Extracellular Enzyme Activity and Stoichiometry Reveal Nutrient Dynamics during Microbially-Mediated Plant Residue Transformation

Abstract

Extracellular enzymes are the major mediators of plant residue and organic matter decomposition in soil, frequently associated with microbial metabolic processes and the biochemical cycling of nutrients in soil ecosystems. However, the dynamic trends and driving factors of extracellular enzymes and their stoichiometry during plant residue transformation remain to be further studied. Here, we investigated the dynamics of extracellular enzymes and enzymatic stoichiometry in the “litter-soil” transformation interface soil (TIS) layer, an essential occurrence layer for microbially-mediated C transformation. The results indicated an unbalanced relationship between substrate resource supply and microbial metabolic demand. Microbial metabolism was limited by C (C/N-acquiring enzymes > 1) and P (N/P-acquiring enzymes < 1) throughout the observed stages of plant residue transformation. The initially higher extracellular enzyme activity reflected the availability of the active components (dissolved carbon (DC), nitrogen (DN), microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP)) in the substrate and the higher intensity of microbial metabolism. With the transformation of plant residues, the active fraction ceased to be the predominant microbial C source, forcing the secretion of C-acquiring enzymes and N-acquiring enzymes to obtain C sources and N nutrients from refractory substrates. Moreover, C/N-acquiring enzymes decreased, while C/P-acquiring enzymes and N/P-acquiring enzymes subsequently increased, which suggested that the microbial demand for N gradually increased and for P relatively decreased. Soil microorganisms can be forced into dormancy or intracellular mineralization due to the lack of substrate resources, so microbial biomass and extracellular enzyme activities decreased significantly compared to initial values. In summary, the results indicated that soil nutrients indirectly contribute to extracellular enzymes and their stoichiometry by affecting microbial activities. Furthermore, extracellular enzymes and their stoichiometry were more sensitive to the response of soil microbial biomass carbon.

Delivery rate alters the effects of tire wear particles on soil microbial activities

“…In the results of β-1,4-N-acetyl-glucosaminidase, we found that the enzyme activity dramatically decreased in the abrupt treatment in phase 2 compared to in phase 1. Although the activities of most soil extracellular enzymes generally decrease over time in normal conditions [40,41], this reduction was remarkable in the abrupt treatment (29.80%) compared to other treatments (control and gradual, 13.16% and 5.59%) (Table 1). According to a previous study, abrupt TWPs pollution can stimulate anaerobic nitrogen metabolism [38], which may potentially reduce the activities of nitrogen cycle-related enzymes in a long run, and this may cause the decrease in β-1,4-Nacetyl-glucosaminidase activity over time in the abrupt delivery treatment.…”

Delivery rate alters the effects of tire wear particles on soil microbial activities

“…In the results of β-1,4-N-acetyl-glucosaminidase, we found that the enzyme activity dramatically decreased in the abrupt treatment in phase 2 compared to phase 1. Although the activities of most soil extracellular enzymes generally decrease over time under normal conditions [42,43], this reduction was more remarkable in the abrupt treatment (29.80%) compared to other treatments (control and gradual, 13.16% and 5.59%) (Table 1). We assumed that these differences were influenced by the prior delivery rates.…”

Mixed plantation forest litter improves microbial nitrogen transformation by increasing nitrogen metabolism related genes and key bacterial taxa in northern China

“…Microbial-driven N metabolism in the soil is vital for sustaining forest ecosystem functioning and stability (Ku et al, 2022). The TN content in MCBP litter was higher than that in both BP and CP litters (Figure 1a), which was because of the highly diverse substrate and nutritional composition (Jia et al, 2021;Liu et al, 2023). This highly diverse substrate composition resulted in higher bacterial diversity and more active N metabolism during litter decomposition (Philippot et al, 2013;.…”