广东湛江桉树人工林碳水通量季节格局及其环境生物控制

doi:10.11707/j.1001-7488.LYKX20230482

摘要/Abstract

摘要：

目的: 量化桉树人工林生态系统的碳水通量和组分并揭示其受环境生物因子的调控作用，为提高人工林碳汇评估准确性及深入认识气候变化背景下环境生物因子对人工林碳循环过程的影响提供依据。方法: 在雷州半岛北部，采用涡度相关法（EC）测定桉树人工林碳水通量，并同步监测空气温度（T_air）、饱和水汽压差（VPD）、光合光量子通量密度（PPFD）、土壤温度（T_soil）、土壤湿度（SM）、降水量（Pre）和归一化植被指数（NDVI）等环境生物因子，分析碳水通量和组分的时间变化及其与环境生物因子的关系。结果: 桉树人工林生态系统总初级生产力（GPP）年均值为2 907.87 g·m^?2a^?1、生态系统呼吸（RE）年均值为1 509.77 g·m^?2a^?1、净生态系统碳交换（NEE）年均值为?1 398.83 g·m^?2a^?1、生态系统蒸散（ET）年均值为1 069.25 mm，表现为碳汇。GPP、RE、NEE、ET昼夜变化呈非对称单峰趋势，峰值和日均值的绝对值均表现为雨季高于旱季。雨季的GPP、RE、ET累积值高于旱季，NEE累积值在旱季和雨季无明显差异。日间NEE变化的主要影响因子为PPFD，当VPD≥15 hPa时NEE积累受到抑制，气温在中等水平（20 ℃<T_air< 27 ℃）时净碳吸收能力最强。夜间NEE变化主要受T_air影响，SM会影响NEE对T_air响应的敏感性。水分利用效率（WUE）在旱季（3.85 g·kg^?1）高于雨季（2.61 g·kg^?1），年均值为3.22 g·kg^?1，季节差异主要由ET主导，与T_air、VPD、PPFD存在显著负相关（P<0.05）。结论: 桉树人工林生态系统在旱季、雨季和全年均表现为碳汇，其碳汇状态和强度由GPP主导。NEE变化主要受PPFD调控，高VPD会抑制生态系统净碳吸收，中等水平温度时生态系统净碳吸收能力最强，SM会影响夜间NEE对T_air响应的敏感性。桉树人工林WUE旱季高于雨季，季节差异主要由ET主导，同时受到T_air、VPD、PPFD的共同影响。

关键词: 涡度协方差, 碳水通量, 环境生物因子, 水分利用效率, 桉树人工林

Abstract:

Objective: This paper aims to quantify the carbon and water flux components of eucalyptus plantation ecosystem, reveal the regulatory role of environmental biological factors on carbon and water cycle, so as to provide a basis for improving the accuracy of carbon sink assessment of plantation ecosystem and further understanding the impact of environmental and biological factors on carbon cycle of plantation ecosystem under the background of climate change. Method: The eddy covariance (EC) technique was used to continuously monitor carbon and water fluxes in a typical eucalyptus plantation ecosystem in the northern part of the Leizhou Peninsula. The environmental biological factors such as air temperature (T_air), vapour pressure deficit (VPD), photosynthetic photon flux density (PPFD), soil temperature (T_soil), soil moisture (SM), precipitation (Pre), and normalized difference vegetation index (NDVI) were simultaneously detected. The temporal variation characteristics of ecosystem carbon and water fluxes and their responses to environmental and biological factors were analyzed. Result: Annual average values of total primary productivity (GPP), respiration (RE), net ecosystem carbon exchange (NEE) and evapotranspiration (ET) of eucalyptus plantation ecosystem were 2 907.87, 1 509.77, ?1 398.83 g·m^?2a^?1 and 1 069.25 mm, respectively, showing a carbon sink as a whole. The diurnal variations of GPP, RE, NEE and ET showed asymmetric unimodal trend, and the absolute values of peak value and daily average value were higher in rainy season than in dry season. The accumulated values of GPP, RE and ET in rainy season were higher than those in dry season, while the accumulated values of NEE had no significant difference between dry season and rainy season. The main influencing factor of daytime NEE variation was PPFD. When VPD ≥ 15 hPa, NEE accumulation was inhibited, and the net carbon absorption capacity was strongest at moderate temperatures (20 ℃ < T_air < 27 ℃). Nocturnal NEE changes were mainly affected by T_air, and SM was able to affect the sensitivity of NEE to T_air. Water use efficiency (WUE) was higher in dry season (3.85 g·kg^?1) than in rainy season (2.61 g·kg^?1), with the mean annual WUE of 3.22 g·kg^?1. The seasonal difference was dominated by ET and negatively correlated with T_air, VPD and PPFD (P<0.05). Conclusion: Eucalyptus plantation ecosystem exhibits carbon sinks during the dry season, the rainy season, and the whole year. The carbon sink status and intensity of eucalyptus plantation ecosystem are dominated by GPP. NEE changes are primarily regulated by PPFD, while high VPD inhibits net carbon sequestration. The net carbon sequestration capacity of the ecosystem is strongest at moderate temperature, and SM affects the sensitivity of NEE to T_air changes at night. WUE of eucalyptus plantation is higher in the dry season compared to the rainy season. This seasonal difference is primarily influenced by ET and is also affected by T_air, VPD, and PPFD.

