乌兰布和沙漠梭梭茎干液流对降雨脉冲的响应

Responses of stem sap flow of Haloxylon ammodendron to rainfall pulses in Ulan Buh Desert

量化荒漠植物生态水文过程对降雨脉冲的响应是理解气候变化对旱区生态系统影响的关键。为深入理解乌兰布和沙漠梭梭(Haloxylon ammodendron)人工林中梭梭对降雨脉冲的响应,于2020年6-10月,应用热扩散技术和气象水文学方法观测了梭梭茎干液流速率(SFD)、人工林微气象因素和土壤水分含量,结果表明:(1)在研究期内选择的17场降雨事件中,降雨后梭梭茎干SFD日均值为0.044 g·cm^(-2)·min^(-1),是雨前的1.16倍。其中9场降雨后SFD日变化曲线由雨前的“双峰型”变为“单峰型”;另外8场降雨则明显改变了梭梭茎干SFD日变化的特征值:降雨后梭梭茎干液流的启动时间由降雨前的8:00提前至7:00左右,其平均峰值也由降雨前的0.067增至0.085 g·cm^(-2)·min^(-1),且在峰值区间维持时间也明显延长。(2)阈值-延迟模型(T-D)可以较好地描述梭梭茎干SFD对降雨脉冲的响应过程;其最低降雨响应阈值为0.8 mm,滞后时间为1.71 d。(3)梭梭茎干SFD与气温、饱和水汽压差、太阳辐射、风速和土壤体积含水量均呈显著正相关关系,与相对湿度呈显著负相关关系,但与降雨量无显著相关关系,说明降雨输入会通过改变梭梭的水分生理特性和土壤水分条件来间接影响其液流的变化。该研究结果有助于深入了解荒漠植物水分利用特征及其对气候变化的响应机制,对于人工固沙林的可持续经营与管理具有重要意义。

Aims Quantifying the responses of eco-hydrological processes of desert plants to rainfall pulses is the key to understand the impact of climate change in dryland ecosystem.Our objective was to explore the responses of stem sap flow of Haloxylon ammodendron to rainfall pulses in a H.ammodendron plantation in the Ulan Buh Desert.Methods From June to October 2020,the stem sap flow of H.ammodendron,micrometeorological factors and soil moisture in the plantation were continuously observed by thermal diffusion probes as well as the hydrometeorological methods,to analyze the characteristics of stem sap flux density(SFD)of H.ammodendron and its response to rainfall.Important findings(1)The average daily SFD was 0.044 g·cm^(-2)·min^(-1)after the rain,which was 1.16 times of that before the rain among the selected 17 rainfall events during the study period.The diurnal variation of SFD were changed from“bimodal pattern”before rain to“unimodal pattern”after rain for 9 of the all events.The characteristic value of daily SFD fluctuation were obviously changed after the other 8 rains.For example,the initiation time of SFD after rain were earlier from 8:00 before rain to 7:00 in the morning.And its peak values of daily SFD were also increased from 0.067 g·cm^(-2)·min^(-1)before rain to 0.085 g·cm^(-2)·min^(-1),and the duration of the peak interval was significantly extended.(2)The impacts of rainfall pulses on the sap flow of H.ammodendron could be well described with the threshold delay model(T-D model).And the lowest rainfall threshold and the lag time of SFD responded to rain were 0.8 mm and 1.71 d,respectively,indicating that the sap flow of this shrub species was sensitive to rainfall pulses and had a certain lag.(3)The SFD of H.ammodendron was significantly positive correlated with atmospheric temperature,vapor pressure deficit,solar radiation,wind speed and soil volumetric water content,and significantly negative correlated with the relative humidity,but no significant correlated with rainfall,suggesting that SFD of H.ammodendronwould be indirectly affected by rainfall pulses by changing the physiological characteristics of the species as well as soil water condition.Our results are helpful to further understand the water use characteristics of desert plants and their response to climate change,and are of great significance for the sustainable management of artificial sand-fixation forests in future.