Stem Carbon Dioxide Efflux of Lignophytes Exceeds That of Cycads and Arborescent Monocots

Thomas E Marler

doi:10.3390/agronomy12010159

Abstract

Tree stem CO2 efflux (Es) can be substantial and the factors controlling ecosystem-level Es are required to fully understand the carbon cycle and construct models that predict atmospheric CO2 dynamics. The majority of Es studies used woody lignophyte trees as the model species. Applying these lignophyte data to represent all tree forms can be inaccurate. The Es of 318 arborescent species was quantified in a common garden setting and the results were sorted into four stem growth forms: cycads, palms, monocot trees that were not palms, and woody lignophyte trees. The woody trees were comprised of gymnosperm and eudicot species. The Es did not differ among the cycads, palms, and non-palm monocots. Lignophyte trees exhibited Es that was 40% greater than that of the other stem growth forms. The Es of lignophyte gymnosperm trees was similar to that of lignophyte eudicot trees. This extensive species survey indicates that the Es from lignophyte tree species do not align with the Es from other tree growth forms. Use of Es estimates from the literature can be inaccurate for understanding the carbon cycle in tropical forests, which contain numerous non-lignophyte tree species.

Highlights

The efflux of carbon dioxide (CO2 ) from tree stem surfaces (Es) has been extensively studied to answer various questions and more fully understand the global carbon cycle [1,2].As with many aspects of biology research, the Es literature is biased toward one subset of biodiversity
The cycad trees were represented by 53 Cycadaceae and 46 Zamiaceae species (Table A1)
The stem circumference ranged from 51–169 cm with a mean of 96 cm

Summary

Introduction

The efflux of carbon dioxide (CO2 ) from tree stem surfaces (Es) has been extensively studied to answer various questions and more fully understand the global carbon cycle [1,2].As with many aspects of biology research, the Es literature is biased toward one subset of biodiversity. Most case studies of tree Es have focused exclusively on lignophyte species with stems comprised mostly of wood constructed by true bifacial secondary cambium. This expansive literature contains only a few examples in which pachycaulous tree species with stems devoid of bifacial secondary cambium were represented [3,4,5,6]. CO2 from root respiration can be transported to stems by way of xylem, and this CO2 can exit xylem within stems to increase the Es above that of stem tissue respiration [7,8]. The movement of CO2 from the internal tissues to stem surfaces can be under the control of temporal storage or re-fixation [11]

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Results