Water use efficiency (WUE) is defined as the amount of carbon assimilated as biomass or grain produced per unit of water used by the crop. One of the primary questions being asked is how plants will ...respond to a changing climate with changes in temperature, precipitation, and carbon dioxide (CO
) that affect their WUE At the leaf level, increasing CO
increases WUE until the leaf is exposed to temperatures exceeded the optimum for growth (i.e., heat stress) and then WUE begins to decline. Leaves subjected to water deficits (i.e., drought stress) show varying responses in WUE. The response of WUE at the leaf level is directly related to the physiological processes controlling the gradients of CO
and H
O, e.g., leaf:air vapor pressure deficits, between the leaf and air surrounding the leaf. There a variety of methods available to screen genetic material for enhanced WUE under scenarios of climate change. When we extend from the leaf to the canopy, then the dynamics of crop water use and biomass accumulation have to consider soil water evaporation rate, transpiration from the leaves, and the growth pattern of the crop. Enhancing WUE at the canopy level can be achieved by adopting practices that reduce the soil water evaporation component and divert more water into transpiration which can be through crop residue management, mulching, row spacing, and irrigation. Climate change will affect plant growth, but we have opportunities to enhance WUE through crop selection and cultural practices to offset the impact of a changing climate.
Cereal production around the world is critical to the food supply for the human population. Crop productivity is primarily determined by a combination of temperature and precipitation because ...temperatures have to be in the range for plant growth and precipitation has to supply crop water requirements for a given environment. The question is often asked about the changes in productivity and what we can expect in the future and we evaluated the causes for variation in historical annual statewide wheat grain yields in Oklahoma, Kansas, and North Dakota across the Great Plains of United States. Wheat (
L.) is adapted to this area and we focused on production in these states from 1950 to 2016. This analysis used a framework for annual yields using yield gaps between attainable and actual yields and found the primary cause of the variation among years were attributable to inadequate precipitation during the grain-filling period. In Oklahoma, wheat yields were reduced when April and May precipitation was limited (
= 0.70), while in Kansas, May precipitation was the dominant factor (
= 0.78), and in North Dakota June-July precipitation was the factor explaining yield variation (
= 0.65). Temperature varied among seasons and at the statewide level did not explain a significant portion of the yield variation. The pattern of increased variation in precipitation will cause further variation in wheat production across the Great Plains. Reducing yield variation among years will require adaptation practices that increase water availability to the crop coupled with the positive impact derived from other management practices, e.g., cultivars, fertilizer management, etc.
Tribological investigations on the macroscopic scale revealed that friction can be influenced in situ by applying electric potentials, if electrically conductive fluid such as an ionic liquid is used ...as a lubricant. Enrichment of charged ions at a steel interface occurs by applying electric surface potentials in a three-electrode setup. As a consequence, the lubrication conditions change. It is supposed that electrically influenced surface adsorption and electrokinetic effects are the main mechanisms by which friction is varied.
Novel satellite measurements of solar‐induced chlorophyll fluorescence (SIF) can improve our understanding of global photosynthesis; however, little is known about how to interpret the controls on ...its spectral variability. To address this, we disentangle simultaneous drivers of fluorescence spectra by coupling active and passive fluorescence measurements with photosynthesis. We show empirical and mechanistic evidence for where, why, and to what extent leaf fluorescence spectra change. Three distinct components explain more than 95% of the variance in leaf fluorescence spectra under both steady‐state and changing illumination conditions. A single spectral shape of fluorescence explains 84% of the variance across a wide range of species. The magnitude of this shape responds to absorbed light and photosynthetic up/down regulation; meanwhile, chlorophyll concentration and nonphotochemical quenching control 9% and 3% of the remaining spectral variance, respectively. The spectral shape of fluorescence is remarkably stable where most current satellite retrievals occur (“far‐red,” >740nm), and dynamic downregulation of photosynthesis reduces fluorescence magnitude similarly across the 670‐ to 850‐nm range. We conduct an exploratory analysis of hourly red and far‐red canopy SIF in soybean, which shows a subtle change in red:far‐red fluorescence coincident with photosynthetic downregulation but is overshadowed by longer‐term changes in canopy chlorophyll and structure. Based on our leaf and canopy analysis, caution should be taken when attributing large changes in the spectral shape of remotely sensed SIF to plant stress, particularly if data acquisition is temporally sparse. Ultimately, changes in SIF magnitude at wavelengths greater than 740 nm alone may prove sufficient for tracking photosynthetic dynamics.
Plain Language Summary
Satellite remote sensing provides a global picture of photosynthetic activity—allowing us to see when, where, and how much CO2 plants are assimilating. To do this, satellites measure a small emission of energy from the plants called chlorophyll fluorescence. However, this measurement is typically made across a narrow wavelength range, while the emission spectrum (650–850 nm) is quite dynamic. We show where, why, and to what extent leaf fluorescence spectra change across a diverse range of species and conditions, ultimately informing canopy remote sensing measurements. Results suggest that wavelengths currently used by satellites are stable enough to track the downregulation of photosynthesis resulting from stress, while spectral shape changes respond more strongly to dynamics in canopy structure and chlorophyll concentration.
