集约化种植柑橘土壤细菌群落多样性与生态系统多功能性的耦合机制研究

Study on the Coupling Mechanism Between Soil Bacterial Community Diversity and Ecosystem Multifunctionality in Intensive Citrus Cultivation Systems

摘要:

高度无序、单一种植导致土地退化，但高强度集约化柑橘种植对土壤微生物群落和多种土壤功能的影响仍不清楚。以不同柑橘种植年限土壤为研究对象，利用高通量测序研究了集约化强度对土壤微生物群落的影响，探究了土壤碳氮磷循环相关的多功能性与微生物多样性、共现网络的耦合机制。结果表明，随着柑橘种植年限的增加，土壤细菌多样性显著下降，香农指数从5 a的7.05下降至30 a的5.79，物种数也从2 110下降至1 153。相比于种植5 a的柑橘土壤，种植30 a的柑橘土壤微生物的网络复杂性更低，微生物类群更少，微生物类群之间的关联性也较低。长时间的柑橘种植导致土壤酸化和养分富集，直接影响细菌群落多样性，改变细菌群落结构和物种组成，导致土壤细菌生活史策略从寡营养型（K-策略）转变为富营养型（r-策略），增加了富营养型细菌群落（放线菌、变形菌）的相对丰度，降低了寡营养细菌群落（酸杆菌门）的相对丰度。微生物共现网络节点数与碳循环多功能性指数（CMF）呈负相关，与氮循环多功能性指数（NMF）、磷循环多功能性指数（PMF）均呈显著正相关，边数与CMF呈负相关，与NMF呈显著正相关，与PMF相关性不显著。总之，养分富集会减少土壤细菌多样性，并削弱地下微生物多样性与生态系统功能之间的关系，上述结果表明长时间的柑橘种植对土壤微生物多样性和多种生态功能具有显著的负效应，为养分富集影响土壤细菌群落和生态系统多功能性的耦合机制提供了新的见解。

Abstract:

【Objective】Intensive monoculture practices can degrade land, but the specific impacts of long-term, high-intensity citrus cultivation on soil microbial communities and soil multifunctionality are not well understood.【Method】This study examined soils from citrus orchards of varying planting durations, using high-throughput sequencing to assess the influence of intensive cultivation on soil microbial communities. It also investigated soil multifunctionality, microbial diversity, and co-occurrence networks associated with carbon, nitrogen, and phosphorus cycling. 【Results】This study indicated that soil bacterial diversity declined significantly as the duration of citrus cultivation increases. The Shannon index decreased from 7.05 in 5-year soils to 5.79 in 30-year soils, with species numbers dropping from 2 110 to 1 153. Microbial network complexity was also reduced in 30-year soils, with fewer taxa and fewer inter-taxa associations than in 5-year soils. Network nodes declined from 1 491 to 815, and edges from 8 449 to 2 369. Network complexity and stability varied significantly across citrus ages, with younger (5-year) soils showing greater complexity and stability than older (30-year) soils. Also, long-term citrus cultivation led to soil acidification, altering bacterial activity, community structure, and species composition. This included an increase in dominant taxa like Proteobacteria, Actinobacteria, and Firmicutes, and a decline in Acidobacteria, Chloroflexi, and Gemmatimonadetes. The relative abundance of nitrogen-cycling bacteria also increased, supporting processes such as nitrogen fixation, aerobic ammonia oxidation, denitrification, and aerobic nitrite oxidation. Changes in microbial diversity and structure correlated closely with shifts in soil multifunctionality, influenced by high-intensity citrus cultivation. The number of microbial network nodes showed a negative correlation with carbon cycle multifunctionality (CMF) and positive correlations with nitrogen cycle (NMF) and phosphorus cycle multifunctionality (PMF). The number of edges correlated negatively with CMF, positively with NMF, and was not significantly associated with PMF. 【Conclusion】Microbial diversity drives the complexity of microbial co-occurrence networks, significantly correlating with the number of network nodes and edges. Collectively, these findings indicate that prolonged citrus cultivation significantly reduces soil microbial diversity and impairs multiple ecological functions.