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Deep Soils (deep + soil)
Selected AbstractsWater Sources of Dominant Species in Three Alpine Ecosystems on the Tibetan Plateau, ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2008De-Yu Duan Abstract Plant water sources were estimated by two or three compartment linear mixing models using hydrogen and oxygen isotope (,D and ,18O) values of different components such as plant xylem water, precipitation and river water as well as soil water on the Tibetan Plateau in the summer of 2005. Four dominant species (Quercus aquifolioides, Pinus tabulaeformis, Salix rehderiana and Nitraria tangutorum) in three typical ecosystems (forest, shrub and desert) were investigated in this study. Stable isotope ratios of the summer precipitations and the soil water presented variations in spatial and temporal scales. ,18O values of N. tangutorum xylem water were constant in the whole growth season and very similar to those of deep soil water. Water sources for all of the plants came from both precipitations and soil water. Plants switched rapidly among different water sources when environmental water conditions changed. Rainwater had different contributions to the plants, which was influenced by amounts of precipitation. The percentage of plant xylem water derived from rainwater rose with an increase in precipitation. Water sources for broad-leaved and coniferous species were different although they grew in the same environmental conditions. For example, the broad-leaved species Q. aquifolioides used mainly the water from deep soil, while 92.5% of xylem water of the coniferous species P. tabulaeformis was derived from rainwater during the growth season. The study will be helpful for us to fully understand responses of species on the Tibetan Plateau to changes in precipitation patterns, and to assess accurately changes of vegetation distribution in the future. [source] Ecohydrological effects of grazing-induced degradation in the Patagonian Monte, ArgentinaAUSTRAL ECOLOGY, Issue 5 2009ALEJANDRO JORGE BISIGATO Abstract Water-limited ecosystems have undergone rapid change as a consequence of changing land use and climate. The consequences of these changes on soil quality and vegetation dynamics have been documented in different regions of the world. In contrast, their effects on soil water, the most limiting resource in these environments, have received less attention, although in recent years increasing efforts have been made to relate grazing, soil water and vegetation functioning. In this paper, we present the results of field observations of plant phenology and soil water content carried out during two successive years at four sites along a degradation gradient caused by grazing in the Patagonian Monte, Argentina. We also developed a simplified soil water balance model to evaluate how changes in plant cover could affect water balance. Our field observations showed that the soil water content in the soil layer where roots of grasses are abundant (0,25 cm) was higher and the growing cycles were longer in degraded than in preserved sites. Similarly, our modelling approach showed that the deep soil (depth > 10 cm) was wetter in the degraded than in the preserved situation. Simulation also suggested a switch from transpiration to a direct evaporation dominance of water losses with degradation. Although reductions in plant cover related to grazing degradation were associated with a decrease in annual transpiration, the simulated soil water loss by transpiration was higher during summer in the degraded than in the well preserved situation. Thus, our field observations seem to be a consequence of ecohydrological changes causing an accumulation of water in the soil profile during the cold season and its transpiration during summer. In conclusion, our results showed that changes in plant cover caused by grazing disturbance can alter the soil water balance, which in turn can affect vegetation function. [source] Temporal coherence of aboveground net primary productivity in mesic grasslandsECOGRAPHY, Issue 3 2008Jana L. Heisler Synchrony in ecological variables over wide geographic areas suggests that large-scale environmental factors drive the structure and function of ecosystems and override more local-scale environmental variation. Described also as coherence, this phenomenon has been documented broadly in the ecological literature and has recently received increasing attention as scientists attempt to quantify the impacts of global changes on organisms and their habitats. Using a mesic grassland site in North America, we assessed coherence in ecosystem function by quantifying similarity in aboveground net primary production (ANPP) dynamics in 48 permanent sampling locations (PSLs) over a 16-yr period. Our primary objective was to characterize coherence across a broad geographic region (with similar ecosystem structure and function), and we hypothesized that precipitation and a similar fire frequency would strengthen coherence between PSLs. All 48 PSLs at our site (Konza Prairie Biological Station, Manhattan, KS, USA; KPBS) were exposed to a similar regional driver of ANPP (precipitation); however, local drivers (including differences in fire frequency and soil depth at different topographic positions) varied strongly among individual PSLs. For the purpose of this assessment, the watershed-level experimental design of KPBS was considered a model, which represented different fire management strategies across the Great Plains Region. Our analyses revealed a site-level (KPBS) coherence in ANPP dynamics of 0.53 for the period of 1984,1999. Annual fire enhanced coherence among PSLs to 0.76, whereas less frequent fire (fire exclusion or a 4-yr fire return interval) failed to further increase coherence beyond that of the KPBS site level. Soil depth also strongly influenced coherence among PSLs with shallow soils at upland sites showing strong coherence across fire regimes and annually burned uplands closely linked to annual precipitation dynamics. The lack of coherence in ecosystem function in PSLs with deep soils and low fire frequencies suggests that conservation and management efforts will need to be more location specific in such areas where biotic interactions may be more important than regional abiotic drivers. [source] Differences in seed mass between hydric and xeric plants influence seed bank dynamics in a dryland riparian ecosystemFUNCTIONAL ECOLOGY, Issue 2 2008J. C. Stromberg Summary 1Dryland riparian zones have steep spatial gradients of soil moisture and flood disturbance, and the component hydrogeomorphic surfaces support hydric to xeric plant species. These systems undergo extremes of flood and drought, a dynamic that may select for persistent soil seed banks. We asked if reliance on this strategy differed among plants in three moisture groups (hydric, mesic and xeric), and if patterns were related to diaspore traits. 