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Journal of Integrative Agriculture  2026, Vol. 25 Issue (3): 965-976    DOI: 10.1016/j.jia.2024.11.012
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Critical role of outside xylem hydraulic conductance in regulating stomatal conductance and water use efficiency in cotton across different planting densities

Yunrui Chen1*, Dayong Fan2*, Ziliang Li1, Yujie Zhang1, Yang He1, Minzhi Chen1, Wangfeng Zhang1, Yali Zhang1#

1 Key Laboratory of Oasis Eco-agriculture, Xinjiang Production and Construction Corps, Shihezi University, Shihezi 832003, China

2 State Key Laboratory of Efficient Production of Forest Resources, Beijing Forestry University, Beijing 100083, China

 Highlights 
New perspective on the relationship between leaf hydraulic conductance (Kleaf) and stomatal conductance (gs): This study provides a novel perspective by partitioning Kleaf into inside-xylem (Kx) and outside-xylem (Kox), elucidating the regulatory mechanisms of Kleaf on gs.
Optimizing planting density to enhance water use efficiency: The research demonstrates that Kox is significantly positively correlated with gs, enabling cotton to maintain leaf photosynthetic rate (AN) while reducing transpirational water loss, thus improving water use efficiency (WUE) across a gradient of planting densities.
Structural basis and influencing factors of Kox: Kox is significantly influenced by leaf anatomical traits, particularly leaf thickness and the volume fraction of inter-cellular air space; it exhibits a significant negative correlation with WUE as planting density increases, underscoring the importance of leaf hydraulic properties for effective plant water management.
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摘要  
水力理论预测叶片水力导度(Kleaf)与气孔导度(gs)之间存在正相关关系;然而,这一理论并未得到充分的观察支持,其潜在机制仍不清楚。目前,将Kleaf细分为木质部内水力导度(Kx)和木质部外水力导度(Kox)为阐明Kleafgs的调节机制提供了新的视角。最优的种植密度可以通过优化gs来提高水分利用效率(WUE);然而,在这一过程中叶片水力特性的变化及其对gsWUE的调节机制尚不明确。我们研究了KxKoxgs、光合速率(AN)和WUE之间的关系,并调查了在12、18、24、36、48、60、72和84株/平方米的8种种植密度下,影响Kox的结构基础。结果显示,随着种植密度的增加,KleafAN保持一致,而Koxgs显著下降。Kox受叶片厚度和细胞间空气空间体积分数的显著影响。KleafKxANgs没有相关性,但Koxgs表现出显著的正相关。此外,KoxWUE显著负相关。这些发现表明,Kox通过调节gs来减少水分损失,同时维持AN,从而在不同种植密度下提高棉花的WUE




Abstract  

Hydraulic theory predicts a positive coupling between leaf hydraulic conductance (Kleaf) and stomatal conductance (gs); however, this theory has not been fully supported by observations, and underlying mechanisms are poorly understood.  Partitioning Kleaf into inside-xylem (Kx) and outside-xylem (Kox) components offers a refined framework for elucidating the regulation of gs by leaf hydraulics.  While optimal planting density may enhance water use efficiency (WUE) through modulation of gs, corresponding changes in leaf hydraulic properties and their influence on gas exchange remain unclear.  We examined relationships among Kx, Kox, gs, leaf photosynthetic rate (AN), and WUE, and analyzed the structural determinants of Kox in cotton grown under eight planting densities: 12, 18, 24, 36, 48, 60, 72, and 84 plants m–2.  Results showed that as planting density increased, Kleaf and AN remained stable, whereas Kox and gs declined significantly.   Leaf thickness and the volume fraction of inter-cellular air space were key structural factors influencing Kox.  Neither Kleaf nor Kx correlated with AN or gs; however, Kox exhibited a significant positive correlation with gs.  Furthermore, Kox was negatively correlated with WUE.  These findings indicate that Kox modulates gs to minimize water loss without compromising AN, thereby enhancing WUE in cotton across varying planting densities.

Keywords:  cotton       leaf hydraulic conductance        water use efficiency        planting density        mesophyll structure        stomatal conductance  
Received: 28 May 2024   Accepted: 24 September 2024 Online: 12 November 2024  
Fund: 
This research was financially supported by the Tianshan Talent Development Program, China for Yali Zhang, the Natural Science Foundation of Xinjiang Production and Construction Corps, China (2024DA002), the Earmarked Fund for XJARS-Cotton, China (XJARS-03).
About author:  #Correspondence Yali Zhang, E-mail: zhangyali_cn@foxmail.com, zhangyali_shzu@163.com * These authors contributed equally to this study.

Cite this article: 

Yunrui Chen, Dayong Fan, Ziliang Li, Yujie Zhang, Yang He, Minzhi Chen, Wangfeng Zhang, Yali Zhang. 2026. Critical role of outside xylem hydraulic conductance in regulating stomatal conductance and water use efficiency in cotton across different planting densities. Journal of Integrative Agriculture, 25(3): 965-976.

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