Trade-off of leaf-scale resource-use efficiencies along the vertical canopy of the subtropical forest

Leaf resource-use efficiencies are key indicators of plant adaptability to climate change, as they depend on both photosynthetic carbon assimilation and available resources. However, accurately quantifying the response of the coupled carbon and water cycles is challenging due to the canopy vertical variability in resource-use efficiencies, which introduces greater uncertainty into the calculations. Here we experimented to ascertain the vertical variations of leaf resource-use efficiencies along three canopy gradients of coniferous (Pinus elliottii Engelmann.) and broad-leaved (Schima Superba Gardn & Champ.) forests over one year in the subtropical region of China. The efficiency of water (WUE), and nitrogen (NUE) showed higher values in the top canopy level for the two species. The maximum efficiency of light (LUE) occurred in the bottom canopy level for both species. The impact of photosynthetic photon flux density (PPFD), leaf temperature (T_leaf), and vapor pressure deficit (VPD) on leaf resource-use efficiencies varied with canopy gradients in slash pine and schima superba. We also observed a trade-off between NUE and LUE for slash pine and between NUE and WUE for schima superba. Moreover, the variation in the correlation between LUE and WUE indicated a change in resource-use strategies for slash pine. These results emphasize the significance of vertical variations in resource-use efficiencies to enhance the prediction of future carbon-water dynamics in the subtropical forest.

CowNflow: A dataset on nitrogen flows and balances in dairy cows fed maize forage or herbage-based diets

Diet and animal characteristics have a significant impact on the nitrogen (N)-use efficiency of dairy cows. A dataset (CowNflow) was built that compiles 28 N-balance experiments with Holstein dairy cows from 1983 to 2019, corresponding to 414 individual N flows, for a wide range of diets and animal characteristics. The dataset is composed of six Microsoft® Excel files that correspond to six levels of information. The main file, “CowNflow_6_Cow_measurements” reports individual weekly measurements of dry matter intake, daily faeces and urine excretion, milk production and composition, cow characteristics, and chemical composition of diets, faeces, urine, and milk. These raw data were used to calculate the N-balance, N-use efficiency, and nutrients’ in vivo total-tract digestibility. The experiments, conducted under standardised conditions, had multiple aims and offered a wide range of diets. Consequently, each diet is classified according to the main forage offered, resulting in six diet types: (1) maize forage (maize silage or dehydrated maize) alone, (2) maize forage and dehydrated lucerne, (3) maize forage and grass hay, (4) maize forage and freshly cut herbage, (5) freshly cut herbage alone, and (6) dehydrated herbage. The other five Excel files provide supplementary information at larger scales and describe experiment characteristics, experimental treatments, offered feeds along with their chemical composition, ingredient composition of compound feeds, and cow characteristics. This dataset can be used to better understand animal and dietary determinants of N-use efficiency and the origin of N losses to the environment, to identify feeding strategies that reduce protein-rich concentrate use, and to decrease environmental impacts of dairy farming with a variety of foraging systems.

New insights into gibberellin signaling in regulating plant growth-metabolic coordination

The Green Revolution of the 1960s boosted cereal crop yields in part through widespread adoption of semi-dwarf plant varieties, many of which were later found to have mutations in either gibberellins (GAs) homeostasis or DELLA proteins. GA is essential for plant growth and developmental regulation and plays an important role in improving crop plant architecture for enhanced grain yield under high nitrogen conditions. A complex regulatory network governs the spatially and temporally controlled genes expression through integrative GA signaling in response to multiple endogenous and environmental cues. In this review, we summarize current advances in understanding the molecular mechanisms of DELLA-dependent and DELLA-independent GA signaling pathways and their contributions to plant developmental and metabolic adaptations to changes in nitrogen availability. The progress in molecular understanding of the plant growth-metabolic coordination will facilitate breeding strategies for future sustainable agriculture and a new Green Revolution.

