Land use change and type of fertilization affect the stability and microbial activity, stoichiometry, and nutrient dynamics in agricultural and forest soils in Avándaro, México

The conversion from natural ecosystems to intensive agriculture can promote different changes due to constant fertilization. Fertilizations provoke high dependency on nutrient inputs and produce changes in nutrient dynamics, microbial activity, and the composition of soil microbial communities. However, few studies evaluate the high dependency on nutrient inputs with biogeochemical, and enzymatic variables and link the results with nutrient stoichiometry analyses to understand the effect on nutrients availability, microbial activity and biogeochemical cycling. The aim of this work was to analyse the effect of agricultural land use and fertilization with organic and inorganic P on soil nutrient dynamics (C, N and P) in Andosols. We divided the article into three sections, the first one that identifies the effect of land use change on biogeochemical, enzymatic activities, and ecological stoichiometry variables and identifies the dominant processes in each plot to answer: does the sites work as open or closed systems in terms of nutrient exchange and energy? The second section uses the results obtained in section one in order to identify the stability of the biogeochemical variables individually due to the change in land use, calculates resistance and resilience indices, and finally, the third section, covers an incubation experiment on soils from an agricultural site and a pine-oak site, which were fertilized with organic and inorganic compounds with the same concentration of P. At the end of this experiment, the changes in microbial activity and biogeochemical and ecological stoichiometric variables, such as threshold element ratio (TER) were identified, contributing with our data to increase the knowledge about the effects of the changes in soil elemental stoichiometry associated to fertilization, on resistance and resilience of soil organic matter transformation, soil nutrients availability and enzymes synthesis. With the variables analysed in these sections we aim to answer the following questions: will organic agriculture modify the stability of soil nutrient transformation, organic nutrient stores and activity of enzymes that degrade organic matter? and, what effects will fertilization have on the enzymatic activities linked to phosphorus? Our results suggest that the availability of PO₄³⁻ and NO₃⁻ are the variables that explain most of the variance that affects the nutrient dynamics in the agricultural plot, concluding that this site depends on nutrient inputs and acts as an open system. We identified that most of the variables are highly resistant; however, the nitrification process shows high vulnerability (less resistance, lower than 0.5) and is affected by the change in land use. In the final section, we found that both types of fertilization (inorganic and organic) negatively affected the activity of the β-glucosidase (BG) enzyme (0.068 μmolPNP g⁻¹ h⁻¹ for the control versus 0.010 and 0.007 μmolPNP g⁻¹ h⁻¹ for each fertilization respectively in the agricultural site). We identified N limitation induced by organic fertilization (Log_eDOC:DON = 3.61 ± 0.4, Log_eTER_C:N = 0.6 ± 0.85; p = 0.02) and C limitation due to inorganic fertilization (Log_eDOC:DOP = 2.66 ± 0.5, Log_eTER_C:P = 3.7 ± 1.3; p = 0.02). In conclusion, our results showed that the change in land use and organic and inorganic fertilizations with P modify processes related not only to P but also to C and N dynamics with changes in microbial activity. This study shows how land use change modify soil nutrients and energy flows in the ecosystem, quantified the vulnerability of soil microbial processes and provides information about the relevance of knowing the nutrient stoichiometry of fertilizer before to be applied.