Genetic and environmental influence on foliar carbon isotope composition, nitrogen availability and fruit yield of 5-year-old mango plantation in tropical Australia

The aim of this study was to quantify the effect of different varieties, planting densities, tree training systems and canopy aspect (north and south) on tree water use efficiency and nitrogen (N) availability in relation to mango fruit yield and fruit size as well as soil fertility (particularly total carbon (C) and total N as well as C and N isotope compositions) in a 5-year-old mango plantation of tropical Australia

How do preharvest applications of nitrogen fertiliser affect branch growth, leaf morphology and fruit, in Mangifera indica (mango) orchards?

The effect of preharvest applications of nitrogen (N) fertiliser to mango trees during the late fruit maturation stage was investigated over 3 years (2012-2014) to determine the effects on canopy growth in 8 year-old 'Kensington Pride' (KP) mango trees grown in Queensland. The experiment consisted of six treatments where 156 g N tree-1 was applied as a single treatment, as 340 g of urea or split between three different times. The N treatments were 1) 100% of N 2 weeks postharvest (control), 2) 50% of N 2 weeks preharvest, plus 50% 2 weeks postharvest, 3) 65% 2 weeks preharvest, plus 35% 2 weeks postharvest, 4) 35% 4 weeks preharvest plus 65% 2 weeks postharvest, and 5) 65% 4 weeks preharvest, plus 35% 2 weeks postharvest. Vegetative growth was investigated at the branch, sub-branch (shoots), growth unit (GU) and leaf scales. Branches from different aspects (north, south, east and west), in the upper and lower canopy were assessed, and for 2 branch types (apical or lateral) was considered. Fruit counts were also considered at the branch level. Results showed that when 50-65% of the N was applied 2 and 4 weeks before harvest with the balance 2 weeks postharvest, the number of branches, branch length and fruit count increased. When 35% N was applied 4 weeks preharvest with the balance 2 weeks postharvest, only stem biomass was increased. Generally, branches in the upper canopy had longer sub-branches, longer and thicker, first level growth units, shorter leaf petioles and shorter and thinner leaves compared to those in the lower canopy. The SPAD N index was lowest in the northern canopy aspect. Differences were also observed between lateral and apical branches. Lateral branches had longer leaves than apical branches while apical branches had a trend for higher leaf area, stem biomass and leaf counts. There were also negative relationships between fruit count and measurements for stem biomass, leaf count and leaf area for apical branches however for lateral branches these relationships were positive. In summary, when a higher proportion of N was applied 2 or 4 weeks prior to harvest the partitioning of growth to leaves and stem increased while low rates of N applied prior to harvest led to increased stem biomass only. Applications of N 2 or 4 weeks prior to harvest resulted in increased fruit count and more efficient nitrogen use efficiency (NUE), although the relationship between fruit count, and leaf and stem growth was dependent on branch type. © 2020 International Society for Horticultural Science. All rights reserved

How weed control and fertilisation influence tree physiological processes and growth at early establishment in an exotic F1 hybrid pine plantation of subtropical Australia

Purpose This study investigated how nitrogen (N) nutrition and key physiological processes varied under changed water and nitrogen competition resulting from different weed control and fertilisation treatments in a 2-year-old F1 hybrid (Pinus elliottii Engelm var. elliottii × P. caribaea var. hondurensis Barr. ex Golf.) plantation on a grey podzolic soil type, in Southeast Queensland. Materials and methods The study integrated a range of measures including growth variables (diameter at ground level (DGL), diameter at breast height (DBH) and height (H)), foliar variables (including foliar N concentration, foliar δ13C and δ15N) and physiological variables (including photosynthesis (An), stomatal conductance (gs), transpiration (E), intrinsic water use efficiency (WUEi) (A/gs) and xylem pressure potential (ΨXPP)) to better understand the mechanisms influencing growth under different weed control and fertilisation treatments. Five levels of weed control were applied: standard (routine), luxury, intermediate, mechanical and nil weed control, all with routine fertilisation plus an additional treatment, routine weed control and luxury fertilisation. Relative weed cover was assessed at 0.8, 1.1 and 1.6 years after plantation establishment to monitor the effectiveness of weed control treatments. Soil investigation included soil ammonium (NH4 +-N), nitrate (NO3 −-N), potentially mineralizable N (PMN), gravimetric soil moisture content (MC), hot water extractable organic carbon (HWETC), hot water extractable total N (HWETN), total C, total N, stable C isotope composition (δ13C), stable N isotope composition (δ15N), total P and extractable K. Results and discussion There were significant relationships between foliar N concentrations and relative weed cover and between tree growth and foliar N concentration or foliar δ15N, but initial site preparation practices also increased soil N transformations in the planting rows reducing the observable effects of weed control on foliar δ15N. A positive relationship between foliar N concentration and foliar δ13C or photosynthesis indicated that increased N availability to trees positively influenced non-stomatal limitations to photosynthesis. However, trees with increased foliar N concentrations and photosynthesis were negatively related to xylem pressure potential in the afternoons which enhanced stomatal limitations to photosynthesis and WUEi. Conclusions Luxury and intermediate weed control and luxury fertilisation positively influenced growth at early establishment by reducing the competition for water and N resources. This influenced fundamental key physiological processes such as the relationships between foliar N concentration, A n, E, gs and ΨXPP. Results also confirmed that time from cultivation is an important factor influencing the effectiveness of using foliar δ15N as an indicator of soil N transformations

Effects of weed control and fertilization at early establishment on tree nitrogen and water use in an exotic F1 hybrid pine of subtropical Australia

Purpose We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δ13C) and nitrogen (N) isotope (δ15N) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F1 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 (NO3 −) and ammonium (NH4 +)), extractable potassium (K+)), soil δ15N and δ13C. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δ15N and foliar δ13C 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 δ15N and foliar δ13C, tree height, height growth rates and tree biomass. Foliar δ15N 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 (Ψxpp) 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 F1 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