Department of Crop Production Ecology, POB 7043, Swedish University of Agricultural Sciences, Sweden.
Ann Bot. 2011 Nov;108(7):1347-53. doi: 10.1093/aob/mcr227. Epub 2011 Sep 6.
The major objective was to identify plant traits functionally important for optimization of shoot growth and nitrogen (N) economy under drought. Although increased leaf N content (area basis) has been observed in dry environments and theory predicts increased leaf N to be an acclimation to drought, experimental evidence for the prediction is rare.
A pedigree of 200 full-sibling hybrid willows was pot-grown in a glasshouse in three replicate blocks and exposed to two water regimes for 3 weeks. Drought conditions were simulated as repeated periods of water shortage. The total leaf mass and area, leaf area efficiency (shoot growth per unit leaf area, E(A)), area-based leaf N content (N(A)), total leaf N pool (N(L)) and leaf N efficiency (shoot growth per unit leaf N, E(N)) were assessed.
In the water-stress treatment, shoot biomass growth was N limited in the genotypes with low N(L), but increasingly limited by other factors in the genotypes with greatest N(L). The N(A) was increased by drought, and drought-induced shift in N(A) varied between genotypes (significant G × E). Judged from the E(A)-N(A) relationship, optimal N(A) was 16 % higher in the water-stress compared with the well-watered treatment. Biomass allocation to leaves and shoots varied between treatments, but the treatment response of the leaf : shoot ratio was similar across all genotypes.
It is concluded that N-uptake efficiency and leaf N efficiency are important traits to improve growth under drought. Increased leaf N content (area basis) is an acclimation to optimize N economy under drought. The leaf N content is an interesting trait for breeding of willow bioenergy crops in a climate change future. In contrast, leaf biomass allocation is a less interesting breeding target to improve yield under drought.
主要目标是确定在干旱条件下对芽生长和氮（N）经济进行优化具有重要功能的植物特征。虽然在干燥环境中观察到叶片 N 含量（面积基础）增加，并且理论预测增加叶片 N 是对干旱的适应，但很少有实验证据支持该预测。
在三个重复块的温室中，用 200 个全同胞杂交柳树的谱系进行盆栽，并暴露于两种水分条件下 3 周。干旱条件是通过反复缺水来模拟的。评估了总叶质量和面积、叶面积效率（单位叶面积的芽生长，E(A)）、基于面积的叶片 N 含量（N(A)）、总叶片 N 池（N(L)）和叶片 N 效率（单位叶片 N 的芽生长，E(N)）。
在水分胁迫处理中，在 N(L)较低的基因型中，芽生物量生长受到 N 限制，但在 N(L)最大的基因型中，受其他因素限制越来越大。干旱增加了 N(A)，并且 N(A)在不同基因型之间存在干旱诱导的变化（显著的 G×E）。根据 E(A)-N(A)关系，与水分充足处理相比，水分胁迫下的 N(A)最佳增加了 16%。叶片和芽之间的生物量分配在处理之间有所不同，但所有基因型的叶片：芽比的处理响应相似。
综上所述，N 吸收效率和叶片 N 效率是在干旱条件下提高生长的重要特征。增加叶片 N 含量（面积基础）是优化干旱条件下氮经济的一种适应。叶片 N 含量是在气候变化未来培育柳树生物能源作物的一个有趣特征。相比之下，叶片生物量分配是提高干旱条件下产量的一个不太有趣的培育目标。
