贡嘎山燕子沟土壤磷海拔梯度特征及影响因素

Variations in Soil P Biogeochemistry and Its Impact Factors along an Altitudinal Gradient in the Yanzigou,Eastern Slope of the Gongga Mountain

土壤磷生物地球化学特征受岩性、气候、土壤年龄、理化性质、地形、植物和微生物活动等因素的共同影响。山地植被和土壤垂直带谱为研究这些因素的相对重要性提供了理想试验场。选取未受人类破坏的贡嘎山燕子沟5个垂直植被带(裸地、高山灌丛带、暗针叶林带、针阔混交林带和阔叶林带,海拔分别为3 761 m、3 600 m、3 403 m、2 700 m和2 334 m),采集了40个土样,测定了土壤的基本理化性质,并采用连续提取法测定了土壤的生物有效磷、铝结合态磷、铁结合态磷、原生矿物磷、有机磷和残余态磷。结果表明,燕子沟土壤A层部分磷形态的空间分布呈现明显的垂直地带性特征。土壤A层的原生矿物磷随海拔的降低而显著降低,有机磷则呈现与原生矿物磷相反的变化趋势。而生物有效磷始终较低,次生矿物磷(铝和铁结合态磷)也较低,残余态磷的含量变化不大,始终是土壤总磷的最大组分。在高海拔地区原生矿物磷是总磷的第二大组分,而在低海拔地区,有机磷则成为总磷的第二大组分。植物是控制燕子沟土壤磷空间分布的相对重要因素,植物一方面通过控制土壤p H进而影响土壤原生矿物磷的含量,另一方面直接吸收生物有效磷,并将其转化为有机磷,导致有机磷随海拔降低而显著增加。此外,植物还通过"泵吸作用"导致总磷在土壤剖面上呈现由表层向底层降低的分布模式。次生矿物磷含量较低表明地球化学作用在影响燕子沟土壤磷生物有效性的作用相对较小。

Soil phosphorus（ P） biogeochemistry is subfected to lithology,climate,topography,soil age and physicalchemical properties of soils,activities of plants and microbes. Mountains,with vertical belts of soils and vegetation due to large altitudinal differences,are ideal experimental areas to evaluate relative importances of these impact factors. In order to investigate spatial patterns of soil P biogeochemistry and impact factors,forty soil samples were collected at five different vegetation belts,which were bare area（ 3 761 m asl（ above sea level））,alpine shrub vegetation（ 3 600 m asl）,dark coniferous forests（ 3 403 m asl）,coniferous and broad leaved forests（ 2 700 m asl）,and broad leaved forests（ 2 334 m asl）. In addition to find out soil physical-chemical properties,soil P forms in A horizon were measured and separated into bioavailable P（ Ex- P）,Al bound P（ Al- P）,Fe bound P（ Fe- P）,Ca bound P（ Ca- P）,organic P（ OP）,and residual P（ Res- P） by a sequential extraction technique. Our results showed that the spatial distributions of soil P forms revealed an obvious vertical zonation. The Ca- P concentrations in the A horizon decreased significantly with decreasing elevations. In contrast,OP concentrations in the A horizon increased significantly downslope. The concentrations of Ex- P,Fe- P and Al- P were always low across the five belts. Res- P concentrations changed rarely along slope gradient and accounted for the largest portion of total P except at the 3 761 m site. In the high altitude sites,the Ca- P was the second largest part of total P; while in the low altitudinal zones,OP became the second largest part of TP. The influences of vegetation on soil P spatial distributions are more important than those of geochemical processes. We confirmed,plants control soil p H and further impact Ca- P contents in soils. Plants transform inorganic P into OP by directly assimilating Ex- P,and thus cause a large increase of OP. In addition,the distribution pattern that total P concentrations in topsoil are higher than that in bottom is mainly a result of ＂pumping＂of plants. The low contents of secondary mineral P（ Fe- P and Al- P） indicates that the effects of geochemical processes（ e. g. absorption） on soil P bioavailability are relatively small.