EFFECTS OF SOLAR RADIATION ON NET ECOSYSTEM EXCHANGE OF BROADLEAVED-KOREAN PINE MIXED FOREST IN CHANGBAI MOUNTAIN, CHINA

doi:10.3773/j.issn.1005-264x.2009.02.004

Abstract

Abstract:

Aims Solar radiation can affect net ecosystem exchange (NEE) of carbon dioxide of forests, because cloud cover alters solar radiation, which in turn alters other environmental factors such as temperature and vapor pressure deficit. Our objective was to analyze the effects of these changes on NEE of broadleaved-Korean pine (Pinus koraiensis) mixed forest in Changbai Mountain.

Methods Our analysis was based on 30-min flux data and routine meteorology data for mid-growing season (June to August) for 2003-2006.

Important findings Cloud cover significantly increased NEE. The light-saturated maximum photosynthetic rate was enhanced 34%, 25%, 4% and 11% on cloudy days compared with clear days in the four years of study. Relative irradiance and clearness index (k_t) were important in quantifying the effects of cloud cover, cloud shape and cloud thickness on solar radiation. When k_twas about 0.5, NEE reached its maximum. When the relative irradiance was over the critical relative irradiance of 37%, NEE was enhanced; maximum NEE occurred at about 75%. Enhancement ofNEE was ascribed to increased canopy assimilation and decreased above-ground respiration, which resulted from increased diffuse radiation and decreased air temperature and vapor pressure deficit with increased cloudiness.

Key words: broadleaved-Korean pine mixed forest, net ecosystem exchange, clearness index, relative irradiance

ZHANG Mi, YU Gui-Rui, ZHANG Lei-Ming, SUN Xiao-Min, WEN Xue-Fa, HAN Shi-Jie. EFFECTS OF SOLAR RADIATION ON NET ECOSYSTEM EXCHANGE OF BROADLEAVED-KOREAN PINE MIXED FOREST IN CHANGBAI MOUNTAIN, CHINA[J]. Chin J Plant Ecol, 2009, 33(2): 270-282.

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URL: https://www.plant-ecology.com/EN/10.3773/j.issn.1005-264x.2009.02.004

https://www.plant-ecology.com/EN/Y2009/V33/I2/270

Figures/Tables 12

Fig. 1 Light response curves of broadleaved Korean pine mixed forest in Changbai Mountain under clear days and cloud days from June to August in the years from 2003 to 2006 PAR: Photosynthetically available radiation

Table 1 Parameter values of light response curve of broadleaved Korean pine mixed forest in Changbai Mountain under clear days and cloud days from June to August in the years from 2003 to 2006

	2003		2004		2005		2006
	多云天气Cloud days	晴朗天气Clear days	多云天气Cloud days	晴朗天气Clear days	多云天气Cloud days	晴朗天气Clear days	多云天气Cloud days	晴朗天气Clear days
初始量子效率α (mg CO₂·μmol^-1)	-0.003 6	-0.002 7	-0.003 7	-0.004 1	-0.003 9	-0.003 2	-0.003 9	-0.004 4
最大光合作用速率P_ec,max(mg CO₂·m^-2s^-1)	-1.309	-0.864	-1.210	-0.902	-1.307	-1.253	-1.213	-1.079
生态系统呼吸R_e (mg CO₂·m^-2s^-1)	0.281	0.217	0.278	0.257	0.244	0.369	0.244	0.337
曲线拟合相关系数的平方R²	0.67	0.50	0.55	0.50	0.60	0.66	0.62	0.56

Fig. 2 Relationship between net ecosystem exchange (NEE) and clearness index kt for the broadleaved Korean pine mixed forest in Changbai Mountain for different intervals of solar elevation angles from June to August in 2003 Dashed line arrow indicate the value of kt at which the NEE reached its maximum; Regression did not include cloud-gap points; Since similar results were found in the years from 2003 to 2006, only 2003 results are shown

