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Wu C.,CAS Xishuangbanna Tropical Botanical Garden | Wu C.,National Forest Ecosystem Research Station at Ailaoshan | Wu C.,University of Chinese Academy of Sciences | Zhang Y.,CAS Xishuangbanna Tropical Botanical Garden | And 8 more authors.
Plant and Soil | Year: 2014

Aims: The aims were to identify the effects of interactions between litter decomposition and rhizosphere activity on soil respiration and on the temperature sensitivity of soil respiration in a subtropical forest in SW China. Methods: Four treatments were established: control (CK), litter removal (NL), trenching (NR) and trenching together with litter removal (NRNL). Soil CO2 efflux, soil temperature, and soil water content were measured once a month over two years. Soil respiration was divided into four components: the decomposition of basic soil organic matter (SOM), litter respiration, root respiration, and the interaction effect between litter decomposition and rhizosphere activity. A two-factor regression equation was used to correct the value of soil CO2 efflux. Results: We found a significant effect of the interaction between litter decomposition and rhizosphere activity (R INT) on total soil respiration, and R INT exhibited significant seasonal variation, accounting for 26 and 31 % of total soil respiration in the dry and rainy seasons, respectively. However, we found no significant interaction effect on the temperature sensitivity of soil respiration. The temperature sensitivity was significantly increased by trenching compared with the control, but was unchanged by litter removal. Conclusions: Though the interaction between litter decomposition and rhizosphere activity had no effects on temperature sensitivity, it had a significant positive effect on soil respiration. Our results not only showed strong influence of rhizosphere activity on temperature sensitivity, but provided a viable way to identify the contribution of SOM to soil respiration, which could help researchers gain insights on the carbon cycle. © 2014 Springer International Publishing Switzerland. Source

You G.,CAS Xishuangbanna Tropical Botanical Garden | You G.,University of Chinese Academy of Sciences | Zhang Y.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.,A+ Network | And 19 more authors.
International Journal of Climatology | Year: 2013

This study seeks a further understanding on climate trends in a subtropical mountain forest, SW China. Air (Ta) and soil temperature (Ts), both in open land (1983-2010) and under a forest canopy (1986-2010), were investigated. Short-term radiation components were also measured simultaneously both in open land and understory to explore the relationships of microclimatic variables. Correlations of Ta and Ts with sunshine hours (St) and wind speed (Ws) were also analysed as driving factors of the temperature trends. The results showed that (1) Understory radiation components were greatly reduced by the forest canopy, showing a strong effect of forest canopy on microclimatic variables. Ts_0 in open land was significantly correlated with solar radiation. Wind speed had significant influences on differences between Ta and Ts_0, between open land Ts_0 and understory Ts_0. The long-term data showed that Ts_0 under forest canopy were closely coupled with Ta in open land. (2) Ta had a larger increase than Ts_0 in open land, and temperature increases in winter were greater than in other seasons. Soil temperature at depths under forest canopy had nearly twice the increases of those on open land; we attributed this to the higher relative increase of Ws over St. (3) A slope change in 1998 was detected in the Ts_0 and Ta difference (Ts_0 - Ta) series, suggesting different response of Ts_0 and Ta since that year. Deceleration of St and stability of Ws may have been factors. This study improves our understanding of warming in a nature reserve where anthropogenic influences are absent. Further studies are needed for the biological and biochemical implications on subtropical mountain forest. Copyright © 2012 Royal Meteorological Society. Source

You G.,CAS Xishuangbanna Tropical Botanical Garden | You G.,University of Chinese Academy of Sciences | Zhang Y.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.,Chinese Ecosystem Research Networks | And 14 more authors.
Hydrological Processes | Year: 2013