2We assessed the composition of soil and litter seed banks (emergence method) and extant vegetation along a riparian hydrogradient, and measured seed persistence (using an indirect method) and diaspore mass and shape variance of the component species. 3Hydroriparian species had smaller diaspores than xeroriparian species, corresponding to differences in selective pressures on seedlings in their respective habitats, but the two groups formed persistent seed banks at approximately equal percentages. Persistent seeds were smaller than transient seeds, but within the persistent seed group there was separation between the smaller-diaspored hydrophytes and larger-diaspored xerophytes. 4Distribution patterns of extant vegetation, in concert with diaspore trait differences among moisture-affinity groups, gave rise to divergent spatial patterns of diaspores within the soil: hydroriparian diaspores were abundant not only along wet channel bars but also in deep soils under floodplain forests and shrublands, presumably owing to dispersal by flood waters. Xeroriparian diaspores were largely restricted to the litter and upper soil layers of their drier, higher, floodplain habitats. With increasing depth in the soil of floodplain forests and shrublands, viable diaspores became smaller and rounder, and plant composition shifted from xeroriparian to hydroriparian species. 5The wide distribution of hydroriparian diaspores in floodplain soils influences disturbance dynamics, increasing the probability that ephemeral wetland communities will develop wherever suitable conditions are stochastically created by floods. Persistent seed banks also allow many xeric annuals to be maintained in dryland riparian zones throughout extended drought, similar to processes that occur in desert uplands. [source] Will photosynthesis of maize (Zea mays) in the US Corn Belt increase in future [CO2] rich atmospheres?GLOBAL CHANGE BIOLOGY, Issue 6 2004An analysis of diurnal courses of CO2 uptake under free-air concentration enrichment (FACE) Abstract The C4 grass Zea mays (maize or corn) is the third most important food crop globally in terms of production and demand is predicted to increase 45% from 1997 to 2020. However, the effects of rising [CO2] upon C4 plants, and Z. mays specifically, are not sufficiently understood to allow accurate predictions of future crop production. A rainfed, field experiment utilizing free-air concentration enrichment (FACE) technology in the primary area of global corn production (US Corn Belt) was undertaken to determine the effects of elevated [CO2] on corn. FACE technology allows experimental treatments to be imposed upon a complete soil,plant,atmosphere continuum with none of the effects of experimental enclosures on plant microclimate. Crop performance was compared at ambient [CO2] (354 , mol mol,1) and the elevated [CO2] (549 ,mol mol,1) predicted for 2050. Previous laboratory studies suggest that under favorable growing conditions C4 photosynthesis is not typically enhanced by elevated [CO2]. However, stomatal conductance and transpiration are decreased, which can indirectly increase photosynthesis in dry climates. Given the deep soils and relatively high rainfall of the US Corn Belt, it was predicted that photosynthesis would not be enhanced by elevated [CO2]. The diurnal course of gas exchange of upper canopy leaves was measured in situ across the growing season of 2002. Contrary to the prediction, growth at elevated [CO2] significantly increased leaf photosynthetic CO2 uptake rate (A) by up to 41%, and 10% on average. Greater A was associated with greater intercellular [CO2], lower stomatal conductance and lower transpiration. Summer rainfall during 2002 was very close to the 50-year average for this site, indicating that the year was not atypical or a drought year. The results call for a reassessment of the established view that C4 photosynthesis is insensitive to elevated [CO2] under favorable growing conditions and that the production potential of corn in the US Corn Belt will not be affected by the global rise in [CO2]. [source] Dynamics of stream nitrate sources and flow pathways during stormflows on urban, forest and agricultural watersheds in central Pennsylvania, USAHYDROLOGICAL PROCESSES, Issue 23 2009Anthony R. Buda Abstract Understanding the influence of storm events on nitrate (NO3,) dynamics is important for efficiently managing NO3, pollution. In this study, five sites representing a downstream progression of forested uplands underlain by resistant sandstone to karst lowlands with agricultural, urban and mixed land-use were established in Spring Creek, a 201 km2 mixed land-use watershed in central Pennsylvania, USA. At each site, stream water was monitored during six storm events in 2005 to assess changes in stable isotopes of NO3, (,15N-NO3, and ,18O-NO3,) and water (,18O-H2O) from baseflow to peakflow. Peakflow fractions of event NO3, and event water were then computed using two-component mixing models to elucidate NO3, flow pathway differences among the five sites. For the forested upland site, storm size appeared to affect NO3, sources and flow pathways. During small storms (<35 mm rainfall), greater