Strong photosynthetic acclimation and enhanced water-use efficiency in grassland functional groups persist over 21 years of CO2 enrichment, independent of nitrogen supply

Melissa Pastore, Tali D. Lee, Sarah E Hobbie, Peter B Reich

Research output: Contribution to journalArticle

Abstract

Uncertainty about long-term leaf-level responses to atmospheric CO2 rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO2 (eCO2) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long-lived perennials. Here, we report the effects of eCO2 on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free-Air CO2 Enrichment experiment, BioCON. Monocultures of species belonging to C3 grasses, C4 grasses, forbs, and legumes were exposed to two levels of CO2 and nitrogen supply in factorial combinations over 21 years. eCO2 increased photosynthesis by 12.9% on average in C3 species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO2 was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO2 was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C4 grasses the least as expected, but did not further diverge over time. Leaf-level water-use efficiency increased by 50% under eCO2 primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO2 in nitrogen-limited systems, and that significant and consistent declines in stomatal conductance and increases in water-use efficiency under eCO2 may allow plants to better withstand drought.

Original languageEnglish (US)
Pages (from-to)3031-3044
Number of pages14
JournalGlobal change biology
Volume25
Issue number9
DOIs
StatePublished - Jan 1 2019

Fingerprint

Photosynthesis
water use efficiency
acclimation
Functional groups
functional group
photosynthesis
Nitrogen
stomatal conductance
grassland
Water
nitrogen
grass
Drought
Water levels
monoculture
gas exchange
Nutrients
herb
Gases
drought

Keywords

  • BioCON
  • CO by N effects
  • elevated CO
  • functional groups
  • global change
  • grassland
  • photosynthesis
  • photosynthetic acclimation
  • stomatal conductance
  • water-use efficiency

Cite this

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title = "Strong photosynthetic acclimation and enhanced water-use efficiency in grassland functional groups persist over 21 years of CO2 enrichment, independent of nitrogen supply",
abstract = "Uncertainty about long-term leaf-level responses to atmospheric CO2 rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO2 (eCO2) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long-lived perennials. Here, we report the effects of eCO2 on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free-Air CO2 Enrichment experiment, BioCON. Monocultures of species belonging to C3 grasses, C4 grasses, forbs, and legumes were exposed to two levels of CO2 and nitrogen supply in factorial combinations over 21 years. eCO2 increased photosynthesis by 12.9{\%} on average in C3 species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO2 was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO2 was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C4 grasses the least as expected, but did not further diverge over time. Leaf-level water-use efficiency increased by 50{\%} under eCO2 primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO2 in nitrogen-limited systems, and that significant and consistent declines in stomatal conductance and increases in water-use efficiency under eCO2 may allow plants to better withstand drought.",
keywords = "BioCON, CO by N effects, elevated CO, functional groups, global change, grassland, photosynthesis, photosynthetic acclimation, stomatal conductance, water-use efficiency",
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T1 - Strong photosynthetic acclimation and enhanced water-use efficiency in grassland functional groups persist over 21 years of CO2 enrichment, independent of nitrogen supply

AU - Pastore, Melissa

AU - Lee, Tali D.

AU - Hobbie, Sarah E

AU - Reich, Peter B

PY - 2019/1/1

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N2 - Uncertainty about long-term leaf-level responses to atmospheric CO2 rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO2 (eCO2) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long-lived perennials. Here, we report the effects of eCO2 on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free-Air CO2 Enrichment experiment, BioCON. Monocultures of species belonging to C3 grasses, C4 grasses, forbs, and legumes were exposed to two levels of CO2 and nitrogen supply in factorial combinations over 21 years. eCO2 increased photosynthesis by 12.9% on average in C3 species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO2 was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO2 was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C4 grasses the least as expected, but did not further diverge over time. Leaf-level water-use efficiency increased by 50% under eCO2 primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO2 in nitrogen-limited systems, and that significant and consistent declines in stomatal conductance and increases in water-use efficiency under eCO2 may allow plants to better withstand drought.

AB - Uncertainty about long-term leaf-level responses to atmospheric CO2 rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO2 (eCO2) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long-lived perennials. Here, we report the effects of eCO2 on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free-Air CO2 Enrichment experiment, BioCON. Monocultures of species belonging to C3 grasses, C4 grasses, forbs, and legumes were exposed to two levels of CO2 and nitrogen supply in factorial combinations over 21 years. eCO2 increased photosynthesis by 12.9% on average in C3 species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO2 was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO2 was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C4 grasses the least as expected, but did not further diverge over time. Leaf-level water-use efficiency increased by 50% under eCO2 primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO2 in nitrogen-limited systems, and that significant and consistent declines in stomatal conductance and increases in water-use efficiency under eCO2 may allow plants to better withstand drought.

KW - BioCON

KW - CO by N effects

KW - elevated CO

KW - functional groups

KW - global change

KW - grassland

KW - photosynthesis

KW - photosynthetic acclimation

KW - stomatal conductance

KW - water-use efficiency

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U2 - 10.1111/gcb.14714

DO - 10.1111/gcb.14714

M3 - Article

VL - 25

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JO - Global Change Biology

JF - Global Change Biology

SN - 1354-1013

IS - 9

ER -