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Lakehead University (2020)

Drought effects on soil enzyme activity

Jones, Connor Aidan

Titre : Drought effects on soil enzyme activity

Auteur : Jones, Connor Aidan

Université de soutenance : Lakehead University

Grade : Master of Science in Forestry 2020

Résumé
Soil extracellular enzyme activity (EEA) is a strong predictor for soil health. EEA cycle nutrients within terrestrial systems, processing carbon, nitrogen, and phosphorous, while also mineralizing and stabilizing gas. These processes are susceptible to disruption from global change drivers. How EEA responds to global change drivers remains poorly understood, however. My objectives were to examine how EEA is affected by drought treatment. Here I conduct a global meta-analysis to observe the EEA of 7 enzymes in response to drought using 384 paired observations from 37 studies. These studies are globally distributed and encompass multiple ecosystems. I then calculated natural log response ratios of EEA values under drought treatment to the control. I tested whether the natural log response ratios differed from zero, and whether they were influenced drought intensity, drought duration, soil depth and aridity. Within this analysis, I evaluated the response of enzymes by distinguishing class, nutrient cycle, and individual identity. This allowed for the comparison between hydrolytic and oxidative functioning while also examining how specific nutrient cycles were impacted. On average across all studies, EEA did not show a significant response to drought treatments. When analyzed by individual groups, the responses of neither hydrolytic nor oxidative enzymes to drought were statistically significant on average. Similarly, there was no significant responses when EEA were classified by element cycles, i.e., carbon, nitrogen, and phosphorous. Among all individual enzymes studied, only alkaline phosphomonoesterase displayed the significant response to drought treatment, showing reduced average alkaline phosphomonoesterase activity under drought than in the control. Further, contrary to our hypothesis, drought intensity and drought duration on average did not significantly influence EEA response to drought. However, the responses of EEA were dependent on soil depth and aridity EEA in the topsoil’s (<10 cm) experienced decreases in activity, whereas those in subsoil (>10 cm in depth) experienced significant increases. Across a global gradient of aridity index (0.092 to 2.28), the responses of EEAs to drought treatments decreased as climatic humidity increased, showing null or even positive responses in arid climates but negative responses in humid climates. My finding showed the evidence that responses of EEA to drought are EEA type-, soil depth- and aridity-dependent responses. This study indicates a stimulation of enzyme activity in deeper soil layers under drought conditions. Furthermore, this increase in EEA response to drought is exacerbated by aridity, wherein more arid regions showed higher susceptibility to increases in EEA under drought. Therefore, arid regions can be expected to be most adversely affected by drought, through the potential vulnerability of soil organic matter loss due to an increase in EEA.

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