October 29, 2021 at 5:51 pm | Updated April 11, 2022 at 6:44 am | 13 min read
Plant research is focused on physicochemical and biochemical attributes, as well as physiological processes to establish basic plant science. These are applied in crop research to improve productivity and also reduce the ecological footprint of conventional farming. Today, we give ten of this year’s important discoveries in plant and crop science the “tl;dr” treatment, providing you with a bite-sized look at each. These articles span photosynthetic efficiency, transpiration, stomatal conductance, root research, quality estimations in crops, and more. Let’s dive in!
Photosynthetic Efficiency in Plantation Intercrop [Sept. 2021]
Intercropping–especially with a nitrogen-fixing species–is often beneficial, as long as we can rule out competition effects. Keeping this in mind, Chinese forestry scientists, Yao, Lan, Liao, Huang, Yu, Ye, and Yang, monitored how the introduction of Dalbergia odorifera, a nitrogen-fixing tree species, affected Eucalyptus urophylla × E. grandis yield potential.
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They compared competition for nitrogen, photosynthetic efficiency, and dry matter accumulation in both species, when they were grown together as an intercrop and separately as monocultures under different nitrogenous fertilizer regimes.
Intercropping was beneficial for Eucalyptus and the tree managed to improve its photosynthetic rates. This resulted from an increase in nitrogen use by 6.57 – 48.46%, which increased chlorophyll synthesis in the plants. With more chlorophyll, more photosynthesis occured, which increased the dry matter yield of Eucalyptus by 7.59 – 97.26%.
In contrast, Dalbergia’s nitrogen utilization dropped by 10.21 – 30.33%, reducing photosynthetic efficiency. The resultant dry matter accumulation decreased by 0.48 – 13.19%. Hence, the scientists concluded that nitrogen-fixing species like Dalbergia did not pose a threat, and could be a sustainable option to manage and improve Eucalyptus productivity.
Quinoa Varieties’ Response to Salinity [Aug. 2021]
About 20% of irrigated agricultural soils are saline and affect crop production in 75% of the countries globally. There is a significant loss in yield and profits due to soil salinity, as it affects plant growth both directly and indirectly.
Crop breeding for saline tolerance is complicated, as the physiological processes involved in stress response are controlled by the external environment. Hence, these physiological processes like photosynthesis, transpiration, and stomatal conductance have to be monitored for phenotyping traits in salt-tolerant plants.
Since measurement of transpiration and stomatal conductance is tedious and time-consuming with traditional methods, there is not much information on these two processes.
Dutch scientists, Roman, van de Zedde, Peller, Visser, van der Linden, and van Loo, tried to get around this problem by using a phenotyping platform – Plantarray 3.0. The platform tracked plant growth, water use, biomass accumulation, and irrigation, using an array of sensors to measure air and soil temperature, and humidity, as well as lysimeters to measure transpiration and stomatal conductance. They tested the performance of two quinoa varieties, Pasto and selRiobamba, under salinity, which ranged from 0–300 mM NaCl.
The crop growth model LINTUL was used to integrate all the physiological processes for analysis.
Figure 1. “Daily patterns of experimental conditions measured by sensors and physiological components derived from Plantarray measurements. The influence of a bright and cloudy day is compared. (A) Light intensity. (B) VPD. (C) Transpiration rate (E). (D) Stomatal conductance (gs). (E) Water use efficiency (WUE). (F) Leaf temperature measured by a thermal camera, Roman et al, 2021. (Image credits: DOI=10.3389/fpls.2021.634311)
The scientists found that increasing salinity had a negative impact on transpiration. In both varieties, transpiration decreased by 60% at 200 mM NaCl. But at 300 mM NaCl, transpiration was reduced more in Pasto (82%) than in selRiobamba (75%).
Stomatal conductance was also reduced by salinity, but to a lesser extent in Pasto (15%) compared to selRiobamba (35%) at 200 mM NaCl. Specific leaf area also saw a reduction.
Due to salinity stress, transpiration is not responsive to light. Stomatal conductance occurs to increase CO2 uptake and minimize water vapor loss in response to changes in vapor pressure deficit (VPD). Through these controls, the two varieties improved their water use efficiency under saline stress.
