细根具有良好的可塑性, 不同根序等级的细根会表现不同的策略来适应土壤资源有效性的改变, 了解各级细根对土壤资源有效性的可塑性反应对认识细根的养分和水分吸收规律、预测碳(C)在地下的分配特点具有重要意义。该文以四川省丹陵县台湾桤木(Alnus formosana)-扁穗牛鞭草(Hemarthria compressa)复合模式为研究对象, 采用施肥处理, 应用土柱法采样, 探讨了施肥对台湾桤木-扁穗牛鞭草模式土壤表层(0-10 cm)和亚表层(10-20 cm)台湾桤木1-5级细根的生物量、形态特征(直径、比根长)、全C和全氮(N)含量的影响。结果表明: (1)台湾桤木1-5级细根直径随根序的增大而增加, 施肥降低土壤表层台湾桤木各级细根直径而增加了土壤亚表层台湾桤木各级细根直径; 台湾桤木1-5级细根比根长则随根序的增加而减小, 施肥增加了台湾桤木各级细根的比根长, 且施肥极显著增加了表层和亚表层台湾桤木前三级细根的比根长(p < 0.01)。(2)台湾桤木1-5级细根生物量均随土层深度的增加而减小, 施肥减少了台湾桤木各个土层各级细根生物量, 且显著降低了台湾桤木前三级细根生物量占总生物量的比例(p < 0.05), 而增加了4、5级细根生物量。(3)台湾桤木3级细根全C最大, 1级根最小, 且土壤表层台湾桤木各级细根全C含量大于亚表层; 施肥降低了台湾桤木各级细根全C含量, 但影响并不显著(p > 0.05)。台湾桤木细根全N含量随根序的增加而降低, 且土壤表层1-5级细根全N含量均高于亚表层; 施肥极显著(p < 0.01)增加了土壤表层1级细根及亚表层1、2级细根的全N含量, 而对于3-5级细根全N含量则影响不显著(p > 0.05)。以上结果显示, 当土壤资源有效性变化时, 各级根序细根会作出不同的可塑性反应, 且施肥对各级细根的影响主要表现在低级根上。
Aims Our objectives were to: 1) examine fine root biomass, morphological characteristics and content of C and N of Alnus formosana in an A. formosana-Hemarthria compressa composite model in Danling, Sichuan Province, China, 2) examine the effects of fertilization on each order of fine roots, and 3) analyze the relationship between soil nutrients and fine root biomass, architecture and content of C and N. Methods In September 2010, we established two subdistricts, eradicated weeds and planted H. compressa. We fertilized one subdistrict with N-P-K fertilizer in April, June, August and October and did not fertilize the other subdistrict. We excavated soil blocks of 20 cm × 20 cm × 10 cm (height) to sample intact fine root branches of at least the first branch orders. We dissected the intact root branches by orders and measured the diameter, specific root length, biomass, and C and N content of each order. Important findings Fertilization reduced fine-root average diameter in soil surface and increased that in soil subsurface. In fine-root orders 1-5, specific root length increased as root order decreased. Fertilization significantly increased specific root length in fine-root orders 1-3 in soil surface and subsurface (p < 0.01). Fertilization reduced fine-root biomass in all soil layers and significantly reduced the ratio of fine-root biomass to total root biomass in orders 1-3 (p < 0.05), while fine root biomass increased in orders 4 and 5. The effect of fertilization on fine-root C content was not significant in all orders (p > 0.05). Soil surface total N content of fine roots of 1-5 orders was higher than that in subsurface. Fertilization significantly (p < 0.01) increased fine-root N content of order 1 fine roots in soil surface and orders 1 and 2 in the subsurface, but had no significant effects on orders 3-5 (p > 0.05).