中文摘要：

采用两因素随机区组设计,设置了5个水分梯度,即40%（W_1）、50%（W_2）、60%（W_3）、80%（W_4）、100%（W_5）的土壤田间持水量（FC）和3个施氮梯度,即模拟氮沉降施加0（对照,N_0）、20（N_1）、40（N_2）g N m~（-2）a~（-1）的硝酸铵,研究了水-氮耦合效应对川西亚高山主要阔叶树种红桦（Betula albosinensis）幼苗根系生理活性的影响及根系在土壤水、氮胁迫下的生理调控机制。结果表明：1）随土壤含水量降低,根系活力和根系呼吸速率显著降低,膜脂过氧化产物（丙二醛）、渗透调节物质（脯氨酸、可溶性蛋白质和可溶性糖）含量及抗氧化物酶（超氧化物歧化酶、过氧化物酶和过氧化氢酶）活性显著升高。2）水-氮耦合效应对红桦幼苗根系生理特征影响显著：施氮（N_1和N_2）在土壤水分良好（W_4和W_5）时使根系活力和根系呼吸速率显著升高,而在土壤水分不足（W_1和W_2）时显著降低了根系活力和根系呼吸速率;且在水分不足时,施氮浓度越大根系活力、MDA含量、脯氨酸及可溶性蛋白质含量变化越显著;在W_3条件下,只有N_1对根系生理功能促进作用显著。3）根系活力和根系呼吸速率与丙二醛含量呈显著负相关性。因此,一定范围内的氮沉降在土壤水分状况良好时对植物根系生理特征具有显著正效应,而在土壤水分不足时则使根系细胞膜系统受损,抑制根系生理活性,但根系可通过增加渗透调节物质含量和增强抗氧化物酶活性来抵御一定范围的环境胁迫。

英文摘要：

The increasing deposition of nitrogen into the atmosphere has affected the stability and productivity of ecosystem. The effects of nitrogen deposition vary in regards to soil water content. There is uneven precipitation distribution and significant water-nitrogen coupling, which directly affects the growth and development of plants. In order to better understand the responses of plant roots to soil water-nitrogen coupling, we exposed seedlings of Betula albosinensis to five different water regiments of field water holding capacity （FC） （40% [ W1 ], 50% [ W2 ], 60% [ W3 ], 80% [ W4 ], and 100% [W4] ）. As well as three different nitrogen （N） regiments （control, 0 [No], 20 IN, I, and 40 IN2] gN m^-2^-1with NH4NO3 ）. These experimental conditions allowed us to determine the root activity and physiology of the seedlings when exposed to various water and nitrogen supplies. The results indicated that a decrease of soil water content prompted the root vigor and root respiration rate to decrease while membrane lipid peroxide （ MDA）, osmotic adjustment substances （ i. e. proline, soluble protein, and soluble sugar） content, and the activity of antioxidant enzymes （i.e. superoxide dismutase, peroxidase and catalase） all increased. Moreover, root physiological characteristics were significantly affected by the water- nitrogen coupling effect. When soil moisture was deficient （ W1 and W2 ）, the addition of nitrogen markedly reduced root activity. However, when adequate soil water （W4 and Ws ） was present, root activity was significantly enhanced. Additionally, the greater the concentration of nitrogen applied, the greater the effects were upon root activity and the contents of proline and soluble MDA. Only the lower concentration of nitrogen addition （ N1 ） significantly improved root physiological functions under 60% FC. Finally, both root vigor and nitrate reductase activity had a significant negative correlation with membrane lipid peroxide level （MDA content）. In conclusion, atm