skip to main content

Title: C 3 plant carbon isotope discrimination does not respond to CO 2 concentration on decadal to centennial timescales

Plant carbon isotope discrimination is complex, and could be driven by climate, evolution and/or edaphic factors. We tested the climate drivers of carbon isotope discrimination in modern and historical plant chemistry, and focus in particular on the relationship between rising [CO2] over Industrialization and carbon isotope discrimination.

We generated temporal records of plant carbon isotopes from museum specimens collected over a climo‐sequence to test plant responses to climate and atmospheric change over the past 200 yr (includingPinus strobus,Platycladus orientalis,Populus tremuloides,Thuja koraiensis,Thuja occidentalis,Thuja plicata,Thuja standishiiandThuja sutchuenensis). We aggregated our results with a meta‐analysis of a wide range of C3plants to make a comprehensive study of the distribution of carbon isotope discrimination and values among different plant types.

We show that climate variables (e.g. mean annual precipitation, temperature and, key to this study, CO2in the atmosphere) do not drive carbon isotope discrimination.

Plant isotope discrimination is intrinsic to each taxon, and could link phylogenetic relationships and adaptation to climate quantitatively and over ecological to geological time scales.

more » « less
Award ID(s):
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Date Published:
Journal Name:
New Phytologist
Page Range / eLocation ID:
p. 2576-2585
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Summary

    Increasing atmospheric CO2is changing the dynamics of tropical savanna vegetation. C3trees and grasses are known to experience CO2fertilization, whereas responses to CO2by C4grasses are more ambiguous.

    Here, we sample stable carbon isotope trends in herbarium collections of South African C4and C3grasses to reconstruct13C discrimination.

    We found that C3grasses showed no trends in13C discrimination over the past century but that C4grasses increased their13C discrimination through time, especially since 1950. These changes were most strongly linked to changes in atmospheric CO2rather than to trends in rainfall climatology or temperature.

    Combined with previously published evidence that grass biomass has increased in C4‐dominated savannas, these trends suggest that increasing water‐use efficiency due to CO2fertilization may be changing C4plant–water relations. CO2fertilization of C4grasses may thus be a neglected pathway for anthropogenic global change in tropical savanna ecosystems.

    more » « less
  2. Summary

    Mesophyll conductance (gm) is the diffusion ofCO2from intercellular air spaces (IAS) to the first site of carboxylation in the mesophyll cells. In C3species,gmis influenced by diverse leaf structural and anatomical traits; however, little is known about traits affectinggmin C4species.

    To address this knowledge gap, we used online oxygen isotope discrimination measurements to estimategmand microscopy techniques to measure leaf structural and anatomical traits potentially related togmin 18 C4grasses.

    In this study,gmscaled positively with photosynthesis and intrinsic water‐use efficiency (TEi), but not with stomatal conductance. Also,gmwas not determined by a single trait but was positively correlated with adaxial stomatal densities (SDada), stomatal ratio (SR), mesophyll surface area exposed toIAS(Smes) and leaf thickness. However,gmwas not related to abaxial stomatal densities (SDaba) and mesophyll cell wall thickness (TCW).

    Our study suggests that greaterSDadaandSRincreasedgmby increasingSmesand creating additional parallel pathways forCO2diffusion inside mesophyll cells. Thus,SDada,SRandSmesare important determinants of C4gmand could be the target traits selected or modified for achieving greatergmandTEiin C4species.

    more » « less
  3. Summary

    Mosses hold a unique position in plant evolution and are crucial for protecting natural, long‐term carbon storage systems such as permafrost and bogs. Due to small stature, mosses grow close to the soil surface and are exposed to high levels of CO2, produced by soil respiration. However, the impact of elevated CO2(eCO2) levels on mosses remains underexplored.

    We determined the growth responses of the mossPhyscomitrium patensto eCO2in combination with different nitrogen levels and characterized the underlying physiological and metabolic changes.

    Three distinct growth characteristics, an early transition to caulonema, the development of longer, highly pigmented rhizoids, and increased biomass, define the phenotypic responses ofP. patensto eCO2. Elevated CO2impacts growth by enhancing the level of a sugar signaling metabolite, T6P. The quantity and form of nitrogen source influences these metabolic and phenotypic changes. Under eCO2,P. patensexhibits a diffused growth pattern in the presence of nitrate, but ammonium supplementation results in dense growth with tall gametophores, demonstrating high phenotypic plasticity under different environments.

    These results provide a framework for comparing the eCO2responses ofP. patenswith other plant groups and provide crucial insights into moss growth that may benefit climate change models.

    more » « less
  4. Abstract Highlights

    A laboratory incubation study was conducted with nitrogen, phosphorus or carbon addition to tropical forest soils. Soil CO2emission was fitted with a Gompertz model and soil microbial abundance was quantified using qPCR. Phosphorus addition increased model parametersCmand soil CO2emission, particularly in the Puerto Rico soils. Soil CO2emission was more limited by phosphorus than nitrogen in tropical forest soils.

    more » « less
  5. Summary

    Plant responses to abiotic environmental challenges are known to have lasting effects on the plant beyond the initial stress exposure. Some of these lasting effects are transgenerational, affecting the next generation. The plant response to elevated carbon dioxide (CO2) levels has been well studied. However, these investigations are typically limited to plants grown for a single generation in a high CO2environment while transgenerational studies are rare.

    We aimed to determine transgenerational growth responses in plants after exposure to high CO2by investigating the direct progeny when returned to baseline CO2levels.

    We found that both the flowering plantArabidopsis thalianaand seedless nonvascular plantPhyscomitrium patenscontinue to display accelerated growth rates in the progeny of plants exposed to high CO2. We used the model species Arabidopsis to dissect the molecular mechanism and found that DNA methylation pathways are necessary for heritability of this growth response.

    More specifically, the pathway of RNA‐directed DNA methylation is required to initiate methylation and the proteins CMT2 and CMT3 are needed for the transgenerational propagation of this DNA methylation to the progeny plants. Together, these two DNA methylation pathways establish and then maintain a cellular memory to high CO2exposure.

    more » « less