Time-Lag Effect Between Sap Flow and Environmental Factors of Larix principis-rupprechtii Mayr

Liu Hong,Jianbin Guo,Jing Ma,Xiao Wang,Zebin Liu,Yanhui Wang,Ziyou Zhang

doi:10.3390/f10110971

Abstract

A time lag between sap flux density (Js) and meteorological factors has been widely reported, but the controlling factors of the time lag are poorly understood. To interpret the time lag phenomenon systematically, thermal dissipation probes were placed into each of eight trees to measure the Js of Larix principis-rupprechtii Mayr. in the Liupan Mountains in Northwest China. Meteorological factors, including vapor pressure deficit (VPD), solar radiation (Rs) and air temperature (Ta), were synchronously measured with Js, and the dislocation contrast method was used to analyze the time lag between Js and the meteorological factors. The analysis indicated the following for the whole experimental period. (1) The time lag between Js and VPD (TLV) and the time lag between Js and Rs (TLR) both exhibited different patterns under different weather conditions, and Js could precede Rs on dry days. (2) Both TLV and TLR varied with the day of the year (DOY) throughout the experimental period; namely, both exhibited a decreasing tendency in September. (3) Reference crop evapotranspiration (ETref) had a greater influence on the time lag than the other meteorological factors and directly controlled the length and direction of TLV and TLR; relative extractable water (REW) modified the relationship between ETref and time lag. (4) The regression analysis results showed differences between the time lags and the environmental factors (ETref and REW) within different ranges of REW. Namely, TLR was better determined by ETref and REW when REW < 0.38, while TLV was better correlated with ETref and REW in the absence of soil water limitations (REW > 0.38). This project provided an important opportunity to advance the understanding of the interaction between plant transpiration and meteorological factors in a changing climate.

Highlights

Plant transpiration accounts for 61% (±15% s.d.) of evapotranspiration and returns approximately39% ± 10% of incident precipitation (P) to the atmosphere, creating a dominant force in the global cycle [1,2]
ETref ranged from 0.3–4.17 mm, and its variations were similar to those of Js ; both parameters remained at a higher level in spring and summer and decreased in autumn, which indicates a connection between sap flow and evapotranspiration demand
We investigated the time lag under different weather conditions, and the results suggested that there was a significant difference between sunny days and rainy days for time lag between Js and Rs (TLR), while for time lag between Js and VPD (TLV), significant differences were found between sunny days and other weather conditions

Summary

Introduction

Plant transpiration accounts for 61% (±15% s.d.) of evapotranspiration and returns approximately39% ± 10% of incident precipitation (P) to the atmosphere, creating a dominant force in the global cycle [1,2]. The hysteresis loop has long been a topic of great interest in a wide range of fields, including hydrology, ecology and plant physiology [10,11,12,13]. Time lag is another form of hysteresis that is defined as the time difference between peak values of Js and meteorological variables [14], the length and direction of a time lag can, in turn, reflect the magnitude of hysteresis [12], and the time lag between sap flux density (Js ) and environmental factors is often identified as a self-protection mechanism of plants to avoid dehydration [15]. With increasingly frequent extreme weather events, investigating time lags is a continuous concern regarding plant and water relationships

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