六盘山主要植被类型冠层截留特征

通过野外观测和模型模拟,研究了六盘山主要森林类型的冠层截留量、冠层截留容量和冠层截留模拟参数的变化.结果表明：六盘山主要森林类型的冠层截留率在8.59%～17.94%,穿透降雨率超过80%,树干茎流率在0.23%～3.10%;冠层截留容量在0.78～1.84 mm,其中叶截留容量在0.62～1.63 mm,枝干截留容量在0.13～0.29 mm,且针叶林的冠层截留容量高于阔叶林.考虑冠层叶面积指数的冠层截留改进模型较原有模型具有更好的模拟精度, 其中,研究区红桦林、华山松林、李灌丛和辽东栎-少脉椴混交林的模拟效果较好,辽东栎林、油松林和华西四蕊槭 石枣子灌丛模拟效果相对较差,这可能与冠层结构、叶面积指数以及降水特性等差异有关.     

土壤增温、隔离降水及其交互作用对杉木幼苗细根生产的影响

为了揭示我国最重要的人工林树种杉木对全球变暖和降水格局改变的地下响应及其适应性,在福建省三明市陈大国有林场开展杉木(Cunninghamia lanceolata)幼苗土壤增温和隔离降水双因子试验,包括对照(CK)、土壤增温5℃(W)、隔离降水50%(P)和土壤增温+隔离降水(WP)4个处理,用微根管法探讨试验1a期间土壤增温、隔离降水及其交互作用对杉木幼苗细根生产量(以细根出生数量表征)的影响。双因素方差分析发现,土壤增温和隔离降水对细根总出生数量没有影响,但两者的交互作用则极显著。与CK相比,W细根总出生数量显著增加,而WP处理细根总出生数量则显著低于W处理和P处理。土壤增温、隔离降水与季节的重复测量方差分析发现,土壤增温×季节、隔离降水×季节对细根出生数量均有显著影响;与CK相比,W处理春季细根出生数量显著增加,P处理秋季细根出生数量显著增加,而WP处理夏季和冬季细根出生数量显著下降。土壤增温、隔离降水与径级的三因素方差分析表明,土壤增温×隔离降水×径级存在显著影响;0—1 mm径级细根出生数量W处理显著高于CK,但WP处理则显著低于W处理和P处理。土壤增温、隔离降水与土层的3因素方差分析表明,土壤增温、隔离降水与土层之间不存在显著的交互作用;仅在20—40 cm土层发现P处理细根出生数量显著高于CK。研究结果表明,土壤增温和隔离降水对杉木幼苗细根生产的影响存在显著的交互作用,这种交互作用还因不同的季节和径级而异。     

1982-2012年中亚地区植被时空变化特征及其与气候变化的相关分析

干旱区植被生态系统对气候变化极为敏感,并且干旱区的植被变化研究对全球碳循环具有重要意义。然而近几十年来,中亚干旱区植被对气候变化的响应机制尚不甚明朗。利用归一化植被指数NDVI数据集和MERRA（Modern-Era Retrospective Analysis for Research and Applications）气象数据,采用经验正交函数（EOF,Empirical Orthogonal Function）和最小二乘法等方法系统分析了31a（1982-2012年）来中亚地区NDVI在不同时间尺度的时空变化特征。进一步分析和研究NDVI与气温和降水的相关性,结果表明：1982-2012年,中亚地区年NDVI总体呈现缓慢增长趋势,而1994年以后年NDVI呈现明显下降趋势,尤其在哈萨克斯坦北部草原地区下降趋势尤为突出。这可能是由于过去30年间,中亚地区降水累计量的持续减少造成的。NDVI的季节变化表明春季NDVI增长最为明显,冬季则显著下降。与平原区相比,中亚山区的NDVI值增长幅度最大,并且山区年NDVI与季节NDVI呈现显著增加趋势（P < 0.05）。中亚地区年NDVI与年降水量正相关,而年NDVI与气温变化存在弱负相关。年NDVI和气温的正相关中心在中亚南部地区,负相关中心则出现在哈萨克斯坦的西部和北部地区;NDVI和降水的相关性中心刚好与气温相反。此外,在近30年间的每年6月至9月,中亚地区NDVI与气温存在近一个月的时间延迟现象。本研究为中亚干旱区生态系统变化和中亚地区碳循环的估算提供科学依据。     

