彩色豆馬勃菌根於重金屬污染土壤之復育效應

Abstract

本研究採用盆栽試驗，以彰化縣重金屬污染之農田土壤作為供試土壤，探討臺灣二葉松（Pinus taiwanensis）與青剛櫟（Cyclobalanopsis glauca）兩種樹種在接種彩色豆馬勃菌（Pisolithus tinctorius, Pt）形成菌根後，是否可達成植物復育之功效。試驗採完全逢機設計，試驗因子為菌根接種之有無，及同性質之兩種污染程度土壤。以觀察苗木形質生長，分析植株各部位之重金屬及養分濃度與蓄積量，測定根域土壤溶液之化學性質、根域土壤之麥角固醇量，以及觀察彩色豆馬勃菌根菌於MMN固體培養基之生長情形作探討。結果顯示供試土壤呈近中性之弱酸性，氮、磷、鈣含量均高於一般土壤，而重金屬鎘與鋅之濃度已高達環保署制定之觀察值及農地優先整治值。由存活率及形質生長之表現顯示，Pt與二葉松及青剛櫟苗木所產生之菌根，有抵抗重金屬逆境之效應。根外菌絲及子實體可比植體吸收較多之重金屬鎘、鋅，且接種組之根部重金屬吸收量較對照組低，可見菌根菌之根外菌絲及子實體具有截留重金屬之能力。由於供試土壤中鋅、鈣含量與菌根域土壤之草酸含量高，可能會降低鎘之有效性，導致以二葉松及青剛櫟復育土壤重金屬之效應不佳。不同鎘濃度固體培養基試驗中之菌絲生長耐受度較盆栽試驗低，可見菌根菌仍須與寄主植物共生，才能發揮較大之效應。接種菌根組根域土壤溶液中之硝酸根、磷酸根、鉀、鈣及鎂離子濃度均較對照組低，可見菌根之存在能有效吸收，減少養分漏失。而可以麥角固醇之測定去推估根域土壤菌絲量，證明麥角固醇測定法於本試驗之適用性。

The purpose of this study was to examine the effect of Pisolithus tinctorius (Pt) mycorrhizae on heavy metal contaminated land remediation. Two seedling species, Pinus taiwanensis and Cyclobalanopsis glauca, were infected with Pt. Using pot culture with the heavy-metal contaminated soil collected from Chang-Hua area completed the experiment. The completely randomized design included two main factors, one was mycorrhizal inoculation and the other was different degrees of polluted soils. The morphological growth, accumulation and concentration of heavy metal and nutrition in each part of plant, chemical properties of rhizosphere and mycorrhizosphere, ergosterol, and the growth of Pt on MMN agar plate were determined at the end of the experiment. The results obtained from this study showed that the soils were weak acidity and their nitrogen, phosphorus and calcium were higher than those of normal soils. The Cd and Zn contents of the soils have already reached the values of remediation priority regulated by Environment Protection Agency. The extraradical mycelium and fruiting body could absorb more Cd and Zn than host plant did, and the accumulation of heavy metal in mycorrhizal roots were less than those in non- mycorrhizal roots. Hence, the extraradical mycelium and fruiting body of mycorrhizal fungi had the ability to hold heavy metals back and could sequestrate them in the roots. The high concentrations of Zn, Ca and oxalic acid in rhizosphere were likely to result in low bioavailability of Cd, so that the phytoremediation effect of Pinus taiwanensis and Cyclobalanopsis glauca mycorrhizal seedlings on heavy-metal contaminated land were not remarkable. The tolerance of hyphal growth treated in the agar plate experiment of different Cd concentration was worse than that in the pot culture. Mycorrhizal fungi had to, obviously, coexist with host plant to achieve the maximum effect. Because the nitric acid, phosphorous acid and potassium, calcium, magnesium ions were lower in mycorrhizal plant than those in non-mycorrhizal plant, mycorrhizae was shown to absorb all kinds of ions effectively, thereby reducing the leakage of nutrition. We could successfully estimate rhizosphere fungal biomass through the measurement of ergosterol, and also showed the suitability of the ergosterol measuring method for this study.