The objective of this study was to evaluate chlorophyll a fluorescence as a stress indicator in Calophyllum brasiliense Cambess seedlings grown with different concentrations of abscisic acid (ABA) under intermittent water deficit condition: daily irrigation without ABA (I); daily irrigation + 10 μM ABA (I 10); daily irrigation + 100 μM ABA (I 100); suspension of daily irrigation without ABA (SI); suspension of daily irrigation + 10 μM ABA (SI 10) and suspension of daily irrigation + 100 μM ABA (SI 100). The intermittent water deficit reduces water status and impairs the photochemical apparatus functioning and seedling quality. The fluorescence measurements helped identify the stress condition of water deficit in the cultivation of C. brasiliense and the beneficial effect of the application of 10 μM of ABA in minimizing stress and facilitating the recovery of seedlings after re-irrigation, while maintaining the integrity and function of the photosynthetic apparatus.

1. INTRODUCTION AND OBJECTIVES

Organic residue in the substrate and the availability of light influence the production of high-quality seedlings for ex situ cultivation of native forest species. This study aimed to evaluate the effect of doses of chicken manure incorporated in the soil and shading levels on the morphophysiological responses and quality of Alibertia edulis (Rich.) A. Rich seedlings. Five doses of chicken manure (CM) were tested, 0.00, 2.08, 4.16, 6.24, and 8.32 g CM kg-1 soil, under two shade conditions, 0% (full sun) and 50% shading. At 215 days after transplanting, the maximum height obtained for A. edulis was 47.35 cm with 5.64 g CM kg-1 soil under 50% shade. Shaded seedlings had a higher number of leaves. The maximum leaf and root areas were 796.64 and 118.83 cm2 with 5.32 and 4.21 g CM kg-1 soil, respectively, both under 50% shade. Seedlings in 0% shade had lower physiological indices. Shading levels did not affect stomatal limitation, but CM contributed to physiological efficiency. Shoot biomass was higher under 50% shade with higher CM doses. The highest quality indexes occurred with 3.98 and 6.28 g kg-1 CM under 0 and 50% shade, respectively. A. edulis seedlings responded positively to the addition of CM to the soil and presented plasticity under contrasting light conditions. A. edulis seedlings produced under 50% shading with the addition of 6.24 g CM kg-1 soil presented high morphophysiological and seedling quality indicators. The addition of 4.32 g CM kg-1 soil contributed to high seedling quality under full sun conditions.

Seed conditioning with bioinputs (biopriming) offers a promising and sustainable alternative to mitigate the adverse effects of salt stress on soybeans. This study aims to evaluate the potential of isolated or combined biopriming using microalgae and different microorganisms in alleviating salinity-induced stress in soybeans in early-stage. Seeds were subjected to five biopriming treatments: Parachlorella sp. microalgae culture, Bacillus subtilis, Trichoderma harzianum, Parachlorella sp. + B. subtilis, and Parachlorella sp. + T. harzianum, along with a control group without biopriming. Subsequently, the seeds were exposed to two conditions: (i) control (0.0 MPa), and (ii) salinity induced by NaCl (-0.8 MPa). Germination, photochemical indicators, and seedling performance were assessed. Salinity impaired root protrusion and seed physiology, resulting in a high percentage of abnormal seedlings, thus creating a stressful condition. However, biopriming alleviated the negative effects of salinity, particularly with T. harzianum, Parachlorella sp. + B. subtilis, and Parachlorella sp. + T. harzianum, which led to high germination rates and normal seedlings. All biopriming treatments, especially the combined ones, reduced the suppression of non-photochemical quenching, thereby enhancing the maximum yield of photosystem II. Seedlings under salt stress without biopriming exhibited short lengths and low fresh and dry mass, whereas those bioprimed with Parachlorella sp. + B. subtilis and Parachlorella sp. + T. harzianum showed significantly higher values. Seed biopriming, especially with Parachlorella sp. microalgae culture combined with B. subtilis or T. harzianum, effectively alleviates the stressful effects of salinity on germination and early-stage growth seedling of soybeans.