黄土丘陵沟壑区植被恢复对土壤微生物生物量碳和氮的影响

对典型黄土丘陵沟壑区陕西延安羊圈沟小流域5年生刺槐、沙棘和杏树人工林及5、15和25年生刺槐人工林土壤进行比较研究，以揭示不同植被及恢复年限对土壤微生物生物量碳和氮的影响.结果表明： 在5年生的3种人工林中,以沙棘林土壤有机碳(SOC)和总氮(TN)含量最高;刺槐林土壤微生物生物量碳(MBC)和微生物生物量氮(MBN)含量显著高于其他两种林地，分别为99.56和28.81 mg·kg^-1，其中MBC含量依次为：刺槐林>沙棘林>杏树林，MBN含量依次为：刺槐林>杏树林>沙棘林;土壤MBC/SOC依次为：刺槐林>沙棘林>杏树林，而MBN/TN为：刺槐林>杏树林>沙棘林，且差异均达到显著水平(P<0.05).随植被恢复年限增长，3种林龄刺槐林的土壤pH值下降，SOC、TN含量、电导率(EC)、MBC和MBN均呈增加趋势.在黄土丘陵沟壑区,种植刺槐比沙棘和杏树更有利于MBC和MBN含量的提高;随着刺槐种植年限的增长，MBC、MBN以及SOC和TN含量均呈增加趋势.

Behavioral responses of Xylotrechus rusticus L. to poplar bark volatiles

Aimed to explore the effects of different vegetations and of the years of vegeta tion restoration on soil microbial biomass carbon and nitrogen, a comparative st udy was conducted, with the 5 year old Robinia pseudoacacia, Hippophae reamno ide and Prunus armeniaca plantations and the 5, 15 and 25 years old R. pseudoacacia plantation in the Yangjuangou catchment of Yanan City of Shaa nxi Province, a typical hilly area of the Loess Plateau, as test objects. The re sults showed that among the three 5-year old plantations, H. reamnoides pl antation had the highest soil organic carbon (SOC) and total nitrogen (TN) conte nts, while R. pseudoacacia plantation had the highest soil microbial biomass carbon (MBC) (9956 mg·kg-1) and nitrogen (MBN) (2881 mg·kg-1) . The MBC was in the order of R. pseudoacacia>H. reamnoides>P. armeniaca, an d that of MBN was of R. pseudoacacia>P. armeniaca>H. reamnoides. The MBC/SOC was in the order of R. pseudoacacia>H.reamnoides>P. armeniaca, and that of MBN/TN was of R. pseudoacacia>P. armeniaca>H. reamnoides, with the differenc es being significant (P<005). With the increasing years of vegetation rest oration, the soil pH in R. pseudoacacia plantation decreased, while the SOC, TN, electricity conductance (EC), MBC, and MBN all had an increasing trend, whi ch illustrated that in the hilly area of Loess Plateau, planting R. pseudoacac ia was more beneficial to the increase of soil MBC and MBN, and, with the incr easing years of this planting, soil MBC, MBN, SOC and TN tended to be increasing.