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Zhang Y.P.,CAS Xishuangbanna Tropical Botanical Garden | Wu C.S.,Ailaoshan Station for Subtropical Forest Ecosystem Studies | Wu C.S.,University of Chinese Academy of Sciences | Liang N.S.,Japan National Institute of Environmental Studies | And 3 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2015

The soil-surface carbon flux is comparable to that of photosynthesis in terrestrial ecosystems. Much soil carbon flux to the atmosphere is due to rhizosphere metabolism (root respiration) and the decomposition of soil microbes (microbial respiration), which are both very sensitive to temperature. With soil temperatures increasing, soil respiration will increase, thereby accelerating global change. To improve our understanding of the response of soil temperature to future warming and to assess the potential effects of global warming on soil respiration in subtropical forests, we experimentally warmed subtropical evergreen broad-leaved forest soils in Ailao Mountain Southwest, China and measured their respiration. This experiment was conducted at the Ailaoshan Station for Subtropical Forest Ecosystem Studies (24°32′N, 101°01′E; 2480 m above sea level) of the Chinese Ecological Research Network, Jingdong County, Yunnan Province. The annual mean air temperature was 11.0°C, with a maximum monthly mean temperature of 15.3°C in July and a minimum monthly mean temperature of 5.1°Cin January. The site has strong rainy seasons (May to October) and dry seasons (November to April the following year). The average annual rainfall was 1882 mm, with 1607 mm (85.4% of the annual total) in the rainy season and 274.2 mm in the dry season (14.6% of the annual total). The soil is yellow brown in this area. Litterfall accumulates to 3—7 cm. Soil humus is dark brown and 10—15 cm thick. The mineral soil layer is loose and dominated by soil aggregates. Surface soils have high water permeability and water conservation ability, high organic carbon, and a pH of 4.5—5. Our artificial warming experiment was conducted in a subtropical forest where wind speed and radiation are both low at the surface. A multi-channel automated chamber system was used to continuously monitor soil CO2effluxes. The system was comprised of 20 automatic chambers (length 90 cm × width 90 cm × height 50 cm) and a control box, and the 20 chambers were divided into 4 treatments (5 chambers per treatment): control, litter removal, trenching, and infrared light warming. The soil efflux of each chamber was measured automatically each hour and environmental factors were measured each half hour. When measuring soil efflux, the chamber was closed for 3 min, then opened for 57 min by opening its lid. Thus, environmental conditions (e.g., wind, rainfall, and litterfall) in chambers were similar to those outside. In the artificial warming experiment, variations in soil temperature and soil water content were observed along with soil respiration. Based on measurements from 2011 to 2013, we concluded that warming did not change the seasonal and diurnal patterns of air temperature near the soil surface, soil temperature, or soil water content of the forest. The warming effects in winter and nighttime were greater than in summer and daytime. Warming decreased soil water content to a larger extent in the rainy season than in the dry season. The temperature increase and soil water decrease resulting from warming had seasonal variations, but not diurnal variations. The experimental warming increased the annual soil temperature by about 2°C; therefore, the warming treatment reached the goal of increasing soil temperature at 5 cm by 2°C. Our infrared warming method achieved a relatively stable warming effect without time lags in soil-temperature variations in the primary subtropical evergreen broad-leaved forest in Ailao Mountain. In this subtropical evergreen broad-leaved forest, soil temperature has previously shown a significant warming trend, so this study can supply information about soil respiration responses. This study also showed that variation in local air temperature, soil temperature, and soil-water content will not change under global warming, but soil-water content will decline with increased temperature, especially in the rainy season. In the forest, soil respiration is affected not only by soil temperature, but also by soil water content. As warming decreases soil water content, the effects of soil water content variation on soil respiration should be examined in future research. © 2005, Ecological Society of China. All rights reserved.


Liu Y.-T.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.-P.,CAS Xishuangbanna Tropical Botanical Garden | Wu C.-S.,Ailaoshan Station for Subtropical Forest Ecosystem Studies | Wu C.-S.,University of Chinese Academy of Sciences | And 4 more authors.
Chinese Journal of Ecology | Year: 2016