Table 2 The value of kt at which net ecosystem exchange (NEE) reached its maximum for the broadleaved Korean pine mixed forest in Changbai Mountain for different intervals of solar elevation angles from June to August in the years from 2003 to 2006

太阳高度角 Solar elevation angle β	晴空指数 Clearness indexk_t
太阳高度角 Solar elevation angle β	2003	2004	2005	2006
30~35o	0.49	0.43	0.49	0.54
35~40o	0.50	0.42	0.51	0.52
40~45o	0.46	0.47	0.50	0.51
45~50o	0.48	0.43	0.48	0.50
50~55o	0.44	0.50	0.50	0.50
55~60o	0.46	0.48	0.47	0.50
60~65o	0.50	0.44	0.56	0.46
65~70o	0.46	0.50	0.51	0.50
平均 Average	0.47	0.46	0.50	0.51

Fig. 3 Relationship between light use efficiency (LUE) and clearness index (kt) for the broadleaved Korean pine mixed forest in Changbai Mountain for different intervals of solar elevation angles from June to August in 2003 Since similar results were found in the years from 2003 to 2006, only 2003 results are shown

Fig. 4 Relationship between net ecosystem exchange (NEE) and relative irradiance for the broadleaved Korean pine mixed forest in Changbai Mountain for different intervals of solar elevation angles from June to August in 2003 Straight line arrow indicate the optimal relative irradiance; dash line arrow indicate the critical relative irradiance; Regression did not include cloud-gap points; Since similar results were found in the years from 2003 to 2006, only 2003 results are shown

Fig. 5 The optimal relative irradiance (a) and critical relative irradiance (b) for the broadleaved Korean pine mixed forest in Changbai Mountain for different intervals of solar elevation angles from June to August in the years from 2003 to 2006

Table 3 The values of optimal relative irradiance and critical relative irradiance for the broadleaved Korean pine mixed forest in Changbai Mountain for different intervals of solar elevation angles from June to August in the years from 2003 to 2006 (%)

太阳高度角 Solar elevation angle β	2003		2004		2005		2006
太阳高度角 Solar elevation angle β	最适相对辐射Optimal relative irradiance	临界相对辐射Critical relative irradiance	最适相对辐射Optimal relative irradiance	临界相对辐射Critical relative irradiance	最适相对辐射Optimal relative irradiance	临界相对辐射Critical relative irradiance	最适相对辐射Optimal relative irradiance	临界相对辐射Critical relative irradiance
30o~35o	75	67	94	34	98	38	53	28
35o~40o	84	54	78	35	82	34	81	54
40o~45o	87	51	80	54	73	44	77	32
45o~50o	59	39	87	64	64	38	70	26
50o~55o	61	26	81	43	71	45	58	40
55o~60o	71	20	74	19	81	24	68	39
60o~65o	87	30	63	20	73	14	45	35
65o~70o	59	19	72	35	75	29	95	45
平均Average	73	38	79	38	77	33	68	37

Fig. 6 Histograms of values of the clearness index (kt) for solar elevation angles β>20o at the broadleaved Korean pine mixed forest in Changbai Mountain from June to August in the years from 2003 to 2006

Fig. 7 Changes of diffuse PAR with the clearness index (kt) for different solar elevation angles from June to August in 2003 Since similar results were found in the years from 2003 to 2006, only 2003 results are shown; the calculation method of diffuse PAR refer to Gu (1999)

Fig. 8 Changes of air temperature (Ta) (a) and 5 cm soil temperature (Ts) (b) with clearness index (kt) for the broadleaved Korean pine mixed forest in Changbai Mountain from June to August in 2003 Since similar results were found for different solar elevation angles in the years from 2003 to 2006, only the result of one interval of solar elevation angle (60°-65°) in 2003 are shown

Fig. 9 Change of vapor pressure deficit VPD with clearness index (kt) for the broadleaved Korean pine mixed forest in Changbai Mountain from June to August in 2003 Since similar results were found for different solar elevation angles in the years from 2003 to 2006, only the result of one interval of solar elevation angle (60°-65°) in 2003 are shown

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