Levine JM, Vilà M, D'Antonio CM, Dukes JS, Grigulis K, Lavorel S (2003) Mechanisms underlying the impacts of exotic plant invasions. Proceedings of the Royal Society London B 270:775-781.
Serra P, Pons X, Saurí D (2003) Post-classification change detection with data from different sensors: some accuracy considerations. International Journal of Remote Sensing 24:3311-3340.
Vilà M, Gómez A, Maron JL (2003) Are alien plants more competitive than their native conspecifics? A test using Hypericum perforatum L. Oecologia 137:211-215.
Avila A, Alarcón M (2003) Precipitation chemistry at a rural Mediterranean site: Between anthropogenic pollution and natural emissions. Journal of Geophysical Research 108:1-11.
Avila A, Alarcón M, Rodrigo A (2003) Heavy metal deposition and cycling at two Mediterranean holm oak (Quercus ilex L.) forests in northeastern Spain. Journal de Physique IV 107:75-78.
Rodrigo A, Avila A, Rodà F (2003) The chemistry of precipitation, throughfall and stemflow in two holm oak (Quercus ilex L.) forests under a contrasted pollution environment in NE Spain. The Science of the Total Environment 305:195-205.
Castells E., Peñuelas J. (2003) Is there a feedback between N availability in siliceous and calcareous soils and Cistus albidus leaf chemical composition?. Oecologia. 136: 183-192.EnllaçDoi: 10.1007/s00442-003-1258-8
The effects of the Mediterranean shrub Cistus albidus on N cycling were studied in two siliceous (granitic-derived and schistic-derived) and one calcareous soil differentiated by their texture and acidity. We aimed to find out whether soils under C. albidus were affected by the release of C compounds from the canopy, and whether phenolic compound production in C. albidus changed depending on the soil N availability. Calcareous soils, with higher clay content and polyvalent cations, had a higher organic matter content but lower net N mineralization rates than siliceous soils, and C. albidus growing therein were characterized by lower foliar N and phenolic compound concentrations. Under C. albidus, all types of soils had higher phenolic compound concentrations and polyphenol oxidase activity. C. albidus presence and leachate addition decreased net N mineralization and increased soil respiration in siliceous soils, and these changes were related to a higher soil C/N ratio under the canopy. In calcareous soils, however, no significant effects of plant presence on N cycling were found. In the studied plant-soil system it is not likely that higher phenolic compound concentrations were selected during evolution to enhance nutrient conservation in soil because (1) higher phenolic compound concentrations were not associated with lower soil fertilities, (2) C compounds released from C. albidus accelerated N cycling by increasing N immobilization and no evidence was found for decreased gross N mineralization, and (3) soil organic N content was more related to soil chemical and physical properties than to the effects of the C. albidus canopy.
Castells E., Peñuelas J., Valentine D.W. (2003) Influence of the phenolic compound bearing species Ledum palustre on soil N cycling in a boreal hardwood forest. Plant and Soil. 251: 155-166.EnllaçDoi: 10.1023/A:1022923114577
The effects of the understory shrub Ledum palustre on soil N cycling were studied in a hardwood forest of Interior Alaska. This species releases high concentrations of phenolic compounds from green leaves and decomposing litter by rainfall. Organic and mineral soils sampled underneath L. palustre and at nearby non-Ledum sites were amended with L. palustre litter leachates and incubated at controlled conditions. We aimed to know (i) whether L. palustre presence and litter leachate addition changed net N cycling rates in organic and mineral soils, and (ii) what N cycling processes, including gross N mineralization, N immobilization and gross N nitrification, were affected in association with L. palustre. Our results indicate that N transformation rates in the surface organic horizon were not affected by L. palustre presence or leachate addition. However, mineral soils underneath L. palustre as well as soils amended with leachates had significantly higher C/N ratios and microbial respiration rates, and lower net N mineralization and N-to-C mineralization compared to no Ledum and no leachates soils. No nitrification was detected. Plant presence and leachate addition also tended to increase both gross N mineralization and immobilization. These results suggest that soluble C compounds present in L. palustre increased N immobilization in mineral soils when soil biota used them as a C source. Increases in gross N mineralization may have been caused by an enhanced microbial biomass due to C addition. Since both plant presence and leachate addition decreased soil C/N ratio and had similar effects on N transformation rates, our results suggest that litter leachates could be partially responsible for plant presence effects. The lower N availability under L. palustre canopy could exert negative interactions on the establishment and growth of other plant species.
Díaz-Delgado R., Lloret F., Pons X. (2003) Influence of fire severity on plant regeneration by means of remote sensing imagery. International Journal of Remote Sensing. 24: 1751-1763.EnllaçDoi: 10.1080/01431160210144732
In this paper we analyse the interactions between fire severity (plant damage) and plant regeneration after fire by means of remote sensing imagery and a field fire severity map. A severity map was constructed over a large fire (2692 ha) occurring in July 1994 in the Barcelona province (north-east of Spain). Seven severity classes were assigned to the apparent plant damage as a function of burning intensity. Several Landsat TM and MSS images from dates immediately before and after the fire were employed to monitor plant regeneration processes as well as to evaluate the relationship with fire severity observed in situ. Plant regeneration was monitored using NDVI measurements (average class values standardized with neighbour unburned control plots). Pre-fire NDVI measurements were extracted for every plant cover category (7), field fire severity class (7), and spatial cross-tabulation of both layers (33) and compared to post-fire values. NDVI decline due to fire was positively correlated with field fire severity class. Results show different patterns of recovery for each dominant species, severity class and combination of both factors. For all cases a significant negative correlation was found between damage and regeneration ability. This work leads to a better understanding of the influence of severity, a major fire regime parameter on plant regeneration, and may aid to manage restoration on areas burned under different fire severity levels.
Filella I., Peñuelas J. (2003) Partitioning of water and nitrogen in co-occurring Mediterranean woody shrub species of different evolutionary history. Oecologia. 137: 51-61.EnllaçDoi: 10.1007/s00442-003-1333-1
We studied the interspecific and intraspecific variation in the development of water stress and in the use of different water and nitrogen sources during the spring (wet season) and summer (dry season) in a shrub community in NE Spain. We measured shoot water potentials, stable deuterium isotopic composition (δD) of xylem sap, leaf mass per area, leaf N and C concentrations, gas exchange, leaf δ13C, and leaf δ 15N of the dominant species (Quercus coccifera, Arbutus unedo, Pistacia lentiscus, Erica multiflora, Globularia alypum). The δD, the δ13C and the shoot water potential values showed diurnal, seasonal, intraspecific and interspecific variation in the source and use of water. There was also seasonal, intraspecific and interspecific variation in the foliar δ15N and N concentrations. In summer, some species (A. unedo, P. lentiscus and E. multiflora) presented significantly different δD values in morning and afternoon measurements likely indicating that they used different sources of water during the day, and a dual root system in these species. We conjecture that dew may be one of these water sources. Species predawn water potential was negatively correlated with species xylem water δD. There was also a positive correlation between δ 13C and δD in P. lentiscus, species for which we took additional samples from nearby sites. These results suggest that the access to water from greater depths allowed the maintenance of more favourable plant water supply. Multivariate principal component analysis based on the studied hydrological and isotope variables clearly separated the seasons (wet spring and dry summer) and the species. The species resulted separated according to their evolutionary history (Pre-Mediterranean and Mediterranean) and the associated root and functional traits. These results show water (and nitrogen) partitioning among coexisting species of the same functional type (Mediterranean woody shrubs). They also show the great intraspecific plasticity of responses to resource availability.
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