Large-scale patterns of stomatal traits in Tibetan and Mongolian grassland species

We aimed to disentangle the influence of environmental variables on the spatial patterns in stomatal occurrence and stomatal traits. We surveyed the stomatal occurrence and the stomatal length (SL), density (SD) and index (SI) of 99 species in 150 grassland sites on the Tibetan and Inner Mongolian Plateau to explore their spatial patterns and evaluate the influence of climate. Of all species studied, two thirds were amphistomatous. The species from the Tibetan Plateau had larger but fewer stomata than those from Inner Mongolia. Among the climate factors examined, temperature and insolation affected SD, SI and SL, whereas the CO₂ partial pressure and the relative humidity affected SD. The climatic variables showed similar effects on the spatial variation of the adaxial and abaxial stomatal traits. We conclude that the low temperature and high insolation at high altitudes may be responsible for the larger and fewer stomata in plants on the Tibetan Plateau. The stomatal parameters that are presented here can be used to model the gas exchanges at the ecosystem scale.     

Staged invasions across disparate grasslands: effects of seed provenance,consumers and disturbance on productivity and species richness

Exotic plant invasions are thought to alter productivity and species richness, yet these patterns are typically correlative. Few studies have experimentally invaded sites and asked how addition of novel species influences ecosystem function and community structure and examined the role of competitors and/or consumers in mediating these patterns. We invaded disturbed and undisturbed subplots in and out of rodent exclosures with seeds of native or exotic species in grasslands in Montana, California and Germany. Seed addition enhanced aboveground biomass and species richness compared with no‐seeds‐added controls, with exotics having disproportionate effects on productivity compared with natives. Disturbance enhanced the effects of seed addition on productivity and species richness, whereas rodents reduced productivity, but only in Germany and California. Our results demonstrate that experimental introduction of novel species can alter ecosystem function and community structure, but that local filters such as competition and herbivory influence the magnitude of these impacts.     

Hidden responses to environmental variation: maternal effects reveal species niche dimensions

Species responses to fluctuating environments structure population and community dynamics in variable ecosystems. Although offspring number is commonly used to measure these responses, maternal effects on offspring quality may be an important but largely unrecognised determinant of long‐term population growth. We selected 29 species across a Mediterranean annual plant phylogeny, and grew populations of each species in wet and dry conditions to determine responses in seed number and maternal effects (seed size, seed dormancy, and seedling growth). Maternal effects were evident in over 40% of species, but only 24% responded through seed number. Despite a strong trade‐off between seed size and seed number among species, there was no consistent trade‐off within species; we observed correlations that ranged from positive to negative. Overall, species in this plant guild show a complex range of responses to environmental variation that may be underestimated when only seed number responses are considered.     

Phylogenetic investigation and divergence dating of Poa (Poaceae,tribe Poeae) in the Australasian region

The Australasian region contains a significant proportion of worldwide Poa diversity, but the evolutionary relationships of taxa from this region are incompletely understood. Most Australasian species have been placed in a monophyletic Poa subgenus, Poa supersection Homalopoa section Brizoides clade, but with limited resolution of relationships. In this study, phylogenetic relationships were reconstructed for Australasian Poa, using three plastid (rbcL and matK genes and the rpl32‐trnL intergenic spacer) and two nuclear [internal/external transcribed spacer (ITS/ETS)] markers. Seventy‐five Poa spp. were represented (including 42 Australian, nine New Guinean, nine New Zealand and three Australian/New Zealand species). Maximum parsimony, maximum likelihood and Bayesian inference criteria were applied for phylogenetic reconstruction. Divergence dates were estimated using Bayesian inference, with a relaxed clock applied and rates sampled from an uncorrelated log‐normal distribution. Australasian Poa spp. are placed in three lineages (section Brizoides, section Parodiochloa and the ‘X clade’), each of which is closely related to non‐Australasian taxa or clades. Section Brizoides subsection Australopoa is polyphyletic as currently circumscribed. In Australasia, Poa has diversified within the last 4.3 Mya, with divergence dating results broadly congruent with fossil data that record the appearance of vegetation with a prominent grassland understorey or shrubland/grassland mosaic vegetation dating from the mid‐Pliocene. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 523–552.     

