Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK.
Universidad Nacional de San Antonio Abad del Cusco, Cusco, Perú.
Glob Chang Biol. 2021 Aug;27(15):3657-3680. doi: 10.1111/gcb.15677. Epub 2021 May 31.
Fine roots constitute a significant component of the net primary productivity (NPP) of forest ecosystems but are much less studied than aboveground NPP. Comparisons across sites and regions are also hampered by inconsistent methodologies, especially in tropical areas. Here, we present a novel dataset of fine root biomass, productivity, residence time, and allocation in tropical old-growth rainforest sites worldwide, measured using consistent methods, and examine how these variables are related to consistently determined soil and climatic characteristics. Our pantropical dataset spans intensive monitoring plots in lowland (wet, semi-deciduous, and deciduous) and montane tropical forests in South America, Africa, and Southeast Asia (n = 47). Large spatial variation in fine root dynamics was observed across montane and lowland forest types. In lowland forests, we found a strong positive linear relationship between fine root productivity and sand content, this relationship was even stronger when we considered the fractional allocation of total NPP to fine roots, demonstrating that understanding allocation adds explanatory power to understanding fine root productivity and total NPP. Fine root residence time was a function of multiple factors: soil sand content, soil pH, and maximum water deficit, with longest residence times in acidic, sandy, and water-stressed soils. In tropical montane forests, on the other hand, a different set of relationships prevailed, highlighting the very different nature of montane and lowland forest biomes. Root productivity was a strong positive linear function of mean annual temperature, root residence time was a strong positive function of soil nitrogen content in montane forests, and lastly decreasing soil P content increased allocation of productivity to fine roots. In contrast to the lowlands, environmental conditions were a better predictor for fine root productivity than for fractional allocation of total NPP to fine roots, suggesting that root productivity is a particularly strong driver of NPP allocation in tropical mountain regions.
细根是森林生态系统净初级生产力(NPP)的重要组成部分,但研究程度远低于地上 NPP。由于方法不一致,特别是在热带地区,跨地点和跨区域的比较也受到阻碍。在这里,我们提出了一个新的全球热带原始雨林地点细根生物量、生产力、停留时间和分配的数据集,这些数据是使用一致的方法测量的,并研究了这些变量与一致确定的土壤和气候特征有何关系。我们的泛热带数据集涵盖了南美的低地(湿润、半落叶和落叶)和山地热带森林,以及非洲和东南亚的高山热带森林的密集监测地块(n=47)。在山地和低地森林类型中,我们观察到细根动态存在很大的空间差异。在低地森林中,我们发现细根生产力与砂含量之间存在很强的正线性关系,当我们考虑到总 NPP 到细根的分数分配时,这种关系甚至更强,这表明理解分配可以增加对细根生产力和总 NPP 的解释能力。细根停留时间是多个因素的函数:土壤砂含量、土壤 pH 值和最大水分亏缺,在酸性、砂质和受水分胁迫的土壤中停留时间最长。另一方面,在热带山地森林中,另一种关系占主导地位,突出了山地和低地森林生物群落的截然不同的性质。根生产力与年平均温度呈很强的正线性关系,根停留时间与山地森林的土壤氮含量呈很强的正函数关系,最后土壤 P 含量的减少增加了生产力向细根的分配。与低地相比,环境条件是细根生产力的更好预测因子,而不是总 NPP 到细根的分数分配,这表明根生产力是热带山区 NPP 分配的一个特别重要的驱动因素。