Which plant traits are most strongly related to post-silking nitrogen uptake in maize under water and/or nitrogen stress?

The impact of grain yield on post-silking N uptake (PostN) in maize has been a major focus of previous studies, although results are mixed as to the direction and magnitude of the relationship between these two variables. The objective of this study was to understand how grain yield and other plant traits interact with exogenous N and water availability to regulate PostN in maize. In a greenhouse experiment, maize was subjected to high or low levels of N and water supply pre-silking during vegetative growth, which created large variations in source and sink components such as ear size and leaf area. Notably, these large differences in source and sink components were generated not by cutting off plant organs but instead by relying on maize response to vegetative-stage N and water stress. These plants were then subject to high and low levels of N and water supply post-silking, and the relationship between plant traits and PostN was characterized. Final grain yield was irrevocably reduced in the treatments where pre-silking water stress occurred compared to the well-watered pre-silking treatments (30 g plant-1-1 vs. 106 g plant-1). Because of the reduced ear sink strength in the treatments experiencing pre-silking water stress, post-silking biomass (PostBM) and PostN accumulated in vegetative organs. This resulted in greater PostN at maturity in the lower yielding treatments when post-silking water and/or N stress occurred (1.1 vs. 0.6 g N plant-1). Due to the shift in assimilate and N partitioning towards vegetative organs, leaf CER and root dry weight during grain-fill were better maintained in the lower yielding treatments. We conclude that while biomass accumulation (PostBM) regulates PostN, under post-silking N or water stress, shifting sink organs from the grain to vegetative structures increases PostN by improving vegetative organ function and enhancing post-silking source-sink ratios.

Luxury Vegetative Nitrogen Uptake in Maize Buffers Grain Yield Under Post-silking Water and Nitrogen Stress: A Mechanistic Understanding.

During vegetative growth maize can accumulate luxury nitrogen (N) in excess of what is required for biomass accumulation. When post-silking N uptake is restricted, this luxury N may mitigate N stress by acting as an N reserve that buffers grain yield and maintains plant function. The objective of this study was to determine if and how luxury accumulation of N prior to silking can buffer yield against post-silking N and/or water stress in maize. In a greenhouse experiment, maize was grown in high (Nveg) and low (nveg) N conditions during vegetative growth. The nveg treatment did not affect biomass accumulation or leaf area by silking but did accumulate less total N compared to the Nveg treatment. The Nveg treatment generated a reserve of 1.1 g N plant-1. Plants in both treatments were then subjected to water and/or N stress after silking. 15N isotope tracers were delivered during either vegetative or reproductive growth to measure N remobilization and the partitioning of post-silking N uptake with and without a luxury N reserve. Under post-silking N and/or water stress, yield was consistently greater in Nveg compared to nveg due to a reduction in kernel abortion. The Nveg treatment resulted in greater kernel numbers and increased N remobilization to meet grain N demand under post-silking N stress. Luxury N uptake at silking also improved leaf area longevity in Nveg plants compared to nveg under post-silking N stress, leading to greater biomass production. While post-silking N uptake was similar across Nveg and nveg, Nveg plants partitioned a greater proportion of post-silking N to vegetative organs, which may have assisted with the maintenance of leaf function and root N uptake capacity. These results indicate that N uptake at silking in excess of vegetative growth requirements can minimize the effect of N and/or water stress during grain-fill.

Long-term Trends in Corn Yields and Soil Carbon under Diversified Crop Rotations.

