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.
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.
Grimmig B., Gonzalez-Perez M.N., Leubner-Metzger G., Vögeli-Lange R., Meins Jr. F., Hain R., Penuelas J., Heidenreich B., Langebartels C., Ernst D., Sandermann Jr. H. (2003) Ozone-induced gene expression occurs via ethylene-dependent and -independent signalling. Plant Molecular Biology. 51: 599-607.EnllaçDoi: 10.1023/A:1022385104386
Recent studies suggest that ethylene is involved in signalling ozone-induced gene expression. We show here that application of ozone increased glucuronidase (GUS) expression of chimeric reporter genes regulated by the promoters of the tobacco class I β-1,3-glucanases (GLB and Gln2) and the grapevine resveratrol synthase (Vst1) genes in transgenic tobacco leaves. 5′-deletion analysis of the class I β-1,3-glucanase promoter revealed that ozone-induced gene regulation is mainly mediated by the distal enhancer region containing the positively acting ethylene-responsive element (ERE). In addition, application of 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, blocked ozone-induced class I β-1,3-glucanase promoter activity. Enhancer activity and ethylene-responsiveness depended on the integrity of the GCC boxes, cis-acting elements present in the ERE of the class I β-1,3-glucanase and the basic-type pathogenesis-related PR-1 protein (PRB-1b) gene promoters. The minimal PRB-1b promoter containing only the ERE with intact GCC boxes, was sufficient to confer 10-fold ozone inducibility to a GUS-reporter gene, while a substitution mutation in the GCC box abolished ozone responsiveness. The ERE region of the class I β-1,3-glucanase promoter containing two intact GCC boxes confered strong ozone inducibility to a minimal cauliflower mosaic virus (CaMV) 35S RNA promoter, whereas two single-base substitution in the GCC boxes resulted in a complete loss of ozone inducibility. Taken together, these data strongly suggest that ethylene is signalling ozone-induced expression of class I β-1,3-glucanase and PRB-1b genes. Promoter analysis of the stilbene synthase Vst1 gene unravelled different regions for ozone and ethylene-responsiveness. Application of 1-MCP blocked ethylene-induced Vst1 induction, but ozone induction was not affected. This shows that ozone-induced gene expression occurs via at least two different signalling mechanisms and suggests an additional ethylene independent signalling pathway for ozone-induced expression of genes involved in phytoalexin biosynthesis.
Filella I, Peñuelas J (2003) Indications of hydraulic lift by Pinus halepensis and its effects on the water relations of neighbour shrubs. Biologia Plantarum 47:209-214.
Martínez-Vilalta J, Mangirón M, Ogaya R, Sauret M, Serrano L, Peñuelas J, Piñol J (2003) Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions. Tree Physiology 23:747-758.
Munné-Bosch S, Peñuelas J (2003) Photo- and antioxidative protection, and a role for salicylic acid drought and recovery in field-grown Phillyrea angustifolia plants. Planta 217:758-766.
Tognetti R, Peñuelas J (2003) Nitrogen and carbon concentrations, and stable isotope ratios in Mediterranean shrubs growing in the proximity of a CO2 spring. Biologia Plantarum 46:411-418.
Peñuelas J, Lluisà J (2003) Emisiones biogénicas de COVs y cambio global ¿Se defienden las plantas contra el cambio climático? Ecosistemas 1.
Ogaya, R, Peñuelas J, Martínez-Vilalta J, Mangirón M (2003) Effect of drought on diameter increment of Quercus ilex, Phillyrea latifolia, and Arbutus unedo in a holm oak forest of NE Spain. Forest Ecology and Management 180:175-184.
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