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土壤是陆地表层系统中最大的碳储库[1],土壤表面碳释放是陆地生态系统中第二大碳通量[2]。一般认为,土壤温湿度是调控土壤呼吸的两个重要环境因子[3];也有研究发现,制约草原生态系统土壤呼吸的主要因子是太阳辐射[4];而降雨引起的干湿交替则直接影响土壤呼吸并通过干扰太阳辐射、土壤水分和土壤温度等间接途径影响土壤呼吸动态[5-6]。据气候模型预测显示,未来全球降雨格局将持续变化,极端干旱和降雨不断升高[7];但降雨对土壤呼吸的影响具有较大的不确定性,其引发的干湿交替过程将显著影响土壤呼吸时空特征、碳通量估算[8]与干旱和半干旱区土壤碳释放过程[9-11]。
现阶段我国研究土壤呼吸对降雨的响应主要集中在森林生态系统[12-13]、草原生态系统[14-15]和农田生态系统[16],对广泛分布于我国西北部干旱与半干旱区的荒漠生态系统的研究鲜有报道,其中,青藏高原的共和盆地是受土地沙漠化影响最严重的区域之一,植被重建是该区域防治土地沙漠化的有效措施[17]。有研究表明,植被恢复可以显著改良土壤理化性质,加速沙成壤进程[18],但水土保持措施也会引起微地形、土壤结构和土壤水分的改变,进而影响土壤呼吸[19]。因此,本研究以共和盆地2013年栽植的中间锦鸡儿(Caragana intermedia Kuang et H. C. Fu)人工防风固沙林为例,通过对比降雨前后土壤呼吸与各环境因子的变化,分析自然降雨对土壤呼吸的干扰途径和影响机制,为完善干旱与半干旱区人工林的碳循环估算模型提供参考[20]。
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选取观测月内无降雨发生的15 d数据,对比不同深度土壤温度(TS)和土壤含水量(VWC)与土壤呼吸速率(RS)的相关性,发现10 cm深度土壤的TS10和VWC10与RS相关性较强(P<0.01)。分别对RS、空气温度(TA)、TS10、VWC10和太阳总辐射(SR)进行相关性检验,结果(表1)表明:RS与各环境因子均表现为显著强相关(P<0.01,|r|>0.6),表明各环境因子均对RS具有显著影响。各环境因子与TA相关性强弱顺序为:TS10>SR>VWC10;与TS10顺序为:TA>VWC10>SR;与VWC10顺序为:TS10>TA>SR;与SR顺序为:TA>TS10>VWC10,即各环境因子间呈SR−TA−TS10−VWC10彼此相关性最强趋势,其可能存在依次相互作用关系。
表 1 环境因子与土壤呼吸速率的相关性
Table 1. Correlation between environmental factors and soil respiration rate
项目
Item空气温度
TA土壤温度(10 cm)
TS10土壤含水量(10 cm)
VWC10太阳总辐射
SR土壤呼吸速率
RS空气温度 TA 1 土壤温度(10 cm) TS10 0.88** 1 土壤含水量(10 cm) VWC10 −0.34** −0.38** 1 太阳总辐射 SR 0.66** 0.37** −0.09** 1 土壤呼吸速率 RS 0.74** 0.66** −0.62** 0.66** 1 注:**表示在0.01级别(双尾)相关性显著;数值为Pearson相关系数r值。
Notes: ** indicates a significant correlation at level 0.01; and the value is the r of Pearson's correlation coefficient.选取7月25日至7月30日连续无降雨发生的6 d分析RS和各环境因子间相互作用的关系,图1表明:每日各环境因子峰值对应的时间顺序呈SR-TA-TS10-VWC10分布,结合各环境因子间的相关性分析,SR-TA-TS10-VWC10间可能表现为能量传递关系,即SR引起TA波动,进而影响TS10,最终引起VWC10变化,其中,RS与SR峰值对应的时间最接近,均为每日13:00—15::00,表明SR是最先影响RS变化的环境因子。
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检验观测月内单日累计降雨量和不同深度TS与VWC的相关性,发现10 cm深度土壤的TS和VWC与降雨量相关性较强(P<0.01)。对比降雨量与RS和各环境因子日均值的关系(图2),自然降雨与RS呈显著负相关(P<0.01),且单日累计降雨量大于0.8 mm时RS均明显受到抑制。降雨结束次日,RS迅速回升,该效应约可持续3 d,且累计降雨量越高RS回升越高。如7月3日发生了该月最大单日降雨,对应出现了当月最小RS日均值0.297 μmol·m−2·s−1,次日RS迅速增长了186%,该效应持续至7月6日,累计增长397%。
图 2 7月土壤呼吸与环境因子日变化
Figure 2. Diurnal changes in soil respiration and environmental factors from July
TA及其离散程度都低于TS10(S2空气=5.74,S2土壤=14.69),自然降雨与二者均呈显著负相关(P<0.01),且单日累计降雨量大于1.4 mm可以明显抑制TA和TS10。自然降雨与VWC10呈显著正相关(P<0.01),单日累计降雨量大于2.8 mm可以明显促进VWC10升高;自然降雨与SR呈显著负相关关系(P<0.01),单日累计降雨量大于0.6 mm时SR明显受到抑制。对比自然降雨与RS和各环境因子间Pearson系数,其相关性表现为:SR(−0.72)>RS(−0.70)>TA(−0.54)>TS10(−0.52)>VWC10(0.41),表明SR对自然降雨的敏感度最高,且大于RS,VWC10最低。
