Seed Quantity or Quality?-Reproductive Responses of Females of Two Dioecious Woody Species to Long-Term Fertilisation

Abstract

Although seed quality and quantity, as well as reproductive performance are important life history stages of plants, little is known about the reproductive responses of trees to environmental changes such as increased anthropogenic deposition of nitrogen (N) and phosphorus (P). Dioecious plants are good models with which to test the environmental impact on female or male reproductive responses individually. We analysed effects of different long-term nutritional availability on the reproductive performance of two dioecious species (Taxus baccata L. and Juniperus communis L.) characterised by different life histories. By using pot experiments with vegetatively propagated plants grown in different fertilisation conditions, we observed an increase in plant growth and strobili production but a decrease in seed efficiency. Seeds produced by fertilised plants had greater seed mass. Fertiliser addition did not change C or N content nor the C/N ratio of T. baccata seeds, but increased N content and the N/P ratio; however, it did lower the C/N ratio in J. communis. Fertilisation did not change the metabolite profile in T. baccata but 18 metabolites were changed in J. communis. The study revealed new links between species life history, environmental changes, and reproduction. The findings imply that future environmental conditions may alter both seed productivity, and quality, as well as plant reproductive behaviour.

Keywords: English yew; common juniper; nitrogen deposition; nutritional availability; resource allocation; seed mass; seed size; seeds metabolome.

Figure 1

Features of Taxus baccata L. (a,b) and Juniperus communis L. (c–f) plants grown in fertilised (a,c,e) and non-fertilised conditions (b,d,f) within the observation period.

Figure 2

Number of Taxus baccata L. mature arils (a,b) and Juniperus communis L. mature cones (c,d) in relation to plant height (cm) in plants grown in fertilised (green, a,c) and non-fertilised (red, b,d) conditions.

Figure 3

Percentage of mature (a) arils of Taxus baccata L. and (b) cones of Juniperus communis L. collected over time from female plants grown in different nutritional conditions (F—fertilised plants, green, NF—non-fertilised plants, red), concerning all collected generative structures.

Figure 4

Correlation matrix and data distribution of seed weight (mg) and morphometric parameters (projected area, mm²; curved length and width, mm) of (a) Taxus baccata L. and (b) Juniperus communis L. seeds, collected from plants grown in fertilised (green) and non-fertilised (red) conditions. Stars indicate significant correlations (* p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 5

Juniperus communis L. dry seeds were analysed using the X-ray method for assessing viability. (a) X-ray film after analysis; (b) non-viable seed, with not properly developed embryo; (c) viable seed, a properly developed embryo with undamaged seed coat; (d) empty seed, coat without embryo.

Figure 6

Results of the metabolome data analysis. (a,d) Principal Component Analysis scores—plot between the selected Principal Components (PC), and (b,e) Partial Least Squares–Discriminant Analysis (PLS-DA)—plot between the selected Principal Components (PC) showing separation between fertilised and non-fertilised dry seeds collected from Taxus baccata L. and Juniperus communis L. plants, grown in fertilised (green) and non-fertilised (red) conditions. The explained variances are shown in brackets; (c,f) VIP scores showing the top 20 important metabolites that contribute the most to the PLS-DA plots of seeds. Colours in the variable importance in projection plot represent relative intensities, where red and blue symbolise higher and lower values, respectively.

Figure 7

Results of the metabolome data analysis of dry seeds collected from Juniperus communis L. plants grown in fertilised (green) and non-fertilised (red) conditions. (a) The clustering result is shown as a heatmap (distance measure using correlation, and clustering algorithm using ward.D); colours represent metabolite relative intensities with red and green symbolising the highest and lowest values, respectively. (b) Metabolic pathway analysis plot created using MetaboAnalyst. Plot depicts several metabolic pathway alternations induced by long-term fertiliser availability. The x-axis represents the pathway impact value computed from pathway topological analysis, and the y-axis is the –log of the p-value obtained from pathway enrichment analysis. The pathways that were most significantly changed are characterised by both a high –log(p) value and a high impact value (top right region).

Figure 8

Plant response to long-term fertiliser availability. * Data summarised after [31,41].

Figure 9

Meteorological conditions during the period of seed development. (a) Monthly maximum (red) and minimum (green) mean values of air temperature (°C). (b) Monthly mean of the total precipitation (mm).