外源新碳在不同肥力土壤中的分配与固定

外源新碳加入土壤后,传统技术尚无法区分其与原土壤有机碳的不同。利用13C稳定同位素方法,通过室内培养实验,探讨玉米秸秆和根茬添加到不同肥力水平土壤后外源新碳在土壤中分配与固定的差异。结果表明:(1)低肥土壤添加叶28 d后土壤有机碳(SOC)含量高于添加根和茎的;高肥土壤添加叶在整个培养期间(1~180 d)SOC含量都高于添加根和茎;两种肥力水平土壤在添加玉米根、茎、叶180 d后SOC含量均接近相等。(2)玉米根、茎、叶的添加对SOC中外源新碳含量以及残体残留率的影响不同,28 d前低肥土壤外源新碳含量高于高肥土壤,28 d后结果与之相反;低肥土壤在培养28 d后添加根的残留率比添加茎和叶的低,高肥土壤在培养7 d后添加叶的残留率比添加根和茎的低。以上结果表明,外源新碳在土壤中的固定受其来源和土壤肥力水平的影响与制约。

Distribution and Sequestration of Exogenous New Carbon in Soils Different in Fertility

Objective]Carbon(C)is a major component of soil organic matter,and crop residues are the main source of soil organic C(SOC). A large volume of studies have demonstrated that straw incorporation into the field is conducive to accumulationof soil organic matter and build-up of soil fertility. However,it is still not yet very clear how incorporation of corn stalk and stubble affects distribution and fixation of SOC in soils different in fertility,and how much extraneous new C contribute relatively to SOC. Once extraneous new carbon is amended into soil,it is very hard for researchers to distinguish new carbon from native organic carbon in the soil with traditional techniques. Therefore the stable isotope labeling technique is applied to an in-lab incubation experiment to explore for differences between soils different in fertility in distribution and fixation of extraneous new carbon after incorporation of corn stalk and stubble.Method]Soil samples were collected from the topsoil layers(0~20 cm)of two fields different in soil fertility,LF and HF in the long-term experimental station of the Shenyang Agricultural University,Liaoning Province,China,in November 2014. The field LF had never been applied with any fertilizer for 27 years, while the field HF had been applied annually with fertilizer equaling to N 270 kg hm-2. The soil samples were crushed gently into bits to pass through a 2 mm sieve and then air-dried to get ready for the incubation experiment. The 13C labeled maize leaf,stalk and root were cut into 2 cm sections,crushed to pass a 40 mesh sieve and mixed at a rate of 1% of the dried soil sample in weight separately with the prepared soil samples that had already been incubated for 7 days as pre-treatment. The mixtures were regulated in moisture content till 60% of field water holding capacity and then put into an incubator for incubation under a constant temperature(25℃)for 180 days. Each treatment had three replicates. During the period of incubation,the mixtures were sampled destructively on D1,D7,D28,D56 and D180 for analysis. Result]Results show that(1)SOC content was found higher in the LF soils amended with maize leaf than in those amended with maize root and stalkafter 28 days of incubation,while it was found higher too in the HF soils amended with maize throughout the whole incubation period;and after 180 days of incubation,the two groups of soils were quite similar in SOC content regardless of type of amendment;(2)the effects of the amendments of maize root,stalk and leaf on content of extraneous new C and residual rate of the substances varied sharply. The content of extraneous new C was found higher during the initial period of the incubation(before D28)in the low fertility soilthan in the high fertility soil,while during the later half,an opposite trend was found. The residual rate of root residue was found lower than that of stalk or leaf residue in the low fertility soil during the later half period,while the residual rate of leaf was found lower than that of root or stalk residue in the high fertility soil. Conclusion]All the above-described findings indicate that the sequestration of extraneous new C was governed by its source and soil fertility level.