Tree rings showing nitrogen impact.

Decoding Tree Rings: Can They Unlock Secrets of Nitrogen Pollution?

Jordan Keane in Climate & Environment December 2025 • 4 min read.

"New research explores how long-term nitrogen deposition impacts tree growth, offering insights into forest health and productivity in a changing world."

The rise in nitrogen (N) deposition, caused by burning fossil fuels and fertilizer use, is a major environmental change. While it's known to boost tree growth, the long-term effects on tree health remain unclear. Factors like climate change and rising CO2 levels further complicate the picture.

Just as analyzing leaf traits helps us understand plant function, studying wood traits is gaining importance. Nitrogen levels affect photosynthesis and growth rates in trees, but a lack of comprehensive models linking nitrogen and wood characteristics has limited long-term research.

Recent research published in Tree Physiology aims to bridge this gap. Borghetti et al. (2016) investigated how environmental factors, including nitrogen deposition, influence wood traits like tree-ring width and xylem anatomy (conduit area and density).

Nitrogen's Tricky Impact: More Isn't Always Better

The study by Borghetti et al. (2016) used a meta-analysis to explore the relationship between nitrogen deposition and xylem traits across various species and environmental conditions. Surprisingly, they found no consistent long-term trends in tree-ring width that would suggest a growth boost from increased CO2.

Furthermore, the researchers didn't find a negative correlation between conduit size and density, challenging the idea of a trade-off between these two traits. However, they did observe that increased nitrogen deposition might lead to improved hydraulic efficiency in xylem due to increased conduit density. This aligns with previous findings from the same group, which linked higher cumulative nitrogen deposition to increased intrinsic water-use efficiency (iWUE).

The study suggests that nitrogen deposition may improve hydraulic efficiency in trees.
It highlights the complexity of the relationship between nitrogen and tree growth.
It emphasizes the need for long-term data and quantitative analysis of wood anatomy.

While Borghetti et al.'s work is a significant step, it's important to consider several factors to fully understand the link between wood traits and nitrogen dynamics. One key question is whether we can apply existing tree nutrition frameworks to understand the effects of nitrogen deposition on hydraulic architecture. Nitrogen deposition involves complex environmental and biological processes, such as soil acidification, nutrient imbalances, and changes in plant respiration and carbon allocation.

Unlocking the Past: What Tree Rings Can Tell Us

Analyzing tree rings and xylem anatomical traits has been crucial in understanding the impact of temperature and drought on tree growth. By studying carbon isotopes in tree rings, scientists can also infer long-term changes in iWUE.

However, determining the effects of increased nitrogen deposition on forest productivity presents unique challenges. Nitrogen concentrations in woody tissues are typically low and vary significantly between species and tissues. Retrospective analysis of stable nitrogen isotopes (15N/14N, δ15N) in tree-ring series offers a promising avenue for studying the long-term effects of nitrogen availability.

Borghetti et al. (2016) have pioneered the use of wood-anatomical traits to understand the effects of long-term nitrogen deposition on wood function, tree growth, and forest productivity. Future studies should address existing caveats (tree size and ontogeny, plasticity, measuring and laboratory protocols) and incorporate other proxies of tree functioning, such as δ15N in tree rings. By distilling information from wood, we can gain a better understanding of tree growth and functioning, enabling us to manage forests more effectively in the face of environmental change.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1093/treephys/tpw111, Alternate LINK

Title: Bridging Long-Term Wood Functioning And Nitrogen Deposition To Better Understand Changes In Tree Growth And Forest Productivity

Subject: Plant Science

Journal: Tree Physiology

Publisher: Oxford University Press (OUP)

Authors: J. Julio Camarero, Marco Carrer, Danielle Way

Published: 2017-01-01

Everything You Need To Know

What specific aspects of tree growth were investigated in the research related to nitrogen deposition?

The study by Borghetti et al. (2016) focused on the relationship between nitrogen deposition and tree growth. This investigation used a meta-analysis to explore how nitrogen deposition influences specific wood traits, such as tree-ring width and xylem anatomy, including conduit area and density, across various species and environmental conditions. The research aimed to determine the long-term effects of increased nitrogen levels from pollution, which is crucial for understanding and managing environmental impacts on forests.

Why is nitrogen deposition considered significant in this research context?

Nitrogen deposition is important because it's a major environmental change resulting from the burning of fossil fuels and fertilizer use. While increased nitrogen can boost tree growth initially, the long-term effects on tree health are complex and not fully understood. This study explored this complex relationship, highlighting how nitrogen deposition may affect traits like hydraulic efficiency in the xylem, which is critical for water transport within the tree. Understanding these impacts is essential for managing forest health in a world affected by climate change and rising CO2 levels.

How do scientists use tree rings to understand the effects of environmental changes?

Tree rings provide a historical record of environmental conditions. By studying tree-ring width and xylem anatomical traits, scientists can understand how factors like nitrogen deposition, temperature, and drought influence tree growth. Additionally, analyzing carbon isotopes in tree rings allows for the inference of long-term changes in intrinsic water-use efficiency (iWUE). These analyses help scientists to bridge the gap between the known impacts of nitrogen and wood characteristics, providing more in depth understanding of the nitrogen's impact on forest health.

What are the broader implications of this research on understanding nitrogen and its effects?

The implications of the research include a better understanding of how nitrogen deposition influences wood traits and tree growth. For instance, increased nitrogen deposition may improve hydraulic efficiency in xylem. However, the long-term effects are complex, and the study challenges some previous assumptions. It suggests the need for comprehensive models that link nitrogen and wood characteristics. The research highlights the importance of long-term data and quantitative analysis of wood anatomy to better manage the impact of environmental changes on forests.

What is the nature of the relationship between nitrogen deposition and tree growth, according to the research findings?

The relationship between nitrogen deposition and tree growth is complex. Research has shown that while nitrogen can initially boost growth, the long-term effects and trade-offs are not fully understood. The study by Borghetti et al. (2016) found no consistent long-term trends in tree-ring width that would suggest a growth boost from increased CO2. They did find a potential improvement in hydraulic efficiency in xylem due to increased conduit density. Other factors, such as climate change and rising CO2 levels, further complicate the understanding of nitrogen's impact.