Data_Sheet_1_Rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance with the change of land use types.docx

Soil microorganisms play an important role in soil ecosystems as the main decomposers of carbon and nitrogen. They have an indispensable impact on soil health, and any alterations in the levels of organic carbon and inorganic nitrogen can significantly affect soil chemical properties and microbial community composition. Previous studies have focused on the effects of carbon and nitrogen addition on a single type of soil, but the response of soil microorganisms to varying carbon and nitrogen inputs under different land soil use types have been relatively understudied, leaving a gap in our understanding of the key influencing factors. To address this gap, we conducted a study in the tropical regions of Hainan province, focusing on four distinct land use types: natural forest soil (NS), healthy banana soil (HS), diseased banana garden soil (DS), and paddy soil (PS). Within each of these environments, we implemented five treatments: CK, RS (rice straw), RSN (rice straw and NH4NO3), RR (rice root), and RRN (rice root and NH4NO3). Our aim was to investigate how soil bacteria response to changes in carbon and nitrogen inputs, and to assess their potential for biological nitrogen fixation. The results showed that the addition of rice straw increased the absorption and utilization of nitrate nitrogen by microorganisms. The addition of rice roots (RR) did not increase the absorption capacity of inorganic nitrogen by microorganisms, but increased the content of poorly soluble organic carbon. Most importantly, the addition of rice straw increased microbial respiration and the utilization efficiency of N2 by microorganisms, and the further addition of ammonium nitrate increased microbial respiration intensity. With the change of soil type, the rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance. Meanwhile, microbial respiration intensity is an important factor influencing the differences in the structure of bacterial communities. The addition of inorganic nitrogen resulted in ammonium nitrogen accumulation, reduced microbial richness and diversity, consequently diminishing the soil microorganisms to resist the environment. Therefore, we believe that with the change of soil types, corresponding soil nutrient retention strategies should be devised and incorporated while reducing the application of ammonium nitrogen, thus ensuring healthy soil development.

土壤微生物作为碳、氮元素的主要分解者，在土壤生态系统中发挥着至关重要的作用，对土壤健康具有不可替代的影响。土壤有机碳与无机氮含量的任何变化，均会显著改变土壤化学性质与微生物群落组成。过往研究多聚焦于碳氮添加对单一类型土壤的影响，但针对不同土地利用类型下，土壤微生物对不同碳氮输入水平的响应机制却相对匮乏，导致我们对关键影响因子的认知存在空白。为填补这一研究空白，本研究在海南省热带区域开展实验，选取4种典型土地利用类型的土壤：天然林土壤（natural forest soil, NS）、健康蕉园土壤（healthy banana soil, HS）、病害蕉园土壤（diseased banana garden soil, DS）以及水稻田土壤（paddy soil, PS）。针对每类土壤，我们设置了5种处理方式：空白对照（CK）、稻秆添加处理（RS, rice straw）、稻秆+硝酸铵添加处理（RSN, rice straw and NH4NO3）、稻根添加处理（RR, rice root）以及稻根+硝酸铵添加处理（RRN, rice root and NH4NO3）。本研究旨在探究土壤细菌对碳氮输入变化的响应规律，并评估其生物固氮潜力。研究结果显示：稻秆添加可提升微生物对硝态氮的吸收与利用效率；稻根添加（RR）虽未提升微生物对无机氮的吸收能力，却可提高难溶性有机碳的含量。尤为关键的是，稻秆添加可增强微生物呼吸作用与对氮气（N2）的利用效率，而额外添加硝酸铵则进一步提升了微生物呼吸强度。随土壤类型变化，稻秆添加可提升微生物固氮能力以及细菌与nifH基因的丰度。与此同时，微生物呼吸强度是影响细菌群落结构差异的关键因子。无机氮添加会导致铵态氮累积，降低微生物群落的丰富度与多样性，进而削弱土壤微生物的环境抗逆能力。据此我们认为，应针对不同土壤类型制定适配的土壤养分留存策略，并在减少硝酸铵施用的同时落实该策略，以保障土壤的健康发育。