and regulating ecosystem function. However, phosphorus (P) deposition effects on the kinetics and thermodynamics of soil enzymes remain poorly understood. Here, an 11-year, multi-level P addition experiment was conducted in the alpine meadows of the Qinghai-Tibet Plateau, a region known as one of the most sensitive to global changes. We measured Vmax, Km and their temperature sensitivities (Q10) for six hydrolytic enzymes, along with soil properties and microbial community composition. P addition significantly reduced total soil organic C (SOC) and soil available N (NH4+-N and NO3--N), but increased dissolved organic N (DON), soil total P (TP) and available P (AP). Furthermore, P addition markedly decreased the abundance of Ascomycota, while increased that of Basidiomycota. However, the abundance of bacterial phyla remained unaffected by P addition. We found that P addition significantly increased the Vmax of β-glucosidase (BG), β-xylosidase (BX), cellobiohydrolase (CBH) and N-acetyl-glucosaminidase (NAG), but decreased that of acid phosphatase (APA) and L-leucine-aminopeptidase (LAP). P addition had no effect on Km of BX and CBH, but significantly lowered it for other enzymes. Specifically, P addition significantly reduced the Vmax-Q10 of BG and BX, but did not affect that of other enzymes. Conversely, P addition significantly increased the Km-Q10 of BG, while decreased the Km-Q10 of NAG, with no change in other enzymes. Variation partitioning analysis confirmed that microbial biomass and fungal community composition are crucial in influencing Vmax, Km, as well as their temperature sensitivities. This study highlights the critical influence of P addition on soil enzyme kinetics and temperature sensitivity and their relationships with microbial community, enhancing predictions of how microbial community and substrate availability interact to regulate the soil nutrient cycle under global environmental changes.

Role of Soil Microbiota Enzymes in Soil Health and Activity Changes Depending on Climate Change and the Type of Soil Ecosystem

The extracellular enzymes secreted by soil microorganisms play a pivotal role in the decomposition of organic matter and the global cycles of carbon (C), phosphorus (P), and nitrogen (N), also serving as indicators of soil health and fertility. Current research is extensively analyzing these microbial populations and enzyme activities in diverse soil ecosystems and climatic regions, such as forests, grasslands, tropics, arctic regions and deserts. Climate change, global warming, and intensive agriculture are altering soil enzyme activities. Yet, few reviews have thoroughly explored the key enzymes required for soil fertility and the effects of abiotic factors on their functionality. A comprehensive review is thus essential to better understand the role of soil microbial enzymes in C, P, and N cycles, and their response to climate changes, soil ecosystems, organic farming, and fertilization. Studies indicate that the soil temperature, moisture, water content, pH, substrate availability, and average annual temperature and precipitation significantly impact enzyme activities. Additionally, climate change has shown ambiguous effects on these activities, causing both reductions and enhancements in enzyme catalytic functions.

Soil bacterial succession with different land uses along a millennial chronosequence derived from the Yangtze River flood plain

Wetlands reclamation has been a traditional and effective practice for obtaining new land to alleviate the pressure induced by population growth. However, the evolution of soil-dwelling microorganisms along with reclamation and the potential influence of land-use patterns on them remain unclear. In this study, a soil chronosequence derived from Yangtze River sediments was established, comprising of circa 0, 60, 160, 280, 2000, and 3000 years, to examine the succession of soil bacterial communities across different land uses. Our analysis revealed obvious development in soil properties and orderly bacterial succession along reclamation gradients. Over time, reclaimed land suffered from varying degrees of abundance loss and biodiversity simplification, with dryland being the most sensitive to reclamation duration changes, whereas woodland and paddies showed slight reductions. Bacterial communities tended to shift from oligotrophs (K-strategist) to copiotrophs (r-strategist) at the phylum level as reclamation proceeded for all land use types. The relative abundance of certain bacterial functional groups associated with the carbon (C) and nitrogen (N) cycles were significantly increased, including those involved in Aerobic chemoheterotrophy, Chitinolysis, Nitrate reduction, Nitrate respiration, and Ureolysis, while other groups, such as those related to Fermentation, Methylotrophy, Nitrification, and Hydrocarbon degradation, exhibited decreased expression. Notably, prolonged reclamation can also trigger ecological issues in soil, including a continuous increase of predatory/exoparasitic bacteria in dryland and woodland, as well as a significant increase in pathogenic bacteria during the later stages in paddy fields. Overall, our study identified the impact of long-term reclamation on soil bacterial communities and functional groups, providing insight into the development of land-use-oriented ecological protection strategies.