RICERCA ITALIANA     

Research program

VEGETATIVE GROWTH CONTROL MECHANISMS IN OLIVE (OLEA EUROPAEA L.) GENOTYPES CHARACTERIZED BY DIFFERENT VIGOUR

University Co-ordinator

Università degli Studi di PALERMO - COLTURE ARBOREE - PALERMO(PA)

Research Unit Leader

Tiziano CARUSO

Description

The research aims to set-up a carbon balance and growth simulation model of two olive genotypes characterised by different vigour. In order to set up the model, functional relations determined from trees grown in different environmental conditions will be used. For this reason, on the two olive genotypes it will be observed the main physiological activities such as primary productivity, both under full sun and in conditions of artificial reduction of the irradiance. The hypothesis is that vegetative potential should be differently affected by the reduction of stress conditions imposed by environmental situation (increased photosynthetic activity obtained reducing photo-inhibition effects, increased stomatic conductance, reduced respiration, etc.).

The artificial reduction of the irradiance, about 50% of the full insolation, will be obtained using a neutral shading shading nets so that the spectral composition of the transmitted light should not be affected. This situation will be frequently checked with a LI-1800 spectroradiometer (LICOR, Lincoln, NE, USA). Shading nets will be used in the spring and summer season (March-September).

Two clones of cv. "Leccino" olive, characterized by different vigour, will be used. In particular, the "Leccino Minerva" (LM) clone is characterized by standard growth; instead, the "Leccino dwarf" (LD) is characterized by a low vegetative vigour (about 50% lower than the standard type).

The research will be carried out in two different environments (A and B sites). In the "A" site all Research Units (RU) of the project will be involved in the measurements. The research will be conducted on trees of this RU and will be available to be used by all the other RUs of this project. Plants are obtained from semi-hardwood cuttings, own-rooted in the spring 2004, hence, at the beginning of the reasearch, will be two-year-old. Trees will be grown in artificial substrate composed by peat, pumice and compost (1:1:1, v:v:v). Observations, in each experimental site, will be carried out on 80 trees: 40 of LD and as many of LM. Twenty trees per genotype will be grown under shading conditions (i-50), the other 20 trees will be grown under full sunlight (i-100).

In site A, plants will be grown in large circular concrete containers (3 cubic meters capacity). In July 2006 and in July 2007, destructive biomass assessment will be performed on 10 trees per genotype (5 per treatment). In detail, fresh and dry weight will be measured separately on leaves, branches, trunk and roots. Moreover, on dry matter samples, carbohydrates, main soluble sugars (glucose, fructose, saccharose, mannitol, etc.) and main mineral elements (N, P, K, Ca, Mg) content will be determined.

In site B, on other 80 trees, grown in 12-liter pots and with the same experimental layout of site A (2 genotypes x 2 different radiation regimes), observations on growth and plant gas-exchange will be carried outto implement a simulation dynamic model of net assimilation and the carbon balance.
The determination of photosynthetic activity, for different values of PPFD and CO2 concentration, will be obtained by the use of a portable gas-exchange measurement system (CIRAS-1, PP-Systems, Hitchin Herts, UK). These observations will be repeated monthly, in reference to phenological stage of the tree, on different leaf-age classes. Finally, temperature effects on leaf photosintetic activity will be evaluated by net assimilation measurements under light-saturation conditions (Amax). Leaves under observation will be sampled to determine chlorophyll (Moram, 1982) and nitrogen content.
Moreover, respiration of each plant part (leaf, root, stem, shoot) will be obtained by the use of an IRGA gas-exchange measurement system (CIRAS-1, PP-Systems, Hitchin Herts, UK) connected to a "cuvette" purposely adapted to the type of vegetative organ under measurement. All the measurements will be done at constant temperature. In particular, root observations will be carried-out "in vivo" in a semi-closed system using plants on pots purposely sealed. Measuring CO2 emission both on plant-less pots (with the same ground) and on planted pots, root respiration will be determined by difference between the above indicated respiration values. Respiration measurement will be done in four different dates (concurrently to the destructive observations): on April and on July of each year.
On each tree, the following measurements will be done: trunk diameter, axis length, number and length of branches and shoots, number of leaves separated in age classes) and leaf area, as well as length of structural and fine-roots. The length of fine-roots will be obtained by Tennant methodology using a mesh with squares 2 cm wide.
At the end of all measurements, both fresh and dry matter partitioning will be done by separating trees in their different fractions: leaves, branches and roots. During the entire trial season, weekly observations on plant growth will be done: on the roots these measurements will be carried out by the use of minirhizotron. On the two different radiative regimes, continuous microclimatic measurements (air and soil temperature, air humidity, soil water content and irradiance ) will be taken by an authomatic weather station.
Finally, data gathered in site B will be used to implement a dynamic simulation model, with daily time-steps, of carbon demand and supply for the complete growth season. Net plant assimilation in the model will be calculated by implementing the equations of the light response of net photosynthetic response curves to light and temperature previously determined by gas-exchange measurements.
Other equations in the model will be implemented also for respiration and growth rates. The growth of each single plant fraction (root, trunk, shoot and leaves), as well as respiration data, will be used for the calculation of daily carbon requirements; corrections to respiration rates will be applied in function of the seasonal and diurnal course of air temperature (Witowski, 1997). The simulation model, will be laid out by a commercial graphical software modelling tool (Stella, Isee Systems, Lebanon, NH, USA). Equations will be integrated on a seasonal time scale with a one-day time step; model outputs will be validated with dry matter growth, and partitioning data obtained in the A site.