火干扰对森林生态系统土壤呼吸组分的影响研究进展

土壤呼吸是陆地生态系统与大气碳交换的主要方式,主要分为自养呼吸和异养呼吸。土壤呼吸不仅是森林生态系统碳循环过程的关键环节,也是森林生态系统能量流动和物质循环的重要生态过程。火作为森林生态系统中一个重要的生态因子,可以在短时间内对土壤呼吸组分造成巨大的影响。火干扰对土壤呼吸组分的影响与火烧强度、火烧频率、火烧持续时间以及火后恢复等因子有关,通过影响植被的根系与组成、微生物群落数量与结构,凋落物的数量以及生态系统的环境和小气候等,进而对土壤呼吸产生影响。火干扰对土壤呼吸影响整体表现为火烧后土壤呼吸速率下降,在几个月至几年内恢复到火烧前水平,之后火继续对土壤呼吸产生影响长达数年至数十年。通过描述火烧强度、火烧频率以及火后恢复时间,阐述火干扰对土壤呼吸组分的直接影响,以及通过火后环境对土壤呼吸组分产生的间接影响,来揭示火干扰对森林生态系统土壤呼吸组分的影响。同时针对火干扰对土壤呼吸组分的影响进行以下3个方面的研究展望：（1）火后产生的黑碳对土壤呼吸组分的影响;（2）火后植被恢复对土壤呼吸组分产生的影响;（3）火后土壤呼吸组分的长期变化规律。     

寒温带湿地火后植被恢复的影响因子

寒温带湿地在维护区域生态平衡方面发挥着重要作用.火是湿地的重要干扰因子.重度火烧会导致湿地生态功能明显退化.火后植被恢复,特别是火后早期植被的恢复是生态系统功能恢复的前提和基础.本文对火后湿地植被恢复影响因子的国内外研究进展进行了综述.寒温带湿地火后植被恢复受到火强度、火面积、火前植被类型、物种更新特性、立地条件等多因子的制约.寒温带湿地火后恢复的长期监测、植被恢复的关键影响因子、冻土层在植被恢复过程中的作用、植被恢复的理论与技术将是今后研究的重要方向.     

燃烧植物产生烟与热的生理生态效应

燃烧植物产生的烟与热对植物的生理生态功能有重要的影响,相关研究已成为生态学研究的热点之一。植物源烟对一些植物种子的萌发和幼苗生长有促进作用,这种促进作用与GA和细胞分裂素的作用相似。在植物烟水溶液中分离得到了具有促进植物种子萌发作用的化合物丁烯羟酸内酯,该物质具有热稳定性、挥发性和有效浓度范围广等特点。丁烯羟酸内酯可以通过纤维素加热产生,因而几乎所有的植物燃烧产生的烟中都可以产生丁烯羟酸内酯。热因子对植物种子萌发有利作用表现为打破种子休眠、清除限制种子萌发的物理、化学因素和减轻种子病原体等方面。大量研究显示,不同植物对烟与热的响应机理存在显著的差异,这是植物群落过火后物种组成改变的重要原因之一。烟与热因子对植物生理生态作用的研究我国开展较少．这与我国是一个森林、草原火灾频繁的国家是不相称的,加强这方面的研究很有必要。另外,今后我国可以在烟与热因子对植物作用的机理,揭示传统用烟火处理土壤促进农林业植物生长的物理和化学本质,以及这些机理在发展有机农业中运用等方面开展深入的研究。     

固氮类植物在陆地生态系统中的作用研究进展

固氮类植物是陆地生态系统中的一个重要功能群,它们广泛存在于陆地生态系统中,是陆地生态系统最重要的氮源,大量研究表明,固氮类植物在陆地生态系统中的生态功能表现出明显的复杂性和多样性,对于生态过程有很强的主导性和控制性.通过与固氮微生物形成不同的共生固氮类型,它们可以改善土壤结构和营养组成以及地表微生境,直接影响碳氮磷循环、种子萌发和植株生长、植被演替、凋落物构成及其分解4个关键生态过程,进而提高群落结构复杂性、生物多样性和初级生产力,促进植被恢复和减少水土流失.未来研究中,应该加强对陆地生态系统固氮过程的定量化分析,确定影响共生固氮的主导因子和生态机制从而为陆地系统的生态恢复提供依据.     

