high-N Environments Research Articles

Accelerated Genetic Gains in Early-Maturing Maize Hybrids following Three Periods of Genetic Enhancement for Grain Yield under Low and High Soil-Nitrogen Environments.

Maize (Zea mays L.) is an important staple, as well as cash crop, in sub-Saharan Africa (SSA). However, its production is severely constrained by low soil nitrogen (low N). Fifty-four early-maturing hybrids developed during three breeding periods, (2008–2010, 2011–2013 and 2014–2016) were evaluated under low (30 kg ha−1) and high (120 kg ha−1) soil nitrogen (N) in Ile-Ife and Mokwa, Nigeria, from 2017 to 2019. The study was designed to (i) determine the genetic gains in grain yield of the early-maturing maize hybrids developed during the three breeding periods, (ii) determine the relationship between grain yield and other agronomic traits and (iii) identify the highest-yielding and most stable hybrids under low- and high-N environments. The 54 hybrids were evaluated using a 6 × 9 lattice design with three replications. Mean squares for hybrids were significant for measured traits under low- and high-N environments, except the mean squares for stalk lodging and EPP under low N. Annual genetic gains in grain yield were 75 kg ha−1 year−1 (2.91%) and 55 kg ha−1 year−1 (1.33%) under low- and high-N environments, respectively, indicating that substantial gains were achieved in the genetic enhancement of the early-maturing hybrids. The hybrids TZdEI 314 × TZdEI 105, TZdEI 378 × TZdEI 173, ENT 12 × TZEI 48 and TZdEI 352 × TZdEI 315 were identified as the highest-yielding and most stable across test environments and should be tested extensively on farms and commercialized in SSA.

Nitrate-induced CLE35 signaling peptides inhibit nodulation through the SUNN receptor and miR2111 repression.

Legume plants form nitrogen (N)-fixing symbiotic nodules when mineral N is limiting in soils. As N fixation is energetically costly compared to mineral N acquisition, these N sources, and in particular nitrate, inhibit nodule formation and N fixation. Here, in the model legume Medicago truncatula, we characterized a CLAVATA3-like (CLE) signaling peptide, MtCLE35, the expression of which is upregulated locally by high-N environments and relies on the Nodule Inception-Like Protein (NLP) MtNLP1. MtCLE35 inhibits nodule formation by affecting rhizobial infections, depending on the Super Numeric Nodules (MtSUNN) receptor. In addition, high N or the ectopic expression of MtCLE35 represses the expression and accumulation of the miR2111 shoot-to-root systemic effector, thus inhibiting its positive effect on nodulation. Conversely, ectopic expression of miR2111 or downregulation of MtCLE35 by RNA interference increased miR2111 accumulation independently of the N environment, and thus partially bypasses the nodulation inhibitory action of nitrate. Overall, these results demonstrate that the MtNLP1-dependent, N-induced MtCLE35 signaling peptide acts through the MtSUNN receptor and the miR2111 systemic effector to inhibit nodulation.

Provenance differences in functional traits and N: P stoichiometry of the leaves and roots of Pinus tabulaeformis seedlings under N addition

To study the response of Pinus tabulaeformis Carrière, an endemic species in China, to N deposition and the adaptive mechanisms involved, the leaves and fine roots functional traits and N:P stoichiometry of Beijing provenances seeding (BY), Shanxi provenances seeding (SY), and Inner Mongolia provenances seeding (NY) were investigated in the this study. Five levels of artificial N addition were applied to seedlings of different provenance for 3 years. Our results showed that, at high-N levels, the specific leaf area of SY plants decreased significantly, while leaf weight ratio increased, which indicated that SY plants have higher light and nutrient absorption capacity under high-N deposition. Leaf total N, leaf N:P ratio, root total N, and root N:P ratio of BY plants increased at medium-N levels, indicating that properly N addition promoted the accumulation of N in BY plants, while N absorption in SY and NY plants was inhibited. Furthermore, N addition promoted the accumulation of P in SY leaves and fine roots. From the adaptation mechanism of P. tabulaeformis, N addition promoted the utilization of nutrients in BY fine roots, which was conducive to the growth of underground parts and the accumulation of biomass. These results also showed that BY plants had adapted to low-N environments. At the same time, P investment in SY leaves and fine roots increased in high-N environments to meet the demands of growth, which also demonstrated adaptation to high-N environments. Owing to the differences in the adaptation mechanism of plants to the environment, the adaptation strategies of P. tabulaeformis of different provenances was significantly different under different nitrogen depositions. This study further provides theoretical foundation for plantation management and vegetation restoration.

