ArticlePDF AvailableLiterature Review

Nighttime Stomatal Conductance and Transpiration in C3 and C4 Plants

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Abstract and Figures

Incomplete stomatal closure during the night is observed in a diverse range of C3 and C4 species (Fig. 1; Supplemental Table S1) and can lead to substantial nighttime transpirational water loss. Although water loss is an inevitable consequence of stomatal opening for photosynthetic carbon gain, nighttime stomatal opening is unexpected because carbon gain is not occurring and the need to cool leaves is reduced or absent. Most species have the ability to close stomata more than is commonly observed at night, as demonstrated by reduced night-time leaf conductance (gnight) in response to water stress, abscisic acid (ABA), and other treatments reviewed in this Update. The magnitude of water loss occurring during the night depends on both gnight and the vapor pressure difference (VPD) between leaves and the air, as well as canopy structure and atmospheric mixing. While gnight has been recorded at up to 90% of daytime conductance, nighttime VPD is typically much lower than daytime. Thus, nighttime transpiration rates (Enight) are typically 5% to 15% of daytime rates, although sometimes as high as 30%, based on gas exchange measurements of individual leaves, whole-plant sap flow, and field scale lysimetry (Benyon, 1999; Snyder et al., 2003; Bucci et al., 2004, 2005; Daley and Phillips, 2006; Scholz et al., 2007). While some methods are more accurate and/or have less uncertainty than others, a few studies have compared methods, generally finding agreement even across measurement scales (e.g. leaf versus whole plant; Green et al., 1989). Drawbacks for each method must be recognized, particularly when comparing species or environments. For example, leaf-level gas exchange typically includes cuticular as well as stomatal components of leaf conductance to water vapor, while sap flow methods typically have attendant uncertainties as to the proportion of the measured flux resulting in bole refilling rather than transpiration from the canopy. Nevertheless, there is broad agreement among the methods and scales that stomata of many species remain partially open during the night. Measurements of minimum leaf conductance induced by ABA application and by drying excised leaves to wilting have been used to separate stomatal (gstomatal) and cuticular (gcuticular) conductance (Rawson and Clarke, 1988; Howard and Donovan, 2007). Conductance measured at maximal stomatal closure can be functionally defined as gcuticular because it is not under guard cell regulation. For a few species, this would include the effect of dust or stomatal plugs that prevent complete closure (Feild et al., 1998). In general, gcuticular estimates range from 0.004 to 0.020 molm-2 s-1 (Rawson and Clarke, 1988; Nobel, 1991; Kerstiens, 1995; Boyer et al., 1997; Burghardt and Riederer, 2003; Howard and Donovan, 2007), far lower than most estimates of gnight (Fig. 1; Supplemental Table S1). Thus, most reported values of gnight are largely influenced by gstomatal. Although awareness of gnight and Enight has recently been growing, little is understood about the phenomena. In particular, the costs and benefits of high gnight and Enight remain largely unknown. However, patterns of occurrence and relationships of these processes with plant physiology are emerging. This Update reviews the occurrence of gnight in C3 and C4 species, plant and environmental factors that affect gnight, and both documented and hypothesized implications of gnight and Enight (Fig. 2). SOURCES OF VARIATION AND FACTORS AFFECTING gnight Variation Among and Within Species Species in which gnight has been documented include a diverse range of genera and life forms (annuals and perennials; monocots, herbaceous dicots, shrubs, and trees; Fig. 1; Supplemental Table S1) native to a diversity of habitats: e.g. wetland (Loftfield, 1921), desert (Donovan et al., 2003; Snyder et al., 2003; Ludwig et al., 2006), neotropical savanna (Bucci et al., 2004, 2005; Domec et al., 2006; Scholz et al., 2007), temperate deciduous and evergreen forests (Benyon, 1999; Oren et al., 2001; Barbour et al., 2005; Daley and Phillips, 2006; Kavanagh et al., 2007), and subalpine forest (Herzog et al., 1998). Many horticultural and crop species have substantial gnight and/or Enight (England, 1963; Rosenberg, 1969; Rawson and Clarke, 1988; Green et al., 1989; Blom-Zandstra et al., 1995; Assaf and Zieslin, 1996; Musselman and Minnick, 2000). Although it has been suggested that sustained nocturnal stomatal opening is not a feature of grasses (Loftfield, 1921), substantial gnight has been observed in Distichlis spicata (C4; Snyder et al., 2003) and wheat (Triticum aestivum; C3; Rawson and Clarke, 1988), among others. Substantial variation in magnitude of maximum gnight has been observed among closely related species (Supplemental Table S1); however, differences among some species are minimal and not biologically significant (see Helianthus species, Supplemental Table S1; Howard and Donovan, 2007). Multiple surveys have shown that gnight varies substantially among species within a particular environment or habitat type (Snyder et al., 2003; Bucci et al., 2004; Daley and Phillips, 2006; Kavanagh et al., 2007), and the relationship of species differences to source environment or habitat remains unclear. Additional studies investigating gnight in a phylogenetic context in native and common garden locations will be required to determine whether species differences in gnight are adaptive. Many studies have also demonstrated genetic variation in magnitude of gnight among cultivars or accessions of single species (Supplemental Table S1). Arabidopsis (Arabidopsis thaliana) natural accessions had a 2.5-fold variation in magnitude of gnight when grown in a common environment, and the variation was correlated to mean annual VPD of the accessions native environment (M. Caird, unpublished data). Although correlative, this relationship suggests the potential for natural selection to have operated on gnight. In addition to genetic variation, there is also evidence for separate genetic control of gnight from gday. Three near-isogenic lines of Arabidopsis differed from their parental lines in either gnight or gday, but not both, providing evidence that these two traits can be regulated independently due to genetic factors alone (M. Caird, unpublished data). Future studies exploiting natural and mutant genotypes will likely play an important role in discovering the genetic factors that influence gnight in plants. Although recent studies of nighttime water loss generally do not consider differences in stomatal density or adaxial and abaxial surface responses, these factors may contribute to within and among species variation in gnight. Not only does stomatal density often differ between adaxial and abaxial leaf surfaces, but the stomata on these surfaces can respond differently to environmental cues such as light. Stomata on the abaxial leaf surface, but not the adaxial surface, remained open at night in cotton (Gossypium hirsutum; Sharpe, 1973) and fava bean (Vicia faba; Aben et al., 1989). Future studies need to considerhowthese factors may affect gnight and Enight, particularly with regard to between and within species variation in gnight. Diurnal Patterns for gstomatal For many species, gnight is not stable throughout the night period. Endogenous, gradual increases in stomatal opening during predawn hours have been reported in many species under natural field conditions as well as in controlled environments (Schwabe, 1952; Muchow et al., 1980; Anderson, 1982; Lasceve et al., 1997; Leymarie et al., 1998, 1999; Donovan et al., 2003; Bucci et al., 2004; Dodd et al., 2005; Howard and Donovan, 2007). In Arabidopsis accession Columbia, a mean minimum gnight of 0.117 mol m-2 s-1 slowly increased to a predawn mean of 0.161 mol m22 s21, amounting to a 38% increase in gstomatal during the night (Lasceve et al., 1997). Arabidopsis mutants with disrupted circadian rhythms do not have increased stomatal opening in predawn hours, indicating gnight has some component of circadian regulation (Dodd et al., 2004, 2005). Lasceve et al. (1997) also found starch deficient Arabidopsis mutants do not have the increased endogenous predawn opening observed in wild-type plants, implying that starch metabolism, possibly through the formation of an osmoticant necessary for guard cell osmoregulation, is an important factor affecting stomatal opening during predawn. Photoperiod length and light intensity can affect the speed and degree to which stomata close in the dark. Incomplete stomatal closure at night resulted from short-day as opposed to long-day photoperiods in Chrysanthemum (Schwabe, 1952). Higher light intensity during the day or longer supplementary lighting intervals (extending light period into the normal night) resulted in faster stomatal closure responses to lights turning off in roses, although closure was still incomplete (Blom-Zandstra et al., 1995). The spectrum of the low intensity supplementary light (25 mol m-2 s-1) also affected gnight, with orange and blue supplementary light preventing complete stomatal closure 2.5 h into the night, while white and no (control) supplementary light resulted in gnight comparable to previously determined gcuticular (0.01 mol m-2 s-1 ; Blom-Zandstra et al., 1995). This evidence, together with evidence of starch-deficient Arabidopsis mutants having decreased nighttime stomatal opening (Lasceve et al., 1997), suggests that daytime conditions and photosynthetic rates can influence gnight. Although the exact mechanism is unclear, it is possible that a byproduct of starch metabolism may affect guard cell osmoregulation at night (Lasceve et al., 1997), causing greater stomatal opening when starch levels are high. Positive correlations have been observed for gnight and gday among species in Great Basin habitats (Snyder et al., 2003). Although only correlative data are available, the relationship may be the result of daytime conditions that allow high photosynthetic rates but also result in high gnight. Alternatively, leaf development and stomatal anatomy that affect gday could be a cause for correlation with gnight. Responses to Atmospheric Water Demand Atmospheric conditions can be important in driving Enight when stomata are open, as evidenced by canopy scale measurements of crop water loss on weighing lysimeters (England, 1963; Rosenberg, 1969). Advection was found to create sufficient evaporative demand to cause 20% to 30% of total daily transpiration to occur at night in alfalfa (Medicago sativa) in the field (Abdel-Aziz et al., 1964) and kiwifruit (Actinidia deliciosa) in orchards (Green et al., 1989). Seginer (1984) extended this concept to show energy requirements and conditions in greenhouses under which Enight occurs in roses using a modified version of the Penman model. In natural systems, increased VPD has been correlated with greater Enight at the scale of sap flux for many tree species (Herzog et al., 1998; Benyon, 1999; Oren et al., 2001; Daley and Phillips, 2006; Kavanagh et al., 2007). A trend for lower gnight with increasing VPD has been observed in some species (Muchow et al., 1980; Oren et al., 2001; Bucci et al., 2004), yet some data indicate lack of any response (Barbour et al., 2005). However, correlative studies such as these do not control