Akale Asegidew, Abdalla Mohanned, Koehler Tina, Sauer Anna M, Diamantopoulos Efstathios, Ahmed Mutez A
Root-Soil Interaction, School of Life Sciences, Technical University of Munich, Freising, 85354, Germany.
Department of Horticulture, Faculty of Agriculture, University of Khartoum, Khartoum North, 13314, Sudan.
Ann Bot. 2025 Dec 8;136(5-6):1131-1142. doi: 10.1093/aob/mcaf182.
Plants have evolved various root adaptive traits to enhance their ability to access soil water in stressful conditions. Although root mucilage has been suggested to facilitate root water uptake in drying soils, its impact during combined edaphic and atmospheric stress remains unknown. We hypothesized that mucilage decreases the saturated soil hydraulic conductivity, and consequently, a genotype with high mucilage production will exhibit lower maximum soil-plant hydraulic conductance and restrict transpiration at relatively low vapour pressure deficit (VPD). On the contrary, in drying soil, mucilage attenuates the gradients in matric potential at the root-soil interface and thus facilitates root water uptake, especially at high VPD.
We compared two cowpea genotypes with contrasting mucilage production rates and subjected them to three consecutively increasing levels of VPD (1.04, 1.8 and 2.8 kPa) while the soil was left to dry out. We measured the transpiration rate and soil and leaf water potentials and estimated canopy and plant hydraulic conductance during soil drying.
In wet soil conditions, the high-mucilage genotype restricted transpiration rate at lower VPD (1.46 kPa) compared with the low-mucilage genotype (1.58 kPa). Likewise, the initial slope of transpiration rate in response to VPD (the maximum conductance) was significantly lower in the high- compared with the low-mucilage genotype. During soil drying, the transpiration rate declined earlier in the low- compared with the high-mucilage genotype, supporting the hypothesis that mucilage helps to maintain the hydraulic continuity between roots and soil at lower water potentials in the high-mucilage genotype.
Root mucilage is a promising trait that reduces water use in wet soil conditions, thereby conserving soil moisture for critical phases (e.g. flowering and grain filling), both on a daily basis (increasing VPD) and on a seasonal time scale (soil drying).
植物已经进化出各种根系适应性特征，以增强其在胁迫条件下获取土壤水分的能力。尽管有研究表明根系黏液有助于在干燥土壤中吸收根系水分，但其在土壤和大气复合胁迫期间的影响仍不清楚。我们推测，黏液会降低饱和土壤导水率，因此，高黏液分泌型基因型将表现出较低的最大土壤-植物导水率，并在相对较低的蒸汽压亏缺（VPD）下限制蒸腾作用。相反，在干燥土壤中，黏液会减弱根-土界面处基质势的梯度，从而促进根系水分吸收，尤其是在高VPD条件下。
我们比较了两种黏液分泌率不同的豇豆基因型，并在土壤逐渐变干的过程中，让它们经历三个连续升高的VPD水平（1.04、1.8和2.8 kPa）。我们测量了蒸腾速率、土壤和叶片水势，并估算了土壤干燥过程中的冠层和植物导水率。
在湿润土壤条件下，与低黏液分泌型基因型（1.58 kPa）相比，高黏液分泌型基因型在较低的VPD（1.46 kPa）时限制了蒸腾速率。同样，与低黏液分泌型基因型相比，高黏液分泌型基因型中蒸腾速率对VPD响应的初始斜率（最大导水率）显著更低。在土壤干燥过程中，低黏液分泌型基因型的蒸腾速率比高黏液分泌型基因型下降得更早，这支持了黏液有助于在高黏液分泌型基因型中较低水势下维持根系与土壤之间水力连续性的假设。
根系黏液是一个有前景的性状，它能在湿润土壤条件下减少水分利用，从而在日常（VPD增加）和季节性时间尺度（土壤干燥）上为关键阶段（如开花和灌浆）保存土壤水分。
