| As an important nutrient capture organ of forest trees,root is one of the energy sources and material foundations for the operation of forest ecosystems.Carbon,nitrogen,and phosphorus are important nutrient elements for plant growth and metabolism,and their nutrient pool has a pivotal effect on the productivity and carbon sequestration potential of forest ecosystems.Global warming is not only manifested as a rise in atmospheric temperature,but the current situation of rising ground temperature cannot be ignored.It is not clear how the root biomass and carbon,nitrogen,and phosphorus nutrient characteristics of forest ecosystems will respond and adapt to changes under air and soil temperature.To this end,this study took the mid-subtropical young Cunninghamia lanceolata saplings as the research object,set up experimental plots for dual-factor interactive control of air warming and soil warming,and set up control(CT),soil warming(W),and atmospheric warming(OTC).The root harvest method was used to determine the root biomass,carbon,nitrogen,and phosphorus content,and carbon,nitrogen,and phosphorus pools of different soil layers and different diameter classes to reveal the effects of different warming methods on the growth and root nutrient accumulation of young Cunninghamia lanceolata.The main results are as follows:(1)soil warming × air warming treatment promotes the growth of young Cunninghamia lanceolata,the average height and DBH are significantly increased by44.10 % and 33.72 %,respectively(P < 0.05).And the soil warming treatment also promoted the increase of basal diameter of young Cunninghamia lanceolata.(2)Fine root(0-2 mm)biomass significantly increased by 138.86% and150.10 % under soil warming ×air warming treatment and soil warming treatment(P< 0.05),and young trees may adopt strategies of increasing investment in fine root biomass to adapt to the warming environment to cope with changes in underground resources.Soil warming × air warming treatment also significantly increased fine roots biomass of 10-20 cm soil layer,coarse root(> 2 mm)biomass and total root biomass of 20-50 cm soil layer(P < 0.05),significantly reducing the proportion of fine root biomass of 0-10 cm soil layer(P < 0.05).Four years after warming,young Cunninghamia lanceolata maintain their growth by increasing the biomass and proportion of deep root systems.(3)Regardless from the distribution of root diameter and soil layer,soil warming treatment,air warming treatment and × air warming treatment all reduce root C content to different degrees.This may be caused by the phenomenon of "carbon dilution" during accelerated growth after warming.With the significant increase of fine roots biomass under soil warming treatment,the fine roots(0-2 mm)C pools increased significantly(P < 0.05).(4)Both soil warming treatment and air warming treatments did not have a significant impact on root N,P content and N,P pools(P > 0.05).Soil warming × air warming treatment significantly increased the N pool of 10-20 mm roots by 0.94%,and the P pool of the roots below 20 mm was significantly higher than the CT treatment by 1.71 times,1.30 times,1.95 times and 3.71 times(P < 0.05).Soil warming × air warming treatment also significantly increased the N pool of the root system in the 20-50 cm soil layer by 86.20%(P < 0.05),and the P pool of the root system in the 10-20 cm and 20-50 cm soil layer was 0.7 times and 1 times higher than that of the CT treatment(P < 0.05).It shows that the simultaneous warming of the atmosphere and the soil can effectively alleviate the plight of the lack of P in the mid-subtropical soil habitat,and is beneficial to the absorption of N and P by the roots of the larger diameter and deeper soil layers of young Cunninghamia lanceolata. |
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