土から空へ:植物が水を持ち上げるために使用するエネルギー量を数値化。(From The Soil to The Sky:UC Santa Barbara researchers are the first to put a number on the amount of energy that plants use to lift water)

2022-09-07 カリフォルニア大学サンタバーバラ校(UCSB)

Plants have an open circulatory system in which water evaporating from the leaves pulls up the water below it.

<関連情報>

• https://www.news.ucsb.edu/2022/020705/soil-sky
• https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JG006922

植物の樹液上昇に必要なグローバルパワーの定量化 Quantifying the Global Power Needed for Sap Ascent in Plants

Gregory R. Quetin,Leander D. L. Anderegg,Alexandra G. Konings,Anna T. Trugman
Journal of Geophysical Research  Published: 17 August 2022
DOI:https://doi.org/10.1029/2022JG006922

Abstract

Terrestrial photosynthesis requires the evaporation of water (transpiration) in exchange for CO₂ needed to form sugars. The water for transpiration is drawn up through plant roots, stem, and branches via a water potential gradient. However, this flow of water—or sap ascent—requires energy to lift the water to the canopy and to overcome the resistance of the plant’s water transporting xylem. Here, we use a combination of field measurements of plant physiology (hydraulic conductivity) and state-of-the-science global estimates of transpiration to calculate how much energy is passively harvested by plants to power the sap ascent pump across the world’s terrestrial vegetation. Globally, we find that 0.06 W/m² is consumed in sap ascent over forest dominated ecosystems or 9.4 PWh/yr (equal to global hydropower energy production). Though small in comparison to other components of the Earth’s surface energy budget, sap ascent work in forests represents 14.2% of the energy compared to the energy consumed to create sugars through photosynthesis, with values up to 18% in temperate rainforests. The power needed for sap ascent generally increases with photosynthesis, but is moderated by both climate and plant physiology, as the most work is consumed in regions with large transpiration fluxes (such as the moist tropics) and in areas where vegetation has low conductivity (such as temperate rainforests dominated by conifer trees). Here, we present a bottom-up analysis of sap ascent work that demonstrates its significant role in plant function across the globe.

Plain Language Summary

Trees transpire up to 100 gallons of water per day, which requires energy to overcome gravity and the resistance of specialized stem transportation tissues. We show that the energy used by trees to move water from the soil to the leaves for transpiration is of the same order of magnitude to the energy harvested by these plants from sunlight during photosynthesis. This work implies that the evolution of vascular plants has created a pump that passively harvests energy to lift water to plant canopies, which is a significant energetic benefit to plant function and helps fuel life on Earth.

Key Points

• Life on Earth is partially fueled by energy passively harvested from the environment to lift sap against frictional forces and gravity
• For the first time, we quantify sap ascent power globally with remotely sensed and field measurements of plant fluxes, states, and traits
• Sap ascent power is 14.2% the size of photosynthetic energy and comparable to the production of all hydropower across the globe