生物土壤结皮对种子萌发和幼苗建植的影响研究进展

生物土壤结皮（BSC）在陆地生态系统中具有重要的生态地位,尤其是旱地生态系统中,BSC占据了种子植物之间的广阔地面。因此,BSC的发展必然影响种子植物更新过程与植被空间格局;但其作用方式、影响程度等因相关研究涉及多气候要素、土壤类型、BSC组成物种和种子植物物种的差异及其不同组合,导致目前的研究结论存在广泛争议。研究综合论述了BSC改变地表微形态对种子传播过程的影响;BSC改变土壤特性（物理、化学、生物学）对种子萌发和幼苗存活与建植等关键环节的影响;并结合种子形态特征及种子萌发、幼苗建植的性状等,综合分析了BSC对种子传播、种子萌发与幼苗建植等更新过程的潜在影响机理;探讨了目前研究矛盾性结论产生的原因。总体来说,深入研究并全面揭示BSC对种子植物更新过程的影响,应加强学科交叉,将分子生物学、植物生理学、生物化学等微观研究,与遥感、野外生态因子过程监测、控制实验等宏观、中观研究结合,从机理到过程方面动态研究BSC对种子植物更新过程的影响,并引入水文模型、气候模型、种群动态模型等模型预测方法,研究气候变化、各类干扰频发的情景下,BSC对种子传播、萌发及幼苗建植过程的潜在影响,以期促进对BSC与种子植物间相互关系的研究,加深对干旱脆弱生态系统植被发展规律的认识。     

光信号与激素调控种子休眠和萌发研究进展

休眠是种子植物在长期进化过程中产生的适应性性状, 通过抑制种子在不适宜的环境中萌发进而保证植物能够在逆境中生存。此外, 休眠有助于种子的长距离运输和扩散, 因此休眠对种子延续和物种保存具有重要意义。种子由休眠向萌发的发育转变不仅关系到物种的繁衍, 而且对保证农业生产中作物的产量和品质也具有重要作用。种子的休眠和萌发受到内源激素和外源光信号的共同调控。其中, 外源光信号主要通过调控内源ABA和GA的生物合成及信号转导进而调控种子休眠和萌发。该文系统综述了外源光信号和内源激素调控种子休眠和萌发的作用通路以及两类信号通路之间的交互作用, 旨在为农业生产中利用光和激素调控种子休眠与萌发提供参考。     

干旱半干旱荒漠地区一年生植物研究综述

1年生植物是干旱半干旱地区植被的重要组成部分,并以其独有的植物特性成为许多植物生态学关键问题研究的最佳试验材料。本文综述了干旱半干旱地区1年生植物的种子萌发对策、幼苗对环境的适应机制、种子传播和种子库等方面的研究成果,并探讨了影响1年生植物种群、群落组成和动态的生物与非生物因素。基于1年生植物类群在荒漠植被系统中重要的生态功能,有关1年生植物的研究成果将有利于荒漠生态系统的保护和恢复、资源的合理利用以及区域的可持续发展。     

光信号与激素调控种子休眠和萌发研究进展

休眠是种子植物在长期进化过程中产生的适应性性状, 通过抑制种子在不适宜的环境中萌发进而保证植物能够在逆境中生存。此外, 休眠有助于种子的长距离运输和扩散, 因此休眠对种子延续和物种保存具有重要意义。种子由休眠向萌发的发育转变不仅关系到物种的繁衍, 而且对保证农业生产中作物的产量和品质也具有重要作用。种子的休眠和萌发受到内源激素和外源光信号的共同调控。其中, 外源光信号主要通过调控内源ABA和GA的生物合成及信号转导进而调控种子休眠和萌发。该文系统综述了外源光信号和内源激素调控种子休眠和萌发的作用通路以及两类信号通路之间的交互作用, 旨在为农业生产中利用光和激素调控种子休眠与萌发提供参考。     

