-The objective of this work was to evaluate the vegetative development and determine the concentration of sodium, potassium, and calcium in watermelon (Citrullus lanatus) grown on two organic substrates and under increasing saline concentrations. The substrates were soil + earthworm humus (S 1 ) and soil + bovine manure (S 2 ), and the saline treatments consisted of irrigation water with different electrical conductivities: 1.36 (control), 3.56, 5.76, and 7.96 dS m -1 . The experimental design used was a randomized complete block in a 2×4 (substrate × conductivity) factorial arrangement with five replicates. Main branch length, root length, stem diameter, leaf number, leaf area, and fresh matter mass of shoots and roots, as well as the sodium, potassium, and calcium contents in the plants, were determined. All phenological parameters interacted with the substrates, and S 1 improved plant performance. Substrates interacted significantly with: leaf area; leaf number; stem diameter; main branch length; root length; fresh matter mass of shoots and roots; and the contents of sodium, potassium, and calcium, in both shoots and roots of watermelon irrigated with saline water for up to 27 days after emergence. There are also interactions between substrates and salinity for stem diameter, main branch length, fresh matter mass of roots, and calcium contents in both shoots and roots, and potassium and sodium contents in the roots.Index terms: Citrullus lanatus, bovine manure, humus of earthworm, salt stress.Desenvolvimento vegetativo e conteúdo de cálcio, potássio e sódio em melancieira sob estresse salino, em substratos orgânicos . Utilizou-se o delineamento experimental de blocos ao acaso, em arranjo fatorial 2×4 (substratos × condutividade), com cinco repetições. Foram determinados comprimento do ramo principal e da raiz, diâmetro do caule, número de folhas, área foliar e massa fresca da parte aérea e da raiz, bem como o conteúdo de sódio, potássio e cálcio nas plantas. Todos os parâmetros fenológicos apresentaram interação com os substratos, e S 1 promoveu melhor desempenho das plantas. Os substratos interagiram significativamente com: área foliar; número de folhas; diâmetro do caule; comprimento do ramo principal; comprimento de raiz; massa de matéria fresca da parte aérea e da raiz; e teores de sódio, potássio e cálcio na parte aérea e nas raízes de melancieiras irrigadas com água salina, até 27 dias após a emergência. Os substratos também interagiram com a salinidade para diâmetro do caule, comprimento do ramo principal, massa de matéria fresca de raiz, e teores de cálcio na parte aérea e raiz, e de potássio e sódio na raiz.Termos para indexação: Citrullus lanatus, esterco bovino, húmus de minhoca, salinidade.

The use of brackish waters is an alternative for the cultivation of fruit-bearing plants in semi-arid regions; nonetheless, sweetsop trees (Annona squamosa L.) are sensitive to these types of waters. However, phosphate fertilization can be a technique used to mitigate the harmful effects of salinity. Thus, our objective was to evaluate the application of phosphorus to mitigate the salinity in irrigation water. The experiment was conducted in a randomized block design, with six treatments S1 (2.5 dS m −1 ) S2 = (4 dS m −1 ), SP1 (2.5 dS m −1 + 1.35 g dm −3 of P 2 O 5 ), SP2 = (4 dS m −1 + 1.35 g dm −3 of P 2 O 5 ), T (control), and P (1.35 g dm −3 of P 2 O 5 ). After 78 days of transplantation, the seedlings were evaluated for the total dry weight (TDW), leaf area (LA), salt tolerance index (STI), water use efficiency (WUE), Na + and K + levels in the shoot and root, chlorophylls a and b, maximum (Fm) and variable (Fv) chlorophyll fluorescence, quantum efficiency of photosystem II (Fv/Fm), total soluble sugar (TSS), total free amino acids (TFAA), proline, and glycine betaine (GB). It was observed that plants treated with SP1 and SP2 show higher results of TDW, LA, STI, WUE, and K in the shoot, Chl a, Chl b, Fm, Fv, Fv/Fm, TFAA, proline, GB, and TSS in relation to S1 and S2. The presence of phosphorus under salinity conditions increased the K + concentration in the shoot, which was responsible for the improvement of pigments as well as increasing the quantum efficiency of photosystem II and carbohydrates, maintaining the growth and, consequently, the salinity tolerance of the sweetsop seedlings.

Objetivou-se com presente trabalho, avaliar o metabolismo bioquímico de plântulas de mamoeiro submetidas a diferentes níveis de salinidade, e cultivados e três tipos de substratos, a fim de determinar qual substrato promoveu um melhor ajustamento osmótico ao estres salino. Para produção das mudas da cultivar Havaí foram utilizados tubetes com capacidade 300 cm3. Empregou-se o delineamento inteiramente casualizado, no esquema fatorial 3x4. Os tratamentos foram compostos por três tipos de substratos: S1= vermiculita+húmus de minhoca (1/1); S2= vermiculita+húmus+esterco caprino (1/1/1); S3= vermiculita+esterco (1/1) e quatro níveis de condutividade elétrica na água de irrigação: C1= 0,0; C2= 2,5; C3= 5,0 e C4= 7,5 dS m-1 com cinco repetições. A solução salina para a irrigação foi obtida com a adição NaCl e monitorada com auxílio de um condutivimetro. Após a emergência das plântulas iniciou-se os tratamentos salinos até o 15º dia após a emergência. Analisou-se o conteúdo de açúcares solúveis totais, aminoácidos livres totais e teor de prolina em parte aérea e raiz. Com base na análise dos dados, observou-se que plântulas de mamoeiro cultivadas em substrato S1 incrementaram os teores de açúcares solúveis totais e aminoácidos solúveis totais em raiz e parte aérea, proporcional ao aumento dos níveis de salinidade. Concluindo, portanto, que o substrato vermiculita+húmus de minhoca (1/1) promoveu um possível ajustamento osmótico às plântulas em condições de estresse salino, através do aumento de compostos nitrogenados.

No abstract

Water deficit inhibits plant growth by affecting several physiological processes, which leads to the overproduction of reactive oxygen species (ROS) that may cause oxidative stress. In this regard, iodine (I) is already known to possibly enhance the antioxidant defense system of plants and promote photosynthetic improvements under adverse conditions. However, its direct effect on water deficit responses has not yet been demonstrated. To verify the efficiency of I concerning plant tolerance to water deficit, we exposed soybean plants to different concentrations of potassium iodide (KI) fed to pots with a nutrient solution and subsequently submitted them to water deficit. A decline in biomass accumulation was observed in plants under water deficit, while exposure to KI (10 and 20 μmol L−1) increased plant biomass by an average of 40%. Furthermore, exposure to KI concentrations of up to 20 μM improved gas exchange (~71%) and reduced lipid peroxidation. This is related to the higher enzymatic antioxidant activities found at 10 and 20 μM KI concentrations. However, when soybean plants were properly irrigated, KI concentrations greater than 10 μM promoted negative changes in photosynthetic efficiency, as well as in biomass accumulation and partition. In sum, exposure of soybean plants to 10 μM KI improved tolerance to water deficit, and up to this concentration, there is no evidence of phytotoxicity in plants grown under adequate irrigation.