Effects Of Soil Warming On Fine Root Turnover And Its Mechanism In A Chinese Fir (Cunninghamia Lanceolata) Plantation

Fine root turnover is an important way of soil carbon return.Climate warming will affect the carbon balance of forest ecosystem by affecting fine root turnover.In order to reveal the effect and mechanism of global warming on fine root turnover,and to improve the prediction of carbon sequestration and carbon source sink function of plantation.A study on the Chinese fir plantation(Cunninghamia lanceolata),the largest single tree species in the world,was carried out in the field in-suit soil warming experimental platform in Sanming Forest Ecosystem and Global Change National Observation and Research Station of Fujian Province.The platform was designed with randomized block with two treatments: warming(+4?)and control,with 5 repeats in each treatment.The fine root turnover(fine root production,fine root mortality and fine root turnover rate)was continuously observed by minirhizotron method from January 2016 to December2019.The results showed that soil warming had a significant effect on the time distribution of fine root production.Soil warming did not change the annual average fine root production.But the warming significantly inhibited the fine root production in spring2016,but promoted fine root production obviously in winter from 2016 to 2018 and spring from 2017 to 2018,and significantly promoted fine root production in 2018.Soil warming and soil depth,soil warming and diameter class have a positive cumulative effect on the fine root production.Soil warming led to the deeper weighted depth distribution of fine root production in summer of annual average,and decreased its stability and fluctuation.Soil warming led to the thinner weighted diameter distribution of fine root production in summer average fine root production from June to August from2016 to 2019,and the diameter distribution of fine root production gradually decreased in the later stage of soil warming(from 2018 to 2019).Soil warming alleviated the temperature limitation of fine root growth and prolonged the suitable temperature for fine root growth in winter,and advanced the suitable temperature in spring that prolonged the fine root growth season.Soil warming also enhanced of carbon input to the underground which increased the fine root production.Soil warming significantly advanced the timing of fine root initiation,indicated that the fine root growth season was prolonged.Soil warming also made the time distribution of fine root production more uneven in 2018.As a result of soil warming,the inter-annual stability of fine root was lower than control,the inter-annual stability of fine root production was also decreased.Soil warming had a significant effect on the time distribution of fine root mortality.Soil warming did not significantly change the annual average fine root mortality,but significantly promoted fine root mortality in winter of 2017,spring and winter of 2018,winter of 2019.Soil warming also promoted fine root production obviously in 2018.As a result of soil warming,fine root mortality tends to be distributed in shallow soil in spring and winter,while it tends to be distributed in deep soil in summer and autumn.And soil warming also caused the average annual fine root mortality to be distributed in deeper soil.As the whole,soil warming reduced the stability of soil weighted depth distribution of fine root mortality at the different time scales.In 2016,soil warming significantly caused the weighted diameter distribution of fine root mortality larger than that in the control,while the weighted diameter distribution of fine root mortality in 2018 was significantly thinner than that in the control.The weighted diameter distribution of fine root mortality gradually decreased in the later stage of soil warming(from 2018 to 2019).In this study,soil warming caused fine root to suffer high temperature and water stress,and increased the risk of fine root embolization,which resulting the increase of fine root mortality.In addition,fine root respiration did not acclimate to soil warming.And soil warming decreased the fine root concentration of non-structural carbon in winter,indicated the metabolic imbalance in fine root,which further accelerated the death of fine root.Soil warming did not change the fine root standing crop,but significantly Increased the annual fine root turnover rate.It was found that fine root respiration did not acclimate to soil warming.However,soil warming decreased the fine root concentration of non-structural carbon in winter.The balance between non-structural carbon concentration and respiration rate in fine root was broken.As a result,soil warming accelerated the fine root turnover rate.In this study,we examined the effect of soil warming on fine root turnover of Chinese fir plantation in humid subtropical.And we revealed the key mechanism of fine root turnover under soil warming,which has an important theoretical significance for predicting the adaptation mechanism of plants to climate change.