Browsing by Author "Strasser, R. J."
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- Mycorrhization of cork oak micropropagated plantlets : its vitality during acclimatization measured with fast fluorescence techniquesPublication . Romano, A.; Strasser, R. J.; Eggenberg, P.; Martins-Loução, M. A.In this work we propose some fluorescense tests, based on a fast data acquisition (10 us per data point with 12 bit resolution) over five orders of magnitude in time (10 us to 1s) with an optoelectronic shutterless instrument (Plant Efficiency Analyser - PEA), to evaluate the response of micropropagated cork oak plantlets with or without mycorrhiza, in vitro and ex vitro conditions. Indexes have been defined which indicate the activity, efficiency, stress resistance, adaptability and developmental complexity of a plant. The shape of the observed fluorescence transient (on a logarithmic time scale) showed the typical Fo-J-I-P levels. The results obtained showed that mycorrhization increases the quantum yield of photochemistry as well as the electron transport and the photosynthetic metabolism. The density of photosynthetic units per leaf area is highly increased in mycorrhized plantlets. Therefore the productivity per leaf area is increased in these plantlets as well. During acclimatization mycorrhized plantlets show a much higher general fitness than non-mycorrhized plantlets in relation to the defined indexes.
- Response of plants to ectomycorrhizae in N-limited conditions: which factors determine its variation?Publication . Corrêa, A.; Strasser, R. J.; Martins-Loução, M. A.In the present work, the following hypotheses were tested: (1) the negative effects of mycorrhization over host plant productivity in N-limited conditions are due to N retention by the fungal partner and not due to excessive C drainage; (2) If mycorrhization results in decreased N uptake, the host plant decreases its C investment in fungal growth. The effects of mycorrhization over a wide range of combinations between N availability, N concentration in plant tissues, and degree of mycorrhizal colonization were studied in Pinus pinaster L. mycorrhizal with Pisolithus tinctorius. Several plant productivity parameters, the seedlings’ N status, chl a fluorescence (JIP test), and mycorrhizal colonization were measured. N was always limiting. A gradient of mycorrhizal effects over the host plant’s growth and vitality was successfully obtained. The mycorrhizal effects on plant growth and N uptake were very strongly and positively correlated, and no evidence was found of a C limitation to growth, confirming hypothesis 1. Indications were found that the plants continued to provide C to the fungus although the N supplied by it was increasingly lower, denying hypothesis 2. A new index, the mycorrhizal N demand–supply balance, was found to efficiently explain, and to have a curvilinear relation with, the variation in response to mycorrhization. The mycorrhizal effect on host plant growth was not related to a negative effect on its photosynthetic performance and, therefore, reflected changes in resource allocation between host plant and mycorrhizal fungus, not in plant vitality.