Impact of potassium ion content of xylem sap and of light conditions on the hydraulic properties of trees
Abstract
Vee transport juurtest lehtedesse on taime ellujäämiseks oluline, kuna mõjutab taime süsiniku omastamist ja teisi elutähtsaid funktsioone. Vesi liigub juurtest lehtedesse mööda juhtkudet, mida nimetaktakse ksüleemiks. Ksüleemi veetranspordivõimet iseloomustab hüdrauliline juhtivus. Taimes liikuv vesi sisaldab alati selles lahustunud aineid, mistõttu nimetatakse seda ksüleemimahlaks. Vee transpordi käivitab aurumine lehestiku pinnalt, mida lühikeses ajaskaalas mõjutab ka ksüleemimahla ioonide sisaldus. Doktoritöö käsitleb ksüleemimahla kaaliumioonide sisalduse, valgustingimuste mõju ja hüdraulika omavahelisi seoseid kiirekasvulistel lehtpuudel nagu hübriidhaab ja arukask. Töö on läbi viidud Järvselja Õppe- ja Katsemetskonna segametsas ning Rõkal asuval metsaökosüsteemi õhuniiskusega manipuleerimise katsealal (FAHM). Töös käsitlen hüdrauliliste ja ksüleemimahla parameetrite ööpäevast muutumist, puukoore eemaldamise ehk floeemi sälkamise mõju hüdraulilise juhtivusele ja ksüleemimahla omadustele, valguse kvaliteedi ja intensiivsuse mõju lehe ning oksa hüdraulilisele juhtivusele. Doktoritöös tõestasin ksüleemimahla ioonide sisalduse mõju katsealuste liikide hüdraulilisele juhtivusele. Leidsin, et suurenenud ksüleemimahla kaaliumioonide sisaldus suurendab hüdraulilist juhtivust, mis avardab meie teadmisi K+ osalusest taimede veevahetuse regulatsioonis. Samuti kattusid hübriidhaava ksüleemimahla ioonide sisalduse ja hüdraulilise juhtivuse ööpäevased rütmid. Floeemi sälkamine mõjutas hübriidhaava hüdraulilist juhtivust ja gaasivahetust, kuid mitte ksüleemimahla omadusi. Valgus mõjutas mitmel eri viisil ksüleemimahla kaaliumioonide sisaldust ja oksa hüdraulilist juhtivust. Nii valgustingimused kui ksüleemimahla ioonide sisaldus mõjutavad oluliselt lehtpuude veetranspordivõimet. Kaaliumioonide sisalduse muutmise teel saavad taimed muutuvates keskkonnatingimustes optimeerida lehtede veevarustust, saavutamaks tasakaalustatud veebilanssi.
Water transfer from roots to leaves is essential for plants to keep up photosynthesis, grow and survive. Water moves from roots to shoots through water-conducting tissue called xylem. The water transport capacity of the xylem is characterized by hydraulic conductance. The water inside plants always contains dissolved substances; therefore, it is called a xylem sap. The main driving force for long-distance water transport in the xylem is transpiration, but hydraulic conductance can also be adjusted via changes in xylem sap ionic content on a short time scale. The objectives of the thesis were to investigate circadian patterns of hydraulic conductance and physico-chemical properties of xylem sap; to evaluate the impact of phloem girdling on branch hydraulic conductance and xylem sap properties; to evaluate the impact of light quality and intensity on leaf and shoot hydraulic properties. The study objects were fast-growing broadleaved trees like hybrid aspen and silver birch. The work was carried out in the mixed forest of Järvselja Training and Experimental Forestry District and the Free Air Humidity Manipulation experimental site (FAHM) located at Rõka. In the thesis, I proved that water transport capacity is modulated by xylem sap ionic content – increased K+ concentration of xylem sap enhances trees hydraulic conductance, indicating the involvement of potassium ions in the regulation of trees hydraulic efficiency. Both hydraulic and physico-chemical properties of xylem sap in trees follow coordinated circadian patterns driven by environmental conditions. Phloem transport disruption by phloem girdling at branch base affects hydraulic properties and gas exchange but not xylem sap properties in hybrid aspen. Both light availability and quality and xylem sap ionic content significantly affect trees hydraulic properties. They enable plants to optimize their water use and ensure positive water balance under changing environmental conditions.
Water transfer from roots to leaves is essential for plants to keep up photosynthesis, grow and survive. Water moves from roots to shoots through water-conducting tissue called xylem. The water transport capacity of the xylem is characterized by hydraulic conductance. The water inside plants always contains dissolved substances; therefore, it is called a xylem sap. The main driving force for long-distance water transport in the xylem is transpiration, but hydraulic conductance can also be adjusted via changes in xylem sap ionic content on a short time scale. The objectives of the thesis were to investigate circadian patterns of hydraulic conductance and physico-chemical properties of xylem sap; to evaluate the impact of phloem girdling on branch hydraulic conductance and xylem sap properties; to evaluate the impact of light quality and intensity on leaf and shoot hydraulic properties. The study objects were fast-growing broadleaved trees like hybrid aspen and silver birch. The work was carried out in the mixed forest of Järvselja Training and Experimental Forestry District and the Free Air Humidity Manipulation experimental site (FAHM) located at Rõka. In the thesis, I proved that water transport capacity is modulated by xylem sap ionic content – increased K+ concentration of xylem sap enhances trees hydraulic conductance, indicating the involvement of potassium ions in the regulation of trees hydraulic efficiency. Both hydraulic and physico-chemical properties of xylem sap in trees follow coordinated circadian patterns driven by environmental conditions. Phloem transport disruption by phloem girdling at branch base affects hydraulic properties and gas exchange but not xylem sap properties in hybrid aspen. Both light availability and quality and xylem sap ionic content significantly affect trees hydraulic properties. They enable plants to optimize their water use and ensure positive water balance under changing environmental conditions.
Description
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Keywords
broad-leaved trees, water exchange, wood, potassium ions, light intensity, ecophysiology