Key Points
We disentangle chlorophyll fluorescence spectra into three distinct components explaining >95% of the variance in the spectral shape
The spectral shape of chlorophyll fluorescence is stable >740 nm, modulated by distinct chlorophyll and nonphotochemical quenching features
Using spectral shape changes to infer plant stress via remote sensing will be challenging—mostly dominated by chlorophyll and structure
The tribological behavior of complex fluids was investigated to study the mechanisms, which cause low friction values. Therefore reciprocating sliding tests using two different geometries ...(cylinder-on-disc, ring-on-disc) were performed. Afterwards the characteristics of the wear scars were analyzed. In addition, in-lubro infrared analysis executed to assign the relative change of the content of water during a tribological test. The mesogenic fluid MF-02/06 (μ≈0.005), imidazolium-based ionic liquids (μ≈0.02) and ionic liquid crystals (μ≈0.01) showed low friction coefficients after a specific running-in time using cylinder-on-disc geometry. The wear scars showed a characteristic grooved structure for the fluids with the lowest friction coefficients. Using in-lubro IR-spectroscopy, it was detected that the water content decreases during the tribological test, which influences the corrosive behavior.
•The tribological behavior of complex fluids was investigated.•A very low coefficient of friction (μ≈0.005) was achieved using a mesogenic fluid.•Ionic liquids and ionic liquid crystals also exhibit low friction values (μ≈0.01).•Decrease of the water content was measured in-lubro using infrared spectroscopy.
Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface‐atmosphere coupling. However, methods to estimate ...ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum‐flux data. At 69 forest sites, annual ha robustly predicted site‐to‐site and year‐to‐year differences in canopy heights (R2 = 0.88, 111 site‐years). At 23 cropland/grassland sites, weekly ha successfully captured the dynamics of vegetation canopies over growing seasons (R2 > 0.70 in 74 site‐years). Our results demonstrate the potential of flux‐derived ha determination for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. The large‐scale and time‐varying ha derived from flux networks worldwide provides a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
Plain Language Summary
Vegetation canopy height is a key descriptor of the Earth surface and is in use by many modeling and conservation applications. However, large‐scale and time‐varying data of canopy heights are often unavailable. This synthesis evaluates the applicability and robustness of the calculation of canopy heights from the momentum flux data measured at eddy covariance flux tower sites (i.e., meteorological observation towers with high frequency measurements of wind speed and surface fluxes). We show that the aerodynamic estimation of annual canopy heights robustly predicts the site‐to‐site and year‐to‐year differences in canopy heights across a wide variety of forests. The weekly aerodynamic canopy heights successfully capture the dynamics of vegetation canopies over growing seasons at cropland and grassland sites. Our results demonstrate the potential of aerodynamic canopy heights for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. Given the amount of data collected and the diversity of vegetation covered by the global networks of eddy covariance flux tower sites, the flux‐derived canopy height has great potential for providing a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
Key Points
Aerodynamic canopy height can be calculated robustly and routinely from the eddy covariance momentum flux data
Our estimates match well with in situ measurements of canopy heights across a wide variety of vegetation and ecosystem types
Aerodynamic canopy height can be used to track the dynamics of vegetation canopies, including plant growth, harvest, and disturbance
The Midwestern US is dominated by corn (Zea mays L.) and soybean (Glycine max L. Merr.) production, and the carbon dynamics of this region are dominated by these production systems. An accurate ...regional estimate of gross primary production (GPP) is imperative and requires upscaling approaches. The aim of this study was to upscale corn and soybean GPP (referred to as GPPcalc) in four counties in Central Iowa in the 2016 growing season (DOY 145–269). Eight eddy-covariance (EC) stations recorded carbon dioxide fluxes of corn (n = 4) and soybean (n = 4), and net ecosystem production (NEP) was partitioned into GPP and ecosystem respiration (RE). Additional field-measured NDVI was used to calculate radiation use efficiency (RUEmax). GPPcalc was calculated using 16 MODIS satellite images, ground-based RUEmax and meteorological data, and improved land use maps. Seasonal NEP, GPP, and RE ( x ¯ ± SE) were 678 ± 63, 1483 ± 100, and −805 ± 40 g C m−2 for corn, and 263 ± 40, 811 ± 53, and −548 ± 14 g C m−2 for soybean, respectively. Field-measured NDVI aligned well with MODIS fPAR (R2 = 0.99), and the calculated RUEmax was 3.24 and 1.90 g C MJ−1 for corn and soybean, respectively. The GPPcalc vs. EC-derived GPP had a RMSE of 2.24 and 2.81 g C m−2 d−1, for corn and soybean, respectively, which is an improvement to the GPPMODIS product (2.44 and 3.30 g C m−2 d−1, respectively). Corn yield, calculated from GPPcalc (12.82 ± 0.65 Mg ha−1), corresponded well to official yield data (13.09 ± 0.09 Mg ha−1), while soybean yield was overestimated (6.73 ± 0.27 vs. 4.03 ± 0.04 Mg ha−1). The approach presented has the potential to increase the accuracy of regional corn and soybean GPP and grain yield estimates by integrating field-based flux estimates with remote sensing reflectance observations and high-resolution land use maps.
