Allocation patterns of nonstructural carbohydrates in response to CO2 elevation and nitrogen deposition in Cunninghamia lanceolata saplings.

Stored nonstructural carbohydrates (NSC) indicate a balance between photosynthetic carbon (C) assimilation and growth investment or loss through respiration and root exudation. They play an important role in plant function and whole-plant level C cycling. CO₂ elevation and nitrogen (N) deposition, which are two major environmental issues worldwide, affect plant photosynthetic C assimilation and C release in forest ecosystems. However, information regarding the effect of CO₂ elevation and N deposition on NSC storage in different organs remains limited, especially regarding the trade-off between growth and NSC reserves. Therefore, here we analyzed the variations in the NSC storage in different organs of Chinese fir (Cunninghamia lanceolata) under CO₂ elevation and N addition and found that NSC concentrations and contents in all organs of Chinese fir saplings increased remarkably under CO₂ elevation. However, N addition induced differential accumulation of NSC among various organs. Specifically, N addition decreased the NSC concentrations of needles, branches, stems, and fine roots, but increased the NSC contents of branches and coarse roots. The increase in the NSC contents of roots was more pronounced than that in the NSC content of aboveground organs under CO₂ elevation. The role of N addition in the increase in the structural biomass of aboveground organs was greater than that in the increase in the structural biomass of roots. This result indicated that a different trade-off between growth and NSC storage occurred to alleviate resource limitations under CO₂ elevation and N addition and highlights the importance of separating biomass into structural biomass and NSC reserves when investigating the effects of environmental change on biomass allocation. [ABSTRACT FROM AUTHOR]