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近年来,全球极端气候[1-2]的一个非常重要的体现是降雪频度和强度的变化[3-4]。研究降雪变化对陆地生态系统碳循环的影响,对于深入理解陆地生态系统碳循环如何响应气候变化具有非常重要的理论和现实意义。土壤碳库是构成陆地生态系统有机碳库的主体[5],土壤呼吸是土壤碳库输出的重要过程[6-7],也是研究全球碳收支最重要的过程之一[8]。研究土壤呼吸的影响因素对理解陆地生态系统碳循环途径及其对气候变化的反馈影响都具有重要意义[9]。冬季土壤呼吸是土壤碳通量的重要组成部分[10-13],也是准确评估碳循环的重要参数,在全球范围内的碳循环过程中扮演着重要的角色。森林生态系统是调控全球变化背景下生态系统碳循环的主要生态系统类型之一,其土壤呼吸对降雪变化非常敏感[10, 14-16]。与天然林相比,人工林更易受极端降雪的影响[17-19],进而改变森林的碳汇格局[2]。因此,人工林被认为是能减缓全球气候变化机制的核心,受到世界各地的关注[19]。目前,我国是世界人工林面积最大的国家[4],人工林面积达6 933万hm2,对陆地碳汇增强的贡献率达39%[20]。然而,在降雪对土壤呼吸影响的研究中,多数集中在自然生态系统[13, 15-16],关于人工林生态系统对降雪变化响应的研究相对缺乏。在对人工林土壤呼吸的研究中,大多仅对生长季土壤呼吸有所研究[21-22],忽略了非生长季的土壤碳输出。此外,少数研究降雪对人工林土壤呼吸的影响大部分集中在全球积雪时间较长的高海拔地区[14]或高纬度地区[23],对温暖地区,尤其是气候过渡带(北亚热带-暖温带)这一敏感地区[24-26]的研究较缺乏。因此,开展关于气候过渡带人工林土壤呼吸对于极端降雪事件响应的影响,具有非常重要的理论和现实意义。基于以上问题,本试验选取位于北亚热带-暖温带气候过渡带的信阳市为研究地区,以2018年1月4–7日信阳市的一次极端降雪为研究契机,根据信阳气象局数据资料,信阳平均累计降雪51.9 mm,平均积雪深度达29 cm,为1951年有气象记录以来该地降雪的历史最高值,这为研究极端降雪对人工绿地土壤呼吸的影响提供了机会。研究该区域土壤呼吸对气候变化的响应更有助于了解人工绿地碳排放对气候变化的响应,可为精确评估与模拟未来气候变化背景下陆地碳循环过程提供数据支持,具有非常重要的理论和现实意义。
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不同降雪处理下土壤温度均表现出显著的时间波动(表1),即土壤温度随降雪的融化而变化;随着试验进行,土壤温度呈升高趋势(图2a)。表2表明:不同处理下,土壤温度存在差异,在增雪处理下土壤平均温度显著低于其它2种处理。时间阶段与处理间有交互作用(表1、图2b),在试验前期,减雪处理下土壤温度显著低于其余2种处理;试验中期,减雪处理下土壤温度最高,增雪处理下土壤温度最低;试验后期,增雪处理下土壤温度显著低于其余2种处理。
表 1 降雪处理及测定时间对土壤温度、土壤湿度和土壤呼吸影响的方差分析结果
Table 1. Results of ANOVA on the effects of snowfall treatment and time on soil temperature, moisture and soil respiration
因子
Factor土壤温度
Soil temperature/℃土壤湿度
Soil moisture/%土壤呼吸速率
Soil respiration/(μmol·m−2·s−1)F P F P F P 时间Time
109.441 <0.001 49.822 <0.001 16.084 <0.001 处理Snow
18.018 <0.001 0.401 0.674 7.642 <0.001 时间×处理Time×Snow 52.327 <0.001 3.505 <0.001 14.596 <0.001 图 2 降雪改变对土壤温度、土壤湿度和土壤呼吸的影响
Figure 2. Impacts of snowfall change on soil temperature, moisture and soil respiration
表 2 不同处理下土壤温度、土壤湿度和土壤呼吸均值(±标准误)
Table 2. Mean values (±SE) of soil temperature, moisture and respiration under different treatments
处理
Treatments土壤温度
Soil temperature
/℃土壤湿度
Soil moisture
/%土壤呼吸
Soil respiration
/(μmol·m−2·s−1)对照CK
3.55±0.18a 23.99±1.92a 0.46±0.05b 减雪
Snow removed3.46±0.07a 24.56±1.99a 0.51±0.02b 增雪
Snow increased3.01±0.11b 24.61±0.63a 0.62±0.02a 注:表中同列不同字母表示不同处理间差异显著(P<0.05)。
Notes: Different letters in the same column in the table indicate significant differences between different processing.(P<0.05).不同时间阶段下土壤湿度有显著变化,在试验中期,土壤湿度显著高于其余2个时期;不同处理下土壤湿度无显著差异(表1、2),且处理与时间阶段有显著交互作用(表1、图2b)。
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对比3个试验阶段,土壤呼吸有显著的时间波动,各处理显著影响了土壤呼吸(表1)。综合整个试验过程,增雪处理下,土壤呼吸速率比去除雪被和对照处理下分别提高了0.11、0.16 μmol·m−2·s−1(表2)。此外,改变降雪处理对土壤呼吸的影响在不同试验阶段并不一致,即改变降雪与处理时间之间存在显著的交互作用(表1)。在试验前期,增雪处理下土壤呼吸速率显著高于减雪处理和对照处理;在试验中期和后期,增减雪处理对土壤呼吸均无显著影响(图2b)。
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图3表明:改变降雪对土壤铵态氮(P=0.92)、硝态氮(P=0.40)含量均无显著影响,但与对照相比,减雪、增雪处理下硝态氮、铵态氮含量均有增加;可利用性氮含量在不同处理下差异也不显著(P=0.33),但增、减雪处理下均提高了可利用性氮的含量。
