Carbon Isotope Dynamics During Grass Decomposition and Soil Organic Matter Formation
Carbon Isotope Dynamics During Grass Decomposition and Soil Organic Matter Formation
复制标题
DOI：
10.2307/1938142
复制
发表时间：
1995-07
期刊：
影响因子：
4.8
通讯作者：
D. Wedin;L. Tieszen;B. Dewey;J. Pastor
中科院分区：
文献类型：
--
作者：
D. Wedin;L. Tieszen;B. Dewey;J. Pastor
我们在明尼苏达州中东部（美国）对四种多年生禾本科植物的地上和地下凋落物进行了为期 2 年的分解研究，分析了大块组织和木质素部分的稳定 C 同位素组成 (s3'C) 的变化：Schizachyrium scoparium (C4)、Agropyron repens (C3)、Poa pratensis (C3) 和 Agrostis scabra (C3)。尽管在分解过程中所有凋落物类型的木质素浓度都增加，并且与散装组织相比，'3C 中的木质素组分持续减少（平均负值多 3.6%），但我们发现散装组织 sl3C 值向木质素 s13C 值收敛，木质素组分的 sl3C 值也没有更高的稳定性。此外，C3 和 C4 物质的 s'3C 值在分解过程中向相反方向移动。因此，我们的数据并不支持分解过程中 s'3C 值因木质素的选择性保存而降低的假设，相反，我们认为同位素变化是由微生物分解者将土壤有机质中的新 C 掺入凋落物引起的。我们估计，在质量损失 70% 的情况下，根据物种的不同，这种新的 C 占凋落物总 C 的 12-19%。在这四个物种加上另一种 C4 草（Andropogon gerardi）在最初以 C3 同位素特征为主的均质土壤上生长的单一栽培中，C4 物种的土壤 s'3C 值增加了 1.6-2.2%o，而 C3 物种在 4 年后保持相对不变。对 C4 物种和实验土壤有机质梯度进行平均，这些地块中总土壤 C 的 14% 必须是新的 C4 C，才能解释这种同位素变化。我们估计，这些新土壤 C 的数量相当于这些地块 4 年来 NPP 总和的 30%。
We analyzed changes in the stable C isotope composition (s3'C) of bulk tissues and lignin fractions during a 2-yr decomposition study in east-central Minnesota (USA) of aboveground and belowground litter from four perennial grass species: Schiza- chyrium scoparium (C4), Agropyron repens (C3), Poa pratensis (C3), and Agrostis scabra (C3). Although lignin concentrations increased for all litter types during decomposition and lignin fractions were consistently depleted in '3C compared to bulk tissues (3.6%o more negative on average), we found neither convergence of bulk tissue sl3C values towards lignin s13C values, nor greater stability of sl3C values for lignin fractions. Furthermore, s'3C values of C3 and C4 species shifted in opposite directions during decomposition. Thus, our data do not support the hypothesis that s'3C values decrease during decomposition because of the selective preservation of lignin and we instead suggest that isotopic shifts are caused by the incorporation of new C from soil organic matter into litter by microbial decomposers. We estimate that this new C comprised 12-19% of the total litter C, depending on species, at the point of 70% mass loss. In monocultures of these four species plus another C4 grass (Andropogon gerardi) growing on initially homogeneous soils with a predominantly C3 isotopic signature, soil s'3C values increased 1.6-2.2%o for the C4 species and remained relatively unchanged for the C3 species after 4 yr. Averaging across the C4 species and the experimental soil organic matter gradient, 14% of the total soil C in these plots must be new C4 C to account for this isotopic shift. We estimate that this amount of new soil C equals 30% of NPP summed over 4 yr in these plots.