Agricultural practices such as including perennial alfalfa ( L.), winter wheat ( L.), or red clover ( L.) in corn ( L.) rotations can provide higher crop yields and increase soil organic C (SOC) over time. How well process-based biogeochemical models such as DeNitrification-DeComposition (DNDC) capture the beneficial effects of diversified cropping systems is unclear. To calibrate and validate DNDC for simulation of observed trends in corn yield and SOC, we used long-term trials: continuous corn (CC) and corn-oats ( L.)-alfalfa-alfalfa (COAA) for Woodslee, ON, 1959 to 2015; and CC, corn-corn-soybean [ (L.) Merr.]-soybean (CCSS), corn-corn-soybean-winter wheat (CCSW), corn-corn-soybean-winter wheat + red clover (CCSW+Rc), and corn-corn-alfalfa-alfalfa (CCAA) for Elora, ON, 1981 to 2015. Yield and SOC under 21st century conditions were projected under future climate scenarios from 2016 to 2100. The DNDC model was calibrated to improve crop N stress and was revised to estimate changes in water availability as a function of soil properties. This improved yield estimates for diversified rotations at Elora (mean absolute prediction error [MAPE] decreased from 13.4-15.5 to 10.9-14.6%) with lower errors for the three most diverse rotations. Significant improvements in yield estimates were also simulated at Woodslee for COAA, with MAPE decreasing from 24.0 to 16.6%. Predicted and observed SOC were in agreement for simpler rotations (CC or CCSS) at both sites (53.8 and 53.3 Mg C ha for Elora, 52.0 and 51.4 Mg C ha for Woodslee). Predicted SOC increased due to rotation diversification and was close to observed values (58.4 and 59 Mg C ha for Elora, 63 and 61.1 Mg C ha for Woodslee). Under future climate scenarios the diversified rotations mitigated crop water stress resulting in trends of higher yields and SOC content in comparison to simpler rotations.

Greenhouse gas emissions and production cost of ethanol produced from biosyngas fermentation process.

Life cycle (LC) of ethanol has been evaluated to determine the environmental and economical viability of ethanol that was derived from biosyngas fermentation process (gasification-biosynthesis). Four scenarios [S1: untreated (raw), S2: treated (torrefied); S3: untreated-chemical looping gasification (CLG), S4: treated-CLG] were considered. The simulated biosyngas composition was used in this evaluation process. The GHG emissions and production cost varied from 1.19 to 1.32 kg-CO2 e/L and 0.78 to 0.90$/L, respectively, which were found to be dependent on the scenarios. The environmental and economical viability was found be improved when untreated feedstock was used instead of treated feedstock. Although the GHG emissions slightly reduced in the case of CLG process, production cost was nominally increased because of the cost incurred by the use of CaO. This study revealed that miscanthus is a promising feedstock for the ethanol industry, even if it is grown on marginal land, which can help abate GHG emissions.

C4 bioenergy crops for cool climates, with special emphasis on perennial C4 grasses.

There is much interest in cultivating C4 perennial plants in northern climates where there is an abundance of land and a potential large market for biofuels. C4 feedstocks can exhibit superior yields to C3 alternatives during the long warm days of summer at high latitude, but their summer success depends on an ability to tolerate deep winter cold, spring frosts, and early growth-season chill. Here, we review cold tolerance limits in C4 perennial grasses. Dozens of C4 species are known from high latitudes to 63 °N and elevations up to 5200 m, demonstrating that C4 plants can adapt to cold climates. Of the three leading C4 grasses being considered for bioenergy production in cold climates--Miscanthus spp., switchgrass (Panicum virgatum), and prairie cordgrass (Spartina pectinata)--all are tolerant of cool temperatures (10-15 °C), but only cordgrass tolerates hard spring frosts. All three species overwinter as dormant rhizomes. In the productive Miscanthus×giganteus hybrids, exposure to temperatures below -3 °C to -7 °C will kill overwintering rhizomes, while for upland switchgrass and cordgrass, rhizomes survive exposure to temperatures above -20 °C to -24 °C. Cordgrass emerges earlier than switchgrass and M. giganteus genotypes, but lacks the Miscanthus growth potential once warmer days of late spring arrive. To enable C4-based bioenergy production in colder climates, breeding priorities should emphasize improved cold tolerance of M.×giganteus, and enhanced productivity of switchgrass and cordgrass. This should be feasible in the near future, because wild populations of each species exhibit a diverse range of cold tolerance and growth capabilities.