Effects of the nitrate and ammonium ratio on plant characteristics and Erythropalum scandens Bl. substrates

PLOS ONE RESEARCH ARTICLE Effects of the nitrate and ammonium ratio on plant characteristics and Erythropalum scandens Bl. substrates Daocheng Ma☯, Weichao Teng☯, Biao Yi, Yongzhi Lin, Yuanyuan Pan, Linghui Wang ID* College of Forestry, Guangxi University, University Road, Nanning, Guangxi Zhuang Autonomous Region, 530004, China a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Ma D, Teng W, Yi B, Lin Y, Pan Y, Wang L (2023) Effects of the nitrate and ammonium ratio on plant characteristics and Erythropalum scandens Bl. substrates. PLoS ONE 18(8): e0289659. https://doi.org/10.1371/journal. pone.0289659 Editor: Adalberto Benavides-Mendoza, Universidad Autónoma Agraria Antonio Narro, MEXICO Received: February 19, 2023 Accepted: July 23, 2023 Published: August 4, 2023 Copyright: © 2023 Ma et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the manuscript and its Supporting Information files. Funding: Financial assistance project: 1. Woody vegetables Erythropalum scandens Bl. undergrowth planting technology research and demonstration (Guangxi Forestry scientific research [2021] No.16); 2. Research and Demonstration on planting technology of Woody vegetable under Arboretum in Nanning (Grant no. Arboretum in Nanning Kezi [2018] No. 01) The ☯ These authors contributed equally to this work. * Abstract Erythropalum scandens Bl. is a woody vegetable with high nitrogen demand that inhabits southern China. Ammonium and nitrate are the two main forms of inorganic nitrogen that plants directly absorb. A pot experiment was performed to determine the growth, physiological responses, and preferences of 12-month-old E. scandens seedlings for ammonium and nitrate. Aboveground and underground growth indexes, biomass, physiological and biochemical indexes (chlorophyll [Chl], soluble sugar, soluble protein and free proline contents), and substrate pH and nitrogen contents were determined under different nitrate and ammonium ratios (0 NO3-: 100 NH4+, 25 NO3-: 75 NH4+, 50 NO3-: 50 NH4+, 75 NO3-: 25 NH4+, and 100 NO3-: 0 NH4+), and the control (0 NO3-: 0 NH4+). The results showed that ammonium and nitrate improved the growth and physiological status of E. scandens seedlings in most of the treatments compared to the control. The aboveground growth status and biomass accumulation of E. scandens seedlings were significantly better under the 0 NO3-: 100 NH4+ treatment during fertilization compared with all other treatments. However, the growth status of the underground parts was not significantly different among treatments. Significant differences in osmoregulator content, except for soluble sugars, and Chl content were observed. Soluble sugars and soluble proteins were highest under the 0 NO3-: 100 NH4+ treatment at the end of fertilization (day 175). However, free proline accumulated during fertilization and the increase in NO3- indicated that excessive use of NO3- had a negative effect on the E. scandens seedlings. The order of accumulating nitrogen content was leaves > roots > stems. The highest N accumulation occurred in the aboveground parts under the 0 NO3-: 100 NH4+ treatment, whereas the highest N accumulation occurred in the underground parts under the 50 NO3-: 50 NH4+ treatment. Substrate pH increased at the end of fertilization (day 175) compared with the middle stage (day 75), while total nitrogen, ammonium, and nitrate were highly significantly different among the treatments. Total nitrogen and NH4+ content were the highest under the 0 NO3-: 100 NH4+ treatment, while NO3- content was the highest under the 100 NO3-: 0 NH4+ treatment. In conclusion, 12-month-old E. scandens seedlings grew best, and had better physiological conditions in NH4+ than NO3-. The 0 NO3-:100 NH4+ treatment (ammonium chloride 3.82 g/plant) resulted in the best PLOS ONE | https://doi.org/10.1371/journal.pone.0289659 August 4, 2023 1 / 19 PLOS ONE funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. A fertilization research about a kind of leafy vegetable in the south of China growth and physiological conditions. Most of the growth and physiological indexes were inhibited with the increase in nitrate. Competing interests: The authors have declared that no competing interests exist. 1 Introduction Erythropalum scandens Bl. (family Olacaceae) is a woody leafy vegetable inhabiting south and southwest China, Vietnam, and other Southeast Asian countries. Its tender leaves and stems have a distinct taste and smell. Due to its high nutritional value and pleasing taste, it is often picked and eaten by farmers [1]. E. scandens has a large planting area in Guangxi, particularly in Daxin County (about 67 hectares), as it is an important national plant resource in western and southern China. The tender stems and leaves are sold as a wild vegetable for 40–100 CNY/ kg. The estimated production output is 66.5 kg/ha/year, with an output value of > 2,660–6,650 CNY/ha/year. Erythropalum scandens also functions in soil and water conservation [2]. It is shade-tolerant in rain forests and limestone mountainous areas, and is a widely distributed “interlayer plant” in Xishuangbanna, Yunnan, and other areas of south and southwest China [3]. Although it grows well under natural conditions, the yield of E. scandens is limited in the natural environment. E. scandens and its germplasm resources have been seriously damaged in the wild. Therefore, how to improve the yield of E. scandens under an artificial cultivation environment, meet the growing demand therefor, and reduce destruction of the wild resource are top priorities. The current study showed that fertilization greatly improved the yield and quality of E. scandens. In addition, Guo [4] reported that a combination of chicken manure (0.8 kg/plant) and cow manure (1.2 kg/plant) was the best method to increase the yield of 24-month-old E. scandens cutting seedlings; their edible parts accumulated carbohydrates, amino acids and other nutrients, as well as medicinal components. The average bud and leaf yield was 20.58 g after 7 months of fertilization. Ma et al. [5,6] showed that the growth and physiological conditions of 18-month-old E. scandens seedlings were optimal under a 2.14 g/plant urea + 4.44 g/ plant superphosphate + 0.67–1.33 g/plant potassium chloride treatment. The number of new leaves per plant under the optimal fertilization treatment was 41.5, and the length of new branches was 147.52 cm. According to these studies, nitrogen plays a very important role in leaf growth and stem development of E. scandens. However, previous studies used organic fertilizers and urea as N sources. The components of organic fertilizers (...truncated)