结合中亚热带江西千烟洲人工针叶林2005、2008和2011年3次树木清查数据以及树木相对生长方程,比较了2008年1月南方冰雪灾害前后的NPP,评价了森林生态系统灾后的恢复能力。结果表明:乡土树种马尾松(Pinus massoniana)与杉木(Cunninghamia lanceolata)比外来树种湿地松(Pinus elliottii)抗灾害能力强;在个体水平上,胸径(D)较大的树木抗灾害能力较差。灾后马尾松与杉木的D增长率降低,而湿地松增大。冰雪灾害导致大量碳(10.44 t C/hm2)从乔木层碳库转移到死生物量碳库,占乔木层碳储量的18.28%。灾前NPP和碳利用效率(CUE)分别为736.23 g C m-2a-1和0.41;灾后经过近4年的恢复,NPP和CUE分别为683.08 g C m-2a-1和0.38。
Plantation forests play a pivotal role in carbon sequestration in terrestrial ecosystems, but enhanced nitrogen(N) deposition in these forests may affect plantation productivity by altering soil N cycling. Hence,understanding how simulated N deposition affects the rate and direction of soil N transformation is critically important in predicting responses of plantation productivity in the context of N loading. This study reports the effects of N addition rate(0, 40, and 120 kg N ha^(-1) a^(-1)) and form(NH_4Cl vs. NaNO_3) on net N mineralization and nitrification estimated by in situ soil core incubation and on-soil microbial biomass determined by the phospholipid fatty acid(PLFA) method in a subtropical pine plantation. N additions had no influences on net N mineralization throughout the year. Net nitrification rate was significantly reduced by additions of both NH_4Cl(71.5) and NaNO_3(47.1%) during the active growing season, with the stronger inhibitory effect at high N rates. Soil pH was markedly decreased by 0.16 units by NH_4Cl additions. N inputs significantly decreased the ratio of fungal-to-bacterial PLFAs on average by 0.28(49.1%) in November. Under NH_4Cl additions, nitrification was positively related with fungal biomass and soil pH. Under NaNO_3 additions,nitrification was positively related with all microbial groups except for bacterial biomass. We conclude that simulated N deposition inhibited net nitrification in the acidic soils of a subtropical plantation forest in China,primarily due to accelerated soil acidification and compositional shifts in microbial functional groups. These findings may facilitate a better mechanistic understanding of soil N cycling in the context of N loading.
Liang KouXinyu ZhangHuimin WangHao YangWei ZhaoShenggong Li
大气氮沉降输入会增加森林生态系统氮素有效性,进而改变土壤N_2O产生与排放,然而有关不同氮素离子(氧化态NO_3^--N与还原态NH_4^+-N)沉降对土壤N_2O排放的影响知之甚少。以大兴安岭寒温带针叶林为研究对象,构建了3种类型(NH_4Cl、KNO_3、NH_4NO_3)和4个施氮水平(0、10、20、40 kg N hm^(-2)a^(-1))的增氮控制试验,利用流动化学分析仪和静态箱-气相色谱法4次/月测定凋落物层和矿质层土壤无机氮含量、土壤-大气界面N_2O净交换通量以及相关环境因子,分析施氮类型和剂量对土壤氮素有效性、土壤N_2O通量的影响探讨氮素富集条件下土壤N_2O通量的环境驱动机制。结果表明:施氮类型和剂量均显著影响土壤无机氮含量,土壤NH_4^+-N的积累效应显著高于NO_3^--N。施氮一致增加寒温带针叶林土壤N_2O排放,NH_4NO_3促进效应最为明显,增幅为442%-677%,高于全球平均水平(134%)。土壤N_2O通量与土壤温度、凋落物层NH_4^+-N含量正相关,且随着施氮水平增加而增加。结果表明大气氮沉降短期内不会导致寒温带针叶林土壤NO_3^--N大量流失,但会显著促进土壤N_2O的排放。此外,外源性NH_4^+和NO_3^-输入对土壤N_2O排放的促进作用具有协同效应,在未来森林生态系统氮循环和氮平衡研究中应该区分对待。
