不同施氮水平下番茄叶片氮含量时空分布特征及SPAD无损诊断模型构建

Temporal and spatial distribution characteristics of nitrogen content in tomato leaves under different nitrogen application levels and construction of the SPAD non-destructive diagnostic model

摘要

为了解决当前温室番茄SPAD氮素诊断时叶位选择混乱、模型适用性差等问题，以温室番茄为研究对象，研究不同氮浓度梯度下不同生育时期、叶位的SPAD值、叶片氮含量及氮肥表观利用率（ANUE）的空间位置变化规律，通过相关性分析筛选最佳诊断叶位，并构建氮含量估测模型。结果表明，（1）番茄叶片氮含量随生育期呈先升后降趋势，上、中叶位大多数在Ⅴ期（定植后110 d）达峰值，下叶位在Ⅳ期（定植后95 d）达峰值；同一时期同一叶位叶片氮含量随施氮水平升高呈先升后降趋势，N3（450 kg·hm^-2）水平下叶片氮含量最高（除下叶位IV期外）；叶片氮含量垂直分布（除IV期外）整体表现为上叶位＞中叶位＞下叶位，低氮水平下不同叶位间差异更显著。（2）各叶位SPAD值随生育期推进呈先升后降变化趋势，空间分布在II期表现为上叶位＞中叶位＞下叶位。（3）Spearman相关性分析显示，Ⅰ~Ⅴ期上叶位SPAD值与氮含量极显著相关（相关系数0.948~0.993， P＜0.01），Ⅵ期（定植后125 d）下叶位二者相关性达极显著水平（相关系数0.908，P＜0.01），确定番茄SPAD氮素诊断最佳叶位为“Ⅰ~Ⅴ期（定植后50~110 d）选上叶位，Ⅵ期（定植后125 d）选下叶位”。（4）番茄叶片氮肥表观利用率（ANUE）以上叶位最高、下叶位最低，上、中叶位随施氮水平升高呈先升后降趋势，各叶位ANUE均在Ⅴ期（定植后110 d）达到峰值。（5）基于最佳叶位SPAD值构建的非线性氮含量估测模型拟合优度R²为0.879 3~0.965 3，其中Ⅱ期（定植后65 d）模型最高；模型验证结果显示，Ⅰ期（定植后50 d）模型可靠性最优（均方根方差 RMSE=0.90%，相对误差 RE=6.55%）。综上所述，番茄SPAD氮素无损诊断应采用“前上后下”的动态叶位选择策略，分生育期构建的氮含量估测模型可实现叶片氮素的精准诊断。

Abstract

To address the current issues of chaotic leaf position selection and poor model applicability in SPAD-based nitrogen diagnosis of greenhouse tomato, this study took greenhouse tomato as the research object and investigated the spatial variation patterns of SPAD value, leaf nitrogen content, and apparent nitrogen use efficiency (ANUE) at different growth stages and leaf positions under gradient nitrogen concentrations. Through correlation analysis, the optimal diagnostic leaf position was identified, and nitrogen content estimation models were established. The results showed that: (1) Tomato leaf nitrogen content increased first and then decreased over the growth stage. The upper and middle leaf positions almost peaked at stage Ⅴ (110 days after transplanting), while the lower leaf position peaked at stage Ⅳ (95 days after transplanting). At the same stage and leaf position, leaf nitrogen content rose initially and then decreased with increasing nitrogen application rates, with the highest value observed under the N3 treatment (450 kg·hm ^-2) (except lower leaf position at stage IV). The vertical distribution of leaf nitrogen content generally followed the order (except stage IV): Upper leaf position > middle leaf position > lower leaf position, with more pronounced differences among leaf positions under low nitrogen conditions. (2) SPAD value at all leaf positions also increased first and then decreased over the growth stage, with a spatial distribution order at stage II of upper leaf position > middle leaf position > lower leaf position. (3) Spearman correlation analysis revealed that SPAD value at the upper leaf position were significantly correlated with nitrogen content during stages Ⅰ-Ⅴ (50-110 days after transplanting), with correlation coefficients ranged from 0.948 to 0.993 (P＜0.01). At stage Ⅵ (125 days after transplanting), the correlation at the lower leaf position also reached a highly significant level (correlation coefficient 0.908,P＜0.01). Accordingly, the optimal leaf positions for SPAD-based nitrogen diagnosis were determined as upper leaf position for stages Ⅰ-Ⅴ and lower leaf for stage Ⅵ. (4) The apparent nitrogen use efficiency (ANUE) of tomato leaves was highest at the upper leaf position and lowest at lower leaf position. ANUE increased first and then decreased with rising nitrogen rate, and peaked at stage Ⅴ for upper and mid leaf positions. (5) Non-linear nitrogen content estimation models constructed based on SPAD value at the optimal leaf positions achieved coefficient of determination (R²) values ranging from 0.879 3 to 0.965 3, with the highest value at stage Ⅱ (65 days after transplanting). Model validation results indicated that the stage Ⅰ (50 days after transplanting) model exhibited the best reliability (RMSE=0.90%, RE=6.55%). In conclusion, non-destructive SPAD-based nitrogen diagnosis for tomato should adopt a dynamic leaf position selection strategy - "upper leaf position in early stages, lower leaf position in later stages" - and the nitrogen content estimation models constructed for different growth stages can enable accurate diagnosis of leaf nitrogen status.

关键词

番茄 / 氮素无损诊断 / SPAD值 / 叶位 / 氮肥利用率

Key words

Tomato / Non-destructive nitrogen diagnosis / SPAD value / Leaf position / Nitrogen use efficiency

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基金资助

国家重点研发计划项目(2023YFD2000600)

内蒙古自治区重点研发和成果转化计划项目(2023YFHH0095)