Urbanization, the migration of populations from rural to urban areas, has been causing great stress on natural environments, leading to air pollution and nitrogen (N) deposition, negatively affecting forest health. Although there is evidence that urbanization has changed forest N cycling, little is known about whether urbanization also changes the availability of phosphorus (P), which is important for plant growth and forest productivity.

To address this question, Dr. HUANG Juan and others from the Research Group for Ecosystem Management (principal investigator is Dr. MO Jiangming) of South China Botanical Garden of Chinese Academy of Sciences, carried out a survey in the Pearl River Delta region, the world's largest urban area in southern China, using two types of representative forests, the evergreen broadleaf forests (BFs) and pine plantations (PPs).

The results showed that leaf N:P ratios in the two forest types were high (20–50) with a significant increasing pattern along the rural-to-urban gradient, suggesting that P limitation was intensified along urbanization. The negative effects of urbanization on soil microorganisms was also observed on the basis of the decreased abundance in actinomycetes and gram-negative bacteria along the rural-to-urban gradient.

There were divergent key factors for P limitation respond to the urbanization in the two forest types. In BF, broadleaf trees showed a greater response to N deposition from urbanization indicating direct leaf N uptake from N deposition is a key factor. Alternatively, in PP, soil acidification is an important factor accelerating P limitation. Our study revealed that urbanization intensifies plant P limitation in subtropical forests, and the effects vary depending on forest types, which provide empirical information to support the management of forest ecosystems and evaluation of urbanization effects on forest health.

This study was published in Science of the Total Environment titled by “Effects of urbanization on plant phosphorus availability in broadleaf and needleleaf subtropical forests” (https://www.sciencedirect.com/science/article/pii/S0048969719323721?via%3Dihub)

Fig. Response of leaf N:P ratios in broadleaf forest (BF) and pine plantation (PP) to urbanization gradient in South China.