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Key message: This work provides insight into the functional changes in above- and belowground tree tissues/organs after thinning and understory removal.Abstract: Non-structural carbon (NSC), which reflects the relationship between the carbon source and carbon sink, plays a key role in the carbon cycle in forest ecosystems. Although thinning and understory removal are two common measures in plantation management, limited information is available on the effects of thinning and understory removal on the NSC of plants, particularly of different tissues/organs. This study investigated the response of the NSC (soluble sugars and starch) concentration of different tissues/organs (current- to 4-year-old needles, inner-bark, xylem, and coarse and fine roots) toward thinning and understory removal in a plantation of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook), which is an evergreen coniferous species. Results showed that thinning significantly increased the NSC concentration of the needles. The NSC concentrations of the inner-bark and xylem did not respond to thinning. In contrast to the aboveground tissues/organs, the NSC concentration of the coarse root was significantly reduced by thinning. Thus, the thinning-induced NSC response of the above- and belowground tissues/organs varied, indicating that the NSC was remobilized after thinning. However, understory removal had a very reduced effect on the NSC concentration of all the mentioned above- and belowground tissues/organs. Our findings suggest the need to simultaneously consider above- and belowground tissues/organs in future forest management studies. [ABSTRACT FROM AUTHOR]

Background and aims: The canopies in evergreen coniferous plantations are often composed of various-aged needles. Plantation management, such as thinning, produced abundant harvest residue, including needles with different needle ages. However, little attention was paid to the effect of needle age on decomposition, although the needle chemical properties varied substantially with leaf ages.Methods: A field experiment was conducted for 3 years to investigate the decomposition of harvest residue needles at different needle ages, and determine the main controlling factors in different stages of decomposition in a Chinese fir plantation.Results: We found that the initial decomposition rate varied 5-fold among different needle ages in a Chinese fir plantation. Litter quality controlled the overall litter decomposition rate, especially the initial decomposition rate. Needle nitrogen content was positively correlated to decomposition rate during the early stage of decomposition. However, it was negatively correlated to decomposition rate during the later stage of decomposition. The contents of needle tannins increased the asymptotic mass remaining (A, proportion of mass remaining at which decomposition approaches zero, i.e., the fraction of slowly decomposing litter). We also found that the initial litter decomposition rates in soil fauna presence were significantly higher than those in soil fauna absence across different needle ages. Moreover, the effect of soil fauna on initial litter decomposition is independent of needle quality.Conclusions: Our results suggest that needle age and plant secondary metabolites should be considered to understand the response of litter decomposition and nutrient cycling to management practices, such as thinning, in conifer plantations. [ABSTRACT FROM AUTHOR]

Masson pine (Pinus massoniana Lamb.), a native species widely distributed in temperate forests in central China, and Loblolly pine (Pinus taeda L.), an exotic tree species introduced to China from southeastern United States, are dominant evergreen conifers that play a pivotal role in maintaining forest structure and functions for the region. We examined the effects of freezing on these species with chlorophyll fluorescence and electrolyte leakage using both field- and laboratory-based experiments in September 2009 and January 2010, respectively. We found that freezing could cause a greater impact on the Loblolly pine than the Masson pine. Although the two species showed similar values of F v /F m and electrolyte leakage before freezing, the Masson pine needles showed lower F v /F m and higher electrolyte leakage ratios than those of the Loblolly pine when treated in low temperatures (−15 to 0°C). We also found that cold-acclimation was crucial for both species to adapt to low temperatures with the F v /F m ratio decreased approximately by 80% in the first freezing hour for the non-acclimated needles of both species while the cold-acclimated needles showed little changes in the F v /F m ratio. This finding is also supported by our measurements of electrolyte leakage. These results suggest that the Loblolly pine could be more susceptible to freezing damages than the Masson pine in central China. [ABSTRACT FROM AUTHOR]