Fine root chemistry and decomposition in model communities of north-temperate tree species show little response to elevated atmospheric CO2 and varying soil resource availability
Fine root chemistry and decomposition in model communities of north-temperate tree species show little response to elevated atmospheric CO2 and varying soil resource availability
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DOI：
10.1007/s00442-005-0191-4
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发表时间：
2005-12-01
期刊：
影响因子：
2.7
通讯作者：
Schmidt, K
中科院分区：
文献类型：
--
作者：
King, JS;Pregitzer, KS;Schmidt, K
大气[CO2]升高有可能通过增加植物凋落物中顽固性成分的含量来改变土壤碳(C)循环，从而降低分解速度。由于细根周转量占年净初级生产力的很大一部分，因此细根分解的变化尤为重要。这些响应可能会受到土壤资源的可用性和优势树种的生活史特征的影响。我们评估了大气[CO2]升高和土壤资源有效性对早晚演替树种的生产和化学、菌根定植和细根分解的影响，这些树种在北温带森林中具有重要的经济和生态意义。采用开顶式气室将颤动杨树和糖枫幼树暴露于大气中的二氧化碳浓度分别为36pa和56pa。土壤资源可利用性由两个处理组成，这两个处理构成了美国上湖州发现的范围。经过2.5年的生长，糖枫由于细根的分配(占总根生物量的30%)比杨树(占总根生物量的7%)相对较大，从而获得了更大的细根现存量。与低土壤资源处理相比，随着土壤资源有效性的增加，杨树细根生物量增加了76%，但仅在[CO2]升高的情况下。糖枫细根生物量随着土壤资源利用率的增加(相对于低土壤资源处理)增加了26%，对N和可溶性酚类物质的[CO2]浓度升高反应不明显，根中C/N值相近，但杨木的木质素含量略高于糖枫，缩合单宁含量低于糖枫。正如碳分配的源-汇模型所预测的那样，碳汇成分(C/N比、可溶性酚类)随着相对碳有效性(增加的[CO2]/低的土壤资源有效性)的增加而增加，然而，生物合成的不同化合物(木质素、淀粉、缩合单宁)并不总是如预测的那样做出反应。我们发现细根的菌根定植不受大气[CO2]或土壤资源有效性的强烈影响，如根麦角甾醇含量所示。总体而言，根部化学成分随碳和土壤资源有效性的增加而发生的绝对变化很小，对土壤真菌生物量或细根分解的比速率没有影响。我们得出结论，根系对土壤碳循环的贡献将主要受细根产量和周转对大气[CO2]升高的响应的影响，而不是基质化学的变化。
Rising atmospheric [CO2] has the potential to alter soil carbon (C) cycling by increasing the content of recalcitrant constituents in plant litter, thereby decreasing rates of decomposition. Because fine root turnover constitutes a large fraction of annual NPP, changes in fine root decomposition are especially important. These responses will likely be affected by soil resource availability and the life history characteristics of the dominant tree species. We evaluated the effects of elevated atmospheric [CO2] and soil resource availability on the production and chemistry, mycorrhizal colonization, and decomposition of fine roots in an early- and late-successional tree species that are economically and ecologically important in north temperate forests. Open-top chambers were used to expose young trembling aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees to ambient (36 Pa) and elevated (56 Pa) atmospheric CO2. Soil resource availability was composed of two treatments that bracketed the range found in the Upper Lake States, USA. After 2.5 years of growth, sugar maple had greater fine root standing crop due to relatively greater allocation to fine roots (30% of total root biomass) relative to aspen (7% total root biomass). Relative to the low soil resources treatment, aspen fine root biomass increased 76% with increased soil resource availability, but only under elevated [CO2]. Sugar maple fine root biomass increased 26% with increased soil resource availability (relative to the low soil resources treatment), and showed little response to elevated [CO2]Concentrations of N and soluble phenolics, and C/N ratio in roots were similar for the two species, but aspen had slightly higher lignin and lower condensed tannins contents compared to sugar maple. As predicted by source-sink models of carbon allocation, pooled constituents (C/N ratio, soluble phenolics) increased in response to increased relative carbon availability (elevated [CO2]/low soil resource availability), however, biosynthetically distinct compounds (lignin, starch, condensed tannins) did not always respond as predicted. We found that mycorrhizal colonization of fine roots was not strongly affected by atmospheric [CO2] or soil resource availability, as indicated by root ergosterol contents. Overall, absolute changes in root chemical composition in response to increases in C and soil resource availability were small and had no effect on soil fungal biomass or specific rates of fine root decomposition. We conclude that root contributions to soil carbon cycling will mainly be influenced by fine root production and turnover responses to rising atmospheric [CO2], rather than changes in substrate chemistry.