Key words: eddy covariance (EC), carbon and water fluxes, environmental biological factor, water use efficiency (WUE), eucalyptus plantation

中图分类号:

S718.55

竹万宽,王志超,杜阿朋,许宇星. 广东湛江桉树人工林碳水通量季节格局及其环境生物控制[J]. 林业科学, 2024, 60(9): 18-32.

Wankuan Zhu,Zhichao Wang,Apeng Du,Yuxing Xu. Seasonal Patterns of Carbon and Water Fluxes and Their Environmental Biological Control in the Eucalyptus Plantation in Zhanjiang of Guangdong Province[J]. Scientia Silvae Sinicae, 2024, 60(9): 18-32.

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缩写 Abbreviation	参数全称 Full name of parameters	单位 Unit
GPP	生态系统总初级生产力 Gross primary productivity	g·m^?2s^?1
RE	生态系统呼吸 Ecosystem respiration	g·m^?2s^?1
NEE	净生态系统碳交换 Net ecosystem carbon exchange	g·m^?2s^?1
ET	蒸散 Evapotranspiration	mm
WUE	水分利用效率 Water use efficiency	g·kg^?1
Tr	蒸腾 Transpiration	mm
E	蒸发 Evaporation	mm
H	显热通量 Sensible heat flux	W·m^?2
LE	潜热通量 Latent heat flux	W·m^?2
R_n	净辐射 Net radiation	W·m^?2
G	土壤热通量 Soil heat flux	W·m^?2
PPFD	光合光量子通量密度 Photosynthetic photon flux density	μmol·m^?2s^?1
NDVI	归一化植被指数 Normalized difference vegetation index	—
T_air	空气温度 Air temperature	℃
T_soil	土壤温度 Soil temperature	℃
SM	土壤湿度 Soil moisture	m³·m^?3
VPD	饱和水汽压差 Vapour pressure deficit	hPa
Pre	降水量 Precipitation	mm

环境因子 Environmental factors	2018—2019 旱季	2019 雨季	2019—2020 旱季	2020 雨季	2020—2021 旱季	2021 雨季	2021—2022 旱季	2022 雨季
环境因子 Environmental factors	Dry season	Rainy season	Dry season	Rainy season	Dry season	Rainy season	Dry season	Rainy season
T_air/℃	21.20±4.11	27.73±2.16	20.64±3..01	28.25±2.23	20.32±4.34	28.27±2.36	19.34±4.18	27.28±2.53
T_{air, max}/℃	24.56±4.48	31.67±2.74	24.84±3.05	32.62±2.54	24.72±3.92	32.62±2.38	23.85±4.35	31.46±2.70
T_{air, min}/℃	18.87±4.36	24.98±2.00	17.42±3.56	25.12±2.22	17.09±5.04	25.07±2.44	16.00±4.28	24.29±2.59
T_soil/℃	21.54±2.48	26.76±1.13	20.95±1.64	26.63±1.43	20.38±2.69	26.81±1.23	19.99±2.21	26.00±1.51
SM/(m³·m^?3)	0.16±0.03	0.20±0.03	0.14±0.02	0.19±0.04	0.15±0.03	0.17±0.04	0.15±0.03	0.21±0.03
PPFD/(mol·m^?2d^?1)	23.02±9.74	34.92±12.28	24.69±9.67	36.31±11.14	27.22±10.13	37.49±12.27	27.35±13.22	38.48±14.04
VPD/hPa	2.99±3.13	5.22±5.19	4.64±3.91	5.92±5.96	3.89±3.39	5.02±4.00	4.08±3.73	7.26±5.93

	旱季 Dry season			雨季 Rainy season
	GPP	RE	ET	GPP	RE	ET
NEE	?0.81***	0.07	?0.36***	?0.84***	0.10**	?0.51***
WUE	0.06	?0.06	?0.63***	0.13***	0.06	?0.59***

环境因子范围 Range of environmental factors	α/(μmol·μmol^?1)	A_max /(μmol·m^?2s^?1)	RE_day/(μmol·m^?2s^?1)	R²	RMSE
VPD≤4 hPa	0.038±0.001	47.640±1.605	3.126±0.137	0.998	0.058
4 hPa<VPD<15 hPa	0.037±0.001	45.296±0.604	2.723±0.144	0.999	0.043
VPD≥15 hPa	0.021±0.003	45.058±3.697	0.807±0.979	0.983	0.128
T_air≤20 ℃	0.043±0.002	30.833±0.782	2.103±0.229	0.995	0.099
20 ℃<T_air<27 ℃	0.043±0.002	41.982±0.974	3.803±0.262	0.997	0.089
T_air≥27 ℃	0.047±0.002	41.846±0.866	4.604±0.375	0.996	0.090
SM≤0.14	0.044±0.002	36.041±0.567	2.887±0.313	0.995	0.088
0.14<SM<0.21	0.046±0.002	39.147±0.600	3.724±0.356	0.995	0.093
SM≥0.21	0.046±0.003	44.629±1.133	5.022±0.627	0.988	0.143

土壤湿度范围 Range of soil moisture	R₂₀/(μmol·m^?2s^?1)	${E_{\mathrm{a}}}/{R} $/K	R²	RMSE
SM≤0.14	3.238±0.064	12.433±1.408	0.795	0.185
0.14<SM<0.21	3.612±0.053	19.084±1.300	0.919	0.138
SM≥0.21	3.522±0.105	27.443±2.667	0.848	0.168