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.

Identity and distribution of weedy Pedicularis kansuensis Maxim. (Orobanchaceae) in Tianshan Mountains of Xinjiang：morphological, anatomical and molecular evidence

Weedy plants affect the biodiversity and ecosystem function as well as the crop and fodder plant production. However, adequate management requires detailed knowledge of the taxonomic identity of these plants. Here, we focused on a hemiparasitic Pedicularis species(Orobanchaceae), which occurs at high densities and results in significant biomass reductions in forage grasses in Bayanbulak Grassland of Xinjiang. The identity of this target species is not clear, with conflicting reports in publications and in herbarium collections. Hence, clear and management-relevant information on demography and reproductive ecology is difficult to be obtained from the literature. Therefore, we analyzed field and archival materials collected from Xinjiang in order to clarify the identity and distribution of the target species. Morphological analyses suggested that the populations at Bayanbulak Grassland should be Pedicularis kansuensis Maxim. rather than P. verticillata L. which has been accepted in the available literature. Phylogenetic analysis with a combination of three barcodes(mat K, rbc L and trn H-psb A) uniting a clade of P. kansuensis and individuals from Bayanbulak Grassland populations with 100% bootstrap support, confirmed the target species to be P. kansuensis. Anatomical investigations and field observations showed that the target species is an annual or biennial herb, which also fits with the life cycle as P. kansuensis. Based on archive material and field observations, we verified that the distribution of P. kansuensis is mainly concentrated in the Tianshan Mountains of Xinjiang.

Root hemiparasitism in Malania oleifera(Olacaceae), a neglected aspect in research of the highly valued tree species

Malania oleifera(Olacaceae)is a valued tree species,mostly because its seeds have high precious fatty acid content(particularly nervonic acid).However,seedling mortality rates are often high and regeneration of this tree has been problematic,which greatly hinders its utilization at a large scale.Cultivation difficulties of some tree species in the family Olacaceae have been attributed to their root hemiparasitic habit.Prompted by field observations and the taxonomic proximity of M.oleifera to root hemiparasites in Olacaceae,we hypothesized that tuberous structures observed on the roots of M.oleifera are parasitic organs known as haustoria.To test this hypothesis,we collected root samples from M.oleifera plants of various ages and growth conditions,investigated the morphological and anatomical features of tuberous structures and their connections to neighboring roots.Our analyses confirmed that M.oleifera are root hemiparasites.To the best of our knowledge,this is the first empirical report on root hemiparasitism in M.oleifera.Because life strategies of root hemiparasitic plants differ greatly from autotrophic plants,the root hemiparasitic habit needs to be taken into account for successful seedling regeneration of M.oleifera.This study establishes the foundation for investigations into a long-neglected but essential aspect in research of these highly valued tree species.