Jinsheng Xie

Accelerated soil carbon turnover under tree plantations limits soil carbon storage.

The replacement of native forests by tree plantations is increasingly common globally, especially in tropical and subtropical areas. Improving our understanding of the long-term effects of this replacement on soil organic carbon (SOC) remains paramount for effectively managing ecosystems to mitigate anthropogenic carbon emissions. Meta-analyses imply that native forest replacement usually reduces SOC stocks and may switch the forest from a net sink to a net source of atmospheric carbon. Using a long-term chronosequence during which areas of subtropical native forest were replaced by Chinese fir, we show by direct measurement that plantations have significantly accelerated SOC turnover compared with native forest, an effect that has persisted for almost a century. The immediate stimulation of SOC decomposition was caused by warmer soil before the closure of the plantation’s canopy. Long-term reductions in SOC mean residence times were coupled to litter inputs. Faster SOC decomposition was associated with lower soil microbial carbon use efficiency, which was due to smaller litter inputs and reduced nutrient availabilities. Our results indicate a previously unelucidated control on long-term SOC dynamics in native forests and demonstrate a potential constraint on climate mitigation when such forests are replaced by plantations.

Ecophysiological process regulates the growth of Cunninghamia lanceolata to suit short-term warming and nitrogen addition in the sub-tropical regions

Key messageUnder warming condition, growth of Cunninghamia lanceolata is not accompanied by increased photosynthetic performance. The combination of warming and N addition seemed to adversely influence leaf carbon balance as Rd/Pnmax and endogenous hormones were strongly affected.AbstractUncertainties about the response of plant eco-physiological mechanisms to elevated temperature and nitrogen (N) deposition make it difficult to predict the performance of plants under future climatic conditions in the sub-tropical regions. We measured photosynthetic parameters, the contents of osmoregulatory substances, oxidant substances, protective enzymes, and endogenous hormones in Cunninghamia lanceolata under conditions of soil warming and N addition. We used six treatments: (1) unwarmed and unfertilized (CT), (2) unwarmed and high N (HN), (3) unwarmed and low N (LN), (4) warmed and unfertilized (W), (5) warmed and high N (WHN), and (6) warmed and low N (WLN). We found that the Rd/Pnmax was the lowest in the W treatment, but the height was almost with the same as that of the CT. Plants under W showed plasticity of protective capacity by increasing peroxidase contents. N addition enhanced photosynthesis and promoted growth. The WLN treatments increased Rd/Pnmax and decreased indoleacetic acid, gibberellin, and cytokinin contents, which might caused reduction in the absorption of nutrients and growth of the plants in the short-term. There were no significant differences in the content of osmoregulatory substances among the different treatments. We conclude different mechanisms may exist between W and N addition treatments that probably depend on adjustments through the physiological and biophysical processes. This study provides a new reference for forest management in view of the future climate changes.