Waterlogging and fire impacts on nitrogen availability and utilization in a subtropical wet heathland (wallum)

• Published in: Plant, Cell and Environment
• Main Authors: Schmidt, S, Stewart, GR
• Format: Article in Journal/Newspaper
• Language: English
• Published: WILEY-BLACKWELL 1997
• Subjects: Plant Sciences; Fire; Mycorrhiza; N-15 Natural Abundance; Nitrate Reductase Activity; Nitrogen Sources; Proteoid Roots; Root Specializations; Subtropical Heathland; Wallum; Waterlogging; N-15 Natural-abundance; Nitrate Utilization; Arctic Plants; Amino-acids; Mycorrhizal Associations; Organic Nitrogen; Soil; Ericaceae; Biology; Forest; 1110 Plant Science; 1314 Physiology; Arctic
• Online Access: https://espace.library.uq.edu.au/view/UQ:57973

Protein, amino acids and ammonium were the main forms of soluble soil nitrogen in the soil solution of a subtropical heathland (wallum). After fire, soil ammonium and nitrate increased 90- and 60-fold, respectively. Despite this increase in nitrate availability after fire, wallum species exhibited uniformly low nitrate reductase activities and low leaf and xylem nitrate, During waterlogging soil amino acids increased, particularly gamma-aminobutyric acid (GABA) which accounted for over 50% of amino nitrogen. Non-mycorrhizal wallum species were significantly (P < 0.05) N-15-enriched (0.3-4.3 parts per thousand) compared to species with mycorrhizal associations (ericoid-type, ecto-, va-mycorrhizal) which were strongly depleted in N-15 (-6.3 to -1.8 parts per thousand). Lignotubers and roots had delta(15)N signatures similar to that of the leaves of respective species. The exceptions were fine roots of ecto-, ecto/va-, and ericoid type mycorrhizal species which were enriched in N-15 (0.1-2 4 parts per thousand). The delta(15)N signatures of delta(15)N(total soil N) and delta(15)N(soil NH4+) were in the range 3.7-4.5 parts per thousand, whereas delta(15)N(soil NO3-) was significantly (P < 0.05) more enriched in N-15 (9.2-9.8 parts per thousand). It is proposed that there is discrimination against N-15 during transfer of nitrogen from fungal to plant partner. Roots of selected species incorporated nitrogen sources in the order of preference: ammonium > glycine > nitrate. The exception were proteoid roots of Hakea (Proteaceae) which incorporated equal amounts of glycine and ammonium.