To improve our understanding of the responses of soil temperature and soil heterotrophic respiration to global warming in forest ecosystem, we simulated the change trend of soil temperature of subtropical evergreen broad-leaved forest in Ailao Mountains using the observed soil temperature data from 1986 to 2013, and computed the time required for a 2 °C increase in soil temperature. We conducted a soil warming experiment in a subtropical evergreen broad-leaved forest in Ailao Mountains. We compared field observations from trenching (NR) and trenching with soil warming (SW) from 2011 to 2013 with simulation results obtained from the WNMM model using future climate data under SRES A2 and B2 scenarios. We found that the soil temperature at 5 cm depth was significantly increased by 0.224 °C•10 a-1 in the last 30 years, and thus it would spend 90 years to increase 2 °C. The apparent respiration temperature sensitivity index (Q10) was 5.17 and 4.50 under the NR and SW treatments, respectively. Based on the Q10 value, under a 2 °C increase in soil temperature, soil heterotrophic respiration under the NR treatment was 14.6% higher than that of the SW treatment. The WNMM model was able to simulate soil water content (P<0.001) and soil temperature (P<0.001) after calibration and validation. By the end of 2100, soil heterotrophic respiration under the NR treatment would be 10.2% and 9.8% higher than that under the SW treatment under SRES A2 and B2 scenarios, respectively, and the soil heterotrophic respiration under the NR and SW treatments would be 7.0% and 6.6% higher under the SRES A2 scenario than under the SRES B2 scenario, respectively. These results indicated that field experiments on soil warming were important for understanding the responses of soil heterotrophic respiration to global warming, and should not be replaced by model simulation in that the latter will overestimate soil heterotrophic respiration. © 2016, Editorial Board of Chinese Journal of Ecology. All rights reserved.


Zhang Y.-P.,CAS Xishuangbanna Tropical Botanical Garden | Wu C.-S.,Ailaoshan Station for Subtropical Forest Ecosystem Studies | Wu C.-S.,University of Chinese Academy of Sciences | Liang N.-S.,Japan National Institute of Environmental Studies | And 3 more authors.
Chinese Journal of Ecology | Year: 2015

To improve our understanding of responses of soil temperature to global warming in forests, we conducted a soil warming experiment in a subtropical evergreen broad-leaved forest in Ailao Mountains, Yunnan, SW China. Based on measurements from 2011 to 2013, we examined warming effects on seasonal and diurnal patterns of soil temperature. The results showed that warming effects in dry season were greater than in rainy season, showing seasonal variations, but not diurnal variations. Soil-surface temperatures increased between January and April, with a 3 T maximum in February. Warming increased soil temperature by 2°C at the soil depth of 5 cm. The warming effect decreased exponentially with soil depth. Based on a 0.5 °C temperature increase, soil warming could reach the depth of 3.82 m in the dry season, 12.04 m in the rainy season, with an annual mean of 6.58 m. © 2015, editorial Board of Chinese Journal of Ecology. All rights reserved.


Wang X.,Chinese Academy of science | Wang X.,University of Chinese Academy of Sciences | Zhang H.,Chinese Academy of science | Zhang H.,University of Chinese Academy of Sciences | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2015

Biomass burning from the Indo-China Peninsula region is an important source of atmospheric mercury (Hg). We isolated 18 unique transport events over 2 years using observations of Hg and CO at a high-altitude background site in southwestern China (Mount Ailao Observatory Station) to assess the transport and impact of Hg emissions from biomass burning. The quantity of Hg emission and the source regions were determined using ΔTGM/ΔCO slopes coupled with backward trajectory analysis and CO emission inventories. The slopes of ΔTGM/ΔCO appeared to be a useful chemical indicator for source identification. Industrial emission sources exhibited slopes in the range of 5.1-61.0 × 10-7 (parts per trillion by volume, pptv/pptv), in contrast to a slope of 2.0-6.0 × 10-7 for typical biomass burning. Transboundary transport of Hg from biomass burning led to episodically elevated atmospheric Hg concentrations during springtime. Hg emissions from biomass burning in the Indo-China Peninsula region from 2001 to 2008 were estimated to be 11.4 ± 2.1 Mg yr-1, equivalent to 40% of annual anthropogenic emissions in the region. In addition, Hg emissions from biomass burning contained a substantial fraction of particulate bound Hg (PBM). Assuming that PBM readily deposits locally (within 50 km), the local Hg deposition caused by the PBM was estimated to be 2.2 ± 0.4 Mg yr-1, up to 1 order of magnitude higher than the PBM deposition caused by anthropogenic emissions during springtime in the region. The strong springtime emissions potentially pose a threat to the ecosystems of the Indo-China Peninsula and southwest China. Key Points ΔTGM/ΔCO slope can be an indicator for source identification ΔTGM/ΔCO slope for biomass burning is about of 2.0 × 10-7 Hg emission from biomass burning was estimated. © 2015. American Geophysical Union. All Rights Reserved.

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