for possible variation due to inherent circadian regulated stomatal opening that might parallel decreasing VPD during the night. Nevertheless, similar correlations have been found when night-time VPD around plants is experimentally manipulated, providing more direct evidence that some species do close stomata in response to higher VPD during the night just as during the daytime (Bakker, 1991). A more thorough understanding of whether VPD regulates gnight in a manner parallel to that of gday will require more studies that manipulate VPD while controlling for other potentially confounding factors, including circadian rhythms. Responses to Water Availability and ABA It is expected that at night stomata will be sensitive to decreased water availability, just as during the daytime, to conserve water. Lower gnight has been associated with decreased plant water status in Hibiscus cannabinus (Muchow et al., 1980), Pseudostuga menziesii (Running, 1976; Blake and Ferrell, 1977), and Helianthus anomalus (Ludwig et al., 2006). In a field experiment, gnight of unirrigated desert shrubs was lower than that of shrubs receiving surface irrigation (Donovan et al., 2003). In greenhouse studies, gnight decreased in response to a water stress treatment in wheat (Rawson and Clarke, 1988) and in Helianthus species (Howard and Donovan, 2007). Similar to drought, increased salinity also reduced gnight in desert shrubs (Donovan et al., 1999). The magnitude of gnight can additionally vary seasonally. For Chrysothamnus nauseosus, gnight was reduced at the end of growing season when soils were dry, while the cooccurring Sarcobatus vermiculatus had higher gnight (relative to gday) by the end of the season (Donovan et al., 2003). The Sarcobatus response may be related to its capacity to accumulate high concentrations of leaf apoplastic solutes (James et al., 2006), which could in turn affect stomatal regulation. Seasonal changes in gnight were also found for Pinus ponderosa, with stomata more open during the night in early summer, like Chrysothamnus (Grulke et al., 2004). ABA can induce stomatal closure during the dark (Rawson and Clarke, 1988; Howard and Donovan, 2007). Similar to responses observed during the daytime, increased concentrations of exogenous ABA resulted in greater stomatal closure at night in Arabidopsis, and stomatal closure in response to ABA was more prominent at higher CO2 (Leymarie et al., 1998, 1999). In P. menziesii seedlings, nighttime leaf resistance was sensitive to the ABA content of leaves (Blake and Ferrell, 1977), indicating ABA induced stomatal closure in response to water stress atnight just as during the daytime. Nutrient Availability Typically, higher nutrient availability, particularly nitrogen (N), is correlated with higher daytime photosynthesis (Lambers et al., 1998). However, varying results have been found for correlations of nutrient supply and on gday (Meinzer et al., 1988; Toft et al., 1989). Similarly, species show different responses of gnight to limited nutrient supply. In two field studies with nutrient treatments, high nutrient plants had lower gnight, but the experimental designs do not allow unambiguous separation of direct effects due to reduced plant demand for nutrient acquisition regulating gnight from indirect effects of plant size or water status (Ludwig et al., 2006; Scholz et al., 2007). Other nutrient response experiments that controlled for plant water status have found differing effects of N-supply on gnight. For example, reduced gnight was observed in N-limited Arabidopsis, but higher gnight was found in N-limited D. spicata and Populus balsamifera subsp. trichocarpa (M. Caird and A. Howard, unpublished data). Still other species showed no gnight response to soil nutrient limitations (Helianthus species;Howard and Donovan, 2007). The relationship between varying gnight responses to nutrients and particular life forms or ecological strategies is unknown and may be related to the underlying causes of nutrient status effects on gday. IMPLICATIONS OF gnight AND Enight Air Pollution Uptake The occurrence of high gnight in many C3 and C4 plant species has important implications for air pollutant uptake (Goknur and Tibbitts, 1984; Segschneider et al., 1995; Musselman and Minnick, 2000; Takahashi et al., 2005). gstomatal is a major factor affecting ozone (O3) uptake in plants (Wieser and Havranek, 1993). Tree species in areas with high levels of O3 exposure can have stomata open at night (Wieser and Havranek, 1993; Matyssek et al., 1995), and nocturnal O3 uptake can be a significant proportion of daily O3 uptake (up to 9%; Grulke et al., 2004). Stomatal responsiveness may be reduced after exposure to O3 (Keller and Hasler, 1984; Skarby et al., 1987). Whole-plant production and carbon allocation in Betula pendula were also more sensitive to nighttime compared to daytime O3 exposure (Matyssek et al., 1995). Thus, O3 damage resulting from night-time uptake may be an important factor for plants. However, gnight may also prove to be useful in areas of high air pollution. For example, H. cannabinus maybe useful as a phytoremediator of NO2 because this species has high gnight and gday (Takahashi et al., 2005). Isotopic Signatures and Modeling Night-time stomatal opening may influence oxygen isotope signatures of within-canopy CO2 (Barbour et al., 2005). This has important implications for models describing ecosystem respiratory CO2 flux and its partitioning into above- and below-ground components. 18O enrichment of leaves will also be affected by gnight, complicating the use of such signatures in detecting genetic or environmental effects on transpiration rate. Variation in magnitude of gnight among species and the regulation and responses of gnight to environmental factors (i.e. VPD) are important considerations in determining how large an impact night-time stomatal opening will have on oxygen isotope signatures. More research on these topics is required and will need to be incorporated into models. Potential for Increased Daytime Carbon Gain Plants may be able to increase their photosynthetic carbon gain by preopening stomata before dawn. This might be especially advantageous in water-limited environments because of a higher potential for early morning carbon gain when temperatures and VPD are lower. Although stomatal responses to light are typically fast, there is some evidence to support the hypothesis that maintaining open stomata at night affects daytime opening. In Xanthium pennsylvanicum, the rate of stomatal opening in light was greater when stomata were open during the night (Mansfield and Heath, 1961). However, there is no evidence for an effect of experimentally lowering gnight on carbon gain or gday during the subsequent day. Additional research is necessary to directly test whether high gnight influences early morning and total daily carbon gain, and if so how much and by what mechanism. Effects on Water Relations Plant water potential is expected to equilibrate with the wettest soil layer in the rooting zone overnight. However, substantial Enight can prevent equilibration from occurring, resulting in soil-plant predawn water potential disequilibrium, or predawn disequilibrium (Donovan et al., 2001), which complicates interpretation of soil moisture availability based on plant water potential measurements. Enight has been observed to contribute to predawn disequilibrium in many species (Donovan et al., 1999, 2001, 2003; Sellin, 1999; Bucci et al., 2004, 2005; Kavanagh et al., 2007). Substantial Enight may additionally reduce a plant’s ability to conduct hydraulic redistribution (HR, also referred to as hydraulic lift; Richards and Caldwell, 1987). HR occurs when some roots are absorbing water from wet soil locations and other roots of the same plant are losing water to relatively dry soil locations. When stomata are open and the atmospheric conditions allow Enight to occur, the water loss through the shoot should decrease the amount released to drier soil layers because of impacts on plant water potentials. Plants in natural populations can simultaneously have both HR and high Enight, although these two processes may vary in magnitude through the growing season (Donovan et al., 2003; Domec et al., 2006). Nutrient Supply and Distribution Significant water loss without simultaneous photosynthetic carbon gain could constitute a major cost to a plant. However, it is possible that Enight may provide a benefit that outweighs this cost. Mobile mineral nutrients are moved into the immediate vicinity of plant roots (i.e. the rhizosphere) by transpiration-driven mass flow of the soil solution (Barber, 1995). Thus, the maintenance of a continuous water stream through the plant during both day and night could potentially result in enhanced nutrient availability to the plant. McDonald et al. (2002) showed that CO2-induced stomatal closure reduced transpiration and N acquisition by Populus deltoides. Using the Barber-Cushman model, the effect of increased water flux on nitrate uptake and nutrient concentration in the rooting zone can be predicted (Barber and Cushman, 1981). The general result is that increasing water flux eliminates or minimizes the depletion zone, which develops in the rhizosphere, by maintaining a supply of nitrate to the root (Barber and Cushman, 1981; Barber, 1995). However, under low nitrate or high root length density conditions, the effect is reduced and total nitrate uptake is not affected dramatically. We are experimentally testing this hypothesis. In addition to supply of nutrients to roots, the distribution of nutrients within plants, particularly phloem-immobile nutrients such as calcium, depends on the xylem flow rate and duration of transpiration (Marschner, 1995). An increase in the total amount of water flowing through the xylem may improve nutrition when organs are Ca deficient. Daley and Phillips (2006) also suggest that gnight may enhance nutrient transport within trees such as paper birch by providing oxygen to sapwood parenchyma cells that function in nutrient transport and storage. [what is the Noct-Transp is used by ray parenchyma cells to refill xylem vessels, requires O2 and glucose to power the cells driving the refilling?] Implications for Growth and Plant Fitness Implications for plant water and nutrient relations suggest that Enight may also impact plant productivity and growth, although experimental evidence on the subject is scarce. It is intuitive that Enight poses costs to plants under water-limiting conditions as evidenced by reduction in gnight in response to water stress. However, more research is necessary to determine what benefits, if any, may either balance or outweigh these costs. CONCLUSION Although research dating back to the late 1800’s describes stomata of many C3 and C4 plant species as incompletely closing during the night, very little is understood about this phenomenon. We have summarized a growing body of evidence showing that gnight is regulated, in many ways similar to daytime stomatal regulation, and that night-time stomatal opening and transpiration have implications for plant growth and physiology. Nevertheless, more research will be necessary to fully appreciate the significance of gnight and Enight. Future research on plant regulation of gnight and the consequences of substantial Enight for water and nutrient relations will be key for understanding the ecological and evolutionary consequences of gnight and Enight in C3 and C4 plants.
