兴安落叶松生态系统CO2浓度及其δ13C动态对环境因子的响应

【目的】探明环境因子对兴安落叶松原始林生态系统CO₂浓度及其δ¹³C动态的影响,深入理解生态系统的碳交换过程,为模拟和预测全球变化与生态系统之间的互馈机制以及科学评估寒温带森林生态系统碳汇能力提供参考。【方法】采用离轴积分腔输出光谱技术对兴安落叶松生态系统不同物候期、不同高度的CO₂浓度及其δ¹³C进行连续高频观测,并分析环境因子与CO₂浓度变化的关系。【结果】1)兴安落叶松生态系统不同高度的CO₂浓度在生长季和日尺度上均呈单峰变化,峰值分别出现在展叶期(522.34μmol·mol^-1)和凌晨(782.81μmol·mol^-1),谷值分别出现在落叶期(406.07μmol·mol^-1)和中午(379.72μmol·mol^-1);δ¹³C变化趋势与CO₂浓度相反;2)CO₂浓度随垂直高度升高而减小,δ     

云南松林土壤水文特征对计划烧除的响应

为探究计划烧除对云南松林土壤水文特征的影响,为计划烧除后森林生态系统服务功能评价提供依据,以云南省新平县实施多年计划烧除的云南松纯林为研究对象,设立20 m×20 m计划烧除样地和不进行计划烧除的自然对照样地各3块。2019年2月实施计划烧除作业,进行样地调查、火烧强度和枯落物储量调查,2020年6月采集土样,测定土壤物理、化学性质和土壤入渗性能。结果表明,计划烧除后土壤容重增加且在0~10 cm土层差异显著;毛管孔隙度和总孔隙度减少但差异不显著;有机质减少并在0~20 cm土层差异显著。计划烧除后土壤自然含水率、饱和持水率、毛管持水率和田间持水量减少但差异不显著;吸湿水量减少并且在0~20 cm土层差异显著。计划烧除后土壤初渗速率、土壤平均入渗速率和土壤稳定入渗率减少;土壤初渗速率和平均入渗速率在不同样地0~20 cm土层差异显著。计划烧除对土壤稳定入渗率的显著影响因素为土壤容重、孔隙度、有机质和饱和持水率。说明计划烧除后云南松林土壤持水性能下降,入渗性能下降,对于入渗性能的影响主要是源于土壤理化性质的改变。     

Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species

Variability of soil CO₂ efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO₂ efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO₂ flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO₂ efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO₂ efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.     

Potential CO2 emissions mitigation through forest prescribed burning: A case study in Patagonia, Argentina

Wildland fire is a natural force that has shaped most vegetation types of the world. However, its inappropriate management during the last century has led to more frequent and catastrophic fires. Wildland fires are also recognized as one of the sources of CO₂ and other greenhouse gases (GHG) that influence global climate change. As one of the techniques used to reduce the risk of destructive wildfires, prescribed burning has the potential of mitigating carbon emissions, and effectively contributes to the efforts proposed as part of the Clean Development Mechanism within the Kyoto protocol. In order to apply this concept to a real case, a simulation study was conducted in pine afforestation in the Andean region of Patagonia, Argentina, with the objective of evaluating the potential of prescribed burning for reducing GHG emissions. The scenario was established for a ten year period, in which simulated prescribed burning was compared to the traditional management scheme, which included the probability of annual average of wildfire occurrence based on available wildfire statistics. The two contrasting scenarios were: (1) managed afforestation, affected by the annual average rate of wildfires occurred in the same type of afforestation in the region, without prescribed burning, and (2) same as (1) but with the application of simulated prescribed burning. In order to estimate carbon stocks, and CO₂ removals and emissions, we followed the guidelines given for GHG inventories on the Agriculture, Forestry and Other Land Uses (AFOLU) sector of the International Panel on Climate Change (IPCC), while the terminology used was the established by IPCC (2003). Data of afforested area, thinnings, and biomass growth were taken from previous surveys in the study area. Downed dead wood and litter (forest fuel load, FFL) was estimated adjusting equations fitted to those fuels, based on field data. Results show that comparing the two scenarios, prescribed burning reduced CO₂ emissions by 44% compared to the situation without prescribed burning. The prescribed burning scenario represented about 12% of the total emissions (prescribed burning plus wildfires). Furthermore, avoided wildfires by simulated prescribed burning allowed an additional 78% GHG emissions mitigation due to extra biomass growth. Simulated prescribed burning in commercial afforestation of Patagonia appears to be an effective management practice not only to prevent wildfires, but also an efficient tool to mitigate GHG emissions. However, more studies in different scenarios would be needed to generalize these benefits to other ecosystems.     