Performance of maize populations under different nitrogen rates in northern Ghana

This study evaluated grain yield performance, stability and agronomic nitrogen-use efficiency (AE) of twelve maize populations under three nitrogen (N) rates at two locations in the Guinea and Sudan savannah zones of Ghana in 2014 and 2015. The N rates used were 0, 30, and 90 kg N ha−1. Computations were made for grain yield and AE. Populations × nitrogen interactions were significant for grain yield and AE at the three N rates. The mean yield of the populations under 0, 30, and 90 kg N ha−1 were 1.42, 4.12, and 6.80 t ha−1, respectively. Mean AE of the populations under low-N and high-N was 90.34 and 59.73 kg kg−1, respectively. Populations LNP-Syn-W, TZPB-LN-Syn and IWD-C2-Syn-F2 were efficient under both low-N and high-N inputs and produced 229.17 kg ha−1 and 572.5 kg ha−1 more grains than the average yield of all the populations under low-N and high-N, respectively. The results of this study indicated that the highest response to selection of N-efficient maize populations is achieved under low-N when the grain yield reduction at low-N is 39% of those of high-N environments.

Performance of tropical early-maturing maize cultivars in multiple stress environments

Maize (Zea mays L.) production in west Africa (WA) is constrained by drought, Striga hermonthica infestation and low soil nitrogen (N). Maize varieties resistant to Striga, drought, and low N are ideal for WA, but genotype × environment interaction on these traits are usually significant due to differential responses of cultivars to growing conditions. Three studies were conducted from 2007 to 2009 at five locations in Nigeria to evaluate the performance of selected early-maturing cultivars under drought stress versus well-watered, Striga-infested versus Striga-free, and in low- versus high-N environments. Drought stress reduced grain yield by 44%, Striga infestation by 65%, and low N by 40%. GGE biplot analysis showed that the genotypes TZE-W DT STR C4, Tillering Early DT, TZE-W DT STR QPM C0 and TZE-Y DT STR C4 performed relatively well in all study environments. TZE-W DT STR C4 and TZE Comp3 C1F2 were outstanding under drought, TZE-W DT STR C4, EVDT-W 99 STR QPM C0 and TZE-W DT STR QPMC0 under Striga infestation and Tillering Early DT, EVDT 97 STRC1, TZE-W DT STR C4, and TZE Comp3 C3 under N deficiency. Maize productivity in WA can be significantly improved by promoting cultivation of genotypes that combine high resistance/tolerance to Striga and drought with improved N-use efficiency.

Microbial Mineralization of Organic Nitrogen Forms in Poultry Litters

Ammonia volatilization from the mineralization of uric acid and urea has a major impact on the poultry industry and the environment. Dry acids are commonly used to reduce ammonia emissions from poultry houses; however, little is known about how acidification affects the litter biologically. The goal of this laboratory incubation was to compare the microbiological and physiochemical effects of dry acid amendments (Al+Clear, Poultry Litter Treatment, Poultry Guard) on poultry litter to an untreated control litter and to specifically correlate uric acid and urea contents of these litters to the microbes responsible for their mineralization. Although all three acidifiers eventually produced similar effects within the litter, there was at least a 2-wk delay in the microbiological responses using Poultry Litter Treatment. Acidification of the poultry litter resulted in >3 log increases in total fungal concentrations, with both uricolytic (uric acid degrading) and ureolytic (urea degrading) fungi increasing by >2 logs within the first 2 to 4 wk of the incubation. Conversely, total, uricolytic, and ureolytic bacterial populations all significantly declined during this same time period. While uric acid and urea mineralization occurred within the first 2 wk in the untreated control litter, acidification resulted in delayed mineralization events for both uric acid and urea (2 and 4 wk delay, respectively) once fungal cell concentrations exceeded a threshold level. Therefore, fungi, and especially uricolytic fungi, appear to have a vital role in the mineralization of organic N in low-pH, high-N environments, and the activity of these fungi should be considered in best management practices to reduce ammonia volatilization from acidified poultry litter.

Responses of coastal phytoplankton populations to nitrogen additions: dynamics of cell-associated dimethylsulfoniopropionate (DMSP), glycine betaine (GBT), and homarine

Dimethylsulfoniopropionate (DMSP) and glycine betaine (GBT) are organic osmolytes abundant in many marine phytoplankton. Herein, we field tested for the first time the hypothesis that GBT production might be favored over DMSP in natural phytoplankton populations growing in high-N environments or when N is added to a system. Concentrations of particulate DMSP (DMSPp; 15–45 nmol·L–1) were equal to, or greater than, concentrations of particulate GBT (GBTp; 0–15 nmol·L–1) in the upper water column. Homarine, another N-containing osmolyte, was detected at lower levels in all samples. These are the first reported values of GBTp, and homarine in seawater. During N enrichment experiments, no consistent pattern of response in the DMSP pool resulted. Under N stress, nitrate addition either caused DMSP to be released but without an equivalent increase in GBT or DMSP dynamics were not affected but GBT increased. In populations under less N stress, GBT levels were similar to those of DMSPpthroughout the experiments. Homarine levels remained low at all times. We conclude that no simple switch between DMSP and GBT occurs as a function of N availability in natural populations. Variable responses to N supply probably resulted from differences in species composition and physiological state of the populations present.

Improvement for tolerance to low soil nitrogen in tropical maize III. Variation in yield across environments

Abstract When improving grain yield of maize (Zea mays L.) grown under low soil N by recurrent selection, it is desirable to maintain or increase the stability of performance across sites differing in N status. The objective of this study was to identify the possible causes of increase variation in grain yield with selection for tolerance to low soil N in four cycles of selection (C0 to C3) of the lowland tropical maize population, Across 8328 BN, when grown in 12 irrigated environments characterized by different radiation and N availabilities. Yield components and patterns of biomass and N partitioning were examined. Correlation analysis of the data collected indicated that some relationships among traits thought to be important to performance differed in magnitude and sign among environments. For example, a positive correlation was observed between grain yield and preflowering N accumulation in the high-N environments, but no association was observed among these traits at low N. Correlations also differed significantly among seasons within an N level for some traits. For example, the correlation between final grain N concentration and N floret−1 at flowering under low N was 0.97 (P An analysis of yield components and N concentrations in plant parts indicated that yield variation in C1 (the selection cycle which had the greatest variation among environments) was associated with an over-investment in preflowering vegetative biomass, without a concomitant increase in post-flowering grain sink size. By C3, the number of kernels plant−1 had been increased, but yield apparently was limited by inadequate source capacity in the latter stages of grain-filling. Cycle 3 also produced 25% more root biomass than C0 when grown with adequate N supply in pots, while aboveground biomass increased by a smaller proportion (9%). Changes in biomass partitioning to roots may be an important adaptation to low-N environments. These results indicate that seasonal differences in the timing and magnitude of N and C supply play a large role in determining the adaptive value of a given trait, even when environments may be similar in the amount of N applied to, or absorbed by, the under nonlimiting N levels, and extensive testing in environments differing in C and N abundance seems essential to establishing progress from such breeding schemes. In addition, more effort to quantify the extent and timing of N stress in each season appears justified.

Predicting the relative effectiveness of direct versus indirect selection for oat yield in three types of stress environments

In breeding crop varieties for stress environments, it must be decided whether to select directly, in the presence of stress, or indirectly, in a nonstress environment. The relative effectiveness of these two strategies depends upon the genetic correlation (r g ) between yield in stress and nonstress environments and upon heritability in each. These parameters were estimated for grain yield of 116 random oat lines grown in nonstress, P-deficient, N-deficient, and late-planted environments. Estimates of r g between yield in nonstress and yield in P-deficient, N-deficient, and late-planted environments were 0.52±0.24, 1.08±0.16, and 0.06±0.24, respectively. No consistent relationship between heritability and environment mean yield was observed. Direct selection in the presence of stress was predicted to be superior for yield in low-P and late-planted environments, but indirect selection in high-N environments was predicted to be as effective as direct selection in producing yield gain in low-N environments. These results confirm that neither high-yield environments nor environments in which the heritability of yield is maximized are necessarily optimum when the goal is to maximize yield gain in stress environments.