Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
Graduate Program in Ecology, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
PLoS One. 2021 Jul 14;16(7):e0254672. doi: 10.1371/journal.pone.0254672. eCollection 2021.
Root lifespan, often is estimated in landscape- and ecosystem-level carbon models using linear approximations. In water manipulation experiments, fine root lifespan can vary with soil water content. Soil water content is generally structured by complex topography, which is largely unaccounted for in landscape- and ecosystem-scale carbon models. Topography governs the range of soil water content experienced by roots which may impact their lifespan. We hypothesized that root lifespan varied nonlinearly across a temperate, mesic, forested catchment due to differences in soil water content associated with topographic position. We expected regions of the landscape that were too wet or too dry would have soils that were not optimal for roots and thus result in shorter root lifespans. Specifically, we hypothesized that root lifespan would be longest in areas that consistently had soil water content in the middle of the soil water content spectrum, while in soils at either very low or very high soil water content, root lifespan would be relatively short. We tested this hypothesis by collecting and analyzing two years of minirhizotron and soil moisture data in plots widely distributed in the Shale Hills catchment of the Susquehanna-Shale Hills Critical Zone Observatory in Pennsylvania. We found that fine root lifespans were longer in traditionally wetter topographic regions, but detected no short term (biweekly) effect of soil moisture on root lifespan. Additionally, depth in soil, soil series, slope face orientation, and season of birth strongly affected root lifespans across the catchment. In contrast, lifespan was unaffected by root diameter or mycorrhizal association. Failure to account for these variables could result in erroneous estimates of fine root lifespan and, consequentially, carbon flux in temperate forested regions.
根寿命通常在景观和生态系统水平的碳模型中使用线性近似来估计。在水分处理实验中，细根寿命会随土壤水分含量而变化。土壤水分含量通常由复杂的地形结构控制，而地形结构在景观和生态系统尺度的碳模型中基本没有被考虑到。地形决定了根系经历的土壤水分范围，这可能会影响它们的寿命。我们假设，由于与地形位置相关的土壤水分含量差异，在一个温带湿润的森林流域，根寿命会呈非线性变化。我们预计过于湿润或过于干燥的景观区域的土壤条件不利于根系，从而导致根寿命较短。具体来说，我们假设在土壤水分含量处于中间范围的区域，根寿命最长，而在土壤水分含量非常低或非常高的土壤中，根寿命相对较短。为了验证这一假设，我们在宾夕法尼亚州的萨斯奎哈纳-页岩丘陵关键区观测站的 Shale Hills 流域的广泛分布的样地中收集并分析了两年的微根窗和土壤湿度数据。我们发现，细根寿命在传统上较湿润的地形区域较长，但没有检测到短期（每两周）土壤湿度对根寿命的影响。此外，土壤深度、土壤系列、坡面朝向和出生季节强烈影响了整个流域的根寿命。相比之下，根直径或菌根关联对寿命没有影响。如果不考虑这些变量，可能会导致对温带森林地区细根寿命和因此碳通量的错误估计。
