Spring phenology rather than climate dominates the trends in peak of growing season in the Northern Hemisphere

Shifts in plant phenology regulate ecosystem structure and function, which feeds back to the climate system. However, drivers for the peak of growing season (POS) in seasonal dynamics of terrestrial ecosystems remain unclear. Here, spatial–temporal patterns of POS dynamics were analyzed by solar-induced chlorophyll fluorescence (SIF) and vegetation index in the Northern Hemisphere over the past two decades from 2001 to 2020. Overall, a slow advanced POS was observed in the Northern Hemisphere, while a delayed POS distributed mainly in northeastern North America. Trends of POS were driven by the start of growing season (SOS) rather than pre-POS climate both at hemisphere and biome scale. The effect of SOS on the trends in POS was the strongest in shrublands while the weakest in evergreen broad-leaved forest. These findings highlight the crucial role of biological rhythms rather than climatic factors in exploring seasonal carbon dynamics and global carbon balance.     

扬子地台西南缘早石炭世早期有孔虫化石带

扬子地台西南缘是早石炭世有孔虫动物群主要发育地区之一。本文通过滇东沾益、黔南独山、桂北罗城、环江、桂林、阳朔及灵川等10条剖面系统研究,首次从泥盆系顶部至维宪统底部建立了Quasiendothyra带,Bisphaera带,Chernyshinella带,Nodochernyshinella带(进而又分为N.tumulosa亚带和S pinotournayellina亚带）,Tuberendothyra带,Spinoendothyra带(分为Paradainella亚带和Psudodainella亚带Dainella带,Globoendothyra带,Palaeopaastaffella带及Eoparastaffella带等10个带和4个亚带,对每个带（及亚带）进行了有孔虫动物群详细分析。本文阐述了以N.tumulosa为代表的节结状次生沉积物有孔虫类出现,是早石炭早期有孔虫演化的一个重要阶段。通过Spinotournayellina,原始的tuberendothyrid,进化的tuberendothyrid至Spinoendothyra的出现。结合其它节结状和无节结状有孔虫层序特征详细分析了Tn2b-Tn3a间隔的有孔虫类一次次更新、演替关系,本文描述Spinotournayellina,Palaeospinoendothyra,Pseudoinflatoendothyra及Pseudodainella等4个新属及它们的模式种,简述了这些分类单位宏演化关系。对沿袭了半个世纪的岩关阶涵义作了修正,正限即为石炭系底界,始于Bisphaera带底界,上限止于Eoparastaffella带底界,并扼要地阐述了与西欧狄南盆地,北美同期地层对比关系。     

Effect of soil water stress on soil respiration and its temperature sensitivity in an 18-year-old temperate Douglas-fir stand

We analyzed 17 months (August 2005 to December 2006) of continuous measurements of soil CO₂ efflux or soil respiration (R_S) in an 18‐year‐old west‐coast temperate Douglas‐fir stand that experienced somewhat greater than normal summertime water deficit. For soil water content at the 4 cm depth (θ) > 0.11 m³ m^?3 (corresponding to a soil water matric potential of ?2 MPa), R_S was positively correlated to soil temperature at the 2 cm depth (T_S). Below this value of θ, however, R_S was largely decoupled from T_S, and evapotranspiration, ecosystem respiration and gross primary productivity (GPP) began to decrease, dropping to about half of their maximum values when θ reached 0.07 m³ m^?3. Soil water deficit substantially reduced R_S sensitivity to temperature resulting in a Q₁₀ significantly < 2. The absolute temperature sensitivity of R_S (i.e. dR_S/dT_S) increased with θ up to 0.15 m³ m^?3, above which it slowly declined. The value of dR_S/dT_S was nearly 0 for θ < 0.08 m³ m^?3, thereby confirming that R_S was largely unaffected by temperature under soil water stress conditions. Despite the possible effects of seasonality of photosynthesis, root activity and litterfall on R_S, the observed decrease in its temperature sensitivity at low θ was consistent with the reduction in substrate availability due to a decrease in (a) microbial mobility, and diffusion of substrates and extracellular enzymes, and (b) the fraction of substrate that can react at high T_S, which is associated with low θ. We found that an exponential (van't Hoff type) model with Q₁₀ and R₁₀ dependent on only θ explained 92% of the variance in half‐hourly values of R_S, including the period with soil water stress conditions. We hypothesize that relating Q₁₀ and R₁₀ to θ not only accounted for the effects of T_S on R_S and its temperature sensitivity but also accounted for the seasonality of biotic (photosynthesis, root activity, and litterfall) and abiotic (soil moisture and temperature) controls and their interactions.     

