| Biochar application improves crop yield,the responses of crops to biochar are various.It is unknown if there were differences in the effects of biochar on crops with different nutrient efficiencies.The response mechanisms to surroundings were different in soybean cultivars with different phosphorus(P)efficiencies.With aims to explore the effect of biochar application on different P efficiency soybeans,and to explicit the growth-regulating mechanism of the high P efficiency soybeans to biochar applications.Two high P efficiency soybean cultivars: Jindou 33 and Liaodou 13,HP and two low P efficiency soybean cultivars: Tiefeng 3 and Jindou 8-14,LP,were used in this study.The effects of biochar on root growth,photosynthetic carbon and nitrogen physiology,dry matter production,nutrient absorption and utilization,and yield of different P efficiency soybeans were tested,the regulating mechanism of the high P efficiency soybean responding to biochar was claimed.The results showed that:1.Biochar application increased root length,root surface area,root volume and specific root length,but decreased root diameter and root mass density of different P efficiency soybeans.When single biochar applied,the differences in root morphologic parameters of the high P efficiency soybean between 5%,10% biochar treatments and the control were significant,and those of the low P efficiency soybean were significant between 10% biochar treatment and the control.The maximum increments in root length,root surface area and root volume of the high P efficiency soybean were 15.5%,29.2% and 44.3% under 5% biochar application.Compared with fertilization,co-application of fertilizer and biochar(1%,5%,and 10%)improved the root growth of the high P efficiency soybean.Compared with fertilizer amendment,biochar application could keep more soybean roots at late growth stages and thus delay the senescence of the root system.2.Biochar application improved soybean dry matter accumulation and yield by increasing the photosynthesis and C and N metabolisms.The increments by biochar for the high P efficiency soybean include: the net photosynthetic rate at the podding stage,the carbohydrates content in leaves,as well as the activities of sucrose phosphate synthase(SPS)and sucrose synthetase(SS)at the reproductive stage,which are key enzymes in C metabolism.Biochar application also increased the leaf Chl,nitrogen balance index and the activity of the N metabolism key enzyme nitrate reductase(NR).Path analysis showed that the largest direct effect to the yield of the high P efficiency soybean was the activity of NR at the podding stage,with a regression coefficient of 0.961,and that of the low P efficiency soybean was the activity of SS at seed filling stage,with a regression coefficient of 0.914.Thus,the response mechanism of different phosphorus efficiency soybeans is different to biochar treatments.3.In the field experiment,the results showed that biochar application improved the absorption and utilization of nutrient in the high P efficiency soybean,thus increased the nutrient accumulation in seed and the whole plant.Biochar increased nutrient concentration in the root of the high P efficiency soybean at early growth stages,increased nutrient accumulation in the stem,leaf and the whole plant;it also increased the nutrient concentration,nutrient content and distribution rate in functional organs during the blooming and podding stages;at seed filling stage,biochar increased the nutrient concentration in leaf;at maturity,biochar increased nutrition transfer from leaves to pods,resulting in an increase in nutrient concentration and content in pods(the N,P and K content of the high P efficiency soybean increased by 22.5%,13.4% and 10.8% by biochar,respectively compared to the control).Coapplication of biochar and fertilizer treatment had a similar effect as above on the low P efficiency soybean,while the N and K utilization efficiencies of the low P efficiency soybean were declined under this treatment.Biochar application also increased N and K harvest index of the high P efficiency soybean,while less change was found in the ecological stoichiometric ratio of N/P among treatments than the low P efficiency soybean did,indicating the better internal stability of N and P of the high P efficiency soybean.For these parameters,coapplication of biochar and fertilizer treatment had a synergistic effect on the high P efficiency soybean.4.In the field experiment,the results showed that biochar application increased soybean biomass by increasing the dry matter accumulation dynamics and improving the “sourcesink” distribution.Compared with the control,biochar increased the dry weight of root,stem and leaf of the high P efficiency soybean at different growth stages,ensuring that the “source” was sufficient,resulting in increases in the average dry matter accumulation rate(by 23.5%)and the whole plant biomass.Biochar increased the maximum dry matter accumulation rate and prolonged the rapid growth time of soybean,which could induce more pods and seeds to increase the “sink”.The pod dry weight at maturity of the high P efficiency soybean increased 24.1% under single biochar treatment comparing with the control.Biochar also reduced the distribution of dry matter in vegetative organs but increased it in pods at maturity,resulting in the decrease in root/shoot ratio and the effective transfer of the dry matter to seeds.Co-application of biochar and fertilizer treatment had similar effects as above on the low P efficiency soybean,and it had a synergistic effect on the biomass accumulation of the high P efficiency soybean,which means that the increment in biomass by coapplication was higher than the sum increment by biochar and fertilizer.5.The field experiment showed that biochar application increased soybean stem diameter,seed number per plant,seed weight per plant and yield.The high P efficiency soybean displayed a higher yield than the low P efficiency soybean and improved more in biochar treatment.Comparing with the control,the two-year yield of the high P efficiency soybean increased by 12.3%,14.6% and 22.2%,under biochar,fertilizer and co-application of biochar and fertilizer treatment,respectively;the yield of the low P efficiency soybean increased 18.1% under co-application of biochar and fertilizer. |
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