Data_Sheet_1_Effects of Growth Medium and Water Stress on Soybean [Glycine max (L.) Merr.] Growth, Soil Water Extraction and Rooting Profiles by Depth in 1-m Rooting Columns.docx

The pattern of soil water availability in frequently watered small pots is different from field environments. In small pots, volumetric soil water content (VSWC) is relatively high throughout the rooting zone due to a lack of suction to remove water from large and midsize capillaries. This necessitates the use of growing media with large pore space to avoid anaerobic conditions and so prohibits the use of field soil (FS) in small pots. We hypothesized that in 1-m rooting columns, the 0.01-MPa gravitational potential difference between top and bottom may permit the use of lightly-amended FS as a growing medium and provide for realistic VSWC and rooting profiles by depth. This study aimed to investigate the effects of amending a typical sand-based potting mix with different proportions of FS on soybean growth [dry matter (DM) accumulation], water use, VSWC and rooting profiles by depth under control and water stress conditions, in 1-m rooting columns (polyvinyl chloride tubes having an inside diameter of 10 cm and length of 1 m). We tested three growth media (0, 50, and 67% FS mixes), watered daily to either 100% of the maximum soil water holding capacity (SWHC; control) or 75% SWHC (stress). VSWC was calculated from time-domain reflectometry measurements. Compared to all growth media, the 67% FS mix resulted in the highest DM accumulation, water use, water use efficiency (WUE), and also produced realistic VSWC and rooting profiles by depth similar to those reported in the literature under field conditions. Compared to the control, the water stress treatment reduced shoot DM by 24%, root DM by 13%, whole-plant DM by 22%, and water use by 25%, but increased root-to-shoot DM ratio by 18% and WUE by 6%. Of the three growth media tested, the 67% FS mix was the most suitable growth medium for controlled environment phenotyping studies of root functional traits affecting drought tolerance in soybean. This study provides novel phenotyping tools to select for root function and yield formation traits that could increase soybean yield under soil water deficit conditions.

频繁浇水的小型盆栽容器内的土壤水分有效性模式与田间环境存在显著差异。由于缺乏可移除大中型毛细管内水分的吸力作用，小型盆栽的整个根系区域内的体积土壤含水量（volumetric soil water content, VSWC）整体相对较高。这使得研究必须采用孔隙度较大的栽培基质以避免厌氧环境，因此无法在小型盆栽中直接使用田间土壤（field soil, FS）。我们提出假说：在1米高的生根柱中，顶部与底部之间0.01 MPa的重力势差，可允许使用轻度改良的田间土壤作为栽培基质，并能获得符合实际的体积土壤含水量与深度分层的根系分布特征。本研究以内径10 cm、长度1 m的聚氯乙烯（polyvinyl chloride, PVC）管构建的1 m生根柱为实验载体，旨在探究在对照与水分胁迫条件下，以不同比例田间土壤改良典型砂质盆栽基质对大豆生长[干物质（dry matter, DM）积累量]、耗水量、体积土壤含水量以及深度分层根系分布特征的影响。我们设置了3种栽培基质（0%、50%与67%的田间土壤混合比例），并每日将基质含水量维持在最大土壤持水量（soil water holding capacity, SWHC）的100%（对照）或75%（胁迫）。体积土壤含水量通过时域反射法测量计算得到。相较于其余两种栽培基质，67%田间土壤混合基质可获得最高的干物质积累量、耗水量与水分利用效率（water use efficiency, WUE），同时其深度分层的体积土壤含水量与根系分布特征与文献报道的田间实际情况高度吻合。与对照处理相比，水分胁迫处理使地上部干物质降低24%、根系干物质降低13%、全株干物质降低22%，耗水量降低25%，但根冠比提升18%，水分利用效率提升6%。在测试的3种栽培基质中，67%田间土壤混合基质最适用于大豆耐旱相关根系功能性状的可控环境表型组研究。本研究为筛选可提升土壤水分亏缺条件下大豆产量的根系功能与产量形成性状提供了全新的表型组研究工具。