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Water use and carbon budget associated with adaptation and competition of C3 and C4 grasses during drought stress

Periodic Report Summary 2 - C3, C4 AND DROUGHT (Water use and carbon budget associated with adaptation and competition of C3 and C4 grasses during drought stress)

The work preformed in the current period of the project included continuation of collection of an extensive germplasm bank of drought-tolerant grasses from a wide range of rainfall gradient in Israel. In addition to the collection three studies have been continued and include:

1. Effects of water stress on the photochemical activity of different ecotypes of the same species differed in their natural surroundings regarding water availability - we took wild barley - Hordeum spontaneum Koch - from the Negev desert (Sde Boker- Sb) and from the Galilee ( Amiad- Am) which is mediterranean environment. Plants were grown under different irrigation conditions (drought an Irrigated), and tested different properties of photochemical reactions, we also measured properties root and shoot total nitrogen and carbon concentration and net uptake, relative water content in the leaves. Electron transport rate in Photosystem II (PSII ETR) were lower for both ecotypes in the drought when compare to the Irrigated treatment, however, this decrease was significantly less in the desert ecotype.

Summary desert ecotypes of wild barley decreased in lower manner their photochemical activity in the leaves under severe drought stress, when compared to Mediterranean ecotype of the same species, the desert ecotype appears repress much less their photochemical ability by non photochemical quenching, when encountered drought stress. The desert ecotype maintains higher concentrations of nitrogen in the shoot under drought when compared to the Mediterranean ecotype; this is perhaps because it has more reducing power, coming from photochemistry, which allows nitrate reduction.

Further investigation revealed that photorespiration contributed to the increase in O2 dependent ETR and to the overall high ETR in the drought treated desert ecotype of H. spontaneum. The drought treated SB ecotype had higher anthocyanin concentration within its leaves. High anthocyanin concentration may prevent light from exciting the PSII reaction center. Overall the results suggest that under drought the SB ecotype maintained high photochemical activity of PSII and low NPQ in comparison to the Am ecotype, The maintenance of this high activity was mostly O2 dependent. The latter results are novel and suggest a new adaptation role for photorespiration in desert plant environments.

2. Survival of Schismus arabicus seedlings exposed to desiccation depends on annual periodicity - S. arabicus exhibits a unique set of adaptations and survival strategies, which enable it to germinate, develop and produce seeds even in years with annual rainfall of less than 100 mm. Since this study deals with annual periodicity, we have continued the experiments throughout the three years of the grant. Our results indicate that survival of S. arabicus seedlings after six different periods of seven to 42 days of desiccation depended on the month of germination of the caryopses (seeds). Seed germination was 80 to 100% in all experiments, regardless the month of germination; however, seedlings that germinated in different months varied in their root and shoot elongation rates. None of about 2500 seedlings that germinated in July (in each of the three years) survived the desiccation treatment. The percentages of surviving seedlings in each month of June of three years were less than 40%. In contrast, over 80% of the seedlings that germinated in each of the months of December and January survived after the desiccation periods of seven to 42 days. The current study demonstrated a novel phenomena indicating that seedling survival in plants may depend on an annual periodicity.

3. A thorough collection of perennial and annual grasses from a wide range of climate zones in Israel was conducted and an extensive germplasm bank of drought-tolerant grasses for future research and for agricultural breeding is being established in a greenhouse in Sde Boker, Israel.