High-energy cosmic-ray electrons and positrons (CREs), which lose energy quickly during their propagation, provide a probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been measured directly up to approximately 2 teraelectronvolts in previous balloon- or space-borne experiments, and indirectly up to approximately 5 teraelectronvolts using ground-based Cherenkov γ-ray telescope arrays. Evidence for a spectral break in the teraelectronvolt energy range has been provided by indirect measurements, although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the Dark Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The largest part of the spectrum can be well fitted by a 'smoothly broken power-law' model rather than a single power-law model. The direct detection of a spectral break at about 0.9 teraelectronvolts confirms the evidence found by previous indirect measurements, clarifies the behaviour of the CRE spectrum at energies above 1 teraelectronvolt and sheds light on the physical origin of the sub-teraelectronvolt CREs.

Photoprotection mechanisms protect photosynthetic organisms, especially under stress conditions, against photodamage that may inhibit photosynthesis. We investigated the effects of short-term immersion in hypo-and hypersalinity seawater on the photosynthesis and xanthophyll cycle in Sargassum fusiforme (Harvey) Setchell. The results indicated that under moderate light [110 μmol(photon) m -2 s -1 ], the effective quantum yield of PSII in S. fusiforme fronds was not reduced by treatment for 1 h in hyposalinity conditions, even in freshwater, but was significantly affected by extreme hypersalinity treatment (90‰ seawater). Under high light [HL, 800 μmol(photon) m -2 s -1 ], photoprotective mechanisms operated efficiently in fronds immersed in freshwater as indicated by high reversible nonphotochemical quenching of Chl fluorescence (NPQ) and de-epoxidation state; the quantum yield of PSII recovered during the subsequent relaxation period. In contrast, fronds immersed in 90‰ seawater did not withstand HL, barely developed reversible NPQ, and accumulated little antheraxanthin and zeaxanthin during HL, while recovery of the quantum yield of PSII was severely inhibited during the subsequent relaxation period. The data provided concrete evidence supporting the short-term tolerance of S. fusiforme to immersion in freshwater compared with hypersalinity conditions. The potential practical implications of these results were also discussed.Additional key words: hypo-and hypersalinity stress; nonphotochemical quenching; Sargassum fusiforme; xanthophyll cycle.