Alternate Partial Root-Zone Drip Nitrogen Fertigation Reduces Residual Nitrate Loss While Improving the Water Use but Not Nitrogen Use Efficiency.

The efficient utilization of irrigation water and nitrogen is of great importance for sustainable agricultural production. Alternate partial root-zone drip irrigation (APRD) is an innovative water-saving drip irrigation technology. However, the coupling effects of water and nitrogen (N) supply under APRD on crop growth, water and N use efficiency, as well as the utilization and fate of residual nitrates accumulated in the soil profile are not clear. A simulated soil column experiment where 30-40 cm soil layer was 15NO3-labeled as residual nitrate was conducted to investigate the coupling effects of different water [sufficient irrigation (W1), two-thirds of the W1(W2)] and N [high level (N1), 50% of N1 (N2)] supplies under different irrigation modes [conventional irrigation (C), APRD (A)] on tomato growth, irrigation water (IWUE) and N use efficiencies (NUE), and the fate of residual N. The results showed that, compared with CW1N1, AW1N1 promoted root growth and nitrogen absorption, and increased tomato yield, while the N absorption and yield did not vary significantly in AW2N1. The N absorption in AW2N2 decreased by 16.1%, while the tomato yield decreased by only 8.8% compared with CW1N1. The highest IWUE appeared in AW2N1, whereas the highest NUE was observed in AW2N2, with no significant difference in NUE between AW2N1 and CW1N1 at the same N supply level. The 15N accumulation peak layer was almost the same as the originally labeled layer under APRD, whereas it moved 10-20 cm downwards under CW1N1. The amount of 15N accumulated in the 0-40 cm layer increased with the decreasing irrigation water and nitrogen supply, with an increase of 82.9-141.1% in APRD compared with that in CW1N1. The utilization of the 15N labeled soil profile by the tomato plants increased by 9-20.5%, whereas the loss rate of 15N from the plant-soil column system decreased by 21.3-50.1% in APRD compared with the CW1N1 treatment. Thus, APRD has great potential in saving irrigation water, facilitating water use while reducing the loss of residual nitrate accumulated in the soil profile, but has no significant effect on the NUE absorbed.

Combined transcriptomic and metabolic analyses reveal potential mechanism for fruit development and quality control of Chinese raspberry (Rubus chingii Hu).

KEY MESSAGE: Combined transcriptomic and metabolic analyses reveal that fruit of Rubus chingii Hu launches biosynthesis of phenolic acids and flavonols at beginning of fruit set and then coordinately accumulated or converted to their derivatives. Rubus chingii Hu (Chinese raspberry) is an important dual functional food with nutraceutical and pharmaceutical values. Comprehensively understanding the mechanisms of fruit development and bioactive components synthesis and regulation could accelerate genetic analysis and molecular breeding for the unique species. Combined transcriptomic and metabolic analyses of R. chingii fruits from different developmental stages, including big green, green-to-yellow, yellow-to-orange, and red stages, were conducted. A total of 89,188 unigenes were generated and 57,545 unigenes (64.52%) were annotated. Differential expression genes (DEGs) and differentially accumulated metabolites (DAMs) were mainly involved in the biosynthesis of secondary metabolites. The fruit launched the biosynthesis of phenolic acids and flavonols at the very beginning of fruit set and then coordinately accumulated or converted to their derivatives. This was tightly regulated by expressions of the related genes and MYB and bHLH transcription factors. The core genes products participated in the biosynthesis of ellagic acid (EA) and kaempferol-3-O-rutinoside (K-3-R), such as DAHPS, DQD/SDH, PAL, 4CL, CHS, CHI, F3H, F3'H, FLS, and UGT78D2, and their corresponding metabolites were elaborately characterized. Our research reveals the molecular and chemical mechanisms of the fruit development of R. chingii. The results provide a solid foundation for the genetic analysis, functional genes isolation, fruit quality improvement and modifiable breeding of R. chingii.

