Enzyme activity in both soil and plants has been used to indicate N deposition and may provide possibilities as a biomonitor. The activities of a range of enzymes involved in the assimilation of N and other nutrients have been measured in response to N additions.Phosphomonoesterase (PME): By increasing the availability of N, the main growth driving nutrient, enhanced N deposition will also increase the demand for other nutrients such as P, albeit by proportionally smaller amounts. Phosphomonoesterase is the dominant phosphatase enzyme responsible for converting organic to inorganic P in most soils and hence changes in PME activity can potentially be used to monitor P availability in the soils.
Nitrate reductase (NR): NR activity has been use as an indicator of N deposition since the early eighties, and the inducibility of NR appears to be one of the most useful indicative responses of bryophytes, especially Sphagnum species, to anthropogenic N (Woodin Press & Lee 1985, Press, Woodin & Lee 1986, Woodin & Lee 1987). Bryophytes respond to and assimilate nitrate very rapidly and efficiently in small quantities but continuous exposure to large N inputs suppresses this response. Sphagnum is capable of assimilating NO3- immediately, showing no lag phase unlike higher plants. In mosses the ability to induce NR activity has thus been used to assess their nitrate exposure history with the inability to induce activity being seen to signify N saturation. The in vivo methodology was developed by Woodin & Lee (1987).
Johnson et al (1999) found that short-term (18 month) N additions to grassland sites had no effect on root-surface PME activity whereas long-term (7 years) additions significantly increased enzyme activity. Addition of P also significantly reduced PME activity. In the long-term plots, PME activity was closely related to extractable soil ammonium. NH4+ extracted in 2M KCl accounted for 67% of the variation in PME activity of Plantago lanceolata in calcareous grassland and 86% of the variation in PME activity of Agrostis capillaris in acid grassland. Activity of PME was an order magnitude lower in P. lanceolata than in A capillaris possibly reflecting the difference in root surface.
Bryophytes respond to and assimilate nitrate very rapidly and efficiently in small quantities but continuous exposure to large N inputs suppresses this response. The ability of mosses to induce NR activity has thus been used to assess nitrate exposure history with the inability to induce activity being seen to signify N saturation . (Woodin Press & Lee 1985, Press, Woodin & Lee 1986, Woodin & Lee 1987). Sphagnum is capable of assimilating NO3- immediately, showing no lag phase unlike higher plants.
Suitability to indicate atmospheric concentrations:
Suitability to indicate atmospheric depositions:
Some evidence with scope for development.
Suitability to indicate environmental impacts:
Sensitivity to other factors:
Sensitive to a range of factors affecting enzyme activity e.g. temperature, moisture and season.
Insufficient evidence, although available literature suggest that the enzyme activity represents a long-term response.
Limited by soil, horizon type, pH and factors affecting plant photosynthesis.
Expertise in field:
Ideally, samples should be collected, cleaned (removal of litter, other species etc) and frozen before being transported to an analytical laboratory by post, and specific conditions for storage and time between collection and freezing. Alternatively they could be transported in the fresh state as quickly as possible (by courier or special delivery) for sample preparation at the analytical laboratory.
Expertise in laboratory:
Specialist chemical analysis of samples is necessary.
Cost (per unit sample): £unknown
Cost Comment: Insufficient information available.