Large losses of soil C and N from soil profiles under pasture in New Zealand during the past 20 years

The conversion of two‐thirds of New Zealand's native forests and grasslands to agriculture has followed trends in other developed nations, except that pastoral grazing rather than cropping dominates agriculture. The initial conversion of land to pasture decreased soil acidity and elevated N and P stocks, but caused little change in soil organic C stocks. However, less is known about C and nutrient stock changes during the last two decades under long‐term pastoral management. We resampled 31 whole soil profiles in pastures spanning seven soil orders with a latitudinal range of 36–46°S, which had originally been sampled 17–30 years ago. We measured total C, total N, and bulk density for each horizon (generally to 1 m) and also reanalyzed archived soil samples of the same horizons for C and N. On average, profiles had lost significant amounts of C (− 2.1 kg C m⁻²) and N (− 0.18 kg N m⁻²) since initial sampling. Assuming a continuous linear decline in organic matter between sampling dates, significant losses averaged 106 g C m⁻² yr⁻¹ (P=0.01) and 9.1 g N m⁻² yr⁻¹ (P=0.002). Removal of C through leaching and erosion appears too small to explain these losses, suggesting losses from respiration exceed the inputs of photosynthate in the soil profile. These results emphasize that resampling soil profiles provide a robust method for detecting soil C changes, and add credence to the suggestion that soil C losses may be occurring in some temperate soil profiles. Further work is required to determine whether these losses are continuing and how losses might be extrapolated across landscapes to determine the implications for New Zealand's national CO₂ emissions and the sustainability of the implied rates of soil N loss.     

施氮和降水格局改变对土壤CH4和CO2通量的影响

氮沉降增加和降水格局改变是全球变化的两项重要内容,但是同时考虑上述两因素对温室气体CH4和CO2通量影响的原位双因子模拟研究还相当有限.本研究以长白山温带阔叶红松林土壤为研究对象,采用静态箱法研究了外施氮源(50 kg N·hm-2·a-1)和增减30％降水对土壤CH4和CO2通量的影响.结果表明:施氮能抑制土壤CH4吸收,有时甚至能将土壤对CH4的吸收转为释放,但这种抑制效应只能维持5d左右,且能在一定程度上改变CH4通量和环境因子(温度、土壤pH、粘粒含量)的相关关系.降水改变未能显著影响土壤CH4通量.对CO2通量而言,施氮能降低土壤CO2排放,长白山阔叶红松林连续施氮第4年的平均抑制效应为27.4％.长期连续施氮的平均抑制效应随施氮时间延长而逐渐增大,一定年限后达到最大值.单次施氮的抑制效应随时间延长逐渐减弱,并在1个月的施氮周期末期基本消失.施氮的抑制效应和土壤充水孔隙度(WFPS)呈显著负相关关系,且升温能增强施氮对CO2释放的抑制效应并延长抑制时间.施氮、降水有可能改变土壤呼吸的温度敏感性.本研究表明,长白山森林土壤氮素尚未达到一定阈值,未来氮沉降增加将抑制CO2的释放和CH4的吸收,因此总体来看施氮抑制土壤碳排放.     

氮添加对长白山阔叶红松林2种树木幼苗光合生理生态特征的影响

植物的光合作用是评估全球变化背景下碳循环的重要环节。目前,氮沉降增加日益明显,作为植物生长关键因子的可利用氮将对植物的光合生理生态过程产生影响。以长白山阔叶红松林主要树种红松和紫椴的幼苗为例,通过模拟氮沉降增加(氮添加量分别为0、23、46和69 kg N hm~(-2)a~(-1))的方法,利用Li-6400光合测定系统分别测算了两个树种的最大净光合速率(A_(max))、气孔导度(G_(smax))和水分利用效率(WUE)的值,并测算了叶氮含量、叶绿素含量、比叶面积、光合氮利用效率(PNUE)的值。通过分析A_(max)随不同施氮量的变化规律,同时结合其他叶片特征参数的变化,进一步探讨植物光合随氮添加的变化原因。研究结果显示:两个树种的A_(max)值在0—46 kg N hm~(-2)a~(-1)的氮添加范围内随施氮量的增加而增大,继续增加施氮量至69 kg Nhm~(-2)a~(-1)则出现下降。叶绿素含量、G_(smax)、PNUE和比叶面积在不同的氮添加水平下的变化规律与A_(max)的一致,且均与A_(max)呈显著正相关关系。叶氮含量与A_(max)的值仅在0—46 kg N hm~(-2)a~(-1)氮添加范围内呈显著正相关。A_(max)与WUE的相关关系不显著。相同氮添加水平下,氮添加对阔叶树种紫椴各生理生态参数(A_(max)、G_(smax)、叶氮含量、比叶面积、PNUE和WUE)的促进程度高于对针叶树种红松各生理生态参数的促进程度。研究结果可为评估氮沉降增加背景下我国东北地区的碳循环提供依据。     