图 3 降雪改变对土壤硝态氮、铵态氮、可利用氮、微生物量碳及微生物量氮的影响
Figure 3. Impacts of changing snowfall on soil NO3--N, NH4+-N and Available-N, MBC and MBN
与对照相比,在增、减雪处理下,人工林土壤微生物量碳(MBC)含量有微弱的提高,而微生物量氮(MBN)含量在减雪下减少,在增雪下有微弱的提高,但在不同处理下,MBC(P=0.56)或MBN(P=0.20)的含量变化并不显著(图3)。
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表3表明:在试验早期,土壤呼吸与土壤温度之间存在接近显著的正相关关系,但在试验中期或后期,土壤呼吸与土壤温度之间无显著相关性。综合整个试验,土壤呼吸与土壤温度间存在显著的负相关关系。不管在试验的各个阶段,还是整个试验过程中,土壤呼吸均不受土壤湿度的调控。整个试验过程土壤呼吸的平均值与微生物量碳之间存在接近显著的正相关关系(表3),土壤呼吸与微生物量氮、铵态氮、硝态氮、可利用性氮含量之间均无显著的相关关系。
表 3 土壤呼吸与环境因子之间的相关分析结果(R值与P值)
Table 3. Results (R and P value)between soil respiration and other environmental factors
自变量Dependent variables 早期Earlier 中期Mid-term 后期Later 平均Mean R P R P R P R P 土壤温度Soil temperature 0.333 0.090 0.185 0.357 −0.117 0.562 −0.740 0.000 土壤湿度Soil moisture −0.012 0.953 0.224 0.262 0.238 0.232 0.240 0.228 微生物量碳MBC − − − − 0.291 0.141 0.351 0.073 微生物量氮MBN − − − − 0.051 0.799 0.291 0.140 铵态氮含量NH4+−N content − − − − 0.137 0.496 0.174 0.385 硝态氮含量NO3−−N content − − − − −0.037 0.856 −0.039 0.848 可利用性氮含量Available N content − − − − 0.120 0.553 0.154 0.443
极端降雪对北亚热带-暖温带气候过渡带人工林土壤呼吸的影响
Effect of Extreme Snowfall on Soil Respiration of Plantations in North Subtropics-Warm Temperature Transition Zone
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摘要:
目的 本研究的主要目的是研究极端降雪对北亚热带-暖温带气候过渡带人工林土壤呼吸的影响机制。 方法 以信阳市人工林为研究对象,以2018年1月信阳市的暴雪为契机,设置增加雪被、自然降雪、去除雪被的控制试验,利用LI-8100测定了不同厚度雪被处理下土壤呼吸的变化,并结合土壤温度、土壤湿度、土壤微生物量碳氮含量、土壤可利用性氮含量等变化,研究土壤呼吸与环境因子之间的关系。 结果 在试验前期,增加雪被显著提高了土壤温度,但增加雪被处理下,试验中后期土壤温度值及整个试验阶段的土壤温度平均值均显著低于对照处理。增加雪被厚度可使土壤呼吸速率提高21.57%,而去除雪被对土壤呼吸速率无显著影响。雪被变化对于微生物量碳氮、土壤可利用性氮含量均无显著影响。增雪处理引起的土壤呼吸速率增加主要由试验前期土壤温度的升高导致的。 结论 极端暴雪可能提高气候过渡带人工林的土壤呼吸速率,但这种提高受到降雪量的影响,30 cm左右的降雪并未显著影响土壤呼吸速率,如果积雪深度继续增加,土壤碳排放速率会有所增强。此外,积雪深度在不同的融雪阶段对土壤呼吸的影响幅度不一致,降雪对土壤呼吸的影响主要发生在积雪完全消融之前这一阶段。本结果可为建立气候变化下的生态系统碳循环模型提供部分数据支持。 Abstract:Objective To study the effect of extreme snowfall on soil respiration of plantations in north subtropics-warm temperate transition zone. Method A controlled experiment including snow addition, natural snowfall and snow remove was conducted in a plantation after a heavy snowfall in January 2018 in Xinyang, He'nan Province. The soil respiration variations under different treatments were measured with LI-8100 in different snow cover depths. The soil temperature, soil moisture, microbial biomass carbon, microbial biomass nitrogen, and soil available nitrogen contents were detected to determine the relationships between soil respiration and environmental factors. Result The results showed that the snow addition significantly elevated soil temperature in the earlier stage of the experiment. However, the soil temperature under snow addition treatment was significantly lower than that in the control during