Drought affects the growth of legumes directly, and indirectly, by reducing total nitrogen fixation. Here, we compiled published data to compare the sensitivity to water deficit on plant growth and total nitrogen fixation traits, i.e., the number of nodules per plant, average nodule mass, and nitrogen fixation per unit nodule mass. Hierarchies of phenotypic plasticity have been established for seeds and organelles, whereby variation in number associates with conserved size. By analogy, our first hypothesis is that there is a hierarchy of plasticities between nitrogen fixation traits. Our second hypothesis is that determinate nodules are more sensitive to water deficit than their indeterminate counterparts, because the latter can reactivate meristems when water becomes available. In our sample, onset of stress treatment averaged 28 d after sowing; median duration of stress was 12 d; and intensity of stress (ratio of shoot biomass between stressed and control) averaged 0.65. These drought conditions (i) reduced total nitrogen fixation and average nodule mass more severely than plant shoot mass, (ii) elicited a hierarchy of plasticities whereby number of nodules per plant varied substantially, and average nodule mass and nitrogen fixation per unit nodule mass were relatively conserved, and (iii) affected more severely Milletioids (determinate, ureide exporting nodules) than their IRLC counterparts (indeterminate, amide exporting nodules).

干旱通过减少总固氮量直接和间接影响豆科植物的生长。在这里，我们汇总了已发表的数据，以比较水分亏缺对植物生长和总固氮性状的敏感性，即每株植物的根瘤数、平均根瘤质量和每单位根瘤质量的固氮量。已经为种子和细胞器建立了表型可塑性的层次结构，其中数量的变化与保守的大小有关。以此类推，我们的第一个假设是固氮性状之间存在可塑性等级。我们的第二个假设是，确定的结节比其不确定的结节对缺水更敏感，因为后者可以在水可用时重新激活分生组织。在我们的样本中，胁迫处理的开始时间平均为播种后 28 天；压力的中位持续时间为 12 天；胁迫强度（胁迫与对照之间的枝条生物量之比）平均为 0.65。这些干旱条件 (i) 总固氮量和平均根瘤质量比植物枝条质量更严重地降低，(ii) 引发了可塑性等级，其中每株植物的根瘤数量变化很大，每单位根瘤质量的平均根瘤质量和固氮量为相对保守，并且 (iii) 与 IRLC 对应物（不确定的酰胺输出结核）相比，Milletioids（确定的，输出脲的结节）受到的影响更严重。