连作对杨树人工林土壤呼吸及各组分的影响

摘要

土壤呼吸是整个陆地生态系统碳循环的关键过程之一.以山东大汶河沿岸沙地不同连作代数杨树人工林(1代林、2代林和3代林)为研究对象,利用ACE自动土壤呼吸监测系统(UK),对3种林分一个生长季(4-10月)的土壤呼吸速率及温湿度进行测定,同时采用壕沟法对3种林分的土壤呼吸进行组分分离,并对土壤呼吸及各组分与土壤温湿度的关系进行模型模拟.结果表明:3种林分的土壤呼吸速率(RS)、自养呼吸速率(RA)和异养呼吸速率(RH)的月变化均为明显的单峰格局;生长季内,3种林分RA贡献率月差异明显,平均贡献率为40.04％;RS及其组分与5 cm处土壤温度存在显著指数关系,与土壤体积含水量没有相关性,土壤温度与土壤体积含水量的复合模型对土壤呼吸速率变化解释能力为80％ ～ 94％;3种林分生长季平均土壤呼吸速率分别为3.12、3.08和2.66μmol/(m2·s),3代林RS和RH均显著低于1代林和2代林.连作导致杨树人工林地土壤呼吸速率减弱,土壤理化性质和微生物量的差异是导致林分间土壤呼吸速率差异的主要原因.揭示连作对杨树人工林土壤呼吸及各组分的影响,以及作用机制,为全面探究杨树人工林连作效应及土壤碳循环,提供数据支撑.%[Background] Soil respiration (RS) is a key step in the carbon cycle of forest ecosystem,which mainly consists of two parts:autotrophic respiration (RA) and heterotrophic respiration (RH).The decisive factors of autotrophic and heterotrophic respiration are different.In addition,the heterotrophic and autotrophic components of soil respiration may respond differently to climate change.Our goal is to assess the relationship between soil respiration and soil temperature and humidity,to determine the relative contribution of autotrophic and heterotrophic respiration to soil respiration,and to investigate the effect of continuous cropping on soil respiration and its components.The study site is located in the sandlot along the Dawen River,Shandong Province of eastern China.[Methods] We took different continuous cropping generations of poplar plantation (i.e.first generation,second generation and third generation) as the research objects.We used a field setup through trenching method to distinguish between heterotrophic and autotrophic respiration,and ACE automatic soil respiration monitoring system to measure the dynamics of soil respiration during the growing season in 2015.Meantime,soil temperature and soil water content at 5 cm depth were also measured by the self-contained temperature and moisture sensor of the instrument mentioned above.We used three empirical models to fit and analyze the relationship between soil respiration,soil temperature and volumetric water content.In addition,the soil bulk density,pH value,soil organic carbon (SOC),total nitrogen (TN) and microbial biomass carbon (MBC) content in 0-20 cm soil depth of three forest types were observed.[Results] 1) Soil respiration and its components presented significant monthly variation as unimodal pattern,and were consistent with the change of soil temperature.2) The average soil respiration rate of three forest types on their growth seasons were 3.12 μmol/(m2·s),3.08 μmol/(m2 · s) and 2.66 μmol/(m2 · s) respectively.RS and RH of the third generation forest were significantly lower than that of the first and second generation forest,while RA showed no significant difference among the three forest types.3) Contribution rate of RA of the first generation,second generation,third generation and overall mean value was 39.39％,38.47％,42.25％ and 40.04％ respectively,and showed seasonal differences,but the difference alone the three stands was not significant.4) Soil temperature and volumetric water content were not significant among the three types of forest during the observation period.Soil respiration and its components showed significant exponential relationship with soil temperature in 5 cm depth,and no significant relationship with volumetric water content.The goodness of the binary mixed model indicated that the combined effects of soil temperature and volumetric water content on soil respiration and its components were 80％-94％.The simulation results showed that the binary mixed model was the best.[Conclusions] In summary,continuous cropping of poplar plantation reduced soil respiration rate and heterotrophic respiration rate,and the difference on soil physical and chemical properties and microbial biomass is the main reason leading to the difference in soil respiration rate alone different stands.This study revealed the effects of continuous cropping on soil respiration and its components,and provided data support for the comprehensive study of continuous cropping effect and soil carbon cycle in poplar plantations.