杨树根际土碳氮磷生态化学计量特征与根序的相关性

Correlation between ecological stoichiometry characteristics of carbon, nitrogen, and phosphorus, and the root order in the rhizosphere soils of poplar plantations

林木细根不同生长发育等级形态特点及功能分异是根系生态学研究的新视角.为深入探索林木根际土壤养分循环过程及根土互作关系,以杨树（Populus×euramericana‘Neva’）人工林为研究对象,按照随机布点原则采集杨树人工林非根际土壤和不同根序细根的根际土壤,测定其全碳（TC）、全氮（TN）、全磷（TP）及速效N、有效P的含量,并计算土壤C、N、P化学计量比.结果显示：（1）杨树人工林根际土壤C、N、P含量与非根际土壤存在显著差异,但不同根序间速效N、有效P含量以及铵硝比（NH_4~＋-N/NO_3^--N）未达到显著差异水平（P〉0.05）.随着根序升高根际土壤TC含量显著下降,而TN含量逐渐增加.1-2级细根根际土壤TP含量显著高于4-5级根（P〈0.05）.（2）杨树细根根际土壤C/N随着根序升高显著降低（P〈0.05）;C/P随着根序升高逐渐下降,但在不同根序间差异不显著（P〉0.05）.（3）基于细菌OTUs的非参数估计指数表明,根际土壤与非根际土壤细菌群落多样性存在显著差异;土壤TC和TN含量及C、N、P化学计量比均与细菌群落丰富性（Chao指数和ACE指数）呈显著相关（P〈0.05）,TP含量与细菌群落相关性不显著.上述结果说明杨树根际土壤C、N、P养分循环呈现依赖于根序的变化特征,不同根序细根根际细菌群落组成和结构的差异性可影响土壤C、N、P循环过程.

The root order-dependent study on fine roots focuses on the morphological and functional heterogeneity of different fine root orders and is a new viewpoint in the root ecology research. The study on the stoichiometric characteristics of soil carbon（C）, nitrogen（N）, and phosphorus（P） can provide a scientific theoretical basis for exploring the relationship between soil nutrient cycling and root-soil interaction in the rhizosphere. Based on Populus × euramericana ‘Neva＇ plantations, the contents of total carbon（TC）, total nitrogen（TN）, total phosphorus（TP）, available nitrogen（AN）, and available phosphorus（AP） in the rhizosphere of different root orders and bulk soils were investigated in the present study, and the stoichiometric characteristics of C, N, and P in the soils were also examined. The results showed significant differences in C, N, and P contents between rhizosphere and bulk soils, whereas the contents of AN and AP, and NH_4~＋-N/NO_3^--N ratio did not show significant difference（P〈0.05）. The TC content in the rhizosphere decreased significantly with increase in root order, while the N content increased gradually. The TP content in the 1–2 levels of fine rhizosphere was significantly higher than that in the 4–5 levels（P〈0.05）. Further, C/N ratio in the rhizosphere decreased significantly with increase in root order, while the decrease in C/P ratio did not show significant differences among root orders（P〈0.05）. The non-parametric estimators based on bacterialoperational taxonomic units（OTUs） showed that there were significant differences in the bacterial community diversity between rhizosphere and bulk soils. Both TC and TN contents in soils, and the stoichiometric characteristics of C, N, and P were significantly correlated with bacterial community richness（Chao index and ACE index）, while the correlation between TP content and bacterial community diversity was not significant（P〈0.05）. It was concluded that the ecological cycling of C, N,and P in poplar rhizosphere depends on root orders, which might play an important role in building the bacterial community in the rhizosphere, and thus affect the cycle process of soil carbon, nitrogen, and phosphorus.