Déficit hídrico associado à micorrizas arbusculares e ácido abscísico no metabolismo fotossintético e crescimento inicial de mudas de Dipteryx alata Vogel

Abstract

The water deficit has been more frequent with climate changes and due to inadequate soil use practices, influencing the patterns of rainfall distribution and the water absorption capacity by plants. Plants develop acclimatization and adaptation mechanisms to ensure their survival in adverse conditions. In this sense, arbuscular mycorrhizal symbiosis (AM) plays an important role in helping plants in combined responses such as changes in abscisic acid (ABA) signaling, which also influences the colonization of arbuscular mycorrhizal fungi (AMF), forming a complex each increasingly studied. The Cerrado, rich in biodiversity and agricultural potential, presents climatic hyperseasonality, which allows plants to be exposed to water deficit. In this context, there is baru (Dipteryx alata Vogel), a fruit tree native to this biome, from which countless products are obtained, wood and non-wood, being one of the most promising native species for cultivation. Obtaining quality seedlings is essential for this potential to be achieved, which makes it necessary to understand their behavior in the face of water scarcity and the ABA-AM complex. Thus, we aim to evaluate the water deficit associated with arbuscular mycorrhizae and abscisic acid in the metabolism and initial growth of D. alata seedlings. For this, we carried out two tests, the first one, in order to evaluate D. alata seedlings grown under water regimes (control: seedlings irrigated daily, and water deficit: suspension of irrigation) associated with inoculation with arbuscular mycorrhizal fungi (AMF): SM - without inoculation; M1 - inoculation with Rhizoglomus heterosporum; M2 - Rhizoglomus clarum; and MO (On farm) - mixture of species without the presence of M1 and M2, in two compared experiments: exogenous application of 50 µM abscisic acid (ABA+) and without application (ABA-). After suspension of irrigation, the photosynthetic rate was monitored daily, until the detection of the first seedlings with values close to zero, characterizing the first time of evaluation of the experiments: F - zero photosynthesis (7 days after irrigation suspension), when the irrigation, and R: recovery - 100 days after F. D. alata seedlings showed less water potential under water deficit, which also impaired gas exchange and caused damage to photosystem II. However, the species showed resilience, balancing its water relations, adjusting photosynthetic metabolism and growth. Inoculation, especially with R. clarum and R. heterosporum, helped the seedlings to reduce water loss, maintaining its relative content, thus increasing the photosynthetic rate and avoiding irreversible damage in photosystem II, which led to higher quality of seedlings. The exogenous ABA applied to the substrate, has a direct and beneficial effect on the colonization of AMF, but does not influence enough to cause an indirect effect on the tolerance of D. alata seedlings to water deficit. The second test had as its main purpose, the quality of the seedlings, which were grown under the same water regimes, but without application of ABA and inoculated or not with R. clarum (AM+). The water deficit impaired water relations such as water potential and water use efficiency (WUE). However, in the AM+ seedlings, in addition to showing increases in the leaf area ratio: total dry mass, chlorophyll index and efficiency of the Rubisco (A/Ci) carboxylation, it guaranteed an increase in the quality of D. alata seedlings. The exogenous application of ABA enhances the colonization of AMF in D. alata, and inoculation with AMF helps in the resilience of seedlings to water deficit, forming seedlings with higher quality.