Isotope signature of maize stem and leaf and investigation of transpiration and water transport

Abstract

Stable isotope signature of plant water contains essential information on water transport pathway and plant transpiration, which has been shown to be a powerful tracer in plant physiological and ecological processes. However, stable isotopes fractionation in processes of plant water transport and the relationship between transpiration rate (E) and effective pathway length (L) and their possible mechanisms are still largely mysterious and confusing. Here, we tested stable isotope signature of maize stem and leaf based on anatomical measurements and modeling, and propose a deuterium deviation in leaf water (Δd) to understand variability leaf water isotope enrichment and transpiration. We found isotopes fractionation occurred in maize stems in arid area. Leaf transpiration rate was strongly affected by Δd. The data revealed L has a negative power relationship with E, with a single power function of L = 284.77E−1.02; and the proportional deviation of leaf 18O enrichment 1 − ΔL/ΔE is negatively correlated with E under low E (E < 2.0 mmol m−2 s−1) and, a positively relationship under high E (E > 2.0 mmol m−2 s−1). Suggesting that a pivotal role of effective path length in driving variations in leaf transpiration rate. The deuterium deviation Δd may have great potential to serve as a new diagnostic tool for understanding pathways of water transport in plant. Care should be taken when examining source-water and estimating roots water uptake using the stable isotope method in arid areas, and further study is needed to be carried out and confirm the conclusions across a range of environmental conditions and species.