Ecol Evol. 2012 Jun;2(6):1235-50. doi: 10.1002/ece3.266.
CO(2)-enrichment experiments consistently show that rooting depth increases when trees are grown at elevated CO(2) (eCO(2)), leading in some experiments to increased capture of available soil nitrogen (N) from deeper soil. However, the link between N uptake and root distributions remains poorly represented in forest ecosystem and global land-surface models. Here, this link is modeled and analyzed using a new optimization hypothesis (MaxNup) for root foraging in relation to the spatial variability of soil N, according to which a given total root mass is distributed vertically in order to maximize annual N uptake. MaxNup leads to analytical predictions for the optimal vertical profile of root biomass, maximum rooting depth, and N-uptake fraction (i.e., the proportion of plant-available soil N taken up annually by roots). We use these predictions to gain new insight into the behavior of the N-uptake fraction in trees growing at the Oak Ridge National Laboratory free-air CO(2)-enrichment experiment. We also compare MaxNup with empirical equations previously fitted to root-distribution data from all the world's plant biomes, and find that the empirical equations underestimate the capacity of root systems to take up N.
CO2 富集实验一致表明，树木在高浓度 CO2（eCO2）环境下生长时，根系深度会增加，从而导致对深层土壤中可用土壤氮（N）的吸收增加。然而，森林生态系统和全球陆面模型中对 N 吸收与根系分布之间的联系仍缺乏充分的描述。在这里，我们使用一种新的根系觅食优化假设（MaxNup）来模拟和分析这种联系，该假设根据土壤 N 的空间变异性来描述根系的分布，根据该假设，给定的总根质量将垂直分布以最大限度地提高年 N 吸收量。MaxNup 为根系生物量的最优垂直分布、最大根系深度和 N 吸收分数（即每年根系吸收的植物可用土壤 N 的比例）提供了分析预测。我们利用这些预测，深入了解橡树岭国家实验室自由空气 CO2 富集实验中树木生长的 N 吸收分数的行为。我们还将 MaxNup 与之前根据全球所有植物生物群落的根系分布数据拟合的经验方程进行了比较，发现经验方程低估了根系吸收 N 的能力。
