Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN 55108;
Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN 55108.
Proc Natl Acad Sci U S A. 2021 Apr 27;118(17). doi: 10.1073/pnas.2016965118.
Whether the terrestrial biosphere will continue to act as a net carbon (C) sink in the face of multiple global changes is questionable. A key uncertainty is whether increases in plant C fixation under elevated carbon dioxide (CO) will translate into decades-long C storage and whether this depends on other concurrently changing factors. We investigated how manipulations of CO, soil nitrogen (N) supply, and plant species richness influenced total ecosystem (plant + soil to 60 cm) C storage over 19 y in a free-air CO enrichment grassland experiment (BioCON) in Minnesota. On average, after 19 y of treatments, increasing species richness from 1 to 4, 9, or 16 enhanced total ecosystem C storage by 22 to 32%, whereas N addition of 4 g N m ⋅ y and elevated CO of +180 ppm had only modest effects (increasing C stores by less than 5%). While all treatments increased net primary productivity, only increasing species richness enhanced net primary productivity sufficiently to more than offset enhanced C losses and substantially increase ecosystem C pools. Effects of the three global change treatments were generally additive, and we did not observe any interactions between CO and N. Overall, our results call into question whether elevated CO will increase the soil C sink in grassland ecosystems, helping to slow climate change, and suggest that losses of biodiversity may influence C storage as much as or more than increasing CO or high rates of N deposition in perennial grassland systems.
面对多种全球变化，陆地生物圈是否将继续作为一个净碳（C）汇是值得怀疑的。一个关键的不确定性是，在二氧化碳（CO）升高的情况下，植物 C 固定的增加是否会转化为长达数十年的 C 储存，以及这是否取决于其他同时变化的因素。我们研究了 CO、土壤氮（N）供应和植物物种丰富度的人为控制如何在明尼苏达州的一个自由空气 CO 富集草原实验（BioCON）中影响长达 19 年的整个生态系统（植物+土壤至 60cm）C 储存。平均而言，经过 19 年的处理后，物种丰富度从 1 增加到 4、9 或 16，会使整个生态系统的 C 储存增加 22%至 32%，而 4gNm ⋅ y 的 N 添加和 +180ppm 的 CO 升高的影响较小（增加的 C 储量不到 5%）。虽然所有处理都增加了净初级生产力，但只有增加物种丰富度才能显著增加净初级生产力，足以抵消增强的 C 损失，并显著增加生态系统的 C 库。三种全球变化处理的影响通常是累加的，我们没有观察到 CO 和 N 之间的任何相互作用。总的来说，我们的结果质疑了升高的 CO 是否会增加草原生态系统的土壤 C 汇，从而有助于减缓气候变化，并表明生物多样性的丧失可能会影响 C 储存，其程度与增加 CO 或在多年生草原系统中高 N 沉积一样多，甚至更多。