Nitrous oxide emissions from cow urine patches in an intensively managed grassland: Influence of nitrogen loading under contrasting soil moisture

In dairy grazing systems, livestock urine patches are hotspots that contribute to global warming, both directly through nitrous oxide (N₂O) emissions, and indirectly, through nitrate leaching. However, under warm-dry temperate environments, N₂O emission factors (EFs) have not been thoroughly evaluated, accounting for the influence of urinary nitrogen (N) concentration and urine volume, and emissions measurement approach through different urine application methods. Here we quantified and compared N₂O emissions and EFs on a moderately well-drained sandy loam soil from urine patches established in naturally expanding effective area (NEEA), representing urine volumes of 2, 3 and 4 L m^-2 (equivalent to urine -N loadings of 141, 211 and 282 kg N ha^-1), and using the uniformly wetted area (UWA) with urine applied at 10 L m^-2 (709 kg N ha^-1), under two different soil moistures (below field capacity, BFC; field capacity, FC). The results showed that cumulative N₂O emissions in the NEEA urine patches were 0.36-0.52 kg N₂O-N ha^-1 over 146 days (early-winter to late-spring). In the UWA urine patches, cumulative N₂O emissions were 2.3 times higher at FC (1.96 kg N₂O-N ha^-1) than BFC (0.87 kg N₂O-N ha^-1). The EFs were similar between UWA (0.09%) and NEEA (0.07-0.10%) at BFC but were significantly higher (P < 0.05-0.1) in UWA (0.26%) than NEEA (0.09-0.16%) at FC. The EFs in NEEA were not affected by urine-N loadings under BFC and FC, ranging between 0.07 and 0.16%. The relatively high versus low urine-N loadings in NEEA enhanced pasture herbage and N-uptake responses under both soil moistures. However, there were no differences in apparent N-use efficiency (ranging from 27 to 39%) across the treatments. The EFs observed in this study are much lower than the existing Australian cattle urine annual EF of 0.4%, and further examination to determine a more accurate EF for the industry is required.

Growth and nitrogen metabolism are associated with nitrogen-use efficiency in cotton genotypes

Crops, including cotton, are sensitive to nitrogen (N) and excessive use can lead to an increase in production costs and environmental problems. We hypothesized that the use of cotton genotypes with substantial root systems and high genetic potentials for nitrogen-use efficiency (NUE) would best address these problems. Therefore, the interspecific variations and traits contributing to NUE in six cotton genotypes having contrasting NUEs were studied in response to various nitrate concentrations. Large genotypic variations were observed in morphophysiological and biochemical traits, especially shoot dry weight, root traits, and N-assimilating enzyme levels. The roots of all the cotton genotypes were more sensitive to low-than high-nitrate concentrations, and the genotype CCRI-69 had the largest root system irrespective of the nitrate concentration. The root morphological traits were positively correlated with N-utilization efficiency and were more affected by genotype than nitrate concentration. Conversely, growth and N-assimilating enzyme levels were more affected by nitrate concentration and were positively correlated with N-uptake efficiency. Based on shoot dry weight, CCRI-69 and XLZ-30 were identified as N-efficient and N-inefficient genotypes, respectively, and these results were confirmed by their contrasting root systems, N metabolism, and NUEs. In the future, multi-omics techniques will be performed to identify key genes/pathways involved in N metabolism, which may have the potential to improve root architecture and increase NUE.

Balancing indicators for sustainable intensification of crop production at field and river basin levels

Adequate tools for evaluating sustainable intensification (SI) of crop production for agro-hydrological system are not readily available. Building on existing concepts, we propose a framework for evaluating SI at the field and river basin levels. The framework serves as a means to assess and visualise SI indicator values, including yield, water-use efficiency and nitrogen-use efficiency (NUE), alongside water and nitrogen surpluses and their effects on water quantity and quality. To demonstrate the SI assessment framework, we used empirical data for both the field level (the Static Fertilization Experiment at Bad Lauchstädt) and the river basin level (the Selke basin, 463 km²) in central Germany. Crop yield and resource use efficiency varied considerably from 1980 to 2014, but without clear trends. NUE frequently fell below the desirable range (<50%), exposing the environment to a large N surplus (>80 kg N ha^-1). For the catchment as a whole, the average nitrate-N concentration (3.6 mg L^-1) was slightly higher than the threshold of 2.5 mg L^-1 nitrate-N in surface water. However, weather and climate-related patterns, due to their effects on transport capacity and dilution, influenced water quantity and quality indicators more than agronomic practices. To achieve SI of crop production in the Selke basin, irrigation and soil moisture management are required to reduce yield variability and reduce N surpluses at field level. In addition, optimum application of fertiliser and manure could help to reduce the nitrate-N concentration below the set water quality standards in the Selke basin. In this way, there is scope for increase in yields and resource use efficiencies, and thus potential reduction of environmental impacts at basin level. We conclude that the framework is useful for assessing sustainable production, by simultaneously considering objectives related to crop production, resource-use efficiency and environmental quality, at both field and river basin levels.

