农田潮土养分耦合循环的微生物学机理研究进展

Research progresses of soil microorganisms driven nutrient coupling cycles in fluvo-aquic soils of China

科学施肥是实现农业增产和土壤健康的重要手段。深入认知土壤微生物驱动的养分元素循环过程对于评价和指导科学施肥具有极为重要的意义。近年来不同施肥策略对土壤微生物影响的认知虽取得长足进步,但多限于单一养分元素的影响。土壤养分元素循环过程及与碳循环过程具有不可分割性,互作和协同也是土壤微生物的重要特性之一。因此,揭示土壤微生物介导的养分元素的耦合会更有助于我们全面了解农田土壤养分循环过程和指导科学施肥。笔者研究团队多年来以中国科学院封丘农业生态试验站养分平衡长期定位试验为平台,利用土壤微生物学、分子生态学、微量热和同位素测定等技术,系统研究了不同施肥策略下潮土微生物介导的碳、氮、磷元素循环及耦合过程。本文综述相关研究成果。对于缺磷潮土,磷肥施用能够提高微生物生物量碳氮、转化酶活性、脲酶活性、呼吸强度及微生物代谢活性等,使得微生物能够保障土壤养分转化与作物养分吸收,增加潮土综合碳氮汇效应,"高效低排"地为生态系统服务;与之相反,缺施磷肥条件下,即使长期施用其它养分如氮肥,潮土微生物代谢效率仍然低下,且代谢过程会损失更多碳氮素,不利于潮土碳氮累积,致使土壤质量无法提高,还加剧了生态环境的污染。在阐明了微生物对潮土养分的响应与反馈后,还进一步揭示了潮土碳磷耦合的微生物学机制,提出了"缺磷耗碳,增碳活磷"的理论框架。长期缺磷使得外源碳经由微生物转化进入潮土有机碳库的比例减少,却增加了外源碳的净矿化量,使得更多外源碳以CO2形式排放到大气,即缺磷潮土不利于外源碳向潮土有机碳的转化。但是,外源碳的添加能够长效刺激缺磷潮土中微生物的增殖,特别是解磷微生物。该过程可以使得土壤化学固持的磷素转移到微生物体内,增加了潮土中潜在有效磷含量,后续可以提供给植物利用,即外源碳的添加能够通过解磷微生物活化土壤中不可利用态磷素。最后,对今后农田土壤养分耦合循环的微生物学研究方向和内容进行了展望。这些结果会加深对科学施肥重要性的认知,有助于指导调控土壤微生物更好地服务农田生态系统。

Scientific fertilization is a pivotal step towards sustainable increase of crop yield without the expense of agroecosystem health.The knowledge on the process of nutrient cycle driven by soil microbes is of great help to evaluate and guide scientific fertilizations.Although mounting investigations had been conducted on the influences of fertilization strategies on soil microorganisms in recent years,they are mainly limited to the cycling of single nutrient involved into soil microorganisms.In view of the integrity and inseparability of nutrients cycling,the related knowledge on their interaction and coordination with microbial processes would greatly contribute to the comprehensive understanding of the influences that fertilizations bring to agroecosystem.Therefore,revealing the nutrients cycling mediated by soil microorganisms will help us to understand the soil nutrient cycling process and guide scientific fertilization.This paper reviews the findings of the group of Prof.Xiangui Lin,in Institute of Soil Science,Chinese Academy of Sciences.Based on a long-term fertilizer experiment located in Fengqiu Agro-Ecological Experimental Station,they have systematically investigated carbon（C）,nitrogen（N）,phosphorus（P） nutrients cycling and their interactions in association with microbial processes,using soil microbiology,molecular ecology,microcalorimetric and isotopic determination technique,etc.The results indicated that the fluvo-aquic soil is mainly limited by phosphorous.Application of phosphorous fertilizers enhanced microbial biomass carbon content,invertase activity,urease activity,respiration rate and microbial metabolic activity in the soil,which could ensure nutrient transformation in the soil and nutrient uptake of crop,as a result increasing sink effects of carbon and nitrogen.On the contrary,if phosphorus fertilization is deficient,even with application of other nutrients such as nitrogen,soil microbial metabolic efficiency still remains low.More carbon and nitrogen will be lost by microbial metabolic processes,which are not conducive to soil carbon and nitrogen accumulation,consequently leading to poor soil quality and intensified environmental pollution.In addition to the response and feedback of soil microorganisms to nutrients in fluvo-aquic soil,this paper further reveals the microbial mechanisms of the coupling of carbon and phosphorus,and summarizes as＂P deficiency leads to C consumption,C supply results in P activation＂.Long-term P deficiency significantly increased the net mineralization of exogenous carbon,which reduced the retention of exogenous C into the soil organic carbon pool mediated by microbial transformation,possibly due to a higher C loss into the atmosphere in the form of CO2.The addition of exogenous C could stimulate microbial proliferation in P-deficient soils,especially P solubilizing microorganisms.The process can shift P from relatively unavailable soil-bound pools into microbial biomass pools through pool cycling;potentially increase soil available P content for crops.Finally,this review looks forward to the future of soil nutrients cycling mediated by soil microorganisms in cropland.These cognitions will deepen the understanding of scientific fertilization and help to guide the regulation of soil microorganisms and better serve the farmland ecosystem.