Seasonal dynamics outweigh management effects on microbial enzyme activity and stoichiometry in regenerative and conventional dryland pastures

Regenerative agriculture has emerged as a sustainable approach to support biodiversity while maintaining an adequate food supply, yet its impacts on soil microbiology remain minimally explored. We investigated how regenerative and conventional agricultural management, along with seasonal fluctuations, influenced soil microbial dynamics in a sheep-grazed dryland experiment in New Zealand. The study was conducted at the Lincoln University Regenerative Dryland experiment established in March 2022. Plots represented low (Olsen P 10 mg/L) and high (Olsen P 20 mg/L) phosphorus input conventional and regenerative agriculture. Conventional plots were sown with a cocksfoot/subterranean clover mix, while regenerative plots contained a diverse 12-species blend. Soil was collected in autumn (May 2024) and spring (October 2024) to assess labile nutrient pools and microbial function using extracellular enzyme activities, enzymatic stoichiometry, and vector analysis. We found that seasonal dynamics exerted strong effects on soil properties. While some management effects were detected in labile phosphorus and nitrogen pools, most potential microbial enzyme activities and stoichiometric indices were primarily influenced by season. Labile carbon increased in spring (1163 to 1593 μg C g soil - 1; + 37%), while nitrogen pools decreased (organic N; - 2.6%; inorganic N - 91% autumn to spring). This coincided with higher total enzyme activity (1628 to 1894 nmol g⁻¹ h⁻¹; + 16.4%), while treatment effects were minimal. Enzymatic stoichiometry and vector analysis indicated potential microbial nitrogen limitation across seasons (vector angles 36.4° – 39.5°). Vector length decreased in spring, suggesting that potential microbial carbon limitation decreased as labile carbon became more abundant. Overall, regenerative management did not differ from conventional management in microbial function under this dryland pasture system, whereas seasonal variability drove changes in nutrient availability and microbial processes. • Seasonal variation in labile nutrients exerted a stronger influence on potential microbial enzyme activities than differences between regenerative and conventional management • Seasonal shifts in labile (hot-water extracted) C and N corresponded with higher potential enzyme activities (CB, LAP, PHOS, XYL) in spring • Labile (hot-water extracted) C strongly predicted enzyme stoichiometric ratios • Enzymatic C:N and C:P ratios varied seasonally, while N:P ratios remained stable