Survey of cultural pratices used in production of viburnums and water use and growth of three viburnum species grown under different shade intensities

nationwide survey of the commercial nursery growers was conducted to identify the cultural practices used in production of viburnums. Daily plant water use of leatherleaf viburnum and Burkwood viburnum in 0%, 30% and 60% shade was determined gravimetrically by weighing each pot on an electronic precision balance. Plant heights, widths, leaf necrosis, number of leaves per plant, leaf area, root and shoot dry weights, root to shoot ratio (R/S) and specific leaf area were determined for leatherleaf, Korean spice and Burkwood viburnum in 0%, 30% and 60% shade. Survey results suggest that using more sustainable production techniques that improve irrigation efficiency will reduce production costs, conserve water, and produce higher quality crops. Nursery producers should consider planting time; selection of components of container substrates, use of inorganic and biological amendments in the substrate; alternative irrigation sources; cost and water efficient irrigation methods; irrigation frequency and use of cyclic irrigation that could improve water and nutrient management of viburnums and other ornamental crops. Sixty percent shade can result in water savings for Burkwood viburnum. Leatherleaf total water use was lowest in 0% shade, however, the greater degree of leaf necrosis and leaf abscission and reduced growth can make the plant less salable. Water use of leatherleaf was lower in 60% than in 30% shade. Shade increased plant height and width, leaf number and leaf area, leaves, stems, roots and total dry weights, and specific leaf area in all species. Root to shoot ratio was reduced by shade in Korean spice and leatherleaf viburnum but was not affected in Burkwood viburnum. Degree of leaf necrosis decreased with increasing shade intensity in all three species. Shading can be a useful means, at least during the hot summer months, for reducing water use and improving growth and quality in Burkwood, Korean spice and leatherleaf viburnum.Horticulture and Landscape Architecture Departmen

Hydroponics

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Can hydraulic design explain patterns of leaf water isotopic enrichment in C3 plants?

H2 18 O enrichment develops when leaves transpire, but an accurate generalized mechanistic model has proven elusive. We hypothesized that leaf hydraulic architecture may affect the degree to which gradients in H2 18 O develop within leaves, influencing bulk leaf stable oxygen isotope enrichment (ΔL ) and the degree to which the Péclet effect is relevant in leaves. Leaf hydraulic design predicted the relevance of a Péclet effect to ΔL in 19 of the 21 species tested. Leaves with well-developed hydraulic connections between the vascular tissue and the epidermal cells through bundle sheath extensions and clear distinctions between palisade and spongy mesophyll layers (while the mesophyll is hydraulically disconnected) may have velocities of the transpiration stream such that gradients in H2 18 O develop and are expressed in the mesophyll. In contrast, in leaves where the vascular tissue is hydraulically disconnected from the epidermal layers, or where all mesophyll cells are well connected to the transpiration stream, velocities within the liquid transport pathways may be low enough that gradients in H2 18 O are very small. Prior knowledge of leaf hydraulic design allows informed selection of the appropriate ΔL modelling framework.K.E.L. was supported by an Australian Postgraduate Award and A.S. was supported by an Australian Postgraduate Award and International Postgraduate Research Support. Australian Research Council, Grant/Award Number: DP17010427

Variability in mesophyll conductance to CO2 in grain legumes

Mesophyll conductance (gm) limits the diffusion of CO2 from sub-stomatal cavities to the carboxylation site and is a significant limitation to photosynthesis. However, there is a lack of complete understanding of gm variability and its regulation under different environmental conditions, and relevant studies in grain legumes are scarce. My research projects aimed to characterize genetic variability in gm, to quantify the response of gm to short- and long-term environmental changes and to assess the relationship of gm with leaf water-use efficiency (WUE) in grain legumes. gm and leaf hydraulic conductance (Kleaf) were examined simultaneously under growth conditions to see if they show coordinated response. gm varied significantly among genotypes for most of the legumes studied, but the genotypes did not vary in cell wall and plasma membrane conductance (measured from the oxygen isotope method). gm responded to growth or measurement environments, increasing rapidly with increasing light intensity but decreasing under blue light. However, genotypes differed in their interactive response to water stress, light intensity and light quality. Rapid response of gm to changes in light intensity was affected by N source (N2-fixing or inorganic-N fed). Short-term temperature response of gm varied between species. Chloroplast membrane conductance varied among species and genotypes and with growth environment. Environmentally driven leaf anatomical traits were not the major factors determining gm, but genotypes differed in the degree to which leaf anatomy influenced gm. Our results did not show coordination between gm and Kleaf. gm was strongly associated with photosynthetic rate but not with stomatal conductance. The results of this project provide useful information for crop genetic improvement through gm in legumes under climate change scenarios. Increasing gm in legumes will increase photosynthetic rate and possibly WUE, when there is no increase in stomatal conductance

The response of mesophyll conductance to short- and long-term environmental conditions in chickpea genotypes.

. Mesophyll conductance (g m) has been shown to vary between genotypes of a number of species and with growth environments, including nitrogen availability, but understanding of g m variability in legumes is limited. We might expect g m in legumes to respond differently to limited nitrogen availability, due to their ability to fix atmospheric N2. Using online stable carbon isotope discrimination method, we quantified genetic variability in g m under ideal conditions, investigated g m response to N source (N2-fixation or inorganic N) and determined the effects of N source and water availability on the rapid response of g m to photosynthetic photon flux density (PPFD) and radiation wavelength in three genotypes of chickpea (Cicer arietinum). Genotypes varied 2-fold in g m under non-limiting environments. N-fed plants had higher g m than N2-fixing plants in one genotype, while g m in the other two genotypes was unaffected. g m response to PPFD was altered by N source in one of three genotypes, in which the g m response to PPFD was statistically significant in N-fed plants but not in N2-fixing plants. There was no clear effect of moderate water stress on the g m response to PPFD and radiation wavelength. Genotypes of a single legume species differ in the sensitivity of g m to both long- and short-term environmental conditions, precluding utility in crop breeding programmes

The response of mesophyll conductance to short- and long-term environmental conditions in chickpea genotypes.

. Mesophyll conductance (g m) has been shown to vary between genotypes of a number of species and with growth environments, including nitrogen availability, but understanding of g m variability in legumes is limited. We might expect g m in legumes to respond differently to limited nitrogen availability, due to their ability to fix atmospheric N2. Using online stable carbon isotope discrimination method, we quantified genetic variability in g m under ideal conditions, investigated g m response to N source (N2-fixation or inorganic N) and determined the effects of N source and water availability on the rapid response of g m to photosynthetic photon flux density (PPFD) and radiation wavelength in three genotypes of chickpea (Cicer arietinum). Genotypes varied 2-fold in g m under non-limiting environments. N-fed plants had higher g m than N2-fixing plants in one genotype, while g m in the other two genotypes was unaffected. g m response to PPFD was altered by N source in one of three genotypes, in which the g m response to PPFD was statistically significant in N-fed plants but not in N2-fixing plants. There was no clear effect of moderate water stress on the g m response to PPFD and radiation wavelength. Genotypes of a single legume species differ in the sensitivity of g m to both long- and short-term environmental conditions, precluding utility in crop breeding programmes