Abstract
The continuous upsurge in soil nitrogen (N) enrichment has had strong impacts on the structure and function of ecosystems. Elucidating how plant ectomycorrhizal fungi (EMF) mutualists respond to this additional N will facilitate the rapid development and implementation of more broadly applicable management and remediation strategies. For this study, we investigated the responses of EMF communities to increased N, and how other abiotic environmental factors impacted them. Consequently, we conducted an eight-year N addition experiment in a poplar plantation in coastal eastern China that included five N addition levels: 0 (N0), 50 (N1), 100 (N2), 150 (N3), and 300 (N4) kg N ha−1 yr−1. We observed that excessive N inputs reduced the colonization rate and species richness of EMF, and altered its community structure and functional traits. The total carbon content of the humus layer and available phosphorus in the mineral soil were important drivers of EMF abundance, while the content of ammonium in the humus layer and mineral soil determined the variations in the EMF community structure and mycelium foraging type. Our findings indicated that long-term N addition induced soil nutrient imbalances that resulted in a severe decline in EMF abundance and loss of functional diversity in poplar plantations.
Highlights
Nitrogen (N) is an essential element that is required for a myriad of important metabolic processes and cellular structures in plants and microorganisms
Subsequent to eight years of N addition, the content of total carbon (TC) and total nitrogen (TN) exhibited a positive relationship with N addition in the humus layer (PTC < 0.001, PTN < 0.001), but no relationship in the mineral soil (PTC = 0.057, PTN = 0.288) (Table 1)
No significant changes in the soil total phosphorus (TP) content were found with the addition of N (p > 0.05), while the available phosphorus (AP) activity decreased with N addition in the mineral soil, from 5.22 to 3.17 mg/kg (p = 0.036) (Table 1)
Summary
Nitrogen (N) is an essential element that is required for a myriad of important metabolic processes and cellular structures in plants and microorganisms. Over the last several decades, the atmospheric deposition of N generated by fertilizer overuse in agricultural-, industrial-, and transportation-related fossil fuel combustion has emerged as a frequent phenomenon in ecosystems that are typically adapted to low N availability [2] Under this situation, the diversity and functionality of forest systems have been significantly affected [3]. The average bulk and throughfall N deposition in China’s forests have currently reached 14.0 kg N ha−1 yr−1 and 21.5 kg N ha−1 yr−1, respectively [4] This continuous increase in N deposition may lead to soil N saturation [5], induce nutrient imbalances, or alter chemical properties, which can give rise to undesirable modifications in plant biodiversity [6]. Alterations in soil properties and vegetation inevitably result in variations in the abundance and community structures of associated microorganisms, such as ectomycorrhizal fungi (EMF) [7]
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