缺水与补水对小麦氮素吸收及土壤残留氮的影响

通过温室培养试验,研究了不同生长期缺水和补充灌水对冬小麦氮素吸收利用和土壤残留的影响．结果表明,在不同生长期缺水及分蘖期补充灌水均能显著降低冬小麦的氮素吸收,增加矿质态氮的土壤残留,土壤残留氮含量介于79．8～113．7mg·kg^-1;越冬、拔节、灌浆期补充灌水可显著提高冬小麦对土壤氮素的吸收能力,不同程度地降低氮素残留,土壤残留氮介于47．2～60．3mg·kg^-1．补充灌水引起的小麦吸氮能力提高与其对氮素的有效利用并不一致．越冬期补水,小麦籽粒吸氮量无显著变化;灌浆期补水,籽粒吸氮量相应提高20．9％;拔节期补水反而使籽粒吸氮量降低19．6％．     

高山林线变化的更新受限机制研究进展

全球林线位置对气候变暖的响应表现为上升、无变化或下降等截然不同趋势,表明影响林线位置及动态的因子十分复杂,除了较普遍认为的低温调控机制外,还存在其它控制林线位置变化的机制。林线向上迁移开始于种子向林线以上的传播及幼苗在林线以上的定居,这些过程中的限制因子均会影响林线的位移,因此研究更新过程及其限制因子对理解高山林线对气候变化的响应具有重要的科学意义。主要从种子和幼苗两个关键阶段综述高山林线森林更新的研究进展。在种子阶段,夏季积温不足导致种子产量和活力下降,风速过低和浓密灌丛限制种子向林线以上传播,近地表的霜冻/水分胁迫和灌木释放的化感物质会阻碍种子在林线以上萌发。在幼苗阶段,除冬季低温外,生长季内较大的温度日振幅和偶然出现的冻害事件也是导致幼苗死亡的重要原因,而低温环境下的强烈光照引起的低温光抑制会显著降低生长季的光合作用;土壤低温、由土壤温度昼夜变化引起的冻举事件、夏季土壤干旱可能会导致幼苗光合作用下降和死亡率上升;积雪太浅会导致生长季早期幼苗水分供应的严重缺乏,但积雪太深会导致幼苗感染真菌的可能性增加;浓密的灌木和草本植物以及植食动物的啃食也会降低林线以上的幼苗存活率。气候变暖对林线幼苗定居的影响复杂且具有很大不确定性,需要进一步研究气候变暖导致的环境因子变化对林线更新各关键阶段的影响。未来气候变暖无疑会导致生长季起始日提前,结束日推迟,这很可能会增加生长季期间尤其是早期的低温冻害事件,对高山林线树种幼苗的存活具有重要影响。在未来研究中,需要找出定义生长季冻害事件的温度阈值,利用长期气象观测数据分析增温背景下生长季早期冻害事件特征的变化趋势,并进一步开展野外模拟增温实验以深刻理解林线树种的种子萌发和幼苗定居与生长季冻害事件的关系,加强对不同地区林线树种的繁殖策略研究,这将有助于人们进一步理解不同区域林线的形成机制并预测未来气候变化条件下林线的动态变化趋势。     

高山林线形成机制及假说的探讨

高山林线作为森林向苔原过渡的敏感带,历来被生态学家视为生态脆弱区、外界干扰信号的放大器和全球变化重要的预警区.20世纪80年代开始,许多研究关注全球变化对高山林线的影响,这一阶段针对林线海拔高度、纬度位置之间的关系及对未来热环境的响应研究已成为众多学者研究的焦点之一.众多学者依据自身研究目的、不同树种出现上限的原因、局部上影响林木的因子间的差异,在区域上对高山林线的形成机制的提出了诸多假说.本文针对这些假说进行了综述和探讨,并就其中不足之处提出质疑,提出今后需要深入研究的几个方向.

