M oun a r t i c l e i n f o
Received 2 July 2015
Received in revised form because it was difficult to measure in a harsh winter environment and because of the historical assumption that soil respiration was close to zero in winter . rophic respiration icroorganisms . during the nonthe Qinghai-Tibet rotrophic respirail microorganisms rctic permafrost in sitive and measurecosystems [5e7] and alpine ecosystems . Over half of the C fixed in growing season can be offset during the non-growing season soil
CO2 flux [8,9]. The annual CO2 exchange estimation would be underestimated when based on growing season alone. The alpine meadow have been reported a C sink during the growing season in the Qinghai-Tibet Plateau [10,11], however, the annual C balance is uncertain since continuous soil CO2 emission have been reported * Corresponding author. Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, #9, Block 4, Renminnanlu Road, Chengdu, China.
Contents lists availab
European Journal ww
European Journal of Soil Biology 71 (2015) 45e52E-mail address: firstname.lastname@example.org (G. Wang).in various ecosystems during the growing season, but comparatively little effort has focused on non-growing season fluxes, partly able at 18 C . In recent years, the large contribution of winter soil CO2 flux to annual budgets has been reported in Arctic tundra1. Introduction
Soil respiration is an important part of the terrestrial C cycle and feedback to global climate change. The terrestrial C budget depends on the balance between C absorbed by photosynthesis and C released by ecosystem respiration , so the C budget will be affected when soil respiration does not offset change in plant productivity. Many studies of soil respiration have been conducted
Soil respiration is mainly composed of autot from roots and heterotrophic respiration from m
With low temperatures and no living plants growing season in the permafrost region of
Plateau, soil respiration mainly comes from hete tion . Recent research has shown that some so can be active at extremely low temperatures in A the cold season and soil respiration remains po24 October 2015
Accepted 26 October 2015
Available online 16 November 2015
Winter soil respiration
Qinghai-Tibet Plateauhttp://dx.doi.org/10.1016/j.ejsobi.2015.10.004 1164-5563/© 2015 Elsevier Masson SAS. All rights resa b s t r a c t
Non-growing season soil CO2 emissions are very important part of the annual C balance in the Arctic tundra ecosystems, but very limited information is available for the permafrost region of the QinghaiTibet Plateau, which hold great quantities of C. We conducted a full year measurement of soil CO2 flux in an alpine meadow and swampmeadow to quantify seasonal dynamics of non-growing season (include winter and initial thaw and freeze period (TFP)) soil CO2 flux and its contribution to annual soil CO2 emissions. Mean soil CO2 flux was higher in TFP (0.38e0.54 mmol m2 s1) than in winter (0.11 e0.23 mmol m2 s1), with significant higher in swamp meadow than alpine meadow in the nongrowing season. Soil temperature explained 76e85% of the yearly variation in the soil CO2 flux, with higher temperature sensitivity (Q10) in the TFP (5.67e9.43) than in other seasons (2.65e2.99). The cumulative non-growing season soil CO2 emission was 228e358 g CO2 m 2, accounted for 25e26% of annual emissions. The integrated contribution of non-growing season to annual emission based on season-specific, annual and growing season Q10 model were 26e27%, 32e34% and 44e45%, respectively, season-specific model may improve the accuracy of estimating the soil CO2 emissions. Our results indicate that non-growing season contributes a large portion of the annual soil CO2 emission in the permafrost region of the Qinghai-Tibet Plateau. Hence, estimating of annual C balance must consider the non-growing season soil CO2 emission, and should not neglect the soil CO2 emission of swamp meadow. © 2015 Elsevier Masson SAS. All rights reserved.Chengdu 610041, China b University of Chinese Academy of Sciences, Beijing 100000, ChinaOriginal article
Non-growing season soil CO2 flux and i
CO2 emissions in two typical grasslands the Qinghai-Tibet Plateau
Tao Zhang a, b, Genxu Wang a, *, Yan Yang a, Tianxu a Key Laboratory of Mountain Surface Processes and Ecological Regulation, Institute of M journal homepage: http : / /werved.contribution to annual soil the permafrost region of ao a, b, Xiaopeng Chen a, b tain Hazards and Environment, Chinese Academy of Sciences, le at ScienceDirect of Soil Biology .e lsevier .com/locate/ejsobi non-growing season at our study site from mid-September to May, and seal them with duct tape. Measurements were made after the al othroughout the non-growing season in this region , so measurements of non-growing season soil CO2 flux are very important for accurately predicting annual soil C budgets.
Similar to Arctic permafrost, there is a long dormant season in the permafrost region of the Qinghai-Tibet Plateau, which possesses large areas with great quantities of C. Among the few studies that address this region, a few have focused on growing season, or the non-permafrost areas of the region [4,10e12]. There is little information about non-growing season soil CO2 flux in this region , so the non-growing season soil CO2 flux remains an uncertainty. Additionally, previous studies mainly focused on a single vegetation type (alpine meadow), however, variation in vegetation type may effect CO2 flux both in summer and winter across Arctic tundra due to different gross primary production, fine root biomass, substrate availability and soil microclimate [14,15]. While the permafrost in this region is largely dominated by alpine meadow, there are also areas of swampmeadow under waterlogged or moist soil conditions occurring in patches or strips in the mountains.
Swamp meadow may release more soil CO2 than the alpine meadow due to the much greater live biomass, soil organic C and microbial C than alpine meadow . In situ measurements including swamp meadow are needed to improve our understanding of the mechanisms of non-growing season soil CO2 flux and annual soil CO2 emission estimation. Estimation of soil CO2 emission is often predicted by the temperature sensitivity of soil respiration (Q10), annual soil emission modeled by a single Q10 may not be accurate, due to seasonal variation in temperature, water, plant phenology and substrate availability [12,17]. Hence, to accurately predict the annual soil CO2 emission, it is necessary to fieldmeasure and model seasonal fluxes on different timescales, including non-growing season.