# Biochemical metabolic enhancement acting as a dominant driver in intra-leaf CO2 diffusional response to soil nitrogen supplying in Soybean

## TL;DR

The study finds that biochemical metabolism, not leaf structure, is the main driver of increased CO2 diffusion in soybean leaves when soil nitrogen increases.

## Contribution

The paper identifies biochemical metabolism as the dominant mechanism behind CO2 diffusion changes in soybean under nitrogen supply.

## Key findings

- Soil nitrogen increases mesophyll conductance (gm) and net photosynthetic rate (An) in soybean.
- Biochemical metabolism, not anatomical changes, is the main driver of CO2 diffusion improvement with nitrogen.
- Water use efficiency is linked to aquaporin-mediated water relations.

## Abstract

Biochemical metabolism and anatomical structure within leaf tissues have been proposed as the two principal mechanisms underpinning the rapid responsiveness of mesophyll conductance (gm) to environmental perturbations; nevertheless, empirical evidence distinguishing which of these factors acts as the dominant driver remains scarce. The response of intra-leaf CO2 diffusion conductance including gm and stomatal conductance (gsc) to soil nitrogen (N) change in soybean was systematically quantified in leaf biochemical and structural characteristics. Our data revealed that (i) soil N made a positive effect on intra-leaf CO2 diffusion and carbon assimilation that gm and An (net photosynthetic rate) exhibited a significant positive response to increasing N supplying from 7.5 to 15.0 g urea m-2 while gsc showed no significant N-dependence. (ii) The enhanced intra-leaf CO2 diffusion capacity induced by N application was principally attributable to the increase in gm.(iii) The enhancement of biochemical metabolism rather than the modifications in the leaf anatomical structure constituted the predominant mechanism by which N supplementation facilitated CO2 diffusion and carbon assimilation in soybean. (iv)Furthermore, the improvement in water use efficiency (WUE) appeared to be more closely linked to aquaporin-mediated water relations, as supported by subsequent correlation analyses.These findings will advance our understanding of the key drivers that shape gm responsiveness to abrupt environmental variations.