The politics of numbers : the normative agendas of global benchmarking

Global benchmarks have grown exponentially over the last two decades, having been both applied to and developed by states, international organisations, corporations, and non-governmental organisations. As a consequence, global benchmarking is now firmly established as a distinct mode of transnational governance. Benchmarking chiefly involves the development of comparative metrics of performance, which typically take the form of highly stylised comparisons which are generated by translating complex phenomena into numerical values via simplification and extrapolation, commensuration, reification, and symbolic judgements. This process of translation takes what might otherwise be highly contentious normative agendas and converts them into formats that gain credibility through rhetorical claims to neutral and technocratic assessment. This politics of numbers has far-reaching ramifications for transnational governance, including the dimensions and effects of indirect power, expertise and agenda-setting, coordination, regulation and certification, and norm contestation and activism. This Special Issue draws upon an emerging literature to explore how and why benchmarks both align with and expand upon established models of International Relations theory and scholarship. It does so by critically examining the role of global benchmarks in key areas such as state ‘failure’, global supply chains, disaster management, economic governance, corporate social responsibility, and human development

Ectomycorrhizal fungi and past high CO2 atmospheres enhance mineral weathering through increased below-ground carbon-energy fluxes

Field studies indicate an intensification of mineral weathering with advancement from arbuscular mycorrhizal (AM) to later-evolving ectomycorrhizal (EM) fungal partners of gymnosperm and angiosperm trees. We test the hypothesis that this intensification is driven by increasing photosynthate carbon allocation to mycorrhizal mycelial networks using 14CO2-tracer experiments with representative tree–fungus mycorrhizal partnerships. Trees were grown in either a simulated past CO2 atmosphere (1500 ppm)—under which EM fungi evolved—or near-current CO2 (450 ppm). We report a direct linkage between photosynthate-energy fluxes from trees to EM and AM mycorrhizal mycelium and rates of calcium silicate weathering. Calcium dissolution rates halved for both AM and EM trees as CO2 fell from 1500 to 450 ppm, but silicate weathering by AM trees at high CO2 approached rates for EM trees at near-current CO2. Our findings provide mechanistic insights into the involvement of EM-associating forest trees in strengthening biological feedbacks on the geochemical carbon cycle that regulate atmospheric CO2 over millions of years

Evolution of trees and mycorrhizal fungi intensifies silicate mineral weathering.

Forested ecosystems diversified more than 350 Ma to become major engines of continental silicate weathering, regulating the Earth's atmospheric carbon dioxide concentration by driving calcium export into ocean carbonates. Our field experiments with mature trees demonstrate intensification of this weathering engine as tree lineages diversified in concert with their symbiotic mycorrhizal fungi. Preferential hyphal colonization of the calcium silicate-bearing rock, basalt, progressively increased with advancement from arbuscular mycorrhizal (AM) to later, independently evolved ectomycorrhizal (EM) fungi, and from gymnosperm to angiosperm hosts with both fungal groups. This led to 'trenching' of silicate mineral surfaces by AM and EM fungi, with EM gymnosperms and angiosperms releasing calcium from basalt at twice the rate of AM gymnosperms. Our findings indicate mycorrhiza-driven weathering may have originated hundreds of millions of years earlier than previously recognized and subsequently intensified with the evolution of trees and mycorrhizas to affect the Earth's long-term CO(2) and climate history

Stomatal and non-stomatal limitations in savanna trees and C4 grasses grown at low, ambient and high atmospheric CO2

[eng] By the end of the century, atmospheric CO2 concentration ([CO2]a) could reach 800 ppm, having risen from ∼200 ppm ∼24 Myr ago. Carbon dioxide enters plant leaves through stomata that limit CO2 diffusion and assimilation, imposing stomatal limitation (LS). Other factors limiting assimilation are collectively called non-stomatal limitations (LNS). C4 photosynthesis concentrates CO2 around Rubisco, typically reducing LS. C4-dominated savanna grasslands expanded under low [CO2]a and are metastable ecosystems where the response of trees and C4 grasses to rising [CO2]a will determine shifting vegetation patterns. How LS and LNS differ between savanna trees and C4 grasses under different [CO2]a will govern the responses of CO2 fixation and plant cover to [CO2]a - but quantitative comparisons are lacking. We measured assimilation, within soil wetting-drying cycles, of three C3 trees and three C4 grasses grown at 200, 400 or 800 ppm [CO2]a. Using assimilation-response curves, we resolved LS and LNS and show that rising [CO2]a alleviated LS, particularly for the C3 trees, but LNS was unaffected and remained substantially higher for the grasses across all [CO2]a treatments. Because LNS incurs higher metabolic costs and recovery compared with LS, our findings indicate that C4 grasses will be comparatively disadvantaged as [CO2]a rises

Data from: C4 savanna grasses fail to maintain assimilation in drying soil under low CO2 compared with C3 trees despite lower leaf water demand

1) C4 photosynthesis evolved when grasses migrated out of contracting forests under a declining atmospheric CO2 concentration ([CO2]a) and drying climate around 30 million years ago. C4 grasses are hypothesised to benefit from improved plant–water relations in open habitats like savannas, giving advantages over C3 plants under low [CO2]a. But experimental evidence in a low CO2 environment is limited and comparisons with C3 trees are needed to understand savanna vegetation patterns. 2) To test whether stomatal conductance (gS) and CO2 assimilation (A) are maintained in drier soil for C4 grasses than C3 trees, particularly under low [CO2]a, we investigated photosynthesis and plant–water relations of three C3 tree and three C4 grass species grown at 800, 400 or 200 ppm [CO2]a over moderate wetting–drying cycles. 3) C4 grasses had a lower soil–to–leaf water potential gradient than C3 trees, especially at 200 ppm [CO2]a, indicating reduced leaf water demand relative to supply. Yet the dependence of gS and A on predawn leaf water potential (a measure of soil water availability) was greater for the C4 grasses than trees, particularly under low [CO2]a. 4) Our findings establish that gS and A are not maintained in drier soil for C4 grasses compared with C3 trees, suggesting that this mechanism was not prevailing in the expansion of C4–dominated grasslands under low [CO2]a. This inherent susceptibility to sudden decreases in soil water availability justifies why C4 grasses have not evolved a resistant xylem allowing operation under drought, but instead shut down below a water potential threshold and rapidly recover. We point to this capacity to respond to transient water availability as a key overlooked driver of C4 grass success under low [CO2]a