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对观测月发生的15次自然降雨事件依据单次连续降雨时长(h)和累计降雨量(mm)进行分类统计,并计算降雨强度(mm·h−1),发现RS变化率与降雨时长、降雨量、降雨强度均显著相关(P<0.05),其相关性表现为:降雨量(r=−0.64)>降雨时长(r=−0.43)>降雨强度(r=−0.40)。对比RS和降雨量与不同深度TS和VWC的相关性,发现RS和降雨量均与150 cm深度的TS150和VWC150相关性最强(rRS-TS=0.68,rRS−VWC =0.60;r雨量−TS=0.35,r雨量−VWC =0.37;P<0.01)。
表2表明:降雨发生后,RS低于雨前水平。降雨在0~4 h,RS变化率随降雨时长增加而降低;降雨在3~4 h时RS变化率降至最低,达-65.30%;降雨时长大于4 h时,RS变化率随降雨时长增加而逐渐升高。降雨过程中,TA变化率表现为随降雨时长增加而降低的趋势,TS150和VWC150的变化率则小幅缓慢升高,但三者变化率均始终低于RS,表明RS对降雨时长的敏感度大于TA、TS150和VWC150。由于SR受昼夜因素影响较大,未参与分析。
表 2 土壤呼吸速率和环境因子对降雨时长的响应
Table 2. Response of soil respiration rate and environmental factors to rainfall time
降雨时长
Rainfall time/h土壤呼吸速率变化率
RS rate of change/%空气温度变化率
TA rate of change/%150 cm土壤温度变化率
TS150 rate of change/%150 cm土壤含水量变化率
VWC150 rate of change/%0~1 −5.18 −3.70 0.13 0.00 1~2 −40.65 −18.06 0.13 0.00 2~3 −56.03 −22.11 0.00 0.24 3~4 −65.30 −23.34 0.13 0.47 4~8 −50.28 −23.78 0.27 0.48 8~12 −42.51 −25.26 0.32 0.57 注:变化率=(降雨后−降雨前)/降雨前×100%
Note:rate of change=(after rain−before rain)/before rain×100%表3表明:单次累计降雨量在0~12 mm,RS变化率随降雨量增加而降低;降雨量达8~12 mm时,RS变化率降至最低,达−87.42%;降雨量大于12 mm时,RS变化率随降雨量增加而逐渐升高。对RS变化率与降雨量进行回归分析(图3左)发现:降雨量可以解释RS变化率的73.5%。当降雨量大于0.07 mm时,RS即受到抑制;当降雨量达10.44 mm时,RS变化率降至最低,抑制率为−94.65%。降雨过程中,TA均低于雨前水平;降雨量为0~5 mm时,TS150和VWC150表现为随降雨量升高而缓慢升高;当降雨量大于5 mm后,TS150和VWC150逐步恢复至雨前水平;三者变化率均始终低于RS,表明RS对降雨量的敏感度大于TA、TS150和VWC150。
表 3 土壤呼吸速率和环境因子对降雨量的响应
Table 3. Response of soil respiration rate and environmental factors to rainfall
降雨量
Rainfall/mm土壤呼吸速率变化率
RS rate of change/%空气温度变化率
TA rate of change/%150 cm土壤温度变化率
TS150 rate of change/%150 cm土壤含水量变化率
VWC150 rate of change/%0~1 −12.96 −11.58 0.24 0.00 1~2 −18.76 −23.97 0.32 0.57 2~5 −50.44 −17.92 0.43 0.77 5~8 −85.49 −16.85 0.00 0.30 8~12 −87.42 −19.15 0.00 0.27 12~16 −78.17 −20.42 0.00 0.00 16~20 −66.67 −17.99 0.00 0.00 图 3 累计降雨量和降雨强度对土壤呼吸速率变化率的影响
Figure 3. Effect of accumulated rainfall and rainfall intensity on soil respiration rate of change
对RS变化率与降雨强度(降雨强度=降雨量/降雨时间)进行回归分析(图3右)发现:降雨强度可以解释RS变化的34%。当降雨强度为0~1.95 mm·h−1时,RS变化率随降雨强度增加而降低;当降雨强度为1.95~4.65 mm·h−1时,RS变化率随降雨强度增加而增加;当降雨强度大于4.65 mm·h−1时,RS变化率再次随降雨强度增加而降低。
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对观测月内无降雨日和自然降雨日RS与不同深度TS数据进行相关性检验,其中,10、90、120、150 cm深度都呈中等程度以上相关关系(P<0.01,|r|≥0.4)。分别对RS和各深度TS数据进行指数方程拟合(P<0.05),结果(表4)表明:自然降雨日各深度Q10值均高于无降雨日45%左右,且整体随土壤深度增加而升高,分别在90 cm和120 cm深度出现最小值和最大值,其中,无自然降雨日Q10值水平均在“2”以下。
表 4 土壤呼吸温度敏感性对降雨干扰的响应
Table 4. Response of the Q10 to rainfall disturbance
