木质素和氮含量对植物残体分解的影响

DECOMPOSITION OF PLANT RESIDUE AS INFLUENCED BY ITS LIGNIN AND N ITROGEN

在 2 5℃和水分含量为 40 0g·kg-1 (以风干土计 )条件下对 1 9种植物残体进行培养实验 ,同时进行田间填埋试验 ,研究残体的木质素和N含量对其在土壤中分解的影响。相关分析表明 ,不同植物残体的分解速率与其初始全N含量呈正相关 ,与初始木质素含量、木质素与N含量之比呈负相关。逐步回归分析进一步表明 ,植物残体的C分解与全N及木质素含量的数学关系可表达成 :Y =B0 +B1 N +B2 L。式中 ,B0 、B1 和B2 为回归系数 ,N和L分别表示植物残体的初始全N含量及木质素含量。Y可分别表示为植物残体C分解的一级动力学常数、培养 9周的CO2 _C矿化率和填埋 2 3周的重量损失率 ,相应的复相关系数 (R2 )分别为 0 .81 2 、0 .82 8 和 0 .799 。此外 ,实验室培养测定的CO2 _C矿化率和填埋试验的残体重量损失率之间具有良好的一致性 (R2 =0 .863 ,n =1 7)。

To quantitatively investigate the influence of plant nitrogen and ligni n content on the residue carbon decomposition, CO 2_C was measured from an incu ba tion experiment with 19 plant residues plus soil under 25 ℃ and water conte nt of 400 g·kg -1 air dried soil over a 9_week period. The 19 residues were sam pled fro m different organs with 13 plants, including Glycine max, Vigna sesquipedalis, D ioscorea esculenta, Luffa cylindrical, Oryza sativa, Zea mays, Triticum aestivum , Saccharum officinarum, Festuca arundinacea, Acorus calamus, Trapa quadrispinos a, Pi ttosporum tobira and Firmiana simplex. Weight loss of these residues was a lso ob tained from a field burying experiment over a 23_week period by using litter bag method. Decomposition of plant residues during the early 3_week incubation period was fa st with a wide variation. Thereafter the decomposition decreased and the variati on among residues became gradually insignificant. Cumulative amount of CO 2_C r el eased over the 9_week incubation period was found to be different among the resi dues. Average of the cumulative CO 2_C emission for all 19 residues was 178.0 m g, ranging from 103.6 mg for Oryza sativa root to 256.2 mg for Pittosporum t obira leaf. Correlation analysis indicated that decomposition of the plant res idue was positively dependent on its initial nitrogen content and negatively dependent o n its initial lignin content as well as the ratio of lignin to nitrogen. A furth er investigation suggested that the decomposition can be quantitatively describe d by Y=B 0+B 1N+B 2L. Parameters B 0, B 1 and B 2 are regressi on coefficients. The N and L represent the initial contents of nitrogen and lignin for a given residue, respectively. The Y could be either the first_order decay rate (B 0=3.51 ×10 -2 , B 1=4.61×10 -4 , B 2=-1.53×10 -4 , R 2=0.812 ** , n=19), or the percentage of CO 2_C re leased over the 9_week period (B 0=100, B 1=0.974, B 2=-0.364, R 2= 0.828 ** , n=19), or the percentage of weight loss over the 23_week period in the field burying e xperiment (B 0=150, B 1=1.496, B 2=-0.572, R 2=0.799 ** , n=17) . In addition, a good agreement (R 2=0.863 ** ,n=17) existed between amounts of the CO 2_C released from the incubation and the weight loss from the field burying experiment. It is concluded that decomposition of the plant residue either expressed as CO 2_ C emission in the laboratory incubation or as weight loss in the field burying e xperiment was significantly dependent on its initial contents of nitrogen and li gnin. Residues with higher nitrogen decomposed fast, while those with higher lig nin content decomposed slowly. Difference in the decomposition for various plant residues can be well identified over a 9_week incubation under 25 ℃ and water content of 400 g·kg -1 air dried soil. A further conclusion is that approx imately 8 0% of the variability in the decomposition can be quantitatively expressed by a linear combination of the initial contents of nitrogen and lignin for a given re sidue. The result also suggests that fraction of the labile carbon for a given p lant reside could be estimated from weight loss in the field burying experiment over a 23_week period.