Variation Partitioning by Partial Redundancy Analysis (Rda)

Partial redundancy analysis was applied to assess the effects of sulphur (S) and nitrogen (N) deposition on epiphytic green algae (mainly Protococcus viridis) on Picea abies needles. Data were collected from 15 sites over the country during 12 years by the Swedish National Environmental Monitoring Program (PMK). The green algae colony thickness and colonization rate depend on three intercorrelated environmental variable groups, namely, geographic location, climatic condition and S and N deposition. The collinearity between the environmental variables complicates the assessment of deposition-induced impact. The total explained variation within algae distribution patterns (eigenvalue=0.811 as 100 per cent) was partitioned among the three environmental variable groups. Analysis showed that a large part of the explained variation (67 per cent) was due to the joint affects of geographic factors, climatic factors and S, N deposition. Climatic factors (temperature sum and relative moisture) alone, and joint affects of climatic and S, N deposition accounted for 13 per cent and 12 per cent of the explained variation, respectively. The pure geographic factors and the pure deposition accounted for less than 5 per cent, respectively. This analysis suggests that the response of green algae to S and N deposition is mainly climate dependent, stronger in a warm and moist climate than in a cool and dry one.