Response of Temperate Forest Ecosystems under Decreased Nitrogen Deposition: Research Challenges and Opportunities

Abstract

Although past increases in emissions and atmospheric deposition of reactive nitrogen (Nr) provided the impetus for extensive research investigating the effects of excess N in terrestrial and aquatic ecosystems, the Clean Air Act and associated rules have led to decreases in emissions and deposition of oxidized N, especially in the eastern U.S., but also in other regions of the world. Thus, research in the near future must address the mechanisms and processes of recovery for impacted forests as they experience chronically less N in atmospheric depositions. Recently, a hysteretic model was proposed to predict this recovery. By definition, hysteresis is any phenomenon in which the state of a property depends on its history and lags behind changes in the effect causing it. Long-term whole-watershed additions of N at the Fernow Experimental Forest allow for tests of the ascending limb of the hysteretic model and provide an opportunity to assess the projected changes following cessation of these additions. A review of 10 studies published in the peer-reviewed literature indicate there was a lag time of 3–6 years before responses to N treatments became apparent. Consistent with the model, I predict significant lag times for recovery of this temperate hardwood ecosystem following decreases in N deposition.

The Nitrogen Cycle of a Cool-Temperate Deciduous Broad-Leaved Forest

“…Similar studies related to the N cycle have been conducted, mainly in coniferous forest ecosystems, since the 1970s [7][8][9][10][11]. In addition, the N biogeochemical research has been ongoing for 30 years at another North American temperate forest site (Fernow Experimental Forest) [12][13][14][15][16][17][18][19][20][21]. They have reported that soil N pools comprise a major proportion of the total N pools.…”

Nitrogen and Boron Dosage Effects on Arginine Accumulation in Scots Pine Needles

“…Environmental regulations worldwide have exhibited a high degree of efficacy with respect to decreasing emissions of pollutants, including and especially N compounds. As a result, atmospheric deposition of N has declined over the past few decades on the global scale [8,24,40,[55][56][57][58][59].…”

“…Excessive competition between trees for nutrients, light, and water is prevented by precommercial cuts (thinning) with retention of a sufficient number of trees to secure high productivity of the site [8], while the supply of nutrients to trees is optimized by fertilization [9][10][11]. Alongside many other factors, the effect of fertilization on tree species depends on the content of nutrients in soil and on fertilizer form and dosage [6,8,[12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Gains in soil C storage under anthropogenic N deposition are rapidly lost following its cessation

“…Conceptual models hypothesize that ecosystem response to reduced N deposition will exhibit a hysteretic model of recovery, in which the time from when atmospheric N deposition is reduced and ecosystem-level changes are detectable (i.e., lag-time) will be different for different ecosystem pools and fluxes 23,24 . Here, we assess the initial recovery of the terrestrial C sink that was supported under high rates of anthropogenic N deposition.…”