A first Holocene leaf wax isotope-based paleoclimate record from the semi-humid to semi-arid south-eastern Caucasian lowlands

The Holocene paleoclimate of the Caucasus region is rather complex and not yet well understood: while existing studies are mainly based on pollen records from high-altitude and humid lowland regions, no records are available from the semi-humid to semi-arid south-eastern Caucasian lowlands. Therefore, this study investigated compound-specific δ²H and δ¹³C isotopes of leaf wax biomarkers from Holocene floodplain soils in eastern Georgia. Our results show that the leaf wax δ²H signal from the paleosols mostly reflects changes in the moisture source and its isotopic composition. Depleted δ²H values before ~8 cal ka bp change towards enriched values after ~5 cal ka bp and become again depleted after ~1.6 cal ka bp. This trend could be caused by Holocene changes of the isotopic compositions of the Black and eastern Mediterranean Sea, and/or by varying contribution of both moisture sources linked with the North Atlantic Oscillation. The leaf wax δ¹³C signal from the paleosols directly indicates varying local water availability and drought stress. Depleted δ¹³C values before ~8 and after ~5 cal ka bp indicate wetter local conditions with higher water availability, whereas more enriched values during the middle Holocene (~8 until at least 5 cal ka bp ) indicate drier conditions with increased drought stress.     

喀斯特山区先锋植物叶片解剖特征及其生态适应性评价--以贵州花江峡谷区为例

通过研究贵州西南部典型喀斯特植被退化区花江峡谷植被现状,选取具一定经济价值和推广价值的先锋植物,采用生物显微制片技术与数理统计方法相结合,报导了6科10种分属不同生活型的植物叶片的解剖结构特征,并进行了比较和解剖因子分析。结果表明研究区喀斯特先锋植物叶片在不同种类之间具有明显差异,这些差异除受遗传因子控制外,环境因子(主要为光照和水分)也有重要作用;生活型不同对先锋植物叶片特征有一定影响,但未表现出规律性。根据叶片适应特征的差异,10种先锋植物可分为3种类型,即旱生或阳生叶类型的构树(Broussonetia papyrifera)、火棘(pyracantha fortuneana)、刺槐(Robinia pseudoacacia)、白三叶(Trifolium repens);偏中生叶类型(香椿的Toona sirensis)、顶坛花椒(Zanthaxylum pinum var．dingtanensis)、黔滇木蓝(In-digofera esquirolii)、忍冬(Lomicera japonica)、紫云英(Astragalus sinicus);偏阴生叶类型的繁缕(Stellaria media)。     

The replacement of native plants by exotic species may affect the colonization and reproduction of aquatic hyphomycetes

The tropical riparian zone has a high diversity of plant species that produce a wide variety of chemical compounds, which may be released into streams. However, in recent decades there has been an extensive replacement of tropical native vegetation by Eucalyptus monocultures. Our objective was to compare fungal colonization of Eucalyptus camaldulensis leaves with fungal colonization of native plant species from riparian zones in Brazilian Cerrado (savannah) streams. The fungal colonization and enzymatic activity significantly influenced leaf litter decomposition. Fungal sporulation rates from leaf litter varied significantly with leaf species, with E. camaldulensis showing the highest sporulation rate (1226 conidia mg⁻¹AFDM day⁻¹) and leaf mass loss (23.2 ± 0.9%). This species has the lowest lignin content and highest N concentration among the studied species. Among the studied native species, we observed the highest sporulation rate for Protium spruceanum (271 conidia mg⁻¹AFDM day⁻¹), Maprounea guianensis (268 conidia mg⁻¹AFDM day⁻¹) and Copaifera langsdorffii (196 conidia mg⁻¹AFDM day⁻¹). Overall, native plant species of the Brazilian Cerrado exhibited recalcitrant characteristics and a higher lignin:N ratio. Therefore, variations in the physical and chemical characteristics of the leaf litter could explain the higher decay rate and reproductive activity observed for E. camaldulensis. However, the detritus of this species were colonized almost exclusively by Anguillospora filiformis (99.6 ± 0.4%) and exhibited a reduction in aquatic hyphomycetes species diversity. Our results suggest that the disturbance in the composition of riparian vegetation and consequently, in the diversity of leaf litter input into streams, could change the patterns and rates of leaf litter utilization by microbial decomposers. These changes may have important consequences in the processing of organic matter and, consequently, in the functioning of freshwater ecosystems.     

