植物對土壤硝化作用的影響

Abstract

本篇論文的目的在探討植物是否具有抑制土壤硝化作用的能力。首先比較了耕地與非耕地之土壤，結果顯示曾經耕作或施肥地區的土壤除了茶園外皆比非耕地之土壤具有較高的硝化活性；其次為了探討這些土壤是否含有揮發性或易分解之硝化作用抑制物質，經過比較剛採回的土壤與放置二星期後之土壤的硝化活性，顯示只有農田及柳杉林土壤放置二星期後，其硝化活性顯著高於新鮮土壤。加入硝化抑制劑後顯示五節芒草原、未經施肥之狼尾草試驗區、茶園及檜木林土壤的硝化菌組成可能以自營性硝化菌為主，此外也證實了五節芒草原土壤仍然具有硝化活性，只是硝化活性相當低。加入碳酸鈣後進行硝化活性的培養則證實除了五節芒草原土壤外，未經施肥之狼尾草試驗區、茶園及檜木林土壤的硝化活性都有顯著的提升，也就是說土壤酸鹼值對於這幾種土壤的硝化活性似乎扮演了相當重要的角色，此外也證實了檜木林土壤的硝化活性雖然偏低，實際上仍然可能存在一群不具活性的硝化菌；為了探討植物根部之分泌物是否影響土壤的硝化作用，乃利用陽明山土進行玉米台南19號、玉米Pioneer 3732、小白菜、五節芒及狼尾草的盆栽試驗，結果顯示這五種植物並沒有明顯抑制硝化作用的現象。另外利用植物根部萃取液加入土壤所進行之硝化活性的培養實驗中，也沒有觀察到硝化作用被抑制的情形。最後以不同銨態氮與硝酸態氮比例的Hoagland's solution栽培玉米台南19號、玉米Pioneer 3732、小白菜、五節芒及狼尾草，探討這些植物對銨態氮的適應性以幫助瞭解植物生長對抑制硝化作用的潛力，結果顯示農作物與野生的植物品種對銨態氮與硝酸態氮的吸收有不同的偏好。

The aim of this study is to elucidate the inhibition of nitrification in plants. Soils of cultivated habitats with eight types, and of uncultivated habitats with four types were sampled. The soil nitrifying activity of the cultivated habitats except for the tea plantation appeared relatively higher compared to the other. The uncultivated habitats showed lower nitrifying activity than the cultivated habitats. To test the existence of volatile or easily decomposable materials that inhibit nitrification, the nitrifying activity of the fresh soils and the soils stored at room temperature for two weeks were compared. The level of the nitrifying activity of the two-week soils from manmade forest of Cryptomeria japania as well as from the farm of Brassica pekinensis Rupr. var. dentata appeared increasing significantly. After adding nitrapyrin to the soil the decreasing nitrifying activity indicated that the autotrophic nitrifiers may constitute most of nitrifers in the soil of Miscanthus grassland, unfertilized Napier grassland, tea plantation, and Chamaecyparis forest. It also revealed that, although the soil nitrifying activity of Miscanthus grassland was low, a small population of nitrifiers still existed. Furthermore, after adding calcium carbonates to the soil the level of nitrifying activity of unfertilized plot of Napier grass, tea plantation, and Chamaecyparis formosensis forest appeared increasing except for Miscanthus grassland. That is, the pH value seems play an important role in the nitrifying activity. It also revealed, although the soil nitrifying activity of the Chamaecyparis forest was low, a large population of restored nitrifiers might have existed. In order to understand the influence of compounds from plant roots on nitrification, pot experiments were carried out by growing maize with clones of Tainan 19 and Pioneer 3732, Brassica chinensis, Miscanthus sinensis var.glaber, and Pennisetum.purpureum schum (cv.7276) on the soil from Yangmingshan area. No inhibition of nitrification was observed in the above materials. In addition, no inhibition of nitrification was found either after adding the root extracts into the soil. To elucidate the potential influence of plant growth on the nitrification inhibition, the culture using Hoagland's solution with different ratios of ammonia-N to nitrate-N was performed. It revealed that cultivars and wild plants have quite different preference to the ammonia-N and nitrate-N. The different preference of plants on absorbing inorganic-N might affect the nitrification of the soils under these plants in the field.