2017 Volume 21 Issue 1 Pages 13-19
Considerable diversity was recognized in the herbaceous understories of hundreds of temperate tree species (approximately 70 years old) grown in a uniformly managed arboretum. Of these, species whose understory diversities were categorized as being nonexistent (Chamaecyparis obtusa, Cryptomeria japonica), poor (Calocedrus decurrens, Nageia nagi, Cladrastis platycarpa), and extremely rich (Taxodium distichum, Celtis sinensis, Ulmus parvifolia) were identified, and soils around their trunks were collected for assessment of their biological and chemical properties. The results of soil bioassays examining the growth of three herbaceous plants (lettuce, Italian ryegrass [both grown from seeds], and Solidago altissima [a perennial weed, grown from rhizome segments]) as well as the macroconidial germination of the fungus Fusarium cuneirostrum were fully consistent with the degree of understory diversity at the sites of soil collection. Considerably high growth of test plants was observed in soils from around T. distichum, C. sinensis, and U. parvifolia, indicating bio-promotive modification of soils by these species. Of the other five species, soils from around C. obtusa and C. japonica exhibited acidity as high as pH 3.9 and 4.2, and these soils showed the strongest inhibition of the growth of three test plants, and also completely inhibited the germination of F. cuneirostrum. Soil EC levels did not show any correspondence to bioassay results. The above results indicate that tree species may play a considerable role in understory biological diversity.