the middle and later stage, and across the whole experiment, respectively. Snow addition elevated the soil respiration rate by 21.57%, but snow remove did not affect the soil respiration. The change of snowfall did not affect the contents of microbial biomass carbon, microbial biomass nitrogen and soil available nitrogen. The elevated soil respiration was mainly ascribed to the elevation of soil temperature in the early stage of the experiment. Conclusion Extreme snowfall may increase soil respiration rate in plantations in the climate transitional zone, but it is affected by snowfall. The snowfall with the depth of about 30 cm will not significantly affect soil respiration rate. If snow depth continues to increase, the soil carbon emission rate will increase. In addition, the impact of snow depth on soil respiration at different stages of snowmelt is not consistent, and the impact of snow on soil respiration mainly occurs before the snow melts completely. This study can provide partial data supporting the establishment of ecosystem carbon cycle model under climate change scenario. -
Key words:
- extreme snowfall
- / soil carbon flux
- / central China
- / plantation
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表 1 降雪处理及测定时间对土壤温度、土壤湿度和土壤呼吸影响的方差分析结果
Table 1. Results of ANOVA on the effects of snowfall treatment and time on soil temperature, moisture and soil respiration
因子
Factor土壤温度
Soil temperature/℃土壤湿度
Soil moisture/%土壤呼吸速率
Soil respiration/(μmol·m−2·s−1)F P F P F P 时间Time
109.441 <0.001 49.822 <0.001 16.084 <0.001 处理Snow
18.018 <0.001 0.401 0.674 7.642 <0.001 时间×处理Time×Snow 52.327 <0.001 3.505 <0.001 14.596 <0.001 表 2 不同处理下土壤温度、土壤湿度和土壤呼吸均值(±标准误)
Table 2. Mean values (±SE) of soil temperature, moisture and respiration under different treatments
处理
Treatments土壤温度
Soil temperature
/℃土壤湿度
Soil moisture
/%土壤呼吸
Soil respiration
/(μmol·m−2·s−1)对照CK
3.55±0.18a 23.99±1.92a 0.46±0.05b 减雪
Snow removed3.46±0.07a 24.56±1.99a 0.51±0.02b 增雪
Snow increased3.01±0.11b 24.61±0.63a 0.62±0.02a 注:表中同列不同字母表示不同处理间差异显著(P<0.05)。
Notes: Different letters in the same column in the table indicate significant differences between different processing.(P<0.05).表 3 土壤呼吸与环境因子之间的相关分析结果(R值与P值)
Table 3. Results (R and P value)between soil respiration and other environmental factors
自变量Dependent variables 早期Earlier 中期Mid-term 后期Later 平均Mean R P R P R P R P 土壤温度Soil temperature 0.333 0.090 0.185 0.357 −0.117 0.562 −0.740 0.000 土壤湿度Soil moisture −0.012 0.953 0.224 0.262 0.238 0.232 0.240 0.228 微生物量碳MBC − − − − 0.291 0.141 0.351 0.073 微生物量氮MBN − − − − 0.051 0.799 0.291 0.140 铵态氮含量NH4+−N content − − − − 0.137 0.496 0.174 0.385 硝态氮含量NO3−−N content − − − − −0.037 0.856 −0.039 0.848 可利用性氮含量Available N content − − − − 0.120 0.553 0.154 0.443 -
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