Data from: What controls variation in carbon use efficiency among Amazonian tropical forests?

Why do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency (CUE: total Net Primary Production (NPP)/ Gross Primary Production (GPP)) may be due to changes in wood residence time (Biomass/NPPwood), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production (NPP: wood, fine roots, and leaves) and autotrophic respiration (Ra; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times <40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times >40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times >40 yrs and in stands with lower fertility, but changes to long-term mean annual temperatures do not impact CUE.为何部分森林的生物量生产效率高于其他森林？碳利用效率（Carbon Use Efficiency, CUE：总净初级生产力（Net Primary Production, NPP）/总初级生产力（Gross Primary Production, GPP））的差异，可能源于木材停留时间（生物量/NPP_木材）、温度或土壤养分状况的变化。我们在亚马逊与安第斯森林的14块1公顷样地中验证了这些假说，测定了净初级生产力（NPP：木材、细根与叶片）及自养呼吸（Ra：木材、根际与叶片呼吸）的多数关键组分。研究发现，养分较低的样地生物量生产效率更低，且根际呼吸更高，表明碳向地下组分的分配有所增加。随后我们对比了木材呼吸与木材生长、根际呼吸与细根生长，结果显示木材停留时间小于40年的森林，其木材与细根的维持呼吸均显著低于停留时间大于40年的森林。对比根际呼吸与细根生长的结果表明，低养分样地的根际生长呼吸显著更高。总体而言，我们发现亚马逊森林中，木材停留时间大于40年的林分以及养分较低的林分，其生物量生产效率更低，但长期年平均温度的变化并不会对碳利用效率产生影响。