The transport of chemical components in homogeneous snowpacks on Urumqi Glacier No.1, eastern Tianshan Mountains,Central Asia

Chemical records from alpine ice cores provide an invaluable source of paleoclimatic and environmental information. Not only the atmospheric chemical composition but also depositional and post-depositional processes are recorded within snow/firn strata. To interpret the environmental and climatic significance of ice core records, we studied the variability of glacier snowpack chemistry by investigating homogeneous snowpacks from October 2003 to September 2006 on Urumqi Glacier No. 1 in eastern Tianshan Mountains, Central Asia. Principle Component Analysis of ionic species in dry and wet seasons revealed the impact of meltwater in redistributing ions in the snowpacks. The 1st, 2nd and 3rd principle components for dry seasons differ significantly, reflecting complex associations between depositional or/and post-depositional processes. The variability trend of ionic concentrations during the wet seasons was found to fit a Gauss Function with significant parameters. The elution factor revealed that more than half of ions are leached out during the wet seasons. Differences with respect to ion snowpack mobility were found. Of the ions studied SO42– was the most mobile and Mg2+ the least mobile. A threshold relationship between air temperatures and the elution process was investigated over the study period. The results indicate that the strong melt /ablation processes and iconic redistribution occur at a threshold air temperature of 0°C. The study found that surface melt on the snowpacks is the main factor causing the alteration of the snowpack chemistry. Rainfall also has an impact on the chemistry but plays a less significant role than the surface melt.     

辽西农林复合系统中杨树水分耗散规律

以辽西杨树-烟草复合系统为研究对象,采用Granier热扩散探针法,对杨树-烟草复合系统的杨树树干液流进行连续观测,并对环境因子(空气温度、空气湿度、净辐射、风速、土壤温度和土壤湿度)进行同步观测。结果表明:杨树液流速率具有明显的早晚低、中午高的单峰型日变化特征,并具有从6月到9月逐渐降低的季节性变化规律,6月液流速率月平均的日变化峰值为5.77×10-3cm/s,9月下降至2.34×10-3cm/s。相关分析表明:净辐射、空气温度、空气湿度是杨树液流速率的主要影响因子,风速和土壤温度次之,土壤湿度影响最小,并建立了依据环境因子估算液流速率的逐步回归模型。树干液流与环境因子之间的数量关系能很好地预测杨树的蒸腾耗水量。     

基于侧柏液流的测定对Granier原始公式系数进行校正

为研究Granier原始公式计算单株树木蒸腾耗水量的准确性,以侧柏作为研究对象,采用热消散方法测定在15、30、50、70和90cm水柱高度形成不同压力梯度下的树干液流通量密度,并以称重法作为对照,利用回归分析方法拟合称重法测定的液流通量密度与热消散法测定的树干液流温差系数(K值),进而建立校正公式.结果表明:基于侧柏校正的Granier公式为Fd=0.0115K0.5581(R2=0.8319).与称重法测定的液流通量密度相比,校正的Granier公式计算的结果略高(6.70±0.02)％,而Granier原始公式计算的则低估(78.53±0.04)％.由此可知,采用校正的Granier公式计算侧柏的液流通量密度具有较高的精度.     

Radial profile of sap flow velocity in mature Xinjiang poplar（Populus alba L. var. pyramidalis） in Northwest China

Estimation of the transpiration rate for a tree is generally based on sap flow measurements within the hydro-active stem xylem. In this study, radial variation of sap flow velocity(Js) was investigated at five depths of the xylem(1, 2, 3, 5 and 8 cm under the cambium) in three mature Xinjiang poplar(Populus alba L. var. pyramidalis) trees grown at the Gansu Minqin National Studies Station for Desert Steppe Ecosystem from May to October 2011. Thermal dissipation probes of various lengths manufactured according to the Granier's design were installed into each tree for simultaneous observation of the radial patterns of Js through the xylem. The radial patterns were found to fit the four-parameter GaussAmp equation. The peak Js was about 27.02±0.95 kg/(dm2?d) at approximately 3 to 5 cm deep from the cambium of the three trees,and the lowest Js appeared at 1 cm deep in most of the time. Approximately 50% of the total sap flow in Xinjiang poplar occurred within one-third of the xylem from its outer radius, whereas 90% of the total sap flow occurred within two-fifth of the xylem. In addition, the innermost point of the xylem(at 8-cm depth), which appeared as the penultimate sap flow in most cases during the study period, was hydro-active with Js,8 of 7.55±3.83 kg/(dm2?d). The radial pattern of Js was found to be steeper in midday than in other time of the day, and steeper diurnal fluctuations were recorded in June, July and August(the mid-growing season). Maximum differences between the lowest Js(Js,1 or Js,8) and the highest Js(Js,3 or Js,5) from May through October were 12.41, 17.35, 16.30, 18.52, 12.60 and 16.04 g/(cm2?h), respectively. The time-dependent changes of Js along the radial profile(except at 1-cm depth) were strongly related to the reference evapotranspiration(ET0). Due to significant radial variability of Js, the mean daily sap flow at the whole-tree level could be over-estimated by up to 29.69% when only a single probe at depth of 2 cm was used. However, the accuracy of the estimation of sap flow in Xinjiang poplar could be significantly improved using a correction coefficient of 0.885.     

缙云山典型树种树干液流日际变化特征及与气象因子关系

运用Granier热扩散探针方法,于2012—2015年8—9月对重庆缙云山自然保护区内3个典型优势木(杉木、马尾松、四川山矾)的树干液流进行测定,并运用微型气象站同步监测太阳辐射(ES)、大气温度(T)、大气相对湿度(RH)、风速(W)、饱和水汽压差(VPD)等气象因子及土壤含水量(SWC),分析3个树种的树干液流在日尺度及典型天气条件(晴、阴、雨)下的差异和特征及其与气象因子的关系。结果表明:树种间导水能力差异表现为四川山矾＞马尾松＞杉木,阔叶树种蒸腾速率高于针叶树种;3个树种树干液流日变化规律均呈现“昼高夜低”的单峰走势;液流启动时间和达到峰值时间均为山矾最早,杉木最晚;典型天气条件下3个树种液流量均呈现晴天＞阴天＞雨天,与晴天液流量相比较,阴、雨天液流量减少幅度为41%至86%;白天树干液流贡献率表现为晴天(94.74%~98.04%)＞阴天(93.63%~96.71%)＞雨天(81.43%~85.43%),夜晚树干液流贡献率表现为雨天(14.57%~18.27%)＞晴天(3.29%~6.37%)＞阴天(1.96%~5.26%);导致雨天夜间液流贡献率最大的因子为SWC;影响3个树种树干液流的主要气象因子为ES和VPD;T、RH、W对3个树种的影响程度都很小,且略有不同。气象因子与杉木、马尾松、四川山矾的树干液流多元回归方程决定系数分别为0.873、0.873、0.903。