ABSTRACT Optimization of the use of water and the possibility of using residues as substrate in the black pepper production chain can yield economic and environmental benefits. The objective of this study was to evaluate the biometric and physiological traits of black pepper plantlets (Piper nigrum L.), cv. Bragantina, at different irrigation levels and soilless substrates. Plantlets were grown for 120 days on three substrates [biosolid + crushed coconut fiber (3:1, by volume); biosolid + granitic rock powder (3:1, by volume); and biosolid + crushed coconut fiber + granitic rock powder (2:1:1, by volume)] and at five irrigation levels [36 % (very low); 55 % (low); 85 % (moderate); 100 % (well-irrigated); and 126 % of the reference irrigation level (over-irrigated)]. The biometric traits evaluated increased as the irrigation levels increased, with the exception of root dry mass, which was not influenced by this factor, nor water use efficiency, which decreased as the irrigation levels increased. In general, plants grown with a mixture of the three wastes (biosolid + crushed coconut fiber + granitic rock powder) exhibited higher values for biometric variables and chlorophyll content when they were moderately, well or over-irrigated, in comparison with the other two substrates. It was possible to achieve the plantlet commercial standard using this three waste mixture and the moderate irrigation level.

RESUMO Em razão da quantidade de água utilizada no setor agropecuário, comparada às outras atividades, a irrigação deve ser feita de forma criteriosa e com base no conhecimento das relações hídricas vegetais. O objetivo deste trabalho foi avaliar o comportamento fisiológico de plantas jovens de pimenta-do-reino (Piper nigrum L.), submetidas a restrições hídricas, assim como o potencial de recuperação após o estresse. As plantas, cultivadas em potes de 5 L, foram submetidas a diferentes níveis de irrigação (100; 78; 58 e 32% da lâmina controle), com manejo realizado por acionamento automático a partir de um sensor de tensão da água no solo. Foram avaliados: potencial osmótico foliar (Ψo), conteúdo relativo de água (CRA), condutância estomática (gs) e pigmentos fotossintéticos. Para avaliar a capacidade de recuperação das plantas, houve reidratação do substrato quando cerca de 50% das plantas de um tratamento apresentassem condutância estomática (gs) próxima a zero. Os diferentes níveis de déficit hídrico reduziram os valores de todas as variáveis. No tratamento 32% foram observados valores de −2,39 MPa para Ψo, 60% para CRA e gs próxima a zero no 28º dia de restrição hídrica. Após três dias de reidratação deste tratamento, a recuperação desses valores foi parcial, não atingindo os valores dos tratamentos 100 e 78%. Plantas de pimenta do reino exibiram elevada susceptibilidade a restrições hídricas e baixa capacidade de recuperação após estresse.

ABSTRACT Due to the amount of water used in the agricultural sector, compared to other activities, irrigation must be done carefully and based on knowledge of plant water relations. The aim of this work was to evaluate the physiological behavior of young black pepper plants (Piper nigrum L.), subjected to water deficit, as well as the potential for recovery after stress. In 5 L pots, the plants were subjected to different irrigation levels (100; 78; 58 and 32% of the control depth), with irrigation management performed by an automatic controller from a water tension sensor in the soil. The following traits were evaluated: leaf osmotic potential (Ψo), relative water content (RWC), stomatal conductance (gs) and photosynthetic pigments. To evaluate the plants’ recovery capacity, substrate rehydration was performed when about 50% of the plants in a treatment had stomatal conductance (gs) close to zero. The different levels of water deficit reduced the values of all traits. In the treatment 32%, values of −2.39 MPa for Ψo, 60% for RWC and gs close to zero were observed on the 28 th day of water restriction. After three days of rehydration of this treatment, the recovery of these values was partial, not reaching the values of the treatments 100 and 78%. Black pepper plants showed high susceptibility to water restrictions and low capacity for recovery after stress.