Optimizing plant density and nitrogen application to manipulate tiller growth and increase grain yield and nitrogen-use efficiency in winter wheat

The growth of wheat tillers and plant nitrogen-use efficiency (NUE) will gradually deteriorate in response to high plant density and over-application of N. Therefore, in this study, a 2-year field study was conducted with three levels of plant densities (75 ×10⁴plants ha⁻¹, D1; 300 ×10⁴plants ha⁻¹, D2; 525 ×10⁴plants ha⁻¹, D3) and three levels of N application rates (120 kg N ha⁻¹, N1; 240 kg N ha⁻¹, N2; 360 kg N ha⁻¹, N3) to determine how to optimize plant density and N application to regulate tiller growth and to assess the contribution of such measures to enhancing grain yield (GY) and NUE. The results indicated that an increase in plant density significantly increased the number of superior tillers and the number of spikes per m²(SN), resulting in a higher GY and higher partial factor productivity of applied N (PFP_N). However, there was no significant difference in GY and PFP_N between plant densities D2 and D3. Increasing the N application rate significantly increased the vascular bundle number (NVB) and area (AVB), however, excess N application (N3) did not significantly improve these parameters. N application significantly increased GY, whereas there was a significant decrease in PFP_N in response to an increase in N application rate. The two years results suggested that increasing the plant density (from 75 ×10⁴plants ha⁻¹to 336 ×10⁴plants ha⁻¹) in conjunction with the application of 290 kg N ha⁻¹N will maximize GY, and also increase PFP_N(39.7 kg kg⁻¹), compared with the application of 360 kg N ha⁻¹N. Therefore, an appropriate combination of increased planting density with reduced N application could regulate tiller number and favor the superior tiller group, to produce wheat populations with enhanced yield and NUE.

Impact of intercropping on the coupling between soil microbial community structure, activity, and nutrient-use efficiencies

Sugarcane-soybean intercropping has been widely used to control disease and improve nutrition in the field. However, the response of the soil microbial community diversity and structure to intercropping is not well understood. Since microbial diversity corresponds to soil quality and plant health, a pot experiment was conducted with sugarcane intercropped with soybean. Rhizosphere soil was collected 40 days after sowing, and MiSeq sequencing was utilized to analyze the soil microbial community diversity and composition. Soil columns were used to assess the influence of intercropping on soil microbial activity (soil respiration and carbon-use efficiency: nitrogen-use efficiency ratio). PICRUSt and FUNGuild analysis were conducted to predict microbial functional profiling. Our results showed that intercropping decreased pH by approximately 8.9% and enhanced the soil organic carbon, dissolved organic carbon, and available nitrogen (N) by 5.5%, 13.4%, and 10.0%, respectively. These changes in physicochemical properties corresponded to increased microbial diversity and shifts in soil microbial communities. Microbial community correlated significantly (p < 0.05) with soil respiration rates and nutrient use efficiency. Furthermore, intercropping influenced microbial functions, such as carbon fixation pathways in prokaryotes, citrate cycle (TCA cycle) of bacteria and wood saprotrophs of fungi. These overrepresented functions might accelerate nutrient conversion and control phytopathogens in soil.

