Biogeochemical monitoring in the garrigue of Ramat Hanadiv as a tool for assessing ecosystem function

The biogeochemical monitoring in Ramat Hanadiv aims at assessing the long-term changes in the status and function of the Mediterranean ecosystem. The monitoring activity is performed in the Phillyrea latifolia-dominated garrigue, and it evaluates the impact of land management by goat grazing and the regulation by climate and the main vegetation components on key processes in the cycling of elements. These processes include the nutrient status of the vegetation, plant litter production and its decomposition. Improved knowledge about the biogeochemical cycles in long-term monitoring allows better understanding of the factors that influence ecosystem function in the Mediterranean region and might help in the development of management strategies for ecosystem conservation.

Ecosystem functioning is comprised of processes, such as plant growth and organic matter decay, by which elements are transferred among different components of the system (organisms, soil). Through element cycling (the biogeochemical cycles) carbon and nutrients are absorbed by plants from the atmosphere and the soil, respectively, and are recycled through decomposition and mineralization processes in the soil. There is considerable knowledge on species composition in Mediterranean ecosystems, but we have a poor understanding about the biogeochemical cycles and their regulation by land management and climatic variables in these systems.

After six years of monitoring (2007-2013), it appears that phosphorus is a major factor limiting plant growth in the shrubland. This conclusion could be drawn from a series of indications, such as low phosphorus concentration and high nitrogen-to-phosphorus ratio in the leaves of P. latifolia, Pistacia lentiscus and Calicotome villosa. In addition, we found high resorption efficiency of phosphorus prior to seasonal leaf fall, low phosphate availability in the soil and a positive relationship between growth rate and phosphate availability.

Goat grazing tended to increase the concentrations of calcium and magnesium, and to decrease the concentration of potassium in the leaves of the shrubs, potentially as a plant-protection measure. Furthermore, P. latifolia litter fall was reduced and litter decomposition was enhanced by grazing as compared to the ungrazed control, at least in one year, thus decreasing the amount of litter on the ground.

The linear relationships between leaf phosphorus and potassium concentrations in P. latifolia and P. lentiscus and the rainfall amount during the year of leaf production indicates that drought can affect ecosystem activity through the nutrient status of the plant, in addition to direct effects on plants and soil. In addition, the production of herbaceous litter at the end of the growing season was mainly related to the rainfall amount during the previous year, which might indicate the importance of the seed yield for biomass production in the subsequent year.

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