资源环境科技发展态势分析平台

Carbon dioxide enrichment of a mature forest resulted in the emission of the excess carbon back into the atmosphere via enhanced ecosystem respiration, suggesting that mature forests may be limited in their capacity to mitigate climate change.

Atmospheric carbon dioxide enrichment (eCO(2)) can enhance plant carbon uptake and growth(1-5), thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration(6). Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth(3-5), it is unclear whether mature forests respond to eCO(2) in a similar way. In mature trees and forest stands(7-10), photosynthetic uptake has been found to increase under eCO(2) without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO(2) unclear(4,5,7-11). Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO(2) exposure. We show that, although the eCO(2) treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO(2), and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests.

Insights into the interactions between pro- and anti-vaccination clusters on Facebook can enable policies and approaches that attempt to interrupt the shift to anti-vaccination views and persuade undecided individuals to adopt a pro-vaccination stance.

Distrust in scientific expertise(1-14) is dangerous. Opposition to vaccination with a future vaccine against SARS-CoV-2, the causal agent of COVID-19, for example, could amplify outbreaks(2-4), as happened for measles in 2019(5,6). Homemade remedies(7,8) and falsehoods are being shared widely on the Internet, as well as dismissals of expert advice(9-11). There is a lack of understanding about how this distrust evolves at the system level(13,14). Here we provide a map of the contention surrounding vaccines that has emerged from the global pool of around three billion Facebook users. Its core reveals a multi-sided landscape of unprecedented intricacy that involves nearly 100 million individuals partitioned into highly dynamic, interconnected clusters across cities, countries, continents and languages. Although smaller in overall size, anti-vaccination clusters manage to become highly entangled with undecided clusters in the main online network, whereas pro-vaccination clusters are more peripheral. Our theoretical framework reproduces the recent explosive growth in anti-vaccination views, and predicts that these views will dominate in a decade. Insights provided by this framework can inform new policies and approaches to interrupt this shift to negative views. Our results challenge the conventional thinking about undecided individuals in issues of contention surrounding health, shed light on other issues of contention such as climate change(11), and highlight the key role of network cluster dynamics in multi-species ecologies(15).