Progressive Nitrogen Limitation of Ecosystem Responses to Rising Atmospheric Carbon Dioxide

Abstract

A highly controversial issue in global biogeochemistry is the regulation of terrestrial carbon (C) sequestration by soil nitrogen (N) availability. This controversy translates into great uncertainty in predicting future global terrestrial C sequestration. We propose a new framework that centers on the concept of progressive N limitation (PNL) for studying the interactions between C and N in terrestrial ecosystems. In PNL, available soil N becomes increasingly limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. Our analysis focuses on the role of PNL in regulating ecosystem responses to rising atmospheric carbon dioxide concentration, but the concept applies to any perturbation that initially causes C and N to accumulate in organic forms. This article examines conditions under which PNL may or may not constrain net primary production and C sequestration in terrestrial ecosystems. While the PNL-centered framework has the potential to explain diverse experimental results and to help researchers integrate models and data, direct tests of the PNL hypothesis remain a great challenge to the research community.

Carbon and oxygen isotope analysis of leaf biomass reveals contrasting photosynthetic responses to elevated CO<sub>2</sub> near geologic vents in Yellowstone National Park

“…We hypothesize that decreased photosynthetic capacity observed in our case could be due to severe reduction in plant available nitrogen in this forest stand due to phenomenon known as progressive nitrogen limitation (PNL). PNL develops because elevated CO 2 leads to N immobilization by plants and microbes which deplete soils of N, causing slower rates of N mineralization progressively reducing the mineral N available for plant uptake in the long term (Gill et al, 2002;Zak et al, 2000;Luo et al, 2004).…”

Fungal Communities Respond to Long-Term CO 2 Elevation by Community Reassembly

“…Fungal communities are well known as decomposers in the ecosystem, by degrading organic matters into biologically available nutrients (26,68,69). Under eCO 2 , both aboveground and belowground plant biomass was stimulated (5-10), providing more organic matters for fungal communities as well as proposing higher demand for biologically available nitrogen (8,(70)(71)(72). Statistical testing suggested significant correlations between the changed network topology and increased soil ammonification rate and plant biomass.…”

“…Such responses were closely related with altered soil and plant properties, especially with increased plant biomass and NH 4 ϩ availability in soil, and thus were expected to sustain as long as the plant biomass is stimulated by eCO 2 . However, studies have shown that the microbial decomposition and plant biomass stimulation by eCO 2 were constrained by limited nitrogen availability in natural soil ecosystems (69,71,72). Therefore, the described responses of fungal community to eCO 2 may be subject to change when a new balance between microbial decomposition, plant biomass and nitrogen availability is reached.…”

Earth System Model Needs for Including the Interactive Representation of Nitrogen Deposition and Drought Effects on Forested Ecosystems

“…Many of the latest versions of ESMs now include N (and a rare few include phosphorus). However, because N is often a limiting nutrient in ecosystems, the focus is on plant response under limited N conditions and on the effects of the progressive N limitation [104] that is expected under elevated CO 2 . Although some models offer prescribed N, more sophisticated ones employ an N pool (bulk or speciated) that is available to both plants and decomposers.…”