亚热带杉木林土壤有机碳及其活性组分对氮磷添加的响应

通过野外氮、磷添加,分析N₀(0 kg N·hm^-2·a^-1)、N₁(50 kg N·hm^-2·a^-1)、N₂(100 kg N·hm^-2·a^-1)、P(50 kg P·hm^-2·a^-1)、N₁P和N₂P等6种处理3年后对亚热带杉木人工林土壤有机碳(SOC)、颗粒有机碳(POC)和水溶性有机碳(WSOC)的影响.结果表明:氮、磷添加对0～20 cm土层SOC含量无显著影响.磷添加显著降低0～5 cm土层POC含量,与无磷处理相比,加磷处理POC含量降低26.1%.WSOC含量对氮、磷添加的响应主要表现在0～5 cm土层,低水平氮添加和磷添加显著提高WSOC含量.在0～5 cm土层,氮添加对POC/SOC值无显著影响,而与无磷添加相比,POC/SOC值在磷添加处理下显著降低15.9%.在5～10和10～20 cm土层,氮、磷添加处理对POC/SOC值无显著影响.在亚热带地区,森林土壤碳稳定性主要受磷含量的调控,短期磷添加易导致表层土壤活性有机碳分解,增加土壤碳稳定性.     

A synthesis: The role of nutrients as constraints on carbon balances in boreal and arctic regions

As in many ecosystems, carbon (C) cycling in arctic and boreal regions is tightly linked to the cycling of nutrients: nutrients (particularly nitrogen) are mineralized through the process of organic matter decomposition (C mineralization), and nutrient availability strongly constrains ecosystem C gain through primary production. This link between C and nutrient cycles has implications for how northern systems will respond to future climate warming and whether feedbacks to rising concentrations of atmospheric CO₂ from these regions will be positive or negative. Warming is expected to cause a substantial release of C to the atmosphere because of increased decomposition of the large amounts of organic C present in high-latitude soils (a positive feedback to climate warming). However, increased nutrient mineralization associated with this decomposition is expected to stimulate primary production and ecosystem C gain, offsetting or even exceeding C lost through decomposition (a negative feedback to climate warming). Increased primary production with warming is consistent with results of numerous experiments showing increased plant growth with nutrient enrichment. Here we examine key assumptions behind this scenario: (1) temperature is a primary control of decomposition in northern regions, (2) increased decomposition and associated nutrient release are tightly coupled to plant nutrient uptake, and (3) short-term manipulations of temperature and nutrient availability accurately predict long-term responses to climate change.     

The effects of elevated CO2 on symbiotic N2 fixation: a link between the carbon and nitrogen cycles in grassland ecosystems

The response of plants to elevated CO₂ is dependent on the availability of nutrients, especially nitrogen. It is generally accepted that an increase in the atmospheric CO₂ concentration increases the C:N ratio of plant residues and exudates. This promotes temporary N-immobilization which might, in turn, reduce the availability of soil nitrogen. In addition, both a CO₂ stimulated increase in plant growth (thus requiring more nitrogen) and an increased N demand for the decomposition of soil residues with a large C:N will result under elevated CO₂ in a larger N-sink of the whole grassland ecosystem. One way to maintain the balance between the C and N cycles in elevated CO₂ would be to increase N-import to the grassland ecosystem through symbiotic N₂ fixation. Whether this might happen in the context of temperate ecosystems is discussed, by assessing the following hypothesis: i) symbiotic N₂ fixation in legumes will be enhanced under elevated CO₂, ii) this enhancement of N₂ fixation will result in a larger N-input to the grassland ecosystem, and iii) a larger N-input will allow the sequestration of additional carbon, either above or below-ground, into the ecosystem. Data from long-term experiments with model grassland ecosystems, consisting of monocultures or mixtures of perennial ryegrass and white clover, grown under elevated CO₂ under free-air or field-like conditions, supports the first two hypothesis, since: i) both the percentage and the amount of fixed N increases in white clover grown under elevated CO₂, ii) the contribution of fixed N to the nitrogen nutrition of the mixed grass also increases in elevated CO₂. Concerning the third hypothesis, an increased nitrogen input to the grassland ecosystem from N₂ fixation usually promotes shoot growth (above-ground C storage) in elevated CO₂. However, the consequences of this larger N input under elevated CO₂ on the below-ground carbon fluxes are not fully understood. On one hand, the positive effect of elevated CO₂ on the quantity of plant residues might be overwhelming and lead to an increased long-term below-ground C storage; on the other hand, the enhancement of the decomposition process by the N-rich legume material might favour carbon turn-over and, hence, limit the storage of below-ground carbon.     