Vegetation in clear‐cuts depends on previous land use: a century‐old grassland legacy

Plant species richness in central and northern European seminatural grasslands is often more closely linked to past than present habitat configuration, which is indicative of an extinction debt. In this study, we investigate whether signs of historical grassland management can be found in clear‐cuts after at least 80 years as coniferous production forest by comparing floras between clear‐cuts with a history as meadow and as forest in the 1870s in Sweden. Study sites were selected using old land‐use maps and data on present‐day clear‐cuts. Species traits reflecting high capacities for dispersal and persistence were used to explain any possible links between the plants and the historical land use. Clear‐cuts that were formerly meadow had, on average, 36% higher species richness and 35% higher richness of grassland indicator species, as well as a larger overall seed mass and lower anemochory, compared to clear‐cuts with history as forest. We suggest that the plants in former meadows never disappeared after afforestation but survived as remnant populations. Many contemporary forests in Sweden were managed as grasslands in the 1800s. As conservation of remaining grassland fragments will not be enough to reduce the existing extinction debts of the flora, these young forests offer opportunities for grassland restoration at large scales. Our study supports the concept of remnant populations and highlights the importance of considering historical land use for understanding the distribution of grassland plant species in fragmented landscapes, as well as for policy‐making and conservation.     

Floristic relationship between scrubland and grassland patches in the Mediterranean landscape of the Iberian Peninsula

In the rural Mediterranean landscape, mosaics of patches of sclerophyllous scrubland and semi-natural grasslands are frequent. The plant communities of these patches, which are physiognomically easy to recognise, are very heterogeneous. The objective of this paper is to determine whether the patches of scrub-grassland represent an integrated response unit of the vegetation with regard to the physical environment (climatic, geographical and edaphic factors) and human use, or whether, on the contrary, this is an independent response. In order to do this a total of 50 sampling sites where scrubland and grassland patches were in contact were studied along a 370 km E-W mesoclimatic gradient from central Spain to Portugal (Iberian Peninsula). Two distinct zones, the east and the west halves of the study area, were identified according to the plant communities. Within each of these zones, each type of patch responded to the previously mentioned factors, differentially and independently. This determined a general lack of inter-community association or floristic correlation between scrub and grassland plant communities in contact. The spatial association is a random process probably related to the particular human management realised on every scrubland and grassland patch. The scrub–grassland pattern, which is characteristic of the Mediterranean landscape, does not represent an integrated response unit of the vegetation to a given environment, but rather the sum of the independent responses to the environment of the two patches in contact.Nomenclature for taxa: T. G. Tutin et al. 1694–1980. Flora Europaea Cambridge University Press, Cambridge.     

三江源地区不同退化程度草地的土壤放线菌区系

用不同分离方法,对三江源地区不同退化程度草地土壤放线菌的数量和多样性进行了比较.从5份土样中共分离放线茵178株,根据表型特征和16S rRNA基因序列分析,分别归入7个已知属:小单孢菌属(Micromonospora)、原小单孢菌属(Promicromonospora)、诺卡氏菌属(Nocardia)、假诺卡氏菌属(Pseudonocardia)、游动放线菌属(Actinoplanes)、韩国生工茵属(Kribbella)和链霉菌属(Streptomyces).其中链霉菌属分离菌株可归入7个表型类群.发现轻度退化高寒草原的土壤放线菌数量,丰度和多样性高于重度退化高寒草原;针茅高寒草原的土壤放线菌数量和多样性高于蒿草高寒草甸,而其中链霉菌的种类低于后者.表明高寒草地的退化程度与其中土壤放线茵的数量和多样性呈负相关.     

Short-term effects of temperature enhancement on growth and reproduction of alpine grassland species

In order to study the effects of temperature enhancement on alpine calcareous grassland species, a warming experiment was carried out in the Berchtesgaden National Park (Southeast Germany, Northern Calcareous Alps) between 2002 and 2004. The study was conducted in stands of the Carex sempervirens and the Carex firma communities; the two most widespread grassland types in the alpine zone of the Northern Calcareous Alps. The temperature of the vegetation stand and the upper soil was passively enhanced using open top chambers (OTCs). The construction of the OTCs was appropriate since temperature was clearly increased while water conditions (humidity, soil water content) were not changed.

By comparing manipulated (temperature enhancement) with non-manipulated plots, the effects of warming on growth and reproduction of selected key species were studied. To test if vegetation response to temperature enhancement is at least partly due to increases in nutrient availability, soil solution concentrations of nitrate and ammonium were analysed.

We found that most of the studied plant species are sensitive to temperature enhancement. Growth and/or reproduction of 12 of the 14 studied species were significantly stimulated by warming. Only two species showed no response; none of the species experienced decreases in growth or reproduction. Dwarf shrubs and graminoids showed a stronger response than herbaceous perennials. A significant effect of warming on nutrient availability could not be detected. The observed response of vegetation is therefore mainly caused by direct and not by indirect temperature effects.