Moderate Nitrogen Deposition Alleviates Drought Stress of Bretschneidera sinensis

Abstract

Droughts are becoming more frequent and intense, and the nitrogen deposition rate is increasing worldwide due to human activities. Young seedlings of Bretschneidera sinensis Hemsl. are susceptible to mortality under drought conditions because their root tips have few root hairs. We studied the effect of nitrogen deposition on the physiological characteristics of two-year-old B. sinensis seedlings under drought stress. Seedlings were grown under no nitrogen deposition (control; N0), low nitrogen deposition (N30, 30 kg·hm−2 year−1), medium nitrogen deposition (N60, 60 kg·hm−2 year−1), and high nitrogen deposition (N90, 90 kg·hm−2 year−1), and were subjected to either the normal watering regime (NW) or drought stress (DW). Under DW, the relative conductivity (RC) of seedlings receiving N60 was not significantly different from that of N0 seedlings, and the RC of seedlings receiving N90 was significantly higher than that of N0 seedlings. Under 10 d DW, N60 treatment increased antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and content of soluble protein, chlorophyll a and a + b, with POD activity and soluble protein significantly increasing by 18.89% and 34.66%, respectively. Under DW, the proline (PRO) content of seedlings treated with N90 increased. Our data suggested that moderate nitrogen deposition could alleviate drought stress by decreasing cell membrane permeability, reducing cell membrane peroxidation, increasing the content of osmoregulatory substances, and reducing the tendency for chlorophyll to decline, whereas high nitrogen deposition increased the sensitivity of B. sinensis seedlings to drought stress and aggravated the degree of stress, thereby affecting growth.