Potential for CO2 emissions mitigation in Europe through prescribed burning in the context of the Kyoto Protocol

The current paper analyses the potential for prescribed burning techniques for mitigating carbon dioxide (CO₂) emissions from forest fires and attempts to show quantitatively that it can be a means of achieving a net reduction of carbon emissions in the context of the Kyoto Protocol. The limited number of available studies suggests that significant reductions in CO₂ emissions can be obtained and that prescribed burning can be a viable option for mitigating emissions in fire-prone countries. The present analysis shows that the potential reduction attained by prescribed burning as a percentage of the reduction in emissions required by the Kyoto Protocol varies from country to country. Out of the 33 European countries investigated, only in one the requirements of the Kyoto Protocol could potentially be achieved by applying prescribed burning, while three other nations showed a potential net CO₂ emissions reduction of about 4–8% of the Kyoto requirements and the majority showed a reduction of less than 2%. This implies that prescribed burning can only make a significant contribution in those countries with high wildland fire occurrence. Over a 5-year period the emissions from wildfires in the European region were estimated to be approximately 11 million tonnes of CO₂ per year, while with prescribed burning application this was estimated to be 6 million tonnes, a potential reduction of almost 50%. This means that for countries in the Mediterranean region it may be worthwhile to account for the reduction in emissions obtained when such techniques are applied.     

高CO2浓度和干旱胁迫对4种树苗光合特性的影响

在不同CO2浓度(380、720 μmol·mol-1)的密闭式生长箱内,对5年生油松和侧柏苗、3年生元宝枫和刺槐苗进行培养,研究CO2浓度升高与干旱胁迫对4种树苗光合特性和水分利用效率的影响.结果表明:高CO2浓度均能增加正常水分和重度干旱胁迫下4个树苗的光合速率(Pn)、胞间CO2浓度(Ci)和瞬时水分利用效率(WUE;),而降低蒸腾速率(Tr)和气孔导度(Cord);在轻度干旱和重度干旱条件下,Pn、Ci、Tr、Cond和WUEi增加,刺槐的WUEi却减少.CO2浓度增加,4个树种在同一干旱时期的碳稳定同位素比值(δ13C)减少.随着干旱胁迫加剧,不同CO2浓度下4个树种的Pn、Tr和Cond减少,而720 μmol·mol-1 CO2浓度下4个树种和380 μmol·mol-1CO2浓度下刺槐和元宝枫的WUEi和δ13C增加,而380μmol·mol-1CO2浓度下油松和侧柏的WUEi和δ13C先增加,到重度干旱时又下降.CO2浓度增加与干旱胁迫的交互作用减弱了干旱胁迫或者CO2浓度增加中的某一因子对气孔变化的敏感性,使得气孔变化缓慢,延迟了水分胁迫的发生.     

Effects of [CO2] and nitrogen on morphological and biomass traits of white birch (Betula papyrifera) seedlings

To investigate the interactive effects of CO₂ concentration ([CO₂]) and nitrogen supply on the growth and biomass of boreal trees, white birch seedlings (Betula papyrifera) were grown under ambient (360 μmol mol⁻¹) and elevated [CO₂] (720 μmol mol⁻¹) with five nitrogen supply regimes (10, 80, 150, 220, and 290 μmol mol⁻¹) in greenhouses. After 90 days of treatment, seedling height, root-collar diameter, biomass of different organs, leaf N concentration, and specific leaf area (SLA) were measured. Significant interactive effects of [CO₂] and N supply were found on height, root-collar diameter, leaf biomass, stem biomass and total biomass, stem mass ratio (SMR), and root mass ratio (RMR), but not on root mass, leaf mass ratio (LMR), leaf to root ratio (LRR), or leaf N concentration. The CO₂ elevation generally increased all the growth and biomass parameters and the increases were generally greater at higher levels of N supply or higher leaf N concentration. However, the CO₂ elevation significantly reduced SLA (13.4%) and mass-based leaf N concentration but did not affect area-based leaf N concentration. Increases in N supply generally increased the growth and biomass parameters, but the relationships were generally curvilinear. Based on a second order polynomial model, the optimal leaf N concentration was 1.33 g m⁻² for height growth under ambient [CO₂] and 1.52 g m⁻² under doubled [CO₂]; 1.48 g m⁻² for diameter under ambient [CO₂] and 1.64 g m⁻² under doubled [CO₂]; 1.29 g m⁻² for stem biomass under ambient [CO₂] and 1.43 g m⁻² under doubled [CO₂]. The general trend is that the optimal leaf N was higher at doubled than ambient [CO₂]. However, [CO₂] did not affect the optimal leaf N for leaf and total biomass. The CO₂ elevation significantly increased RMR and SMR but decreased LMR and LRR. LMR increased and RMR decreased with the increasing N supply. SMR increased with increase N supply up to 80 μmol mol⁻¹ and then leveled off (under elevated [CO₂]) or stated to decline (under ambient [CO₂]) with further increases in N supply. The results suggest that the CO₂ elevation increased biomass accumulation, particularly stem biomass and at higher N supply. The results also suggest that while modest N fertilization will increase seedling growth and biomass accumulation, excessive application of N may not stimulate further growth or even result in growth decline.     

