水热条件及坡向对长白山区蒙古栎林土壤呼吸的影响

Effects of Hydrothermal Conditions and Slope Aspect on Soil Respiration of Mongolian Oak Forests in Changbai Mountains

在蒙古栎林地阳坡和阴坡各设置3块样地(20 m×30 m),每个样地随机布置土壤聚氯乙烯(PVC)环9个(上、中、下每个坡位各3个,环高5.0 cm、内径19.5 cm)。应用LGR便携式温室气体分析仪(915-0011,USA)配备土壤呼吸气室(PS3000,China)测定土壤呼吸速率,利用仪器自带温湿度探头就近同步测量土壤环周围5 cm深度土壤温度和体积含水量。测量自2017年4月12日—10月28日,每次测量时间间隔7 d。试验样地外500 m处设置自动气象站(CR1000,USA),用于自动测定空气和土壤温度和土壤体积含水量,净辐射、光合有效辐射和降水等环境因子。分析了2个坡向蒙古栎林土壤呼吸速率的差异,并探索水热因子对不同坡向蒙古栎林土壤呼吸及其月通量的影响。结果表明:在研究时段内,阳坡土壤温度显著高于阴坡(P<0.05),阳坡土壤体积含水量和土壤呼吸速率均显著低于阴坡(P<0.05)。日尺度上,土壤呼吸速率与土壤温度呈指数函数关系(P<0.01),但阴坡二者之间的关系更加显著,阴坡土壤呼吸温度敏感系数大于阳坡;阳坡土壤呼吸速率与土壤体积含水量呈线性关系(P<0.05),阴坡二者关系不显著;引入土壤体积含水量数据能够提高土壤呼吸模型的预测精度,且阳坡土壤呼吸速率主要受土壤体积含水量、土壤温度和体积含水量的交互作用影响,阴坡土壤呼吸速率主要受土壤温度和体积含水量影响。月尺度上,土壤呼吸速率与土壤平均温度呈显著指数关系(P<0.05),阳坡的温度敏感性高于阴坡,土壤呼吸速率与月降水量呈显著线性关系(P<0.01)。生长季,阳坡和阴坡蒙古栎林土壤呼吸通量,分别为398.22、470.99 g·m^(-2),阴坡比阳坡高18.27%。坡向影响蒙古栎林生态系统土壤呼吸速率,水热条件对不同坡向土壤呼吸的影响程度不同,导致土壤呼吸排放通量的差异。月尺度上,土壤呼吸通量呈单峰曲线形式,与土壤温度呈显著的指数关系,但温度敏感系数高于日尺度;月降水量与蒙古栎林月土壤呼吸通量呈显著相关。

Three plots(20 m×30 m)were set up on the sunny and shady slopes in Mongolian oak forest,and 9 soil polyvinyl chloride(PVC)rings were randomly arranged in each plot(5.0 cm high and 19.5 cm inner diameter,3 for upper,middle and lower slope respectively).The soil respiration rate was measured by LGR portable greenhouse gas analyzer(915-0011,USA)equipped with soil respiration chamber(PS3000,China),the soil temperature and volumetric water content at a 5-cm depth around the soil ring was synchronously measured by the detector equipped with the instrument.The measurement began on April 12 and finished on October 28 in 2017,with the time interval of each measurement for 7 d.The soil temperature and volumetric water content,net radiation,photosynthetically active radiation,precipitation and other environmental factors were automatically measured by an automatic weather station(CR1000,USA)which was set 500 m away from the sample site.The difference of soil respiration rate in two slope directions of Mongolian oak forest was analyzed,and the influence of hydro-thermal factors on soil respiration and monthly flux in different slope directions were explored.During the study period,the soil temperature of sunny slope was significantly higher than that of shady slope(P<0.05)but the soil volumetric water content and soil respiration rate was significantly lower than that of shady slope(P<0.05).On the diurnal scale,the soil respiration rate exponentially with soil temperature(P<0.01),and the relationship in shady slope was more closely.The temperature sensitive coefficient of soil respiration in shady slope was higher than that of sunny slope.There was a linear relationship between soil respiration rate and soil volumetric water content in sunny slope(P<0.05),however,the relationship in shady slope is not significant.Adding soil volumetric water content data can improve the prediction accuracy of the model.The soil respiration rate in sunny slope is mainly influenced by soil volumetric water content and the interaction of soil temperature and volumetric water content,while soil respiration rate was mainly influenced by soil temperature and the soil volumetric water content.On the monthly scale,there was a significant exponential relationship between soil respiration rate and soil average temperature(P<0.05),the temperature sensitivity of shady slope was higher than that of sunny slope,and soil respiration rate was significantly correlated with monthly precipitation for both forest ecosystems(P<0.01).During the whole growth season,soil respiration of shady slope was 470.99 g·m^(-2),which was 18.27%higher than that of sunny slope(398.22 g·m^(-2)).These results suggest that the slope variable will affect the soil respiration rate of Mongolian oak forest ecosystem on the local scale,the influence degree and the influence mechanism of water and heat conditions on soil respiration are different in different slope,and finally lead to the difference of soil respiration flux.The soil respiration fluxes were shown as a single peak curve form on the seasonal scale,and had significant exponential relationship with soil temperature,however,the temperature sensitivity coefficient of soil respiration was higher than that of diurnal scale.The monthly precipitation was closely related to the monthly flux of soil respiration in the Mongolian oak forest.