In its latest assessment report the IPCC stresses the need for carbon dioxide removal (CDR) to counterbalance residual emissions to achieve net zero carbon dioxide or greenhouse gas emissions. There ...are currently a wide variety of CDR measures available. Their potential and feasibility, however, depends on context specific conditions, as among others biophysical site characteristics, or availability of infrastructure and resources. In our study, we selected 13 CDR concepts which we present in the form of exemplary CDR units described in dedicated fact sheets. They cover technical CO
2
removal (two concepts of direct air carbon capture), hybrid solutions (six bioenergy with carbon capture technologies) and five options for natural sink enhancement. Our estimates for their CO
2
removal potentials in 2050 range from 0.06 to 30 million tons of CO
2
, depending on the option. Ten of the 13 CDR concepts provide technical removal potentials higher than 1 million tons of CO
2
per year. To better understand the potential contribution of analyzed CDR options to reaching net-zero CO
2
emissions, we compare our results with the current CO
2
emissions and potential residual CO
2
emissions in 2050 in Germany. To complement the necessary information on technology-based and hybrid options, we also provide an overview on possible solutions for CO
2
storage for Germany. Taking biophysical conditions and infrastructure into account, northern Germany seems a preferable area for deployment of many concepts. However, for their successful implementation further socio-economic analysis, clear regulations, and policy incentives are necessary.
Water stress can positively or negatively impact grape yield and yield quality, and there is a need for wine growers to accurately regulate water use. In a four-year study (2010–2013), energy balance ...fluxes were measured with an eddy-covariance (EC) system in a North Carolina vineyard (Vitis vinifera cv. Chardonnay), and evapotranspiration (ET) and the Crop Water Stress Index (CWSI) calculated. A multiple linear regression model was developed to upscale ET using air temperature (Ta), vapor pressure deficit (VPD), and Landsat-derived Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI). Daily ET reached values of up to 7.7 mm day−1, and the annual ET was 752 ± 59 mm, as measured with the EC system. The grapevine CWSI was between 0.53–0.85, which indicated moderate water stress levels. Median vineyard EVI was between 0.22 and 0.72, and the EVI range (max–min) within the vineyard was 0.18. The empirical models explained 75%–84% of the variation in ET, and all parameters had a positive linear relationship to ET. The Root Mean Square Error (RMSE) was 0.52–0.62 mm. This study presents easily applicable approaches to analyzing water dynamics and ET. This may help wine growers to cost-effectively quantify water use in vineyards.
Germany 2050: For the first time Germany reached a balance between its sources of anthropogenic CO2 to the atmosphere and newly created anthropogenic sinks. This backcasting study presents a ...fictional future in which this goal was achieved by avoiding (∼645 Mt CO2), reducing (∼50 Mt CO2) and removing (∼60 Mt CO2) carbon emissions. This meant substantial transformation of the energy system, increasing energy efficiency, sector coupling, and electrification, energy storage solutions including synthetic energy carriers, sector‐specific solutions for industry, transport, and agriculture, as well as natural‐sink enhancement and technological carbon dioxide options. All of the above was necessary to achieve a net‐zero CO2 system for Germany by 2050.
Plain Language Summary
Here a net‐zero‐2050 Germany is envisioned by combining analysis from an energy‐system model with insights into approaches that allow for a higher carbon circularity in the German system, and first results from assessments of national carbon dioxide removal potentials. A back‐casting perspective is applied on how net‐zero Germany could look like in 2050. We are looking back from 2050, and analyzing how Germany for the first time reached a balance between its sources of CO2 to the atmosphere and the anthropogenic sinks created. This would consider full decarbonization in the entire energy sector and being entirely emission‐free by 2050 within three priorities identified as being the most useful strategies for achieving net‐zero: (a) Avoiding‐ (b) Reducing‐ (c) Removing emissions. This work is a collaboration of interdisciplinary scientists with the Net‐Zero‐2050 cluster of the Helmholtz Climate Initiative HI‐CAM.
Key Points
The net‐zero system shows that for countries like Germany, avoiding CO2 emissions was the largest contribution to achieve net‐zero CO2
With the three strategies of emissions avoidance, reduction, and removal, Germany has achieved its net‐zero CO2 goal for the first time
In addition, to natural sink enhancement carbon dioxide removal (CDR) options, technological CDR measures combined with geological CO2 storage were necessary to reach net‐zero CO2
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