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To get an optimal mode of irrigation and nitrogen supply for table grape production in North China, a pot experiment was conducted to investigate the effects of different irrigation modes and N application rates on dry matter accumulation and distribution, yield, water use efficiency, and nitrogen use efficiency of table grape. The irrigation modes included conventional drip irrigation (CDI, with sufficient irrigation), alternate partial root-zone drip irrigation (ADI, with 50% amount of the irrigation water of CDI) and fixed partial root-zone drip irrigation (FDI, with 50% amount of the irrigation water of CDI). The nitrogen application rates were set at 0.4 (N1), 0.8 (N2) and 1.2 (N3) g·kg-1 dry soil. The results showed that compared with CDI, ADI and FDI reduced new shoot pruning amount by 34.8% and 11.2%, respectively. New shoot pruning amount increased with increasing N application rates, being highest under CDIN3. Dry matter accumulation of ADI was the highest, being 5.1% and 12.8% higher than CDI and FDI. Dry matter accumulation was higher under N2 and N3 than N1. Compared with CDI and FDI, leaf to fruit ratio reduced but harvest index significantly increased in ADI, while those variables showed no significant difference among diffe-rent N application rates. The ratio of pruning amount to the biomass accumulated in the current year in ADIN2 was the lowest among the treatments. Compared with CDI and FDI, ADI increased grape fruit yield by 6.0% and 10.4%, respectively. Fruit yield was enhanced with increasing nitrogen application rates under the same irrigation condition, with the highest yield under the ADIN2 and ADIN3. Water use efficiency (WUE) increased significantly in ADI compared with CDI and FDI, with the highest value being observed in ADI coupled with N2 or N3. Nitrogen use efficiency (NUE) showed a trend of ADI＞CDI＞FDI. In addition, NUE decreased with increasing nitrogen supply level across the irrigation modes. In conclusion, ADIN2 could reduce the redundant growth of grape tree, promote the transfer of dry matter to fruit, which increased yield and use efficiency of both water and nitrogen, which is a suitable coupling water and nitrogen supply mode for grape production in northern China.

Effects of biochar amendment on bacterial and fungal communities in the reclaimed soil from a mining subsidence area.

Biochar amendment of soil is well known to improve soil fertility and microbial function. However, little is known about the effect of biochar addition to reclaimed soil in coal mining subsidence area on microbial community. A plant soil cultivation experiment was conducted with wheat grown and four treatments were included: P and K fertilizer (CK); NPK inorganic fertilizer (NPK); NPK inorganic fertilizer and straw (NPKS); and NPK inorganic fertilizer and biochar (NPKB). The results indicated that biochar amendment significantly increased the concentrations of NH4+-N, total N, and available P and K compared with the NPK. Biochar addition also significantly increased the grain yield and total biomass of wheat. Furthermore, biochar amendment treatment increased the absolute abundance and altered the community structure of soil bacteria and fungi in the reclaimed soil. Illumina MiSeq sequencing showed that the addition of biochar increased α-diversity of bacteria and relative abundances of Proteobacteria, Actinobacteria, and Bacteroidetes, whereas the relative abundance of Firmicutes were decreased by 61%. However, biochar addition did not change the relative abundance of dominant fungal phyla. Redundancy analysis (RDA) suggested that total N, available P, and K contents were the key factors correlated with changes in microbial community structure. Overall, our results suggest that biochar amendment in reclaimed soil in coal mine subsidence area could increase wheat yield and abundance and alter microbial community compositions.

Effect of Different Substrates on Soil Microbial Community Structure and the Mechanisms of Reductive Soil Disinfestation.

Reductive soil disinfestation (RSD) has recently attracted much attention owing to its effectiveness for controlling pathogens. In this study, we aimed to evaluate the effects of different C/N substrates on RSD and to explore the changes in microbial community structure during RSD treatment. The experimental set up included 10 groups, as follows: CK, without substrates; RSD treatments with alfalfa (Medicago sativa L.)[AL], maize (Zea mays Linn. Sp.) straw [MS], and rice (Oryza sativa L.) straw [RS], with three levels of addition (0.5% [L], 2% [M], and 5% [H]), yielding ALL, ALM, ALH, MSL, MSM, MSH, RSL, RSM, and RSH groups. Compared with CK, RSD treatments significantly increased the content of NH 4 + -N, and effectively eliminated the accumulated NO 3 - -N in the soil. The relative abundances of organic acid producers, including Clostridium, Coprococcus, and Oxobacter, in all RSD groups were significantly higher than those in the CK by day 21. Moreover, on day 21, Aspergillus and Fusarium in all RSD groups were significantly lower than those in the CK. In summary, RSD treatments clearly increased the relative abundances of organic acid generators and effectively inhibited pathogens; however, when the C/N was too low and the amount of addition too high, ammonia poisoning and rapid growth of some microorganisms (e.g., Pseudallescheria and Arthrographis) may occur.

Effects of biochar application on the abundance and community composition of denitrifying bacteria in a reclaimed soil from coal mining subsidence area.