兴安落叶松(Larix gmelinii)火后种子萌发影响因子

林火干扰是影响兴安落叶松林结构和功能的主要因子之一。兴安落叶松种群火后更新受多种因子的影响,并决定着该群落演替轨迹。通过在大兴安岭呼中自然保护区的火烧迹地内设置原位控制实验,利用增强回归树分析方法,量化研究了落叶松火后恢复初期不同影响因子（温度、有机质层厚度、覆盖度等）对种子萌发的相对重要性。研究结果表明：落叶松火后种子萌发的最主要影响因子为温度,第二影响因子为种源,第三影响因子为草本覆盖度,分别解释了幼苗数量变异的28.51%、22.40%、20.66%;各影响因子的相对重要性在不同地形条件下有明显差异：温度在山坡顶部和阳坡底部占有重要影响,种源在阳坡中部和阴坡中部最为重要,土壤含水量在阴坡底部占有重要地位。同时,去除土壤表面有机质可以显著提高种子萌发数量,去除地面杂草则会使种子萌发数量降低。从研究结果可知,落叶松火后种子萌发在不同地形（环境条件）下的限制因子不同,人工辅助需因地制宜采取相应措施,才能更有效地促进种子萌发与森林恢复。     

基于3PGS-MTCLIM模型模拟根河林区火后植被净初级生产力恢复及其影响因子

林火是大兴安岭林区主要的干扰因子,且对森林生态系统的碳平衡有着重要影响.火干扰强度以及不同地形条件所导致的山地气候差异是影响火后植被净初级生产力恢复过程的主导因素.本研究以内蒙古根河林区为例,使用多时相的Landsat TM遥感数据(2008—2012年)和1980—2010年间的气象资料,结合山地小气候模型MTCLIM与光能利用效率模型3PGS,模拟森林火后植被净初级生产力(NPP)的时空恢复过程,并探讨不同火烧强度和地形因子对NPP恢复进程的影响.结果表明: 3PGS-MTCLIM模型能够较准确地在小尺度范围内模拟NPP的空间分布格局,模拟结果与样地具有较好的对应关系,R²=0.828;3PGS-MTCLIM模型模拟火后NPP下降百分比在43%~80%,相对于火前NPP水平该区域的平均恢复周期大约为10年;火烧强度对火后恢复具有显著影响,火烧强度越强,NPP恢复所需要的周期越长,火后NPP恢复速度呈现先快后慢的增长趋势;地形因子中,海拔对火后NPP恢复程度的影响最明显,其次为坡度,而坡向的影响最小.     

Fire indirectly benefits fitness in two invasive species

Ecosystems perturbed from their natural disturbance regimes are more vulnerable to establishment and dominance of exotic plant species. Restoration efforts that reintroduce fire have achieved mixed success in reducing the abundance of exotic plants. The responses of many native species to fire are well known; fire-adapted species respond directly (heat and smoke cue germination) and indirectly (post-fire environment benefits seedling survivorship and growth) to fire. However, the direct and indirect effects of fire are unknown for most exotic plant species. We tested the direct and indirect effects of fire on two exotic invaders of Asian origin, Ailanthus altissima and Lonicera maackii, in North American woodlands. To quantify the direct effects of fire, we compared germination rates of seeds exposed to varying levels of heat and smoke in a laboratory and placed at different soil depths during a prescribed fire in the field. We examined the indirect effects of fire by comparing seedling recruitment in burned and unburned woodland plots. Results indicate that neither A. altissima nor L. maackii have germination cues associated with fire. However, both species have greater seedling recruitment in burned as compared to unburned areas in the field. Although seeds of these invasive species are not specifically adapted to fire, they still benefit from post-fire environments and pose a challenge to restoration of fire-maintained ecosystems. Future studies using our approach will allow land managers to better predict how communities will respond to restoration efforts and to understand variability observed in past restoration projects.     

