An appropriate ammonium: nitrate ratio promotes the growth of centipedegrass: insight from physiological and micromorphological analyses

Abstract

Reasonable nitrogen fertilizer application is an important strategy to maintain optimal growth of grasslands, thereby enabling them to better fulfil their ecological functions while reducing environmental pollution caused by high nitrogen fertilizer production and application. Optimizing the ammonium (NH4+):nitrate (NO3-) ratio is a common approach for growth promotion in crops and vegetables, but research on this topic in grass plants has not received sufficient attention. Centipedegrass, which is widely used in landscaping and ecological protection, was used as the experimental material. Different NH4+:NO3- ratios (0: 100, 25:75, 50:50, 75:25, 100:0) were used as the experimental treatments under hydroponic conditions. By monitoring the physiological and morphological changes under each treatment, the appropriate NH4+:NO3- ratio for growth and its underlying mechanism were determined. As the proportion of ammonium increased, the growth showed a “bell-shaped” response, with the maximum biomass and total carbon and nitrogen accumulation achieved with the NH4+:NO3- ratio of 50:50 treatment. Compared with the situation where nitrate was supplied alone, increasing the ammonium proportion increased the whole plant biomass by 93.2%, 139.7%, 59.0%, and 30.5%, the whole plant nitrogen accumulation by 44.9%, 94.6%, 32.8%, and 54.8%, and the whole plant carbon accumulation by 90.4%, 139.9%, 58.7%, and 26.6% in order. As a gateway for nitrogen input, the roots treated with an NH4+:NO3- ratio of 50:50 exhibited the highest ammonium and nitrate uptake rate, which may be related to the maximum total root length, root surface area, average root diameter, root volume, and largest root xylem vessel. As a gateway for carbon input, leaves treated with an NH4+:NO3- ratio of 50:50 exhibited the highest stomatal aperture, stomatal conductance, photosynthetic rate, transpiration rate, and photosynthetic products. The NH4+:NO3- ratio of 50:50 treatment had the largest stem xylem vessel area. This structure and force caused by transpiration may synergistically facilitate root-to-shoot nutrient translocation. Notably, the change in stomatal opening occurred in the early stage (4 hours) of the NH4+:NO3- ratio treatments, indicating that stomates are structures that are involved in the response to changes in the root NH4+:NO3- ratio. In summary, we recommend 50:50 as the appropriate NH4+:NO3- ratio for the growth of centipedegrass, which not only improves the nitrogen use efficiency but also enhances the carbon sequestration capacity.

Innovative Fertiliser Based on Urea and Ammonium Nitrate Solution with Potassium Thiosulphate as a Crucial Factor in Shaping Plant Yield and Its Parameters

“…Yang et al [56] found such dependencies in the early stages of wheat growth. For most species, fertilisers had the greatest effect on the growth and development of plants in which the NH 4 + :NO 3 − ratio was 50:50 [57]. The application of the higher nitrogen dose probably caused physiological stress at the beginning of spring wheat vegetation in our own research.…”

Application of Urea and Ammonium Nitrate Solution with Potassium Thiosulfate as a Factor Determining Macroelement Contents in Plants

“…In view of the above, it is extremely important to adjust the doses of fertilizers to the fertilization needs of particular plant species while taking into account the direct and indirect effects of fertilizers on the course of physiological and biochemical processes in plants. Fertilization with ammonium nitrogen, nitrate nitrogen and potassium in appropriate proportions has a particular influence on the uptake of nitrogen by plants and the synthesis of organic nitrogen compounds [48,49]. The content of nitrogen in wheat is strictly correlated with the dose of N fertilizer [50,51] and the time of its application [35].…”

“…According to Hao et al [48], the application of N fertilizers containing both nitrate nitrogen and ammonium nitrogen can produce higher crop yields than those containing only one of these forms of nitrogen. An example of the former is urea and ammonium nitrate, whose positive effect on plant growth, development and chemical composition was observed in this study.…”

“…Excessive N fertilization, especially with N-NH 4 -and N-NO 3 −, can reduce the uptake of calcium by plants [54]. In a study by Hao et al [48], the greatest effect of nitrogen on plant biomass was achieved with a ratio of NH 4 + :NO 3 − of 50:50. Fertilizers applied in such proportions had a beneficial effect on plant roots increasing their length, surface area, diameter, volume and xylem, as well as on the leaf stomata-their aperture, conductivity, rate of photosynthesis and its products or transpiration.…”