山西吕梁山南段森林乔木层碳密度

森林在区域和全球碳循环中起着关键作用,不同森林类型生物量和碳密度的精确估算是区域森林碳储量研究的重要基础。以2005和2010年吕梁山南段2期森林资源清查资料为基础,采用加权生物量回归模型法和转换因子连续函数法对森林乔木层的生物量进行估算,发现前者估算结果显著高于后者(P0.01),加权生物量回归模型法更适宜于中小尺度生物量估算。依据回归模型法获得的28×112(物种×样方)碳密度矩阵,对森林群落进行TWINSPAN分类和DCA、CCA排序;采用单因素方差分析和相关分析对不同生境条件下乔木层的碳密度进行研究。结果表明:吕梁山南段森林群落可分为8个群系,不同群系间碳密度差异显著(P0.01),其中辽东栎+色木槭群系和辽东栎+油松群系显著高于其他群系,白皮松+侧柏群系最低。2010年乔木层碳密度显著高于2005年,平均每年以1.54 t·hm-2的速度增加。乔木层碳密度与海拔或坡度呈显著相关,随海拔或坡度的增加碳密度呈先增后降的趋势。阴坡和半阴坡(北坡和东坡)碳密度大于阳坡和半阳坡(南坡与东南坡),山脊碳密度最小。因地制宜进行物种选择和抚育管理,可显著提高森林碳密度。     

土壤有机碳和氮分解对温度变化的响应趋势与研究方法

总结了土壤中碳和氮贮量与温度的关系、土壤碳和氮分解对温度时空差异和直接加热升温的响应,以及土壤碳和氮分解对低温冻结及冻融循环的响应趋势,讨论了其研究方法的误差和不确定性,并对今后的研究提出了一些建议．气候变暖在短期内将使土壤碳和氮分解加速并引起CO2释放量增加,而长期过程中却并不一定会引起土壤碳和氮分解加速．合理解释不同研究结果的差异,除了需要系统分析土壤碳和氮分解对温度变化响应的机制外,还需要充分认识土壤碳和氮分解对温度变化响应的长期过程和短期过程的差异,以及研究方法、植被、土壤和气候等因素的影响．     

Interactive Effects of Fire, Elevated Carbon Dioxide, Nitrogen Deposition, and precipitation on a California Annual Grassland

Although it is widely accepted that elevated atmospheric carbon dioxide (CO₂), nitrogen (N) deposition, and climate change will alter ecosystem productivity and function in the coming decades, the combined effects of these environmental changes may be nonadditive, and their interactions may be altered by disturbances, such as fire. We examined the influence of a summer wildfire on the interactive effects of elevated CO₂, N deposition, and increased precipitation in a full-factorial experiment conducted in a California annual grassland. In unburned plots, primary production was suppressed under elevated CO₂. Burning alone did not significantly affect production, but it increased total production in combination with nitrate additions and removed the suppressive effect of elevated CO₂. Increased production in response to nitrate in burned plots occurred as a result of the enhanced aboveground production of annual grasses and forbs, whereas the removal of the suppressive effect of elevated CO₂ occurred as a result of increased aboveground forb production in burned, CO₂-treated plots and decreased root production in burned plots under ambient CO₂.The tissue nitrogen–phosphorus ratio, which was assessed for annual grass shoots, decreased with burning and increased with nitrate addition. Burning removed surface litter from plots, resulting in an increase in maximum daily soil temperatures and a decrease in soil moisture both early and late in the growing season. Measures of vegetation greenness, based on canopy spectral reflectance, showed that plants in burned plots grew rapidly early in the season but senesced early. Overall, these results indicate that fire can alter the effects of elevated CO₂ and N addition on productivity in the short term, possibly by promoting increased phosphorus availability.     

环境微生物学的组学技术应用和突破（英文稿）

由于研究环境变化和微生物群落的需要,近年来高通量组学技术得到了迅猛开发和应用.其中,基于测序和芯片技术的宏基因组学是一个关键的、最成熟的组学技术,为大多数的其它组学技术提供了支撑.相比较而言,宏转录组学、宏蛋白质组学和宏代谢组学也取得了少数的有限成功,但已经显示出可喜的潜力.所有的组学技术都有赖于生物信息学,使得后者成为组学技术应用的一个主要的技术瓶颈.这些新的组学技术对环境微生物学领域产生了革命性的影响,极大地丰富了我们对于环境微生物基因资源和功能活性的了解.