Content may be subject to copyright.
Update on Nighttime Stomatal Conductance in Plants
Nighttime Stomatal Conductance and Transpiration
in C
3
and C
4
Plants
1[W]
Mairgaret h A. Caird*, James H. Richards, and Lisa A. Donovan
Department of Land, Air, and Water Resources, University of California, Davis, California 95616 (M.A.C.,
J.H.R.); and Department of Plant Biology, University of Georgia, Athens, Georgia 30602 ( L.A.D.)
Incomplete stomatal closure during the night is
observed in a diverse range of C
3
and C
4
species
(Fig. 1; Supplemental Table S1) and can lead to sub-
stantial nighttime transpirational water loss. Although
water loss is an inevitable consequence of stomatal
opening for photosynthetic carbon gain, nighttime
stomatal opening is unexpected because carbon gain
is not occurring and the need to cool leaves is reduced
or absent. Most species have the ability to close sto-
mata more than is commonly observed at night, as
demonstrated by reduced nighttime leaf conduc-
tance (g
night
) in response to water stress, abscisic acid
(ABA), and other treatments reviewed in this Update.
The magnitude of water loss occurring during the
night depends on both g
night
and the vapor pressure
difference (VPD) between leaves and the air, as well as
canopy structure and atmospheric mixing. While g
night
has been recorded at up to 90% of daytime conduc-
tance, nighttime VPD is typically much lower than
daytime. Thus, nighttime transpiration rates (E
night
)
are typically 5% to 15% of daytime rates, although
sometimes as high as 30%, based on gas exchange
measurements of individual leaves, whole-plant sap
flow, and field scale lysimetry (Benyon, 1999; Snyder
et al., 2003; Bucci et al., 2004, 2005; Daley and Phillips,
2006; Scholz et al., 2007). While some methods are
more accurate and/or have less uncertainty than
others, a few studies have compared methods, gener-
ally finding agreement even across measurement
scales (e.g. leaf versus whole plant; Green et al.,
1989). Drawbacks for each method must be recog-
nized, particularly when comparing species or envi-
ronments. For example, leaf-level gas exchange typically
includes cuticular as well as stomatal components of
leaf conductance to water vapor, while sap flow
methods typically have attendant uncertainties as to
the proportion of the measured flux resulting in bole
refilling rather than transpiration from the canopy.
Nevertheless, there is broad agreement among the
methods and scales that stomata of many species re-
main partially open during the night.
Measurements of minimum leaf conductance in-
duced by ABA application and by drying excised
leaves to wilting have been used to separate stomatal
(g
stomatal
) and cuticular (g
cuticular
) conductance (Rawson
and Clarke, 1988; Howard and Donovan, 2007). Con-
ductance measured at maximal stomatal closure can
be functionally defined as g
cuticular
because it is not
under guard cell regulation. For a few species, this
would include the effect of dust or stomatal plugs that
prevent complete closure (Feild et al., 1998). In general,
g
cuticular
estimates range from 0.004 to 0.020 mol m
22
s
21
(Rawson and Clarke, 1988; Nobel, 1991; Kerstiens,
1995; Boyer et al., 1997; Burghardt and Riederer, 2003;
Howard and Donovan, 2007), far lower than most
estimates of g
night
(Fig. 1; Supplemental Table S1).
Thus, most reported values of g
night
are largely influ-
enced by g
stomatal
.
Although awareness of g
night
and E
night
has recently
been growing, little is understood about the phenom-
ena. In particular, the costs and benefits of high g
night
and E
night
remain largely unknown. However, patterns
of occurrence and relationships of these processes with
plant physiology are emerging. This Update reviews
the occurrence of g
night
in C
3
and C
4
species, plant and
environmental factors that affect g
night
, and both docu-
mented and hypothesized implications of g
night
and
E
night
(Fig. 2).
SOURCES OF VARIATION AND FACTORS
AFFECTING g
night
Variation Among and Within Species
Species in which g
night
has been documented include
a diverse range of genera and life forms (annuals and
perennials; monocots, herbaceous dicots, shrubs, and
trees; Fig. 1; Supplemental Table S1) native to a diver-
sity of habitats: e.g. wetland (Loftfield, 1921), desert
(Donovan et al., 2003; Snyder et al., 2003; Ludwig et al.,
2006), neotropical savanna (Bucci et al., 2004, 2005;
Domec et al., 2006; Scholz et al., 2007), temperate
deciduous and evergreen forests (Benyon, 1999; Oren
1
This work was supported by the National Science Foundation
(through a graduate research fellowship to M.A.C., and grant nos.
IBN–0416581 and DEB–0419969 [to J.H.R.], and IBN–0131078 and
IBN–0416627 [to L.A.D.]) and the California Agricultural Experi-
ment Station.
* Corresponding author; e-mail macaird@ucdavis.edu; fax 530–
752–1552.
The author responsible for distribution of materials integral to the
findings presented in this article in accordance with the policy
described in the Instructions for Authors (www.plantphysiol.org) is:
Mairgareth A. Caird (macaird@ucdavis.edu).
[W]
The online version of this article contains Web-only data.
www.plantphysiol.org/cgi/doi/10.1104/pp.106.092940
4 Plant Physiology, January 2007, Vol. 143, pp. 4–10, www.plantphysiol.org Ó 2007 American Society of Plant Biologists
et al., 2001; Barbour et al., 2005; Daley and Phillip s,
2006; Kavanagh et al., 2007), and subalpine forest
(Herzog et al., 1998). Many horticultural and crop
species have substantial g
night
and/or E
night
(England,
1963; Rosenbe rg, 1969; Rawson and Clarke, 1988; Green
et al., 1989; Blom-Zandstra et al., 1995; Assaf and
Zieslin, 1996; Musselman and Minnick, 2000). Al-
though it has been suggested that sustained nocturnal
stomatal ope ning is not a feature of grasses (Loftfield,
1921), substantial g
night
has been observed in Distichlis
spicata (C
4
; Snyder et al., 2003) and wheat (Triticum
aestivum;C
3
; Rawson and Clarke, 1988), among others.
