Parasitic fungus mediates change in nitrogen‐exposed boreal forest vegetation

Abstract

Summary1 Experimental additions of N to an old-growth boreal forest resulted in elevated levels of free amino acids in leaves of the dominant dwarf-shrub Vaccinium myrtillus and increased attack from a parasitic fungus, Valdensia heterodoxa . 2 Glutamine additions to the leaf surface of V. myrtillus increased disease incidence by an average of almost three times compared to controls and suggested a causal connection between amino acid availability and fungal infection. 3 Increased abundance of the grass Deschampsia flexuosa followed N addition but infection by the parasitic fungus, which causes premature leaf loss of its primary host V. myrtillus , explained four times as much of the variation in grass abundance as N did. 4 Nitrogen deposition can have marked effects on vegetation by affecting the interaction between dominant hosts and their natural enemies. A shift in abundance of dominating species occurred within 3 years of treatment, with nitrogen loads similar to those deposited over large areas in Europe and North America, suggesting that such effects may by important for the vegetation of large areas subjected to low levels of nitrogen input.

Upwind impacts of ammonia from an intensive poultry unit

“…Bobbink et al, 2010;Krupa, 2003) while nitrogen deposition as a whole causes declines in higher plant diversity (Sala et al, 2000;Stevens et al, 2004), increased susceptibility to secondary stresses (e.g. Power et al,1998;Strengbom et al, 2002), and altered soil processes (Phoenix et al, 2012).…”

Potential Approaches to Developing Lichen-Based Critical Loads and Levels for Nitrogen, Sulfur and Metal-Containing Atmospheric Pollutants in North America

“…The abundance of the mildew fungus Podosphaera myrtillina on Vaccinium was increased ten-fold by 25 kg N ha -1 yr -1 compared to 0.5 kg N ha -1 yr -1 . As a consequence, Vaccinium density decreased, and Deschampsia cover increased (Strengbom et al, 2002). In addition, shoots of Vaccinium myrtillis were significantly more damaged by larvae such as the moth Orgyia antrana after addition of 12.5 kg N ha -1 yr -1 in the first year of treatment .…”

“…decreasing Vaccinium myrtillus, occurred above ≥6 kg N ha -1 yr -1 (Strengbom et al, 2003) and increased growth of Deschampsia flexuosa with ≥5 kg N ha -1 yr -1 (Kellner and Redbo-Torstensson, 1995). Vaccinium myrtillus showed an increased attack by parasites when nitrogen fertilization was ≥12.5 kg N ha -1 yr -1 (Strengbom et al, 2002;. Bryophyte species are also sensitive; the biomass of the mosses Pleurozium schreberi and Dicranum polysetum fertilized with 25 and 30 kg N ha -1 yr -1 respectively was reduced by 60% and 78% respectively after four years (Mäkipää, 1998 …”

“…On the other hand, nitrogen fertilization with 30 kg N ha -1 yr -1 (atmospheric nitrogen deposition 12 kg N ha -1 yr -1 ) did not change the ground vegetation in a montane forest within three years (Schleppi et al, 1999). Valdensia heterodoxa (right) in a nitrogen addition experiment in a boreal forest in North Sweden (Strengbom et al, 2002).…”

Disease in Natural Plant Populations, Communities, and Ecosystems: Insights into Ecological and Evolutionary Processes

“…Springer et al (119) showed that calcium levels and rust disease are inversely related; unusual plant communities associated with serpentine outcrops may thus be particularly vulnerable to disease due to low calcium levels. In contrast, disease levels often increase as nitrogen is added to an environment (87,91,120); such patterns are also known with agricultural crops. Strengbom et al (120) explored the relationship between nitrogen addition and disease in boreal forests known to be nitrogen limited (Fig.…”