落叶松林土壤可溶性碳、氮和官能团特征的时空变化及与土壤理化性质的关系

土壤可溶性有机碳(DOC)、可溶性有机氮(DON)及其官能团特征在土壤碳、氮循环中作用非常重要。对25个不同年龄落叶松林样地、4个深度(0-20、20-40、40-60和60-80 cm)土壤DOC、DON、有机物官能团(芳香性、分子量和疏水性)特征指标(254、260、272 nm和280 nm的单位吸光度值SUVA:吸光度值/DOC含量)和土壤理化指标(土壤全碳SOC、全氮SON、pH值、电导率、容重)进行测定,旨在探究它们的时、空变化特征及与土壤理化指标相关关系。在空间尺度上,与SOC、SON一致,表层土壤DOC、DON多显著高于深层(P<0.05),但是4个单位吸光度值SUVA₂₅₄、SUVA₂₆₀、SUVA₂₇₂和 SUVA₂₈₀均不存在差异(P>0.05);在时间尺度上,仅表层土壤DOC、SOC 和SON随落叶松年龄显著线性增长(P<0.05),而深层DOC、SOC、SON、不同层土壤DON及各官能团指标均没有显著变化(P>0.05)。可见,土壤可溶性有机物内碳的累积(7 mg kg^-1 a^-1)是SOC累积的一部分(762 mg kg^-1 a^-1),但其DON及可溶性有机物芳香性比例、分子量大小及疏水性容量等官能团特征并未受落叶松生长时间以及土壤深度的显著影响。进一步回归分析表明这些官能团指标随土壤DOC含量增加而指数下降,深层土壤同时受DON显著影响。表层土壤DOC、DON与土壤SOC、SON、土壤电导率显著正相关(P<0.05),深层相关不显著(P>0.05),而官能团指标与土壤理化性质的相关性在各个土层均不显著,显示出表层土壤可溶性有机物的量,而不是官能团组成对土壤理化性质影响显著,而深层土壤可溶性有机物量对土壤理化性质不构成显著影响。对于从可溶性组分、官能团角度,分析落叶松人工林成长过程中土壤碳、氮时空变化具有科学意义。

Temporal and spatial variations of DOC, DON and their function group characteristics in larch plantations and possible relations with other physical-chemical properties

Soil dissolved organic carbon (DOC) and nitrogen (DON), and their composition play key roles in soil carbon sequestration and nutrient cycling. In this paper, DOC, DON and specific ultraviolet absorbance (SUVA at 254 nm, 260 nm, 272 nm and 280 nm, equaling to the measured absorbance divided by the DOC concentration) of dissolved organic matter, as well as soil physical-chemical parameters (soil organic carbon SOC, soil total nitrogen SON, pH value, electrical conductivity and bulk density) were determined in 0-20, 20-40, 40-60 and 60-80cm soil layers of 25 chronosequence larch plantations. The aim of this paper is to explore the temporal-spatial change of DOC, DON, SOC, SON and functional group (aromaticity, apparent molecular size and hydrophobic capacity) parameters, and their influences on soil physical-chemical properties. In the vertical profile, DOC, DON, SOC and SON in surface soil layer were significantly higher than those in the deep soil layers (P<0.05), while no significant differences were found in SUVA₂₅₄, SUVA₂₆₀, SUVA₂₇₂ and SUVA₂₈₀ (P>0.05); During of the development larch plantation, DOC, SOC and SON at the surface soil (0-20cm) linearly increased with larch age (P<0.05), while no significant changes were observed in deep soils. DON, aromaticity, apparent molecular size and hydrophobic capacity of all testified soil layers did not significantly change with larch age (P>0.05). Thus, DOC accumulation at surface 0-20cm soil (7 mg kg^-1 a^-1) should be a part of the SOC accumulation (762 mg kg^-1 a^-1), while no marked temporal changes were observed in both SON, DON and functional groups. Different from the significant space-temporal changes in total and dissolved C and N, composition of functional group relating to aromaticity, apparent molecular size and hydrophobic capacity were not affected by larch age and soil depth (P>0.05). A further regression analysis showed that these functional groups exponentially decreased with DOC and also significantly related to DON in the deep layer. Pearson correlations showed DOC and DON in surface soil positively correlated with SOC, SON and soil electrical conductivity (P<0.05), while no significant relations between SUVA₂₅₄, SUVA₂₆₀, SUVA₂₇₂, SUVA₂₈₀ and soil physical-chemical properties were found in each soil layer. This indicates that quantity, rather than composition of dissolved organic matter could determine soil physical-chemical property, especially in surface soil. Our findings have scientific significance in understanding dynamics processes of soil carbon and nitrogen from the view of soluble components and functional groups during the plantation development.