The crop model LINTUL showed that radiation use efficiency was lower in Pasto than in selRiobamba, due to salinity.
After six weeks of stress, Pasto growth was significantly lower than that of selRiobamba. Pasto had 50% and 70% less biomass at 200 mM and 300 mM NaCl, respectively. While selRiobamba’s biomass accumulation decreased by only 35% and 50% at 200 mM and 300 mM NaCl, respectively.
The Pasto cultivar uses a “conservative-growth” growth strategy, whereas the selRiobamba variety uses an “acquisitive-growth” strategy and manages to optimize its productivity.
Controlling Stomatal Conductance [Jul. 2021]
Figure 2: “Remote control for stomatal movement. Green light can activate the GtACR1 channel in guard cells that surround an open pore (left). Active GtACR1 channels release chloride ions, which automatically also causes the efflux of potassium ions and the release of water (middle). Because of the slackening of the guard cells the stomatal pores in the leaf surface close (right). (Image: Lehrstuhl für Botanik I / Universität Würzburg)” (Image credit: https://www.uni-wuerzburg.de/en/news-and-events/news/detail/news/fernbedienung-fuer-pflanzen-1/)
Stomatal conductance in leaves has a significant influence on the global cycling of carbon and water. Half of the rain that falls on land is returned to the atmosphere by transpiration, so knowing how to control stomatal conductance is vital.
The stoma is an opening that is formed by the guard cells. When guard cells are turgid due to the accumulation of osmolytes, the internal pressure increases, and cells move apart opening the stomata. When the guard cells are flaccid due to loss of osmolytes, the pressure is reduced and the cells flop, closing the stomata.
A group of experts in plant physiology and biophysics, Huang, Ding, Roelfsema, Scherzer, Khaled, Al-Rasheid, Gao, Hedrich, and Konrad, explored the role of the anions channel in the plasma membrane, to find out if they alone were responsible for stomatal opening.
The scientists assessed whether the anion channel ACRI could be activated by light pulses, allowing it to be used as a “light switch” to control the guard cells in tobacco plants.
The experiment was successful. When anion channels were activated by blue-green light, it triggered action by the stress hormone ABA and CO2. The resulting movement of chlorine and nitrate ions produced a current, which opens potassium channels and causes the exit of potassium ions from the cells. As a consequence, the guard cells lose pressure and the stomata close, even when environmental conditions would normally favor open stomata. So, using the new optogenetics tool it is possible to control stomatal conductance, see Figure 2.
Improving Leaf Area Index Estimation in Pine [Mar. 2021]
Instead of field and direct estimation, which can be time-consuming and expensive, increasingly, vegetation indices (VIs) are being used to calculate above-ground biomass from remotely sensed imagery, as a measure of forest productivity.
Leaf Area Index (LAI), a popular vegetative index, is used as an estimate of photosynthetic efficiency, productivity, and response to fertilization. However, LAI calculated based on remote sensed spectral imaging has historically not been very accurate, as seen in loblolly pines productivity prediction.
A team of US-based forestry scientists, Kinane, Montes, Albaugh, and Mishra, wanted to reduce the effect of observation errors from Landsat 5 TM and 7 ETM on LAI estimates of fertilized and irrigated plots, revisiting measurements made between 1992 to 2004. They compared the results of their new model with LAI calculated manually from field observations of 1667 trees in each of 16 plots by a canopy analyzer, see Figure 3.
Figure 3. “Peak leaf area index measurements for the sixteen Southeast Tree Research and Education Site (SETRES) plots in Scotland County, North Carolina over the study period (1992–2004). Peak leaf area index typically occurred in August or September of any given year, Kinane et al, 2021. (Image credits: Remote Sens. 2021, 13(6), 1140; https://doi.org/10.3390/rs13061140)
The scientist found that the best below canopy LAI measurements were obtained by tracking the normalized difference moisture index. For nutrition, a nonlinear model gave the best estimate of LAI. The new model that the scientists developed could be used to evaluate LAI changes more accurately over area and time with the same images, giving a better picture of historical changes in loblolly plantation productivity.
Understanding Contribution to Soil Carbon [Sept. 2021]
Belowground carbon has been recognized as a significant carbon pool and is now considered a key component of the global carbon cycle. However, little is known about “belowground net primary production” (BNPP). It is assumed that likely sources of carbon could be root biomass and carbon-rich root exudates, but these remain poorly documented.
