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THE DYNAMICS OF GROWTH AND NUTRIENT ACCUMULATION BY FRUITS OF GREVILLEA LEUCOPTERIS MEISSN., A PROTEACEOUS SHRUB, WITH SPECIAL REFERENCE TO THE COMPOSITION OF XYLEM AND PHLOEM SAP
Author(s) -
HOCKING PETER J.
Publication year - 1983
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1983.tb02702.x
Subject(s) - xylem , phloem , botany , exudate , nutrient , biology , transpiration , horticulture , photosynthesis , ecology
S ummaryGrevillea leucopteris is a large xeromorphic shrub from nutrient‐deficient sandy heathland in south‐western Australia. The fruit of G. leucopteris is a follicle which contains two seeds. Leaves and follicles have very low levels of essential nutrients, but seeds have very high levels, especially N, P and trace elements, as well as substantial oil reserves (30% w/w). Grevillea leucopteris appears to be a Ca accumulator because of the very high concentrations of this element in leaves, follicles and seeds. Phloem exudate from incisions in fruiting branches and xylem sap were used to study transport of nutrients to fruits. Phloem sap had 14 to 17% sugar. Glutamine was the major amino compound in xylem and phloem sap. Arginine comprised 37% of the N in xylem sap but was absent in phloem, suggesting its release from storage pools in roots and stems and metabolism in leaves. K dominated the mineral spectrum of phloem sap, and Ca that of xylem. Ca levels in xylem and phloem sap were very high (200 and 500 μ g cm −2 respectively), and K: Ca ratios were very low: xylem 0.5: phloem 3.7. The phloem: xylem concentration ratio for all minerals was 8.7. Reduced transpiration by enclosing fruits in plastic bags or foil changed their K: Ca ratios from 0.95 to 3.13 or 4.48. Each fruit used 11.5 cm 3 of water during growth, 76% estimated to arrive in the xylem, the rest via the phloem. The water use efficiency of G. leucopteris fruits was 29.9 cm −3 g −1 dry matter produced, close to values reported for mesomorphic species such as lupin and pea. The high levels of Ca in G. leucopteris fruits are due to high levels of Ca in transport fluids rather than elevated transpiration.