巨桉凋落叶分解对牧草生长和光合特性及土壤酶活性的影响

采用盆栽试验,研究了巨桉凋落叶(0、50、100、150g凋落叶分别与8kg土壤混合)在分解过程中对牧草老芒麦和红三叶生长和光合生理特性的影响以及几种土壤酶活性的动态响应。结果显示:(1)两种牧草的草层高和生物量均随土壤中凋落叶剂量增大而减小,草层高受抑制的程度随分解时间延长而先强后弱。(2)凋落叶处理促进了老芒麦的净光合速率(Pn),使其对光和CO2的适应范围增大,表观量子效率(AQY)(50g处理除外)和羧化速率(CE)升高,对红三叶的光适应范围也有促进作用,并在低剂量(50g)下提升其Pn、AQY和CE,但降低其CO2适应范围;两种牧草暗呼吸速率(Rd)或光呼吸速率(Rp)几乎在各凋落叶处理下均高于CK。(3)红三叶的生长和光合生理受到的化感综合效应(平均0.317)小于老芒麦(平均0.380),表现出更强的抗性。(4)凋落叶在分解到20~60d时明显促进了土壤磷酸酶活性,在20~40d时明显促进了蔗糖酶活性,之后促进作用减弱,并与两种受体草层高受抑制作用的动态变化趋势一致;过氧化氢酶和脲酶活性受影响的程度较小。研究认为,巨桉凋落叶分解,通过释放化感物质直接或间接地作用于受体,尽管受体可能通过提高对光和CO2的利用能力来应对化感胁迫,但其呼吸消耗增大,生长始终表现为受到抑制。

Effects of Decomposing Leaf Litter of Eucalyptus grandis on Growth and Photosynthetic Traits of Two Forage Grasses and Activities of Several Soil Enzymes

A pot experiment was carried out to study the effect of decomposing leaf litter of Eucalyptus grandis on the growth and photosynthetic traits of two forage grass species (Elymus sibiricus and Trifolium pratense),and as well as on the activity dynamics of several soil enzymes.Leaf litter was applied at rate of 0,50,100,150 gram per pot,each containing 8 kg soil,resulting into four treatments,i.e.,CK,L⁵⁰,L¹⁰⁰ and L¹⁵⁰,respectively.Results were shown as follows:(1)Tussock height and biomass production in both grasses decreased with the increasing rate of leaf litter,and the inhibition effect declined as the exposure time prolonged.(2)Application of leaf litter promoted the photosynthetic rate (Pⁿ),expanded the adaptation interval of light intensity and CO² concentration,and increased the apparent quantum yield (AQY) (except treatment L¹⁵⁰) and carboxylation efficency of rubisco (CE) of E.sibiricus.Comparatively,decomposition of leaf litter resulted in the expansion of light utilization,but the shrink of CO² utilization in T.pratense species.Meanwhile,Pⁿ,AQY and CE of T.pratense were only promoted by treatment L⁵⁰.For both target plants,the dark respiration rate (R^d) or/and photorespiration rate (R^p) were generally increased by application of leaf litter at three rates.(3)An average synthesis effect of 0.317 and 0.380 were observed in T.pratense and E.sibiricus,respectively and the former exhibited stronger resistance ability.(4)Similarly,the activities of phosphatase and saccharase increased during 20~60 d and 20~40 d,respectively,but with the passage of time the promotion effect on activities of both enzymes decreased,which was in accordance with the inhibition dynamics on tussock height.Neither the urease activity nor the catalase activity was altered to a large extent by the leaf litter decomposition.Based on the results,we concluded that the decomposition of E.grandis leaf litter affects the growth of both grass species directly or indirectly by releasing allelochemicals.Despite that the two grass species may respond to this effect by enhancing the ability to utilize light and CO²,their growth was limited throughout the experiment period,because their energy consumption rate was promoted.