Substantial variation in magnitude of maximum
g
night
has been observed among closely related species
(Supplemental Table S1); however, differences among
some species are minimal and not biologically signif-
icant (see Helianthus species, Supplemental Table S1;
Howard and Donovan, 2007). Multiple surveys have
shown that g
night
varies substa ntially among species
within a particular environment or habitat type (Snyder
et al., 2003; Bucci et al., 2004; Daley and Phillips, 2006;
Kavanagh et al., 2007), and the relationship of species
differences to source environment or habitat remains
unclear. Additional studies investigating g
night
in a
phylogenetic context in native and common garden
locations will be required to determine whether spe-
cies differences in g
night
are adaptive.
Many studies have also demonstrated genetic vari-
ation in magnitude of g
night
among cultivars or ac-
cessions of single species (Supplemental Table S1).
Arabidopsis (Arabidopsis thaliana) natural accessions
had a 2.5-fold variation in magnitude of g
night
when
grown in a common envi ronment, and the variation
was correlated to mean annual VPD of the accessions
native environment (M. Caird, unpublished data). Al-
though correlative, this relationship suggests the
potential for natur al selection to have operated on
g
night
. In addition to genetic variation, there is also
evidence for separate genetic control of g
night
from g
day
.
Three near-isogenic lines of Arabidopsis differed
from their parental lines in either g
night
or g
day
, but not
both, providing evidence that these two traits can be
regulated independently due to genetic factors alone
(M. Caird, unpublished data). Future studies exploiting
natural and mutan t genotypes will likely play an im-
portant role in discovering the genetic factors that
influence g
night
in plan ts.
Although recent studies of nighttime water loss
generally do not consider differences in stomatal den-
sity or adaxial and abaxial surface responses, these
factors may contribute to within and among species
variation in g
night
. Not only does stomatal density often
differ between adaxial and abaxial leaf surfaces, but
the stomata on these surfaces can respond differently to
environmental cues such as light. Stomata on the
Figure 1. Histogram summarizing reported g
night
in species among
different plant functional groups. For each species, g
night
was averaged
from all reported values with units in mol m
22
s
21
presented in
Supplemental Table S1 and thus represents a mixture of field and
greenhouse studies. The black two-headed arrow at the top left of the
graph represents the range for reported g
cuticular
taken from many
species, and reported g
night
within this range may be largely due to
g
cuticular
rather than g
stomatal
. A complete listing of species with refer-
ences is provided in Supplemental Table S1.
Figure 2. Diagram summarizing sources of vari-
ation (internal and external) affecting g
night
and
transpiration (E
night
), and consequences of g
night
and E
night
at the individual plant and larger scales.
Nighttime Stomatal Conductance in Plants
Plant Physiol. Vol. 143, 2007 5
abaxial leaf surface, but not the adaxial surface, re-
mained open at night in cotton (Gossypium hirsutum;
Sharpe, 1973) and fava bean (Vicia faba; Aben et al.,
1989). Future studies need to consider how these factors
may affect g
night
and E
night
, particularly with regard to
between and within species variation in g
night
.
Diurnal Patterns for g
stomatal
For many species, g
night
is not stable throughout the
night period. Endogenous, gradual increases in sto-
matal opening during predawn hours have been
reported in many species under natural field condi-
tions as well as in controlled environments (Schwabe,
1952; Muchow et al., 1980; Anderson, 1982; Lasceve
et al., 1997; Leymarie et al., 1998, 1999; Donovan et al.,
2003; Bucci et al., 2004; Dodd et al., 2005; Howard and
Donovan, 2007). In Arabidopsis accession Columbia, a
mean minimum g
night
of 0.117 mol m
22
s
21
slowly in-
creased to a predawn mean of 0.161 mol m
22
s
21
,
amounting to a 38% increase in g
stomatal
during the
night (Lasceve et al., 1997). Arabidopsis mutants with
disrupted circadian rhythms do not have increased sto-
matal opening in predawn hours, indicating g
night
has
some component of circadian regulation (Dodd et al.,
2004, 2005). Lasceve et al. (1997) also found starch-
deficient Arabidopsis mutants do not have the in-
creased endogenous predawn opening observed in
wild-type plants, implying that starch metab olism,
possibly through the formation of an osmoticant nec-
essary for guard cell osmoregulation, is an important
factor affecting stomatal opening during predawn.
Photoperiod length and light intensity can affect the
speed and degree to which stomata close in the dark.
Incomplete stomatal closure at night resulted from
short-day as opposed to long-day photoperiods in
Chrysanthemum (Schwabe, 1952). Higher light inten-
sity during the day or longer supplementary lighting
intervals (extending light period into the normal
night) resulted in faster stomatal closure responses to
lights turning off in roses, although closure was still
incomplete (Blom-Zandstra et al., 1995). The spect rum
of the low intensity supplementary light (25 mmol m
22
s
21
)alsoaffectedg
night
, with orange and blue supplemen-
tary light preventing complete stomatal closure 2.5 h
into the night, while white and no (control) supplemen-
tary light resulted in g
night
comparable to previously
determined g
cuticular
(0.01 mol m
22
s
21
; Blom-Zandstra
et al., 1995). This evidence, together with evidence of
starch-deficient Arabidopsis mutants having de-
creased nighttime stomatal opening (Lasceve et al.,
1997), suggests that daytime conditions and photo-
synthetic rates can influence g
night
. Although the exact
mechanism is unclear, it is possible that a byproduct
of starch metabolism may affect guard cell osmoreg-
ulation at night (Lasceve et al., 1997), causing greater
stomatal opening when starch levels are high. Positive
correlations have been observed for g
night
and g
day
among species in Great Basin habitats (Snyder et al.,
2003). Although only correlative data are available, the
relationship may be the result of daytime conditions
that allow high photosynthetic rates but also result
in high g
night
. Alternatively, leaf development and
stomatal anatomy that affect g
day
could be a cause for
correlation with g
night
.
Responses to Atmospheric Water Demand
Atmospheric conditio ns can be importan t in driving
E
night
when stomata are open, as evidenced by canopy
scale measurements of crop water loss on weighing
lysimeters (England, 1963; Rosenberg, 1969). Advec-
tion was found to create sufficient evaporative demand
to cause 20% to 30% of total daily transpiration to occur
at night in alfalfa (Medicago sativa) in the field (Abdel-
Aziz et al., 1964) and kiwifruit (Actinidia deliciosa)in
orchards (Green et al., 1989). Seginer (1984) extended
this concept to show energy requirements and condi-
tions in greenhouses under which E
night
occurs in roses
using a modified version of the Penman model.
In natural systems, increased VPD has been corre-
lated with greater E
night
at the scale of sap flux for many
tree species (Herzog et al., 1998; Benyon, 1999; Oren
et al., 2001; Daley and Phillips, 2006; Kavanagh et al.,
2007). A trend for lower g
night
with increasing VPD has
been observed in some species (Muchow et al., 1980;
Oren et al., 2001; Bucci et al., 2004), yet some data indi-
cate lack of any response (Barbour et al., 2005). How-
ever, correlative studies such as these do not control for
possible variation due to inherent circadian regulated
stomatal opening that might parallel decreasing VPD
during the night. Nevertheless, similar correlations
have been found when nighttime VPD around plants
is experimentally manipulated, providing more direct
evidence that some species do close stomata in re-
sponse to higher VPD during the night just as during
the daytime (Bakker, 1991). A more thorough under-
standing of whether VPD regulates g
night
in a manner
parallel to that of g
day
will require more studies that
manipulate VPD wh ile controlling for other potentially
confounding factors, including circadian rhythms.
Responses to Water Availability and ABA
It is expected that at night stomata will be sensitive
to decreased water availability, just as during the
daytime, to conserve water. Lower g
night
has been asso-
ciated with decreased plant water status in Hibiscus
cannabinus (Muchow et al., 1980), Pseudostuga menziesii
(Running, 1976; Blake and Ferrell, 1977), and Helian-
thus anomalus (Ludwig et al., 2006). In a field experi-
ment, g
night
of unirrigated desert shrubs was lower
than that of shrubs receiving surface irrigation (Donovan
et al., 2003). In greenhouse studies, g
night
decreased in
response to a water stress treatment in wheat (Rawson
and Clarke, 1988) and in Helianthus species (Howard
and Donovan, 2007). Similar to drought, increased
salinity also reduced g
night
in desert shrubs (Donovan
et al., 1999).
The magnitude of g
night
can additionally vary season-
ally. For Chrysothamnus nauseosus, g
night
was reduced at
Caird et al.