Dormancy and the fire-centric focus: germination of three Leucopogon species (Ericaceae) from South-eastern Australia

BACKGROUND AND AIMS: Germination studies of species from fire-prone habitats are often focused on the role that fire plays in breaking dormancy. However, for some plant groups in these habitats, such as the genus Leucopogon (Ericaceae), dormancy of fresh seeds is not broken by fire cues. In the field, these same species display a flush of seedling emergence post-fire. Dormancy and germination mechanisms therefore appear complex and mostly unknown. This study aimed to identify these mechanisms by establishing dormancy class and testing the effects of a set of typical germination cues, including those directly related to fire and entirely independent of fire. METHODS: To classify dormancy, we assessed seed permeability and embryo morphology, and conducted germination experiments at seasonal temperatures in incubators. To test the effects of fire cues on germination, factorial combinations of smoke, heat and dark treatments were applied. Ageing treatments, using burial and seasonal incubation, were also tested. Germination phenology was established. KEY RESULTS: Seeds were dormant at release and had underdeveloped embryos. Primary dormancy of the study species was classified as morphophysiological. Seasonal temperature changes overcame primary dormancy and controlled timing of germination. Fire cues did not break primary dormancy, but there was a trend for smoke to enhance germination once this dormancy was overcome. CONCLUSIONS: Despite the fact that fire is a predominant disturbance and that many species display a flush of emergence post-fire, seasonal temperatures broke the primary physiological dormancy of the study species. It is important to distinguish between fire being responsible for breaking dormancy and solely having a role in enhancing levels of post-fire germination for seeds in which dormancy has been overcome by other factors. Biogeographical evidence suggests that morphological and physiological factors, and therefore seasonal temperatures, are likely to be important in controlling the dormancy and patterns of post-fire germination of many species in fire-prone regions.     

Fire‐related cues and germination from the soil seed bank of senescent remnants of mallee vegetation on Eastern Kangaroo Island

Plant communities dominated by narrow‐leaved mallee (Eucalyptus cneorifolia) are almost entirely confined to north‐eastern Kangaroo Island, South Australia, an area which has been extensively cleared for agriculture. Consequently, surviving examples consist mostly of small remnants which are thought to be senescent due to the exclusion of fire. This senescence is associated with the loss of many native understory species. Prescribed burns have been suggested as a management tool to stimulate the restoration of native plants from the soil seed bank; however, no seed bank studies have previously been conducted on Kangaroo Island and the seed bank literature usually focuses on particular species rather than on plant communities. We conducted an experiment to investigate the effects of the fire‐related cues heat and smoke on the germination of plants from the seed bank in soil sampled from 10 long‐ungrazed narrow‐leaved mallee sites on Kangaroo Island. Eighty trays of soil were monitored in a controlled glasshouse for five months after being subjected to heat and/or smoke treatments. The overall number of native, but not exotic, plant species germinating from the soil seed bank was significantly increased by all three fire‐related treatments (heat, smoke and heat plus smoke) compared with the control (no fire‐related treatment). Different plant life forms exhibited varying responses to heat and smoke treatments. The results of this study illustrate that the application of fire‐related treatments to soil seed banks in controlled glasshouse conditions can stimulate the recruitment of native species, including several species of conservation concern. These findings also indicate the potential of using these treatments for the ex situ germination of fire dependent species for revegetation purposes and indicate aspects of prescribed burns that may be important for restoring different components of native vegetation.     

干扰对动物传播森林植物种子有效性影响的研究进展

干扰在森林生态系统中普遍存在,并影响森林的更新和演替.动物传播种子是种子更新的必经阶段,其对森林干扰的响应在一定程度上能够预测未来的森林群落组成和结构变化,对于明确森林演替方向具有重要意义.本文论述了森林干扰对动物传播种子有效性(包括动物传播种子的数量和质量)影响研究的生态学意义,全面揭示了自然干扰(火干扰、林窗干扰等)和人为干扰(生境破碎化、狩猎、采伐等)对动物传播种子数量、传播距离以及传播后幼苗更新影响的研究进展,指出干扰通过影响动物种群动态,进而造成动物传播种子数量发生了改变,动物传播种子的距离对干扰的响应基本表现出轻微负相关;干扰对传播后幼苗更新的影响结果因干扰类型的不同而复杂多变,干扰迹地环境因子的变化也影响着传播后的种子萌发和幼苗更新.干扰对动物传播种子有效性影响研究中存在的问题,主要表现为火干扰迹地恢复过程、增益性的干扰(如抚育、间伐、林窗)等对种子传播有效性影响研究的匮乏,以及忽略了温带森林内的干扰对动物传播种子的影响等.今后,应开展干扰对种子传播有效性的长期研究;对于干扰多发地带的森林,应高度重视增益性干扰影响动物传播植物种子的研究.     

