研究表明氮肥深施能够减少稻田中氮素淋失、提高氮肥利用率；然而，我们对于稻田土壤微生物，特别是微生物中的丰富物种和稀有物种对于氮肥深施的响应知之甚少，而这一过程对于我们理解农业生态系统的生物多样性和功能至关重要。在本研究中，我们利用二代测序技术和生态模型理论，研究了不同氮肥施用条件下水稻根际土壤中丰富和稀有类群在水稻生长4个阶段的多样性模式及其组装机制。结果显示，在水稻根际土壤中丰富物种和稀有物种具有不同的分布模式：丰富物种广泛存在于各样品中，而稀有物种不是普遍存在的。随机过程在丰富菌群和稀有菌群的群落构建过程中均起着主导作用，其中扩散限制在丰富菌群中起着更重要的作用，而漂移等非主导过程在稀有菌群中起着更重要的作用。扩散限制对氮肥深施下丰富物种和稀有物种的影响高于不施氮肥和传统撒施；然而均值扩散对不施氮肥和传统撒施下稀有物种的影响高于氮肥深施处理。网络分析表明，与稀有物种相比，丰富物种相互之间连接紧密且占据网络的中心位置。尽管如此，大部分的关键物种由稀有物种组成，它们可能在维系网络稳定过程中发挥重要作用。总之，我们的研究结果突出了氮肥深施下根际土壤中丰富菌群和稀有菌群生态机制和共发生模式。

一方面，中国亚热带红壤区水稻土母质和肥力水平多变；另一方面，细菌多样性和群落组成在土壤生态系统过程和功能中发挥关键作用。但是水稻土的母质和肥力对细菌多样性和群落组成的影响如何仍不清楚，不同母质和肥力水平条件下驱动水稻土细菌多样性、群落组成和特异微生物种群变化的关键因素尚不明确。因此，本研究采集亚热带红壤区具有不同母质（第四纪红黏土或第三纪红砂岩）和不同肥力水平（高肥力或低肥力）的典型样地水稻土样品，通过454高通量测序测定细菌16S rRNA基因的V4−V5区，分析细菌多样性指数和群落组成变化。采用two-way ANOVA和two-way PERMANOVA探明母质和肥力对细菌多样性和群落组成的影响；主坐标分析（PCoA）、冗余分析（RDA）和多元回归树分析（MRT）明确细菌群落的变化，以及驱动该变化的关键土壤因子；共现网络分析阐明属水平特异细菌种群和关键土壤因子的关系；宏基因组差异分析工具（STAMP）确定不同土壤样品间差异物种。结果显示，母质和肥力对水稻土细菌多样性指数变化的贡献相似。但是肥力水平对细菌群落组成的影响要远大于母质。土壤因子，特别是土壤质地与细菌多样性指数密切相关。RDA分析发现土壤有机碳（SOC）是影响细菌群落组成的首要因素，并且25.5 g kg⁻¹有机碳含量是驱动高肥力和低肥力土壤细菌群落组成分异的关键阈值。共现网络分析暗示高肥力水平下，由于土壤环境的改善，细菌趋向于合作关系，并且富营养型细菌占主导地位。STAMP分析发现高肥力水稻土中Massilia和Rhodanobacter等富营养型细菌大量富集；而低肥力土壤中Anaerolinea等贫营养型细菌占主导。研究结果表明，不同母质和肥力水稻土中，土壤质地影响细菌多样性指数变化；而养分水平，特别是有机碳水平决定细菌群落组成的变化。

The optimized nitrogen fertilization location differs in different rice-growing regions.  We optimized nitrogen deep-point application in root-growing zone (NARZ) for transplanted rice in subtropical China.  Field plot experiments were conducted over two years (2014–2015) in a double-rice cropping system to evaluate the effects of nitrogen (N) fertilizer location on grain yield and N use efficiency (NUE).  Four different nitrogen deep-point application methods (DN) were compared with traditional broadcast application (BN) using granular urea.  The results showed that grain yield,  recovery efficiency of N (RE_N), agronomic efficiency of N (AE_N), and partial factor productivity of N (PFP_N) significantly increased 10.3–63.4, 13.7–56.7, 24.7–201.9 and 10.2–63.4%, respectively, in DN treatment compared to BN, respectively.  We also find that DN treatments increased grain yield as well as grain N content, and thus grain quality, in comparison with conventional BN treatment.  Correlation analysis indicated that significant improvement in grain yield and NUE mainly resulted from increases in productive panicle number and grain N content.  In our proposed NARZ method, granular urea should be placed 0 to 5 cm around the rice seeding at a 12-cm depth druing rice transplanting.  In NARZ, balanced application of N, P and K further improved grain yield and NUE over treatments with a single N deep-point application.  High N uptake by the rice plant did not cause significant soil fertility depletion, demonstrating that this method could guarantee sustainable rice production.    
 

We have had little understanding on the effects of different types and quantities of biochar amendment on soil N transformation process and the microbial properties. In this study, various biochars were produced from straw residues and wood chips, and then added separately to a paddy soil at rates of 0.5, 1 and 2% (w/w). The effects of biochar application on soil net N mineralization and nitrification processes, chemical and microbial properties were examined in the laboratory experiment. After 135 d of incubation, addition of straw biochars increased soil pH to larger extent than wood biochars. The biochar-amended soils had 37.7, 7.3 and 227.6% more soil organic carbon (SOC), available P and K contents, respectively, than the control soil. The rates of net N mineralization and nitrification increased significantly as biochars quantity rose, and straw biochars had greater effect on N transformation rate than wood biochars. Soil microbial biomass carbon increased by 14.8, 45.5 and 62.5% relative to the control when 0.5, 1 and 2% biochars (both straw- and wood-derived biochars), respectively, were added. Moreover, biochars amendments significantly enhanced the concentrations of phospholipid fatty acids (PLFAs), as the general bacteria abundance increased by 161.0% on average. Multivariate analysis suggested that the three rice straw biochar (RB) application levels induced different changes in soil microbial community structure, but there was no significant difference between RB and masson pine biochar (MB) until the application rate reached 2%. Our results showed that biochars amendment can increase soil nutrient content, affect the N transformation process, and alter soil microbial properties, all of which are biochar type and quantity dependent. Therefore, addition of biochars to soil may be an appropriate way to disposal waste and improve soil quality, while the biochar type and addition rate should be taken into consideration before its large-scale application in agro-ecosystem.