Electron microscope studies of Fasciola hepatica. 13. Fine structure of newly excysted juvenile

The gross morphology and fine structure of the newly excysted juvenile fluke are described. The tegument is organized as in the adult, with a spine-containing surface syncytium connected to a perinuclear region lying below the muscle layers. It differs from the adult, however, in having only one type of perinuclear region and one type of secretory body. The digestive system has all the morphological characteristics of a secretory epithelium, rather than an absorptive one. It has numerous dense secretory bodies, ribosomes, and GER, an irregular apical surface due to eccrine secretion, and a lumen filled with a moderately dense material derived from the dispersed secretory granules.The excretory system closely resembles that of the adult, but has, in addition, part of its ascending ducts ciliated and concretions as well as lipid droplets as visible excretory products. The muscle is identical with that of the adult and the parenchyma is also very similar to the adult, although it has more lipid droplets and is associated in a less complex way with cells of other organ systems. Groups of embryonic cells are present and are characterized by a dense, invaginated nucleus surrounded by a very thin layer of cytoplasm.     

Canopy photosynthetic production in a Japanese larch stand. I. Seasonal and vertical changes of leaf characteristics along the light gradient in a canopy

In an 18 year old Japanese larch stand, leaf characteristics such as area, weight, gross photosynthetic rate and respiration rate were studied in order to obtain basic information on estimating canopy photosynthesis and respiration. The leaf growth courses in area and weight from bud opening were approximated by simple logistic curves. The growth coefficient for the area growth curve was 0.155–0.175 day⁻¹, while that for the weight growth was 0.112–0.117 day⁻¹. The larger growth coefficient in area growth caused the seasonal change in specific leaf area (SLA) that increased after bud opening to its peak early in May at almost 300 cm² g⁻¹ and then decreased until it leveled off at about 140 cm²g⁻¹. The change inSLA indicates the possibility that leaf area growth precedes leaf thickness growth. The relationship between the coefficientsa andb of the gross photosynthetic rate (p)-light flux density (1) curve (p=bI/(1+aI)) and the mean relative light flux density (I′/I ₀) at each canopy height were approximated by hyperbolic formulae:a=A/(I′/I ₀)+B andb=C/(I′/I ₀)+D. Leaf respiration rate was also increased with increasingI′/I ₀. Seasonal change of gross photosynthetic rate and leaf respiration rate were related to mean air temperature through linear regression on semilogarithmic co-ordinates.     

Ecosystem functions in natural and anthropogenic ecosystems across the East African coastal forest landscape

Habitat identity and landscape configuration significantly shape species communities and affect ecosystem functions. The conservation of natural ecosystems is of particular relevance in regions where landscapes have already been largely transformed into farmland and where habitats suffer under resource exploitation. The spillover of ecosystem functions from natural ecosystems into farmland may positively influence agricultural productivity and human livelihood quality. We measured three proxies of ecosystem functioning: Pollinator diversity (using pan traps), seed dispersal (with a seed removal experiment), and predation (using dummy caterpillars). We assessed these ecosystem functions in three forest types of the East African dry coastal forest (Brachystegia forest, Cynometra forest, and mixed forest), as well as in adjoining farmland and in plantations of exotic trees (Eucalyptus mainly). We measured ecosystem functions at 20 plots for each habitat type, and along gradients ranging from the forest into farmland. We also recorded various environmental parameters for each study plot. We did not find significant differences of ecosystem functions when combining all proxies assessed, neither among the three natural forest types, nor between natural forest and plantations. However, we found trends for single ecosystem functions. We identified highest pollinator diversity along the forest margin and in farmlands. Vegetation cover and blossom density affected the level of predation positively. Based on our findings, we suggest that flowering gardens around housings and woodlots across farmland areas support ecosystem functioning and thus improve human livelihood quality. We conclude that levels of overall ecosystem functions are affected by entire landscapes, and high landscape heterogeneity, as found in our case, might blur potential negative effects and trends arising from habitat destruction and degradation.