| Forest is a main contributor to terrestrial Carbon (C) sink. It is important to get insight into the carbon cycling in forest ecosystems for evaluating the forests sink/source function and understanding the feedback between terrestrial ecosystem and atmosphere. As a major path by which soil C fixed via photosynthesis return to atmosphere, soil respiration is closed related to CO2 concentration ([CO2]) within forest canopy. The CO2 derived from Rs not only directly influences the atmosphere [CO2] in canopy, but also can serve as the substrate supply for photosynthesis. Although the temperate broadleaved deciduous forest accounts for two thirds area of the forest in Northeast China, the spatio-temporal variations in CO2 concentration ([CO2]) have not been quantified exactly. Therefore, it is essential to explore the spatiotemporal variations in Rs and [CO2] in order to get insight into carbon cycling process in forest ecosystems. Our purposes were to quantify the seasonal and spatial variations of Rs, and diurnal and seasonal variations and vertical gradients of the [CO2] in a representative temperate broadleaved deciduous forest in this region, and to explore their controlling factors based on an infrared gas analyzer (LI-COR 6400, Li-Cor Inc., Lincoln, NE, USA) equipped with a portable chamber (LI-6400-9, Li-Cor Inc.. USA), an 8-level [CO2] profile, and related micrometeorological measurements.(1) The inter-plot and intra-plot variations of RS, RH, and their corresponding T5 and W5 all exhibited distinct seasonal patterns. The intra-plot variations of RS, RH, temperature sensitivity of Rs and RH, W5, total soil organic carbon content and the soil organic carbon content at A horizon, leaf-litter and total litter fall, fine root biomass (R1) and necromass. and maximum leaf area index (LAIm) were higher than those for inter-plot, with the soil bulk density. T5, and soil organic carbon content at Ao horizon (CAO) in the opposite situation. At local scale, cumulative Rs was significantly related to CAO and R1 across the eight plots. The base RH at 0℃(R0h) had a significant relation with CAO.LAIm was closely related to cumulative (g C·m-2) and mean RH (μmol CO2·m-2·s-1), and R0h.the difference between the cumulative Rs for the growing season estimated by total regression model (pooled all the eight plots,718.25 g C·m-2), plot-specific model (726.76 g C·m-2), collar-specific model (724.29 g C·m-2), and mean respiration rate method (739.33 g C·m-2) was less than 3%, which indicated a potential simple method for estimating the annual Rs in normal year in this local site.(2)At a daily scale, the maximum [CO2] occurred at night or sun rise, while the minimum occurred in the afternoon for all levels. This pattern was predominant in the summer. The diurnal course of the [CO2] was a "V" shape in the winter but a "U" shape in the other seasons. The [CO2] decreased with the height increasing, particularly in summer nights. During the daytime of summer, the daily mean [CO2] within the canopy was substantially lower than the ambient [CO2], suggesting that the vegetation acted as a CO2 sink due to its photosynthesis. Daily mean [CO2] above the canopy peaked in spring and autumn, and reached the minimum in summer, while that near the forest floor showed a "unimodal" seasonal pattern with its maximum in summer. The diurnal dynamics of the [CO2] and their vertical gradients during the growing season were jointly controlled by the atmospheric boundary layer (ABL) and the forest carbon metabolism, while those during the dormant season were mainly controlled by the ABL. The seasonal dynamics of the [CO2] near the forest floor were mainly determined by soil respiration, while those above the canopy were jointly controlled by canopy photosynthesis and ecosystem respiration.This study suggested that Rs and [CO2] had significant spatiotemporal variations. Because of lack of diurnal variation of Rs, their relations at short time scale were not mentioned in this thesis. The interaction of the Rs and [CO2] need to be further explored at the context of global elevating CO2. |
PDF Full Text Request