To fill this information gap, a team of soil scientists, Yang, Wang, and An, studied the underground carbon contribution of grasslands fenced for 1, 5, 10, 25, and 30 years. They used the in-growth soil cores-13C method to determine the source of soil carbon.
The scientists found that BNPP increased in older fenced areas at a rate of 61.54~140.23 gC·m−2·yr− 1. Root-derived carbon, which accounted for 57-81% of BNPP, was found to be the significant source of carbon, not root biomass. The contribution of root-derived carbon to BNPP however, decreased with fencing years.
Overall, root-derived carbon contributed 3-5% of the soil organic carbon each year. Fencing increases root carbon content which results in root-derived carbon.
Reducing Nitrogen Fertilizer Use [Feb. 2021]
Awareness of the environmental impacts of intensive farming methods is on the rise, and with that awarenes comes a growing emphasis on sustainable agricultural practices.
To find sustainable alternatives to nitrogen fertilizers, Finnish agricultural scientist, Owusu-Sekyere, tested the micronutrient and dry mater yeild effects of using pig slurry compost on three crops- broad beans (Vicia faba L.), field lupines (Lupinus albus L.), and wheat (Triticum aestivum L.).
The three crops were grown in pots under controlled conditions in a greenhouse. The four treatments were as follows:
1) unfirtilized control,
2) conventional chemical NPK fertilizers,
3) pig slurry compost and 50% of NPK fertilizers,
4) pig slurry compost with quartz sand and 50% NPK
The rate of nitrogen through the NPK fertilizers was 200 mg N kg−1 soil.
Though micronutrient uptake and use were lower in pig slurry treatments as opposed to the full NPK treatment, it is recommended as a viable alternative as the results obtained are comparable. Both pig slurry and the mineral fertilizers increased seed yield by 10-32%, and shoot and root dry matter by 36% and 21%, respectively.
Both pig slurry and the fertilizers increased micronutrients in seed: iron by 3-28%, zinc by 10-26%, and copper by 6-31%. Selenium in seeds was higher due to fertilizers being enriched with this micronutrient. Pig slurry increased selenium in seeds of wheat and beans but not lupines.
Thus, it should be possible to substitute 50% of chemicals with pig slurry. This practice would have the added benefit of reducing the likelihood of water pollution by slurry waste from pig farms. This excitng discovery paves the way to turn a potential pollutant into a soil nutrient when used properly.
Differentiating Tomato Varieties with NIRs [Sept. 2021]
Figure 4. “The effect of the first derivatives (1st D) on the spectra obtained from tomato varieties. Ekram (blue), Harver (red) and Izmer (green),” Najjar and Abu-Khalaf, 2021. (Image credits: Sustainability 2021, 13, 10747. https://doi.org/10.3390/su131910747)
With production around 6.4 million tons annually, tomato (Solanum lycopersicum E.) is easily one of the most important food crops in the world today.
Najjar and Abu-Khalaf, agricultural scientists from Palestine, tested the ability of vis-NIR spectroscopy (550-1100nm) to predict quality parameters like firmness, soluble sugar contents (SSC), titratable acidity (TA), and taste (SSC/TA), and distinguish between three popular local tomato varieties, Ekram, Harver, and Izmer in different ripening stages.
They tested ninety intact samples using non-destructive Vis-NIR spectroscopy, and compared results with traditional laboratory methods. The data was analyzed using partial least square (PLS) and principal component analysis (PCA).
The PCA showed that the Vis-NIR spectroscopy can distinguish the three varieties successfully. While the PLS showed the predicted values of all quality parameters except firmness had a high correlation with standard methods, with an R2 of 0.85.
The scientists recommend the use of Vis-NIR spectroscopy for rapid, precise, and non-destructive estimation of quality parameters and authentication for tomato production in Palestine, see Figure 4.
Extending Shelf Life of Tomatoes [Sept. 2021]
Post-harvest monitoring of tomato with Near-infrared spectroscopy (NIRs) is increasing, as conditions during storage and transport can greatly impact fruit. The problem with tomatoes is that they are perishable and suffer a loss of quality quickly. Tomato is important for its nutraceuticals and is used as a fresh vegetable and processed product, and it is important to extend its storage time and reduce waste.