干扰因素
Interference factor拟合因子
Fit factor拟合方程
Fitted equation拟合度
R2温度敏感系数
Q10无自然降雨日
Non_rainy dayTS10 RS = 0.73e0.035T 0.46 1.42 TS90 RS = 0.006e0.031T 0.34 1.37 TS120 RS = 0.002e0.042T 0.33 1.53 TS150 RS = 0.004e0.04T 0.37 1.50 自然降雨日
Rainy dayTS10 RS = 0.243e0.073T 0.47 2.07 TS90 RS = e0.069T 0.31 1.99 TS120 RS = e0.08T 0.36 2.23 TS150 RS = e0.077T 0.42 2.17
自然降雨对高寒沙地中间锦鸡儿人工林土壤呼吸的影响
Effects of Natural Rainfall on Soil Respiration of Caragana Plantation in Alpine Sandland
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摘要:
目的 本研究以青海共和盆地中间锦鸡儿人工林为研究对象,分析其土壤呼吸与环境因子的关系及自然降雨对土壤呼吸和环境因子的影响机制,以期为高寒沙区人工林土壤碳通量估算和碳循环研究提供依据和理论参考。 方法 于2018年7月,在观测样内地开展30 d的连续定位观测试验,对其土壤呼吸速率和环境因子变化及自然降雨过程进行定量分析研究。 结果 (1)土壤呼吸受太阳总辐射、空气温度、土壤温度和土壤含水量等环境因子影响,其中,太阳总辐射影响较直接;(2)无降雨日土壤呼吸主要受表层(10 cm)土壤温湿度影响,降雨过程中主要受深层(150 cm)土壤温湿度影响。累计降雨量大于0.8 mm的自然降雨对土壤呼吸日均值有抑制作用,且激发效应通常出现在降雨结束次日,约持续3 d;(3)大于0.07 mm的自然降雨发生即抑制土壤呼吸速率,其在累计降雨量达10.44 mm、降雨时长达3~4 h时抑制率最高;(4)自然降雨可使Q10值短期升高。 结论 研究区土壤呼吸主要源于植物根系自养呼吸,自然降雨过程对其具有显著抑制作用,并在降雨结束次日出现激发效应;同时,自然降雨可使Q10值升高。 Abstract:Objective Caragana intermedia plantation in Gonghe Basin of Qinghai province was used to analyze the relationship between soil respiration and environmental factors, and the effects of natural rainfall on soil respiration and environmental factors, so as to provide reference for estimation of soil carbon flux and the study of carbon cycle in the alpine sandy plantations. Method A 30-days' continuous positioning observation was conducted in July, 2018. The changes of soil respiration rate, environmental factors and natural rainfall process were analyzed quantitatively. Result (1) The soil respiration was affected by environmental factors such as solar radiation, air temperature, soil temperature and soil moisture, among which the total solar radiation showed a more direct effect. (2) Soil respiration in non rainy day was mainly affected by soil temperature and moisture of the surface soil layer, while during rainfall, it was mainly affected by deep soil temperature and moisture. The natural rainfall with cumulative rainfall more than 0.8 mm showed an inhibitory effect on the daily average of soil respiration, and the excitation effect usually occurred on the next day after the end of rainfall, and lasted about 3 days. (3) Soil respiration rate was inhibited when the rainfall was more than 0.07 mm, and the inhibition rate was the highest when the cumulative rainfall reached 10.44 mm and rainfall time reached 3−4 hours. (4) Natural rainfall