不同降水年型下长期施肥旱地小麦产量效应

以黄土高原30年长期肥料定位试验为基础,依据降水将生育年划分为干旱年、平水年和丰水年,研究不同施肥方式对黄土高原冬小麦产量、肥料贡献率和降水利用率的影响.结果表明: 小麦连续种植30年中,氮磷配施和氮磷钾配施下小麦产量、肥料贡献率和降水利用率显著高于不施肥和单施肥处理,氮磷钾配施下小麦产量、肥料贡献率和降水利用率分别达到3480 kg·hm^-2、61.45 kg·kg^-1、6.13 kg·mm^-1·hm^-2;不同降水年型下,丰水年小麦产量、肥料贡献率和降水利用率相对较高;使用逐步回归分析可知,不同降水年型下小麦产量主要受氮磷肥施用量、休闲期降水和越冬期降水影响.黄土旱塬可以通过提高氮磷用量同时适当施用钾肥,以及在休闲期做好蓄水保墒工作来提高小麦产量.     

北京山区侧柏-荆条系统水分来源对降雨事件的响应

分析了北京鹫峰山区侧柏、荆条枝条水及其潜在水分来源的氢氧同位素特征,运用IsoSource模型解析侧柏、荆条系统水分利用来源的季节变化及其对降雨事件的响应.结果表明:旱季初期(4月)研究区0～20 cm土层富集土壤水¹⁸O值,20 cm以下该值则随着土层深度增加逐渐减小,侧柏主要利用前2～3 d降雨补充的0～30 cm层土壤水;旱季末期(6月)侧柏和荆条分别利用当天雨水补充的0～10和10～30 cm层土壤水;雨季(7月)侧柏利用前期降水补给的0～40 cm层土壤水(59.3%)和近期降水(12.5%),荆条则利用近期降雨供给的0～30 cm层土壤水;侧柏的土壤水分来源逐月加深,至生长季末(11月)其主要利用60～80 cm层土壤水(前2～3 d降雨补给),而荆条枝条水δ¹⁸O值远离各水分来源δ¹⁸O值.两物种对水分的竞争压力小,适应本区域气候特征,尤其在应对特大暴雨等极端天气时,植物系统垂直分布的水分来源能够有效分流洪峰,减小暴雨瞬时破坏力.     

State-of-the-Art Review of Biocementation by Microbially Induced Calcite Precipitation (MICP) for Soil Stabilization

Biocementation is a recently developed new branch in geotechnical engineering that deals with the application of microbiological activity to improve the engineering properties of soils. One of the most commonly adopted processes to achieve soil biocementation is through microbially induced calcite precipitation (MICP). This technique utilizes the metabolic pathways of bacteria to form calcite (CaCO₃) that binds the soil particles together, leading to increased soil strength and stiffness. This paper presents a review of the use of MICP for soil improvement and discusses the treatment process including the primary components involved and major affecting factors. Envisioned applications, potential advantages and limitations of MICP for soil improvement are also presented and discussed. Finally, the primary challenges that lay ahead for the future research (i.e. treatment optimization, upscaling for in situ implementation and self-healing of biotreated soils) are briefly discussed.     

