Genetic and environmental controls of tree water and nitrogen use efficiency of 5-year-old mango plantation in relation to mango fruit yield and size as well as soil fertility in tropical Australia

Purpose: This study was aimed to quantify the effect of different variety, planting density, training system and canopy position on tree water and nitrogen use efficiencies in relation to mango fruit yield and size as well as soil fertility in a 5-year-old mango plantation of tropical Australia.

Material and Methods: Soil (0-10 cm) and mango foliar samples were collected from a 5-year-old, factorial field experiment testing 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 positions (north vs south) on foliar total carbon (TC, %), total nitrogen concentration (TN, %), and stable carbon (C) and nitrogen (N) isotope compositions (δ¹³C and δ¹⁵N) as well as the corresponding total C, total N and δ¹³C and δ¹⁵N in the surface soil of tropical Australia. In addition, mango fruit yields and sizes were determined. Soil and foliar total C and N as well as δ¹³C and δ¹⁵N were determined on mass spectrometers at Griffith University. Each of the above treatment was replicated 6 times for foliar samples and 3 times for soil samples.

Results: There were significant genetic effect on foliar total N concentration (TN, %), tree water use efficiency (WUE) as reflected by foliar δ¹³C, N use efficiency (NUE) as indicated by foliar TN and δ¹⁵N, mango fruit yield and sizes in the 5-year-old mango plantation of tropical Australia. Overall, mango variety of Keitt had higher tree WUE and NUE as well as higher mango yield and greater fruit size, compared with those of mango variety of Calypso. There were also significant environmental influences on mango tree WUE and NUE as well as mango yield and fruit size. In particular, high planting density had higher tree NUE, and lower WUE as well as higher N loss, 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 convention training system also had higher tree NUE and WUE, compared with the single leader training system. The northern side of tree canopy (sunny side) had lower fruit number, compared with the southern side (shady side) of tree canopy.

Conclusion: There were significant genetic and environmental influences on tree WUE and NUE as well as mango fruit yield and sizes in the 5-year-old mango plantation, highlighting the significant and exciting opportunities to improve mango tree WUE and NUE as well as fruit yield and soil fertility with both genetic selection and site management regimes.