Vegetation succession on the dunes near Oostvoorne,The Netherlands,since 1934, interpreted from air photographs and vegetation maps

The vegetation succession on the dunes near Oostvoorne, The Netherlands has been followed by means of a novel combination of repeated large-scale vegetation mapping and air photograph interpretation. Vegetation units have been discerned on the formation level because these could be distinguished fairly easily on the photographs and because the rates of change are appropriate to the time interval chosen. Nineteen formations were distinguished. Five 1:6250 maps were constructed, reflecting the formation pattern in 1934, 1943, 1959, 1972 and 1980. An overlay with 2736 grid points at 25 m field distance was used to quantify changes in the formation pattern.The results suggest a pronounced multiple pathway succession with nevertheless three principal trajectories of succession from pioneer to woodland vegetation. The outer dunes, which have originated since 1910, are distinct in successional characteristics from the inner dunes, which already existed but were released from heavy grazing pressure in 1910. The rate of change in the outer dunes was high in the beginning and is slowly decreasing eversince. In the inner dunes it went the other way around. Through visual extrapolation the likely formation patterns in 1910 and in 2000 were estimated.Transition frequencies proved highly variable for most formations. Moreover, strong spatial dependence was found. Limitations in the use of Markov models in cases of long-term succession in heterogeneous environments are discussed.Nomenclature follows the same sources as in van der Maarel et al. (1984).Field work carried out 1980–1981 when the authors were at the Division of Geobotany, University of Nijmegen. We thank Jos Rijntjes, Nijmegen, for his cooperation in the field. Vegetation maps were prepared and calculations performed at Uppsala. We thank the Foundation Het Zuid-Hollands Landschap, Rotterdam, for providing facilities and a grant for fieldwork as well as additional means to reproduce the vegetation maps. Two reviewers gave useful comments.     

Oomycetes along a 120,000 year temperate rainforest ecosystem development chronosequence

The occurrence of plant-associated oomycetes in natural ecosystems and particularly during long-term ecosystem development is largely unknown. Using DNA sequencing, we investigated the frequency and host relationships of plant-root-associated oomycete communities along a 120 000 y glacial chronosequence, comprising site ages with rapid compositional change (“early succession”; 5–70 y old soil); relatively stable higher-diversity sites (“mature”, 280–12000 y); and ancient, nutrient-limited soils with declining plant biomass and stature (“retrogression”, 60 000, 120 000 y). Plant-associated oomycetes were frequent in early successional sites, occurring in 38–65% of plant roots, but rare (mean 3%) in all older ecosystems. Oomycete OTUs occurred non-randomly with plant host species, and were more frequent on those plant species that declined most strongly in abundance between ecosystem ages. While oomycetes were common in early succession, their absence in older sites suggests a limited role in later stages of ecosystem development.     

Rapid development of phosphorus limitation in temperate rainforest along the Franz Josef soil chronosequence

The aim of this study was to examine how shifts in soil nutrient availability along a soil chronosequence affected temperate rainforest vegetation. Soil nutrient availability, woody plant diversity, composition and structure, and woody species leaf and litter nutrient concentrations were quantified along the sequence through ecosystem progression and retrogression. In this super-wet, high leaching environment, the chronosequence exhibited rapid soil development and decline within 120,000 years. There were strong gradients of soil pH, N, P and C, and these had a profound effect on vegetation. N:P_leaf increased along the chronosequence as vegetation shifted from being N- to P- limited. However, high N:P_leaf ratios, which indicate P-limitation, were obtained on soils with both high and low soil P availability. This was because the high N-inputs from an N-fixing shrub caused vegetation to be P-limited in spite of high soil P availability. Woody species nutrient resorption increased with site age, as availability of N and P declined. Soil P declined 8-fold along the sequence and P resorption proficiency decreased from 0.07 to 0.01%, correspondingly. N resorption proficiency decreased from 1.54 to 0.26%, corresponding to shifts in mineralisable N. Woody plant species richness, vegetation cover and tree height increased through ecosystem progression and then declined. During retrogression, the forest became shorter, more open and less diverse, and there were compositional shifts towards stress-tolerant species. Conifers (of the Podocarpaceae) were the only group to increase in richness along the sequence. Conifers maintained a lower N:P_leaf than other groups, suggesting superior acquisition of P on poor soils. In conclusion, there was evidence that P limitation and retrogressive forests developed on old soils, but N limitation on very young soils was not apparent because of inputs from an abundant N-fixing shrub.Electronic Supplementary Material Supplementary material is available in the online version of this article at .     

半椎板切除全椎管减压治疗退行性腰椎管狭窄症的效果观察

目的:探讨半椎板切除全椎管减压治疗退行性腰椎管狭窄症的手术效果。方法:2005年7月-2009年6月手术治疗退行性腰椎管狭窄症的患者162例,均行半椎板切除全椎管减压结合椎弓根内固定及后外侧植骨融合术。结果:随访6～24个月,平均10.5个月,术后JOA评分由术前的(15.26±5.26)分提高到术后的(21.38±5.16)分(配对t检验P<0.05)。结论:行半椎板切除全椎管减压结合椎弓根内固定及后外侧植骨融合手术治疗腰椎管狭窄症既可以起到椎管彻底减压的目的,又可以尽可能保留脊柱后柱结构的稳定性及完整性。     

半椎板切除全椎管减压治疗退行性腰椎管狭窄症的效果观察

目的：探讨半椎板切除全椎管减压治疗退行性腰椎管狭窄症的手术效果。方法：2005年7月．2009年6月手术治疗退行性腰椎管狭窄症的患者162例,均行半椎板切除全椎管减压结合椎弓根内固定及后外侧植骨融合术。结果：随访6～24个月,平均10．5个月,术后JOA评分由术前的（15．26±5．26）分提高到术后的（21．38±5．16）分（配对t检验P〈0．05）。结论：行半椎板切除全椎管减压结合椎弓根内固定及后外侧植骨融合手术治疗腰椎管狭窄症既可以起到椎管彻底减压的目的,又可以尽可能保留脊柱后柱结构的稳定性及完整性。     

开放式空气CO2浓度增高对水稻颖花分化和退化的影响

在大田栽培条件下 ,研究开放式空气CO2 浓度增加 (FACE) 2 0 0 μmol·mol-1的处理对水稻每穗 1、2次枝梗及其颖花的分化数、退化数、现存数及退化率的影响 .结果表明 ,FACE处理对每穗 1、2次枝梗的分化数及 1次枝梗的退化数、退化率均无显著影响 ,但使 2次枝梗的退化数、退化率显著提高 ,使 2次枝梗现存数明显减少 ;FACE处理对每穗 1、2次颖花的分化数和 1次颖花的退化数、现存数、退化率均无显著影响 ,但使每穗 2次颖花的退化数和退化率显著提高 ;FACE处理使每穗颖花现存数显著减少主要是因为FACE处理使现存 1次枝梗上 2次枝梗大量退化引起 2次颖花退化所致 ;FACE处理使 1次颖花现存数占全穗的比率显著增加 ,使 2次颖花现存数占全穗的比率显著降低 .