306 research outputs found

    Using the dynamics of productivity and precipitation-use efficiency to detect state transitions in Eurasian grasslands

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    Using the dynamics of productivity and precipitation-use efficiency to detect state transitions in Eurasian grasslands

    Precipitation trend increases the contribution of dry reduced nitrogen deposition

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    Abstract Given the leveling off in oxidized nitrogen emissions around the world, the atmospheric deposition of reduced nitrogen (NH x  = NH3 + NH4 +) has become progressively critical, especially dry deposition, which presents great threats to plant growth. A combination of historical deposition data of measured wet NH x and modeled dry NH x in China suggests that dry NHx deposition has been increasing substantially (4.50% yr−1, p < 0.05) since 1980. Here, chemical transport model (WRF-EMEP) results indicate that variation in NH3 emissions is not a dominant factor resulting in the continually increasing trends of dry NH x deposition, while climate change-induced trends in precipitation patterns with less frequent light rain and more frequent consecutive rain events (with ≥2 consecutive rainy days) contribute to the increase in dry NH x deposition. This will continue to shift NH x deposition from wet to dry form at a rate of 0.12 and 0.23% yr−1 (p < 0.05) for the period of 2030–2100 in China under the RCP4.5 and RCP8.5 scenarios, respectively. Further analysis for North America and Europe demonstrates results similar to China, with a consistent increase in the contribution of dry NHx deposition driven by changing precipitation patterns from ~30% to ~35%. Our findings, therefore, uncover the change of precipitation patterns has an increasing influence on the shifting of NH x deposition from wet to dry form in the Northern Hemisphere and highlight the need to shift from total NH x deposition-based control strategies to more stringent NH3 emission controls targeting dry NH x deposition in order to mitigate the potential negative ecological impacts

    China’s current forest age structure will lead to weakened carbon sinks in the near future

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    Forests are chiefly responsible for the terrestrial carbon sink that greatly reduces the buildup of CO2 concentrations in the atmosphere and alleviates climate change. Current predictions of terrestrial carbon sinks in the future have so far ignored the variation of forest carbon uptake with forest age. Here, we predict the role of China’s current forest age in future carbon sink capacity by generating a high-resolution (30 m) forest age map in 2019 over China’s landmass using satellite and forest inventory data and deriving forest growth curves using measurements of forest biomass and age in 3,121 plots. As China’s forests currently have large proportions of young and middle-age stands, we project that China’s forests will maintain high growth rates for about 15 years. However, as the forests grow older, their net primary productivity will decline by 5.0% ± 1.4% in 2050, 8.4% ± 1.6% in 2060, and 16.6% ± 2.8% in 2100, indicating weakened carbon sinks in the near future. The weakening of forest carbon sinks can be potentially mitigated by optimizing forest age structure through selective logging and implementing new or improved afforestation. This finding is important not only for the global carbon cycle and climate projections but also for developing forest management strategies to enhance land sinks by alleviating the age effect

    Photosynthetic capacity dominates the interannual variation of annual gross primary productivity in the Northern Hemisphere

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    Annual gross primary productivity (AGPP) of terrestrial ecosystems is the largest carbon flux component in ecosystems; however, it's unclear whether photosynthetic capacity or phenology dominates interannual variation of AGPP, and a better understanding of this could contribute to estimation of carbon sinks and their interactions with climate change. In this study, observed GPP data of 494 site-years from 39 eddy covariance sites in Northern Hemisphere were used to investigate mechanisms of interannual variation of AGPP. This study first decomposed AGPP into three seasonal dynamic attribute parameters (growing season length (CUP), maximum daily GPP (GPPmax), and the ratio of mean daily GPP to GPPmax (αGPP)), and then decomposed AGPP into mean leaf area index (LAIm) and annual photosynthetic capacity per leaf area (AGPPlm). Furthermore, GPPmax was decomposed into leaf area index of DOYmax (the day when GPPmax appeared) (LAImax) and photosynthesis per leaf area of DOYmax (GPPlmax). Relative contributions of parameters to AGPP and GPPmax were then calculated. Finally, environmental variables of DOYmax were extracted to analyze factors influencing interannual variation of GPPlmax. Trends of AGPP in 39 ecosystems varied from −65.23 to 53.05 g C m−2 yr−2, with the mean value of 6.32 g C m−2 yr−2. Photosynthetic capacity (GPPmax and AGPPlm), not CUP or LAI, was the main factor dominating interannual variation of AGPP. GPPlmax determined the interannual variation of GPPmax, and temperature, water, and radiation conditions of DOYmax affected the interannual variation of GPPlmax. This study used the cascade relationship of “environmental variables-GPPlmax-GPPmax-AGPP” to explain the mechanism of interannual variation of AGPP, which can provide new ideas for the AGPP estimation based on seasonal dynamic of GPP.ISSN:0048-9697ISSN:1879-102

    The “Regulator” Function of Viruses on Ecosystem Carbon Cycling in the Anthropocene

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    Viruses act as “regulators” of the global carbon cycle because they impact the material cycles and energy flows of food webs and the microbial loop. The average contribution of viruses to the Earth ecosystem carbon cycle is 8.6‰, of which its contribution to marine ecosystems (1.4‰) is less than its contribution to terrestrial (6.7‰) and freshwater (17.8‰) ecosystems. Over the past 2,000 years, anthropogenic activities and climate change have gradually altered the regulatory role of viruses in ecosystem carbon cycling processes. This has been particularly conspicuous over the past 200 years due to rapid industrialization and attendant population growth. The progressive acceleration of the spread and reproduction of viruses may subsequently accelerate the global C cycle
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