Seedling survival in a northern temperate forest understory is increased by elevated atmospheric carbon dioxide and atmospheric nitrogen deposition

Abstract

We tested the main and interactive effects of elevated carbon dioxide concentration ([CO 2 ]), nitrogen (N), and light availability on leaf photosynthesis, and plant growth and survival in understory seedlings grown in an N-limited northern hardwood forest. For two growing seasons, we exposed six species of tree seedlings (Betula papyrifera, Populus tremuloides, Acer saccharum, Fagus grandifolia, Pinus strobus, and Prunus serotina) to a factorial combination of atmospheric CO 2 (ambient, and elevated CO 2 at 658 lmol CO 2 mol À1 ) and N deposition (ambient and ambient 130 kg N ha À1 yr À1 ) in open-top chambers placed in an understory light gradient. Elevated CO 2 exposure significantly increased apparent quantum efficiency of electron transport by 41% (Po0.0001), light-limited photosynthesis by 47% (Po0.0001), and light-saturated photosynthesis by 60% (Po0.003) compared with seedlings grown in ambient [CO 2 ]. Experimental N deposition significantly increased light-limited photosynthesis as light availability increased (Po0.037). Species differed in the magnitude of light-saturated photosynthetic response to elevated N and light treatments (Po0.016). Elevated CO 2 exposure and high N availability did not affect seedling growth; however, growth increased slightly with light availability (R 2 5 0.26, Po0.0001). Experimental N deposition significantly increased average survival of all species by 48% (Po0.012). However, seedling survival was greatest (85%) under conditions of both high [CO 2 ] and N deposition (Po0.009). Path analysis determined that the greatest predictor for seedling survival in the understory was total biomass (R 2 5 0.39, Po0.001), and that carboxylation capacity (V cmax ) was a better predictor for seedling growth and survival than maximum photosynthetic rate (A max ). Our results suggest that increasing [CO 2 ] and N deposition from fossil fuel combustion could alter understory tree species recruitment dynamics through changes in seedling survival, and this has the potential to alter future forest species composition.

Is the growth of temperate forest trees enhanced along an ambient nitrogen deposition gradient?

“…In particular, our results should be considered alongside other studies suggesting that elevated N deposition may enhance seedling survival (Sefcik et al 2007), lead to competitive exclusion of characteristic species by more nitrophilic vegetation (Bobbink et al 1998), and affect species dominance and overall biodiversity (Vitousek et al 1997). Further, the influence of deposition on red maple growth may be yet another anthropogenic perturbation (e.g., fire suppression, logging, land clearing) that is contributing to the proliferation of this ''super-generalist'' species in some forests (Abrams 1998).…”

Photosynthesis acclimation, leaf nitrogen concentration, and growth of four tree species over 3 years in response to elevated carbon dioxide and nitrogen treatment in subtropical China

“…Nitrogen availability is important for leaf photosynthesis because leaf chlorophyll concentration, Rubisco (ribulose-1-5-biphosphate carboxylase), and plant growth all increase with the greater N availability (Kutik et al 1995;Xu et al 2002;Bondada and Syvertsen 2003;Huang et al 2008). Downregulation of photosynthesis would occur with elevated CO 2 concentration exposure due to the N limitation effect (Sefcik et al 2006(Sefcik et al , 2007Hyvönen et al 2007). Plants grown with high N availability would increase light-saturated photosynthetic rate, alleviating the downregulation responses for plants grown under elevated CO 2 concentration (Saxe et al 1998;Medlyn et al 1999;Reich et al 2006;Sefcik et al 2007).…”

Effect of nitrogen availability on forest understorey cover and its consequences for tree regeneration in the Austrian limestone Alps

“…N-availability may directly affect various performance measures of seedlings. Nitrogen was found to decrease recruitment rates of trees in early successional plant communities (Henry et al 2004), to affect the seedling survival of several tree species (Catovsky and Bazzaz 2000;Sefcik et al 2007), especially those of mid-successional trees (Catovsky and Bazzaz 2002), and it may also change tree seedling growth rates (Walters and Reich 2000;Falkengren-Grerup 1995;Emmett 1999;Leuschner 1999;De Vries et al 2006).…”