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Community ecology
Mittelbach, G. M. 2012. Sinauer Associates, Inc. Publishers. Sunderland, Massachusetts USA. www.sinauer.com. 400 pages + 166 illustrations. Paperback. ISBN 978-0-87893-509-3. Price: US$72.95
After clearcutting xerothermic oakwoods once natural in the forest-steppe loess regions of Hungary, the perennial understorey grass Brachypodium pinnatum has been persisting for decades by establishing microhabitats from shade to full sun. In this paper, we explore variation in leaf anatomy for plants growing in different microhabitat light regimes (full shade under oak canopy, half shade near shrubs, and in unshaded grassland) in situ, and for plants reciprocally transplanted between these microhabitats. Leaf lamina thickness and mesophyll thickness were about 1.5 times greater in the grassland in situ than in oak subcanopy due to an additional layer of mesophyll cells and to 25-32% taller mesophyll cells. Mesophyll thickness and the proportion of veins plus sclerenchyma were lower for plants transplanted from either full or half shade to full sun than in situ plants in the grassland. Parenchymatous bundle sheath tended to be thicker in the grassland than in the two other microhabitats. Mean intervenial distance remained invariable among microsites. These adjustments in leaf anatomy may be a considerable part, but presumably not the dominant component of the medium-term (one year) light acclimation of B. pinnatum and the species success in microsites with contrasting light climate appearing side-by-side during secondary vegetation succession.
Pressure-volume (p-V) analysis, instantaneous transpiration rate and relevant leaf structural information were used to compare leaf water relations for 23 angiosperm species from semiarid temperate loess-, sand- and saline steppe grasslands and several associated habitats representing a water availability gradient. For the species studied, the most marked differences occurred between grasses and dicots. Grasses in our survey possessed low (highly negative) osmotic potential both at water saturation and at turgor loss, moderate transpiration rate, relatively high leaf dry matter proportion (DMP) and - except for the sclerophyllous Festuca species - high specific leaf area (SLA, area per unit dry mass). In contrast, dicots had lower bulk tissue elasticity, higher (less negative) osmotic potentials, intense transpiration, and lower SLA andDMP than grasses. Therefore, grasses mainly invest in osmotic potential to extract water from drying soil, while dicots rely on relatively inelastic tissue that decreases water potential by a rapid drop of turgor with turgor loss occurring at relatively high water content. Habitat effects were significant for osmotic parameters only. Osmotic potential at full turgor and at turgor loss decreased in the following order: loess grassland ? sand grassland ??saline grassland ? loess wall. Life form influenced leaf structure only, since annuals possessed markedly higher SLA and lower DMP than perennials. Comparison of habitat specialist species within the same genus revealed that certain congeners (Achillea and Aster spp.) do not differ significantly in leaf water relations, thus they might rely on similar water supply in the three steppes. Other congeners (Festuca, Kochia and Plantago spp.) differed considerably, thus for these plants leaf function and structure must be different to ensure survival under the contrasting water regime. For the two generalist grasses (Cynodon dactylon and Dactylis glomerata) habitat-specific populations showed a tendency of increasing capacity for water extraction from soil (more negative water potential) with increasing habitat dryness, although differences were significant only between the extremes of the water availability gradient.
Leaf morphology, coarse structure and anatomy were compared for two invasive C 4 , two non-invasive C 4 , and two expanding native C 3 grass species grown in their original, high-light semiarid temperate habitat, and in a growth room under variable moderate light and favourable supply of water and nutrients. It was hypothesised that (H 1 ) among C 4 grasses leaf structural response will be greater for invasive than for non-invasive species, and (H 2 ) for plants of high spreading capacity C 4 species will be less responsive than C 3 species. Leaf mass per area was lower in the growth room than in the field by 43.4–54% and 5.7–21.2% for grasses of high spreading capacity and for non-invasive C 4 species, respectively. Little or no response was observed in the proportion of epidermis and mesophyll, but the proportional area of veins plus sclerenchyma was greater in the field than in the growth room for the invasive C 4 Sorghum halepense , and the spreading C 3 Bromus inermis and Calamagrostis epigeios , while it did not differ for the two non-invasive C 4 grasses and the invasive C 4 Cynodon dactylon . Leaf intervential distance was invariant for C 4 grasses (except for the non-invasive Chrysopogon gryllus ) and the C 3 C. epigeios , but changed by 25.1% for the C 3 B. inermis . These results suggest that among C 4 grasses invasive species expceed non-invasive ones in the plasticity of leaf coarse structure, but not that of leaf morphology and anatomy. However, leaf structure was not less plastic in invasive C 4 than in expanding C 3 grasses except for intervential distance.
