Chlorophyll fluorescence response of red spruce and balsam fir to a watershed calcium fertilization experiment in New Hampshire

Abstract

Decreases in soil exchangeable calcium (Ca) due to acid deposition have been linked with declines of forest species in the northeastern United States, particularly red spruce (Picea rubens Sarg.). In 2005, chlorophyll fluorescence measurements were taken on red spruce and balsam fir (Abies balsamea (L.) Mill.) trees growing on two watersheds at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire. One watershed had been fertilized with CaSiO3 in 1999 to replace the soil Ca losses of the past 50 years, and the other was a reference watershed. In March, there were no differences in any chlorophyll fluorescence parameter between sites or species. In August, however, dark-adapted ratios of variable fluorescence to maximum fluorescence (Fv/Fm) were significantly greater (p = 0.05) in the Ca-treated watershed for both spruce and fir, and spruce values were significantly greater than fir. No differences were found in the light-adapted fluorescence parameters. These results suggest that both spruce and fir respond to increases in Ca availability, even though fir does not exhibit the decline symptoms seen in spruce. It is unclear what physiological effect is responsible for the observed differences in Fv/Fm. The Fv/Fm values appear to respond to differences in Ca availability in forest tree species; thus, the ratio has the potential to be used in these two watersheds at HBEF to determine if other forest species are also responding to Ca additions.