Abstract:

【Objective】 Poplar plantations are one of the most important planted forests in China. They play a key role in regional C cycling. However, Solidago canadensis L. has increasingly invaded poplar plantations recently in Jiangsu Province, which may substantially affect the C cycling of these plantations. In this study, we investigated the effects of invasion by S. canadensis on soil respiration in poplar plantations (Populus deltoides ‘I-35’) and explored the factors regulating soil respiration across the invaded and non-invaded poplar communities. 【Method】 Our experimental site is located at the Dongtai Forest Farm in Yancheng, Jiangsu Province, eastern China (120°49' E, 32°52' N). The farm has a climate classified as Cfa (Humid subtropical climate). The mean annual temperature is 13.7 ℃ and the mean annual precipitation is 1 051 mm. The soil of the forest farm comprised desalted sandy meadow soil with a pH 8. Our invasion experiment was established in November 2018. We chose 8-year-old pure poplar plantations with uniform site conditions and management measures either with or without S. canadensis invasion as our plots. We used a randomized design with four replicates. Each replicate subplot was 25 m × 30 m with a 50 m buffer zone between any two adjacent subplots. Soil temperature and moisture were measured once a month in March and April 2019. Soil cores, 4 cm in diameter, were collected in March 2019 in each subplot. Soil samples were transferred to our lab, air-dried, ground, and then, total C and N (TC and TN) content was measured by combustion using an elemental analyzer. Soil respiration was measured by using LI-COR 6400. An analysis of variance was applied to examine the effects of invasion on the measured variables and a regression analysis was used to explore the factors regulating soil respiration. 【Result】 The invasion of S. canadensis greatly altered the microclimate and soil properties. We found the invasion significantly increased soil moisture (P <0.001) and TN content (P <0.05). Furthermore, the invasion decreased soil m(C)/m(N) (C/N ratio, P<0.05). Effects of invasion on TC content, soil temperature, and pH were not significant (all P >0.05). Importantly, the invasion of S. canadensis significantly increased soil respiration in poplar plantations (P<0.001). The increases in soil respiration under invasion were associated with changes in microclimate and soil properties as indicated by correlations of soil respiration with microclimate and soil properties. The step-wise regression analysis showed that soil moisture was the dominant factor in regulating variations in soil respiration. 【Conclusion】 In general, the invasion of S. canadensis increases the carbon dioxide emissions of soil systems of poplar plantations leading to increasing loss of C in the soil system. Moreover, the invasion of S. canadensis changes the C exchange process of poplar plantations. Our results contribute to the further understanding of belowground C cycling in response to plant invasions and the associated mechanisms. Furthermore, our results suggest that C cycling models of terrestrial ecosystem should consider the impacts of plant invasion to improve predictions of future climate change.

Key words: Solidago canadensis L., plant invasion, poplar plantation, soil respiration