scholarly journals Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

2013 ◽  
Vol 10 (7) ◽  
pp. 4937-4956 ◽  
Author(s):  
J. H. Shim ◽  
H. H. Powers ◽  
C. W. Meyer ◽  
A. Knohl ◽  
T. E. Dawson ◽  
...  
Keyword(s):  
Vapor Pressure Deficit ◽  
Ecosystem Respiration ◽  
Isotope Composition ◽  
Water Source ◽  
Leaf Water ◽  
Evaporative Demand ◽  
Physiological Regulation ◽  
Rain Pulses ◽  
Flux Model ◽  
Soil Moisture Availability

Abstract. We conducted high frequency measurements of the δ18O value of atmospheric CO2 from a juniper (Juniperus monosperma) woodland in New Mexico, USA, over a four-year period to investigate climatic and physiological regulation of the δ18O value of ecosystem respiration (δR). Rain pulses reset δR with the dominant water source isotope composition, followed by progressive enrichment of δR. Transpiration (ET) was significantly related to post-pulse δR enrichment because the leaf water δ18O value showed strong enrichment with increasing vapor pressure deficit that occurs following rain. Post-pulse δR enrichment was correlated with both ET and the ratio of ET to soil evaporation (ET/ES). In contrast, the soil water δ18O value was relatively stable and δR enrichment was not correlated with ES. Model simulations captured the large post-pulse δR enrichments only when the offset between xylem and leaf water δ18O value was modeled explicitly and when a gross flux model for CO2 retro-diffusion was included. Drought impacts δR through the balance between evaporative demand, which enriches δR, and low soil moisture availability, which attenuates δR enrichment through reduced ET. The net result, observed throughout all four years of our study, was a negative correlation of post-precipitation δR enrichment with increasing drought.

scholarly journals Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

2013 ◽  
Vol 10 (1) ◽  
pp. 1-48 ◽  
Author(s):  
J. H. Shim ◽  
H. H. Powers ◽  
C. W. Meyer ◽  
A. Knohl ◽  
T. E. Dawson ◽  
...  
Keyword(s):  
Vapor Pressure Deficit ◽  
Ecosystem Respiration ◽  
Isotope Composition ◽  
Water Source ◽  
Leaf Water ◽  
Evaporative Demand ◽  
Physiological Regulation ◽  
Rain Pulses ◽  
Flux Model ◽  
Soil Moisture Availability

Abstract. We conducted high frequency measurements of the δ18O value of atmospheric CO2 from a juniper (Juniperus monosperma) woodland in New Mexico, USA, over a four-year period to investigate climatic and physiological regulation of the δ18O value of ecosystem respiration (δR). Rain pulses reset δR with the dominant water source isotope composition, followed by progressive enrichment of δR. Transpiration (ET) was significantly related to post-pulse δR enrichment because leaf water δ18O value showed strong enrichment with increasing vapor pressure deficit that occurs following rain. Post-pulse δR enrichment was correlated with both ET and the ratio of ET to soil evaporation (ET / ES). In contrast, soil water δ18O value was relatively stable and δR enrichment was not correlated with ES. Model simulations captured the large post-pulse δR enrichments only when the offset between xylem and leaf water δ18O value was modeled explicitly and when a gross flux model for CO2 retro-diffusion was included. Drought impacts δR through the balance between evaporative demand, which enriches δR, and low soil moisture availability, which attenuates δR enrichment through reduced ET. The net result, observed throughout all four years of our study, was a negative correlation of post-precipitation δR enrichment with increasing drought.

Nocturnal stomatal conductance and implications for modelling δ18O of leaf-respired CO2 in temperate tree species

2005 ◽  
Vol 32 (12) ◽  
pp. 1107 ◽  
Author(s):  
Margaret M. Barbour ◽  
Lucas A. Cernusak ◽  
David Whitehead ◽  
Kevin L. Griffin ◽  
Matthew H. Turnbull ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Oxygen Isotope ◽  
Tree Species ◽  
Ricinus Communis ◽  
Ecosystem Respiration ◽  
Isotope Composition ◽  
Theoretical Work ◽  
Oxygen Isotope Composition ◽  
Flux Model ◽  
The One

Variation in the oxygen isotope composition of within-canopy CO2 has potential to allow partitioning of the ecosystem respiratory flux into above- and below-ground components. Recent theoretical work has highlighted the sensitivity of the oxygen isotope composition of leaf-respired CO2 (δRl) to nocturnal stomatal conductance. When the one-way flux model was tested on Ricinus communis L. large enrichments in δRl were observed. However, most species for which the isotope flux partitioning technique has been or would be applied (i.e. temperate tree species) are much more conservative users of water than R. communis. So, high stomatal conductance and very high enrichment of δRl observed may not be typical for temperate tree species. Using existing gas-exchange measurements on six temperate tree species, we demonstrate significant water loss through stomata for all species (i.e. statistically significantly greater than cuticular loss alone) at some time for some leaves during the night. δRl values predicted by the one-way flux model revealed that δRl might be very much more enriched than when the net flux alone is considered, particularly close to sunrise and sunset. Incorporation of the one-way flux model into ecosystem respiration partitioning studies will affect model outputs and interpretation of variation in the oxygen isotope composition of atmospheric CO2.

