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Soil-surface CO2 efflux and its spatial and temporal variations in a youngponderosa pine plantation in northern California

机译：加利福尼亚北部年轻松树人工林的土壤表面CO2流出及其时空变化

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Soil-surface CO2 efflux and its spatial and temporal variations were examined in an 8-y-old ponderosa pine plantation in the Sierra Nevada Mountains in California from June 1998 to August 1999. Continuous measurements Of Soil CO2 efflux, soil temperatures and moisture were conducted on two 20 x 20 m sampling plots. Microbial biomass, fine root biomass, and the physical and chemical properties of the soil were also measured at each of the 18 sampling locations on the plots. It was found that the mean soil CO2 efflux in the plantation was 4.43 mu mol m(-2) s(-1) in the growing season and 3.12 mu mol m(-2) s(-1) in the nongrowing season. These values are in the upper part of the range of published soil-surface CO2 efflux data. The annual maximum and minimum CO2 efflux were 5.87 and 1.67 mu mol m-2 s-1, respectively, with the maximum occurring between the end of May and early June and the minimum in December. The diurnal fluctuation Of CO2 efflux was relatively small (< 20%) with the minimum appearing around 09.00 hours and the maximum around 14.00 hours. Using daytime measurements Of Soil CO2 efflux tends to overestimate the daily mean Soil CO2 efflux by 4-6%. The measurements taken between 09.00 and 11.00 hours (local time) seem to better represent the daily mean with a reduced sampling error of 0.9-1.5%. The spatial variation of soil CO2 efflux among the 18 sampling points was high, with a coefficient of variation of approximately 30%. Most (84%) of the spatial variation was explained by fine root biomass, microbial biomass, and soil physical and chemical properties. Although soil temperature and moisture explained most of the temporal variations (76-95%) Of Soil CO2 efflux, the two variables together explained less than 34% of the spatial variation. Microbial biomass, fine root biomass, soil nitrogen content, organic matter content, and magnesium content were significantly and positively correlated with soil CO2 efflux, whereas bulk density and pH value were negatively correlated with CO2 efflux. The relationship between soil CO2 efflux and soil temperature was significantly controlled by soil moisture with a Q(10) value of 1.4 when soil moisture was <14% and 1.8 when soil moisture was >14%. Understanding the spatial and temporal variations is essential to accurately assessment of carbon budget at whole ecosystem and landscape scales. Thus, this study bears important implications for the study of large-scale ecosystem dynamics, particularly in response to climatic variations and management regimes.
机译：从1998年6月至1999年8月，在加利福尼亚内华达山脉的8年生黄松松人工林中调查了土壤表面CO2排放及其时空变化。对土壤CO2排放，土壤温度和湿度进行了连续测量在两个20 x 20 m的采样区上。在样地的18个采样点中的每一个处都测量了微生物生物量，细根生物量以及土壤的物理和化学性质。结果表明，人工林的平均土壤CO2排放量在生长期为4.43μmol m（-2）s（-1），在非生长期为3.12μmol m（-2）s（-1）。这些值在已发表的土壤表面CO2外排数据范围的上部。每年的最高和最低二氧化碳排放量分别为5.87和1.67μmol m-2 s-1，最高发生在5月底至6月初，最低发生在12月。 CO2流出量的日变化相对较小（<20％），最小值出现在09.00小时左右，最大值出现在14.00小时左右。使用白天的土壤CO2外排量往往会使每日平均土壤CO2外排量高估4-6％。在09.00和11.00小时（本地时间）之间进行的测量似乎更好地代表了日均值，减少了0.9-1.5％的采样误差。 18个采样点之间土壤CO2流出量的空间变化较大，变化系数约为30％。大部分（84％）的空间变化是由细根生物量，微生物生物量以及土壤物理和化学性质所解释。尽管土壤温度和湿度解释了土壤CO2外排的大部分时间变化（76-95％），但这两个变量加起来解释了不到34％的空间变化。微生物量，细根生物量，土壤氮含量，有机质含量和镁含量与土壤CO2排放量呈显着正相关，而容重和pH值与CO2排放量呈负相关。土壤CO2排放与土壤温度之间的关系受到土壤水分的显着控制，当土壤水分<14％时Q（10）值为1.4，当土壤水分> 14％时Q（10）值为1.8。了解空间和时间变化对于准确评估整个生态系统和景观规模的碳预算至关重要。因此，这项研究对大规模生态系统动力学的研究具有重要意义，特别是对气候变化和管理制度的响应。

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