Interest in soil extracellular enzyme activity as an indicator of microbial community function and resource allocation toward nutrient acquisition has been increasing in recent years. However, extracellular enzymes secreted by plant roots have received little attention outside of a few studies examining enzyme production on a small scale or in artificial environments. As a result, little is known about the extent of root enzyme activity and the degree to which these enzymes help roots exploit pools of organic nutrients in the soil. The objective of this study was to characterize the activities of a variety of nitrogen and phosphorus acquiring enzymes on the roots of a diverse range of plants.
Results/Conclusions
We observed relatively high rates of phosphatase activity compared to the surrounding soil on the roots of every plant we examined. Rates of root phosphatase activity were the highest ever recorded in our laboratory, exceeding rates of 14,000 nmol/h/g on roots of the non-mycorrhizal invasive herb garlic mustard (Alliaria petiolata). We also observed relatively high rates of root chitinase activity for all plants in our study. Chitin is a nitrogenous polymer that is a constituent of fungal cell walls, and chitinase activity is thought to be associated with N acquisition. Protein degrading enzymes such as peptidases are also associated with N acquisition, and we examined roots for leucine amino peptidase and glycine amino peptidase activity. No roots had any significant glycine amino peptidase activity, while a small proportion exhibited relatively low rates of leucine amino peptidase activity. Again, the highest rates of leucine amino peptidase activity we observed among roots were for garlic mustard. Overall, our results suggest that relatively high activities of nitrogen and phosphorus acquiring extracellular enzymes on root surfaces are widespread among a diverse range of plants.