R.W. Sterner and J.J. Elser. 2002. Ecological Stoichiometry - the biology of elements from molecules to biosphere. Princeton University Press, Princeton, New Jersey, 439 pp. (with 117 figures and tables). ISBN: 0-691-07491-9, paperback, price: USD 29.95, GBP 19.95. M. Black and H.W. Pritchard (eds.) 2002. Dessication and survival in plants. Drying without dying. CABI Publishing, Wallingford, x+412 pp. ISBN: 0-85199-534-9, hardback, price: GBP 75.00. B.D. Booth, S.D. Murphy, C.J. Swanton. 2003. Weed ecology in natural and agricultural systems. CABI Publishing, Wallingford, viii+303 pp. ISBN 0-85199-528-4, paperback, price: GBP 35.00, USD 60.00.
Recent research indicates that the soil microbial community, particularly arbuscular mycorrhizal fungi (AMF), can influence plant invasion in several ways. We tested if 1) invasive species are colonised by AMF to a lower degree than resident native species, and 2) AMF colonisation of native plants is lower in a community inhabited by an invasive species than in an uninvaded resident community. The two tests were run in semiarid temperate grasslands on grass (Poaceae) species, and the frequency and intensity of mycorrhizal colonisation, and the proportion of arbuscules and vesicles in plant roots have been measured. In the first test, grasses representing three classes of invasiveness were included: invasive species, resident species becoming abundant upon disturbance, and non-invasive native species. Each class contained one C3 and one C4 species. The AMF colonisation of the invasive Calamagrostis epigejos and Cynodon dactylon was consistently lower than that of the non-invasive native Chrysopogon gryllus and Bromus inermis, and contained fewer arbuscules than the post-disturbance dominant resident grasses Bothriochloa ischaemum and Brachypodium pinnatum. The C3 and C4 grasses behaved alike despite their displaced phenologies in these habitats. The second test compared AMF colonisation for sand grassland dominant grasses Festuca vaginata and Stipa borysthenica in stands invaded by either C. epigejos or C. dactylon, and in the uninvaded natural community. Resident grasses showed lower degree of AMF colonisation in the invaded stand compared to the uninvaded natural community with F. vaginata responding so to both invaders, while S. borysthenica responding to C. dactylon only. These results indicate that invasive grasses supposedly less reliant on AMF symbionts have the capacity of altering the soil mycorrhizal community in such a way that resident native species can establish a considerably reduced extent of the beneficial AMF associations, hence their growth, reproduction and ultimately abundance may decline. Accumulating evidence suggests that such indirect influences of invasive alien plants on resident native species mediated by AMF or other members of the soil biota is probably more the rule than the exception.
Bornholdt, S. and Schuster, H. G. (eds.), 2003. Handbook of Graphs and Networks - From the Genome to the Internet. Wiley-VCH, Weinheim, xvi+417 pp. ISBN: 3-527-40336-1, hardcover, price: GBP 80.00, EUR 120.00. Tuba, Z. (ed.), 2005. Ecological Responses and Adaptations of Crops to Rising Atmospheric Carbon Dioxide. Food Products Press (Member of the Haworth Press, Inc.), Binghamton, xvi+414 pp. ISBN-10: 1-56022-120-8, hardbound, price: USD 79.95; ISBN-10: 1-56022-121-6, paperback, price: USD 49.95.
