Impacts of elevated nitrogen inputs on oak reproductive and seed ecology

Abstract

The effects of increased anthropogenic inputs of reactive nitrogen (N) have been studied at the Harvard Forest Chronic N Experiment, where NH 4 NO 3 has been applied experimentally since 1988 to increase atmospheric deposition rates $ 6-and $ 18-fold above ambient. This paper asks whether conditions favorable to primary production also resulted in plastic increases to flower, fruit, and seedling traits, and focuses primarily on the oaks that dominate the hardwood stands of the Harvard Forest experiment. Litterfall samples collected between 1996 and 2001 revealed that flowers and fruits were significantly more abundant in N-treated plots, and an analysis of oak tree abundance found significant variation both among and within plots. Acorn samples collected during 2003 and 2004 (a mast and a postmast year) were therefore analyzed using ANCOVA models that included an estimate of oak tree abundance. This tree abundance estimate was the only significant driver of increased acorn production during the mast year, and in both years it was a significant factor on plots receiving the highest levels of N. In the postmast year, acorn production was increased in direct response to N-related factors other than tree abundance. Our comparisons of control and N-treated plots for acorn quality traits (e.g. rates of acorn damage, germination percentage, seedling growth) revealed negligible or only transient differences. Shifts in overall acorn abundance -particularly disproportionate N-mediated increases during nonmast years -could have a wide range of ecological consequences beyond the more frequently examined impacts of N deposition on primary production and carbon sequestration.

Effects of nitrogen deposition on reproduction in a masting tree: benefits of higher seed production are trumped by negative biotic interactions

“…For example, N‐fertilization increases tree growth and seed production (Callahan et al . ; Smaill et al . ) and can benefit seed dispersal by indirectly affecting behaviour of animal dispersers (Yi et al .…”

“…Previous studies suggested that N‐fertilization enhances reproduction of large‐seeded, masting plants, such as oaks, by boosting their growth, seed production and seed size (Callahan et al . ; Smaill et al . ).…”

Composition and carbon dynamics of forests in northeastern North America in a future, warmer worldThis article is one of a selection of papers from NE Forests 2100: A Synthesis of Climate Change Impacts on Forests of the Northeastern US and Eastern Canada.

“…Other studies have found that seeds from parental plants reared in elevated CO 2 may have higher C:N ratios and develop into smaller, slower-growing seedlings (Huxman et al 1998;Ward et al 2000). Reproductive impacts of increased N deposition are equivocal: plant fecundity may increase or remain unchanged as a result of increased N availability (Gordon et al 1999;Callahan et al 2008). Bergweiler and Manning (1999) found that, even when O 3 levels caused only nominal damage in vegetative tissue, flower production and reproductive success were significantly reduced.…”

Comparative analysis of the influence of climate change and nitrogen deposition on carbon sequestration in forest ecosystems in European Russia: simulation modelling approach

“…Authors usually mention two possible sources of positive influence: (1) increased carbon dioxide concentration and temperature (Boisvenue and Running, 2006;Cole et al, 2010;Coops and Waring, 2001;Ellsworth et al, 2012;Moore et al, 2006) and (2) increased input of nitrogen compounds with precipitation (Callahan et al, 2008;Högberg, 2012;Vetter et al, 2005). Some authors showed that warming may stimulate decomposition of soil organic matter (Kirschbaum, 1994;Lloyd and Taylor, 1994;.…”