Other N Indicators

Pollutants: 

Ecosystems: 

Description: 

  1. FNIS is a functional N index for each species and is based on mineralization rates of various forms of soil N (Diekmann and Falkengren-Grerup, 1998). Species N indices for nitrate and ammonium are calculated as the weighted averages of mineralised N in plots where the species are present. The species indices for ammonium and nitrate are then combined to produce the Functional N Index for each Species (FNIS).
  2. Ndev was developed by Diekmann and Falkengren-Grerup (2002) to reflect soil N status in respect to N and pH at which individual species occurred, and hence to predict response to enhanced N deposition. Ndev was calculated for all species at the study sites of southern Sweden, based on their observed versus expected nitrificaiton rates at a given soil pH, and was then used to predict changes in species abundance.
  3. Life history traits, which may be affected by disturbance, have been used to classify species into groups. Traits include life form, phenology, plant height, anatomy, growth rate, foliar N content and others (Lavorel et al. 1997, 1999).

Previous experience:

  1. Diekmann and Falkengren-Grerup (1998) found that FNIS explained more floristic variability that Ellenberg N values and was a reliable expression of species response to N availability in deciduous forest soil of southern Sweden.
  2. Ndev was shown to be related to species frequency change in Swedish study sites and other areas of central Europe and able to predict species response to short-term fertilizer experiments (Diekmann and Falkengren-Grerup, 1998).
  3. Life history traits such as plant height, leaf anatomy, foliar N and phenology were significantly correlated with species change in Swedish forest sites, but were not as good predictors as Ndev (Diekmann and Falkengren-Grerup, 1998). Species likely to increase in abundance in response to enhanced N deposition are those favoured by a high soil nitrification rate at a given soil pH, tall stature, a hydro or helomorphic anatomy, large foliar N content and late phenological development.

Suitability to indicate atmospheric concentrations:

Unsuitable

Suitability to indicate atmospheric depositions:

Current evidence is not adequate to support a robust relationship between FNIS, Ndev or life history traits and N deposition, although these parameters represent responses to atmospheric deposition.

Suitability to indicate environmental impacts:

By definition each of these indices represent changes in the ecosystem related to varying nitrogen supply. There is some evidence for all 3 indicators, of an ability to indicate species richness, but more research is needed.

Sensitivity to other factors:

More research is needed, particularly on the interaction with different soil types.


Timescale:

These methods are more suited to the assessment of long-term change in deposition (several years/decades).

Limitations:

The available evidence is confined to forest ecosystems. More research is needed.


Expertise in field:

Staff with specialist plant identification skills, and specialist soil identification and sampling skills.

Expertise in laboratory:

Specialist soil processing skills and equipment are needed. Soils should be sent to specialist laboratories. Measurement of mineralisation is highly empirical (dependent on moisture levels) and samples must be stored under specific conditions (preferably in deep freeze).


Cost (per unit sample):  £unknown

Cost Comment:  Insufficient information. The combination of soil analysis and plant survey likely to require > 4 days survey work and 5 days analytical time. Processing of many sites in parallel may reduce costs.


Robustness: