Improving maize carbon and nitrogen metabolic pathways and yield with nitrogen application rate and nitrogen forms.

Reduced fertilizer efficiency caused by excessive use of nitrogen (N) fertilizer is a major problem in agriculture and a hot topic of research. Most studies have focused on the effect of N application rate on N efficiency, whereas there are limited studies on changing the N form to improve N yield and efficiency. Here, the effects of different N application rates and nitrate-to-ammonium N ratios on post-anthesis carbon (C) and N metabolism and maize yield under shallow-buried drip irrigation were investigated. Two rates of N application (210 kg·ha-1 (NA1) and 300 kg·ha-1 (NA2)) and three nitrate-to-ammonium N ratios (2:1 (NF1), 3:1 (NF2), and 4:1 (NF3)) were utilized. Post-anthesis photosynthetic characteristics, activities of key enzymes in photosynthetic C and N metabolism, nonstructural carbohydrate content, post-anthesis N accumulation and transportation, yield, and N-use efficiency were determined. At both N application rates, NF2 treatment enhanced photosynthetic activity in the ear-leaf at silking stage and promoted key enzyme activities of C and N metabolic pathways, compared with NF1 and NF3. Furthermore, NF2 significantly increased nonstructural carbohydrate accumulation (4.00-64.71%), post-anthesis N accumulation and transportation (11.00-38.00%), and grain yield (2.60-13.08%). No significant differences between NA1 and NA2 were observed under NF2 in most of the measured variables; however, NA1 had higher N-use efficiency. Thus, the optimal treatment under shallow-buried drip irrigation was a N application rate of 210 kg ha-1 and a nitrate-to-ammonium N ratio of 3:1. These findings provide theoretical guidance on appropriate N applications for high-yield maize production.

A microbial ecosystem enhanced by regulating soil carbon and nitrogen balance using biochar and nitrogen fertiliser five years after application.

The indiscriminate use of nitrogen fertiliser (NF) is a obstruction to improve soil quality and crop yields. However, the effect of biochar and NF on soil microbial ecosystem (SME) and crop yields is unknown. A five-year field experiment in China aimed to evaluate the effects of biochar and nitrogen fertiliser (NF) combination on soil structure, C-to-N ratio (CNR), microbial biomass, and spring maize yield. Biochar and NF were applied at different rates, and the combined application resulted in a soil solid-liquid-gas ratio closer to the ideal value. The use of biochar alone and in combination with NF significantly increased soil's C, N, and CNR. A moderate application of biochar and NF resulted in favourable biological and chemical properties of the soil. The application of biochar and NF at moderate levels led to an increase in SME, with the B8N150 producing the highest yield. The highest yield of B8N150 represents a 24.25% increase compared to the unfertilized control and a 9.04% increase compared to B0N150. Moderate use of biochar and NF could be beneficial in areas with similar climatic conditions.

Impact of Drip Irrigation and Nitrogen Fertilization on Soil Microbial Diversity of Spring Maize.

Given the shortage of water resources and excessive application of nitrogen fertilizers in irrigated areas, we explored the effect of water−nitrogen coupling on soil microbial diversity in maize fields irrigated using shallow buried droppers. A field experiment (split-plot design) was used with irrigation amounts set at 40%, 50%, and 60% of the conventional amount; furthermore, 13 water and nitrogen coupling treatments were designed. The secondary area was the nitrogen application level, corresponding to 50%, 70%, and the original conventional application amounts. The results showed that the effect of irrigation amount on bacterial community composition was greater than that of nitrogen, whereas the effect of nitrogen on fungi was greater than that on bacteria. No significant difference was detected in the α diversity index or species richness of bacteria and fungi. Available phosphorus and organic carbon contents significantly correlated with the community structure of soil bacteria (p < 0.05). The relative abundances of bacteria and fungi were stable with the decrease of nitrogen application rate at the irrigation rate of 2000 m3 ha−1. With the decrease of irrigation amount, the relative abundance of bacteria and fungi was stable under the treatment of 210 kg ha−1 nitrogen fertilizer. Moreover, the relative abundance of nitrogen-fixing bacteria related to the nitrogen cycle was increased by irrigation of 2000 m3 ha−1 and nitrogen application of 210 kg ha−1. Moderate reduction of subsequent N supply should be as a prior soil management option in a high N input agroecosystem.