玉米叶面积指数的CHRIS/PROBA数据反演分析

叶面积指数(LAI)是衡量植被生态状况和估算作物产量的一个重要指标。LAI的反演是定量遥感研究的重要内容。传统的经验统计反演方法基于单一观测角度的遥感数据进行,忽略了地物反射率的方向性。若在反演中加入多观测角度的信息,则有可能提升LAI反演的精度。以2008年甘肃省张掖市玉米实验区为研究区,利用欧空局的CHRIS/PROBA多角度高光谱数据对比分析了传统植被指数NDVI、RVI、EVI的变化规律及其反演玉米叶面积指数LAI的精度,并根据NDVI随观测角度的变化规律,构造出新型多角度归一化植被指数MNDVI,分别对实测叶面积指数进行线性回归并利用实测数据对估算LAI进行精度验证,结果表明：新型MNDVI指数相比于传统NDVI、RVI、EVI对LAI的反演精度有了显著提升,估算模型决定系数R²达到0.716,精度验证均方根误差为0.127,平均减小了33.3%。     

Fire severity and surface rock fragments cause patchy distribution of soil water repellency and infiltration rates after burning

Although fire‐induced soil water repellency (SWR) and its effects on soil hydrology and geomorphology have been studied in detail, very few studies have considered the effect of rock fragments resting on the soil surface or partly embedded in soil. In this research, we have studied the effect of rock fragments on the strength and spatial distribution of fire‐induced SWR at different fire severities. A fire‐affected area was selected for this experiment and classified into different zones according to fire severity (unburned, low, moderate and high) and rock fragment cover (low, <20% and high, >60%). During 7 days after fire, SWR and infiltration rates were assessed in the soil surface covered by individual rock fragments and in the midpoint between two adjacent rock fragments (with maximum spacing of 20 cm). SWR increased with fire severity. Rock fragments resting on the soil surface increased the heterogeneity of the spatial distribution of fire‐induced SWR. SWR increased significantly with rock fragment cover in bare areas under moderate and high fire severity, but quantitatively important changes were only observed under high fire severity. In areas with a low rock fragment cover, water repellency from soil surfaces covered by rock fragments increased relative to bare soil surfaces, with increasing SWR. In areas with a high rock fragment cover, SWR increased significantly from non‐covered to covered soil surfaces only after low‐severity burning. Rock fragment cover did not affect infiltration rates, although it decreased significantly in soil surfaces after high‐severity burning in areas under low and high rock fragment cover. Copyright © 2013 John Wiley & Sons, Ltd.     

黄土高原旱作区马铃薯叶片和土壤水势对垄沟微集雨的响应特征

于2011年在黄土高原半干旱地区以平地不覆膜为对照,研究了不同沟垄和覆膜方式对马铃薯叶片和土壤水势水势的影响。结果表明：不同沟垄和覆膜方式在不同土层和不同生育期对土壤和叶片水势的影响差异显著。（1）土壤水势日变化趋势：0～20 cm土层,土垄处理在开花期为先下降后上升型,土垄和覆膜垄处理在块茎膨大期为先下降后上升型,覆膜垄和全膜双垄沟播处理在成熟期为先下降后上升型,其余为逐渐下降型;20～40 cm土层,各处理土壤水势呈逐渐下降趋势。（2）叶片水势日变化趋势：开花期和块茎膨大期表现为双低谷型,双低谷分别在13：00和17：00,成熟期为“V”型,即单低谷型,低谷出现在17：00。各处理变化趋势相同,但水势存在差异。土垄处理在水分关键期（开花期和块茎膨大期）叶片水势显著高于其他处理,而全膜双垄沟播处理在成熟期最高。（3）生育期土壤水势和叶片水势均表现为先减小后增大的趋势。20～40 cm土层对叶片水势影响较大,土垄处理在该土层具有较好的水分状态,蒸腾作用较强加速了水分运移速率,是导致覆膜垄和全膜双垄沟播处理水势低于土垄的主要原因。在前期降雨较少的年份,由于较小的蒸腾作用,土垄处理可以保证马铃薯承受较小的水分胁迫;在前期降雨量较多的年份,覆膜垄和全膜双垄沟播处理则可以凭借其较大的蒸腾作用发挥较大的增产效果。     

