Effects of soil moisture, needle age and leaf morphology on carbon and oxygen uptake, incorporation and allocation: a dual labeling approach with 13CO2 and H218O in foliage of a coniferous forest. (2nd September 2020)

• Record Type: Journal Article
• Authors: Wang, Ao; Siegwolf, Rolf T W; Joseph, Jobin; Thomas, Frank M; Werner, Willy; Gessler, Arthur; Rigling, Andreas; Schaub, Marcus; Saurer, Matthias; Li, Mai-He; Lehmann, Marco M
• Editors: Cernusak, Lucas
• Is Part Of: Tree physiology. Volume 41:Number 1(2021)
• Page Start: 50
• Page End: 62
• Publication Date: 2020-09-02
• Subjects: assimilates -- carbon isotopes -- drought -- non-structural carbohydrates (NSC) -- oxygen isotopes -- sugars; Trees -- Physiology -- Periodicals; 582.16
• DOI: 10.1093/treephys/tpaa114
• Languages: English
• ISSNs: 0829-318X

Abstract

Abstract: The carbon and oxygen isotopic composition of water and assimilates in plants reveals valuable information on plant responses to climatic conditions. Yet, the carbon and oxygen uptake, incorporation and allocation processes determining isotopic compositions are not fully understood. We carried out a dual-isotope labeling experiment at high humidity with 18 O-enriched water (H2 18 O) and 13 C-enriched CO2 ( 13 CO2 ) with attached Scots pine ( Pinus sylvestris L.) branches and detached twigs of hemiparasitic mistletoes ( Viscum album ssp. austriacum ) in a naturally dry coniferous forest, where also a long-term irrigation takes place. After 4 h of label exposure, we sampled previous- and recent-year leaves, twig phloem and twig xylem over 192 h for the analysis of isotope ratios in water and assimilates. For both species, the uptake into leaf water and the incorporation of the 18 O-label into leaf assimilates was not influenced by soil moisture, while the 13 C-label incorporation into assimilates was significantly higher under irrigation compared with control dry conditions. Species-specific differences in leaf morphology or needle age did not affect 18 O-label uptake into leaf water, but the incorporation of both tracers into assimilates was two times lower in mistletoe than in pine. The 18 O-label allocation in water from pine needles to twig tissues was two times higher for phloem than for xylem under both soil moisture conditions. In contrast, the allocation of both tracers in pine assimilates were similar and not affected by soil moisture, twig tissue or needle age. Soil moisture effects on 13 C-label but not on 18 O-label incorporation into assimilates can be explained by the stomatal responses at high humidity, non-stomatal pathways for water and isotope exchange reactions. Our results suggest that non-photosynthetic 18 O-incorporation processes may have masked prevalent photosynthetic processes. Thus, isotopic variation in leaf water could also be imprinted on assimilates when photosynthetic assimilation rates are low.