When and what fraction of water input are plant able to seize: an alternative perspective on tracing root water uptake using water stable isotopes

Abstract:

One tool for investigating the water uptake by roots in Earth’s critical zone has been stable isotope analysis. Apart from a certain number of studies aimed to identify the types of water source (such stream water, fog water and groundwater versus soil water) used by plants, more studies focused on pin-pointing the location of plant water uptake at the moment of sampling. Despite the importance of location-related knowledge about plant water uptake, to get promising result usually involves challenges that associated with known sources of isotopic variability in ecohydrological compartments. Firstly, challenges on sampling the right water pool due to the nature of heterogeneity in the field. Secondly, challenges on generalizing and upscaling the often achieved site-specific and/or snap-shot results about plant individuals. Thirdly, challenges on dealing with the known processes of fractionation that mainly occur during plant water uptake and soil water extraction.

Motivated by our research experience in rocky karst regions (where plant-available water is stored in high heterogeneous soil-rock complex), we highlight an alternative perspective that distinguishing when and what fraction of water input are plant able to seize, by reviewing both classic and new example studies that characterized the utilization of precipitation as a function of its amount and timing. We also discuss in what aspects the related results from the highlighted perspective can release limitations of traditional utilization of stable isotope data, as well as the associated obstacles.