Data Sheet 1_Plant-beneficial bacteria are promoted in pasture-crop rotations in the Uruguayan Pampa, contributing to soil health and crop performance.pdf

IntroductionUnderstanding how pasture-crop rotation design influences long-term soil health and microbial dynamics is crucial for sustainable agroecosystems. Pasture-crop rotations may alleviate soil degradation, but their long-term effects or legacy on soil and rhizosphere microbiomes, including potential recruitment of plant-beneficial microorganisms, and their link to crop yield need to be better understood. This study examines how land use intensity and grazed pasture legacy influence soil and rhizosphere prokaryotic diversity, composition, functionality, and crop productivity.
MethodsA gradient of land use intensities ranging from continuous cropping (CCG), short (SR) and long (LR) pasture-crop rotations, permanent improved pasture (PIP), and natural grassland (NGL) were sampled in a long-term field experiment established in 1995 in the Uruguayan Pampa. Moreover, two stages of the rotation, one year after pasture sown with sorghum (SRS, LRS) and two years after pasture with soybean (SRG, LRG), were studied to assess the persistence of pasture-derived legacies. Soil physicochemical and biological properties were measured to evaluate soil health along with crop productivity. Bulk soil, soybean, and sorghum rhizosphere prokaryotic communities were analyzed across land use intensities using 16S rRNA gene amplicon sequencing and functional assays on rhizosphere bacterial isolates.
ResultsResults showed a partial retention of soil health assessed through selected soil properties, i.e. soil organic C, total N, and soil extractable protein content were higher in LRG compared to CCG, while an intermediate response was observed in SRG. LR preserved the pasture legacy, maintaining bulk soil prokaryotic community composition similar to PIP and distinct from CCG, while SR converged to CCG and diverged from PIP. Soybean rhizosphere prokaryotic diversity and composition was strongly shaped by crop type and by soybean inoculation with Bradyrhizobium elkanii, overriding the effects of intensification and pasture legacy. Key soil taxa (Streptomyces, Solibacillus, Sphingomonas and Bradyrhizobium) were linked with improved soil functionality. Linking 16S rRNA gene sequencing data of rhizosphere taxa with rhizobacterial isolates showed that Pseudomonas, Bacillus, and Microbacterium, all exhibiting multiple plant-beneficial activities in vitro, were enriched in pasture rotations.
DiscussionThis study highlights that pasture-crop rotation design, particularly pasture duration and plant composition, influences prokaryotic services and soil health, contributing towards the development of resilient agroecosystems.

引言
探究牧草-作物轮作模式如何影响长期土壤健康与微生物动态，对可持续农业生态系统而言至关重要。牧草-作物轮作可缓解土壤退化，但其对土壤及根际（rhizosphere）微生物组的长期效应或遗留效应，包括潜在招募植物有益微生物的过程，以及与作物产量的关联，仍有待更深入的研究。本研究旨在探究土地利用强度与放牧牧草遗留效应，如何影响土壤及根际原核生物（prokaryotic）的多样性、群落组成、功能特性与作物生产力。

方法
本研究于1995年在乌拉圭潘帕斯草原建立的长期田间定位试验中，选取了涵盖连作（continuous cropping, CCG）、短期（short, SR）与长期（long, LR）牧草-作物轮作、永久改良牧场（permanent improved pasture, PIP）以及天然草地（natural grassland, NGL）的土地利用强度梯度样地。此外，本研究还设置了两个轮作阶段：牧草播种高粱后1年（SRS, LRS）以及牧草播种大豆后2年（SRG, LRG），以评估牧草遗留效应的持续性。研究测定了土壤理化与生物学特性，以评估土壤健康状况与作物生产力；同时针对不同土地利用强度下的原状土壤（bulk soil）、大豆与高粱根际原核生物群落，采用16S rRNA基因扩增子测序（16S rRNA gene amplicon sequencing）技术以及根际细菌分离株功能测定法进行分析。

结果
研究结果显示，通过选定的土壤指标评估的土壤健康状况得到部分保留：相较于连作（CCG），长期轮作大豆后（LRG）的土壤有机碳、全氮以及土壤可提取蛋白含量更高，而短期轮作大豆后（SRG）的相关指标则处于中间水平。长期牧草-作物轮作（LR）保留了牧草遗留效应，其原状土壤原核生物群落组成与永久改良牧场（PIP）相似，且与连作（CCG）显著不同；而短期轮作（SR）则趋同于连作（CCG），并偏离永久改良牧场（PIP）的群落特征。大豆根际原核生物的多样性与群落组成主要受作物类型以及大豆接种埃氏慢生根瘤菌（Bradyrhizobium elkanii）的调控，其影响强度超过土地利用强度强化与牧草遗留效应。关键土壤类群包括链霉菌属（Streptomyces）、索氏芽孢杆菌属（Solibacillus）、鞘氨醇单胞菌属（Sphingomonas）以及慢生根瘤菌属（Bradyrhizobium），这些类群与土壤功能提升密切相关。将根际类群的16S rRNA基因测序数据与根际细菌分离株数据相结合后发现，假单胞菌属（Pseudomonas）、芽孢杆菌属（Bacillus）以及微杆菌属（Microbacterium）这三类在体外实验中均展现出多种植物有益活性的类群，在牧草轮作样地中显著富集。

讨论
本研究表明，牧草-作物轮作模式，尤其是牧草种植时长与植物群落组成，会影响原核生物服务功能与土壤健康状况，有助于构建韧性更强的农业生态系统。