Institute for Sustainable Agro-ecosystem Services, The University of Tokyo, Tokyo 188-0002, Japan.
Ann Bot. 2011 Sep;108(3):575-83. doi: 10.1093/aob/mcr184. Epub 2011 Aug 1.
Increasing physical water scarcity is a major constraint for irrigated rice (Oryza sativa) production. 'Aerobic rice culture' aims to maximize yield per unit water input by growing plants in aerobic soil without flooding or puddling. The objective was to determine (a) the effect of water management on root morphology and hydraulic conductance, and (b) their roles in plant-water relationships and stomatal conductance in aerobic culture.
Root system development, stomatal conductance (g(s)) and leaf water potential (Ψ(leaf)) were monitored in a high-yielding rice cultivar ('Takanari') under flooded and aerobic conditions at two soil moisture levels [nearly saturated (> -10 kPa) and mildly dry (> -30 kPa)] over 2 years. In an ancillary pot experiment, whole-plant hydraulic conductivity (soil-leaf hydraulic conductance; K(pa)) was measured under flooded and aerobic conditions.
Adventitious root emergence and lateral root proliferation were restricted even under nearly saturated conditions, resulting in a 72-85 % reduction in total root length under aerobic culture conditions. Because of their reduced rooting size, plants grown under aerobic conditions tended to have lower K(pa) than plants grown under flooded conditions. Ψ(leaf) was always significantly lower in aerobic culture than in flooded culture, while g(s) was unchanged when the soil moisture was at around field capacity. g(s) was inevitably reduced when the soil water potential at 20-cm depth reached -20 kPa.
Unstable performance of rice in water-saving cultivations is often associated with reduction in Ψ(leaf). Ψ(leaf) may reduce even if K(pa) is not significantly changed, but the lower Ψ(leaf) would certainly occur in case K(pa) reduces as a result of lower water-uptake capacity under aerobic conditions. Rice performance in aerobic culture might be improved through genetic manipulation that promotes lateral root branching and rhizogenesis as well as deep rooting.
日益增加的水资源短缺是灌溉水稻（Oryza sativa）生产的主要制约因素。“有氧水稻栽培”旨在通过在有氧土壤中种植植物而不淹没或积水来实现每单位水投入的最大产量。本研究旨在（a）确定水分管理对根系形态和水力导度的影响，以及（b）它们在有氧栽培中植物-水关系和气孔导度中的作用。
在两年内，在高产品种（“Takanari”）中监测根系系统发育、气孔导度（g(s)）和叶片水势（Ψ(leaf)）在淹水和有氧条件下，在两种土壤水分水平（接近饱和（>-10 kPa）和轻度干燥（>-30 kPa））下的变化。在辅助盆栽实验中，在淹水和有氧条件下测量整株植物水力导率（土壤-叶水力导率；K(pa)）。
即使在接近饱和的条件下，不定根的出现和侧根的增殖也受到限制，导致有氧栽培条件下总根长减少 72-85%。由于根系大小的减小，有氧栽培条件下生长的植物的 K(pa)往往低于淹水栽培条件下生长的植物。与淹水培养相比，有氧培养中的 Ψ(leaf)总是显著降低，而当土壤水分接近田间持水量时，g(s)保持不变。当 20cm 深处的土壤水势达到-20kPa 时，g(s)不可避免地降低。
节水栽培中水稻的不稳定表现通常与 Ψ(leaf)的降低有关。即使 K(pa)没有明显变化，Ψ(leaf)也可能降低，但如果由于有氧条件下吸水能力降低导致 K(pa)降低，则必然会出现较低的 Ψ(leaf)。通过促进侧根分枝和根发生以及深根的遗传操作，可以提高有氧培养中水稻的性能。