Are germination cues for soil‐stored seed banks different in structurally different fire‐prone communities?

Many plant species are dependent on soil‐stored seeds for their persistence in fire‐prone systems. Seed germination is often stimulated by fire‐related cues including heat and smoke, but the way these cues promote germination may differ between structurally distinct plant communities with historically different fire regimes. In this study, we examined the effects of heat, smoke and their interactions on the germination of soil‐stored seeds from shrubby woodlands and herbaceous forests in south‐east Australia. The effect of these treatments on species richness, diversity and composition, and species richness and density of germinants within life‐forms (grass, forb and shrub) were assessed. Soils from each community were subjected to low heat (40°C), low heat with smoke, smoke, high heat (80°C), high heat with smoke and untreated (control) before being placed in a glasshouse, where the germinants were identified and counted. Greater species richness was stimulated by high heat treatments and smoke in both communities, a trend driven by shrubs and forbs, rather than grasses. Greater species diversity was stimulated by high heat with smoke in both communities. Greater densities of grass germinants were stimulated by all treatments, except low heat, in both communities. For forbs and shrubs, the effect of treatment depended on community. Compared to the control, low heat with smoke (forbs) and both low heat and low heat with smoke (shrubs) increased densities in the woodland but not in the forest. There were unique species compositions, different from the control, in all treatments in the forest but not in the woodland, where composition in low heat was not different from the control. These results indicate the importance of high soil temperatures and smoke in both communities. In the absence of wildfires, recurring prescribed burns that heat the soil to low temperatures are likely to reduce plant richness, diversity, and density resulting in a change in understorey species composition and structure.     

Combined effects of heat shock, smoke and darkness on germination of Epacris stuartii Stapf., an endangered fire-prone Australian shrub

Epacris stuartii (Epacridaceae) is an endangered heathland shrub in which seedling recruitment occurs almost exclusively after fire. Seed viability and multiple seed dormancy mechanisms were examined to explore why levels of seedling recruitment were low after some fires, despite high rates of pre-fire seed production. The individual and combined effects of heat shock, smoke derivatives and darkness on germination were tested in the laboratory using an orthogonal logit-linear model, a form of analysis ideally suited to hypotheses concerning multiple germination cues. Seed viability (56%) was found not to be limiting. After 89 days of incubation, germination was significantly enhanced by heat shock, smoke treatment and continuous darkness but there were no significant interactions. These effects were equal in magnitude and additive such that maximum germination (42% of viable seeds) was stimulated when all three treatments were combined, significantly less germination occurred in response to any two treatments combined (22–23%), any single treatment stimulated germination at levels (10–11%) significantly less than two treatments and the lowest levels of germination occurred among untreated seeds (4%). Relative to the untreated control, germination was stimulated by smoke derivatives in high concentrations but not in low concentrations. The effect of darkness diminished with time so that after 270 days of incubation darkness had no significant effect on germination, while heat and smoke still enhanced germination significantly, additively and interchangeably. More prolonged germination of seeds exposed to light on the soil surface than buried seed may spread the risk of desiccation of emerging seedlings over multiple rainfall events. The role of heat and smoke derivates suggests that fire management is a crucial tool for influencing seedling recruitment and hence the survival of E. stuartii at its only known location. Received: 3 November 1996 / Accepted: 15 June 1997     

Evidence for direct effects of fire‐cues on germination of some perennial forbs common in grassy ecosystems

