Donald’s ideotype and growth redundancy: a pot experimental test using an old and a modern spring wheat cultivar

Human selection for high crop yield under water-limited conditions should have led modern cereal cultivars to invest less in root biomass, be it unconsciously. To test this hypothesis we conducted a pot experiment with two spring wheat cultivars, one old and one modern, both widely grown in the semi-arid regions of China. Using the replacement series method introduced by de Wit, we showed that the older landrace (Monkhead) was significantly more competitive than the more-modern cultivar (92-46). However, when grown in pure stand, old Monkhead had grown root biomass 3.5 times modern 92-46, whereas modern 92-46 gained a 20% higher grain yield. We also found modern 92-46 significantly increased root biomass per plant and root allocation (i.e., root biomass/total individual biomass) as its frequency in mixtures decreased, whereas old Monkhead did not respond in a similar way. This result suggests that the roots of modern cultivars may have gained an ability to recognize neighboring root systems and show more plastic self-restraining response to intra-cultivar competition.

在水分受限的栽培环境中，为获取高产作物而开展的人工选育（无论是否有意识地进行），本应促使现代谷类作物品种减少对根系生物量的投入。为验证这一假说，我们采用盆栽试验，供试材料为两个在中国半干旱地区广泛种植的春小麦品种——一个为古老地方品种，另一个为现代栽培品种。借助de Wit提出的替代系列法，我们发现古老地方品种Monkhead的竞争能力显著强于现代栽培品种92-46。但在单一种植条件下，古老品种Monkhead的根系生物量达到现代品种92-46的3.5倍，而现代品种92-46的籽粒产量则高出20%。此外我们还观察到，随着现代品种92-46在混播群落中的占比降低，其单株根系生物量及根系分配比例（即根系生物量/单株总生物量）均显著提升，而古老品种Monkhead并未出现类似响应。该结果表明，现代栽培品种的根系或许已演化出识别邻近根系的能力，并能对种内竞争产生更具可塑性的自我抑制响应。