Abstract
The carbon balance of forests is controlled by many component processes of carbon acquisition and carbon loss and depends on the age of vegetation, soils, species composition, and the local climate. Thus, examining the carbon balance of different forests around the world is necessary to understand the global carbon balance. Nevertheless, the available information on the carbon balance of Larix principis-rupprechtii forests in the Qinling Mountains remains considerably limited. We provide the first set of results (2010–2013) from a long-term project measuring forest-atmosphere exchanges of CO2 at the Qinling National Forest Ecosystem Research Station (QNFERS), and compare the net ecosystem exchange (NEE) based on biometric measurements with those observed via the eddy covariance method. We also compare the total ecosystem respiration via scaled-up chamber and eddy covariance measurements. The net primary productivity (NPP) was 817.16 ± 81.48 g·C·m−2·y−1, of which ΔBliving and Dtotal accounted for 77.7%, and 22.3%, respectively. Total ecosystem respiration was 814.47 ± 64.22 g·C·m−2·y−1, and cumulative annual soil respiration, coarse woody debris respiration, stem respiration, and leaf respiration were 715.47 ± 28.48, 15.41 ± 1.72, 35.28 ± 4.78, and 48.31 ± 5.24 g·C·m−2·y−1, respectively, accounting for 87.85%, 1.89%, 4.33%, and 5.93% of the total ecosystem respiration. A comparison between ecosystem respiration from chamber measurements and that from eddy covariance measurements showed a strong linear correlation between the two methods (R2 = 0.93). The NEE of CO2 between forests and the atmosphere measured by eddy covariance was −288.33 ± 25.26 g·C·m−2·y−1, which revealed a carbon sink in the L. principis-rupprechtii forest. This number was 14% higher than the result from the biometric measurements (−336.71 ± 25.15 g·C·m−2·y−1). The study findings provided a cross-validation of the CO2 exchange measured via biometric and eddy covariance, which are beneficial for obtaining the true ecosystem fluxes, and more accurately evaluating carbon budgets.
Highlights
Forests play a critical role in the global carbon cycle [1,2], and since the 1990s, substantial data have been acquired to clarify the contributions of forest ecosystems to the global carbon cycle [3,4,5].The Qinling Mountains in central China provide an important climate boundary between the southern subtropics and the northern temperate zone, where the typical vegetation of both climate zones is present together with astonishingly high biodiversity [6]
Our study found that the net ecosystem exchange (NEE) measured by the eddy covariance method was 14% higher than that measured by the biometric, which is consistent with Wang et al [26]
There was still a discrepancy between the biometric and eddy covariance measurements, which may be due to the complicated error sources
Summary
Forests play a critical role in the global carbon cycle [1,2], and since the 1990s, substantial data have been acquired to clarify the contributions of forest ecosystems to the global carbon cycle [3,4,5]. The Qinling Mountains in central China provide an important climate boundary between the southern subtropics and the northern temperate zone, where the typical vegetation of both climate zones is present together with astonishingly high biodiversity [6]. Information relevant to the carbon balance from forests in the Qinling Mountains remains considerably limited. There is an urgent need for increased knowledge about the carbon fluxes in various mountain forests, especially those in the Qinling Mountains. Forests 2018, 9, 67 demonstrated that mountain forests are ‘hot spots’ for carbon cycling and are expected to be more strongly affected by climate change than lowland forests due to their sensitivity to warming [7,8].
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