固氮树种对桉树人工林土壤团聚体酶活性及其化学计量比的影响.

Soil enzyme activity and its stoichiometric ratio are important indicators reflecting soil nutrient availability and microbial growth and metabolic nutrient requirements. However, the effects of nitrogen-fixing tree species on soil aggregate-associated enzyme activities and ecoenzymatic stoichiometric characteristics in Eucalyptus plantations are still unclear. In this study, an 11-year-old pure E. urophylla plantation(PP)and an 11-year-old mixed E. urophylla and Dalbergia odorifera plantation(MP)in the Shaoping Experimental Field of the Tropical Forestry Experimental Centre of Chinese Academy of Forestry were selected as the research objects. Soil aggregates which were collected from 0-10 cm soil layer were classified into >2 mm, 1-2 mm, 0.25-1 mm, and <0.25 mm fractions by the improved dry-sieving procedure. And then the soil physicochemical properties and the activities of hydrolase [β -glucosidase(BG), N-acetyl-glucosidase(NAG), leucine aminopeptidase(LAP)and acid phosphatase(ACP)] related to soil carbon(C), nitrogen(N)and phosphorus(P)cycling in soil aggregates were measured and the effects of mixing nitrogen-fixing tree species with Eucalyptus on soil enzyme activities and its stoichiometry were examined. The results were as follows:(1)The dominant soil aggregates were >2 mm fractions which were higher than other aggregates. The contents of SOC, TN, NO3--N, AP, pH and activities of BG, NAG, ACP were significantly increased on each aggregate fractions except for LAP, respectively, in MP than in PP.(2)pH, TN, AP, NO3--N, NH4+-N had significant correlation with the ecoenzymatic stoichiometry. The redundancy analysis(RDA)found that the contents of NO3--N, SOC, and AP were key factors affecting the soil hydrolase enzyme activities and its stoichiometry.(3)The ecoenzymatic stoichiometry of C, N, P in this area was 1:0.86:0.74 [deviated from the global pattern(1:1:1)] which indicated that the soil microorganisms in this area were easily limited by C source. The C:N and C:P ratio of enzyme stoichiometric in most of the soil aggregates in MP were lower than those in PP, and significant differences were found in <0.25 mm fractions(P<0.05). Our findings suggest that the introduction of nitrogen-fixing tree species into eucalyptus plantations can not only alleviate the C source limitation of soil microbial growth and metabolism, but also effectively alleviate the N and P limitation of soil in this region. Findings from this study provide a scientific basis for the application of nitrogen-fixing tree species in improving soil quality and productivity of eucalyptus plantations. [ABSTRACT FROM AUTHOR]