Cairo-based agricultural scientists, Shehata, Abdelrahman, Megahed, Abdeldaym, El-Mogy, Abdelgawad tested four post-harvest treatments’ ability to extend shelf-life and retain quality of tomatoes.
The scientists treated the tomatoes with calcium chloride (CaCl2), chitosan, hydrogen peroxide (H2O2), and ozonated water, and stored them at 10 °C for 28 days. During this time, they regularly monitored the following quality parameters:
• Weight loss,
• Fruit color,
• Total soluble solids (TSS),
• Titratable acidity,
• Total carotenoids, and
• Ascorbic acid content (AsA).
All four treatments were useful in extending the shelf life and improving quality during storage compared to the control, see Figure 5. Chitosan and calcium chloride were the most effective treatments. The scientists found that AsA and carotenoids played a significant role in maintaining fruit quality.
Figure 5: “Weight loss% (A), firmness (B), and total soluble solid (°Brix) (C) of treated tomato fruit as affected by the interaction between the treatments and storage periods,” Shehata et al. 2021. (Image credits: https://doi.org/10.3390/ horticulturae7090309)
Establishing Apricot Cultivar Quality [Jan. 2021]
Another fresh produce rich in nutraceuticals is Apricot (Prunus armeniaca L.), which grows primarily in Mediterranean countries, Morocco being a major global producer of the fruit. To stay competitive, it is necessary to ensure that the cultivars grown in the country meet consumers’ requirements, and perform at least as well as the continuous stream of new cultivars produced elsewhere.
Ayour, Alahyane, Harrak, Neffa, Taourirte, and Benichou, scientists from Food science, Agri-Food Technology, and Bioorganic and Macromolecular Chemistry backgrounds came together to find the main physicochemical, and biochemical quality parameters that characterize the varieties grown in Morocco – “Maoui,” “Canino,” and “Delpatriarca.”
- “Canino” is large, and a rich source of β-carotene, a carotenoid (113.67 μg per g−1 of fresh weight) and has a soluble solids content of ~17.20 °Brix.
- “Delpatriarca” has high organic acid content, especially of ascorbic acid (27.35 g/kg fresh weight).
- “Maoui” has a soluble solids content of ~16 °Brix and high water content of 83.77%.
The scientists found that several of the attributes were interrelated. For example, the relationship between total carotenoids concentration and color parameters indicates that they can be included in ripening as well as quality indices. The experiment clearly showed that the three cultivars differed in consumer quality metrics.
Based on their findings, the scientists recommend juicy “Maoui” for use as fresh fruits, and “Canino” and “Delpatriarca” for processing.
The concentration of nutrients in plants is used to evaluate nutrient removal from the soil, and nutrient use efficiency, as well as for making fertilizer recommendations. By optimizing nutrient use by plants, scientists hope to produce more food while simultaneously reducing the ecological impact of agriculture.
Infrared and near-infrared spectroscopy is replacing traditional chemical procedures to estimate plant nutrients, as the new technique is rapid, less expensive, and non-polluting. However, the ability of spectroscopy to determine nutrient concentrations in rice is relatively unknown.
An international team of agricultural scientists from Europe and Africa, Johnson, Sila, Senthilkumar, Shepherd, and Saito conducted a massive experiment, spanning 20 sub-Saharan African countries to study infrared spectroscopy use in rice.
They collected rice grains and straw samples from 1,628 fields, and analyzed them using three wavelength bands: near-infrared (NIR) 7498–4000 cm−1, mid-infrared (MIR) 4000–600 cm−1, and a combination of NIR-MIR, 7498–600 cm−1.
They wanted to establish the effects of agro-ecological zones and production systems on nutrient concentrations in rice grains and straw.
Second derivative spectra were used to predict six macronutrients -N, P, K, Ca, Mg, and S, and seven micronutrients -Na, Fe, Mn, B, Cu, Mo, and Zn, using a partial least-squares regression (PLSR) model.
The scientists successfully developed chemometric models able to predict concentrations of seven of the nutrients N, P, K, Ca, Mg, Mn, and Cu, accurately, while predictions of S, Fe, and B, were deemed satisfactory, but required further improvement.