Climate change and nesting behaviour in vertebrates: a review of the ecological threats and potential for adaptive responses

Nest building is a taxonomically widespread and diverse trait that allows animals to alter local environments to create optimal conditions for offspring development. However, there is growing evidence that climate change is adversely affecting nest‐building in animals directly, for example via sea‐level rises that flood nests, reduced availability of building materials, and suboptimal sex allocation in species exhibiting temperature‐dependent sex determination. Climate change is also affecting nesting species indirectly, via range shifts into suboptimal nesting areas, reduced quality of nest‐building environments, and changes in interactions with nest predators and parasites. The ability of animals to adapt to sustained and rapid environmental change is crucial for the long‐term persistence of many species. Many animals are known to be capable of adjusting nesting behaviour adaptively across environmental gradients and in line with seasonal changes, and this existing plasticity potentially facilitates adaptation to anthropogenic climate change. However, whilst alterations in nesting phenology, site selection and design may facilitate short‐term adaptations, the ability of nest‐building animals to adapt over longer timescales is likely to be influenced by the heritable basis of such behaviour. We urgently need to understand how the behaviour and ecology of nest‐building in animals is affected by climate change, and particularly how altered patterns of nesting behaviour affect individual fitness and population persistence. We begin our review by summarising how predictable variation in environmental conditions influences nest‐building animals, before highlighting the ecological threats facing nest‐building animals experiencing anthropogenic climate change and examining the potential for changes in nest location and/or design to provide adaptive short‐ and long‐term responses to changing environmental conditions. We end by identifying areas that we believe warrant the most urgent attention for further research.     

Giant tortoise habitats under increasing drought conditions on Aldabra Atoll—Ecological indicators to monitor rainfall anomalies and related vegetation activity

Aldabra Atoll has the largest population of giant tortoises (Aldabrachelys gigantea) in the world. As such an important biological resource, it is necessary to understand how the effects of climate change will impact this keystone species; in particular the frequency of drought, which is likely to affect tortoise habitat. To assess whether drought frequency has changed over the last 50 years on Aldabra, we calculated the standardized precipitation index (SPI) to identify drought periods using monthly rainfall data collected during 1969–2013. We found that drought frequency has increased to more than six drought months per year today compared with about two months per year in the 1970s (t = 2.884, p = 0.006). We used MODIS normalized difference vegetation index (NDVI) as a proxy for vegetation activity, to determine how vegetation has responded to the changing drought frequency between 2000 and 2013. We found that Aldabra’s vegetation is highly responsive to changes in rainfall: anomalies in long-term mean monthly NDVI across Aldabra were found to decrease below the mean during most drought periods and increase above the mean during most non-drought periods. To investigate the response of tortoise habitat to rainfall, we extracted mean NDVI anomalies for three key habitat types. Open mixed scrub and grasslands, the preferred habitat of tortoises, showed the greatest decrease in vegetation activity during drought periods, and the greatest increase in average greenness during non-drought periods. Recent analysis has shown vegetation changes on Aldabra in recent decades. If these changes are caused by decreased precipitation, then the increased frequency of drought could impact the tortoise population, in both the short and long term, by limiting the quality and quantity of forage and/or shade availability within favoured habitats, and by changing the habitat composition across the atoll.     

High resolution methylation analysis of the HoxA5 regulatory region in different somatic tissues of laboratory mouse during development

Homeobox genes encode a group of DNA binding regulatory proteins whose key function occurs in the spatial-temporal organization of genome during embryonic development and differentiation. The role of these Hox genes during ontogenesis makes it an important model for research. HoxA5 is a member of Hox gene family playing a central role during axial body patterning and morphogenesis. DNA modification studies have shown that the function of Hox genes is partly governed by the methylation-mediated gene expression regulation. Therefore the study aimed to investigate the role of epigenetic events in regulation of tissue-specific expression pattern of HoxA5 gene during mammalian development. The methodology adopted were sodium bisulfite genomic DNA sequencing, quantitative real-time PCR and chromatin-immunoprecipitation (ChIP). Methylation profiling of HoxA5 gene promoter shows higher methylation in adult as compared to fetus in various somatic tissues of mouse being highest in adult spleen. However q-PCR results show higher expression during fetal stages being highest in fetal intestine followed by brain, liver and spleen. These results clearly indicate a strict correlation between DNA methylation and tissue-specific gene expression. The findings of chromatin-immunoprecipitation (ChIP) have also reinforced that epigenetic event like DNA methylation plays important role in the regulation of tissue specific expression of HoxA5.