Data from: Comparative water use by maize, perennial crops, restored prairie, and poplar trees in the US Midwest

Water use by plant communities across years of varying water availability indicates how terrestrial water balances will respond to climate change and variability as well as to land cover change. Perennial biofuel crops, likely grown mainly on marginal lands of limited water availability, provide an example of a potentially extensive future land cover conversion. We measured growing-season evapotranspiration (ET) based on daily changes in soil profile water contents in five perennial systems—switchgrass, miscanthus, native grasses, restored prairie, and hybrid poplar—and in annual maize (corn) in a temperate humid climate (Michigan, USA). Three study years (2010, 2011 and 2013) had normal growing-season rainfall (480–610 mm) whereas 2012 was a drought year (210 mm). Over all four years, mean (±SEM) growing-season ET for perennial systems did not greatly differ from corn (496 ± 21 mm), averaging 559 (±14), 458 (±31), 573 (±37), 519 (±30), and 492 (±58) mm for switchgrass, miscanthus, native grasses, prairie, and poplar, respectively. Differences in biomass production largely determined variation in water use efficiency (WUE). Miscanthus had the highest WUE in both normal and drought years (52–67 and 43 kg dry biomass ha−1 mm−1, respectively), followed by maize (40–59 and 29 kg ha−1 mm−1); the native grasses and prairie were lower and poplar was intermediate. That measured water use by perennial systems was similar to maize across normal and drought years contrasts with earlier modeling studies and suggests that rain-fed perennial biomass crops in this climate have little impact on landscape water balances, whether replacing rain-fed maize on arable lands or successional vegetation on marginal lands. Results also suggest that crop ET rates, and thus groundwater recharge, streamflow, and lake levels, may be less sensitive to climate change than has been assumed.不同水分可利用性年份下植物群落的用水特征，可揭示陆地水收支如何响应气候变化、气候变异性以及土地覆盖变化。有望主要种植于水分受限边际土地的多年生生物燃料作物，便是未来潜在大规模土地覆盖转换的典型案例。我们在美国密歇根州温带湿润气候区，针对5种多年生种植系统——柳枝稷（switchgrass）、芒草（miscanthus）、本土草本植物、恢复草原以及杂交杨树——以及一年生玉米（maize/corn），基于土壤剖面含水量的日变化测定了生长季蒸散发（evapotranspiration, ET）。本研究涵盖4个生长季：2010、2011和2013年的生长季降雨量处于正常水平（480–610 mm），而2012年为干旱年份（降雨量仅210 mm）。在全部4个生长季中，多年生种植系统的平均（±标准误，standard error of the mean, SEM）蒸散发与一年生玉米（496 ± 21 mm）无显著差异；其中柳枝稷、芒草、本土草本植物、恢复草原以及杂交杨树的平均蒸散发分别为559（±14）、458（±31）、573（±37）、519（±30）和492（±58）mm。生物量生产的差异在很大程度上决定了水分利用效率（water use efficiency, WUE）的变化。芒草在正常年份和干旱年份均具有最高的水分利用效率，分别为52–67和43 kg干生物量·hm⁻²·mm⁻¹，其次为玉米（40–59和29 kg·hm⁻²·mm⁻¹）；本土草本植物和恢复草原的水分利用效率较低，杂交杨树则处于中等水平。本研究测得的多年生系统用水量在正常和干旱年份均与玉米相近，这与此前的建模研究结果相悖，表明在该气候区，雨养多年生生物质作物无论替代耕地的雨养玉米，还是边际土地的演替植被，对景观水收支的影响都十分有限。本研究结果还表明，作物蒸散发速率以及由此关联的地下水补给、径流量和湖泊水位，可能比此前假设的对气候变化更不敏感。