Figure legends

Figure 1 Soil temperature (oC, 10 cm) (a) and soil moisture (%, 10 cm) (a) under different plant diversity and N addition level from April to October 2019. Mean (±se, n = 4 or 8) soil temperature (c) and soil moisture (d) for the whole growing season under different plant diversity and N addition level in 2019. We applied the linear mixed effects models to test the effects of treatments (plant diversity and N addition) on soil temperature and soil moisture. We set treatments as fixed factors, time and block as random factors in each model to account for variation among repeated measurements of soil temperature and moisture. Points and lines with different shape represent different nitrogen addition levels, points with different colour represent different plant diversity levels. N represents nitrogen addition, D represents plant diversity.
Figure 2 Average first flowering day (a), last flowering day (b), flowering duration (c), and flower number (d) under different plant diversity and N addition levels. All the analyses were performed using the linear mixed effects models to test the effects of treatments (plant diversity and N addition) on flower phenology. Treatments were treated as fixed factors, block was treated as a random factor. Points and lines with different shape represent different N addition levels, points with different colour represent different plant diversity levels. N represents nitrogen addition, D represents plant diversity.
Figure 3 Average leaf mass (a), leaf area (b), specific leaf area (c), leaf carbon content (d), leaf nitrogen content (e), and leaf C/N ratio (f) under different plant diversity and N addition levels. All the analyses were performed using the linear mixed effects models to test the effects of treatments (plant diversity and N addition) on leaf traits. Treatments were treated as fixed factors, block was treated as a random factor. Points and lines with different shape represent different N addition levels, points with different colour represent different plant diversity levels. N represents nitrogen addition, D represents plant diversity.
Figure 4 Average M. Sativa biomass (a), relative biomass (b), relative abundance (c), and relative height (d) under different plant diversity and N addition levels. All the analyses were performed using the linear mixed effects models to test the effects of treatments (plant diversity and N addition) on plant traits of M. Sativa . Treatments were treated as fixed factors, block was treated as a random factor. Points and lines with different shape represent different N addition levels, points with different colour represent different plant diversity levels. N represents nitrogen addition, D represents plant diversity.
Figure 5 Partial correlations between the flowering events and the light acquisition traits, nutrient acquisition traits, and abiotic factors after controlling N addition and plant diversity levels. The x-axis shows the factors of which the correlations with the flowering events are examined. The size and colour of the circles indicate the strength and sign of the correlation. Differences in circle size and colour indicate the level of dependency of the correlation between the flowering events and the examined factor after controlling N addition and plant diversity levels. FFD, first flowering day; LFD, last flowering day; FD, flowering duration; FN, flowering numbers; LM, leaf mass; LA, leaf area; LL, leaf length; LW, leaf width; SLA, specific leaf area; LN, leaf nitrogen content; LC, leaf carbon content; LCN, leaf carbon/ nitrogen ratio; AB, aboveground biomass; PA, plant abundance; PH, plant height; RB, relative biomass; RA, relative abundance; RH, relative height; AN, available soil nitrogen; SM, soil moisture; ST, soil temperature. *P <0.05; **P <0.01; ***P <0.01.
Figure 6 Relative contributions of light acquisition traits, nutrient acquisition traits, and abiotic factors to flowering events. Variation partitioning analysis was to identify the variance in the first flowering day (a), the last flowering day (b), flowering duration (c), and flowering numbers (d) explained by these three groups of biotic and abiotic factors.
Figure 7 A structural equation modelling of plant diversity loss and N addition on the first flowering day (a), the last flowering day (b), the flowering duration (c), and flower number (d). Red and black arrows represent significant positive and negative pathways, respectively. Solid and dashed arrows indicate significant and non-significant pathways, respectively. Numbers near the arrow indicate the standardized path coefficients indicating the effect size of the relationship with * indicating P < 0.05, ** indicatingP < 0.01, and *** indicating P < 0.001. Arrow width is proportional to the strength of the relationship.R2 represent the proportion of variance explained for each dependent variable. The goodness-of-fit statistics for the structural equation modelling are shown below each model. N, nitrogen.