Abstract：

As a sensitive transitional zone between forest and tundra, timberline has always been considered by ecologists to be an ecologically fragile zone, an amplifier of outside interference signals, and a global climate change early warning zone. Since the 1980s, many studies have been made on the effects of global climate change on alpine timberline, mainly addressed the re-lationships of the upper limits of timberline with altitude and latitude, and in particular, the re-sponses of timberline location to global warming. Several hypotheses were proposed to examine the timberline formation of various tree species affected by environmental factors. This paper sum-marized these hypotheses, and discussed some potential studies in the future.     

川西高山林线土壤活性碳、氮对短期增温的响应

随着温室效应的加剧,受低温限制的高山林线生态系统对全球气候变暖较为敏感,可能直接影响到植物的生长和土壤碳氮过程.本研究假设气候变暖会改变高山生态系统土壤活性碳氮含量,在四川省理县米亚罗高山生态系统定位站,采用开顶式模拟增温装置(OTC)模拟增温对土壤活性碳、氮的短期影响.分别于2017年4、7和10月,采集OTC以及对照样地(CK)内土壤有机层和矿质土壤层的原状土壤,测定土壤可溶性有机碳(DOC)、土壤微生物生物量碳(MBC)、土壤可溶性有机氮(DON)和土壤微生物生物量氮(MBN)含量.结果表明: 模拟增温使年均气温升高0.88 ℃,土壤有机层和矿质土壤层的年均温度分别提高0.48和0.23 ℃.模拟增温没有显著改变土壤有机质和含水量,但显著提高了矿质土壤层的pH值,同时显著降低了非生长季矿质土壤层的DOC、DON含量;季节变化对两个层次的DOC、DON和MBN含量有极显著影响,而MBC没有明显的季节动态;增温和季节交互作用对矿质土壤层的DOC和DON有显著影响.土壤有机层的MBC、MBN含量显著高于矿质土壤层.土壤活性碳、氮与土壤有机质和含水量呈极显著正相关,MBC、MBN与土壤pH呈极显著正相关,MBN与土壤温度呈显著负相关.     

长白山次生杨桦林优势更新幼苗空间分布及环境解释

为了解长白山次生杨桦林中优势更新幼苗的空间分布及其与环境因子之间的关系,以5.2 hm²（200 m×260 m）固定样地更新幼苗的全面定位调查和环境因子调查本底数据为基础,对样地内个体数量排序前5的优势更新幼苗进行分析。结果表明：在中小距离尺度上,水曲柳（Fraxinus mandshurica）（0-90 m）、色木槭（Acer mono）（0-60 m）、紫椴（Tilia amurensis）（0-60 m、90-150 m）和假色槭（Acer pseudo-sieboldianums）（0-90 m）更新幼苗的空间分布关系为显著正自相关,呈聚集性分布;群落水平上,环境变量和空间变量对5种优势更新幼苗的空间分布变异解释能力为61%,其中,纯粹空间变量的解释度为56%,而纯粹环境变量的解释度不足1%;种群水平上,环境因子对更新幼苗的空间分布有一定影响,其中,水曲柳幼苗的空间分布与土壤有机质、土壤全钾和土壤水分显著相关,色木槭幼苗的空间分布与土壤有机质和土壤全磷显著相关,紫椴幼苗的空间分布与土壤全磷显著相关,假色槭幼苗的空间分布与土壤水分显著相关;簇毛槭（Acer barbinerve）幼苗的空间分布与环境因子未表现出显著的相关性。长白山次生杨桦林中优势更新幼苗多为聚集性分布,环境因子对其分布有一定影响。     

森林幼苗更新对光环境异质性的响应研究进展

在分析森林光环境异质性特点的基础上,从幼苗的光合、热耗散、生物量累积和分配、形态特征、萌发和种群动态等方面综述了国内外在森林幼苗更新对光环境异质性响应的研究进展.从森林物种多样性维持、森林演替和植被恢复角度探讨了幼苗更新对光环境异质性不同响应的生态学意义,并对今后该方面研究提出建议.     