6 Plant Physiol. Vol. 143, 2007
the end of growing seaso n when soils were dry, while
the cooccurring Sarcobatus vermiculatus had higher g
night
(relative to g
day
) by the end of the season (Donovan
et al., 2003). The Sarcobatus response may be related to
its capacity to accumulate high concentrations of leaf
apoplastic solutes (James et al., 2006), which could in
turn affect stomatal regulation. Seasonal changes in
g
night
were also found for Pinus ponderosa, with stomata
more open during the night in early summer, like
Chrysothamnus (Grulke et al., 2004).
ABA can induce stomatal closure during the dark
(RawsonandClarke,1988; Howard and Donovan, 2007).
Similar to responses observed during the daytime, in-
creased concentrations of exogenous ABA resulted in
greater stomatal closure at night in Arabidopsis, and
stomatal closure in response to ABA was more prom-
inent at higher CO
2
(Leymarie et al., 1998, 1999). In P.
menziesii seedlings, nighttime leaf resistance was sensi-
tive to the ABA content of leaves (Blake and Ferrell,
1977), indicating ABA induced stomatal closure in re-
sponse to water stress at nightjustas duringthedaytime.
Nutrient Availability
Typically, higher nutrient availability, particularly
nitrogen (N), is correlated with higher daytime photo-
synthesis (Lambers et al., 1998). However, varying
results have been found for correlations of nutrient
supply and g
day
(Meinzer et al., 1988; Toft et al., 1989).
Similarly, species show different responses of g
night
to
limited nutrient supply. In two field studies with nu-
trient treatments, high nutrient plants had lower g
night
,
but the experimental designs do not allow unam-
biguous separation of direct effects due to reduced
plant demand for nutrient acquisition regulating g
night
from indirect effects of plant size or water status
(Ludwig et al., 2006; Scholz et al., 2007). Other nutrient
response exp eriments that controlled for plant water
status have found differing effects of N supply on g
night
.
For example, reduced g
night
was observed in N-limited
Arabidopsis, but h igher g
night
was found in N-limited
D. spicata and Populus balsamifera subsp. trichocarpa
(M. Caird and A. Howard, unpublished data). Still
other species showed no g
night
response to soil nutrient
limitations (Helianthus species; Howard and Donovan,
2007). The relationship between varying g
night
re-
sponses to nutrients and particular life forms or eco-
logical strategies is unknown and may be related to the
underlying causes of nutrient status effects on g
day
.
IMPLICATIONS OF g
night
AND E
night
Air P ollution Uptake
The occurrence of high g
night
in many C
3
and C
4
plant
species has important implications for air pollutant
uptake (Goknur and Tibbitts, 1984; Segschneider et al.,
1995; Musselman and Minnick, 2000; Tak ahashi et al.,
2005). g
stomatal
is a major factor affecting ozone (O
3
)
uptake in plants (Wieser and Havranek, 1993). Tree
species in areas with high levels of O
3
exposure can
have stomata open at night (Wieser and Havranek,
1993; Matyssek et al., 1995), and nocturnal O
3
uptake
can be a significant proportion of daily O
3
uptake (up to
9%; Grulke et al., 2004). Stomatal responsiveness may
be reduced after exposure to O
3
(Keller and Hasler,
1984; Skarby et al., 1987). Whol e-plant production and
carbon allocation in Betula pendula were also more
sensitive to nighttime compared to daytime O
3
expo-
sure (Matyssek et al., 1995). Thus, O
3
damage resulting
from nighttime uptake may be an important factor for
plants. However, g
night
may also prove to be useful in
areas of high air pollution. For example, H. cannabinus
may be useful as a phytoremediator of NO
2
because this
species has high g
night
and g
day
(Takahashi et al., 2005).
Isotopic Signatur es and Modeling
Nighttime stomatal opening may influence oxygen
isotope signatures of within-canopy CO
2
(Barbour et al.,
2005). This has importan t implications for models
describing ecosystem respiratory CO
2
flux and its
partitioning into above- and below-ground compo-
nents.
18
O enrichment of leaves will also be affected
by g
night
, complicating the use of such signatures in
detecting genetic or environmental effects on transpi-
ration rate. Variation in magnitude of g
night
among
species and the regulation and responses of g
night
to
environmental factors (i.e. VPD) are important consid-
erations in determining how large an impact nighttime
stomatal opening wil l have on oxygen isotope signa-
tures. More research on these topics is required and will
need to be incorpo rated into models.
Potential for Increased Daytime Carbon Gain
Plants may be able to increase their photosynthetic
carbon gain by preopening stomata before dawn. This
might be especially advantageous in water-limited
environments because of a higher potential for early
morning carbon gain when temperatures and VPD are
lower. Although stomatal responses to light are typi-
cally fast, there is some evidenc e to support the hy-
pothesis that maintaining open stomata at night affects
daytime opening. In Xanthium pennsylvanicum, the rate
of stomatal opening in light was greater when stomata
were open during the night (Mansfield and Heath,
1961). However, there is no evidence for an effect of
experimentally loweri ng g
night
on carbon gain or g
day
during the subsequent day. Additional research is
necessary to directly test whether high g
night
influences
early morning and total daily carbon gain, and if so how
much and by what mechanism.
Effects on Water Relations
Plant water potential is expected to equilibrate with
the wettest soil layer in the rooting zone overnight.
However, substantial E
night
can prevent equil ibration
Nighttime Stomatal Conductance in Plants
Plant Physiol. Vol. 143, 2007 7
from occurring, resulting in soil-plant predawn water
potential disequilibrium, or predawn disequilibrium
(Donovan et al., 2001), which complicates interpreta-
tion of soil moisture availability based on plant water
potential measurements. E
night
has been observed to
contribute to predawn disequilibrium in many specie s
(Donovan et al., 1999, 2001, 2003; Sellin, 1999; Bucci
et al., 2004, 2005; Kavanagh et al., 2007).
Substantial E
night
may additionally reduce a plant’s
ability to conduct hydraulic redistribution (HR, also
referred to as hydraulic lift; Richards and Caldwell,
1987). HR occurs when some roots are absorbing water
from wet soil location s and other roots of the same
plant are losing water to relatively dry soil locations.
When stomata are open and the atmospheric condi-
tions allow E
night
to occur, the water loss through the
shoot should decrease the amount released to drier
soil layers because of impacts on plant water poten-
tials. Plants in natural populations can simultaneously
have both HR and high E
night
, although these two
processes may vary in magnitude through the grow-
ing season (Donovan et al., 2003; Domec et al., 2006).
Nutrient Supply and Distri bution
Significant water loss without sim ultaneous photo-
synthetic carbon gain could constitute a major cost to a
plant. However, it is possible that E
night
may provide a
benefit that outweighs this cost. Mobile mineral nutri-
ents are moved into the immediate vicinity of plant
roots (i.e. the rhizosphere) by transpiration-driven
mass flow of the soil solution (Barber, 1995). Thus,
the maintenance of a continuous water stream through
the plant during both day and night could potentially
result in enhanced nutrient availability to the plant.
McDonald et al. (2002) showed that CO
2
-induced
stomatal closure reduced transpiration and N acqui-
sition by Populus deltoides.
Using the Barber-Cushman model, the effect of
increased water flux on nitrate uptake and nutrient
concentration in the rooting zone can be predicted
(Barber and Cushman, 1981). The general result is that
increasing water flux eliminates or minimizes the
depletion zone, which develops in the rhizosphere,
by maintaining a supply of nitrate to the root (Barber
and Cushman, 1981; Barber, 1995). However, under
low nitra te or high root length density conditions, the
effect is reduced and total nitrate uptake is not affected
dramatically. We are experimentally testing this hy-
pothesis.
In addition to supply of nutrients to roots, the
distribution of nutrients within plants, particularly
phloem-immobile nutrients such as calcium, depends
on the xylem flow rate and duration of transpiration
(Marschner, 1995). An increase in the total amount of
water flowing through the xylem may improve nutrit-
ion when organs are Ca deficient. Daley and Phillips
(2006) also suggest that g
night
may enhance nutrient
transport within trees such as paper birch by provid-
ing oxygen to sapwood parenchyma cells that function
in nutrient transport and storage.
Implications for Gro wth and Plant Fitness
Implications for plant water and nutrient relations
suggest that E
night
may also impact plant productivity
and growth, although experimental evidence on the
subject is scarce. It is intuitive that E
night
poses costs to
plants under water-limiting conditions as evidenced by
reduction in g
night
in response to water stress. However,
more research is necessary to determine what benefits,
if any, may either balance or outweigh these costs.
