Rangarajan Harini, Lynch Jonathan P
Department of Plant Science, The Pennsylvania State University, University Park, PA 16802, USA.
Ann Bot. 2025 Dec 8;136(5-6):997-1011. doi: 10.1093/aob/mcae201.
Root axes with greater penetration ability are often considered to be beneficial in hard soils. We hypothesized that maize root phenotypes with greater plasticity (meaning reduced elongation in response to mechanical impedance, i.e. a 'stop signal') have fitness advantages over phenotypes with reduced plasticity (i.e. unimpeded root elongation) in native (virgin, uncultivated) soils, by reallocating root foraging to softer, presumably wetter, soil domains, and that the value of the stop signal reduced with soil cultivation and crop domestication.
We used OpenSimRoot to simulate native and cultivated soils and evaluated maize root phenotypes with varying axial and lateral root penetration ability in water, nitrogen (N) and impedance regimes associated with Neolithic agriculture.
The stop signal was advantageous in native soils but was less beneficial in cultivated, irrigated soils. Reduced root foraging in hard, dry topsoil enabled root growth in deeper domains where water is available, resulting in an improved balance of resource expenditure and acquisition. The value of the stop signal declined during crop domestication with the advent of irrigation, which increased water availability in the topsoil. Soil cultivation reduced N availability, while irrigation increased N leaching, resulting in a shift in the fitness landscape, with greater lateral root length (i.e. reduced plasticity) being advantageous by colocalizing root foraging with N availability. The importance of the stop signal is evident in modern high-input systems in which drought is a limiting factor.
Our results support the hypotheses that the reduction of lateral root growth by mechanical impedance is adaptive in native soil, but became less adaptive with soil cultivation and irrigation associated with Neolithic agriculture.
具有更强穿透能力的根轴通常被认为在坚硬土壤中具有优势。我们推测，在原生（未开垦、未耕种）土壤中，具有更大可塑性的玉米根表型（即对机械阻抗反应时伸长减少，也就是“停止信号”）相较于可塑性降低的表型（即根不受阻碍地伸长）具有适应性优势，因为前者能将根系觅食重新分配到更软、可能更湿润的土壤区域，并且随着土壤耕种和作物驯化，停止信号的价值降低。
我们使用OpenSimRoot模拟原生土壤和耕种土壤，并评估了在与新石器时代农业相关的水、氮（N）和阻抗条件下，具有不同轴向和侧向根穿透能力的玉米根表型。
停止信号在原生土壤中具有优势，但在耕种的灌溉土壤中益处较小。在坚硬、干燥的表土中减少根系觅食，能使根系在有水源的更深区域生长，从而改善资源消耗与获取的平衡。随着灌溉的出现，停止信号的价值在作物驯化过程中下降，灌溉增加了表土的水分供应。土壤耕种降低了氮的有效性，而灌溉增加了氮的淋失，导致适应性格局发生变化，更大的侧根长度（即更低的可塑性）因使根系觅食与氮的有效性共定位而具有优势。在干旱是限制因素的现代高投入系统中，停止信号的重要性很明显。
我们的结果支持以下假设：机械阻抗导致侧根生长减少在原生土壤中具有适应性，但随着与新石器时代农业相关的土壤耕种和灌溉，其适应性降低。
