水肥耦合效应对楸树苗期叶片净光合速率和SPAD值的影响

以楸树无性系004-1苗木为研究对象,采用三因素五水平二次回归通用旋转组合设计,通过盆栽试验测定不同处理下楸树苗木叶片净光合速率(Pn)和SPAD值,并建立其与土壤水分(W)、施氮量(N)和施磷量(P)回归模型,分析土壤水分、施氮量和施磷量的主因子、单因素及耦合效应对楸树苗木叶片Pn和SPAD值的影响。研究结果表明:(1)W和N对楸树苗木叶片Pn和SPAD均有显著正效应,并且N主效应大于W,而施磷量主效应不显著;(2)单因素效应分析结果表明,楸树苗木叶片Pn和SPAD值随着N的增加均呈现出先增大后减小的变化趋势,与N类似,叶片Pn和SPAD值对W的响应曲线也呈现出类似的"抛物线式"变化趋势;(3)W×N对楸树苗木Pn和SPAD值均存在显著耦合正效应,但Pn和SPAD值与W×N的响应曲面关系图有所不同:随着土壤水分和施氮量的同时增加,叶片Pn逐渐增加,而叶片SPAD值呈现出先增加后减小的变化趋势;(4)楸树苗木叶片Pn与SPAD值呈现出极显著正相关关系(P0.0001)。总体而言,与土壤水分和施磷量相比,楸树生长更容易受土壤施氮量限制,此外,通过合理水肥配施措施,能一定程度提高楸树苗木的光合生产力和叶片SPAD值。

Interactive effects of soil water and fertilizer application on leaf net photosynthetic rate and SPAD readings of Catalpa bungei seedlings

Recent studies have examined problems related to water and fertilizer consumption, including the excessive application of these resources and their use in forest management. Many forest researchers maintain that the choice of suitable irrigation and fertilization strategies for seedling culture and field planting could save water and improve production. Catalpa bungei is a common, high-quality timber tree. The Chinese government plans to promote large-scale planting of C. bungei in appropriate areas; thus, information about irrigation and fertilization of this species is important. Response surface methodology (RSM) can be used to design experiments, establish models, assess significance, and determine optimal conditions. In addition, RSM can be used to analyze how process variables affect responses and to generate three-dimensional plots. Rotatable central composite design (RCCD) is a common experimental method for studying the relationship between plant growth and soil water or fertilizer. Here, we used RCCD for a pot experiment with three factors, five levels, and 20 runs to examine leaf net photosynthetic rate (Pn) and SPAD values of C. bungei seedlings (clone 004-1). Mathematical models were established to examine the effects of main factors, monofactors, and the combination of soil water (W), nitrogen (N), and phosphorus (P) application on Pn and SPAD. Both W and N had significant positive effects on leaf Pn and SPAD values (the sequence of main factor effects was N > W); P did not affect these variables significantly. Analysis of monofactor effects showed that the values of leaf Pn and SPAD increased initially and then decreased with increasing N or W, indicating that leaf Pn and SPAD would be limited in seedlings subjected to excessive irrigation and fertilizer application. RSM based on RCCD showed that the interaction W × N had a significant positive effect on leaf Pn and SPAD: Pn values increased gradually with increasing W and N, while SPAD first increased and then decreased. The W × P and N × P interactions had no significant effects on leaf Pn or SPAD. In addition, leaf Pn and SPAD were positively correlated (P < 0.0001). Our results showed that N, rather than W or P, was the most important limiting factor in the growth of C. bungei seedlings, and we conclude that leaf Pn and SPAD in C. bungei can be promoted by rational irrigation and fertilization practices. Our findings provide fundamental information for seedling culture and afforestation of C. bungei.