N沉降下川中丘陵地区柏树人工林根系分泌物特征及其介导的根际C、N转化过程

Root exudates characteristics and associated soil C and N transformation processes of Cupressus funebris plantation in hilly region of central Sichuan under N deposition

尽管根系分泌物在调控森林土壤功能和土壤生物地球化学循环过程中具有重要作用,但目前关于N沉降下森林根系分泌物输入特征及其介导的根际土壤C、N过程认识还甚为有限。本研究以川中丘陵地区典型柏树人工林为试验对象,通过不同N添加水平模拟N沉降强度,于2020年不同季节对根系分泌物进行原位收集和分析,并同步分析了根际与非根际土壤的微生物生物量和土壤C、N矿化速率的变化,以揭示不同N添加处理对根系分泌物C输入季节动态变化规律及其介导的土壤C、N微生物过程差异。结果表明:(1)N添加显著降低了柏树人工林根系分泌物C输入速率与年通量,且高N处理对分泌物C输入的抑制作用更强烈。(2)N添加显著抑制了柏树人工林土壤C、N矿化速率以及土壤微生物C、微生物N的根际效应,且高N处理对土壤C、N微生物过程根际效应的抑制幅度更大。(3)根系C、N过程根际效应大小呈现春、夏季逐渐升高,秋、冬季逐渐降低的季节动态变化,且夏季根际效应值最高。N沉降显著降低了柏树人工林的根系分泌速率与通量,并明显抑制了根际土壤C、N转化微生物过程,且抑制效应强度与N添加水平有关,证实了森林根系分泌物-微生物特征-土壤养分转化过程之间存在密切的偶联效应。本研究结果丰富了全球变化下森林根际生态过程的科学认识,为川中丘陵区大面积的人工林适应性管理与生态恢复实践提供一定的科学依据。

Root exudates play an important role in regulating forest soil function and soil biogeochemical cycling.However,current understanding on input characteristics of forest root exudates and C and N processes mediated by rhizosphere soil under N deposition is still limited.This study took cypress(Cupressus funebris)plantation in the hilly area of central Sichuan as the research object.Different levels of N addition were used to simulate atmospheric N deposition.In 2020,root exudates were collected and analyzed in different seasons,and microbial biomass and C and N mineralization rate of rhizosphere/non-rhizosphere soils were analyzed,to reveal the seasonal variations of C input rate of root exudates,and the differences in soil C and N microbial process mediated by root exudates under different N addition treatments.The results showed that:(1)N addition significantly reduced C input rate and annual flux of root exudates in cypress plantation,with higher N addition having stronger inhibitory effect on C input of root exudates.(2)N addition significantly inhibited the rhizosphere effects of soil C and N mineralization and soil microbial C and N,with stronger inhibition effect of higher N treatment on soil C and N microbial processes.(3)The rhizosphere effect of root C and N process showed seasonal variation that gradually increased in spring and summer,and decreased in autumn and winter,peaking in summer.Our results demonstrated that N addition significantly reduced the rate and flux of root exudates of cypress forest,and significantly inhibited the microbial C and N transformation in rhizosphere soil.The intensity of inhibitory effect was related to N addition level,which confirmed the close relationship between forest root exudates-microbial characteristics-transformation processes of soil nutrients.Our results improved the understanding of forest rhizosphere processes under global change and provided scientific basis for adaptive management and ecological restoration of large-scale plantation forests in hilly area of central Sichuan.