Individual size but not additional nitrogen regulates tree carbon sequestration in a subtropical forest

Abstract

Recent studies have indicated that tree carbon accumulation in subtropical forests has been negatively affected by global change phenomena such as warming and drought. However, the long-term effect of nitrogen addition on plant carbon storage remains poorly understood in these regions. In this study, we conducted a 10-year field experiment examining the effect of experimental N addition on plant growth and carbon storage in a subtropical Chinese fir forest. The N levels were 0 (control), 60, 120, and 240 kg ha−1 yr−1, and the N effects on tree carbon were divided into stand and individual levels. The results indicated that tree carbon storage at the stand scale was not affected by long-term N addition in the subtropical forest. By contrast, significant impacts of different tree size classes on carbon sequestration were found under different N treatments, which indicated that the amount of plant carbon sequestration was significantly enhanced with tree size class. Our findings highlight the importance of community structure and growth characteristics in Chinese fir forests, in which individual size but not additional N regulates tree carbon sequestration in this subtropical forest.

A threefold difference in plant growth response to nitrogen addition between the laboratory and field experiments

“…However, negative even no significant relationships of plant growth with the changes in N dose or treatment duration have also been reported (Schulte‐Uebbing and De Vries , Wu et al. ). Moreover, the dependence of the plant response to N addition upon the N‐addition frequency could be negative (Melgar et al.…”

“…As a consequence, a reducing rate of the leaf photosynthesis and an increasing carbon consumption with age are approved even under N fertilization (Ryan and Yoder , Schulte‐Uebbing and De Vries , Wu et al. ). Comparing the age of the woody plants in the lab and field experiments, the mean age was much greater in the field (17.3 yr) than lab (0.8 yr) conditions (Fig.…”

“…Therefore, younger woody plants in the lab and the reduced plant responses to N addition with age are accounted for the greater differences for woody plants between the lab and field conditions (Vadeboncoeur , Schulte‐Uebbing and De Vries , Wu et al. ). These results indicate that, including the abiotic conditions in the lab and field, biotic factors, for example, growth forms and age, should be additionally considered when translating the lab results to the field.…”

“…Numerous studies have demonstrated that the availability of both water and nutrient transportation is decreasing with woody age or size because of the increased hydraulic resistance (Bond 2000, Hubbard et al 2001. As a consequence, a reducing rate of the leaf photosynthesis and an increasing carbon consumption with age are approved even under N fertilization (Ryan and Yoder 1997, Schulte-Uebbing and De Vries 2017, Wu et al 2017. Comparing the age of the woody plants in the lab and field experiments, the mean age was much greater in the field (17.3 yr) than lab (0.8 yr) conditions (Fig.…”

“…Therefore, nonlinear relationships of plant growth with N dose or duration have been suggested by numerous studies (Magill et al 2000(Magill et al , H€ ogberg et al 2006). However, negative even no significant relationships of plant growth with the changes in N dose or treatment duration have also been reported (Schulte-Uebbing and De Vries 2017, Wu et al 2017). Moreover, the dependence of the plant response to N addition upon the N-addition frequency could be negative (Melgar et al 2010), neutral (Zhang et al 2015), or positive (Silber et al 2003).…”