NIR was best able to predict three nutrient concentrations, MIR only one, and the combination NIR-MIR six nutrients. Hence the scientists recommend NIR-MIR as a cost-effective means of analyzing rice quality.
Nutrient concentrations varied both in rice and straw. The variations depended on both agricultural zones and production methods. Irrigated lowland fields produced rice with the highest NPK concentrations compared with rice in rainfed uplands and lowlands.
Straw from all three production systems were found to have K deficiencies, while P was lacking in straw from rainfed uplands. Overall, straw showed a 2% N, 16% P, and 16% K deficiency.
The scientists also concluded identified soil attributes, rice productivity, and nutrient use, as areas of further study before they can confidently make site-specific recommendations for fertilizer use.
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Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
Ayour, J., Alahyane, A., Harrak, H., Neffa, M., Taourirte, M., & Benichou, M. (2021). Assessment of Nutritional, Technological, and Commercial Apricot Quality Criteria of the Moroccan Cultivar “Maoui” Compared to Introduced Spanish Cultivars “Canino” and “Delpatriarca” towards Suitable Valorization. Journal of Food Quality, vol. 2021, Article ID 6679128, 12 pages, https://doi.org/10.1155/2021/6679128
Huang, S., Ding, M., Roelfsema, et al. (2021). Optogenetic control of the guard cell membrane potential and stomatal movement by the light-gated anion channel GtACR1, Science Advances, 7 (28), DOI: 10.1126/sciadv.abg4619
Johnson, J. M., Sila, A., Senthilkumar, K., Shepherd, K.D., & Saito, K. (2021). Application of infrared spectroscopy for estimation of concentrations of macro – and micronutrients in rice in sub-Saharan Africa. Field Crops Research, 270 (1), 108222,ISSN 0378-4290.
Kinane, S.M., Montes, C.R., Albaugh, T.J., & Mishra, D.R. (2021). A Model to Estimate Leaf Area Index in Loblolly Pine Plantations Using Landsat 5 and 7 Images. Remote Sens., 13, 1140. https://doi.org/10.3390/rs13061140
Najjar, K.; Abu-Khalaf, N. Non-Destructive Quality Measurement for Three Varieties of
Tomato Using VIS/NIR Spectroscopy. Sustainability 2021, 13, 10747. DOI.org/10.3390/su131910747
Owusu-Sekyere, A. (2021) Micronutrients use efficiency and dry matter yield of annual crops as affected by inorganic and organic amendments, Journal of Plant Nutrition, 44:15, 2245-2257, DOI: 10.1080/01904167.2021.1889586
Roman, V.J., van de Zedde, R., Peller, J., Visser, R. G. F., van der Linden, C.G., & van Loo, E.N. (2021). High-Resolution Analysis of Growth and Transpiration of Quinoa Under Saline Conditions. Frontiers in Plant Science, 12, DOI=10.3389/fpls.2021.634311
Shehata, S.A.; Abdelrahman, S.Z.; Megahed, M.M.A.; Abdeldaym, E.A.; El-Mogy,
M.M.; Abdelgawad, K.F. Extending Shelf Life and Maintaining Quality of
Tomato Fruit by Calcium Chloride, Hydrogen Peroxide, Chitosan, and
Ozonated Water. Horticulturae 2021, 7, 309. https://doi.org/10.3390/
Universität Würzburg. (2021, Sept, 7). Remote Control for Plants. Retrieved from https://www.uni-wuerzburg.de/en/news-and-events/news/detail/news/fernbedienung-fuer-pflanzen-1/
Yang, X., Wang, B., & An, S. (2021).Root derived C rather than root biomass contributes to the soil organic carbon sequestration in grassland soils with different fencing years. Plant Soil https://doi.org/10.1007/s11104-021-05144-z
Yao, X., Lan, Y., Liao, L., Huang, Y., Yu,S. Ye, S., & Yang, M. (2021). Effects of nitrogen supply rate on photosynthesis, nitrogen uptake and growth of seedlings in a Eucalyptus/Dalbergia odorifera intercropping system. Plant Biology, https://doi.org/10.1111/plb.13341
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