A reflexion on the environmental effect on the transmission of COVID-19

2021 ◽  
Author(s):  
Victor L Barradas ◽  
Monica Ballinas
Keyword(s):  
Solar Radiation ◽  
Air Temperature ◽  
Low Temperatures ◽  
Minimum Distance ◽  
Vapor Pressure Deficit ◽  
Environmental Parameters ◽  
Air Humidity ◽  
Evaporative Demand ◽  
Small Water ◽  
The Hours

<p>This research is a general reflection of the possible transmission not only of COVID-19 but of any influenza disease depending on environmental parameters such as solar radiation, air humidity and air temperature (vapor pressure deficit), evoking the Penman-Monteith model regarding the evaporation of the water that constitutes the small water droplets (aerosols) that carry the virus. In this case the evapotranspiration demand of the atmosphere with which it can be deduced that the spread of the disease will be higher in those places with less evaporative demand, that is, high air humidity and / or low temperatures, and / or low radiation intensities, and vice versa. It can also be deduced that the hours of greatest potential contagion are the night hours, while those with the lowest risk are between 2:00 p.m. and 4:00 p.m. On the other hand, in those rooms with low temperatures the contagion would be more effective. So, considering that the drops produced by a sneeze, by speaking or breathing can go beyond two meters away, it is roughly explained that the use of face masks and keeping a safe minimum distance of two meters can limit transmission of viruses and / or infections. However, this practice is not entirely safe as the environment can play an important role. What is recommended to reduce the spread of these pathogens is to produce high evaporative demands: increasing solar radiation, and increasing air temperature and reducing air humidity, which is practice that can be effective in closed rooms.</p>

scholarly journals Environmental effects on efficacy of herbicides for postemergence goosegrass (Eleusine indica) control

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Avat Shekoofa ◽  
James T. Brosnan ◽  
Jose J. Vargas ◽  
Daniel P. Tuck ◽  
Matthew T. Elmore
Keyword(s):  
Soil Moisture ◽  
Environmental Effects ◽  
Vapor Pressure Deficit ◽  
Sandy Soils ◽  
Silica Sand ◽  
Soil Drying ◽  
Silt Loam ◽  
Evaporative Demand ◽  
Eleusine Indica ◽  
High Soil Moisture

AbstractExperiments were conducted to understand environmental effects on efficacy of herbicides used to control goosegrass (Eleusine indica L. Gaertn.). Herbicides were applied to goosegrass maintained at soil moisture contents (VMC) of < 12%, 12 to 20%, or > 20%. Herbicides included fenoxaprop-p-ethyl (140 g ha−1), topramezone (25 g ha−1), foramsulfuron (44 g ha−1), 2,4-D + dicamba + MCPP + carfentrazone (860 + 80 + 270 + 28 g ha−1), and thiencarbazone-methyl + foramsulfuron + halosulfuron-methyl (22 + 45 + 69 g ha−1). Goosegrass control increased as VMC increased. Vapor pressure deficit (VPD) and air temperature were manipulated to determine effects of evaporative demand on foramsulfuron. Effects of soil drying were also studied following foramsulfuron application. Reductions in transpiration rate (TR) and leaf area were greatest with foramsulfuron applications to goosegrass in silt-loam under high evaporative demand (3 kPa VPD, 38 °C). Foramsulfuron had no effect on goosegrass in silica-sand regardless of evaporative demand. TR dropped to 0.2 mmh−1 within eight days after application to goosegrass in silt-loam compared to 18 days in silica-sand. Overall, foramsulfuron efficacy on goosegrass was maximized under conditions of high soil moisture and evaporative demand, and may be reduced in sandy soils that hold less water.

scholarly journals How dry was the Younger Dryas? Evidence from a coupled <i>δ</i><sup>2</sup>H–<i>δ</i><sup>18</sup>O biomarker paleohygrometer applied to the Gemündener Maar sediments, Western Eifel, Germany

2019 ◽  
Vol 15 (2) ◽  
pp. 713-733 ◽  
Author(s):  
Johannes Hepp ◽  
Lorenz Wüthrich ◽  
Tobias Bromm ◽  
Marcel Bliedtner ◽  
Imke Kathrin Schäfer ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Younger Dryas ◽  
Late Glacial ◽  
Climatic Conditions ◽  
Leaf Water ◽  
Early Holocene ◽  
Unexpected Finding ◽  
Temperature Dependent ◽  
The Past ◽  
Natural Climate

