Pigment ratios of the mediterranean bryophyte pleurochaete squarrosa respond to simulated nitrogen deposition

Abstract

Nitrogen (N) deposition alters ecosystem structure and functioning. To study potential impacts on Mediterranean ecosystems, we designed a field fertilization experiment where NH4NO3 was added at four rates (0, 10, 20 and 50 kg N ha−1 year−1). The terricolous moss Pleurochaete squarrosa was sampled and pigments extracted in spring-autumn 2008 and spring 2009. Simulated N deposition increased lutein and VAZ pigments to chlorophyll ratios in autumn 2008; β-carotene to chlorophyll ratio was reduced in spring 2009; (neoxantin + lutein) to β-carotene increased with N supply and this was explained as higher investment in light-harvesting complexes than in reaction centres. Response of carotene to chlorophylls and of (neoxantin + lutein)/β-carotene to N enrichment were only evident when soil NH4 and Mn, respectively, were used as covariates. Thus, covariance analyses are highly recommended to detect N fertilization effects on terricolous species when field experiments are set up in highly heterogeneous environments.