贺州市城乡交错区的生态功能、生态模式与生态建设对策

城乡交错区具有显著的边缘效应,与城市之间在资源上有互补性、生态上有共生性、经济上和发展上有相依性,是城市生态的稳衡器和城市进一步发展的基础。贺州作为生态资源优势明显的全国“多规合一”规划试点市县之一,要用可持续发展和景观生态学理论指导市域城乡交错区的建设, 在系统和整体的层次上构建一系列优化的生态结构模式, 形成绿色林地农田、绿色街道及居住小区为基质, 以特色建筑、基塘、湖泊、街区绿地为镶嵌体, 以道路及其绿化带、河涌、溪流沟渠为廓道, 谐调有序、持续高效的生态景观格局。应采取进一步加强环境教育, 提高公众环境意识, 加强土地利用规划和村镇建设规划, 严格环境管理, 加快推行生态工业和生态农业等一系列对策措施, 确保生态建设目标的实现。     

浙江省木本植物区系特征及其与引种驯化的关系

本文对浙江省木本植物区系特征进行分析,探讨该省木本植物区系与引种驯化的关系,旨在为园林工作者更好地开展引种驯化工作、切实提高引种成功率提供参考。     

中国东北样带土壤氮的分布特征及其对气候变化的响应

根据2001年中国东北样带土壤全氮和有效氮的实测数据,结合CO₂浓度倍增与不同土壤湿度的模拟试验数据,对土壤全氮和有效氮的梯度分布、影响因子分析及其对气候变化的响应进行研究.结果表明,样带土壤表层全氮和有效氮的梯度分布与土壤有机碳的分布基本一致:沿经度呈现东高西低的趋势,局部由于土壤退化而出现低谷.土壤全氮的剖面分布和土壤有机碳相似,而土壤有效氮则有所不同.样带土壤全氮和有效氮与土壤pH、有机碳、全磷、全硫、全锌、土壤活性碳、有效磷、有效钾、有效锰、有效锌、土壤容重、田间持水量、土壤总孔度等因子均呈显著或极显著的相关关系.样带土壤全氮和有效氮与降雨量之间呈极显著的正相关关系(r=0.682,P＜0.001和0.688,P＜0.001).短期培养试验中,CO₂浓度倍增和不同土壤湿度下土壤全氮和有效氮的变异较小(变异系数分别是5.55%和3.84%),但可反映一定的变化趋势.     

长白山云冷杉林幼苗幼树空间分布格局及其更新特征

长白山云冷杉针阔混交林是我国东北主要的森林类型之一,其乔木树种幼苗幼树的结构和动态决定着未来林分的结构和生长动态。在长白山地区设置一块具有代表性的云冷杉针阔混交林幼苗幼树更新样地,统计分析幼苗幼树更新特征,绘制地径结构图、树高结构图及其空间分布图。运用点格局分析中的单变量O-ring统计方法,分析更新树种的空间分布格局;用双变量O-ring统计方法,分析更新树种种间的空间关联性。研究结果表明:(1)更新树种组成有冷杉(Abies nephrolepis)、色木槭(Acer mono)、紫椴(Tilia amurensis)、红皮云杉(Picea koraiensis)、红松(Pinus koraiensis)、蒙古栎(Quercus mongolica)、春榆(Ulmus japonica)7种,其中以冷杉、色木槭为主,更新幼苗幼树的地径近似呈倒J型分布,树高结构近似呈双峰分布;(2)所有更新树种、冷杉、色木槭在小尺度1—10 m的范围内呈聚集分布,随着尺度增加,聚集程度减弱,逐渐趋于均匀分布和随机分布,紫椴、云杉和红松在空间所有尺度上以随机分布为主;(3)更新树种之间的空间关联性在小尺度范围上正关联性比较多,较大尺度范围上负关联性比较多,随着尺度增加,空间关联性减弱。     

Sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change at landscape and local scales

The sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change are increasingly discussed in terms of climate change, often forgetting that climate is only one aspect of environmental variation. As treeline heterogeneity increases from global to regional and smaller scales, assessment of treeline sensitivity at the landscape and local scales requires a more complex approach than at the global scale. The time scale (short‐, medium‐, long‐term) also plays an important role when considering treeline sensitivity. The sensitivity of the treeline to a changing environment varies among different types of treeline. Treelines controlled mainly by orographic influences are not very susceptible to the effects of warming climates. Greatest sensitivity can be expected in anthropogenic treelines after the cessation of human activity. However, tree invasion into former forested areas above the anthropogenic forest limit is controlled by site conditions, and in particular, by microclimates and soils. Apart from changes in tree physiognomy, the spontaneous advance of young growth of forest‐forming tree species into present treeless areas within the treeline ecotone and beyond the tree limit is considered to be the best indicator of treeline sensitivity to environmental change. The sensitivity of climatic treelines to climate warming varies both in the local and regional topographical conditions. Furthermore, treeline history and its after‐effects also play an important role. The sensitivity of treelines to changes in given factors (e.g. winter snow pack, soil moisture, temperature, evaporation, etc.) may vary among areas with differing climatic characteristics. In general, forest will not advance in a closed front but will follow sites that became more favourable to tree establishment under the changed climatic conditions.     

An experimental test of limits to tree establishment in Arctic tundra

1 Five treeline species had low seed germination rates and low survivorship and growth of seedlings when transplanted into Alaskan tundra. Seed germination of all species increased with experimental warming, suggesting that the present treeline may in part result from unsuccessful recruitment under cold conditions.
2 Growth, biomass and survivorship of seedlings of treeline species transplanted into tundra were largely unaffected by experimental warming. However, transplanted seedlings of three species ( Betula papyrifera , Picea glauca and Populus tremuloides ) grew more when below‐ground competition with the extant community was reduced. All three measures of transplant performance were greater in shrub tundra than in the less productive tussock or heath tundra. Establishment of trees in tundra may thus be prevented by low resource availability and competition.
3 Two species ( Alnus crispa and Populus balsamifera ) had low seed germination and survivorship of germinated seeds; transplants of these species did not respond to the manipulations and lost biomass following transplanting into tundra. Isolated populations of these two species north of the present treeline in arctic Alaska probably became established during mid‐Holocene warming rather than in recent times.
4 Of all the species studied here, Picea glauca was the most likely to invade intact upland tundra. Its seeds had the highest germination rates and it was the only species whose seedlings survived subsequently. Furthermore, transplanted seedlings of Picea glauca had relatively high survivorship and positive growth in tundra, especially in treatments that increased air temperature or nutrient availability, two factors likely to increase with climate warming.     

Recent invasion of the mountain birch Betula pubescens ssp. tortuosa above the treeline due to climate change: genetic and ecological study in northern Sweden

Mountain birch, Betula pubescens ssp. tortuosa, forms the treeline in northern Sweden. A recent shift in the range of the species associated with an elevation of the treeline is commonly attributed to climate warming. Using microsatellite markers, we explored the genetic structure of populations along an altitudinal gradient close to the treeline. Low genetic differentiation was found between populations, whereas high genetic diversity was maintained within populations. High level of gene flow compensated for possible losses of genetic diversity at higher elevations and dissipated the founding effect of newly established populations above the treeline. Spatial autocorrelation analysis showed low spatial genetic structure within populations because of extensive gene flow. At the treeline, significant genetic structure within the juvenile age class at small distances did not persist in the adult age class, indicating recent expansion of young recruits due to the warming of the climate. Finally, seedling performance above the treeline was positively correlated with parameters related to temperature. These data confirm the high migration potential of the species in response to fluctuating environmental conditions and indicate that it is now invading higher altitudes due to the recent warming of the climate.     