Understanding the temperature and moisture sensitivity of soil organic matter （SOM） mineralization variations with changes in land cover is critical for assessing soil carbon （C） storage under global change scenarios We determined the differences in the amount of SOM mineralization and the temperature and moisture sensitivity of soils collected from six land-cover types, including an orchard, a cropland, and four forests, in subtropical south- eastern China. The responses of SOM mineralization to temperature （5, 10, 15, 20, and 25~C） and moisture （30%, 60%, and 90% of water-holding capacity [WHC]） were investigated by placing soil samples in incubators. Soil C mineralization rate and cumulative C mineralization were higher in orchard and cropland soils than in other forest soils. With increasing temperature, soil C mineralization rates and cumulative C mineralization increased with the rise of WHCo The temperature sensitivity of soil C mineralization was not affected by land-cover type and incubation moisture. All soil temperature treatments showed a similar response to moisture. Cropland soil was more respon- sive to soil moisture than other soils. Our findings indicate that cropland and orchard soils have a higher ability to emit CO2 than forest soils in subtropical southeastern China.
为了探讨不同林龄杉木人工林氮素获取策略,选择了江西千烟洲森林生态研究站红壤区的3种林龄杉木人工林(5年生幼龄林、13年生中龄林和30年生成熟林)作为研究对象,利用稳定性同位素^(15)N示踪技术研究了它们的氮素吸收策略。结果表明,杉木对硝态氮的吸收受林龄影响,成熟林的吸收速率最高,为(5.72±0.24)μg N g^(-1)干重h^(-1),而中龄林和幼龄林的吸收速率相当,分别为(1.57±0.13)μg N g^(-1)干重h^(-1)和(2.36±0.22)μg N g^(-1)干重h^(-1)。幼龄林((34.33±1.20)μg N g^(-1)干重h^(-1))和成熟林((34.18±2.32)μg N g^(-1)干重h^(-1))对铵态氮的吸收速率相似,均显著高于中龄林((23.33±1.39)μg N g^(-1)干重h^(-1))。杉木对甘氨酸的吸收不受林龄的影响。3种年龄的杉木均对铵态氮表现出强的获取能力,其中成熟林杉木对硝态氮的获取能力明显弱于对铵态氮的获取,但却强于对甘氨酸的获取。这样的结果反映了林龄能影响杉木人工林对无机氮的吸收,但未影响对有机氮的吸收;杉木偏好吸收铵态氮,对硝态氮和甘氨酸的吸收很少。如果能把氮素形态考虑进对杉木人工林的施肥管理当中,那么可能会极大地改善杉木的生产力。
Atmospheric nitrogen （N） deposition may affect carbon （C） sequestration in terrestrial ecosystem. The main objective of this paper was to test the hypothesis that N addition would increase CO2 emission in the N limited meadow steppe in Inner Mongolia, China. Response of CO2 fluxes to simulated N deposition was studied in the growing season of 2008 and 2009 by static chamber and gas chromatograph techniques. Parallel to the flux mea- surements, soil temperature, soil moisture, TOC, DOC, soil NH4~ and NO3- were measured at the same time. The results indicated that two-year N additions had no significant effect on NH4＋, but slightly increased NO3- in the later period. The HN treatment tended to increase CO2 fluxes in the two years, and LN treatment tended to decrease CO2 fluxes in 2008, and shifted to increase CO2 fluxes in later growing season of 2009. N addition significantly in- creased the aboveground biomass and root biomass. The correlation between CO2 fluxes and moisture or tempera- ture factors did not significantly change due to N addition, but N addition enhanced the moisture sensitivity of CO2 fluxes as well as the temperature sensitivity of CO2 fluxes. These results suggest that the increasing ammonium N deposition would be likely to stimulate CO2 fluxes in the meadow steppe of Inner Mongolia, China.
