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.

Effects of weeding and fertilization on soil biology and biochemical processes and tree growth in a mixed stand of Dalbergia odorifera and Santalum album

In southern China,the eucalyptus plantation industry has been severely restricted by government policy over concerns on negative environmental impacts.In its place,large-scale plantations of high-value tropical tree species such as nitrogen-fixing Dalbergia odorifera and hemiparasite Santalum album have been widely cultivated including in mixed-species plantations.However,despite their poor growth,little information is available on suitable silvicultural practices of these plantations.Therefore,we subjected an 8-year-old mixed stand of D.odorifera and S.album to weeding,fertilization,weeding+fertilization,or no(CK)treatments and measured soil microbial biomass,respiration,nutrients,nitrogen mineralization and leaching and tree growth and litter production.Weeding and fertilization decreased microbial biomass but increased soil respiration,inhibited mineralization,had not effect on leaching of soil nitrogen,and improved the nutrient status of plantation soil.All practices improved the growth of D.odorifera.In the mixed plantation,fertilization increased litter production and nutrient content,but weeding and weeding+fertilization decreased growth of S.album and litter production in mixed plantation because weeding decreased the number of S.album haustoria in underground plant roots.In conclusion,fertilization is recommended;however,weeding-related practices are inappropriate for D.odorifera and S.album mixed plantations.These conclusions have important implications for managing other parasite or mixed-species plantations.