Soil environment, physiological metabolism and ornamental traits of Zinnia response to water and nitrogen combination in a cold and arid environment

In response to the prominent issues of water shortage and intensified soil desertification in the arid regions of Northwest China, this study aimed to optimize the water and nitrogen (N) management plan for ornamental Zinnia. Using the tall Zinnia variety “Pink Dream” as the experimental material, a two-year field experiment was conducted in the oasis area of Hexi Corridor using the integrated water and fertilizer management technology under subsurface drip irrigation. Three irrigation gradients (W1, 55%∼65% field capacity (FC); W2, 65%∼75% FC; W3, 75%∼85% FC) and three N application levels (N1, 90 kg·ha -1 ; N2, 150 kg·ha -1 ; N3, 210 kg·ha -1 ) were respectively established. The local water and fertilizer management practice (W3 level combined with 270 kg·ha -1 N application) was used as the control (CK), resulting in a total of ten treatments. The effects of different water-N regulations on rhizosphere soil environment, plant physiological metabolism, growth and development, and ornamental traits of Zinnia were systematically explored. The results indicated that in both growing seasons, the W2N2 and W2N3 treatments significantly ( P < 0.05) outperformed the CK and other treatments in terms of dry matter accumulation and ornamental value, with increases ranging from 7.20% to 153.47%. However, the optimal photosynthetic assimilation capacity and physiological and biochemical indicators were recorded in W2N2 treatment, which was significantly higher than that in CK and other treatments, with an increase of 8.76% to 45.50%. The W1N1 water and nitrogen management mode reduced Zinnia nutrient deficiency, decreased leaf area, photosynthetic rate, growth and physiological-biochemical indicators Also, the W3N3 mode did not enhance the above indicators while reduced its ornamental value. In addition, increasing the nitrogen fertilizer application rate from N1 to N3 led to an average increase of 14.51% and 37.56% in the total nitrogen (TN) and soil organic matter (SOM) content of the 0–60 cm soil layer, respectively. In contrast, raising the irrigation level from W1 to W3 resulted in an increase of 7.10% and 26.92% in the TN and SOM content, respectively. Entropy weight-TOPSIS evaluation identified W2N2 (0.988) as the optimal regime, providing scientific support for efficient Zinnia cultivation and ecological-landscape coordination in arid oases.