| With the accumulation of the studies on the relationship between global changes and plant community,plant functional traits as a bridge of plant form,structure and ecosystem process have been paid a great deal of attention.Ecologists are increasingly adopting traitbased approaches to explore responses of plant traits to environmental change as well as effects of plant traits on ecosystem processes,in order to understand and predict the mechanisms of ecosystem process and functioning.However,earlier researches on plant functional traits most focused on aboveground vegetation sub-system,the evaluation of belowground root traits and functions are still poorly understood.Furthermore,the understanding of the variation in plant functional traits nowadays is mostly limited to the species level.The nitrogen deposition from the atmosphere will greatly increase the soil acidification and nutrient enrichment.Fine roots,as the important organ of plants,play an important role in carbon and mineral nutrients cycling.The understanding of variations and responses of root functional traits to nitrogen deposition is of important to explore the resource-use strategies and the adaptation of plants to the fluctuating environment.Meanwhile,the changes of root traits could be used to predict the ecosystem processes.Based on the above,to explore the relationship of plant fine root functional traits and ecological process,a field experiment based on an ex-arable field was designed with 3 levels of N deposition which was simulated by N application,i.e.0 kg ha-1 yr-1,45 kg ha-1 yr-1 and 90 kg ha-1 yr-1 and 2 levels of lime addition,i.e.0 kg ha-1 yr-1 and 110 kg ha-1 yr-1.Samples of the dominant plant species were collected during the succession,aimed to determine root traits response to environmental changes and its effects on ecosystem respiration,as well as their relationship with soil properties,microbial community and nutrient limitations,and to reveal responses of root traits to N deposition and effects of root traits to ecosystem respiration.The main results are as followed:1)N deposition significantly decreased soil pH and microbial biomass,but significantly increased the NO3--N content,DOC and the bacterial PLFA.Acidity mitigation significantly increased the PLFA contents,soil pH and microbial biomass.Environmental changes caused by N deposition and acidity mitigation would lead to the changes in root traits.Furthermore,effects on ecosystem respiration differed at the community and functional group levels.Generally,at the community level,diameter and RTD increased,but SRL and RN decreased.When splitting into functional group level,plants with conservative traits showed the same response strategy as plant community to environmental changes,while acquisitive plants were the opposite.2)Root traits would directly influence ecosystem respiration.Root traits would also indirectly influence ecosystem respiration through changes in soil properties,microbial community and nutrient limitations.Root traits displayed the largest direct effect on ecosystem respiration at the community level.The effects of root traits on ecosystem respiration resulted from the significantly indirect effects of soil properties and microbial community at the functional group level.Partial least squares path models(PLS-PMs)revealed that three functional traits,RTD,RC and RCN,directly and/or indirectly controlled ecosystem respiration.Overall,our results revealed that the responses of morphology and chemical traits of fine roots obviously differed among plant community,functional groups and season following N deposition and acidity mitigation.The different mechanisms of changes in root traits on ecosystem respiration suggest that the links between response traits and effect traits.Deciphering the associations between fine root traits and ecosystem respiration,would help us understand the mechanism underlying terrestrial ecosystem functionality as well as the capability to steer the biotic roles in enhancing ecosystem sustainability. |
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