关键词: 秋季施肥, 养分贮存, 造林效果, 生长, 养分回流

Abstract:

Objective: In the present study, we explored optimal fall fertilization regime by investigating seedling quality and field performance of Populus tomentosa in order to provide a theoretical basis for nursery accurate fertilization management. Furthermore, we examined the inner-mechanism of growth and nutrient resorption in field. Method: In this study, triploid P. tomentosa was used as experimental materials. Fertilization was carried out in fall after the formation of terminal buds, once a week for consecutive six weeks (from September 2 to October 7). A completely randomized block design with one factor was used to set four fertilization levels: 0, 5, 10, 20 g fertilizer per seedling totally (a water-soluble commercial fertilizer: 20%N + 20%P₂O₅ + 20%K₂O + TE). Seedling height, diameter and stem biomass (or stem volume) were measured at the beginning and end of each growing season. We also determined nutrient concentration and non-structural carbohydrate (NSC) levels in stems and roots in nursery, as well as nutrient concentration in green and senesced leaves in field. Result: 1) In nursery, fall fertilization had little effect on seedling growth, but significantly increased N and NSC accumulation, especially in roots. The N concentration in stems and roots increased by 2.4%-12.0%, 17.4%-48.1%, respectively, and the root starch concentration increased by 17.9%-34.5%. Fall fertilization with N, P and K was mainly enhanced N storage but no significant effect on P or K storage, indicating the preference for N utilization. 2) In field, the growth of height, diameter and stem volume reached the maximum when the fertilizer amount was 10 g per seedling (increased by 40.0%, 80.4%and 85.3% respectively compared with the control), fully exhibiting the effects of fall fertilization in the nursery. When fertilization rate increased to 20 g per seedling, the seedling growth was inhibited and the survival rate the minimum of (63.3%) after afforestation. The result demonstrated that it is important to optimize fall fertilization rate. 3) Furthermore, the enhance of growth (10 g fertilizer per seedling) increased N resorption efficiency (71%) and decreased N leaching loss from deciduous leaves (56.4%). 4) Our results also showed that the changes of nutrient resorption were associated with shifts of multi-elements in leaves rather than single-element. Nitrogen resorption was negatively related to N and K concentration in senesced leaves, while positively related to P concentration in green and senesced leaves. Phosphorus resorption was positively related to N concentration in green leaves. Conclusion: N storage, NSC levels with field performance of seedlings are important indicators to evaluate the effect of fall fertilization. Infield, the increments of growth increase N resorption from leaves and sequence, decrease N leaching. It is paramount to optimize fall fertilization rate, however it is particularly important to determine the reasonable amount of fertilization in fall. Nutrient storage, NSC accumulation and field performance of triploid P. tomentosa seedlings are benefit when fertilization rate is 10 g fertilizer per seedling, but when fertilization rate is 20 g fertilizer per seedling, it has a negative effect.

Key words: Fall fertilization, nutrient storage, field performance, growth, nutrient resorption