Determining photosynthetic responses of forest species to elevated [CO2]: Alternatives to FACE

Free air CO₂ enrichment (FACE) experiments are considered the most reliable approach for quantifying our expectations of forest ecosystem responses to changing atmospheric CO₂ concentrations [CO₂]. Because very few Australian tree species have been studied in this way, or are likely to be studied in the near future because of the high installation and maintenance costs of FACE, there are no clear answers to questions such as: (1) which species will be the winners in Australia's natural forests and what are the implications for biodiversity and carbon (C) sequestration; and (2) which will be the most appropriate species or genotypes to ensure the sustainability of Australia's plantation forests.     

O_3浓度升高对桢楠和闽楠幼苗光合作用、抗氧化能力及生物量的影响

[目的]探讨O_3浓度升高对两种亚热带树木幼苗的影响,并分析其敏感性差异及原因。[方法]本试验以1年生桢楠和闽楠幼苗为材料,采用开顶式气室(OTCs),研究未过滤大气、100 nmol·mol-1(E1)、150 nmol·mol-1(E2)O_3处理对光合作用、抗氧化能力和生物量的影响。[结果]研究表明:(1) O_3熏蒸主要通过非气孔限制因素降低了两树种的净光合速率(Pn)。其中对于桢楠,E2对Pn的不利影响大于E1。而对于闽楠,8月份E2的Pn大于E1,而9月份和10月份小于E1。(2) O_3熏蒸提高了两树种的抗氧化能力,表现为总酚含量和总抗氧化能力随着O_3浓度的升高逐渐升高,而E2的还原型抗坏血酸含量低于E1。(3) O_3熏蒸降低了两树种根、茎、叶及总干质量,及降低了闽楠的根茎比。[结论]O_3熏蒸降低了两树种的光合作用,提高了抗氧化能力,最终减少了生物量。根据Pn和生物量,确定闽楠较桢楠对O_3浓度升高更加敏感。两树种间的O_3敏感性差异与气孔导度和抗氧化物质的背景水平及其对O_3浓度升高的响应有关。     

Effects of winter selective tree harvest on soil microclimate and surface CO2 flux of a northern hardwood forest

Soil surface CO₂ flux (S_flux) is the second largest terrestrial ecosystem carbon flux, and may be affected by forest harvest. The effects of clearcutting on S_flux have been studied, but little is known about the effect of alternative harvesting methods such as selective tree harvest on S_flux. We measured S_flux before and after (i) the creation of forest canopy gaps (simulating group tree selection harvests) and (ii) mechanized winter harvest but no tree removal (simulating ground disturbance associated with logging). The experiment was carried out in a sugar maple dominated forest in the Flambeau River State Forest, Wisconsin. Pre-treatment measurements of soil moisture, temperature and S_flux were measured throughout the growing season of 2006. In January–February 2007, a harvester created the canopy gaps (200–380 m²). The mechanization treatment consisted of the harvester traveling through the plots for a similar amount of time as the gap plots, but no trees were cut. Soil moisture and temperature and S_flux were measured throughout the growing season for 1 year prior to harvest and for 2 years after harvest. Soil moisture and temperature were significantly greater in the gap than mechanized and control treatments. Instantaneous S_flux was positively correlated to soil moisture and soil temperature at 2 and 10 cm, but temperature at 10 cm was the single best predictor. Annual S_flux was not significantly different among treatments prior to winter 2007 harvest, and was not significantly different among treatments after harvest. Annual (+1 std. err.) S_flux averaged 967 + 72, 1011 + 72, and 1012 + 72 g C m⁻² year⁻¹ in the control, mechanized and gap treatments, respectively, for the 2-year post-treatment period. The results from this study suggest selective group tree harvest significantly increases soil moisture and temperature but does not significantly influence S_flux.     

氮沉降对米槠天然林土壤有机碳及微生物群落结构的影响

目的 研究氮（N）沉降对亚热带常绿阔叶天然林土壤有机碳和微生物群落结构的影响,为亚热带森林生态系统碳循环过程的研究提供依据。 方法 选取中亚热带典型米槠天然林为研究对象,采用随机区组试验设计,设3个N沉降水平：对照（CK,0 kg·hm−2·a−1）、低N（LN,40 kg·hm−2·a−1）和高N（HN,80 kg·hm−2·a−1）。 结果 在0～10 cm土层,与对照相比,高N和低N处理总微生物生物量显著增加,低N处理土壤有机碳含量增加27.4%,而高N对土壤有机碳无显著影响;在10～20 cm土层,N沉降（低N和高N处理）对土层有机碳含量和总微生物及各类群生物量均无显著影响。相关分析和随机森林模型结果分析表明,N沉降导致土壤可溶性有机碳（DOC）、全氮（TN）、C/N和微生物生物量增加是驱动表层土壤有机碳累积的关键因子;主成分分析表明,N沉降显著改变0～10 cm土层土壤微生物群落结构,而对10～20 cm土层土壤微生物群落结构无显著影响。 结论 在亚热带常绿阔叶天然林中,短期低N沉降增加能够提高土壤碳储量,但长期N沉降对土壤碳吸存的影响仍不清楚。