Description:
Insect pests: It is generally thought that the increased infestations of insect pests particularly sucking insects, observed following N addition from the atmosphere or as fertiliser, is a response to increased N content of the plants. While the presence of certain pests may indicate an effect of N deposition, their absence does not indicate the lack of an effect and the introduction of pests in order to observe change is not acceptable.
Soil invertebrates: The composition of soil fauna may reflect the N status of the soil, although the application of high doses of nitrogen has had mixed results.
Previous experience:
For insect pests, the infestation of beech aphid Phyllaphis fagi in a N fertilization experiment, increased significantly with increasing N concentration in leaves and N/P ratios respectively (Fluckiger and Braun, 1998). The occurrence of insect damage to pine needles in permanent plots in Scotland was positively correlated with modelled N deposition (range 7-22 kg N ha-1 yr-1). This relationship was associated with a negative relationship between the years of needles retained and modelled N deposition (NEGTAP, 2001).
For soil fauna, the abundance of Nematoda, Oligochaeta and microarthropodes, especially Collembola, had increased in some studies, but decreased in others after fertilizers (>150 kg N ha-1 yr-1) (Abrahamsen and Thompson, 1979; Huhta et al., 1983; Vilkamaa and Huhta, 1986). A one-time application of 100 kg N ha-1 yr-1 (as NH4NO3) in Eastern France, produced an effect on soil microorganisms which was still significant after 23 years (Deleporte and Tillier, 1999). A reduction in the nitrogen deposition in a Pinus sylvestris stand to preindustrial levels increased the species diversity of microarthropods due to a decreased dominance of some species (Boxman et al., 1995). In Sweden, a significant decrease of snails over 14-46 years in areas with N deposition of 15-25 kg N ha-1 yr-1 was observed, while in areas with N deposition of 3-6 kg N ha-1 yr-1 no significant changes were found (Gardenfors et al.,1995).
Suitability to indicate atmospheric concentrations:
Not suitable.
Suitability to indicate atmospheric depositions:
There is some evidence to suggest a link between abundance of certain species and N deposition. However the relationship is not robust and further work is needed.
Suitability to indicate environmental impacts:
By definition, changes in invertebrates would represent a biological impact of nitrogen. However, However the relationship is not robust and further work is needed.
Sensitivity to other factors:
There will be sensitivity to many other factors, which affect the growth of the insect pests and their hosts and the competitive growth of soil invertebrates.
Timescale:
No evidence available, likely to be a response over many years.
Limitations:
The method is in principle relevant for most terrestrial ecosystems, but the main concerns are the sensitivity to other factors which limit its practicle application.
Expertise in field:
Agency staff may be trained to check for and monitor insect pests. Surveys of soil fauna require skilled staff to both develop and apply the methods.
Expertise in laboratory:
Identification of soil fauna require skilled staff.
Cost (per unit sample): £unknown
Cost Comment: Insufficient information.
Robusness: 