# Quantifying Cunninghamia lanceolata Foliar Water Uptake and Reverse Transport Provides a New Approach to Improving Drought Tolerance

## TL;DR

This study shows how Cunninghamia lanceolata can absorb fog water through its leaves to reduce drought stress and identifies thresholds for reverse water transport.

## Contribution

The study quantifies leaf water uptake and reverse transport thresholds in Cunninghamia lanceolata, offering a new approach to improving drought tolerance.

## Key findings

- Cunninghamia lanceolata seedlings can absorb fog water when soil water content is below 60% of field capacity.
- Reverse water transport occurs from leaves to stem and soil when soil water is between 30-60% of field capacity.
- Leaf water uptake improves leaf water potential and content, with utilization rates up to 16.26% in the xylem.

## Abstract

Foliar water uptake (FWU), an important source of supplemental water for plants, provides a novel pathway for alleviating drought stress. However, quantitative analysis of reverse water transport after water uptake in plant leaves has been insufficient, which has become a bottleneck in the study of adaptive plant survival under drought stress. This study investigates
Cunninghamia lanceolata
(
C. lanceolata
) using pot experiments with controlled watering, simulated fog environments, and stable isotope techniques to quantitatively explore the conditions that facilitate water absorption in
C. lanceolata
seedlings under drought stress, the thresholds for reverse water movement in various organs, and whether FWU enhances drought resistance. The results indicated that FWU occurred when the soil water content (SWC) fell below 60% of field capacity for 2 h in a foggy water environment. After 12 h of fog water treatment, the leaf water potential (LWP) and leaf water content (LWC) of
C. lanceolata
seedlings significantly improved under drought stress. When SWC exceeded 60% of field capacity, retrograde transport did not occur. When SWC ranged between 45% and 60% of field capacity, leaf water uptake retrograde transport to the stem, resulting in an increase in δ

D
value by 20.54‰ ± 5.16‰. When SWC dropped between 30% and 45% of field capacity, retrograde transport to the rhizosphere soil occurred, with δ

D
values increasing by 30.94‰ ± 1.4‰. Water absorbed by leaves can move along the leaf‐stem‐root water potential gradient into the xylem and surrounding soil, with maximum utilization rates of 16.26%, 11.13%, and 1.66%, respectively, thereby improving the plant's water status. From the above, it can be seen that
C. lanceolata
can effectively alleviate drought stress through leaf water uptake, and the reverse water transport threshold can be used as a research basis to provide new ideas for plants to cope with drought stress.

These findings demonstrate that
C. lanceolata
can effectively alleviate drought stress by absorbing fog water through their leaves. Additionally, the identified water threshold for reverse water transport provides a foundation for future research, offering new insights into plant strategies for coping with drought stress.