绿肥翻压促进柑橘园土壤磷素活化周转的特征及机理

China is the largest citrus cultivation country in the world. The citrus orchard has a high annual input of chemical phosphate (P) fertilizer, which is easily fixed by the soil as insoluble inorganic P, induced the imbalance of soil carbon to P ratio (C:P), low bioavailability and ineffective P accumulation. Orchard intercropping green manure is a sustainable orchard management method to reduce P input and increase P efficiency. Especially, green manure turnover to soil will improve C:P, thus have a specific impact on soil microbial activity and soil P cycling. Studies showed that green manure could significantly improve soil microbial biomass and activity, decrease soil insoluble inorganic P and increase soil labile P pools. However, due to previously technical limitations, there is lack of knowledge of the process of microbial transformation from soil insoluble inorganic P and chemical P into the labile P pools. Therefore, this application intends reveal the effect of green manure on soil P turnover cycle and its related microbial community dynamics by using liquid 31P-nuclear magnetic resonance method and high-throughput sequencing technology. And in further, through the oxygen isotope labeling, the dynamic characteristics of the insoluble inorganic P and chemical P cycle as well as its microbial driving mechanism under green manure will be investigated. This study aims to provide a scientific basis for realizing the goal of “reducing P and increasing efficiency” in citrus orchards in China.

我国是世界上柑橘种植面积最大的国家。柑橘园化学磷肥投入量巨大，且极易被土壤固定为难溶性无机磷，由此造成土壤无机磷累积、碳磷比失衡和磷素生物有效性降低。柑橘园间作绿肥是果园“减磷增效”和可持续性发展的重要途径，特别是绿肥翻压后可有效改善土壤碳磷比，从而对土壤微生物和磷素周转产生特定影响。已有研究表明，绿肥翻压后不仅提高了土壤微生物生物量和活性，同时还降低了土壤难溶性无机磷含量、提高了土壤活性磷组分含量。但是，由于先前技术手段的限制，微生物驱动土壤难溶性无机磷和肥料磷的周转过程及其机制并不清楚。为此，本申请拟采用液态31P-核磁共振波谱和高通量测序技术，揭示绿肥翻压下土壤磷组分及关键微生物群落的动态关联特征；在此基础上，通过磷氧同位素标记法，阐明绿肥翻压下土壤难溶性无机磷和肥料磷的周转循环过程及其微生物驱动机制。项目的实施可为实现我国柑橘园“减磷增效”的目标提供科学依据。

果园土壤磷素出现大量盈余现象，这不仅降低磷肥的施用效益，加剧不可再生的磷矿资源耗竭，也增加水体生态环境污染的风险。绿肥作为一种清洁的有机肥源，能够活化土壤难溶性磷，促进土壤磷素周转循环，并提高磷素生物有效性。对此，本项目开展的主要研究内容和结果如下：（1）通过开展连续7年栽培绿肥的田间定位试验，采用Tiessen磷分级方法，研究了绿肥覆盖和翻压对土壤磷组分含量变化和磷素活化周转的影响。结果表明，与清耕对照处理相比，绿肥覆盖和翻压处理在各采样年份均提高了土壤全磷，Resin-Pi、NaHCO3-P、NaOH-P和Residual-P含量，降低了Dil.HCl-Pi和Conc.HCl-P含量，处理间差异性随绿肥利用年限的增加而增加；其中，各指标翻压处理均优于覆盖处理，且0-20 cm土层变化最为明显。（2）通过开展添加两种不同碳氮比的绿肥的培养试验，采用土壤磷分级方法、土壤酶学和高通量测序技术，研究了两种不同磷含量土壤中磷组分及磷循环关键微生物对绿肥翻压的响应。结果表明，在高磷和低磷土壤中，绿肥能够提高土壤有效磷（AP）和微生物量磷（MBP）含量，而葡萄糖可提高土壤MBP含量，但土壤AP含量有所降低。与对照相比，绿肥和葡萄糖均显著提高两种土壤中酸性和碱性磷酸酶活性以及pqqC和phoD基因丰度。（3）通过开展外源添加人工标记的磷酸盐氧同位素的肥料磷的盆栽试验，采用磷酸盐氧同位素示踪技术，结合土壤酶学和磷循环功能基因定量技术，研究了绿肥翻压促进微生物对土壤中肥料磷周转分配的作用机制。结果表明，对于柑橘而言，绿肥显著增加低磷土壤中柑橘的生物量、株高、茎粗，而在高磷土壤中仅显著增加柑橘的茎粗，生物量和株高无显著变化；绿肥处理下高磷和低磷土壤中柑橘新叶磷含量显著增加，而对根，茎和老叶磷含量无显著变化。