Effects of weed control and fertilization at early establishment on tree nitrogen and water use in an exotic F_1 hybrid pine of subtropical Australia

摘要

Purpose We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δ~(13)C) and nitrogen (N) isotope (δ~(15)N) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F_1 hybrid (Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Barr. ex Golf.)) plantation grown on a yellow earth in southeast Queensland of subtropical Australia. Materials and methods Treatments included routine weed control, luxury weed control, intermediate weed control, mechanical weed control, nil weed control, and routine and luxury fertilization in a randomised complete block design. Initial soil nutrition and soil fertility parameters included (hot water extractable organic carbon (C) and total nitrogen (N), total C and N, C/N ratio, labile N pools (nitrate (NO_3~-) and ammonium (NH_4~+)), extractable potassium (K~+)), soil δ~(15)N and δ~(13)C. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δ~(15)N and foliar δ~(13)C were also measured at early establishment. Results and discussion Foliar N concentration at 1.25 years was significantly different amongst the weed control treatments and was negatively correlated to the relative weed cover at 1.1 years. Foliar N concentration was also positively correlated to foliar δ(15)N and foliar δ~(13)C, tree height, height g rowth rates and tree biomass. Foliar δ~(15)N was negatively correlated to the relative weed cover at 0.8 and 1.1 years. The physiological measurements indicated that luxury fertilization and increasing weed competition on these soils decreased leaf xylem pressure potential (ψ~(xpp )) when compared to the other treatments. Conclusions These results indicate how increasing N resources and weed competition have implications for tree N and water use at establishment in F_1 hybrid plantations of southeast Queensland, Australia. These results suggest the desirability of weed control, in the inter-planting row, in the first year to maximise site N and water resources available for seedling growth. It also showed the need to avoid over-fertilisation, which interfered with the balance between available N and water on these soils.