caused a short-term increase of the sensitivity of soil respiration to temperature. Conclusion Soil respiration in the study area is mainly due to plant root autotrophic respiration, the natural rainfall process has a significant inhibitory effect on it, and the excitation effect occurs in the next day after the rain ends. Natural rainfall can increase the sensitivity of soil respiration to temperature. -
Key words:
- alpine sandland
- / plantation
- / soil respiration
- / natural rainfall
- / temperature quotient
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表 1 环境因子与土壤呼吸速率的相关性
Table 1. Correlation between environmental factors and soil respiration rate
项目
Item空气温度
TA土壤温度(10 cm)
TS10土壤含水量(10 cm)
VWC10太阳总辐射
SR土壤呼吸速率
RS空气温度 TA 1 土壤温度(10 cm) TS10 0.88** 1 土壤含水量(10 cm) VWC10 −0.34** −0.38** 1 太阳总辐射 SR 0.66** 0.37** −0.09** 1 土壤呼吸速率 RS 0.74** 0.66** −0.62** 0.66** 1 注:**表示在0.01级别(双尾)相关性显著;数值为Pearson相关系数r值。
Notes: ** indicates a significant correlation at level 0.01; and the value is the r of Pearson's correlation coefficient.表 2 土壤呼吸速率和环境因子对降雨时长的响应
Table 2. Response of soil respiration rate and environmental factors to rainfall time
降雨时长
Rainfall time/h土壤呼吸速率变化率
RS rate of change/%空气温度变化率
TA rate of change/%150 cm土壤温度变化率
TS150 rate of change/%150 cm土壤含水量变化率
VWC150 rate of change/%0~1 −5.18 −3.70 0.13 0.00 1~2 −40.65 −18.06 0.13 0.00 2~3 −56.03 −22.11 0.00 0.24 3~4 −65.30 −23.34 0.13 0.47 4~8 −50.28 −23.78 0.27 0.48 8~12 −42.51 −25.26 0.32 0.57 注:变化率=(降雨后−降雨前)/降雨前×100%
Note:rate of change=(after rain−before rain)/before rain×100%表 3 土壤呼吸速率和环境因子对降雨量的响应
Table 3. Response of soil respiration rate and environmental factors to rainfall
降雨量
Rainfall/mm土壤呼吸速率变化率
RS rate of change/%空气温度变化率
TA rate of change/%150 cm土壤温度变化率
TS150 rate of change/%150 cm土壤含水量变化率
VWC150 rate of change/%0~1 −12.96 −11.58 0.24 0.00 1~2 −18.76 −23.97 0.32 0.57 2~5 −50.44 −17.92 0.43 0.77 5~8 −85.49 −16.85 0.00 0.30 8~12 −87.42 −19.15 0.00 0.27 12~16 −78.17 −20.42 0.00 0.00 16~20 −66.67 −17.99 0.00 0.00 表 4 土壤呼吸温度敏感性对降雨干扰的响应
Table 4. Response of the Q10 to rainfall disturbance
干扰因素
Interference factor拟合因子
Fit factor拟合方程
Fitted equation拟合度
R2温度敏感系数
Q10无自然降雨日
Non_rainy dayTS10 RS = 0.73e0.035T 0.46 1.42 TS90 RS = 0.006e0.031T 0.34 1.37 TS120 RS = 0.002e0.042T 0.33 1.53 TS150 RS = 0.004e0.04T 0.37 1.50 自然降雨日
Rainy dayTS10 RS = 0.243e0.073T 0.47 2.07 TS90 RS = e0.069T 0.31 1.99 TS120 RS = e0.08T 0.36 2.23 TS150 RS = e0.077T 0.42 2.17 -
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