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Evergreen Mediterranean Forest (evergreen + mediterranean_forest)

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Life Sciences100%

Selected Abstracts

Drought changes phosphorus and potassium accumulation patterns in an evergreen Mediterranean forest

FUNCTIONAL ECOLOGY, Issue 2 2007
J. SARDANS
Summary 1Climate models predict more extreme weather in Mediterranean ecosystems, with more frequent drought periods and torrential rainfall. These expected changes may affect major process in ecosystems such as mineral cycling. However, there is a lack of experimental data regarding the effects of prolonged drought on nutrient cycling and content in Mediterranean ecosystems. 2A 6-year drought manipulation experiment was conducted in a Quercus ilex Mediterranean forest. The aim was to investigate the effects of drought conditions expected to occur over the coming decades, on the contents and concentrations of phosphorus (P) and potassium (K) in stand biomass, and P and K content and availability in soils. 3Drought (an average reduction of 15% in soil moisture) increased P leaf concentration by 18·2% and reduced P wood and root concentrations (30·9% and 39·8%, respectively) in the dominant tree species Quercus ilex, suggesting a process of mobilization of P from wood towards leaves. The decrease in P wood concentrations in Quercus ilex, together with a decrease in forest biomass growth, led to an overall decrease (by approximately one-third) of the total P content in above-ground biomass. In control plots, the total P content in the above-ground biomass increased 54 kg ha,1 from 1999 to 2005, whereas in drought plots there was no increase in P levels in above-ground biomass. Drought had no effects on either K above-ground contents or concentrations. 4Drought increased total soil soluble P by increasing soil soluble organic P, which is the soil soluble P not directly available to plant capture. Drought reduced the ratio of soil soluble inorganic P : soil soluble organic P by 50% showing a decrease of inorganic P release from P bound to organic matter. Drought increased by 10% the total K content in the soil, but reduced the soil soluble K by 20·4%. 5Drought led to diminished plant uptake of mineral nutrients and to greater recalcitrance of minerals in soil. This will lead to a reduction in P and K in the ecosystem, due to losses in P and K through leaching and erosion, if the heavy rainfalls predicted by IPCC (Intergovernmental Panel on Climate Change) models occur. As P is currently a limiting factor in many Mediterranean terrestrial ecosystems, and given that P and K are necessary for high water-use efficiency and stomata control, the negative effects of drought on P and K content in the ecosystem may well have additional indirect negative effects on plant fitness. [source]

Seasonal and annual variation of carbon exchange in an evergreen Mediterranean forest in southern France

GLOBAL CHANGE BIOLOGY, Issue 4 2008
V. ALLARD
Abstract We present 9 years of eddy covariance measurements made over an evergreen Mediterranean forest in southern France. The goal of this study was to quantify the different components of the carbon (C) cycle, gross primary production (GPP) and ecosystem respiration (Reco), and to assess the effects of climatic variables on these fluxes and on the net ecosystem exchange of carbon dioxide. The Puéchabon forest acted as a net C sink of ,254 g C m,2 yr,1, with a GPP of 1275 g C m,2 yr,1 and a Reco of 1021 g C m,2 yr,1. On average, 83% of the net annual C sink occurred between March and June. The effects of exceptional events such the insect-induced partial canopy defoliation that occurred in spring 2005, and the spring droughts of 2005 and 2006 are discussed. A high interannual variability of ecosystem C fluxes during summer and autumn was observed but the resulting effect on the annual net C budget was moderate. Increased severity and/or duration of summer drought under climate change do not appear to have the potential to negatively impact the average C budget of this ecosystem. On the contrary, factors affecting ecosystem functioning (drought and/or defoliation) during March,June period may reduce dramatically the annual C balance of evergreen Mediterranean forests. [source]