Altered plant carbon partitioning enhanced forest ecosystem carbon storage after 25 years of nitrogen additions

Abstract

Summary Decades of atmospheric nitrogen (N) deposition in the northeastern USA have enhanced this globally important forest carbon (C) sink by relieving N limitation. While many N fertilization experiments found increased forest C storage, the mechanisms driving this response at the ecosystem scale remain uncertain. Following the optimal allocation theory, augmented N availability may reduce belowground C investment by trees to roots and soil symbionts. To test this prediction and its implications on soil biogeochemistry, we constructed C and N budgets for a long‐term, whole‐watershed N fertilization study at the Fernow Experimental Forest, WV, USA. Nitrogen fertilization increased C storage by shifting C partitioning away from belowground components and towards aboveground woody biomass production. Fertilization also reduced the C cost of N acquisition, allowing for greater C sequestration in vegetation. Despite equal fine litter inputs, the C and N stocks and C : N ratio of the upper mineral soil were greater in the fertilized watershed, likely due to reduced decomposition of plant litter. By combining aboveground and belowground data at the watershed scale, this study demonstrates how plant C allocation responses to N additions may result in greater C storage in both vegetation and soil.

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

“…Although many, perhaps most, studies were multifaceted in their scope, for brevity only the main focus and findings are summarized. All told, these studies comprise a sample period that extends from three years [39] to 30 years of treatment [12]. Table 1.…”

“…There was, however, a high degree of interspecific variability in such a response. Despite slower tree growth, excess N has led to greater storage of C in soil and vegetation [12]. Finally, there has been a pronounced shift in herb layer composition that arose from increases in a nitrophilic species, blackberry (Rubus allegheniensis Porter) (hereafter, Rubus) [55], that competitively eliminated numerous N-efficient herbaceous species, resulting in a loss of plant diversity [11].…”

“…Bobbink et al [3] predicted similar increases in N deposition by 2030. Although most terrestrial ecosystems studied were initially herb-and grass-dominated [4,5], recent decades have witnessed an expansion of studies in forest ecosystems [6][7][8][9][10][11][12][13]. Seminal papers on then-new perspectives of N biogeochemistry, e.g., [14][15][16], changed our views of N in forest ecosystems from a predominantly growth-limiting nutrient to one whose excess could threaten the structure and function of forests, including net primary productivity and biodiversity, a phenomenon called N saturation [17].…”

Decoupling of Carbon and Nitrogen Under Elevated CO2 in a Typical Alpine Ecosystem

“…According to the optimal allocation theory, plants would allocate more biomass towards organism acquiring the most limiting resources (McCarthy and Enquist 2007). For this study, enhanced N availability from N deposition reduced the plant dependence on root systems for absorbing nutrients and subsequently lowered belowground C investments to roots (Eastman et al 2021), allowing plants to invest more C towards acquiring other limiting resources. This altered biomass allocation strategy suggests that plant biomass allocation patterns under global changes are closely linked with resource availability.…”

Soil pH drives poplar rhizosphere soil microbial community responses to ozone pollution and nitrogen addition

“…While elevated O 3 levels and reactive nitrogen (N) deposition often co‐occurs (Feng, Shang, Li, et al, 2019; Zeng et al, 2019), there have been very few studies exploring the potential interactive effects of these two variables on rhizosphere microbial communities. N fertilisation can profoundly alter plant growth, physiology, and productivity, all of which may shape the associated soil microbial community (Eastman et al, 2021; Zhang et al, 2018). Prior studies of O 3 × N interactions have primarily focused on aboveground effects and have yielded contradictory results, with some authors having reported that N addition can reverse the negative impact of O 3 exposure (Handley & Grulke, 2008; Mills et al, 2016), whereas others observed the opposite effect (Azuchi et al, 2014; Brewster et al, 2018) or detected no relationship between these variables (Feng, Shang, Li, et al, 2019; Harmens et al, 2017; Li et al, 2020).…”