Diurnal depression in leaf hydraulic conductance at ambient and elevated [CO2] reveals anisohydric water management in field-grown soybean and possible involvement of aquaporins

Anna M. Locke, Donald Richard Ort

Research output: Contribution to journalArticle

Abstract

•We measured diurnal leaf hydraulic conductance (Kleaf) and related factors.•Kleaf declines at midday in field-grown soybean despite open stomata.•The decline in Kleaf reflects similar decreases in leaf water potential.•Transcription of some aquaporin genes changes over the course of the day, which likely impacts Kleaf. Diurnal cycles of photosynthesis and water use in field-grown soybean (Glycine max) are tied to light intensity and vapor pressure deficit (VPD). At high mid-day VPD, transpiration rates can lead to a decline in leaf water potential (Ψleaf) if leaf hydraulic conductance (Kleaf) is insufficient to supply water to intercellular airspaces in pace with demand. Kleaf is determined by leaf xylem conductivity to water, as well as extra-xylem pathways that are likely mediated by aquaporin water transport proteins. When transpiration demand exceeds the maximum capacity of Kleaf to supply water, high tension in the water column can cause cavitation in xylem, and these emboli-blocked xylem vessels reduce water transport and thus lower Kleaf. Stomatal conductance typically remains high at mid-day for soybean, suggesting either a mid-day increase in Kleaf or that photosynthesis may be maintained at the cost of leaf water status, indicative of an anisohydric water management strategy in soybean. This study examined diurnal fluctuations in Kleaf and Ψleaf, showing a mid-day depression in Kleaf in a pattern closely reflecting that of Ψleaf, indicating that Kleaf depression is the result of cavitation in leaf xylem. The diurnal depression of Kleaf was not prevented by growth at elevated [CO2], which lowered stomatal conductance. Diurnal transcription patterns of aquaporin genes showed that a total of 34 genes belonging to 4 aquaporin families were expressed in soybean leaves, of which 22 were differentially expressed between at least two time points. These data suggest that mid-day Kleaf depression was driven primarily by cavitation at increasing xylem water tensions, but that aquaporins are also likely involved in diurnal regulation of soybean leaf water status. It is further concluded that because soybean photosynthesis is typically sustained at mid-day, Kleaf even at the depressed level was in excess of that needed to sustain a stomatal conductance sufficient to prevent depression of photosynthesis in soybean.

Original languageEnglish (US)
Pages (from-to)39-46
Number of pages8
JournalEnvironmental and Experimental Botany
Volume116
DOIs
StatePublished - Aug 1 2015

Fingerprint

aquaporins
water management
soybean
fluid mechanics
soybeans
hydraulics
xylem
leaves
water
photosynthesis
cavitation
stomatal conductance
vapor pressure
leaf water potential
water supply
transpiration
transcription (genetics)
gene
genes
embolism

Keywords

  • Cavitation
  • Diurnal
  • Leaf hydraulic conductance
  • Leaf water potential

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Agronomy and Crop Science
  • Plant Science

Cite this

@article{28e66b0ee7fb4537a0a15149eaef9651,
title = "Diurnal depression in leaf hydraulic conductance at ambient and elevated [CO2] reveals anisohydric water management in field-grown soybean and possible involvement of aquaporins",
abstract = "•We measured diurnal leaf hydraulic conductance (Kleaf) and related factors.•Kleaf declines at midday in field-grown soybean despite open stomata.•The decline in Kleaf reflects similar decreases in leaf water potential.•Transcription of some aquaporin genes changes over the course of the day, which likely impacts Kleaf. Diurnal cycles of photosynthesis and water use in field-grown soybean (Glycine max) are tied to light intensity and vapor pressure deficit (VPD). At high mid-day VPD, transpiration rates can lead to a decline in leaf water potential (Ψleaf) if leaf hydraulic conductance (Kleaf) is insufficient to supply water to intercellular airspaces in pace with demand. Kleaf is determined by leaf xylem conductivity to water, as well as extra-xylem pathways that are likely mediated by aquaporin water transport proteins. When transpiration demand exceeds the maximum capacity of Kleaf to supply water, high tension in the water column can cause cavitation in xylem, and these emboli-blocked xylem vessels reduce water transport and thus lower Kleaf. Stomatal conductance typically remains high at mid-day for soybean, suggesting either a mid-day increase in Kleaf or that photosynthesis may be maintained at the cost of leaf water status, indicative of an anisohydric water management strategy in soybean. This study examined diurnal fluctuations in Kleaf and Ψleaf, showing a mid-day depression in Kleaf in a pattern closely reflecting that of Ψleaf, indicating that Kleaf depression is the result of cavitation in leaf xylem. The diurnal depression of Kleaf was not prevented by growth at elevated [CO2], which lowered stomatal conductance. Diurnal transcription patterns of aquaporin genes showed that a total of 34 genes belonging to 4 aquaporin families were expressed in soybean leaves, of which 22 were differentially expressed between at least two time points. These data suggest that mid-day Kleaf depression was driven primarily by cavitation at increasing xylem water tensions, but that aquaporins are also likely involved in diurnal regulation of soybean leaf water status. It is further concluded that because soybean photosynthesis is typically sustained at mid-day, Kleaf even at the depressed level was in excess of that needed to sustain a stomatal conductance sufficient to prevent depression of photosynthesis in soybean.",
keywords = "Cavitation, Diurnal, Leaf hydraulic conductance, Leaf water potential",
author = "Locke, {Anna M.} and Ort, {Donald Richard}",
year = "2015",
month = "8",
day = "1",
doi = "10.1016/j.envexpbot.2015.03.006",
language = "English (US)",
volume = "116",
pages = "39--46",
journal = "Environmental and Experimental Botany",
issn = "0098-8472",
publisher = "Elsevier",

}

TY - JOUR

T1 - Diurnal depression in leaf hydraulic conductance at ambient and elevated [CO2] reveals anisohydric water management in field-grown soybean and possible involvement of aquaporins

AU - Locke, Anna M.

