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Xylem Formation Responded To N Deposition In A Warm-temperate Forest


The influences of global climatic changes on tree growth in forest ecosystem are very important for deeply understanding the forest ecosystem structure, function and succession. Especially, in recent decades, anthropogenic induced N deposition has had profound impacts on tree growth in N-limited forests.

To investigate the impacts of N deposition on tree growth, Professor Huang of Forest Ecology and Modeling Lab at South China Botanical Garden of Chinese Academy of Sciences instructed his PhD student Shaokang Zhang to use micro-coring method to monitor the cambium activity and xylem formation (enlarging, wall thickening and mature xylem) dynamics of Chinese red pine under the understory N treatment (25kg ha-1 yr-1). The results showed that the short-term (3 years) low-concentration N addition had no significant influence on the cambium activity and the dynamics of xylem formation. This study may indicate that in the commonly believed N-limited forest ecosystems, low-concentration N deposition may not significantly change the secondary growth of tree. However, in the longer term, further studies are still needed to investigate if the xylem formation would be affected (positively or negatively) by the N deposition.

This study entitled with “Intra-annual dynamics of xylem growth in Pinus massoniana submitted to an experimental nitrogen addition in Central China” was recently published on Tree Physiology (Impact factor in 2017: 3.653). The research was founded by the 100 Talents Program of the Chinese Academy of Sciences, National Natural Science Foundation of China and the CAS President's International Fellowship.



Figure 0. Microcore section of Pinus massoniana 400) containing cambial cells, enlarging, wall thickening, and mature xylem cells.

Figure 1. Number of cambial and differentiating xylem cells of Chinese red pine in 2014 and 2015 in Central China. Bars represent the standard deviations among trees.

Figure 2. Sigmoid functions representing xylem cell production of Chinese red pine in 2014 and 2015 in Central China. The enclosed vertical bars represent average and 5% and 95% confidence intervals of the bootstrapped t-statistics calculated by 10,000 replications. t-Test is considered significant when both confidence intervals are either higher or lower than zero. Since we did not observe the whole growing season in 2014 and 2015, the sigmoid function illustrated in the figure is based on the observed data.

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