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. (28th November 2021)

• Record Type: Journal Article
• Authors: Maier, Chris A.; Johnsen, Kurt H.; Anderson, Pete H.; Palmroth, Sari; Kim, Dohyoung; McCarthy, Heather R.; Oren, Ram
• Is Part Of: Global change biology. Volume 28:Number 4(2022)
• Page Start: 1458
• Page End: 1476
• Publication Date: 2021-11-28
• Subjects: allometry -- biomass -- carbon -- coarse root -- elevated CO2 -- free‐air CO2 enrichment -- net primary production -- Pinus taeda (loblolly pine); Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15999
• Languages: English
• ISSNs: 1354-1013

Abstract

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. Abstract : Coarse roots account for 20%–30% of carbon stored in ecosystem biomass. At the Duke free‐air carbon enrichment study, 17 years of elevated CO2 enrichment and 6 years of nitrogen amendments increased total coarse root biomass by 48%, differentially altered pine and broadleaved root allometry, root distribution with depth and root:shoot ratio. Averaged over the study (1997–2010), eCO2 increased pine, broadleaved and total coarse root net primary productivity (NPP) by 49%, 373% and 86% respectively. A sustained increase in root NPP under eCO2 over the study period indicated that soil nutrients were sufficient to maintain root growth response to eCO2 .