AU - Ort, Donald Richard

PY - 2015/8/1

Y1 - 2015/8/1

N2 - •We measured diurnal leaf hydraulic conductance (Kleaf) and related factors.•Kleaf declines at midday in field-grown soybean despite open stomata.•The decline in Kleaf reflects similar decreases in leaf water potential.•Transcription of some aquaporin genes changes over the course of the day, which likely impacts Kleaf. Diurnal cycles of photosynthesis and water use in field-grown soybean (Glycine max) are tied to light intensity and vapor pressure deficit (VPD). At high mid-day VPD, transpiration rates can lead to a decline in leaf water potential (Ψleaf) if leaf hydraulic conductance (Kleaf) is insufficient to supply water to intercellular airspaces in pace with demand. Kleaf is determined by leaf xylem conductivity to water, as well as extra-xylem pathways that are likely mediated by aquaporin water transport proteins. When transpiration demand exceeds the maximum capacity of Kleaf to supply water, high tension in the water column can cause cavitation in xylem, and these emboli-blocked xylem vessels reduce water transport and thus lower Kleaf. Stomatal conductance typically remains high at mid-day for soybean, suggesting either a mid-day increase in Kleaf or that photosynthesis may be maintained at the cost of leaf water status, indicative of an anisohydric water management strategy in soybean. This study examined diurnal fluctuations in Kleaf and Ψleaf, showing a mid-day depression in Kleaf in a pattern closely reflecting that of Ψleaf, indicating that Kleaf depression is the result of cavitation in leaf xylem. The diurnal depression of Kleaf was not prevented by growth at elevated [CO2], which lowered stomatal conductance. Diurnal transcription patterns of aquaporin genes showed that a total of 34 genes belonging to 4 aquaporin families were expressed in soybean leaves, of which 22 were differentially expressed between at least two time points. These data suggest that mid-day Kleaf depression was driven primarily by cavitation at increasing xylem water tensions, but that aquaporins are also likely involved in diurnal regulation of soybean leaf water status. It is further concluded that because soybean photosynthesis is typically sustained at mid-day, Kleaf even at the depressed level was in excess of that needed to sustain a stomatal conductance sufficient to prevent depression of photosynthesis in soybean.

AB - •We measured diurnal leaf hydraulic conductance (Kleaf) and related factors.•Kleaf declines at midday in field-grown soybean despite open stomata.•The decline in Kleaf reflects similar decreases in leaf water potential.•Transcription of some aquaporin genes changes over the course of the day, which likely impacts Kleaf. Diurnal cycles of photosynthesis and water use in field-grown soybean (Glycine max) are tied to light intensity and vapor pressure deficit (VPD). At high mid-day VPD, transpiration rates can lead to a decline in leaf water potential (Ψleaf) if leaf hydraulic conductance (Kleaf) is insufficient to supply water to intercellular airspaces in pace with demand. Kleaf is determined by leaf xylem conductivity to water, as well as extra-xylem pathways that are likely mediated by aquaporin water transport proteins. When transpiration demand exceeds the maximum capacity of Kleaf to supply water, high tension in the water column can cause cavitation in xylem, and these emboli-blocked xylem vessels reduce water transport and thus lower Kleaf. Stomatal conductance typically remains high at mid-day for soybean, suggesting either a mid-day increase in Kleaf or that photosynthesis may be maintained at the cost of leaf water status, indicative of an anisohydric water management strategy in soybean. This study examined diurnal fluctuations in Kleaf and Ψleaf, showing a mid-day depression in Kleaf in a pattern closely reflecting that of Ψleaf, indicating that Kleaf depression is the result of cavitation in leaf xylem. The diurnal depression of Kleaf was not prevented by growth at elevated [CO2], which lowered stomatal conductance. Diurnal transcription patterns of aquaporin genes showed that a total of 34 genes belonging to 4 aquaporin families were expressed in soybean leaves, of which 22 were differentially expressed between at least two time points. These data suggest that mid-day Kleaf depression was driven primarily by cavitation at increasing xylem water tensions, but that aquaporins are also likely involved in diurnal regulation of soybean leaf water status. It is further concluded that because soybean photosynthesis is typically sustained at mid-day, Kleaf even at the depressed level was in excess of that needed to sustain a stomatal conductance sufficient to prevent depression of photosynthesis in soybean.

KW - Cavitation

KW - Diurnal

KW - Leaf hydraulic conductance

KW - Leaf water potential

UR - http://www.scopus.com/inward/record.url?scp=84925943751&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84925943751&partnerID=8YFLogxK

U2 - 10.1016/j.envexpbot.2015.03.006

DO - 10.1016/j.envexpbot.2015.03.006

M3 - Article

AN - SCOPUS:84925943751

VL - 116

SP - 39

EP - 46

JO - Environmental and Experimental Botany

JF - Environmental and Experimental Botany

SN - 0098-8472

ER -