城市绿地生态系统雨季土壤呼吸对降雨变化的响应

Response of Soil Respiration of Urban Green-land Ecosystem to Precipitation Events in Fuzhou City

全球气候变化的可能后果之一是干旱频繁,强降雨增多。城市绿地生态系统土壤呼吸是陆地碳循环的重要组成部分,探讨强降雨对城市绿地生态系统土壤呼吸的影响,有助于预知在全球变化背景下土壤CO2排放的可能反馈机制。在多年定位试验的基础上,开展降雨改变试验,采用全自动多通量箱对降雨前后城市绿地生态系统土壤呼吸(Rs)和环境因子等进行原位全天候连续监测,分析Rs对正常降雨、增加50%降雨(增雨)和减少50%降雨(减雨)的响应。结果表明,(1)增雨显著提高了土壤湿度(W,0~5cm),而对土壤温度(T,0~5cm)没有显著影响(P>0.05)。与对照相比,增雨导致Rs显著提高了1.43%(P<0.05),减雨对Rs无显著影响(P>0.05)。(2)土壤湿度与Rs呈显著负相关(P<0.05),土壤温度与Rs呈显著正相关(P<0.05),且对Rs有一定的促进趋势。(3)降雨时间为20min时,Rs的下降率最大;20min以后,Rs下降率逐渐变小,说明降雨时间越长,土壤释放CO2速率越慢,当降雨达到一定时间后,土壤释放CO2速率有所回升;回归分析发现,降雨量与呼吸速率的变化率呈二次相关关系(P<0.05),总体上降雨促进了Rs。(4)不同降雨处理均对土壤温度敏感系数(Q10)表现出显著的影响,其中增雨和减雨均降低了土壤水分敏感性;不同降雨时期土壤水分敏感性大致表现为:在雨季开始和结束时,Rs对水分敏感性较高,而雨季中期Rs对水分敏感性较低。这意味着在城市绿地生态系统中,增雨或减雨均对Rs有不同程度的刺激作用,这很可能减弱城市绿地生态系统土壤的固碳潜力。

Changing precipitation patterns and its corresponding changes in soil water content are critical in regulating soil respiration.Determining the responses of soil respiration to changing precipitation regimes in urban green-land ecosystem is favor to the improvement of precision of C cycling.However,our understanding of the effects of precipitation on soil respiration is still very limited,particularly for urban green-land ecosystem.This study was conducted to investigate the effects of soil respiration to heavy rainfall in urban green-land ecosystem,and a field precipitation manipulation experiment was conducted to examine the response of soil respiration and its temperature sensitivity to increased(+50%)and decreased precipitation(-50%).The results showed that,(1)Increased precipitation significantly elevated soil moisture(W,0~5 cm)but had no effect on soil temperature(T,0~5 cm).Soil respiration was substantially enhanced by 1.43%under increased precipitation treatment compared with that in the control plots.(2)There was a strong negative correlation between soil moisture and Rs(P<0.05),while a strong negative correlation with soil temperature(P<0.05).(3)The decrement rate of Rs increased with the rainfall time,when at 20 min rainfall,the decrement rate of Rs was highest,while after 20 min rainfall,the decrement rate of Rs gradually decreased.Regression analysis found that there was a quadratic function between the decrement rate and rainfall,and rainfall was contributed to the Rs.(4)The relationship between Rs and soil temperature at 5 cm depth(T)as well as soil water content at 5 cm depth could be better explained by an exponential equation which contains soil moisture parameter c.Strong rainfalls had varying effects on temperature sensitivities of Rs(Q10)during different periods of the wet season.The soil moisture sensitivity of Rs was decreased after rainfall.The moisture sensitivities during different periods of the wet season were characterized as follow:wet season<early wet season<after the wet season.The results suggest that both increased and decreased precipitation can stimulate soil respiration with different extents.Changing precipitation patterns,therefore,may weaken soil C sequestration in forest ecosystems,and exert a positive feedback on atmosphere CO2 concentration at the climatic transitional zone from a subtropical to a warm temperate zone.