全球变暖背景下土壤微生物呼吸的热适应性:证据、机理和争议

土壤微生物呼吸的热适应性被认为是决定陆地生态系统对全球变暖反馈作用的潜在重要机制,可能显著改变未来的气候变化趋势,然而学术界对于这一机制是否真实存在尚有分歧。阐述了土壤微生物呼吸的热适应性概念,从证据、机理和争议3方面对已有研究进展进行了综述和分析。土壤微生物呼吸的热适应性是微生物在群落尺度上对温度变化的适应性,具有坚实的生物学与生态学理论基础,研究者们运用各类指标已在许多实验中证实土壤微生物物种及群落的呼吸过程能够在高温环境产生适应性变化。土壤微生物呼吸的热适应性机理涉及生物膜结构变化、酶活性变化、微生物碳分配比例变化和微生物群落结构变化等方面。关于土壤微生物呼吸热适应性的争议可能是由研究方法、微生物物种及环境条件的差异引起的。根据对已有研究的分析,认为土壤微生物呼吸的热适应性是真实存在的,未来的研究可进一步探索土壤微生物呼吸的热适应性机理,深入研究环境和全球变化对土壤微生物呼吸的热适应性影响,定量评估土壤微生物呼吸的热适应性对陆地生态系统反馈过程的影响。     

Thermal adaptation of heterotrophic soil respiration in laboratory microcosms

Respiration of heterotrophic microorganisms decomposing soil organic carbon releases carbon dioxide from soils to the atmosphere. In the short term, soil microbial respiration is strongly dependent on temperature. In the long term, the response of heterotrophic soil respiration to temperature is uncertain. However, following established evolutionary trade‐offs, mass‐specific respiration (R_mass) rates of heterotrophic soil microbes should decrease in response to sustained increases in temperature (and vice‐versa). Using a laboratory microcosm approach, we tested the potential for the R_mass of the microbial biomass in six different soils to adapt to three, experimentally imposed, thermal regimes (constant 10, 20 or 30 °C). To determine R_mass rates of the heterotrophic soil microbial biomass across the temperature range of the imposed thermal regimes, we periodically assayed soil subsamples using similar approaches to those used in plant, animal and microbial thermal adaptation studies. As would be expected given trade‐offs between maximum catalytic rates and the stability of the binding structure of enzymes, after 77 days of incubation R_mass rates across the range of assay temperatures were greatest for the 10 °C experimentally incubated soils and lowest for the 30 °C soils, with the 20 °C incubated soils intermediate. The relative magnitude of the difference in R_mass rates between the different incubation temperature treatments was unaffected by assay temperature, suggesting that maximum activities and not Q₁₀ were the characteristics involved in thermal adaptation. The time taken for changes in R_mass to manifest (77 days) suggests they likely resulted from population or species shifts during the experimental incubations; we discuss alternate mechanistic explanations for those results we observed. A future research priority is to evaluate the role that thermal adaptation plays in regulating heterotrophic respiration rates from field soils in response to changing temperature, whether seasonally or through climate change.     

增温对蒙古栎林土壤呼吸及组分的影响

为明确气候变暖对蒙古栎林土壤碳排放的潜在影响,以三江平原蒙古栎次生林为研究对象,分析5—11月土壤呼吸组分对增温（1℃）和断根交互处理的响应。结果表明,增温使未断根组表层土壤平均升高1.35℃,断根组表层土壤平均升高0.65℃,表层土壤含水量平均升高0.02m³/m³（P<0.05）,土壤总呼吸速率增加11.9%（P<0.05）,土壤异养呼吸无显著变化（P>0.05）。各月份土壤异养呼吸速率占土壤总呼吸速率的比例均达到50%以上。土壤温度与土壤总呼吸速率、土壤异养呼吸速率均呈现指数正相关关系（P<0.01）,土壤体积含水量与土壤总呼吸速率、土壤异养呼吸速率呈现线性负相关关系（P<0.01）。增温会导致土壤呼吸温度敏感性(Q₁₀)降低,其中土壤总呼吸Q₁₀值降低0.45,土壤异养呼吸Q₁₀值降低0.39。不同月份Q₁₀存在差异,其中9月份最高,其次为8月份和10月份,11月份最低。双因素方差分析表明,以增温、断根为自变量时主效应存在（P<0.05）,二者无显著交互作用（P>0.05）。模拟气候变暖初期蒙古栎林土壤总呼吸速率会显著升高,增加的土壤碳排放会进一步促进气候变暖,不同季节土壤呼吸速率升高幅度存在差异,夏季土壤碳排放要高于其它季节,而Q₁₀则是于夏季和秋季的过渡时段更高。     

Non-climatic thermal adaptation: implications for species' responses to climate warming

There is considerable interest in understanding how ectothermic animals may physiologically and behaviourally buffer the effects of climate warming. Much less consideration is being given to how organisms might adapt to non-climatic heat sources in ways that could confound predictions for responses of species and communities to climate warming. Although adaptation to non-climatic heat sources (solar and geothermal) seems likely in some marine species, climate warming predictions for marine ectotherms are largely based on adaptation to climatically relevant heat sources (air or surface sea water temperature). Here, we show that non-climatic solar heating underlies thermal resistance adaptation in a rocky–eulittoral-fringe snail. Comparisons of the maximum temperatures of the air, the snail''s body and the rock substratum with solar irradiance and physiological performance show that the highest body temperature is primarily controlled by solar heating and re-radiation, and that the snail''s upper lethal temperature exceeds the highest climatically relevant regional air temperature by approximately 22°C. Non-climatic thermal adaptation probably features widely among marine and terrestrial ectotherms and because it could enable species to tolerate climatic rises in air temperature, it deserves more consideration in general and for inclusion into climate warming models.     

Soil Respiration and Student Inquiry: A Perfect Match

This activity explores the cycling of carbon between the atmosphere (primarily as CO₂) and biomass in plants, animals, and microscopic organisms. Students design soil respiration experiments using a protocol that resembles current practice in soil ecology. Three methods for measuring soil respiration are presented. Student-derived questions direct soil research projects.