Effects of Nitrogen Application Rate and Transplanting Density on Source-Sink Characteristics of Black Rice in Cool Regions of Northeast China

SHI Yuhang; DAI Yaxuan; LI Danping; XING Ye; REN Shaoqi; JIN Shan; LIU Haifeng

doi:10.15933/j.cnki.1004-3268.2026.04.004

Abstract：To establish high-yield cultivation technique suitable for black rice in cool regions of Northeast China,a field experiment was conducted using the black rice Yanhei 205 as experimental material.Three nitrogen application rates(N1:100 kg/ha,N2:130 kg/ha,and N3:160 kg/ha)and three transplanting densities(D1:5.1×10⁵ plants/ha,D2:3.4×10⁵ plants/ha,and D3:2.5×10⁵ plants/ha)were designed to determine the optimal combination that coordinated the source-sink relationship and achieved high yield.The results showed that N3 and D3 treatments improved photosynthetic performance and enhanced source capacity.Tiller number,plant height,chlorophyll a content,chlorophyll b content,and dry weight of aboveground part generally increased with the increase of nitrogen application rate and decrease of transplanting density.D3 treatment had the highest carotenoid content,which was significant higher than D1 treatment,whereas nitrogen application rate had no significant effect on carotenoid content.However,sink capacity of N3 and D3 treatments was lower,and no advantages were observed in dry matter translocation,yield components,or final grain yield.Among treatment combinations,N3D3 treatment exhibited superiority in photosynthetic pigment accumulation and gas exchange,with a maximum net photosynthetic rate of 18.49 μmol/(m²·s)at the heading stage,which was the highest value among all treatments during the entire growth period,indicating that this combination was optimal for enhancing photosynthetic capacity at the individual-plant level.N2 and D1 treatments had the highest sink capacity.The number of effective panicles,spikelet number per panicle,and seed setting rate increased initially and then decreased with the increase of nitrogen application rate,reaching maximum values under N2 treatment.Meanwhile,N2 treatment had the highest conversion rate and apparent export rate of matter from leaves and stems,and D1 treatment also had the highest conversion rate and apparent export rate of matter from leaves.Regarding treatment combinations,although N2D3 treatment achieved the highest sink capacity(6 930.74 kg/ha),but did not had the highest grain yield.N2D1 treatment produced the second-highest sink capacity(6 563.72 kg/ha),and had the greatest grain yield(5 889.98 kg/ha)among all treatments,indicating that it was the most effective strategy for enhancing sink capacity and yield formation in black rice.Principal component analysis revealed that grain yield exhibited the highest loading value(0.76)in PC2,which represented sink-related traits.In conclusion,the black rice cultivar Yanhei 205 can be characterized as a sink-limited rice genotype;the recommended nitrogen application rate is 130 kg/ha,and the transplanting density is 5.1×10⁵ plants/ha in cool regions of Northeast China,the source-sink relationship is well coordinated under this combination,and grain yield can reach 5 889.98 kg/ha.