加拿大一枝黄花入侵对杨树人工林土壤呼吸的影响

【目的】杨树是我国重要的人工林栽培树种,近年大量的加拿大一枝黄花(Solidago canadensis L.)入侵杨树人工林生态系统,研究加拿大一枝黄花对杨树人工林土壤呼吸的影响,有助于进一步认识陆地人工林生态系统的地下碳(C)循环对植物入侵的响应及其机制。【方法】2018年11月以江苏省东台林场内加拿大一枝黄花入侵和未入侵的8年生相同立地条件下杨树人工林群落为研究对象并建立固定样地,采用长期野外试验监测的研究方法对土壤呼吸以及土壤温度和湿度进行监测,同时钻取土芯测定样地土壤理化性质,对比加拿大一枝黄花入侵与未入侵条件下杨树人工林群落土壤呼吸的变化规律,探讨加拿大一枝黄花入侵杨树人工林后各个非生物因子变化对土壤呼吸的影响。【结果】加拿大一枝黄花的入侵显著增加了杨树人工林的土壤呼吸(P <0.001),且主导这种变化的非生物因子是入侵导致的土壤湿度的变化。加拿大一枝黄花入侵会通过改变土壤理化性质来影响土壤呼吸,显著增加杨树人工林的土壤湿度(P <0.001),同时显著增加土壤总氮含量(P <0.05),降低土壤碳氮比(P <0.05),但对于土壤总碳含量的增加并不显著(P >0.05),对土壤温度和pH的影响也不显著(P >0.05)。【结论】加拿大一枝黄花的入侵增加了杨树人工林土壤系统二氧化碳的排放量,增加了土壤系统的C损失,改变了杨树人工林土壤的C交换过程。

Effects of Solidago canadensis L. invasion on soil respiration in poplar plantations (Populus deltoides)

【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.