Phenology and thermal requirements of the species Cyperus difformis L. in southern Brazil

Cyperus difformis L. is a Cyperaceae, annual, of natural occurrence in marshy environments in southern Brazil, considered a weed in irrigated rice crops. Studies on its development are scarce, especially regarding its cycle and thermal requirements. Therefore, the objective of this work was to determine the base temperature, the thermal sum and the duration of the different sub-periods of the biological cycle of the species. The experiment was carried out at the Campus of the Universidade Federal de Santa Maria – UFSM, Santa Maria, Rio Grande do Sul, in four sowing seasons. In a completely delineated design and factorial scheme involving five soil water conditions (water depth and 50% soil water retention capacity [WRC]) from the sowing, water depth and 50% WRC introduced 21 days after emergence and 100% WRC during the whole cycle, with six repetitions each. Each experimental unit consisted of a cultivated in pot plant with 11 L capacity filled with soil. The cycle of the plants was subdivided into the sowing-emergence sub-periods, emergence-emission of the floral tassel and emission of the floral-maturing physiological tassel, being estimated the thermal requirements for the species. The conditions of the soil water condition the base temperature, the sum of the degree-days and the duration of the species cycle. The base temperature varies for each treatment, the sum of degrees-day decreases with the water deficit and the plants under flood accelerate the biological cycle.

Response of Eragrostisplana and Eragrostis pilosa(L.) P. Beauv. submitted on flooded soil

The development of Eragrostis planaand Eragrostis pilosawas evaluated in a greenhouse when submitted to different soil moisture conditions. The design was completely randomized, consisting of a factorial 2x3, with the following factors: Eragrostis accessions and soil moisture levels (50% of water retention capacity (WRC), 100% of WRC and soil with water depth of 10 cm). The morphological-anatomical parameters of the plants were evaluated and the aerenchyma and adventitious roots were quantified. In addition, the photosynthetic pigments and the electron transport capacity of the photosynthetic chain were quantified, with the intention of verifying if the amount of water in the soil interferes with these parameters. Similar responses were observed between the two species when submitted to a water table environment, where there were larger aerenchymal formations in the roots and stems, as well as adventitious roots at the soil surface, inferring adaptations for survival to anaerobic stress. Negative effects on the transport of electrons and the formation of chlorophyll pigments were observed for both species when submitted to the hypoxic environment and, consequently, there was reduction of dry mass of shoot and roots, as well as reduction in the emission of tiller. It is concluded that the irrigation water management and the water blade in the rice crop are important, together with the control of invasive plants, considering the negative effects caused to the growth and development of these plants.

Phenology and dry mass production of Urochloa plantaginea and Urochloa platyphylla submitted to different water quantities in the soil

The genetic variability and genetic versatility of plants belonging to Poaceae provide morphophysiological responses that allow these individuals to adapt to environmental changes, especially in relation to soil moisture. Urochloa plantaginea and U. platyphylla are grasses typical of dry environment, also found as weeds in rice fields, where there are high amounts of water in the soil. The objective of this work is to analyze the development of these two species in different environments, subjecting them to three different amounts of water in the soil. Morphological parameters were analyzed in order to verify and quantify which suffered alteration with respect to water variation. Caryopsis of the two species were collected in a commercial irrigated rice crop. Seeds were sown in pots containing a substrate-sand system, and housed in a greenhouse, where during the experiment the control of different moisture contents (shallow water table, 100% of field capacity and 50% of field capacity) took place. Weekly evaluations were carried out according to the parameters analyzed. The following parameters were evaluated: duration of the vegetative and reproductive life cycle, number of the inflorescences per plant, number of branches per inflorescence, number of spikelets per branch, number of seeds per plant, and dry mass production. The U. plantaginea cycle had shorter duration under the shallow water table, while for U. platyphylla the shorter duration was under the condition 50% of field capacity. Both species produced higher dry mass of shoots under the condition of 100% of field capacity. The main responses observed for both species, due to the flooding, were the change of the cycle, reduced dry matter production, and reduced seed production.