title: Photosynthetic overcompensation under nocturnal warming enhances grassland carbon sequestration.
abstract: A mechanistic understanding of the carbon (C) cycle-climate change feedback is essential for projecting future states of climate and ecosystems. Here we report a novel field mechanism and evidence supporting the hypothesis that nocturnal warming in a temperate steppe ecosystem in northern China can result in a minor C sink instead of a C source as models have predicted. Nocturnal warming increased leaf respiration of two dominant grass species by 36.3%, enhanced consumption of carbohydrates in the leaves (72.2% and 60.5% for sugar and starch, respectively), and consequently stimulated plant photosynthesis by 19.8% in the subsequent days. Our experimental findings confirm previous observations of nocturnal warming stimulating plant photosynthesis through increased draw-down of leaf carbohydrates at night. The enhancement of plant photosynthesis overcompensated the increased C loss via plant respiration under nocturnal warming and shifted the steppe ecosystem from a minor C source (1.87 g C x m(-2) x yr(-1)) to a C sink (21.72 g C x m(-2) x yr(-1)) across the three growing seasons from 2006 to 2008. Given greater increases in daily minimum than maximum temperature in many regions, plant photosynthetic overcompensation may partially serve as a negative feedback mechanism for terrestrial biosphere to climate warming.
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing 100093, China. swan@ibcas.ac.cn
authors.forename: Shiqiang
authors.initials: S
authors.lastname: Wan
authors.forename: Jianyang
authors.initials: J
authors.lastname: Xia
authors.forename: Weixing
authors.initials: W
authors.lastname: Liu
authors.forename: Shuli
authors.initials: S
authors.lastname: Niu
mesh_terms: D000818:Animals; D002244:Carbon / Q000378:metabolism*; D002940:Circadian Rhythm; D017753:Ecosystem; D010788:Photosynthesis / Q000502:physiology*; D006109:Poaceae / Q000502:physiology*; D012987:Soil; D013997:Time Factors
chemical_list: D012987:Soil; D002244:Carbon