Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Creswick, Victoria, Australia.
Department of Agronomy, Bangladesh Agricultural University, Mymensingh, Bangladesh.
PLoS One. 2018 Jun 14;13(6):e0198928. doi: 10.1371/journal.pone.0198928. eCollection 2018.
Through stimulation of root growth, increasing atmospheric CO2 concentration ([CO2]) may facilitate access of crops to sub-soil water, which could potentially prolong physiological activity in dryland environments, particularly because crops are more water use efficient under elevated [CO2] (e[CO2]). This study investigated the effect of drought in shallow soil versus sub-soil on agronomic and physiological responses of wheat to e[CO2] in a glasshouse experiment. Wheat (Triticum aestivum L. cv. Yitpi) was grown in split-columns with the top (0-30 cm) and bottom (31-60 cm; 'sub-soil') soil layer hydraulically separated by a wax-coated, root-penetrable layer under ambient [CO2] (a[CO2], ∼400 μmol mol-1) or e[CO2] (∼700 μmol mol-1) [CO2]. Drought was imposed from stem-elongation in either the top or bottom soil layer or both by withholding 33% of the irrigation, resulting in four water treatments (WW, WD, DW, DD; D = drought, W = well-watered, letters denote water treatment in top and bottom soil layer, respectively). Leaf gas exchange was measured weekly from stem-elongation until anthesis. Above-and belowground biomass, grain yield and yield components were evaluated at three developmental stages (stem-elongation, anthesis and maturity). Compared with a[CO2], net assimilation rate was higher and stomatal conductance was lower under e[CO2], resulting in greater intrinsic water use efficiency. Elevated [CO2] stimulated both above- and belowground biomass as well as grain yield, however, this stimulation was greater under well-watered (WW) than drought (DD) throughout the whole soil profile. Imposition of drought in either or both soil layers decreased aboveground biomass and grain yield under both [CO2] compared to the well-watered treatment. However, the greatest 'CO2 fertilisation effect' was observed when drought was imposed in the top soil layer only (DW), and this was associated with e[CO2]-stimulation of root growth especially in the well-watered bottom layer. We suggest that stimulation of belowground biomass under e[CO2] will allow better access to sub-soil water during grain filling period, when additional water is converted into additional yield with high efficiency in Mediterranean-type dryland agro-ecosystems. If sufficient water is available in the sub-soil, e[CO2] may help mitigating the effect of drying surface soil.
通过刺激根系生长，增加大气二氧化碳浓度（[CO2]）可能有助于作物获得亚表层土壤水分，这可能会延长旱地环境中的生理活动，尤其是因为在高二氧化碳浓度下（e[CO2]），作物的水分利用效率更高。本研究在温室实验中，调查了浅层土壤和亚表层土壤干旱对小麦生理响应的影响。在实验中，小麦（Triticum aestivum L. cv. Yitpi）在有蜡涂层的可穿透根系的层将顶层（0-30 厘米）和底层（31-60 厘米；“亚表层”）土壤水力分离的分柱中生长，在环境二氧化碳浓度（a[CO2]，约 400 μmol mol-1）或高二氧化碳浓度（e[CO2]，约 700 μmol mol-1）[CO2]下生长。通过在顶层或底层土壤层或两者均不进行 33%的灌溉，从茎伸长开始对干旱进行胁迫，导致有四种水分处理（WW、WD、DW、DD；D = 干旱，W = 充分浇水，字母分别表示顶层和底层土壤的水分处理）。从茎伸长到开花，每周测量叶片气体交换。在三个发育阶段（茎伸长、开花和成熟）评估地上和地下生物量、籽粒产量和产量构成。与 a[CO2]相比，e[CO2]下净同化率更高，气孔导度更低，导致内在水分利用效率更高。高二氧化碳浓度刺激地上和地下生物量以及籽粒产量，但在整个土壤剖面中，充分浇水（WW）的刺激作用大于干旱（DD）。在顶层或底层土壤层的任何一层或两层都施加干旱，与充分浇水的处理相比，地上生物量和籽粒产量都降低。然而，当仅在顶层土壤层施加干旱（DW）时，观察到最大的“二氧化碳施肥效应”，这与 e[CO2]刺激根生长有关，特别是在充分浇水的底层。我们认为，在高二氧化碳浓度下，地下生物量的刺激将使在灌浆期更好地获得亚表层土壤水分，在以地中海型旱地农业生态系统中，更多的水将转化为更高效率的额外产量。如果亚表层土壤中有足够的水分，e[CO2]可能有助于减轻表层土壤干燥的影响。
