How weed control and fertilisation influence tree physiological processes and growth at early establishment in an exotic F1 hybrid pine plantation of subtropical Australia
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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.
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.
KeywordsEstablishment silviculture Foliar δ13C and δ15N Nitrogen and water competition Tree growth and physiology
Respect and gratitude go to colleagues in the Centre for Forestry and Horticulture (now known as the Environmental Futures Centre) at Griffith University, for their assistance with field work, guidance and persistence and to Mr. Scott Byrne and Mr. and Mrs. Diocares of Griffith University for their technical assistance. The authors also acknowledge the operating funding and technical support from the Forestry Plantations Queensland viz. Dr. Ken Bubb, Mr. Paul Keay, Dr. Marks Nester, Mr Ian Last, and for the numerous staff who were responsible for the development and maintenance of the experimental site. Paula Ibell was supported by a research scholarship grant through the Australian Research Council and an extension scholarship from the Centre for Forestry and Horticulture Research, Griffith University.
- Barber BL (1986) In, Nonstomatal effects of water stress on photosynthesis in loblolly pine (Pinus taeda L.) seedlings, Auburn University, ALGoogle Scholar
- Colbert SR, Jokela EJ, Neary DG (1990) Effects of annual fertilisation and sustained weed control on dry matter partitioning, leaf area and growth efficiency of juvenille Loblolly and Slash Pine. For Sci 36:995–1014Google Scholar
- Department of Primary Industries Forestry (DPIF) (2006) Meterological records 2006. Beerburrum Forestry Office, BeerburrumGoogle Scholar
- Ehleringer JR, Hall AE, Farquar GD (1993) Stable isotopes and plant carbon—water relations. Academic Press, San DiegoGoogle Scholar
- Field C, Mooney HA (1986) The photsynthesis-nitrogen relationship in wild plants. In: On the economy of plant form and function. In: Givnish TJ (ed) Proceedings of the Sixth Maria Moors Cabot Symposium, ‘ Evolutionary Constraints on Primary Productivity: Adaptive Patterns of Energy Capture in Plants’. Cambridge University Press, Cambridge, pp 25–55Google Scholar
- Johnson JD (1984) A rapid technique for estimating total surface area of pine needles. For Sci 30:913–921Google Scholar
- Kershaw KA (ed) (1973) Quantative and Dynamic Plant Ecology. Edward Arnold, LondonGoogle Scholar
- Livingstone NJ, Whitehead D, Kelliher FM, Wang Y-P, Grace JC, Walcroft AS, Byers JN, McSeveny TM, Millard P (1998) Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. Don tree. Plant Cell Environ 21:795–803CrossRefGoogle Scholar
- Nadelhoffer KJ, Fry B (1994) Nitrogen isotope studies in forest ecosystems. In: Lajtha K, Michener RH (eds) Stable isotopes in ecology and environmental science. Blackwell Scientific Publications, Oxford, p 316Google Scholar
- Philip MS (1994) Measuring Trees and Forests. CAB International, WallingfordGoogle Scholar
- VSN International (2011) GenStat 14th edition. VSN International, Hemel Hempstead UK. Webpage: Genstst.co.ukGoogle Scholar
- Xu ZH, Saffigna PG, Farquhar GD, Simpson JA, Haines RJ, Walker S, Osborne DO, Guinto D (2000) Carbon isotope discrimination and oxygen isotope composition in clones of the F1 hybrid between slash pine and caribbean pine in relation to tree growth, water-use efficiency and foliar nutrient concentration. Tree Physiol 20:1209–1218CrossRefGoogle Scholar