In grassy ecosystems of south‐eastern Australia, fire maintains richness of native forbs. It is commonly thought that fire promotes regeneration indirectly by reducing competition for light and providing gaps for recruitment, rather than directly stimulating germination. However, physiological dormancy and morphophysiological dormancy are common, and few studies have explored responses to fire‐cues among dormant or hard‐to‐germinate forbs. Recent studies from other fire‐prone ecosystems suggest that in some cases, fire‐cues may not alleviate physiological or morphophysiological dormancy, but instead promote germination in combination with treatments which alleviate dormancy. We experimentally tested the prevailing hypothesis that perennial forbs common in south‐eastern Australian grassy ecosystems do not germinate in direct response to fire. Responses to fire‐cues both inherently and in combination with treatments which alleviate dormancy were investigated for seven species. Two fire‐cues (smoke and heat) plus a treatment of both heat + smoke were applied to fresh seed at three temperatures (35/25°C, 30/20°C and 25/15°C). Following this, the effect of fire‐cues on seed that had undergone warm stratification, cold stratification and dry‐after‐ripening was investigated. Three species — Arthropodium strictum, Cheiranthera cyanea and Dianella revoluta — responded to fire‐cues inherently, although germination in C. cyanea was low. High germination of D. revoluta was found when fire‐cues were combined with warm stratification. Fire‐cues had no effect on germination of Brunonia australis, Burchardia umbellata and Eryngium ovinum. Germination of Stypandra glauca was zero following all treatment combinations. Our finding that fire‐cues promote germination of three of the seven study species did not provide sufficient evidence to reject the current hypothesis that germination of perennial forbs is not typically promoted by fire‐cues. However, this study highlights the important direct role fire‐cues can play in promoting germination of some perennial forbs both inherently and in combination with treatments used to alleviate physiological dormancy.     

Does Fire Trigger Seed Germination in the Neotropical Savannas? Experimental Tests with Six Cerrado Species

The Cerrado (Brazilian savanna) is a biodiversity hotspot with a history of fire that goes back as far as 10 million years. Fire has influenced the evolution of several aspects of the vegetation, including reproduction and life cycles. This study tested how fire by‐products such as heat and smoke affect the germination of six species common to two Cerrado open physiognomies: wet grasslands and the campo sujo (grassland with scattered shrubs and dwarf trees). We subjected seeds collected in northern Brazil to heat shock and smoke treatments, both separately and combined, using different temperatures, exposure times, and smoke concentrations in aqueous solutions. High temperatures and smoke did not break seed dormancy nor stimulate germination of the Cerrado study species. However, seeds were not killed by high temperatures, indicating that they are fire‐tolerant. Our findings differed from those of other fire‐prone ecosystems (mostly of Mediterranean vegetation), where fire stimulates germination. Moreover, we provide important information regarding germination strategies of non‐woody Cerrado plants, showing the importance of considering the tolerance of seeds to high temperatures when evaluating fire‐related traits in fire‐prone ecosystems.     

Response surfaces for the combined effects of heat shock and smoke on germination of 16 species forming soil seed banks in south‐east Australia

Abstract There is limited understanding of how fire‐related cues such as heat shock and smoke can combine to affect the germination response of seeds from fire‐prone vegetation because combinations of multiple levels of both cues have rarely been investigated. Germination response surfaces were determined for the combination of heat shock and smoke by applying factorial combinations of temperature (up to 100°C) and aerosol smoke (0–20 min) to 16 species that form soil seed banks in the Sydney region of south‐eastern Australia. Duplicate populations of three species were also examined to assess the constancy of a species response surface. Of the 19 populations examined, 16 showed a germination response to both the fire cues, which combined interactively in 14 populations, and independently in two. No population responded only to a single cue; however, seeds of 11 populations responded to heat in the absence of smoke, and nine responded to smoke in the absence of heat. Heat applied in the absence of smoke negatively affected germination in seven populations, either progressively as temperature increased, or above a set temperature. Negative germination responses over part of the temperature range were fully reversed at higher temperatures for unsmoked seeds of four populations (curvilinear heat response). Smoke effects were most frequently positive over all or part of the range of durations used, and when combined with heat frequently fully or partially reversed negative heat effects. Three populations required the obligatory combination of smoke and heat. A novel response to the cues was observed for three species, with smoke reversing negative heat effects at 75°C, being supplanted by a positive heat response of unsmoked seed at 100°C. The response surface for duplicate populations of two of the three species examined was variable. Heat shock and smoke frequently combined to affect germination, in both positive and negative ways. Consequently, to gain an accurate assessment of the response of seeds to fires, an experimental design that samples within the potential response zones of germination cues is essential.