深松耕对玉米根茎叶氮磷比及地上生物量的影响

植物器官的氮磷比（N/P）可以揭示植物生长发育过程的营养平衡。深松耕作为黄土高原半干旱区一种较好的农田耕作方法被广泛应用，尽管已被证实深松耕可以提高作物产量和地上生物量，但深松耕是否影响作物器官N/P及从作物器官N/P角度能否解释地上生物量增加的机制尚有待进一步研究。该研究于2016－2018年在黄土高原区设置了不同耕作方法（深松耕、旋耕、翻耕和免耕）和施氮量（基肥200 kg/hm2、基肥200 kg/hm2+拔节期肥100 kg/hm2）的田间裂区试验，研究了不同处理对玉米地上生物量、不同器官（根、茎和叶）中N/P的影响以及其N/P与地上生物量的关系。结果表明：1）相比翻耕、免耕，深松耕能显著提高地上生物量（P<0.05），2016和2018年深松耕的地上生物量比翻耕、免耕分别提高了9.56%、9.29%和4.67%、5.94%；2）相比翻耕、免耕，深松耕和旋耕均能显著降低根、叶的N/P（P<0.05），深松耕的根、叶N/P分别为19.90、17.74，降幅最大；施肥措施及耕作方法与施肥措施的交互作用对根、茎和叶的N/P无显著影响；3）通过结构方程模型分析发现，耕作方法通过影响根和叶N/P，间接影响地上生物量，效应值分别为0.10和0.14，耕作方法对地上生物量无直接显著影响，说明根和叶的N/P是影响地上生物量的两个重要的间接因素；通过线性混合效应模型分析得出，地上生物量与根、叶N/P呈显著负相关关系，与茎N/P无相关性。研究表明，深松耕通过降低玉米根和叶N/P、促进植物氮磷营养平衡的生态策略来提高地上生物量。研究结果对进一步揭示耕作与施肥对玉米生产与农田生态系统氮磷平衡的影响机制具有一定的借鉴意义。

Effects of subsoiling tillage on N/P ratios in roots, stems, leaves, and aboveground biomass in maize

Nitrogen and phosphorus in Plant organs have been two of the most important indicators of crop growth. The N/P stoichiometry in various organs has generally been selected to represent the balance of nutrients during plant growth. Alternatively, subsoiling tillage has widely been used as a better farming in the semi-arid area of Loess Plateau. Although subsoiling tillage can boost the crop yield and aboveground biomass, it remains unclear whether subsoiling tillage impacts crop N/P, or whether crop organ N/P can explain the mechanism of aboveground biomass growth. The goal of this research was to examine the mechanism of aboveground biomass production from the aspect of plant N/P. A field split plot experiment was carried out in the Loess Plateau, China, from 2016 to 2018, in order to investigate the effects of subsoiling tillage and fertilization on aboveground biomass, the N/P of roots, stems, and leaves of maize, particularly on the relationship between N/P stoichiometry and aboveground biomass. Furthermore, eight treatments were set, where tillage practices as main factors included subsoiling tillage (T1), rotary tillage (T2), plow tillage (T3), and no-tillage (T4), whereas, as secondary factors included two measures of fertilization: N0 (basic fertilizer 200 kg N/hm2) and N1 (basic fertilizer 200 kg N/hm2 + jointing stage fertilizer 100 kg N/hm2). The specific analysis was also associated with the split-plot variance, structural equation modeling, and a linear mixed-effect model. The results revealed that: (1) T1 significantly enhanced the aboveground biomass (P<0.05), where increased by 9.56 %, and 9.29% in 2016, while 4.67 %, and 5.94% in 2018, compared with T3 and T4. (2) Similarly, both T1 and T2 considerably reduced the N/P of roots and leaves (P<0.05). T1 presented the greatest drop, with the N/P of roots and leaves of 19.90 and 17.74, respectively. Nevertheless, there was no significant effect of integrated fertilization and tillage practices on N/P of roots, stems, and leaves. (3) Effect of tillage practices on the root, and leaf N/P indirectly transferred 39% of the variation in aboveground biomass, according to structural equation modeling, with a total effect value of 0.24. Specifically, tillage practices indirectly affected aboveground biomass via the N/P of roots and leaves, with the effect values of 0.10 and 0.14, respectively. But there was no direct effect of tillage on the N/P of roots, stems, and leaves. Correspondingly, the nitrogen and phosphorus content of roots and leaves were two key indirect determinants to regulate the aboveground biomass. In addition, the random slope model better characterized the link between root, leaf N/P, and biomass, where the explanatory degree increased by 425 and 133%, respectively, indicating over fixed effects. More importantly, aboveground biomass was inversely linked with the N/P of roots and leaves, but there was no correlation with the N/P of stems, according to the linear mixed effect model. Consequently, T1 can be expected to boost the aboveground biomass via the lower N/P in maize leaves and roots, while the higher nitrogen and phosphorus nutrition balance. The findings can serve as a sound reference for the fertilization and the promotion of deep tillage, while greatly contribute to understanding the effects of tillage and fertilization on maize production, particularly nitrogen and phosphorus balance in farmland ecosystems.