关于新疆准噶尔盆地中侏罗世奥勃鲁契夫银杏(Ginkgo obrutschewii Seward)叶表皮构造的讨论

通过对新疆准噶尔盆地白杨河地区中侏罗世奥勃鲁契夫银杏(Ginkgo obrutschewii Seward)模式产地及其邻区该种叶化石表皮构造的研究,笔者认为应以采自白杨河模式产地的化石材料作为认定该种主要特征的依据。尽管G.obrutschewii的外部形态和叶表皮构造可能具有一些变异特征,但综合而言,该种叶表皮构造主要特征似应为:表皮气孔器特征通常为下气孔式,上下表皮细胞均普遍发育强度不同的角质化丘状或低缓的乳状突起,垂周壁略直或微弯;气孔器单唇式,保卫细胞近孔缝处唇状加厚强烈,副卫细胞通常强烈角质化,表面常发育瘤状或团块状角质化加厚。目前对该种叶化石的采集及其表皮构造的研究尚不充分,相关研究有待进一步深入。近年来,俄罗斯学者归于本种的产于新疆福海的银杏叶片化石,及其对本种叶表皮构造特征的补充等,尚值得商榷。     

A dynamic relationship between the leaf phenology and rainfall regimes of Hawaiian tropical ecosystems: A remote sensing approach

Hypertemporal MODIS time series data provide a unique opportunity to investigate a dynamic relationship between leaf phenology and the climatic pattern of diverse, cloud‐prone Hawaiian ecosystems. Harmonic analysis summarized the complex greenness signals of Hawaiian tropical ecosystems into two main phenological wave forms – a moisture‐limited and a light‐limited type. Greenness maximums occurred during the wet season in dry and mesic ecosystems, and during the dry season in wet forests. The magnitude and periodicity of greenness fluctuations were also rainfall‐dependent. The annual greenness amplitude increased with increasing mean annual precipitation (MAP) in dry and mesic ecosystems. In wetter environments where MAP was greater than 3000 mm, however, annual greenness amplitude decreased with MAP. Annual greenness periodicity was stronger in drylands than in wet forests, and it weakened as annual precipitation increased. This result shows that rainfall is less important as a limiting factor in wet forests than it is in drylands. Therefore, leaf phenology is not governed by rainfall seasonality as forest wetness increases in the region.     

Latitudinal variation of leaf morphological traits from species to communities along a forest transect in eastern China

Comprehensive information on geographic patterns of leaf morphological traits in Chinese forests is still scarce. To explore the spatial patterns of leaf traits, we investigated leaf area (LA), leaf thickness (LT), specific leaf area (SLA), and leaf dry matter content (LDMC) across 847 species from nine typical forests along the North-South Transect of Eastern China (NSTEC) between July and August 2013, and also calculated the community weighted means (CWM) of leaf traits by determining the relative dominance of each species. Our results showed that, for all species, the means (± SE) of LA, LT, SLA, and LDMC were 2860.01 ± 135.37 mm², 0.17 ± 0.003 mm, 20.15 ± 0.43 m² kg^–1, and 316.73 ± 3.81 mg g^–1, respectively. Furthermore, latitudinal variation in leaf traits differed at the species and community levels. Generally, at the species level, SLA increased and LDMC decreased as latitude increased, whereas no clear latitudinal trends among LA or LT were found, which could be the result of shifts in plant functional types. When scaling up to the community level, more significant spatial patterns of leaf traits were observed (R ² = 0.46–0.71), driven by climate and soil N content. These results provided synthetic data compilation and analyses to better parameterize complex ecological models in the future, and emphasized the importance of scaling-up when studying the biogeographic patterns of plant traits.