Left atrial (LA) distension has been demonstrated to be linked with aortic stiffness in different patient populations. Three-dimensional (3D) speckle-tracking echocardiography (STE) seems to be a promising tool for volumetric and functional evaluation of the LA. The aim of the present study was to determine whether correlations exist between 3DSTE-derived LA volume-based and strain parameters characterizing all phasic functions of the LA and echocardiographic aortic elastic properties in healthy subjects. The study included 19 healthy volunteers (mean age: 37.9 ± 11.4 years, 11 men) who had undergone complete two-dimensional (2D) Doppler transthoracic echocardiography extended with the assessment of aortic elastic properties and 3DSTE. Results: None of LA volumes correlated with echocardiographic aortic elastic properties. Active atrial stroke volume correlated with aortic stiffness index (ASI, r = 0.45, p = 0.05). None of other volume-based functional properties signifcantly correlated with aortic stiffness parameters. Global peak 3D strain correlated with aortic strain (r = ‒0.46, p = 0.05). global radial pre-atrial contraction strain correlated with ASI (r = ‒0.49, p = 0.04) and AS (r = ‒0.50, p = 0.04). Conclusions: Correlations exist between 3DSTE-derived LA functional parameters and eschocardiographic aortic elastic properties in healthy subjects.
The influence of simulated climate change on soil respiration was studied in a field experiment on 4 m × 5 m plots in the semiarid temperate Pannonian sand forest-steppe. This ecosystem type has low productivity and soil organic matter content, and covers large areas, yet data on soil carbon fluxes are still limited. Soil respiration rate — measured monthly between April and November from 2003 to 2006 — remained very low (0.09 — 1.53 μmol CO 2 m −2 s −1 ) in accordance with the moderate biological activity and low humus content of the nutrient poor, coarse sandy soil. Specific soil respiration rate (calculated for unit soil organic matter content), however, was relatively high (0.36–7.92 μmol CO 2 g −1 C org h −1 ) suggesting substrate limitation for soil biological activity. During the day, soil respiration rate was significantly lower at dawn than at midday, while seasonally clear temperature limitation in winter and water limitation in summer were detected. Between years, annual precipitation appeared to be important in determining soil carbon efflux intensity. Nocturnal warming increased soil temperature in 1 cm depth at dawn by 1.6°C on the average, and decreased topsoil (0–11 cm) moisture content by 0.45 vol%. Drought treatment decreased soil moisture content by an average of 0.81 vol%. Soil respiration rate tended to decrease by 7–15% and 13–15% in response to heat and drought treatment, respectively, although the changes were not statistically significant. Nocturnal warming usually prevented dew formation, and that probably also influenced soil respiration. Based on these results, we expect a reduction in the volume and rate of organic matter turnover in this ecosystem in response to the anticipated climate change in the region.
Introduction
Myocardial contractility of the left ventricle (LV) is related to arterial distensibility. Sport activity is frequently associated with changes in both LV and arterial functions. This study aimed to find correlations between three-dimensional speckle-tracking echocardiography-derived segmental LV deformation parameters and echocardiographically assessed aortic stiffness index (ASI) in athletes. This study comprised 26 young elite athletes (mean age: 26.7 ± 8.4 years, nine men).
Results
Among segmental circumferential strains (CSs), only that of apical anterior (r = 0.40, p = 0.05), septal (r = 0.47, p = 0.01), inferior (r = 0.59, p = 0.001), lateral (r = 0.44, p < 0.05), and midventricular anteroseptal (r = 0.44, p < 0.05) segments correlated with ASI, whereas LV-CS of the midventricular anterior segment showed a correlation tendency. Only longitudinal strain of basal anteroseptal (r = −0.46, p < 0.05) and inferoseptal (r = −0.57, p < 0.01) segments showed correlations with ASI, whereas that of the basal anterior segment had only a tendency to correlate. Some segmental multidirectional strains also correlated with ASI.
Conclusions
Correlations could be demonstrated between increased aortic stiffness and circular function of the apical and midventricular LV fibers and longitudinal motion of the basal septum and LV anterior wall (part of LV outflow tract) in maintaining circulation in the elite athletes.