event NO3, fractions than event water fractions indicated the prevalence of atmospheric NO3, source contributions at peakflow. During larger storms (>35 mm rainfall), event NO3, fractions were less than event water fractions at peakflow suggesting that NO3, was flushed from stored sources via shallow subsurface flow pathways. For the urbanized site, wash-off of atmospheric NO3, was an important NO3, source at peakflow, especially during short-duration storms where event water contributions indicated the prevalence of overland flow. In the karst lowlands, very low fractions of event water and even lower fractions of event NO3, at peakflow suggested the dominance of ground water flow pathways during storms. These ground water flow pathways likely flushed stored NO3, sources into the stream, while deep soils in the karst lowlands also may have promoted NO3, assimilation. The results of this study illustrated how NO3, isotopes and ,18O-H2O could be combined to show key differences in water and NO3, delivery between forested uplands, karst valleys and fully urbanized watersheds. Copyright © 2009 John Wiley & Sons, Ltd. [source] Invasive Acacia auriculiformis Benth. in different habitats in Unguja, ZanzibarAFRICAN JOURNAL OF ECOLOGY, Issue 1 2009Riitta Kotiluoto Abstract Acacia auriculiformis Benth., Mimosaceae, has been introduced relatively recently as a plantation tree to the island of Unguja, Zanzibar. It has been reported to establish itself outside the plantations, but it is not known if the success of establishment depends on habitat quality. We investigated the occurrence of A. auriculiformis in 5-m-wide sample lines, which started from the edge of acacia plantations and reached farthermost the distance of 1 km. The results of 7.24 ha studied showed that: (1) A. auriculiformis occurred in most of the studied habitats in Unguja and appeared to be more abundant in deep soils than in shallow coral-derived soils. However, statistical analyses suggested that the species has little preference or avoidance towards any of the habitats, even though forests , the least disturbed habitats , seemed to have less acacias than other more disturbed habitats. (2) The number of acacias decreased rapidly with the distance from an acacia plantation, and most of the found acacias were still young, below three metres tall. Our results suggest that the invasion of A. auriculiformis is at its beginning in Unguja. If no preventive measures are taken, A. auriculiformis may have an increasing impact on local ecosystem in the future. Résumé Acacia auriculiformis Benth., une mimosacée, a été introduit assez récemment sous forme de plantation dans l'île d'Unjuga, à Zanzibar. On a rapporté qu'il s'était établi de lui-même en dehors des plantations, mais on ne sait pas si la réussite de cette installation dépend de la qualité de l'habitat. Nous avons étudié la présence d'Acacia auriculiformis sur des bandes échantillons de cinq mètres de large qui commençaient à la lisière des plantations d'acacia et s'éloignaient jusqu'à un kilomètre. Les résultats obtenus sur les 7,24 ha étudiés montrent que 1) Acacia auriculiformis existe dans la plupart des habitats étudiés à Unjuga et semble plus abondant dans des sols profonds que dans des sols peu profonds dérivés des coraux. Cependant, les analyses statistiques suggèrent que l'espèce montre peu de préférences ou de rejet envers aucun des habitats, même si les forêts , les habitats les moins perturbés , semblent contenir moins d'acacias que d'autres habitats plus perturbés et que 2) le nombre d'acacias diminue rapidement quand on s'éloigne des plantations d'acacias, et que la plupart des acacias trouvés sont encore jeunes et mesurent moins de trois mètres de haut. Nos résultats suggèrent que l'invasion d'Acacia auriculiformis en est encore à ses début sur Unjuga. Si l'on ne prend pas de mesures préventives, A. auriculiformis pourrait avoir un impact croissant sur l'écosystème local dans le futur. [source] Patterns of invasion within a grassland communityJOURNAL OF ECOLOGY, Issue 5 2002A. Kolb Summary 1Relatively few studies have looked for patterns of invasion by non-native species within communities. We tested the hypotheses that: (i) some types of microhabitats within a community are more invasible than others; (ii) microhabitat types that differ in invasion also differ in resource availability; and (iii) invasibility is mediated by effects of these resources on competition between native and non-native species. 2To test the first two hypotheses, we measured plant cover and soils in a coastal grassland in northern California. Consistent with these hypotheses, cover of non-native plants was consistently high where nitrogen-fixing shrubs had recently grown, in the bottoms and sides of gullies and on deep soils, and these microhabitats tended to have relatively high nitrogen or water availability. 3Cover and number of native species tended to be lower where cover of non-native species was higher, indicating that non-native species as a group negatively affected native species. However, the number of non-native species also tended to be lower where the total cover of non-natives was higher. This suggests that a few non-native species excluded natives and other non-natives alike. 4To test the third hypothesis, we grew a common non-native, the annual grass Lolium multiflorum, and a common native, the perennial grass Hordeum brachyantherum, at different levels of water and nitrogen. The relative competitive ability of the native was higher at lower nitrogen availability but not at lower water availability. When 10-week-old native plants were grown with non-native seedlings and nitrogen was relatively low, the native out-competed the non-native. However, the non-native out-competed the native at all resource levels when species were both grown as seedlings. Competition between native and non-native grasses in this system may thus help prevent invasion by non-natives in microhabitats where nitrogen availability is low, but invasion may be relatively irreversible. [source] | ||||||||||