Abstract Computation of integral water capacity (IWC), as an alternative criterion for soil water availability to plant, requires developing of weighting function (ω(h)) for each limiting factor may prevail within a particular water or suction range (e. g., hd and hw) in the root medium and diminish water availability to plant. So far defining hd and hw limits for a particular limiting factor has been primarily soil property based. We investigated the possibility of plant response based ω (h) as a proxy. For this purpose, a sandy clay loam soil was evenly compacted to three bulk densities (Db) of 1.35, 1.55 and 1.75 Mg m-3 in large (30 cm diameter and 70 cm depth) PVC tubes (called pots hereafter). Sunflower (Helianthus Annuus L) seedlings were planted in the pots and after their full establishment (at late vegetative growth stage) root pruning was implemented by cutting off approximately 75%, 50%, 25% and 0% of the root branches in the 0-25 cm section along the root crown. Two periods of wetting and drying cycles were subsequently imposed and soil water contents and midday leaf stomatal conductance were routinely measured. At the end of the experiment total root length in the samples separately taken from three sections (5-25, 25-50 and 50-70 cm) of each pot was measured using GSA image analyzer software and converted to root length density (RLD). Relative stomatal conductance (g/gc), presumably varying between 0 to 1 and comprising impact of all water availability limiting factors in the root medium, as function of h were developed and substituted for ω(h) and the plant response based integral water capacity (IWCP) was then computed and compared between various imposed treatments and with least limiting water range (LLWR) and plant available water (PAW). For the treatments without root pruning (L4), increase in soil compaction (from D1 to D2 and from D1 to D3) reduced IWCP by about 17.5% and 20.5%, respectively. The corresponding decreases for LLWR were, 22% and 66%, respectively, and negligible for PAW. These results showed that PAW is almost irresponsive and LLWR is over responsive to soil compaction or bulk density while IWCP seems reflect more realistic influence of soil compaction on soil water availability to plants. Decrease in IWCP from L4 to L1 was by 43%. In contrary to LLWR and PAW, our proposed method showed the effect of root length density on plant available water.

中文翻译：

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基于向日葵植物不同土壤和根长密度下的气孔导度重新审视整体水分容量

摘要 积分水容量 (IWC) 的计算，作为植物土壤水分可用性的替代标准，需要为每个限制因素开发加权函数 (ω(h)) 在特定的水或吸力范围内可能占优势（例如，hd 和hw) 在根培养基中并减少植物的水分供应。到目前为止，定义特定限制因素的 hd 和 hw 限制主要是基于土壤特性。我们研究了基于 ω (h) 作为代理的植物响应的可能性。为此，将砂质粘壤土均匀压实至三个体积密度 (Db) 1.35、1.55 和 1.75 Mg m-3 的大型（直径 30 厘米，深度 70 厘米）PVC 管（以下称为盆）。将向日葵 (Helianthus Annuus L) 幼苗种植在盆中，在它们完全建立后（在营养生长后期），通过剪掉大约 0%、50%、25% 和 0% 的根枝来实施剪根。 -25 厘米沿根冠的截面。随后实施两个周期的润湿和干燥循环，并定期测量土壤含水量和中午叶片气孔导度。在实验结束时，使用 GSA 图像分析仪软件测量从每个盆的三个部分（5-25、25-50 和 50-70 厘米）分别取出的样品中的总根长，并转换为根长密度（RLD） . 相对气孔导度 (g/gc)，大概在 0 到 1 之间变化，包括根介质中所有水分可用性限制因素的影响，开发了作为 h 的函数并替代了 ω(h)，然后计算了基于植物响应的积分水容量 (IWCP)，并在各种施加的处理之间进行了比较，并使用了最小限水范围 (LLWR) 和植物可用水 (PAW)。对于不修剪根部 (L4) 的处理，土壤压实度的增加（从 D1 到 D2 和从 D1 到 D3）分别使 IWCP 减少了约 17.5% 和 20.5%。LLWR 的相应降低分别为 22% 和 66%，而 PAW 则可以忽略不计。这些结果表明，PAW 几乎没有反应，LLWR 对土壤压实或容重过度响应，而 IWCP 似乎更真实地反映了土壤压实对植物土壤水分有效性的影响。IWCP 从 L4 到 L1 减少了 43%。与 LLWR 和 PAW 相反，