Soil Respirations And Their Environmental Responses For Urban Forest Patches And Greening Landscapes Of Tianjin,China

As a huge carbon sink that absorbs CO₂ and releases O₂,urban forest ecosystems play a very important role in the global carbon cycle and relief of greenhouse effect.With the continuous advancement of urbanization,a large number of patchy remnant forests in the transition zone between the city and the countryside.However,as an important part of urban forests,there are few studies on soil respiration in urban forest patches.This study selects urban forest patches and greening landscapes as research objects,and soil respiration rates(Rs)and their influencing factors in urban forest patches and greening landscapes were measured by using the portable soil carbon flux automatic analyzer ACE in order to investigate diurnal and seasonal variation of soil respiration in urban forest patches and greening landscapes,and to contrast their different responses to the environmental changes.The main results are as follows:(1)The diurnal variation trend of Rs in urban forest patches and greening landscapes was a single-peak curve.However,the difference of the peak time of their Rs in different seasons;The mean of daily variation of Rs was expressed as urban forest patches>greening landscapes,and daytime>nighttime;The daily variation of Rs was mainly affected by the combined effects of soil temperature(ST)and soil water content(SWC).Correlation analysis showed that during the growing season,the daily change of Rs was mainly affected by the synergy of ST and SWC,and Rs was positively correlated with ST and SWC;During the dormant period,the daily change of Rs has no significant correlation with ST.However,it is mainly controlled by SWC and had a significant negative correlation with SWC.(2)Rs in urban forest patches and greening landscapes showed typical seasonal patterns,but the maximum Rs appeared in July and August,respectively,and the minimum Rs appeared in January,which was consistent with the seasonal variation of ST.The annual average of Rs manifests as urban forest patches>greening landscapes.If linear regression model was performed to estimate the relationships between R_s and ST,SMA analysis found that Rs of greening landscapes easy to change with ST fluctuations.However,the response of Rs in urban forest patches to ST was more moderate than greening landscapes.The correlation between Rs and SWC showed an opposite trend in the growing and dormant periods.SMA analysis found that urban forest patches had higher water use efficiency than greening landscapes during their carbon assimilation and metabolism processes in growing season and the urban forest patches was more sensitive to the change of SWC than urban green landscapes under their dormant conditions.(3)The relationship between Rs and fine root biomass(FRB)in urban forest patches and greening landscapes has a significant linear positive correlation.The SMA analysis showed that proportion of autotrophic respiration in greening landscapes was higher than urban forest patches,but this did not mean that urban forest patches were difficult to maintain carbon balance.We speculated that heterotrophic respiration caused by soil microorganisms may play a major role in urban forest patches.The results showed that the soil microbial community structure of urban forest patches can accelerate the Rs and soil carbon turnover rate,and contribute to carbon balance of urban ecosystems.The CCA analysis showed that Rs of urban forest patches were mainly affected by ST,FRB,organic carbon,carbon/nitrogen ratio,total nitrogen,bacteria and actinomycetes;but the Rs of greening landscapes were mainly controlled by total phosphorus,total potassium,available potassium and fungi.