Effects Of Soil Warming On Fine Root Production In A Chinese Fir (Cunninghamia Lanceolata) Plantation

Currently,there is large quantity of research on the responses of fine roots to warming,but there are still some controversies.Fine root growth has a direct effect on fine root biomass,and thus affects the plants' abilities to acquire soil resources and resist environmental stresses such as drought.Yet,how root production responds to soil warming is not clearly understood.In the present study,a simulated soil warming experiment was carried out in Sanming Forest Ecosystem and Global Change Research Station,Fujian Province,China,to investigate the effect of soil warming on fine root production in a young Chinese fir(Cunninghamia lanceolata)plantation.Both the soil warming treatment and the control(non-warming)had five replicated 15 ×15 plots.Soil warming was accomplished with buried heating cable technology,and soil temperature was elevated to 4? above ambient.We measured monthly change in fine root production using minirhizotron method from January 2016 to December 2017.For each plot,we analyzed root length production and the correlations between monthly production of root system and environmental factors,including air temperature,rainfall,soil temperature,soil water content in different layers and Chinese fir seeding height increment.In addition,we also analyzed the effect of soil warming on the seasonal patterns of fine root production and annual variation,diameter distribution and vertical distribution.The results showed that:(1)The interaction of warming and month had a very significant effect on fine root length production.Compared with the control,processing of fine root production in dynamic pattern of soil warming is more unstable,it's even more uneven over time,and have a greater lability in the interannual changes.At the same time,the soil warming will make the time of fine roots production start and peak will earlier,the end time of fine roots production delay and the growth season is prolonged.In March and April 2016,soil warming inhibited fine root production while soil warming significantly promoted fine root production in December 2016 and January,February 2017,respectively.Soil warming had no significant effect on the total height increment of Chinese fir saplings.However,the seasonal distribution pattern of height growth varies between different treatments.And the peak of height growth is later with the peak of fine root production.Person correlation analysis showed that there was a significant negative correlation between the monthly fine root production of different soil layers and the monthly average atmospheric temperature and soil temperature,which was positively correlated with the soil moisture content.And with the increase of soil depth,the correlation coefficient of soil moisture content,soil temperature and the monthly fine root production is increased.Covariance analysis shows that the soil moisture content,soil temperature and the monthly height increment of the trees had a significant effect on the seedling yield.(2)The influence of soil warming on fine root production in different seasons varied.Soil warming reduced fine root production in spring 2016,but in spring 2017 and winter of 2016 and 2017,soil warming promoted fine root production obviously.Soil warming has different effects on fine root production in different years.Between the annual,soil warming had no effect on the fine roots production in 2016,but significantly increased the fine root production in 2017.(3)The proportion of fine roots with the diameter of 0.5-1 mm accounted for the highest proportion of the total fine roots both in control and soil warming treatment,and soil warming in different seasons has significant influence on the diameter distribution of fine roots.Fine roots of the 0-0,5 mm and 0.5-1 mm diameter classes respond to warming more significantly.Soil warming significantly inhibited fine root production of the 0-0.5 mm diameter in the spring and summer 2016,and in the winter significantly promoted fine root production of the 0.5-1 mm and 1-1.5 mm diameter classes.Soil warming in winter and spring of 2017 also significantly promoted fine root production of the 0.5-1 mm diameter class.(4)Soil warming has a significant effect on the vertical distribution of fine root production.The peak of fine root production appear in 0-10 cm soil layer in control,while the peak of fine root production with soil warming appeared in 10-20 cm soil layer.In addition,the extinction coefficient 8 of fine root production with soil depth in soil warming is greater than that of control.High ? values correspond to a greater proportion of fine roots at depth and low ? values imply a greater proportion of fine roots near the soil surface.It indicates that soil warming lead to a tendency for fine root production to be distributed to the deeper soil layer to search for water,which is related to the drought condition at the surface soil after warming.In conclusion,the soil warming prolongs the growing season of fine root production,but that also makes the monthly distribution of fine root production more unstable.Soil warming suppressed fine root production in the first year,while promoted fine root production in the second year.The changes of monthly fine root production are related to soil temperature,moisture content and aboveground growth.Soil warming resulted in a significant change in the diameter distribution of fine roots production in different seasons.Fine root production was distributed to deeper soils with the decline in soil moisture content after warming.