The response of coarse root biomass to long-term CO2 enrichment and nitrogen application in a maturing Pinus taeda stand with a large broadleaved component

Chris A Maier; Kurt H Johnsen; Pete H Anderson; Sari Palmroth; Dohyoung Kim; Heather R McCarthy; Ram Oren

doi:10.1111/gcb.15999

The response of coarse root biomass to long-term CO₂ enrichment and nitrogen application in a maturing Pinus taeda stand with a large broadleaved component

Glob Chang Biol. 2022 Feb;28(4):1458-1476. doi: 10.1111/gcb.15999. Epub 2021 Nov 28.

Authors

Chris A Maier¹, Kurt H Johnsen², Pete H Anderson¹, Sari Palmroth³, Dohyoung Kim⁴, Heather R McCarthy⁵, Ram Oren^{6

7}

Affiliations

¹ USDA Forest Service, Southern Research Station, Research Triangle Park, North Carolina, USA.
² USDA Forest Service, Southern Research Station, Asheville, North Carolina, USA.
³ Nicholas School of the Environment, Duke University, Durham, North Carolina, USA.
⁴ Department of Biological Sciences & Environmental Change Initiative, University of Notre Dame, Notre Dame, Indiana, USA.
⁵ Department of Microbiology and Plant Biology, University of Oklahoma, Norman, Oklahoma, USA.
⁶ Nicholas School of the Environment & Pratt School of Engineering, Duke University, Durham, North Carolina, USA.
⁷ Department of Forest Science, University of Helsinki, Helsinki, Finland.

PMID: 34783402
DOI: 10.1111/gcb.15999

Abstract

Elevated atmospheric CO₂ (eCO₂ ) typically increases aboveground growth in both growth chamber and free-air carbon enrichment (FACE) studies. Here we report on the impacts of eCO₂ and nitrogen amendment on coarse root biomass and net primary productivity (NPP) at the Duke FACE study, where half of the eight plots in a 30-year-old loblolly pine (Pinus taeda, L.) plantation, including competing naturally regenerated broadleaved species, were subjected to eCO₂ (ambient, aCO₂ plus 200 ppm) for 15-17 years, combined with annual nitrogen amendments (11.2 g N m^-2 ) for 6 years. Allometric equations were developed following harvest to estimate coarse root (>2 mm diameter) biomass. Pine root biomass under eCO₂ increased 32%, 1.80 kg m^-2 above the 5.66 kg m^-2 observed in aCO₂ , largely accumulating in the top 30 cm of soil. In contrast, eCO₂ increased broadleaved root biomass more than twofold (aCO₂ : 0.81, eCO₂ : 2.07 kg m^-2 ), primarily accumulating in the 30-60 cm soil depth. Combined, pine and broadleaved root biomass increased 3.08 kg m^-2 over aCO₂ of 6.46 kg m^-2 , a 48% increase. Elevated CO₂ did not increase pine root:shoot ratio (average 0.24) but increased the ratio from 0.57 to 1.12 in broadleaved species. Averaged over the study (1997-2010), eCO₂ increased pine, broadleaved and total coarse root NPP by 49%, 373% and 86% respectively. Nitrogen amendment had smaller effects on any component, singly or interacting with eCO₂ . A sustained increase in root NPP under eCO₂ over the study period indicates that soil nutrients were sufficient to maintain root growth response to eCO₂ . These responses must be considered in computing coarse root carbon sequestration of the extensive southern pine and similar forests, and in modelling the responses of coarse root biomass of pine-broadleaved forests to CO₂ concentration over a range of soil N availability.

Keywords: Pinus taeda (loblolly pine); allometry; biomass; carbon; coarse root; elevated CO2; free-air CO2 enrichment; net primary production.

MeSH terms

Biomass
Carbon Dioxide
Nitrogen*
Pinus taeda*
Soil

Substances

Soil
Carbon Dioxide
Nitrogen