Soil extracellular enzymes characteristics and their controlling factors along the elevation gradient in Qinghai-Tibet Plateau, China

Soil extracellular enzyme activities (EEAs) and ecoenzymatic stoichiometry (EES) play an essential role in soil nutrient cycling and organic matter decomposition. Understanding EEAs and EES variation patterns and their influencing factors could offer direct information about the soil structure, function, and soil response to anthropogenic disturbances and climate change. This issue is noteworthy, especially in high-altitude areas where climate change is imminent and vegetation is diversified. This study measured different soil EEAs and EES characteristics and explored their key controlling factors along nine altitudes ranging from 2500 m to over 5200 m in the Qinghai-Tibet Plateau of western China. We also analyzed the effects of plant microhabitats on soil EEAs and EES. The results showed that most soil EEAs and EES had significant variability in spatial characteristics, and enzymatic activity increased with altitude. Compared to the soil nutrient distribution which also increased with altitude, this same change trend of soil EEAs and soil nutrients was inconsistent with the resource allocation theory. Microorganisms might mediate the effects of environmental factors on soil EEAs by altering the enzyme production efficiency. Specific soil EEAs (EEAs/g SOC), like soil enzyme carbon: phosphorus ratios (ECP), and nitrogen: phosphorus ratios (ENP), showed an opposing trend in variation, which decreased with increasing altitude. Plant microhabitats significantly promoted soil EEAs due to the accumulation of soil nutrients (carbon, nitrogen and phosphorus). Soil EEAs and EES's spatial variability was mainly determined by edaphic factors, accounting for >70.24 % and 55.67 % of latitudinal variations, respectively. Generally, carbon and nitrogen limitations were substantial in this area and gradually alleviated with increasing altitude. This study provided a data support for ecological protection of the Qinghai-Tibet Plateau based on the spatial variation of soil EEAs and nutrient limitation.