CONCLUSION
Although research dating back to the late 1800’s
describes stomata of many C
3
and C
4
plant species as
incompletely closing during the night, very little is
understood about this phenomenon. We have sum-
marized a growing body of evidence showing that
g
night
is regulated, in many ways similar to daytime
stomatal regulation, and that nighttime stomatal open-
ing and transpiration have implications for plant
growth and physiology. Nevertheless, more research
will be necessary to fully appreciate the sign ificance of
g
night
and E
night
. Future research on plant regulation of
g
night
and the consequences of substantial E
night
for
water and nutrient relations will be key for under-
standing the ecological and evolutionary conse-
quences of g
night
and E
night
in C
3
and C
4
plants.
Supplemental Data
The following materials are available in the online version of this article.
Supplemental Table S1. A summary of C
3
and C
4
plant species reported
in the literature as having significant g
night
and/or nighttime transpi-
rational water loss or incomplete stomatal closure at night.
Received November 11, 2006; accepted November 22, 2006; published January
8, 2007.
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... For terrestrial plants, Q n consists of two significant ecophysiological and ecohydrological components: transpiration of water from the canopy and stem water refilling at night (Daley & Phillips 2006;Caird et al., 2007;Forster, 2014). Both processes influence forest water budgets and plant responses to water stress (Zeppel et al., 2014;Chen et al., 2020). ...
... Growing evidence has suggested that in some plants the stomata remained open or partially open at night (Gindel, 1970;Caird et al., 2007;Fisher et al., 2007;Zhao et al., 2017), and that incomplete stomata closure provides the structure basic for nocturnal transpiration. Vapor pressure deficit (VPD) has been identified in some studies as the most crucial environmental driver of nocturnal transpiration Dawson et al., 2007;Wu et al., 2020;Zeppel et al., 2014). ...
... Driving force of nocturnal sap flow in mangroves Q n is driven by environmental factors and biotic factors, separately or synergistically. Previous studies suggested that VPD was the main environmental factor driving E n because VPD between the leaf surface and the atmosphere provided conditions for stomata to open or partially open at night (Caird et al., 2007;Dawson et al., 2007;Zeppel et al., 2010). Wind speed affected the moisture movement around plant canopy (Fricke 2019 ) and thus influenced on nocturnal water loss (Chen et al. 2020), which also could not be ignored. ...
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As part of the plant water-use process, plant nocturnal sap flow ( Q ) has been demonstrated to have important ecophysiological significance to compensate for water loss. The purpose of this study was to explore nocturnal water-use strategies to fill the knowledge gap in mangroves, by measuring three species co-occurring in a subtropical estuary. The Q existed persistently and contributed markedly over 5.5%~24.0% of the daily sap flow ( Q ) across species, which was associated with two processes, nocturnal transpiration ( E ) and nocturnal stem water refilling ( R ). The diversity of stem recharge patterns and response to sap flow to high salinity conditions were the main reasons for the differences in Q / Q among species. For Kandelia obovata and Aegiceras corniculatum , R was the main contributor to Q , which driven by the demands of stem water refilling after diurnal water depletion and high salinity. In contrast, Avicennia marina maintained a low Q , driven by vapor pressure deficit, and the Q mainly used for E , which adapts to high salinity conditions by limiting water dissipation at night. We conclude that the diverse ways Q properties act as water-compensating strategies among the co-occurring mangrove species might help the trees to overcoming water scarcity.
... Chabrand et al., 2017). At night, stomata are essentially closed, yet progressive preopening is usually observed before dawn (Caird et al., 2007). Overall, the ability of stomata to track fast changes in irradiance or maintain low transpiration throughout the night enhances plant water use efficiency (Caird ...
... We have also addressed the possibility that maltose, the main outcome of starch breakdown, acts as a signal for nighttime stomatal preopening, but we failed in establishing a causal relationship. Since the first observation one century ago that stomata preopen throughout the night (Loftfield, 1921), this behaviour has been reported in many species (Schwabe, 1952;Caird et al., 2007). Based on gas exchange experiments in Vicia faba, it was suggested that a by-product of starch metabolism could be the molecular link between daytime photosynthesis and stomatal preopening in the following night (Easlon and Richards, 2009). ...
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In leaves, stomata open during the day to favour CO 2 entry for photosynthesis, and close at night to prevent inefficient transpiration of water vapour. Plants’ days and nights are paced by light availability and anticipated by the circadian clock, but how rhythmic stomatal movements are interlocked with the environment and the physiology of the plant remains elusive. Leaf transitory starch appears as a plausible integrator therein. Here, we developed PhenoLeaks, a pipeline to analyse the diel (24-h) dynamics of transpiration, and used it to screen a series of Arabidopsis mutants impaired in starch metabolism. We show that the diel dynamics of transpiration are driven by a sinusoidal, endogenous rhythm that overarches days and nights. We uncover that a number of severe mutations in starch metabolism affect the endogenous rhythm through a phase shift, resulting in delayed stomatal movements throughout the daytime and reduced stomatal preopening during the night. Nevertheless, analysis of tissue-specific mutations revealed that neither guard-cell nor mesophyll-cell starch metabolism are strictly required for normal diel patterns of transpiration. We propose that leaf starch metabolism affects the endogenous stomatal rhythm by modulating cross-tissue sugar homeostasis, which interacts with the circadian clock that in turn affects guard-cell ion transport. One-sentence summary The PhenoLeaks pipeline for monitoring diel transpiration dynamics reveals that leaf starch metabolism sets the timing of the endogenous stomatal rhythm.
... Plants need to regrow as early as possible when relieved from the drought. The ability of a plant to resume growth and productivity by reintroducing water after severe drought stress is known as contribute up to 50% of total water loss in drought stressed plants during day and 60% during night [27,28]. In the light of this, the current studies aimed to validate the role of SD and RT in the drought tolerance and recovery in barley. ...
... up to 50% of total water loss in drought stressed plants during day and 60% durin [27,28]. In the light of this, the current studies aimed to validate the role of SD an the drought tolerance and recovery in barley. ...
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The fast and efficient recovery could be an important trait defining the efficacy of plant drought adaptation. In this work, we aimed to develop and set of simple and appropriate physiological proxies that could be used as reliable indicator to predict plant drought responses and validate the role of specific physiological traits such as root length, stomata density, and residual transpiration, in the drought tolerance and recovery in barley. Eighty barley (Hordeum vulgare L.) genotypes were subjected to progressive droughting until the soil moisture level reached 10%, following by rewatering. Plants were visually scored at the end of drought period and two weeks after rewatering. SPAD values and chlorophyll fluorescence Fv/Fm ratio were also measured, alongside with stomatal density (SD) and residual transpiration (RT). The same genotypes were treated with 15% (w/v) of polyethylene glycol (PEG) 8000 applied to seeds germinating in paper rolls following by quantification of changes in the root growth patterns. Responses to drought stress varied among the genotypes, and drought tolerance and recovery scores were significantly correlated with each other. Changes in SPAD value, Fv/Fm ratio and root length significantly correlated with the drought tolerance and recovery indices. Both indices correlated strongly with the SD and RT of irrigated plants, although in an unexpected direction. We have also correlated the extent of plants drought tolerance to their ability to grow in saline soils (a condition often termed as a “physiological drought”) and found a positive association between these two traits. The fact that drought tolerant genotype also possessed higher salinity tolerance implying some common mechanisms conferring both traits. Plants having less SD and more RT under irrigated conditions showed higher drought tolerance. It is concluded that lower SD and higher RT under optimal conditions may be used as proxies for drought tolerance in barley.
... According to Tolk et al. (2006), in semiarid and arid regions, the nighttime ET o can be up to 15% of the total ET o . Caird et al. (2007) reported that nighttime transpiration rates are normally 5-15% of ET o,d and may occasionally reach 30% of daily ET o . According to Irmak (2011), seasonal nighttime evaporative losses in Nebraska ranged between 0.11 and 0.19 mm/night for two years, with a maximum of 0.50 mm/night. ...
Preprint
Estimating reference evapotranspiration (ET ) at 24 h timesteps has been considered sufficiently accurate for a long time. However, recent advances in weather data acquisition have made it feasible to apply hourly procedures in ET computation. Hourly timesteps can improve the accuracy of ET estimates, as data averaged daily may misrepresent evaporative power during parts of the day. The objective of the present study is to assess the differences between daily ET computations performed on 24 h (ET ) and hourly (ET ) timesteps for rice-wheat cropping systems in the Ganga Basin, India. The meteorological data for computing reference evapotranspiration were collected from an automatic weather station located in an experimental plot at IIT Kanpur, India. Daily and hourly ET computations were performed according to the FAO-PM (Allen et al, 1998) equation for rice and wheat cropping seasons. Diurnal variations of meteorological parameters resulted in underestimation of ET when the daily time step is considered. No significant difference was observed during wet periods. It is also observed that the hourly estimates of ET were able to capture the abrupt changes in climate variables, while the daily ET fails to get it as it considers the average values only. As a result, the sums of hourly values are more reliable for ET estimates in the Ganga Plains.
