Effects of long-term nitrogen addition on leaf secondary metabolites of the dominant plant species in a temperate deciduous broad-leaved forest

doi:10.17521/cjpe.2024.0262

Abstract

Abstract:

Aims Plant secondary metabolites (PSMs) are closely related to plant growth, development, and the ability to resist biotic and abiotic stresses, playing a crucial role in plant adaptation strategies to the environment. However, the response of leaf PSMs to long-term nitrogen (N) addition in forest ecosystems remains insufficiently studied, which largely limits our ability to grasp the changes in tree resistance and forest ecosystem stability under N deposition.

Methods Our study is based on an 12-year N addition experiment platform, focusing on four dominant plant species in the temperate deciduous forest of Donglingshan: including the plants Betula platyphylla and Corylus mandshurica in the birch forest and Quercus mongolica and Deutzia grandiflora in the oak forest. We investigated responses of soil physicochemical properties in two forest types, leaf phenolic PSMs (i.e., total phenolic, flavonoid, and tannin) contents of four plant species, and tree growth to long-term N addition.

Important findings The results showed that soil water and nutrient contents of birch forest were higher than those of oak forest. N addition significantly decreased soil pH in birch forest and soil water content in oak forest, and increased soil total phosphorus content in oak forest. Overall, the responses of dominant plant species to N addition exhibited contrasting trends, with leaf PSMs showing an increasing trend in the birch forest and a decreasing trend in the oak forest, particularly under high N addition treatments. The leaf phenolic PSMs contents of the four plant species exhibited a trade-off with leaf nutrient contents which was regulated by soil water and nutrient availability. Additionally, after N addition, B. platyphylla showed a decreasing trend in relative growth rate, whereas Q. mongolica showed an increasing trend. These results suggested different nutrient allocation and growth-defense balance strategies among different forest types under N deposition. Compared to the birch forest, the oak forest, which was relatively poor in water and nutrients, was likely to experience vulnerability-related issues (e.g. increased levels of insect herbivory and higher abundance of pathogens) earlier under the influence of long-term high N deposition.

Key words: nitrogen deposition, temperate deciduous broad-leaved forest, plant secondary metabolites, soil physicochemical property, nutrient allocation strategy

ZHAO Chang-Ti, XIA Qing-Lin, TIAN Di, CHEN Bing-Rui, ZHU Rui-De, LIU Xiao-Han, YU Guo, JI Cheng-Jun. Effects of long-term nitrogen addition on leaf secondary metabolites of the dominant plant species in a temperate deciduous broad-leaved forest[J]. Chin J Plant Ecol, 2024, 48(12): 1576-1588.

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Figures/Tables 5

Fig. 1 Effect of nitrogen (N) addition on soil physicochemical properties in Betula platyphylla forest and Quercus mongolica forest (n = 9 individuals × 3 treatments × 2 forests = 54). The “×” symbol represents the mean value for each group. Each subplot displays the p-values for statistical differences between the forest types in the top right corner (ns, p > 0.05; **, p < 0.01; ***, p < 0.001). Different lowercase letters indicate significant differences between treatments (p < 0.05). CK, control, 0 kg N·hm-2·a-1; N50, low nitrogen, 50 kg N·hm-2·a-1; N100, high nitrogen, 100 kg N·hm-2·a-1.

Fig. 2 Effects of nitrogen addition on leaf phenolic secondary metabolites content of four dominant plants in temperate deciduous broad-leaved forest (n = 9 individuals × 3 treatments × 4 species = 108). The “×” symbol represents the mean value for each group. Different lowercase letters indicate significant differences between different treatments (p < 0.05). CK, control, 0 kg N·hm-2·a-1; N50, low nitrogen, 50 kg N·hm-2·a-1; N100, high nitrogen, 100 kg N·hm-2·a-1.

Fig. 3 Principal component (PC) analysis diagram of leaf phenolic secondary metabolites and nutrient content for four dominant plants in temperate deciduous broad-leaved forest (A) and relationship between the first principal component (PC1) and soil physicochemical properties (B-F) (n = 9 individuals × 3 treatments × 4 species = 108). Different colors represent different species groups. Deep-colored dots represent the mean values of each species, while light-colored dots represent the sample points. The regression line is depicted with a solid line if p < 0.05, otherwise with a dashed line. FLA, flavonoid content; LC, leaf carbon content; LN, leaf nitrogen content; LP, leaf phosphorus content; pH, soil pH; STC, soil organic carbon content; STN, soil total nitrogen content; STP, soil total phosphorus content; SWC, soil water content; TA, tannin content; TP, total phenolic content.

Fig. 4 Principal component analysis diagram of leaf secondary metabolites and nutrient content for Betula platyphylla forest (A) and Quercus mongolica forest (B) (n = 9 individuals × 3 treatment × 2 species = 54). Different colors represent different nitrogen treatments. Barplots show PC1 and PC2 score differences across nitrogen treatments, with significant differences indicated by different lowercase letters (p < 0.05). FLA, flavonoid content; LC, leaf carbon content; LN, leaf nitrogen content; LP, leaf phosphorus content; TA, tannin content; TP, total phenolic content. CK, control, 0 kg N·hm-2·a-1; N50, low nitrogen, 50 kg N·hm-2·a-1; N100, high nitrogen, 100 kg N·hm-2·a-1.

Fig. 5 Effects of nitrogen addition to the relative growth rate of Betula platyphylla and Quercus mongolica (n = 9 individuals × 3 treatments = 27). The “×” symbol represents the mean value for each group. “ns” indicates relative growth rate of each tree species have no significant differences among different nitrogen treatments (p < 0.05). CK, control, 0 kg N·hm-2·a-1; N50, low nitrogen, 50 kg N·hm-2·a-1; N100, high nitrogen, 100 kg N·hm-2·a-1.

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