Abstract. Causes of the Late Glacial to Early Holocene transition phase and particularly the Younger Dryas period, i.e. the major last cold spell in central Europe during the Late Glacial, are considered to be keys for understanding rapid natural climate change in the past. The sediments from maar lakes in the Eifel, Germany, have turned out to be valuable archives for recording such paleoenvironmental changes. For this study, we investigated a Late Glacial to Early Holocene sediment core that was retrieved from the Gemündener Maar in the Western Eifel, Germany. We analysed the hydrogen (δ2H) and oxygen (δ18O) stable isotope composition of leaf-wax-derived lipid biomarkers (n-alkanes C27 and C29) and a hemicellulose-derived sugar biomarker (arabinose), respectively. Both δ2Hn-alkane and δ18Osugar are suggested to reflect mainly leaf water of vegetation growing in the catchment of the Gemündener Maar. Leaf water reflects δ2H and δ18O of precipitation (primarily temperature-dependent) modified by evapotranspirative enrichment of leaf water due to transpiration. Based on the notion that the evapotranspirative enrichment depends primarily on relative humidity (RH), we apply a previously introduced “coupled δ2Hn-alkane–δ18Osugar paleohygrometer approach” to reconstruct the deuterium excess of leaf water and in turn Late Glacial–Early Holocene RH changes from our Gemündener Maar record. Our results do not provide evidence for overall markedly dry climatic conditions having prevailed during the Younger Dryas. Rather, a two-phasing of the Younger Dryas is supported, with moderate wet conditions at the Allerød level during the first half and drier conditions during the second half of the Younger Dryas. Moreover, our results suggest that the amplitude of RH changes during the Early Holocene was more pronounced than during the Younger Dryas. This included the occurrence of a “Preboreal Humid Phase”. One possible explanation for this unexpected finding could be that solar activity is a hitherto underestimated driver of central European RH changes in the past.

scholarly journals Effects of leaf length and development stage on the triple oxygen isotope signature of grass leaf water and phytoliths: insights for a proxy of continental atmospheric humidity

2019 ◽  
Vol 16 (23) ◽  
pp. 4613-4625 ◽  
Author(s):  
Anne Alexandre ◽  
Elizabeth Webb ◽  
Amaelle Landais ◽  
Clément Piel ◽  
Sébastien Devidal ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Climate Model ◽  
Isotope Composition ◽  
Leaf Growth ◽  
Development Stage ◽  
Mean Value ◽  
Leaf Length ◽  
Leaf Water ◽  
Grass Species ◽  
Leaf Biomass

Abstract. Continental relative humidity (RH) is a key climate parameter, but there is a lack of quantitative RH proxies suitable for climate model–data comparisons. Recently, a combination of climate chamber and natural transect calibrations have laid the groundwork for examining the robustness of the triple oxygen isotope composition (δ′18O and 17O-excess) of phytoliths, that can preserve in sediments, as a new proxy for past changes in RH. However, it was recommended that besides RH, additional factors that may impact δ′18O and 17O-excess of plant water and phytoliths be examined. Here, the effects of grass leaf length, leaf development stage and day–night alternations are addressed from growth chamber experiments. The triple oxygen isotope compositions of leaf water and phytoliths of the grass species F. arundinacea are analysed. Evolution of the leaf water δ′18O and 17O-excess along the leaf length can be modelled using a string-of-lakes approach to which an unevaporated–evaporated mixing equation must be added. We show that for phytoliths to record this evolution, a kinetic fractionation between leaf water and silica, increasing from the base to the apex, must be assumed. Despite the isotope heterogeneity of leaf water along the leaf length, the bulk leaf phytolith δ′18O and 17O-excess values can be estimated from the Craig and Gordon model and a mean leaf water–phytolith fractionation exponent (λPhyto-LW) of 0.521. In addition to not being leaf length dependent, δ′18O and 17O-excess of grass phytoliths are expected to be impacted only very slightly by the stem vs. leaf biomass ratio. Our experiment additionally shows that because a lot of silica polymerises in grasses when the leaf reaches senescence (58 % of leaf phytoliths in mass), RH prevailing during the start of senescence should be considered in addition to RH prevailing during leaf growth when interpreting the 17O-excess of grass bulk phytoliths. Although under the study conditions 17O-excessPhyto do not vary significantly from constant day to day–night conditions, additional monitoring at low RH conditions should be done before drawing any generalisable conclusions. Overall, this study strengthens the reliability of the 17O-excess of phytoliths to be used as a proxy of RH. If future studies show that the mean value of 0.521 used for the grass leaf water–phytolith fractionation exponent λPhyto-LW is not climate dependent, then grassland leaf water 17O-excess obtained from grassland phytolith 17O-excess would inform on isotope signals of several soil–plant-atmosphere processes.

