Mitigation of High Temperatures with Ascophyllum nodosum Biostimulants in Papaya (Carica papaya L.) Seedlings

High temperatures can interfere with plant metabolism and physiology, compromising productivity. One tactic to minimize the effects of heatwaves on agriculture is the use of bio-stimulants. This study evaluated two commercial products (Baltiko (R) and Acadian (R)) containing Ascophyllum nodosum in 'Alian & ccedil;a' papaya (Carica papaya L.) seedlings. Six doses (0, 1, 2, 3, 4, and 8 mL L-1) were applied weekly for four weeks at two distinct times, considering moderate and high temperatures. The results indicated distinct effects on gas exchange, seedling development, and nutrient content in leaves and roots. During the moderate temperature period, increasing doses enhanced gas exchange and aerial development, along with increases in potassium and boron levels in the leaves, while root growth decreased. Acadian (R) provided higher levels of boron in leaves and roots compared to Baltiko (R). During the period of elevated temperature, increases were observed in leaf area, root dry mass, and leaf content of phosphorus, potassium, sulfur, and zinc, along with potassium in the roots. These increases were primarily attributed to the effects of the applied biostimulants. A lower dose (3 mL L-1) is recommended during mild temperatures, while a higher dose (6 mL L-1) is suggested for elevated temperatures.