Sardans J., Peñuelas J., Rodà F. (2006) The effects of nutrient availability and removal of competing vegetation on resprouter capacity and nutrient accumulation in the shrub Erica multiflora. Acta Oecologica. 29: 221-232.EnllaçDoi: 10.1016/j.actao.2005.10.006
Nutrient availability is increasing in the Mediterranean Basin due to the great number and intensity of fires and higher levels of anthropomorphic pollution. In the experiment described in this paper, we aimed to determine the effects of N and P availability and of the removal of competing vegetation on resprouter capacity, biomass, and nutrient accumulation in Erica multiflora. Plants of the resprouter species E. multiflora were clipped to 0% of aerial biomass in a post-fire Mediterranean shrubland and fertilisation experiments and removal of competing vegetation were established in a factorial design. The resprouting of clipped plants was monitored during the first year after clipping and at the end of the year, all plant resprout populations were harvested and their resprout structure, biomass and N and P content measured. N fertilisation had no significant effect on leaf biomass either at plant level or on the total aerial biomass per stump unit area; however N concentration in resprout biomass did increased. P fertilisation slightly increased resprouting vigour and had a significant effect on P content of the leaf biomass. The removal of competing vegetation increased the ratio between leaf biomass and stem biomass, the lateral expansion of resprout, the hierarchy of resprouts branching, and the P content of stems, above all when P fertilisation was applied. These results show that as a response to decreased competition E. multiflora has the capacity to modify the relative proportions of the nutrients in the aerial biomass. All these characteristics allow E. multiflora to persist in increasingly disturbed Mediterranean ecosystems and contribute to the retention of nutrients in the ecosystem during early resprouting phases. © 2006 Elsevier SAS. All rights reserved.
Sardans J., Peñuelas J., Rodà F. (2006) Plasticity of leaf morphological traits, leaf nutrient content, and water capture in the Mediterranean evergreen oak Quercus ilex subsp. ballota in response to fertilization and changes in competitive conditions. Ecoscience. 13: 258-270.EnllaçDoi: 10.2980/i1195-6860-13-2-258.1
We manipulated nutrient availability and competing vegetation to investigate the phenotypic plasticity of leaf morphology and nutrient content of saplings and seedlings of the evergreen holm oak Quercus ilex subsp. ballota in response to nutrient pulses. Different factorial experimental designs were established with N and/or P pulse fertilization as factors in a field experiment in Catalonia (northeast Spain) and with P fertilization, soil type, and competitive situation as factors in a pot experiment. In the field, P fertilization decreased leaf mass per area (LMA) 9-13% in the 3 y following the fertilization application. No significant effect was observed from variations in N supply in any leaf cohort. In the pot experiment, P fertilization increased the leaf size, pre-dawn leaf water content, and root growth and decreased the LMA. P fertilization strongly increased P leaf concentrations, as in the field experiment. Neighbour competition induced increases in LMA in the second leaf cohort and in leaf density and size in both leaf cohorts; it also reduced root growth and tended to increase P leaf concentrations. Soil type had a significant effect on individual leaf area, leaf mass, and LMA, the latter being higher in siliceous soils than in calcareous and artificial soils. The pattern of change in leaf thickness across the different soil types was the opposite of that for leaf P concentrations, P contents per unit of leaf area, and leaf density. These results point to a morphological leaf plasticity in response to P availability, competitive situation, and soil type. The relations between the changes in leaf morphology, leaf nutrient content, root growth, and pre-dawn leaf water content changed depending on the factor that induced them. However, leaf morphological traits changed in combination with other plant traits such as root growth and nutrient contents in order to balance resource availability and production capacity under different environmental conditions, such as changing degrees of neighbour competition or water availability. This plasticity of sclerophyllous leaf traits in response to nutrient pulses makes Quercus ilex subsp. ballota well suited to adapt to the unpredictable changes and stress situations likely to result from current and immediate future climate and other changes in the Mediterranean region.
Sardans J., Rodà F., Peñuelas J. (2006) Effects of a nutrient pulse supply on nutrient status of the Mediterranean trees Quercus ilex subsp. ballota and Pinus halepensis on different soils and under different competitive pressure. Trees - Structure and Function. 20: 619-632.EnllaçDoi: 10.1007/s00468-006-0077-z
Nutrient availability is a key factor in Mediterranean ecosystems that affects the primary productivity and the community structure. The great variability of its natural availability is now increasing due to frequent fires, pollution events and changes in rainfall regime associated to climate change. Quercus ilex ssp. ballota and Pinus halepensis are the most abundant tree species in the NW Mediterranean basin. They frequently compete in the early and middle successional stages. We investigated the effects of N and P pulse supplies on nutrient uptake capacity in these two species in an after-fire field area and in nursery conditions on different soil types and competing conditions. In the field, N fertilisation had weak effects on nutrient concentration and mineralomass likely as a consequence of this nutrient not being limiting in this field site whereas P fertilisation increased the P mineralomass and the Mg, S, Fe, K and Ca concentrations and mineralomass in the different biomass fractions of both species 1 and 3 years after fertilisation application. In the nursery experiments, P fertilisation increased the mineralomass and concentrations of P, Mg, S, Fe, K and Ca in all biomass fractions including the roots in both species and in different soils and competition conditions. The increment of nutrient mineralomass was due to both the increase of growth and of nutrient concentrations. Both species were able to absorb significant amounts of the P applied by fertilisation (between 5 and 20%) in short time (18 months). Competing vegetation decreased the positive effects of P fertilisation, and in many cases the negative effect of competing vegetation on nutrient mineralomass was stronger when P availability was increased by fertilisation. Q. ilex subsp ballota showed a greater competitive ability for P than the more pioneer species Pinus halepensis in the field but not in the nursery conditions. Pinus halepensis had greater nutrient mineralomass in calcareous than in siliceous soils. Q. ilex subsp. ballota had a higher root biomass allocation and root nutrient allocation than P. halepensis, but both species showed a high capacity to increase their nutrient uptake when its availability increased by fertilisation, thus assuring a great nutrient reserve for future growth periods and contributing to retain nutrients in the ecosystem. © Springer-Verlag 2006.
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