scholarly journals Diel variations in the carbon isotope composition of respired CO<sub>2</sub> and associated carbon sources: a review of dynamics and mechanisms

2011 ◽  
Vol 8 (9) ◽  
pp. 2437-2459 ◽  
Author(s):  
C. Werner ◽  
A. Gessler
Keyword(s):  
Carbon Isotope ◽  
Isotope Fractionation ◽  
Temporal Dynamics ◽  
Carbon Allocation ◽  
Ecosystem Respiration ◽  
Isotope Composition ◽  
Carbon Sources ◽  
Mechanistic Explanation ◽  
Short Term ◽  
Theoretical Understanding

Abstract. Recent advances have improved our methodological approaches and theoretical understanding of post-photosynthetic carbon isotope fractionation processes. Nevertheless we still lack a clear picture of the origin of short-term variability in δ13C of respired CO2 (δ13Cres) and organic carbon fractions on a diel basis. Closing this knowledge gap is essential for the application of stable isotope approaches for partitioning ecosystem respiration, tracing carbon flow through plants and ecosystems and disentangling key physiological processes in carbon metabolism of plants. In this review we examine the short-term dynamics in δ13Cres and putative substrate pools at the plant, soil and ecosystem scales and discuss mechanisms, which might drive diel δ13Cres dynamics at each scale. Maximum reported variation in diel δ13Cres is 4.0, 5.4 and 14.8 ‰ in trunks, roots and leaves of different species and 12.5 and 8.1 ‰ at the soil and ecosystem scale in different biomes. Temporal variation in post-photosynthetic isotope fractionation related to changes in carbon allocation to different metabolic pathways is the most plausible mechanistic explanation for observed diel dynamics in δ13Cres. In addition, mixing of component fluxes with different temporal dynamics and isotopic compositions add to the δ13Cres variation on the soil and ecosystem level. Understanding short-term variations in δ13Cres is particularly important for ecosystem studies, since δ13Cres contains information on the fate of respiratory substrates, and may, therefore, provide a non-intrusive way to identify changes in carbon allocation patterns.

The dominant environmental driver of leaf water stable isotope enrichment differs for H-2 compared to O-18

2020 ◽  
Author(s):  
Matthias Cuntz ◽  
Lucas A Cernusak ◽  
Keyword(s):  
Stable Isotope ◽  
Relative Humidity ◽  
Air Temperature ◽  
Gordon Equation ◽  
Isotope Composition ◽  
Environmental Variable ◽  
Leaf Water ◽  
Source Water ◽  
Stable Isotope Composition ◽  
Water Stable Isotope

&lt;p&gt;Several important isotopic biomarkers derive at least part of their signal from the stable isotope composition of leaf water (e.g., leaf wax &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H, cellulose &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O, lignin &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O). In order to interpret these isotopic proxies, it is therefore helpful to know which environmental variable most strongly controls a given leaf water stable isotope signal. We collated observations of the stable isotope compositions of leaf water, xylem water, and atmospheric vapour, along with air temperature and relative humidity, to test whether the dominant driver of leaf water &lt;sup&gt;2&lt;/sup&gt;H concentration could differ from that of &lt;sup&gt;18&lt;/sup&gt;O concentration. Our dataset comprises 690 observations from 35 sites with broad geographical coverage. We limited our analysis to daytime observations, when the photosynthetic processes that incorporate the leaf water isotopic signal primarily take place. The Craig-Gordon equation was generally a good predictor for daytime bulk leaf water stable isotope composition for both &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H (R&lt;sup&gt;2&lt;/sup&gt;=0.86, p&lt;0.001) and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O (R&lt;sup&gt;2&lt;/sup&gt;=0.63, p&lt;0.001). It showed about 10% admixture of source water was caused by unenriched water pools such as leaf veins or the P&amp;#233;clet effect. Solving the Craig-Gordon equation requires knowledge of relative humidity, air temperature, and the stable isotope compositions of source water and atmospheric vapour. However, it is not possible to invert the Craig-Gordon equation to solve for one of these parameters unless the others are known. Here we show that the two isotopic signals of &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O are predominantly driven by different environmental variables: leaf water &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H correlated most strongly with the &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H of source water (R&lt;sup&gt;2&lt;/sup&gt;=0.68, p&lt;0.001) and atmospheric vapour (R&lt;sup&gt;2&lt;/sup&gt;=0.63, p&lt;0.001), whereas leaf water &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O correlated most strongly with air relative humidity (R&lt;sup&gt;2&lt;/sup&gt;=0.46, p&lt;0.001). We conclude that these two isotopic signals of leaf water are not simply mirror images of the same environmental information, but carry distinct signals of different climate factors, with crucial implications for the interpretation of downstream isotopic biomarkers.&lt;/p&gt;

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