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Purpose: 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. Material and Methods: Mango foliar samples were collected from a 5-year-old, factorial field experiment, where we tested the effects of two mango varieties (Calypso vs Keitt); two planting densities (medium vs high); two training systems (single leader vs conventional); and two sampling canopy aspects (north vs south) on foliar total C (%), total N (%), and stable C and N isotope compositions (δ13C and δ15N). The 0–10 cm of surface soils were also assessed for total C, total N, and δ13C and δ15N of different varieties, planting densities, and training systems. In addition, mango fruit yield, and fruit size were measured. Results: There were significant genetic effects on foliar total N, tree water use efficiency (WUE) as reflected by foliar δ13C, N availability as indicated by foliar total N and δ15N, mango fruit yield, and fruit size in 5-year-old mango trees in tropical Australia. Overall, Keitt had higher foliar δ13C and N availability (higher total N and lower δ15N) as well as higher mango yield and greater fruit size, compared with those of Calypso. There were also significant environmental influences on foliar δ13C and N availability. In particular, high planting density had higher N availability (higher total N), and lower foliar δ13C as well as higher N loss (higher δ15N), compared with those of medium planting density. High planting density treatment also had higher soil total N, compared with that of medium planting density treatment. The conventional training system had higher N availability and foliar δ13C, compared with those of the single leader training system. The northern side of tree canopy (sunny side) had lower fruit number, compared with that of the southern side (shady side) of tree canopy. Conclusion: There were significant genetic and environmental influences on tree WUE and N availability as well as mango fruit yield and fruit size in the 5-year-old mango trees. Among them, Keitt's fruit was significantly larger than Calypso and had higher foliar δ13C (higher WUE). Although high planting density increased soil total N, it also resulted in lower foliar δ13C and more N loss. Our results highlighted the significant potential for improvement of foliar δ13C and N availability as well as fruit yield and soil fertility with both genetic selection and site management regimes. [ABSTRACT FROM AUTHOR]

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 F 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 δC and δN) and physiological variables (including photosynthesis (A), stomatal conductance (g), transpiration ( E), intrinsic water use efficiency (WUE) ( A/g) and xylem pressure potential (Ψ)) 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 (NH-N), nitrate (NO-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 (δC), stable N isotope composition (δN), 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 δN, but initial site preparation practices also increased soil N transformations in the planting rows reducing the observable effects of weed control on foliar δN. A positive relationship between foliar N concentration and foliar δC 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 WUE. 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, E, g and Ψ. Results also confirmed that time from cultivation is an important factor influencing the effectiveness of using foliar δN as an indicator of soil N transformations. [ABSTRACT FROM AUTHOR]

Purpose: We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δC) and nitrogen (N) isotope (δN) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F 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) and ammonium (NH)), extractable potassium (K)), soil δN and δC. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δN and foliar δC 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 δN and foliar δC, tree height, height growth rates and tree biomass. Foliar δN 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) 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 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. [ABSTRACT FROM AUTHOR]

Background and aims: The aim of weed control and fertilization in forest plantations was to increase tree growth by reducing competition for available nutrients and water. However, treatments that influence weed biomass can also have significant impacts on soil carbon (C) and nitrogen (N) cycling which can in turn lead to changes in the dynamics of stable C (δC) and N (δN) isotope compositions in soils and tree foliage. Methods: We examined the key C and N cycling processes influenced by routine and luxury weed control and fertilization treatments as reflected by soil and foliar δC and δN and long-term tree growth in an 8-year old F hybrid pine ( Pinus elliottii x P. caribaea) plantation in southeast Queensland, Australia. Weed control treatments varied by treatment frequency and intensity while fertilization treatments varied by the application of N, phosphorus (P), potassium (K) and micronutrients. Different soil and canopy sampling positions were assessed to determine if sampling position enhanced the relationships among soil N transformations and tree N use, water use efficiency and carbon gain under the early establishment silviculture. Results: Routine weed control was associated with increased weed biomass returned to the soil, compared with luxury weed control. Soil δC increased at the 0-5 cm soil sampling depth in both the inter-planting (IPR) and planting row (PR) as a result of the routine weed control treatments. In addition, soil δC was significantly higher as a result of fertilisation treatment in the 0-5 cm soil sampling depth in the PR. Soil δC was negatively correlated to soil δN at the 0-5 cm soil sampling depth in the IPR. Soil δN increased in the 0-5 and 5-10 cm soil sampling depths in the IPR, as a result of more frequent (luxury) weed control. Foliar δN and tree water use efficiency (WUE) (as indicated by foliar δC) were positively correlated with tree growth at age 8 years. While relationships between δC and δN in the soil and foliage varied depending on soil sampling depth and position, and with canopy sampling position where there were consistent relationships between soil δC (or δN) and foliar δN. Conclusions: This study demonstrates how early establishment silviculture has important implications for soil C and N cycling and how soil δC and δN were consistent with changes in soil C cycling and N transformations as a result of weed control treatments, while foliar δN was linked to more rapid N cycling as reflected in the soil δN, which increased tree growth and tree WUE (as reflected by foliar δC). [ABSTRACT FROM AUTHOR]

Soil carbon (C) and nutrient pools under different plantation weed control and fertilizer management treatments were assessed in a 7-year-old, F1 hybrid ( Pinus elliottii var. elliottii × Pinus caribaea var. hondurensis) plantation in southeast Queensland, Australia. This research aimed to investigate how early establishment silvicultural treatments would affect weed biomass, soil C, nitrogen (N) and other nutrient pools; and soil C (δ13C) and N isotope composition (δ15N) to help explain the key soil processes regulating the soil C and nutrient pools and dynamics. Soils were sampled in June 2006 in both the planting row and in the inter-planting row at three depths (0–5, 5–10, and 10–20 cm). Soil parameters including total and labile C and N pools; soil δ13C and δ15N; total phosphorus (P); extractable potassium (K); moisture content and weed biomass were investigated. The luxury weed control treatments significantly reduced weed biomass and its organic residues returned to the soil in the first 7 years of plantation development. This resulted in significant variations at some depths and positions in soil δ13C, δ15N, extractable K, hot water extractable organic C (HWEOC), hot water extractable total N (HWETN), potentially mineralizable N (PMN), and soil moisture content (MC). Luxury weed control in the absence of luxury fertilization also significantly decreased extractable K. There was a significant interaction between soil depth and sampling position for soil total C, total N, HWEOC, and HWETN. Weed biomass correlated positively with soil total N, δ13C, PMN, MC, HWEOC, and HWETN. Luxury weed control treatments significantly reduced weed biomass leading to a reduction of soil organic matter. Soil δ13C and δ15, together with the other soil labile C and N pools, were sensitive and useful indicators of soil C dynamics and N cycling processes in the exotic pine plantation of subtropical Australia. [ABSTRACT FROM AUTHOR]

A correction to the article "Effects of weed control and fertilization on soil carbon and nutrient pools in an exotic pine plantation of subtropical Australia," that was published in a previous issue is presented.