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Li L.-h.,CAS Xishuangbanna Tropical Botanical Garden | Li L.-h.,University of Chinese Academy of Sciences | Zhang Y.-p.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.-p.,Chinese Academy of Sciences | And 10 more authors.
Chinese Journal of Ecology | Year: 2011

Photosynthetically active radiation (PAR) is an important ecological factor affecting the energy transformation and matter production of plant ecosystem. Studies on the spatiotemporal distribution patterns of PAR in a plant ecosystem are helpful to understand the physiological and ecological characteristics and photosynthesis of the ecosystem. In this paper, the temporal and vertical distributions of PAR in a coniferous and inftropical evergreen forest in Ailaoshan Mountains of Southwest China were analyzed. At daily scale, the intensity of PAR during passing through the forest canopy decreased gradually. At monthly scale, the PAR flux varied in each forest layer, with the maximum and minimum values above the canopy in February and January, respectively. The diurnal change of the PAR above the canopy (PAR1) presented a single-peak curve, while that of the PAR at the bottom of the canopy (PAR2) and in the arbor sub-layers (PAR3 and PAR4) and shrub layer (PAR5) presented an irregular single-peak curve. The PAR1, PAR2, PAR3, PAR4 and PAR5 fluxes at yearly scale were 8824.98, 682.20, 403.09, 216.62 and 208.52 mol • m-2, and the ratios of yearly PAR2, PAR3, PAR4 and PAR5 to PAR1 were 7.73%, 4.57%, 2.45% and 0.92%, respectively. The average PAR1, PAR2, PAR3, PAR4 and PAR5 in rain season were 89.77%, 89.34%, 97.32%%, 116.36% and 115.09% of those in dry season, respectively.

Zhao J.,CAS Xishuangbanna Tropical Botanical Garden | Zhao J.,University of Chinese Academy of Sciences | Zhang Y.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.,Ailaoshan Station for Subtropical Forest Ecosystem Research | And 8 more authors.
Ecological Informatics | Year: 2012

Digital cameras have been used in phenological observations for their high accuracy and low labor cost. Most studies successfully use greenness indices derived from digital images for timing the events related to leaf development. However, when timing the leaf senescence events, wide discrepancies between actual and estimated dates are common. In this study, images of three species (two from an evergreen broad-leaved forest and one from a seasonal rain forest) were used to estimate three phenological events of leaf development and senescence. Other than the greenness index, a redness index was also employed. Different annual patterns in color indices developed among the species. The redness index was more accurate when estimating leaf senescence, while the greenness index was more accurate for estimating leaf development events in . Acer heptalobum and . Machilus bombycina. The absolute differences in estimations of phenological events ranged from -. 3 to 1. day, which is more accurate than estimates based on the greenness index only (-. 2 to 27. days). With the introduction of the redness index, this technique has been much improved and is possible to be applied to more species. Furthermore, variations of color indices during periods of phenological events were highly related to the climatic factors with a time lag of around 10. days. Because of the ease of use and efficiency (. i.e., automatic daily data output), digital cameras are expected to be used in ecosystem process modeling, networks of phenology assessment and validation of the remote sensing results from satellites. © 2012.

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.

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.

Tan Z.-H.,CAS Xishuangbanna Tropical Botanical Garden | Tan Z.-H.,University of Chinese Academy of Sciences | Zhang Y.-P.,CAS Xishuangbanna Tropical Botanical Garden | Zhang Y.-P.,Ailaoshan Station for Subtropical Forest Ecosystem Research | And 8 more authors.
Atmospheric Environment | Year: 2011

Old-growth forests are primarily found in mountain ranges that are less favorable or accessible for land use. Consequently, there are fewer scientific studies on old-growth forests. The eddy covariance method has been widely used as an alternative approach to studying an ecosystem's carbon balance, but only a few eddy flux sites are located in old-growth forest. This fact will hinder our ability to test hypotheses such as whether or not old-growth forests are carbon neutral. The eddy covariance approach was used to examine the carbon balance of a 300-year-old subtropical evergreen broadleaved forest that is located in the center of the largest subtropical land area in the world. The post-QA/QC (quality assurance and control) eddy covariance based NEP was ∼ 9tC ha-1 yr-1, which suggested that this forest acts as a large carbon sink. The inventory data within the footprint of the eddy flux show that ∼6tC ha-1 yr-1 was contributed by biomass and necromass. The large-and-old trees sequestered carbon. Approximately 60% of the biomass increment is contributed by the growth of large trees (DBH>60cm). The high-altitude-induced low temperature and the high diffusion-irradiation ratio caused by cloudiness were suggested as two reasons for the large carbon sink in the forest we studied. To analyze the complex structure and terrain of this old-growth forest, this study suggested that biometric measurements carried out simultaneously with eddy flux measurements were necessary. © 2010 Elsevier Ltd.

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