Polysaccharide,proline,and anti-oxidation enzyme activities of Thailand rosewood(Dalbergia cochinchinensis)seedlings exposed to exponential fertilization

Thailand rosewood(Dalbergia cochinchinensis)is a vulnerable high value tree species in subtropical and tropical Southeast Asia.The demand for the rehabilitation of the natural habitat of the species requires high-quality seedlings.However,current fertilizer regimes tend to deliver a coarse rate of fertilizers that result in a low uptake efficiency and a high risk of nutrient excess.Exponential fertilization is an effective approach to promote seedling quality through identifying an optimum dose out of a range of applications.In this study,Thailand rosewood seedlings were cultured in a mixed substrate of perlite,vermiculite,and peat(2:2:3,v/v/v)and received exponential fertilization from 0(control),through 100,200,300,400,and 600 mg nitrogen(N)per plant over a four-month cultural rotation.Height,diameter,and shoot biomass increased with fertilizer rate and were maximized at 300 mg N per plant.This application also reduced nutrient deficiencies and avoided excess supply compared to higher rates.Polysaccharide,proline,and anti-oxidation enzyme activities tended to be greater in unfertilized controls or in over-fertilized high dosages,with lower activities around 100–300 mg N plant(-1).Application of 300 mg N per plant was identified as the optimum dosage as it maximized nutrient reserves,polysaccharide and proline contents,and anti-oxidants without causing any symptoms from excess fertilizer toxicity.Future work is required to identify the effects of N-fixation on the formation of nutritional reserves in Thailand rosewood seedlings subjected to exponential fertilization.