... This structure determines the interception of light by the plant or the energy charge by transpiration (Escalona et al., 2003) which are essential for the WUE. Furthermore, WUE is dependent on water losses during non-assimilatory periods (cuticular and nocturnal transpiration) (Caird et al., 2007), and also depends on respiration in leaves, stems, and roots throughout the day. And consequently, it is expected that there will not be a direct relationship between NAR and SLA, which is directly related to biomass production (Blum, 2009). ...
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Introduction. Basil (Ocimum basilicum L.) is a little-known crop in the Bolivian highlands as its response to water use efficiency (WUE) in a Walipini-type greenhouses. Objective. To evaluate the behavior of two varieties of basil and the water use efficiency (WUE) in the application of foliar biofertilizer in a Walipini-type greenhouse. Materials and methods. The experiment was installed at the Ventilla Ecological Farm, in the Central Highlands of Bolivia, with an experimental period of 135 days (July 13 to November 25), 2014. A factorial experiment with two factors (varieties: Nufar F1 and Italian Large Leaf) and two levels of foliar biofertilizer (Biol) was used under a completely randomized block design. Results. Through the WUE, specific leaf area, and net assimilation rate relationship, it was observed that basil had a better development in Walipini-type greenhouse (underground greenhouse) since biomass accumulation was not significantly affected. The results showed that the production of basil in this environment using foliar biofertilizer, Biol, differ mainly by the variety rather than by the doses of Biol, showing that Nufar F1 had better development. Conclusion. A significant relationship was observed between Nufar F1 and Italian large Leaf for biomass weight when applying Biol at two different levels. It shows that there does not necessarily have to be a positive and significant relationship between biomass accumulation and WUE, so it is presumed that basil can develops regularly in Walipini-type greenhouses under semi-arid region conditions.
... Early observations of circadian regulation of photosynthetic potential under constant levels of internal CO 2 Fredeen et al. 1991) also supported the view that variable stomata conductance could not be the only determinant of the night depression of photosynthesis (Farré and Weise 2012). Nocturnal stomatal opening with high gas conductance is correlated with elevated photosynthesis performances and growth rates in several species, and has likely a genetic background (Caird et al. 2007;Resco de Dios et al. 2016). ...
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Although many photosynthesis related processes are known to be controlled by the circadian system, consequent changes in photosynthetic activities are poorly understood. Photosynthesis was investigated during the daily cycle by chlorophyll fluorescence using a PAM fluorometer in Pulmonaria vallarsae subsp. apennina , an understory herb. A standard test consists of a light induction pretreatment followed by light response curve (LRC). Comparison of the major diagnostic parameters collected during day and night showed a nocturnal drop of photosynthetic responses, more evident in water-limited plants and consisting of: (i) strong reduction of flash-induced fluorescence peaks (FIP), maximum linear electron transport rate (J max , ETR EM ) and effective PSII quantum yield (Φ PSII ); (ii) strong enhancement of nonphotochemical quenching ( NPQ ) and (iii) little or no change in photochemical quenching qP , maximum quantum yield of linear electron transport ( Φ ), and shape of LRC ( θ ). A remarkable feature of day/night LRCs at moderate to high irradiance was their linear-parallel course in double-reciprocal plots. Photosynthesis was also monitored in plants subjected to 2–3 days of continuous darkness (“long night”). In such conditions, plants exhibited high but declining peaks of photosynthetic activity during subjective days and a low, constant value with elevated NPQ during subjective night tests. The photosynthetic parameters recorded in subjective days in artificial darkness resembled those under natural day conditions. On the basis of the evidence, we suggest a circadian component and a biochemical feedback inhibition to explain the night depression of photosynthesis in P. vallarsae .
... If stomata are the main entry path for plant volatiles, several aspects need to be considered. First, as plants close their stomata at night [23], this would imply that plants are not able to perceive volatiles during nighttime, despite the fact that herbivore-induced plant volatiles such as GLVs are released as danger cues at night [24]. Another important aspect to consider is the developmental stage of stomata in leaves. ...
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Herbivore-induced plant volatiles regulate defenses in undamaged neighboring plants. Understanding the mechanisms by which plant volatiles are taken up, perceived, and translated into canonical defense signaling pathways is an important frontier of knowledge. Volatiles can enter plants through stomata and the cuticle. They are likely perceived by membrane-associated receptors as well as intracellular receptors. The latter likely involves metabolization and transport across cell membranes by volatile transporters. Translation of volatiles into defense priming and induction typically involves mitogen-activated protein kinases (MAPKs), WRKY transcription factors, and jasmonates. We propose that the broad range of molecular processes involved in volatile signaling will likely result in substantial spatiotemporal and ontogenetic variation in plant responsiveness to volatiles, with important consequences for plant–environment interactions.
Article
During prolonged dry periods, non-rainfall water (NRW) plays a vital role as water input into temperate grasslands, affecting the leaf surface water balance and plant water status. Previous chamber and laboratory experiments investigated air–leaf water exchange during dew deposition, but overlooked the importance of radiative cooling on air–leaf water exchange because the chamber is a heat trap, preventing radiative cooling. To complement these previous studies, we conducted a field study, in which we investigated the effect of radiatively-induced NRW inputs on leaf water isotope signals and air–leaf water exchange in a temperate grassland during the dry-hot summers of 2018 and 2019. We carried out field measurements of the isotope composition of atmospheric water vapor, NRW droplets on foliage, leaf water, xylem water of root crown, and soil water, combined with meteorological and plant physiological measurements. We combined radiation measurements with thermal imaging to estimate leaf temperatures using different methods, and computed the corresponding leaf conductance and air–leaf water exchange. Our results indicate that radiative cooling and leaf wetting induced a switch of direction in the net water vapor exchange from leaf-to-air to air-to-leaf. The leaf conductance and air–leaf water exchange varied by species due to the species-specific biophysical controls. Our results highlight the ecological relevance of radiative cooling and leaf wetting in natural temperate grasslands, a process which is expected to influence land surface water budgets and may impact plant survival in many regions in a drier climate.
Article
Nocturnal water uses (Qn) significantly affect global water budgets and diurnal water cycles, which are currently suffering from restrictions of soil drought and soil water depletion caused by climate change and worldwide greening. Recent studies have recognized the vital influence of soil water availability on Qn, but responses of nocturnal water use strategy to soil moisture variation were not fully understood. For example, the effect of soil water content (θ) on the trade-offs between two components of Qn, stem water refilling (Re) and nocturnal transpiration (Tn), was rarely involved and remained unclear. This study analyzed the nocturnal sap flow of typical afforestation species, poplar plantation, under different soil water conditions in a seasonal arid region of northern China. Results indicated that higher θ significantly promoted Qn through enhancing the stomatal conductance but had less influence on the proportion of nocturnal water use to daily water use (Qn%) (7 %∼10 %). With the decline of soil water conditions, significant linear correlations between Qn and θ shifted from deep soil layers to the soil surface. The influence of meteorological factors on Qn depended on soil water condition, and the explanation of nocturnal vapor pressure deficit (VPDn) to Qn became weaker with increasing soil moisture. Negative linear relations between the proportion of stem water refilling to Qn (Re%) and θ were shown within treatments, but a significantly higher Re% was observed under more sufficient soil water. These opposite responses of Re% to θ reflected the different adaptions of Qn to soil water availability on short- and long-scales. This study highlights the crucial role of soil moisture in the nocturnal water use and balance strategy of a seasonal-arid poplar plantation. Our results help better understand the nocturnal transpiration processes in the context of global climate change.
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Plain Language Summary Forests comprise the largest share of Earth's vegetated surface area and play an integral role in its hydrological cycle. Forests transfer moisture from below the surface to the atmosphere via transpiration, affecting surface moisture budgets and weather patterns at local‐to‐regional scales. Our ability to accurately predict transpiration in forests is thus critical to reliable weather prediction and more informed water resource management. The most accurate predictions stem from process‐oriented models with detailed representations of plant hydraulic architecture and leaf stomata regulation. These models, however, rely on inputs that are not widely available and thus are not well‐suited for predictions across broader spatial scales. Here, we sought to identify models that could be readily applied using conventional input data streams to predict daily transpiration across a wide diversity of forested ecosystems and over large spatial scales. This was carried out by evaluating predictions emanating from four models of varying complexity against two independent estimates of daily transpiration. We found the most parsimonious models to be those requiring few meterological variables and one forest structural variable as input, achieving an accuracy 33% higher and explaining 16% greater variance than the most complex models requiring additional meteorological and forest structural variables as input.