Developing Transgenic Agronomic Traits for Crops: Targets, Methods, and Challenges

The last two decades have witnessed a surge of investment by the agricultural biotechnology industry in the development of transgenic agronomic traits. These are traits that improve yield performance by modifying endogenous physiological processes such as energy capture, nutrient utilization, and stress tolerance. In this chapter we provide a foundation for understanding these fundamental processes and then outline approaches that have been taken to use this knowledge for yield improvement. We characterize the current status of product development pipelines in the industry and illustrate the trait discovery process with three important examples-bacterial cold-shock proteins, alanine aminotransferase, and auxin-regulated genes. The challenges with developing and commercializing an agronomic trait product are discussed.

Genetic variation in N-use efficiency and associated traits in Indian wheat cultivars

Nitrogen (N) fertilizer represents a significant cost for the grower and may also have environmental impacts through nitrate leaching and N2O (a greenhouse gas) emissions associated with denitrification. The objectives of this study were to quantify the genetic variability in N-use efficiency (NUE) in Indian spring wheat cultivars and identify traits for improved NUE for application in breeding. Twenty eight bread wheat cultivars and two durum wheat cultivars were tested in field experiments in two years in Maharashtra, India. Detailed growth analysis was conducted at anthesis and harvest including dry matter (DM) and N partitioning. Senescence of the flag leaf was assessed from a visual score every 3-4 days from anthesis to complete flag-leaf senescence and fitted against thermal time to estimate the onset and end of post-anthesis senescence. Grain yield (GY) was reduced under low N (LN) by an average of 1.46 t ha-1 (-28%). Significant N × genotype level interaction was observed for grain yield and NUE. Above-ground N uptake at harvest was reduced from 162 kg N ha-1 under high N (HN) to 85 kg N ha-1 under low N (LN) conditions, while N-utilization efficiency (grain DM yield per unit crop N uptake at harvest; NUtE) increased from 32.7 to 44.6 kg DM kg-1 N. Genetic variation in GY under LN related mainly to variation in N uptake at harvest rather than NUtE; and the N × genotype effect for GY was mainly explained by the interaction for N uptake at harvest. Averaging across years, the linear regression of onset of flag-leaf senescence on GY amongst cultivars was significant under both HN (R2 0.16. p < 0.05) and LN (R2 0.21, p < 0.05) conditions. Onset of flag-leaf senescence was positively associated with N uptake at anthesis under HN (R2 0.34, p < 0.001) and LN (R2 0.22, p < 0.01) conditions. Flag-leaf senescence timing was not associated with post-anthesis N uptake. It is concluded that increased N accumulation at anthesis was correlated with flag-leaf senescence timing and that N accumulation at anthesis is an important trait for enhancing grain yield and NUE of wheat grown under low to moderate N supply in India.

Forest growth along a rainfall gradient in Hawaii: Acacia koa stand structure, productivity, foliar nutrients, and water- and nutrient-use efficiencies

We tested whether variation in growth of native koa (Acacia koa) forest along a rainfall gradient was attributable to differences in leaf area index (LAI) or to differences in physiological performance per unit of leaf area. Koa stands were studied on western Kauai prior to Hurricane Iniki, and ranged from 500 to 1130 m elevation and from 850 to 1800 mm annual precipitation. Koa stands along the gradient had basal area ranging from 8 to 42 m²/ha, LAI ranging from 1.4 to 5.4, and wood increment ranging from 0.7 to 7.1 tonnes/ha/year. N, P, and K contents by weight of sun leaves (phyllodes) were negatively correlated with specific leaf mass (SLM, g m^-2) across sites; on a leaf area basis, N increased whereas P and K decreased with SLM. LAI, aboveground woody biomass increment, and production per unit leaf area (E) increased as phyllode δ¹³C became more negative. The δ¹³C data suggested that intrinsic water-use efficiency (ratio of assimilation to conductance) increased as water availability decreased. In five of the six sites, phyllode P contents increased as LAI increased, but biomass increment and E were not correlated with phyllode nutrient contents, suggesting that productivity was limited more by water than by nutrient availability. Because vapor pressure deficits increased with decreasing elevation, actual water-use efficiency (ratio of assimilation to transpiration) was lower at drier, low-elevation sites. There was a trade-off between intrinsic water-use efficiency and production per unit of canopy N or P across the gradient. In summary, koa responds to water limitation both by reducing stand LAI and by adjusting gas exchange, which results in increased intrinsic water-use efficiency but decreased E.