模拟增温和降水变化对北京东灵山辽东栎种子出苗和幼苗生长的影响

气候变化将增加地表平均气温、改变降水格局, 会影响到种子出苗和幼苗生长, 进而影响物种的更新动态。为探讨增温和降水变化对东灵山地区建群树种辽东栎(Quercus mongolica)种子出苗和一年生幼苗生长和适应状况的影响, 该文利用环境控制生长箱开展了温度和降水量的双因素控制实验, 温度设置3个梯度: 月平均气温(对照)、增温2 ℃和增温6 ℃; 降水量设置3个梯度: 月平均降水量(对照)、减水30%和加水30%。结果表明: 1)辽东栎的种子出苗率和一年生幼苗的生长对增温和降水变化的响应不一致, 种子出苗率主要受到降水及其与温度交互作用的影响, 幼苗生长仅受到温度和降水独立作用的影响; 2)春季增温2 ℃或降水量增加均使辽东栎种子出苗期提前; 增温6 ℃与降水量减少的水热组合延迟了种子出苗期并使其存活率和出苗率显著降低, 但在此温度下增加降水量则增加了出苗速率和出苗率。3)增温2 ℃对其生长无显著影响, 增温6 ℃则在不同水分条件下显著地增加了幼苗的比叶面积、抑制了叶的伸长生长, 同时也显著降低了各器官生物量积累, 并减少了幼苗生物量向根的分配; 降水量减少降低了幼苗根生物量, 但未影响总生物量和根冠比, 降水量增加显著促进了幼苗地上部分的生长, 特别是叶的生长。因此, 适当地增温或增加降水量将增加辽东栎幼苗的更新潜力, 但增温和降水量减少导致的干旱化将显著降低幼苗的更新潜力。     

Regional changes in the elevational distribution of the Alpine Rock Ptarmigan Lagopus muta helvetica in Switzerland

The Alpine Rock Ptarmigan Lagopus muta helvetica is considered to be particularly vulnerable to climate change because it lives exclusively above the treeline in alpine habitats and is adapted to cold climates. Its Swiss population index has decreased over the last two decades. A considerable shrinkage in distributional area is predicted with further climate change. We assess whether the Alpine Rock Ptarmigan has moved to higher elevations in recent years in the Swiss Alps, and whether such elevational shifts have differed between regions and seasons, using observations recorded by volunteers over a 29‐year period. The elevational shifts differed greatly between regions. In the Eastern and Southern Alps, Ptarmigans were increasingly recorded at higher elevations, with a mean uphill shift of 6.4–9.4 m/year over the last three decades, a pattern that could not be explained by the yearly variation in weather conditions, whereas there was only a moderate upward shift (1.5–3.2 m/year) in the Northern Alps and almost no shift in the Western Alps. Elevational changes were generally greater than those observed in other bird species. The observed upward shift in the Eastern and Southern Alps is among the fastest observed in animals and plants, and may be caused by an upward shift of the treeline and reforestation of formerly cut or unforested areas. The observed elevational shift of the distribution of the Alpine Rock Ptarmigan has led to a reduction in the range of this subspecies, which is restricted to the Alps and isolated from other populations.     

Reproduction and seedling establishment of Picea glauca across the northernmost forest‐tundra region in Canada

The northern boundary of boreal forest and the ranges of tree species are expected to shift northward in response to climate warming, which will result in a decrease in the albedo of areas currently covered by tundra vegetation, an increase in terrestrial carbon sequestration, and an alteration of biodiversity in the current Low Arctic. Central to the prediction of forest expansion is an increase in the reproductive capacity and establishment of individual trees. We assessed cone production, seed viability, and transplanted seedling success of Picea glauca (Moench.) Voss. (white spruce) in the early 1990s and again in the late 2000s at four forest stand sites and eight tree island sites (clonal populations beyond present treeline) in the Mackenzie Delta region of the Northwest Territories, Canada. Over the past 20 years, average temperatures in this region have increased by 0.9 °C. This area has the northernmost forest‐tundra ecotone in North America and is one of the few circumpolar regions where the northern limit of conifer trees reaches the Arctic Ocean. We found that cone production and seed viability did not change between the two periods of examination and that both variables decreased northward across the forest‐tundra ecotone. Nevertheless, white spruce individuals at the northern limit of the forest‐tundra ecotone produced viable seeds. Furthermore, transplanted seedlings were able to survive in the northernmost sites for 15 years, but there were no signs of natural regeneration. These results indicate that if climatic conditions continue to ameliorate, reproductive output will likely increase, but seedling establishment and forest expansion within the forest‐tundra of this region is unlikely to occur without the availability of suitable recruitment sites. Processes that affect the availability of recruitment sites are likely to be important elsewhere in the circumpolar ecotone, and should be incorporated into models and predictions of climate change and its effects on the northern forest‐tundra ecotone.