Abstract:

This study explored the response of leaf epidermal characteristics， anatomical structure and photosynthetic characteristics of Poa pratensis to nitrogen application level. Six P. pratensis varieties were used， including three introduced varieties from the United States： Merit， Jackrabbit and Park， two native wild populations from Shanxi： Yingxian and Hunyuan， and one P. pratensis strain， ‘Taihang’， bred from wild populations from Shanxi. The treatments comprised two nitrogen levels： N₁， 10 g·m^-2 （low nitrogen） and N₂， 40 g·m^-2 （normal nitrogen）. Freehand slicing and paraffin sectioning were used to prepare slides. The leaf upper and lower epidermal thickness， cell length∶width， cell density， stomatal index， stomatal length∶width， stomatal density， leaf thickness， sclerenchyma thickness， vascular bundle area， stomatal conductance， and net photosynthetic rate were measured using an optical microscope. It was found that the upper and lower epidermal thickness， leaf thickness， sclerenchyma thickness， vascular bundle area， stomatal conductance and net photosynthetic rate of P. pratensis leaves under the N₁ treatment were significantly lower than those under the N₂ treatment， while the stomatal size in N₁ was not significantly different from that under the N₂ treatment. Under the N₂ treatment， the leaf thicknesses of Jackrabbit and Park were significantly higher than those of Hunyuan and Yingxian. The leaf thickness of Park was the largest， reaching 173.39 μm. The leaf vascular bundle area of Jackrabbit was significantly higher than that of Hunyuan and Park. The net photosynthetic rate of Merit was the highest， reaching 17.23 μmol CO₂·m^-2·s^-1. This value was 45.16% higher than that of the lowest， Park. Correlation analysis showed that net photosynthetic rate was positively correlated with upper and lower epidermal thickness， sclerenchyma thickness， vascular bundle area and stomatal conductance. The N₁ （low） nitrogen treatment resulted in thinning of P. pratensis leaves， decreased vascular bundle area， and decreased stomatal conductance and net photosynthetic rate. Leaf stomatal conductance and net photosynthetic rates of P. pratensis var. ‘Taihang’ were higher than those of other varieties under the N₁ treatment， and ‘Taihang’ had lower sensitivity to low nitrogen.

Key words: nitrogen application rate, Poa pratensis, epidermis characteristic, anatomical structure, photosynthetic characteristics