Study On The Effect And Mechanism Of Boron-phosphorus Interaction In Brassica Napus

Brassica napus(B.napus)requires a larger amount of boron(B)and phosphorus(P),and is extremely susceptible to B and P deficiencies.Lack of available B in the soil causes the rapeseed to flowering without seed-set,and lack of available P in the soil leads to the reduction of branching and seed-set,both of which severely reduce the seed yield of B.napus.However,both B and P deficiencies in the main rapeseed producing areas are in common,so B and P has always been the main nutrient limiting factors for the high yield of rapeseed in China.Application of the chemical B fertilizer and P fertilizer are effective agronomic practice to increase crop productivity.However,the non-renewable phosphate and borate rocks are depleting.Moreover,excessive application of B fertilizer easily poses a serious toxic threat to plants,and inappropriate application of P not only leads to the waste of fertilizer resources but also brings adverse effects on human living environment.Nutrient interaction plays an important role in plant growth and yield formation.Thus,understanding of how B.napus coordinates P and B nutrition for its optimized growth and yield is crucial for the B and P fertilizer management strategy.So far,documents of how these two essential elements interact are limited.Based on the above research background and purpose,field,pot and hydroponic experiments were conducted in this study to investigate the interactive effects of B and P and its mechanism in B.napus.The main results obtained from the study are as follows:(1)Effect of combined application of B and P fertilizers on seed yield,phosphorus use efficiency and soil bacterial community of B.napusThe seed yields of B.napus were lowest when B fertilizers or P fertilizers were not applied(P₉₀B₀ or P₀B₉,the subscript values of P and B indicate the amount of P fertilizer and B fertilizer applied per hectare,the same below).Compared with plants receiving no B fertilizer(treatment P₉₀B₀),application of B fertilizer to plants receiving a normal P supply(P₉₀)increased the seed yield by 30.8%-2181.6%.Compared with plants receiving no P fertilizer(treatment P₀B₉),application of P fertilizer to plants receiving a normal B supply(B₉)increased the seed yield by 134.5%-523.9%.Balanced B and P applications improved seed yield and phosphorus fertilizer efficiency(PUE).The combination of low P and low B(P₄₅B_4.5)had higher seed yield and PUE than the combination of low P and high B(P₄₅B₁₈),and the combination of high P and high B(P₁₈₀B₁₈)had higher seed yield and PUE than the the combination of high P and low B(P₁₈₀B_4.5).The synergic fertilizer application rates of B and P for rapeseed are 4.5-9 kg borax/hm² and 90-135 kg P₂O₅/hm².The B-efficient(B-deficiency-resistant)rapeseed cultivar‘Zhongshuang 11'(‘ZS11')and‘Huagaoyou No.1'(‘HGY1')had greater yields than B-inefficient(B-deficiency-sensitive)rapeseed cultivar‘Westar 10'(W10)in all treatments,indicating that a significant cultivar difference in the synergistic effects of B and P.Sequencing of 16S r RNA genes showed that the P₉₀B₉ treatment increased the diversity and relative abundance of soil bacteria in comparison with the P₉₀B₀ or P₀B₉ treatment.(2)Effects of combined application of B and P on P nutrition status in B.napusBalanced application of B and P benefitted seed yield.Compared with high P and low B combination,high P and high B combination optimized the plant growth and promoted the distribution of P to seeds,thereby increasing the seed yield of rapeseed at the ripening stage,and this effect was more obvious in the B-inefficient cultivar‘W10'than in the B-efficient cultivar‘ZS11'.Compared with low P and high B combination,low P and low B combination promoted the absorption of P at the seedling and bolting stages and the distribution of P to seeds at the ripening stage,and then enhanced photosynthetic efficiency and thus guaranteed the high yield.Interestingly,under low P conditions,high B supply upregulated the expression of the P-starvation-induced gene Bna C3.SPX3 and P transport genes Bna PHT1s in roots,indicating that low B promoted P absorption by roots may be a Bna PHT1s-independent process.Significant differences of B and P interaction on the total P absorption and distribution at the ripening stage,seed yield and net photosynthetic rate between‘W10'and‘ZS11'might reflect the distinct cultivar properties.(3)Effects of combined application of B and P on B nutrition status in B.napusUnder low B conditions,increased P supply significantly promoted the growth of rapeseed at seedling and bolting stages.However,high P and low B combination inhibited the transfer of B to seeds at the mature stage,and aggravated the B deficiency symptoms of the B-inefficient cultivar‘W10',including fewer effective branches and siliques,resulting in a significant decrease in yield of‘W10'compared with low P or medium P and low B combination,while no obvious B deficiency was observed in‘ZS11'at low B supply,and low B and high P combination only led to a slight decrease in the yield of‘ZS11'relative to low B and medium P combination.Under high B conditions,increased P promoted the B absorption in plants and B distribution ratio in seeds,which significantly increases the seed yield by 6.0-10.6 times.Further analysis revealed that appropriate combination of B and P increased the B concentration of newly initiated leaves and seeds,reduced the excessively high P/B ratio in plants and kept elements relatively stable in B-deficient plants,thereby alleviating the inhibitory effect of deficient B on the growth and seed yield of B.napus.B-inefficient cultivar‘W10'and B-efficient cultivar‘ZS11'had significant differences in the response of B-P interaction to plant P/B ratio and root morphological parameters,which may reflect distinct cultivar characteristics.In conclusion,coordinated application of B and P fertilizer affected soil enzymes activity and bacterial population abundance in rhizosphere soils of Brassica napus,and significantly affected the concentration of available B and P in soils.This could facilitate the absorption of P and its transport to seeds,and increase the B concentration in the new tissues,thereby enhanced photosynthetic efficiency and guaranteed the formation of yield,which is the key physiological mechanism of the synergic effect between B and P in Brassica napus.In addition,the positive synergistic effects differ among rapeseed cultivars.This finding not only enriched our understanding of the interaction between B and P in higher plants,but also provided the basis for optimizing the application of B and P fertilizers in agriculture.