Phillips Richard P, Fahey Timothy J
Department of Natural Resources, Cornell University, Ithaca, New York 14853, USA.
Ecology. 2006 May;87(5):1302-13. doi: 10.1890/0012-9658(2006)87[1302:tsamai]2.0.co;2.
Previous research on the effects of tree species on soil processes has focused primarily on the role of leaf litter inputs. We quantified the extent to which arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree species influence soil microbial activity and nutrient availability through rhizosphere effects. Rhizosphere soil, bulk soil, and fine roots were collected from 12 monospecifc plots (six AM and six ECM tree species) planted on a common soil at the Turkey Hill Plantations in Dryden, New York. Rhizosphere effects were estimated by the percentage difference between rhizosphere and bulk soil samples for several assays. Rhizosphere effects on soil microbes and their activities were significant for ECM species but in only a few cases for AM species. In AM tree species, microbial biomass, net N mineralization, and phosphatase enzyme activity in the rhizosphere were 10-12% greater than in bulk soil. In ECM tree species, rhizosphere effects for microbial biomass, C mineralization rates, net N mineralization, and phosphatase activity were 25-30% greater than bulk soil, and significantly greater than AM rhizosphere effects. The magnitude of rhizosphere effects was negatively correlated with the degree of mycorrhizal colonization in AM tree species (r = -0.83) and with fine root biomass (r = -0.88) in ECM tree species, suggesting that different factors influence rhizosphere effects in tree species forming different mycorrhizal associations. Rhizosphere effects on net N mineralization and phosphatase activity were also much greater in soils with pH < 4.3 for both AM and ECM tree species, suggesting that soil pH and its relation to nutrient availability may also influence the magnitude of rhizosphere effects. Our results support the idea that tree roots stimulate nutrient availability in the rhizosphere, and that systematic differences between AM and ECM may result in distinctive rhizosphere effects for C, N, and P cycling between AM and ECM tree species.
先前关于树种对土壤过程影响的研究主要集中在凋落物输入的作用上。我们量化了丛枝菌根（AM）树种和外生菌根（ECM）树种通过根际效应影响土壤微生物活性和养分有效性的程度。根际土壤、块状土壤和细根是从纽约州德莱登市火鸡山种植园一块普通土壤上种植的12个单树种样地（6种AM树种和6种ECM树种）采集的。通过几种测定方法，用根际和块状土壤样品之间的百分比差异来估计根际效应。根际对土壤微生物及其活性的影响在ECM树种中很显著，但在AM树种中只有少数情况如此。在AM树种中，根际微生物生物量、净氮矿化和磷酸酶活性比块状土壤高10 - 12%。在ECM树种中，根际对微生物生物量、碳矿化率、净氮矿化和磷酸酶活性的影响比块状土壤高25 - 30%，且显著大于AM树种的根际效应。根际效应的大小与AM树种的菌根定殖程度呈负相关（r = -0.83），与ECM树种的细根生物量呈负相关（r = -0.88），这表明不同因素影响形成不同菌根共生关系的树种的根际效应。对于AM和ECM树种，在pH < 4.3的土壤中，根际对净氮矿化和磷酸酶活性的影响也大得多，这表明土壤pH及其与养分有效性的关系也可能影响根际效应的大小。我们的结果支持这样一种观点，即树木根系刺激根际养分有效性，并且AM和ECM之间的系统差异可能导致AM和ECM树种之间在碳、氮和磷循环方面产生独特的根际效应。