As a new soil amendment, biochar has become an environmentally friendly material. The application of biochar is one of the most promising management practice to improve soil quality. Using a reclaimed soil from a coal mine subsidence area, the plat soil cultivation experiment in this study investigated the effects of biochar application at varying rates on soil properties, the abundance and composition of soil denitrifier communities. Biochar application significantly increased the crop yield which might be associated with the increased level of cation exchange capacity (CEC), total nitrogen (N), ammonium-N, available phosphorus (P) and potassium (K) in soil. In combination with N fertilizer, the abundance of both nirK and nirS genes significantly increased only at biochar application rate of 4% compared with the nil-biochar treatment. Biochar application significantly increased the community diversity of nirK gene, while not for nirS gene. Redundancy analysis showed that the level of nitrate-N (NO3--N), available P, and pH in soil significantly affected community structure of nirK gene, while the nirS community composition was only affected by soil NO3--N level. Our results indicate that biochar application to the reclaimed soil in coal mine subsidence area could influence the abundance and diversity of soil denitrifiers and improve soil nutrients thus crop yield.

[Effects of nitrogen forms on the growth, yield and fruit quality of tomato under controlled alternate partial root zone irrigation].

The effects of nitrogen (N) forms (ammonium-N and nitrate-N) on the growth, yield and fruit quality of tomato plants (cv. Zhongyan 988) under controlled alternate partial root zone irrigation (APRI) were examined in a split-root experiment. Under the same irrigation mode and/or controlled soil water limitation treatment, ammonium-N promoted plant growth at the early stage, while nitrate-N improved plant growth and development at the later stage leading to higher biomass accumulation and fruit yield at harvest. Under APRI and the same soil water conditions, plants of the nitrate-N treatment improved the content of vitamin C and the ratio of soluble sugar to organic acid and thus facilitated fruit quality when compared with those of the ammonium-N treatment. Plant height and leaf area under APRI treatment were lower compared with conventional irrigation (CK) under the same N form, but the stem diameter under APRI treatment with 60% theta(f) (field water capacity, theta(f)) soil moisture showed a slight increase at the late growth stage. Under the same N form, fruit yield was significantly lower in APRI treatment than that of the CK. Compared with the CK, fruit yield decreased by 22.4%-26.3% under the APRI treatment with 40% theta(f) soil moisture. Under 60% theta(f) soil moisture, the APRI treatment significantly improved fruit quality and water-use efficiency compared with the CK regardless small reduction (5.3%-5.4%) in fruit yield. The experimental results suggested that the APRI treatment with the lower limitation of soil moisture controlled at 60% theta(f), and nitrate-N supply would be the optimal option in terms of sustainable use of water resource and fertilizer.

[Effects of nitrogen form and its supply position on maize seedling growth under partial root-zone water stress].

A split root system consisting of two compartments was installed to study the effects of nitrogen form and its supply position on the growth of maize seedlings under partial root-zone water stress. Polyethylene glycol (PEG 6000) was added to the nutrient solution in one compartment to simulate partial root-zone water stress, while nitrogen was set as three forms (nitrate nitrogen, ammonium nitrogen, and their 1 : 1 mixture) and supplied to just one compartment (water-stressed or non-water-stressed compartment). Photosynthetic and other physiological indices were examined. Comparing with the nitrogen supplied to water-stressed compartment, the nitrogen supplied to non-water-stressed compartment improved the photosynthetic rate (P(n)), maximum net photosynthetic rate (P(max)), light saturation point (LSP), CO2 saturation point (CSP), chlorophyll content, root activity, nitrogen uptake, and biomass accumulation, but reduced the photorespiration rate (R(p)), CO2 compensation point (CCP), abscisic acid (ABA) concentration in xylem sap, and nitrogen- and water use efficiency of the plants. Supplying nitrate nitrogen or its mixture with ammonium nitrogen improved the P(n), P(max), LSP, CSP, nitrogen uptake, and biomass accumulation, but reduced the CCP, R(p), ABA concentration in xylem sap, and nitrogen- and water use efficiency of the plants, compared with supplying ammonium nitrogen. All the results showed that supplying same nitrogen forms to non-water-stressed compartment was more beneficial to the plant growth but disadvantageous to the plant nitrogen- and water use, compared with supplying the nitrogen forms to water-stressed compartment, and supplying nitrate nitrogen or its mixture with ammonium nitrogen promoted the plant growth but reduced the plant nitrogen- and water use, compared with supplying ammonium nitrogen.