Study On The Low Seed Setting Percentage Of Leymus Chinensis Based On Photosynthetic Product Distribution

Leymus chinensis(Trin.),a rhizomatous,perennial grass,is one of the dominant forage species in Songnen grassland of Northeast China.It is rich in crude protein and crude fat.It is not only having a high palatability,but also has a high tolerance to arid and saline-alkaline environments.Thus,Leymus chinensis plays an important role in animal husbandry at the local and even northern areas.However,under natural conditions,the seed setting percentage and low seed yield are low,which restricts the restoration of degraded natural grasslands and the establishment of artificial grasslands.Therefore,it is has great scientific significance to explore the internal mechanism of low seed setting percentage of Leymus chinensis.In the study,a full factor experimental was used and the follow works were done: 1)the relative contribution of spike,reproductive shoot leaves and vegetative shoot leaves at heading and filling stages were studied using a stable carbon isotope tracing technique;2)the effects of nitrogen application on the translocation and distribution of photosynthetic product and seed setting were studied;3)the effects of blocking the belowground distribution of photosynthetic product on the seed setting were studied.The results show that:(1)At heading stage,the photosynthetic capacity of the spike was the strongest,and the reproductive and vegetative shoot leaves were 0.03 and 0.14 times of that of the spike respectively,the photosynthetic capacity of the three at the heading stage was similar to that at the filling stage;Compared with the filling stage,the photosynthetic ability of reproductive shoot leaves in heading stage was higher,and the spike and vegetative shoot leaves between the two stages were no significant difference;The percentage of photosynthetic products from spike transport to spike and seed(32.32%,19.11%)was significantly higher than that of reproductive(4.34%,4.74%)and vegetative shoot leaves(1.70%,1.34%);At the filling stage,32.07% of the photosynthetic products from spike were transported to seeds,which was higher than that at the heading stage;In addition,no matter in heading stage or filling stage,more than 35% and 60% of photosynthetic products of the reproductive shoot leaves and vegetative shoot leaves were reserved for their stem and leaf growth,and more than 15% and 18% of photosynthetic products were transported and distributed to belowground organs.(2)Compared with the control,the number seeds of per spike,seed setting percentage and thousand seeds weight increased by 5.75%,7.61% and 4.95% under nitrogen application;Nitrogen fertilizer increased the photosynthetic capacity of spike and vegetative shoot leaves by 71.22% and 45.05%(P < 0.05),respectively,compared with the control;After nitrogen application,35.07% and 2.03% of the photosynthetic products of spike and vegetative shoot leaves were transported to seeds,which showed an increasing trend compared with the control.Despite all this,nitrogen application doesn't change the rule of nearby transport of photosynthetic products.(3)Rhizome cutting(30 cm severing spacing)during the filling stage increased the number seeds of per spike and the thousand seeds weight by 14.94% and 5.02%,respectively(P < 0.05),and the actual seed yield significantly increased by 25.18%(P < 0.05);However,the rhizome severing spacing of 15 cm have lower the number seeds of per spike,the thousand seeds weight and the seed yield of Leymus chinensis than that of the control.In summary,the relative contribution of spike to seed setting was the largest,the photosynthetic product of spike at heading stage was mainly used for the morphological construction of spike,while the photosynthetic product of spike at filling stage was mainly used for seed filling development;At heading and filling stage,most of the photosynthetic products of the reproductive shoot leaves and vegetative shoot leaves are used for the growth and development of its stems,leaves and belowground organs,which had little contribution to seed setting.Finally,it's result in Leymus chinensis has a lower seed setting percentage;Nitrogen application significantly enhanced the photosynthetic capacity of spike and vegetative shoot leaves,and promoted the photosynthetic products from spike and vegetative shoot leaves to spike and seeds,so that the number of seeds per spike,seed setting percentage and thousand seeds weight showed an increasing trend;In agronomic practice,based on the principle of translocation and distribution of photosynthetic products,proper rhizome cutting(30 cm severing distance)at the filling stage promote the transport of photosynthetic products to sexual reproductive organs,can increase the yield of seeds.In the study,the problem of low seed setting of Leymus chinensis was clarified in the view of distribution in photosynthetic products,which provided a scientific theoretical basis for improving the seed yield in practice.