North American sagebrush-steppe bunchgrasses primarily establish from seed; however, the importance of parental plant carbon from flag leaves or within the seed head itself to reproduction in perennial bunchgrasses is unknown. To address this, we experimentally removed flag leaves and shaded seed heads to assess their importance to reproduction in the exotic bunchgrass crested wheatgrass (Agropyron cristatum), which has high seed head photosynthetic capacity and readily establishes from seed, and the native grass, squirreltail (Elymus elymoides), which has lower seed head photosysnthetic capacity and does not establish as readily from seed. We hypothesized that inflorescence shading would have a greater negative impact on crested wheatgrass reproduction than in squirreltail. In crested wheatgrass, shading did not affect total propagule production but did reduce both total filled seeds and filled seed specific mass (dry mass per unit area). Flag leaf removal stimulated seed filling and increased seed specific mass, especially in unshaded seed heads, suggesting flag leaves are competitive carbon sinks in crested wheatgrass. In contrast, flag leaf removal and shading in squirreltail resulted in similar reductions in total propagules, fewer filled seed produced and lower specific seed mass, indicating similar contributions to reproductive effort by both structures. These results indicate seed head photosynthetic activity is an adaptive reproductive feature in both grasses, but the contrasting effects of flag leaf removal may reflect long-term adaptive responses to grazing pressures that differed in crested wheatgrass's native range compared to those in North American sagebrush steppe.

北美鼠尾草-草原束草主要是从种子中生出来的。然而，尚不清楚旗叶或种子头内部的亲本植物碳对多年生束草繁殖的重要性。为了解决这个问题，我们实验性地去除了旗叶和带阴影的种子头，以评估它们对异国束草冠毛小麦草（Agropyron cristatum）繁殖的重要性，该种子草具有较高的光合作用能力，易于从种子和原生草，鼠尾草（披碱草），其具有较低的种子头光合能力，并且不易从种子中建立。我们假设花序遮光对冠状小麦草的繁殖比对鼠尾草有更大的负面影响。在冠状小麦草中，遮光不会影响繁殖体的总产量，但会降低总填充种子和填充种子的比重（每单位面积的干重）。去除旗叶会刺激种子充实，并增加种子比重，尤其是在未遮蔽的种子头中，表明旗叶是有冠小麦草中的竞争性碳汇。相反，去除旗叶和鼠尾草遮荫导致总繁殖体减少类似，产生的填充种子减少，种子比重降低，表明两种结构对繁殖力的相似贡献。