重庆铁山坪马尾松树干液流变化规律及其个体差异

Variation of stem sap flows of Pinus massoniana forest and its differences among individual trees at Tieshanping of Chongqing

为精准测算马尾松林蒸腾耗水和准确量化评估马尾松林涵养水源服务功能,采用热扩散式探针对马尾松林的不同树木个体进行长期连续监测,研究马尾松树干液流不同时间尺度及径向的变化规律,分析其个体差异及影响因素。结果表明:1)不同季节、天气的马尾松液流速率日变化均有差异,各季节晴天的液流速率日变化均呈“单峰”型,春、夏季阴天也呈明显的“峰—谷”变化,雨天则均呈低水平直线(<0.10 g/(cm^(2)·min));2)马尾松日液流速率年内变化总体呈“单峰”型,一般在7—8月达到峰值(>0.15 kg/(cm^(2)·d)),年际变化差异明显;液流速率具有明显的径向变化及个体差异,呈一元二次函数关系(P<0.01);3)马尾松个体的优势度、叶面积指数均对液流速率产生显著影响(P<0.01),其中叶面积指数是影响液流速率的重要冠层因素,但监测期内树种类型对液流速率的影响并不明显(P>0.05);4)多数马尾松个体的液流速率与气温、潜在蒸发、太阳辐射总量、最大太阳辐射强度、风速均呈正相关(P<0.01),与空气相对湿度、降雨量则呈负相关(P<0.01),且多数树木个体的液流速率与气象因子均呈多元函数关系(P<0.01),其中太阳辐射总量是影响液流速率的主要气象因子。综上,马尾松林树木个体的液流速率时空变异明显,且受优势度、叶面积指数及气象条件等多种因素综合影响,可为分布式测算三峡库区马尾松林的蒸腾耗水提供科学依据。

[Background]Stand transpiration accounts for 50%-90%of the total forest evapotranspiration.Stem sap flow directly determines transpirations of individual tree and stand.Study on stem sap flow is helpful to scientifically understand variation of forest transpiration and accurately evaluate the water conservation service of forest.Pinus massoniana forest is the most important forest type in the shelter-forest system of the Three Gorges Reservoir Area,which plays an important role in maintaining the ecological security of the Three Gorges Reservoir.[Methods]Taking Pinus massoniana forest at Tieshanping of Chongqing in the Three Gorges Reservoir area as the research project and using thermal diffusion probes to long-term continuously observe the sap flow of different individual trees in 2010—2012,temporal and radial variation of sap flow from Pinus massoniana were studied by methods of drawing the scatter plots and fitting the regression equations,and difference of sap flow among individual trees and its influencing factors were analyzed by methods of the univariate analysis of variance and the Pearson correlation analysis.[Results]1)The diurnal variation of sap flow velocity for Pinus massoniana was different in different seasons and weather.The diurnal variation of sap flow velocity having a“one-peak”pattern in sunny days in each season also presented a significant change of“peak-valley”in cloudy days in spring and summer,while it presented a low level straight line(<0.10 g/(cm^(2)·min))in rainy days.2)The annual variation of daily sap flow velocity for Pinus massoniana with obvious interannual variation generally presented a“one-peak”pattern,which generally reached the peak in July and August(>0.15 kg/(cm^(2)·d)).The sap flow velocity presented an obvious radial variation and individual difference,which was a quadratic function of one variable(P<0.01).3)Dominance and leaf area index of individual Pinus massoniana had significant effects on sap flow velocity(P<0.01),and the leaf area index was an important canopy factor affecting sap flow velocity,but tree species had no obvious effect on sap flow velocity during the monitoring period(P>0.05).4)Sap flow velocity of most individual Pinus massoniana was positively correlated with air temperature,potential evaporation,total solar radiation,max of solar radiation intensity and wind speed(P<0.01),and negatively correlated with relative humidity and rainfall(P<0.01).There was a multivariate function relationship between sap flow velocity of most individual trees and meteorological factors(P<0.01),of which the total solar radiation was the main meteorological factor affecting sap flow velocity.[Conclusions]The temporal and spatial variation of sap flow velocities of individual trees in Pinus massoniana forest is obvious and comprehensively affected by dominance,leaf area index and meteorological conditions,which may provide a scientific basis for distributed evaluating transpiration of Pinus massoniana forest in the Three Gorges Reservoir area.