Data From: Root Distributions Predict Shrub-Steppe Responses to Precipitation Intensity

Precipitation events are becoming more intense around the world, changing the way water moves through soils and plants. Plant rooting strategies that sustain water uptake under these conditions are likely to become more abundant (e.g., shrub encroachment). Yet, it remains difficult to predict species responses to climate change because we typically do not know where active roots are located or how much water they absorb. Here, we applied a water tracer experiment to describe forb, grass, and shrub root distributions. These measurements were made in 8 m by 8 m field shelters with low or high precipitation intensity. We used tracer uptake data in a soil water flow model to estimate how much water respective plant root tissues absorb over time. In low precipitation intensity plots, deep shrub roots were estimated to absorb the most water (93 mm yr-1) and shrubs had the greatest aboveground cover (27%). Grass root distributions were estimated to absorb an intermediate amount of water (80 mm yr-1) and grasses had intermediate aboveground cover (18%). Forb root distributions were estimated to absorb the least water (79 mm yr-1) and had the least aboveground cover (12%). In high precipitation intensity plots, shrub and forb root distributions changed in ways that increased their water uptake relative to grasses, predicting the increased aboveground growth of shrubs and forbs in these plots. In short, water uptake caused by different rooting distributions predicted plant aboveground cover. Our results suggest that detailed descriptions of active plant root distributions can predict plant growth responses to climate change in arid and semi-arid ecosystems.

全球范围内的降水事件正变得愈发强烈，这改变了水分在土壤与植物间的运移路径。在此类条件下能够维持水分吸收的植物根系策略（如灌木扩张（shrub encroachment））或将愈发普遍。然而，当前仍难以准确预测物种对气候变化的响应——这是因为我们通常无法明确活根系的具体分布位置，也难以量化其吸收的水分总量。本研究通过水示踪实验（water tracer experiment），系统刻画了非禾本草本植物（forb）、草本植物与灌木的根系分布特征。相关测量在规格为8 m × 8 m的野外防雨棚中开展，棚内设置低、高两种降水强度梯度。我们将示踪剂吸收数据代入土壤水流模型（soil water flow model），以此估算不同植物根系组织随时间推移的吸水量。在低降水强度样地中，深层灌木根系的估测吸水量最高（93 mm yr⁻¹），且灌木的地上盖度也最大（27%）；草本植物根系的估测吸水量处于中等水平（80 mm yr⁻¹），地上盖度同样为中等（18%）；非禾本草本植物根系的估测吸水量最低（79 mm yr⁻¹），地上盖度也最小（12%）。在高降水强度样地中，灌木与非禾本草本植物的根系分布发生改变，使其相对于草本植物的吸水量有所提升，这预示着此类样地中灌木与非禾本草本植物的地上生长量将有所增加。简言之，由不同根系分布所决定的水分吸收能力，可以预测植物的地上盖度。本研究结果表明，对活植物根系分布的精细化描述，能够预测干旱与半干旱生态系统中植物对气候变化的生长响应。