R. Tognetti

A B S T R A C T Understanding to what extent species mixtures modify the growth of trees and their responses to climate, in comparison with pure stands, is important to support forest adaptation and mitigation strategies. In this sense, information stored in tree rings can be useful to evaluate whether the positive relationship between species diversity and tree productivity holds true under disturbance (e.g., drought). This paper aimed at assessing (i) how radial growth of trees responded to local variation in climate patterns (Standardised Precipitation-Evapotranspiration Index; SPEI), and (ii) whether there was a relationship with intrinsic water use efficiency (WUE i) and tree-ring δ 18 O in two important tree species, occurring in pure and mixed forest stands. Three sites with similar topographic and pedo-climatic conditions were identified in a single location in the Italian Alps. The first two are characterized by pure stands, respectively dominated by European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.). The third site refers to a mixed stand of both previous species. In particular, in order to assess the annual changes in WUE i , we analysed δ 13 C in tree rings. The influence of the stomatal conductance was also investigated through δ 18 O. Our results indicated that: (i) Basal Area Increments (BAI) consistently increased in all stands except for the pure Scots pine stand, in the 1994–2003 period; (ii) SPEI highlighted a drought period between 1991 and 2007 (62.2% of the average precipitation); and (iii) the WUE i values were generally higher in pure than in mixed stands, especially for European beech. The divergence between BAI and SPEI values in the 1990s and early 2000s could be a consequence of moderate thinning. We conclude that past forest management (namely thinning) can be more influential on tree growth than current climatic oscillations.

The olive tree is a traditionally nonirrigated crop that occupies quite an extensive agricultural area in Mediterranean-type agroecosystems. Improvements in water-use efficiency of crops are essential under the scenarios of water scarcity predicted by global change models for the Mediterranean region. Recently, irrigation has been introduced to increase the low land productivity, but there is little information on ecophysiological aspects and quality features intended for a sagacious use of water, while being of major importance for the achievement of high-quality products as olive oil. Therefore, deficit irrigation programmes were developed to improve water-use efficiency, crop productivity and quality in a subhumid zone of Southern Italy with good winter–spring precipitation. The response of mature olive trees to deficit irrigation in deep soils was studied on cultivars Frantoio and Leccino by examining atmospheric environment and soil moisture, gas exchange and plant water status, as well as oil yield and chemical analysis. Trees were not irrigated (rainfed) or subjected to irrigation at 66% and 100% of crop evapotranspiration (ETC), starting from pit hardening to early fruit veraison. Improvements in the photosynthetic capacity induced by increasing soil water availability were only of minor importance. However, plant water status was positively influenced by deficit irrigation, with 66% and 100% of ETC treatments hardly differing from one another though consistently diverging from rainfed plants. The effect of water stress on photosynthesis was mainly dependent on diffusion resistances in response to soil moisture. Leccino showed higher instantaneous water-use efficiency than Frantoio. Crop yield increased proportionally to the amount of seasonal water volume, confirming differences between cultivars in water-use efficiency. The unsaturated/saturated and the monounsaturated/polyunsaturated fatty acid ratios of the oil also differed between cultivars, while the watering regime had minor effects. Although irrigation can modify the fatty acid profile, polyphenol contents were scarcely affected by the water supply. Irrigation to 100% of ETC in the period August–September might be advisable to achieve high-quality yields, while saving consistent amounts of water.

Five-year-old olive plants (cvs. Frantoio and Moraiolo) grown in large pots were exposed for seven months to ambient or high atmospheric CO2 concentration ((CO2)) in free-air CO2 enrichment facility. Exposure to elevated (CO2) enhanced net photosynthesis and decreased stomatal conductance, leading to greater water use efficiency. Stomatal density also decreased in elevated (CO2), while the ratio of intercellular to atmospheric

Human activities have increased the number of environmental constraints for olive plants. Water, soil and air pollution are rapidly becoming important environmental concerns for plant growth and producti- vity. In addition to pollution problems, modifications in gaseous composition of the atmosphere, as well as terr e- strial solar radiation changes associated with pollution, are the new factors studied by olive

The olive oil mill wastewater (OMWW) or “vegetation water” derives from the extraction of olive (Olea europaea L.) oil and contains suspended matter consisting of olive pulp, mucilage, pectin, oil, etc., in a relatively stable emulsion. The use of these wastewaters on soils may enhance their fertility, thanks to the fertilizing properties of the waste. However, the long term use of OMWW as fertilizer may lead to some disadvantages because of its potential leaching into the water table. In order to prevent this environmental problem in Italy a maximum application rate of 80 m3 ha-1 year-1 is allowed. The use of plants characterized by high water consumption, such as poplar, could be a means to limit water table pollution problems while enhancing the OMWW degradation. Selection of poplar clones with high transpiration rate is compulsory for OMWW remediation purposes, though should be balanced with water saving potential, particularly in the present Mediterranean environment. With this aim, a pilot system of Short Rotation Coppice (SRC) poplar plantation was established in spring 2009, in soil polluted with OMWW. The poplar clones used were Populus x euramericana clone I-214 and Populus x generosa x Populus nigra clone Monviso, with contrasting functional and structural traits. After one year, sap flow measurements were done using the thermal dissipation method.
Data were recorded connecting the probes to an acquisition data system composed by a low cost open-source electronic platform. Sap flow results showed significant differences between clones in transpiration during dry and wet period. Discussion on how these traits can be useful for effective selection of poplar clones suitable for plantation in OMWW polluted soils is provided.