| Feed,especially the high-protein feed is seriously lacking in China now.Over 80%of protein feed of China is imported.This condition severely restricted the healthy development of animal husbandry of our country.Toona sinensis?A.Juss.?Roem?TS?is a perennial deciduous tree of the genus Toona of family Meliaceae.TS have been widely cultivated in China,and their young buds are treasured as forest-vegetables.However,the millions of tones of mature leaves of TS are never utilized.Actually,the mature leaves of TS are nutritious,and they possess huge feed development potential.But the massive accumulation of nitrate of mature leaves of TS severely limits their utilization.In this study,the mature leaves of TS were used as experimental materials.The composition and content of nutritional components,such as crude protein,amino acids and minerals of TS mature leaves were determined by chemical analysis methods.In addition,sheep feeding experiment and biomass assessment were conducted.The feeding value and development potential of TS mature leaves were also evaluated.Meanwhile,the content of key forage components?protein,flavonoids and total nitrate?in leaves of TS from different developmental stages were analyzed,and their antioxidant activity were determined by ORAC,DPPH and FRAP methods.By comprehensive analyzing of nutritional content and healthy benefits,the accumulation characteristics of key forage components in mature leaves of TS were defined,and their optimal forage-harvesting period were preliminarily determined.Furthermore,through analyzing the nitrate reduction effects of three agronomic measures:basal fertilizer treatments,foliar application treatments and preharvest treatments,on mature leaves of TS,this study screened out several effective methods to reduce nitrate content in forage-used TS.The main results were listed as follows:?1?The mature leaves of TS were rich in crude protein?16.25–17.78%?,mineral elements?K,Ca,P,Mg and Fe,etc.?and amino acids?essential amino acids took up to 33.12–34.60%?,and low in crude fat?3.10–5.45%?.Meanwhile,mature leaves of TS were welcomed by sheep,and no adverse reaction was observed.The mature leaves of TS were suggested to be nutritious woody feed resources,and had high forage development value.?2?The mature leaves of TS from different develop stages were rich in crude protein and flavonoids,and had outstanding antioxidant activity,but also had the excessive accumulation of nitrate.The average crude protein contents of mature leaves of TS from different develop stages were 13.17–22.65%,which were much higher than that of conventional grain feed,and the content was decreased with the increase of maturity.The flavonoids were continuously accumulated with the maturation of TS,and the average flavonoids content in the mature leaves of TS was 1586.77 mg·100 g-1,which was much higher than that it in fruits and vegetables,such as blueberries.Antioxidant activity of leaves of TS increased continuously with the maturation of TS,and a very significant?P<0.01?positive correlation between antioxidant activity and flavonoids content was detected.Large amounts of nitrates were detected in TS from different harvest time(range from 2306.39 to 7346.80 mg·kg-1).The accumulation of nitrates in TS presented a“V”shape along with its maturity.Comprehensively considering the nutritional value and health care effects of TS,July and August were suggested to be the optimum harvest time for the forage-used TS.?3?Three agronomic measures,including basal fertilizer treatments,foliar application treatments and preharvest treatments,could all affect the accumulation of total nitrate in the mature leaves of TS,and the effect differences were not significant?P>0.05?.In basal fertilizer treatments,the accumulation of total nitrate in the mature leaves of TS decreased first and then increased with the increase of N,P and K,and gradually decreased with the increase of dicyandiamide.By the combined treatment,the total nitrate content could decrease by30.90%at most when compared with the control.In foliar application treatments,the accumulation of total nitrate increased first and then decreased with the concentration increasements of Mo and B,decreased first and then increased with the concentration increasements of Mn and slowly increased with the concentration increasements of Zn.By the combined treatment,the total nitrate content could decrease by 15.97%at most when compared with the control.In preharvest treatments,increasing the intensity of light and prolonging the duration of illumination had the best effects on the total nitrate reduction of TS.The total nitrate content could be decreased by 46.33%by continuous illumination for 72 h.Pre-harvest irrigation could promote the accumulation of total nitrate in the mature leaves of TS,which could lead to a increasement of up to 77.79%.At the same time,the effects of basic fertilizer treatments and pre-harvest treatments on the expression of nitrate reductase of TS?Ts NR?were also discussed.Results showed that the differences were not significant?P>0.05?and there was no significant correlation between Ts NR expression and total nitrate content?P>0.05?.The regulation mechanism of nitrate accumulation in TS should be further analyzed in combination with the nitrogen metabolism pathway next. |
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