干旱胁迫下胡杨实生幼苗氮素吸收分配与利用

胡杨(Populus euphratica)是塔里木河流域荒漠河岸林的建群种,水分和氮素是限制胡杨幼苗的存活及早期生长的主要因子。利用~(15)N同位素示踪技术分析水和氮素的交互作用对胡杨幼苗不同生长阶段氮素的吸收分配利用及幼苗生长的影响,进一步探究氮素对胡杨实生苗早期形态建成的作用及对干旱胁迫的缓解效应,以期提高幼苗的存活率。实验以一年生胡杨实生幼苗为研究对象,采用温室内盆栽实验,设置4个干旱处理(D_1、D_2、D_3、D_4,土壤相对含水量为:20%—25%、40%—45%、60%—65%、80%—85%)和3种氮素水平(N_0、N_1、N_2:0、3、6 g/盆)测定胡杨幼苗的生长指标和各部分的Ndff、分配率及利用率。结果表明:胡杨幼苗在土壤相对含水量60%—65%(D_3)、氮素添加量3 g/盆(N_1)时,其生长表现为最佳状态;干旱胁迫下,不同氮素添加量对胡杨幼苗各部分的Ndff值存在显著差异,N_2低于N_1;随干旱胁迫减弱(D_3、D_4),植株在生长早期(25 d)根部吸收的~(15)N优先向地上部分转运,生长后期(75 d)植株Ndff最高,其中以根系中Ndff最高;不同生长期幼苗各部分的~(15)N分配存在显著差异,根系~(15)N分配率较高,但不同氮量处理间差异不显著;随生长期的推移,植株对~(15)NH_4~(15)NO_3的利用率表现为粗根最大,各处理中D_3N_1处理均显著高于其他处理。结论:轻度干旱胁迫下添加适量的氮素能够增强植株对氮素的吸收征调能力,优化水资源获取以维持生存的重要机制。

Characteristics of nitrogen absorption, distribution, and utilization by Populus euphratica seedlings under drought stress

Populus euphratica is a dominant species in desert riparian forests in the Tarim River Basin. The survival and growth of P. euphratica seedlings is limited by water and nitrogen. In this experiment, a ¹⁵N isotope tracer technique was used to explore the effects of different water and nitrogen levels on nitrogen absorption, distribution, and utilization by P. euphratica at different growth stages. We studied the effects of nitrogen on the early morphogenesis of P. euphratica seedlings and on the mitigation of drought stress to improve the survival rate of seedlings. Seedlings of P. euphratica were subjected to four different soil water treatments (D₁, D₂, D₃, and D₄ with relative soil water contents of 20%-25%, 40%-45%, 60%-65%, and 80%-85%, respectively) and three nitrogen application levels (N₀, N₁, N₂:0, 3, 6 g·pot^-1) and then the growth index, nitrogen derived from fertilizer (Ndff), nitrogen distribution rate, and nitrogen utilization rate were determined. The results showed that P. euphratica seedlings had the best growth performance when the relative soil water content was 60%-65% (D₃) and the nitrogen application level was 3 g·pot^-1 (N₁). Under drought stress, there were significant differences in the Ndff values of different parts of seedlings under different nitrogen application levels, and the Ndff values were lower in the N₂ treatment than in the N₁ treatment. With greater soil water availability (D₃, D₄), the ¹⁵N taken up by the roots was preferentially transported to the above-ground plant parts during the early growth period (25 d). The Ndff was the highest, especially in the root system, in the late growth period (75 d). The distribution of ¹⁵N differed significantly among different parts of the seedlings. The ¹⁵N distribution rate was highest in the roots, but there was no significant difference in the ¹⁵N distribution rate among the N₀, N₁, and N₂ treatments. As seedling growth progressed, the roots had the highest nitrogen utilization rate, and this rate was significantly higher in the D₃N₁ treatment than in all the other treatments. Our results indicate that adding appropriate amounts of nitrogen can enhance the ability of plants to absorb nitrogen under slight drought stress.