Effects of gradual soil drought stress on the growth, biomass partitioning, and chlorophyll fluorescence of Prunus mongolica seedlings

The present study aimed to determine the effects of gradual drought stress on Prunus mongolica seedlings. The growth and chlorophyll fluorescence of the seedlings were investigated under drought and control conditions. The short- term (21 day) decline in soil water content from 30.46% to 15.55% did not significantly influence the growth of P. mongolica seedlings but increased the height, basal diameter, crown, leaf number, stem mass, leaf mass, and root mass of the seedlings. The growth of the drought group reached the maximum, but remained lower than that of the control group, within 21 days. Compared with the control group, the drought group showed 1.46%, 9.65%, 9.44%, 5.19%, 29.09%, 19.20%, and 0.03% lower height, basal diameter, crown, leaf number, stem mass, leaf mass, and root mass, respectively. With the gradual manifestation of soil drought through the decline in soil water content from 15.55% to 11.38% from 21 days to 42 days, growth of the drought group became significantly lower than that of the control group (P < 0.05). The minimal fluorescence decreased and then increased, whereas the nonphotochemical quenching initially increased and then decreased. Thus, P. mongolica can protect the PSII reaction center from damage at the early stage of drought stress. The maximal fluorescence, the maximum quantum yield of PSII, and the photochemical quenching slightly decreased during the initial period of drought stress. These results suggest that drought can slightly influence the openness of PSII reaction centers. This influence was further proven by the decreased quantum yield of PSII. This study provided insights into the adaptive mechanism of P. mongolica seedlings under drought and may serve as a theoretical basis to protect the P. mongolica population. Comparing these responses is crucial for elucidating the drought-tolerance mechanisms in P. mongolica cultivars.