Negative trends of measured pan evaporation are widely reported. Studies of the factors that underlie this reduction in pan evaporation have not reached a consensus about the controlling factors. Most studies employ statistical analysis (correlation analysis or stepwise regression) to identify the controlling climatic variables; in contrast, few studies have employed physical-based theories. In addition, observations of pan evaporation and related climatic variables are reported to be influenced by anthropogenic activities. Consequently, the observed trends of climatic variables in a nature reserve would be useful for understanding regional climate change. The present study site is located in Ailaoshan National Nature Reserve, SW China, which is free of anthropogenic activity. In this study, we firstly applied the adjusted PenPan model to estimate the pan evaporation. Then, using this physical-based model, we identified a positive trend in pan evaporation, with a much larger increase in the dry season than in the wet season. The model results indicate that the change in the aerodynamic component is larger than that in the radiative component. In contrast to the reduction in wind speed and sunshine hours that has been reported in previous studies at various sites, we found that wind speed and sunshine hours have increased in recent decades, thereby explaining the increase of the pan evaporation rate. Wind speed made the greatest contribution to the change in pan evaporation, followed by sunshine duration. This study indicates that the potential evaporation has increased at this site despite the widely reported reduction in measured pan evaporation. During the dry season, the availability of water for agriculture and agroforestry could be threatened. © 2012 John Wiley & Sons, Ltd. Source

You G.,CAS Xishuangbanna Tropical Botanical Garden | You G.,University of Chinese Academy of Sciences | Zhang Y.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.,A+ Network | And 21 more authors.
International Journal of Biometeorology | Year: 2013

Our current understanding is that plant species distribution in the subtropical mountain forests of Southwest China is controlled mainly by inadequate warmth. Due to abundant annual precipitation, aridity has been less considered in this context, yet rainfall here is highly seasonal, and the magnitude of drought severity at different elevations has not been examined due to limited access to higher elevations in this area. In this study, short-term micrometeorological variables were measured at 2,480 m and 2,680 m, where different forest types occur. Drought stress was evaluated by combining measurements of water evaporation demand (Ep) and soil volumetric water content (VWC). The results showed that: (1) mean temperature decreased 1 °C from 2,480 m to 2,680 m and the minimum temperature at 2,680 m was above freezing. (2) Elevation had a significant influence on Ep; however, the difference in daily Ep between 2,480 m and 2,680 m was not significant, which was possibly due to the small difference in elevation between these two sites. (3) VWC had larger range of annual variation at 2,680 m than at 2,480 m, especially for the surface soil layer. We conclude that the decrease in temperature does not effectively explain the sharp transition between these forest types. During the dry season, plants growing at 2,680 m are likely to experience more drought stress. In seeking to understand the mountain forest distribution, further studies should consider the effects of drought stress alongside those of altitude. © 2012 ISB. Source

You G.-Y.,CAS Xishuangbanna Tropical Botanical Garden | You G.-Y.,University of Chinese Academy of Sciences | Zhang Y.-P.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.-P.,Chinese Academy of Sciences | And 9 more authors.
Beijing Linye Daxue Xuebao/Journal of Beijing Forestry University | Year: 2011

Soil temperature is an important factor affecting plant growth and soil respiration. We analyzed the long-term data of soil temperature in the open areas and interior forests observed at the Ailaoshan Station for Subtropical Forest Ecosystem Study(ASSFE). Compared with open areas, interior forests had a lower mean soil temperature(by 2.4°C), a lower mean maximum soil temperature(by 13.4°C) and a higher minimum soil temperature(by 3.4°C), which implies a strong canopy shading effect on soil temperature. The difference between soil temperature inside forests and in open areas was higher in dry seasons than in wet seasons. Soil temperature increased with a stronger trend in dry seasons than in wet seasons. Soil temperature of interior forests had a stronger rising trend(0.017°C/year) than in open areas(0.010°C/year). In conclusion, soil temperature is generally rising, while the difference of soil temperature and air temperature is decreasing, and so is the soil temperature difference between open areas and interior forests. Consequently, the distribution elevation of subtropical montane evergreen broad-leaved forest will be driven upward by the trend of warming, and carbon balance and soil respiration will be inevitably disturbed as a result of rising soil temperatures. Source

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