Growth and development of olive under low temperature stress influenced by phosphate fertilizer application

Objectives The growth of olive trees in Gansu is always stressed by low temperatures in spring season every year. Phosphorous fertilization is studied to alleviate the stress and promote the growth of olive seedlings.

Methods In this experiment, olive cultivar of ‘Ezhi No.8’ was used as experimental material and NaH₂PO₄·2H₂O as phosphate. The application rates of P₂O₅ were 0, 15, 30, 45, 60 and 75 g per olive tree(expressed as P0, P15, P30, P45, P60 and P75), and natural low temperature was used for low temperature stress treatments. Accordingly, the leaves and roots of olive were collected on 16 September (17.6℃), 15 November (3.1℃) and 30 December (–5.3℃) in 2018. Those temperatures were the averaged values of the sampling date and two days before the sampling. These plant samples were used to determine the leaf frost index, osmotic adjustment substance, membrane damage index, antioxidant enzyme activity, chlorophyll content, phosphorus content, root vigor and morphology, as well as biomass of olive seedlings.

Results Under low temperatures of 3.1℃ and –5.3℃, the application of P reduced the frost damage index, leaf membrane permeability, superoxide anion production rate and malondialdehyde content, but increased the contents of proline, soluble protein, soluble sugar, chlorophyll and P, antioxidant enzyme activities, and root vigor. Under P45 treatment at 3.1℃, the activities of SOD, CAT and ascorbate peroxidase (APX) in olive leaves were increased by 104.75%, 95.02% and 100.01%, and the chlorophyll and P contents increased by 114.83% and 33.66% compared with P0, respectively; although the root development and aboveground biomass accumulation of oil olive seedlings were all inhibited at under low temperature, the root dry weight, length, surface area, volume and number of root tips in P45 treatment were significantly higher than those in P0 by 80.27%, 42.60%, 28.79%, 55.50% and 25.01%, respectively, but the average root diameters had no significant difference among the different P treatments; and the plant height and above-ground dry weight were increased by 48.48% and 34.51%, respectively.

Conclusions Low temperature inhibits the growth and development of olive seedlings, appropriate application of phosphate could effectively alleviate the stress and enhance the cold resistance of the olive seedlings as a whole. Our results suggested that an optimum application rate of phosphorus fertilizer was P₂O₅ 45 g/plant under low temperature stress.