Melatonin and Indole-3-Acetic Acid Synergistically Regulate Plant Growth and Stress Resistance.

Plant growth and development exhibit plasticity, and plants can adapt to environmental changes and stress. Various phytohormones interact synergistically or antagonistically to regulate these responses. Melatonin and indole-3-acetic acid (IAA) are widespread across plant kingdom. Melatonin, an important member of the neuroendocrine immune regulatory network, can confer autoimmunity and protect against viral invasion. Melatonin functions as a plant growth regulator and biostimulant, with an important role in enhancing plant stress tolerance. IAA has a highly complex stress response mechanism, which participates in a series of stress induced physiological changes. This article reviews studies on the signaling pathways of melatonin and IAA, focusing on specific regulatory mechanisms. We discuss how these hormones coordinate plant growth and development and stress responses. Furthermore, the interactions between melatonin and IAA and their upstream and downstream transcriptional regulation are discussed from the perspective of modulating plant development and stress adaptation. The reviewed studies suggest that, at low concentrations, melatonin promotes IAA synthesis, whereas at high levels it reduces IAA levels. Similarly to IAA, melatonin promotes plant growth and development. IAA suppresses the melatonin induced inhibition of germination. IAA signaling plays an important role in plant growth and development, whereas melatonin signaling plays an important role in stress responses.

[Effects of NaCl stress on polyamines metabolism in vegetable soybean].

By adopting vermiculite culture, this paper studied the malondialdehyde (MDA) content and polyamines (PAs) metabolism in the seeds of two vegetable soybean cultivars with different salt tolerance under the stress of 100 mmol NaCl x L(-1). NaCl stress increased the MDA contents in the seeds of the two cultivars significantly, but the increment was lower for salt-resistant cultivar 'Lülingtezao' (LL) than for salt-sensitive cultivar 'Lixianggaochan 95-1' (LX). In the whole period of NaCl stress, LL seeds had higher contents of free spermine (Spm), conjugated Spm, conjugated spermidine (Spd), bound Spd and bound putrescine (Put), higher values of (Spd+Spm)/Put and (cPAs+bPAs)/fPAs, and lower value of Put/PAs, and had higher content of free Spd in the mid and late period (9-15 d) of NaCl stress, as compared with LX seeds. In a longer term (6-15 d) of the stress, LL seeds maintained a higher activity of arginine decarboxylase (ADC) and a lower activity of polyamine oxidase (PAO). All the results suggested that LL seeds had stronger capabilities for polyamines synthesis and for the transformation of Put to Spd and Spm and of free polyamine to conjugated and bound polyamines, which effectively inhibited the membrane lipid peroxidation, possibly being one of the important reasons for the stronger salt tolerance of LL.

[Change characteristics of climate and water resources in west Liaohe River Plain].

Based on the 1951-2007 observation data of precipitation and temperature from Tongliao, Kailu, and Zhalute meteorological stations as well as the related hydrologic data from Tongliao hydrological survey bureau and water affairs bureau, the change characteristics of the climate and water resources in west Liaohe River Plain were studied. The results showed that in 1951-2007, the precipitation in its periodical changes in study area had a decreasing trend. The tendency rate of precipitation was -13.2 mm x (10 a)(-1), and the instability of precipitation was increased. The runoff of four inbound rivers including Xilamulun all decreased, with the mean annual runoff in 2001-2007 being only 22.8% of that in 1990-1994. From 1951 to 2007, the runoff of west Liaohe River decreased, and the days of its zero flow increased. Since 2001, the River had been zero flow. The groundwater overdraft area and the funnel area in Keerqin Region in 2006 increased by 8.5 times and 15.5 times, respectively, compared with those in 1978; and the average groundwater level in Keerqin Region, Kailu County, and Naiman Banner in 2006 increased by 3.76 m, 2.77 m, and 1.93 m, respectively, compared with that in 1980. Since the 1970s, the number of electromechanical well in study area was increasing, irrigation amount had a fluctuated rise, and the proportion of agricultural water consumption had different extent decrease. Therefore, to exploit and use the water resources in atmosphere, to popularize water-saving irrigation technologies, and to make a reasonable arrangement of industrial structure were the effective measures in realizing the sustainable utilization of water resources in west Liaohe River Plain.