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Stomatal responses to ABA and CO2 were investigated in Arabidopsis thaliana (L.) Heynh. wild-type and ABA insensitive mutants (abi1-1, abi2-1, abi1-1abi2-1) at the whole plant and at the isolated epidermis levels. In wild-type plants, feeding roots with ABA (1–50 µM) triggered a rapid drop in leaf conductance which levelled off during the following photoperiods, and strongly inhibited the increase in conductance induced by light. The rapid response was strongly inhibited in abi1-1, abi2-1 and abi1-1abi2-1 double mutants, but a residual long-term decrease in leaf conductance was still observed. In wild-type plants, exogenous ABA strongly enhanced the response to CO2 removal. Conversely, in the absence of CO2 the effect of ABA was drastically reduced in epidermal strip experiments. These results reveal a strong interaction between sensing of ABA and CO2 in stomata of A. thaliana. Despite an initially wide stomatal aperture in abi-1, abi-2 and double mutant plants, their stomatal responses to light and CO2 removal were half those of wild-type plants. Moreover these responses were totally independent of the presence of ABA, suggesting that ABI1 and ABI2 are either directly involved in the interaction between the two signalling pathways or, alternatively located upstream of this point of interaction.
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Over the night, stomata of wheat leaves took several hours to reach their most closed position and began to open some hours before dawn. The pattern and amount of night transpiration was changed by current vapour pressure deficit (VPD) but not by VPD or transpiration during the previous day. Mean night transpiration per unit VPD was unchanged by current VPD. Night transpiration of whole plants increased linearly with VPD though genotypes differed significantly in amount. The most profligate genotype transpired at 50 g m-2 leaf h-1 at a VPD of 30 mbar which was twice the rate of the most thrifty genotype. Attempts were made to estimate the proportion of night transpiration occurring through the stomata and the cuticle by three methods: comparisons of stressed and unstressed leaves, wilting patterns of detached leaves, and transpiration rates of detached leaves in ABA solutions. The methods gave equivalent rankings of the genotypes and similar absolute values for the 'cuticular component', which contributed 13-50% of total night transpiration. We conclude that transpiration could exceed 0.5 mm per night in unstressed crops, though this would be considerably reduced by selection of genotypes with both low cuticular and low stomatal transpiration.
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N acquisition often lags behind accelerated C gain in plants exposed to CO2-enriched atmospheres. To help resolve the causes of this lag, we considered its possible link with stomatal closure, a common first-order response to elevated CO2 that can decrease transpiration. Specifically, we tested the hypothesis that declines in transpiration, and hence mass flow of soil solution, can decrease delivery of mobile N to the root and thereby limit plant N acquisition. We altered transpiration by manipulating relative humidity (RH) and atmospheric [CO2]. During a 7-d period, we grew potted cottonwood (Populus deltoides Bartr.) trees in humidified (76% RH) and non-humidified (43% RH) glasshouses ventilated with either CO2-enriched or non-enriched air (~1000 vs ~380 μmol mol–1). We monitored effects of elevated humidity and/or CO2 on stomatal conductance, whole-plant transpiration, plant biomass gain, and N accumulation. To facilitate the latter, NO3– enriched in 15N (5 atom%) was added to all pots at the outset of the experiment. Transpiration and 15N accumulation decreased when either CO2 or humidity were elevated. The disparity between N accumulation and accelerated C gain in elevated CO2 led to a 19% decrease in shoot N concentration relative to ambient CO2. Across all treatments, 15N gain was positively correlated with root mass (P<0.0001), and a significant portion of the remaining variation (44%) was positively related to transpiration per unit root mass. At a given humidity, transpiration per unit leaf area was positively related to stomatal conductance. Thus, declines in plant N concentration and/or content under CO2 enrichment may be attributable in part to associated decreases in stomatal conductance and transpiration.
Article
Night water consumption of rockwool-grown rose plants was measured during winter months in two separate greenhouses where a night temperature of 17° ± 1°C was maintained. The air relative humidity in one of the greenhouses (A) was controlled during the night hours by frequent fan operation, whereas the second greenhouse (B) was equipped with a dehumidifier and a thermal screen. The average heat transfer coefficient and the energy consumption for maintenance of the desired temperature in greenhouse B were lower than in greenhouse A and the average water consumption of rose plants in greenhouse B was also lower by 57% than in greenhouse A. A significant correlation (r2 = 0.94) was found between the heat load of the greenhouse and the night water loss from the plants. Stomata were open and transpiration occurred during the night heating period. Cessation of heating was accompanied by stomatal closure and decreased transpiration. The difference in water loss between the plants in the two greenhouses was attributed to a difference in convective heat flux through the plant canopy from the heating elements near the ground to the cold roof. The possibility that the night transpiration of rose plants and probably of other plant species might be affected by thermal convection is proposed.
Article
The extent of night-time stomatal opening in field-grown kenaf (Hibiscus cannabinus L.), a C3 dicotyledon, and sorghum [Sorghum bicolor (L.) Moench], a C4 grass, and the factors controlling the opening were studied at high and low soil water status. Since saturation deficit (δe) and temperature varied together in the field, the response of stomatal conductance (gs) to these individual factors was determined under controlled environment conditions in a leaf chamber apparatus. At both high and low soil water status, the stomata of sorghum were closed from sunset to sunrise, whereas with kenaf partial stomatal opening was observed throughout the night. Initiation of night opening occurred in response to decreasing temperature, but the degree of opening was determined by plant water status. The importance of night-time stomatal opening on the water relations of the crop is discussed.
Article
Photosynthetic and stomatal responses of Tamarix chinensis to temperature, light, and humidity were investigated in the field in New Mexico and in the laboratory. Transpiration rates for T. chinensis were similar to those of several herbaceous plants and co-occurring phreatophytes. Net photosynthetic rates and water use efficiency of T. chinesis were lower than for other species. Photosynthesis was light saturated at a photon flux density equal to 44% of full sunlight. Carbon dioxide assimiliation was tightly coupled to irradiance below light saturation. Leaf resistances remained low at photon flux densities above one-third of full sunlight, but increased linearly with decreasing photon flux density below that level. Shading for 5 min resulted in a doubling of leaf resistance. The rapid response of stomata to changing light conditions is probably an adaptation to conserve moisture when light is limiting to photosynthesis. Optimal leaf temperatures for photosynthesis were 23@?-28@? C, which correspond roughly to ambient temperatures during the early part of the day when evaporative demand was relatively low. T. chinensis stomata appeared to respond directly to changes in the leaf-to-air absolute humidity gradient. At constant temperature, leaf resistance increased linearly with increases in the leaf-air humidity gradient. Midday depressions of gas exchange invariably occurred in the field, despite the fact that the plants had an abundant water supply. These depressions resulted from increases in leaf resistance in response to increasing evaporative demand of the air. This response results in improved water use efficiency during the hottest portion of the day. Plant water potential decreased from pre-dawn values of about -0.9 MPa to minimal values of about -2.6 MPa by midmorning. Improvements in bulk water status were often observed during the afternoon when leaf resistances were higher. Diurnal patterns suggested that leaf resistance was largely a function of temperature, light, and humidity, rather than plant water status.
Article
An experiment was conducted near. Sydney, Australia to determine the adaxial and abaxial stomatal responses of cotton (Gossypium hirsutum L.) to environmental factors under noncycling field conditions. Cotton plants were grown in small lysimeter pans and transpiration was measured by strain guage lysimeters. Leaf temperature, ambient temperature and other micrometeorological parameters were monitored continuously, Stomatal resistances were regularly measured for both surfaces with a diffusion resistance porometer developed by the author. It was found that under field conditions, the adaxial and abaxial stomata differ in their response to light, water stress, and ambient temperature. Under most conditions, including darkness and. drought, the adaxial surface was considerably higher in resistance than the abaxial surface. However, the differences in resistance between the two surfaces disappeared under a combination of high light and temperature conditions. High transpiration rates and low leaf resistance were associated with high ambient temperatures. With sufficient soil moisture there was no evidence of midday stomatal closure even under sew;re light and temperature regimes. It was found that sampling the resistance of one surface alone (particularly the adaxial) did not give an accurate estimate of the overall leaf resistance. In addition, it was also found that similar .resistances on both surfaces under any one set of environmental conditions does not necessarily imply that this will be so under all conditions. Please view the pdf by using the Full Text (PDF) link under 'View' to the left. Copyright © . .