桉树人工林土壤细菌群落对不同免炼山林地更新模式的季节动态响应

Seasonal dynamic response of soil bacterial community of Eucalyptus plantations to different non-slash-burning woodland renewal models

【目的】桉树人工林单一树种多代连栽的炼山经营模式对土壤质量及其生态环境产生剧烈扰动,已引起社会的广泛关注,而采用免炼山造林这种模式是解决上述问题的重要可能措施之一,然而在免炼山造林模式下,作为土壤生态环境重要组成部分的土壤微生物群落如何响应,仍知之甚少。【方法】以连续经营15年的3代人工林更新迹地为研究对象,分析不同免炼山造林模式下土壤细菌群落结构和功能的季节动态响应。研究对象为3种不同采伐剩余物保留措施的随机区组试验:移除采伐剩余物、平铺采伐剩余物、将采伐剩余物带状堆放,并以采伐前的第3代桉树人工林为对照,结合4个季节对土壤化学性质指标研究,并基于测序结果预测土壤微生物潜在功能差异。【结果】林地更新后3种处理的化学性质均呈现相比于采伐前先下降后随时间恢复趋势,且恢复速度快慢上依次是平铺>带状堆放>移除。3种采伐剩余物处理方式均在秋冬季相比于采伐前降低了细菌群落的丰富度和均匀度并增加了多样性,其中移除处理的变化幅度最大。不同采伐剩余物处理方式和季节一起显著地改变了门水平上的细菌群落组成,且本研究发现Proteobacteria、Actinobacteria、Chloroflexi和Acidobacteria 4种菌门均易受到季节变化的影响。潜在功能预测分析表明,土壤中的细菌群落确实会受到林地更新的影响而激活,并且会随着季节变化出现能量的释放使用和储存维持的现象。Heatmap分析说明了氮含量变化和土壤细菌群落丰度变化存在重要联系。【结论】3种免炼山林地更新模式和季节均会对土壤化学性质和微生物群落环境产生影响,其中移除处理导致的化学性质恢复速度最慢,对微生物群落的扰动最大,而采用平铺采伐剩余物处理方式是三者中相对更优的选择。在季节方面,结果表明,土壤细菌群落中某些菌门和功能基因对季节的变化产生动态响应,这一发现有助于更好地了解自然季节和采伐剩余物管理如何差异影响桉树人工林的土壤微生物生态。

【Objective】The slash-burning woodland renewal model of Eucalyptus plantation with a single tree species and multiple generations of continuous planting has caused severe disturbances to the soil quality and ecological environment,which has attracted widespread attention from society,and the model of non-slash-burning woodland renewal has been adopted.It is one of the most important possible measures to solve the above problems.However,we still know very little about the response of the soil microbial community as an important part of the soil ecological environment under the non-slash-burning woodland renewal model.【Method】Taking three generations of plantation renewal sites that have been continuously operated for 15 years as the research object,the seasonal dynamic response of the structure and function of soil bacterial communities under different non-slash-burning woodland renewal models was analyzed.The research object was a randomized block experiment with three different logging residue retention measures:removing logging residues,paving logging residues,stacking logging residues in strips,and taking the third-generation Eucalyptus plantation before logging as a control,combining the four seasons to study the soil chemical property indicators,and predicting the potential functional differences of soil microorganisms based on the sequencing results.【Results】The chemical properties of the three treatments after the woodland renewal showed a trend of first decreasing and then recovering over time compared with that before harvesting,and the recovery speed was in the order of flat paving>band stacking>removal.The three logging residue treatment methods all reduced the abundance and uniformity of the bacterial community and increased the diversity in autumn and winter compared to those before logging,while the removal treatment had the largest change.Different logging residue treatment methods and seasons significantly changed the bacterial community composition at the phylum level,and this study found that Proteobacteria,Actinobacteria,Chloro lexi and Acidobacteria are all susceptible to seasonal changes.The analysis of potential function prediction showed that the bacterial community in the soil will indeed be activated by forest renewal,and the phenomenon of energy release,use and storage maintenance will appear with seasonal changes.Heatmap analysis showed that there was an important relationship between changes in nitrogen content and changes in soil bacterial community abundance.【Conclusion】The three renewal modes and seasons of non-slash-burning woodland renewal models will affect the chemical properties of soil and the microbial community environment.Among them,the chemical properties recovered by the removal treatment are the slowest and have the greatest disturbance to the microbial community.In summary,we believe that the use of tiled logging residue processing method is the relatively better choice among the three.In terms of seasons,our results showed that certain phyla and functional genes in soil bacterial communities have a dynamic response to seasonal changes,which helps to better understand how differences between natural seasons and different non-slash-burning woodland renewal models affect soil microbial ecology in Eucalyptus plantations.