| At present,the research on straw returning to the field mainly focuses on the effects on soil physical and chemical properties and crop yield,It is rare to report the physiological and ecological effects on farmland weeds.In this paper,the effects of different amount of rice straw returning(0 kg/hm2、300 kg/hm2、600 kg/hm2)on photosynthetic performance,root growth and nutrition metabolism of main grasses in wheat field(Beckmannia syzigachne,Alopecurus japonicus Steud)weve studied by field experiment.The effects of different amount of wheat straw returning(0 kg/hm2、200 kg/hm2、400 kg/hm2)on photosynthetic performance,root growth and nutrition metabolism of main grasses in rice field(Echinochloa crusgalli,Leptochloa chinensis(L.)Nees).The findings are as follows:1.Without the competition from wheat,the quantity of the straw-returning can inhibit the photosynthesis capacity of the Beckmannia syzigachne and Alopecurus japonicus Steud during the entire growth period,while the quantity of the straw-returning as 600 kg/hm2 has most significant effects on the photosynthetic parameters of Beckmannia syzigachne and Alopecurus japonicus Steud during the mature period,for which the net photosynthetic rates of Beckmannia syzigachne and Alopecurus japonicus Steud significantly were reduced as 40.09%and 30.61%respectively,and the photosynthetic performance indexes were significantly reduced as 35.22%and 20.64%.Straw-returning to the field could also effectively inhibit the root system growth of Beckmannia syzigachne and Alopecurus japonicus Steud at the tillering stage and the mature stage.Among them,at the mature stage with quantity of the straw-returning as 600 kg/hm2,the total root length,total root surface area and total volume of Beckmannia syzigachne and Alopecurus japonicus Steud were significantly reduced by 30.51%,60.90%,77.94%and 51.7%,42.24%,38.33%respectively.straw-returning to the field would also affect the accumulation of N and P elements in the leaves of Beckmannia syzigachne and Alopecurus japonicus Steud.Among them,as for Alopecurus japonicas Steud with the straw-returning,the content of nitrogen and phosphorus was significantly reduced by 4.35%to 12.84%and 8.82%to 21.51%at the tillering stage,respectively.The content of nitrogen was significantly reduced by 18.16%to 19.31%at mature stage,and the content of phosphorus was increased significantly 26.30%to 36.68%.The change of element content of Beckmannia syzigachne showed the same trend.Straw-returning to the field also reduced the accumulation of dry mass of Beckmannia syzigachne and Alopecurus japonicus Steud.The dry weight of Beckmannia syzigach ne and Alopecurus japonicus Steud decreased significantly by 8.17%to 16.67%and 11.32%to 20.13%at mature period,and the inhibition effect of Beckmannia syzigachne and Alopecurus japonicus Steud was more significant at the amount of straw-returning as 600kg/hm2.2.Under the associated condition of gramineous weeds and wheat,the effect of rice straw-returning on the growth and development of Beckmannia syzigachne and Alopecurus japonicus Steud showed a similar effect without wheat competition,but the inhibition effect on Alopecurus japonicus Steud was shown more obvious.The dry weight of Alopecurus japonicus Steud was significantly decreased by 20.16%to 24.81%at mature period.At the same time,the straw-returning was promoted the growth and development of wheat.Thereinto,at amount of straw-returning 600 kg/hm2 in the mature stage,the net photosynthetic rate and photosynthetic performance index of wheat increased significantly by 34.35%to 35.83%and 43.36%to 57.03%respectively;The total root length,the total surface area and total volume of the wheat roots were increased to varying degrees,but only in the competitive environment of Beckmannia syzigachne and wheat,the total surface area of wheat roots was shown a significant difference,with an increment of 43.01%.The straw-returning would also promote the accumulation of N and P elements in the first full leaf expansion of wheat,but the increment of the two elements in the mature period was significantly smaller than that in the tillering period,and the N content of wheat was increased significantly by 6.98%to 31.98%and 3.54%to 8.66%respectively during the tillering period and the mature period,the content of P element was increased significantly by 9.78%to 16.4%during the tillering stage,which only was increased significantly by 9.45%to 13.07%under the amount of straw-returning as 600 kg/hm2 at the mature stage.The dry weight of wheat was increased significantly by 6.65%to 12.35%,and the theoretical yield was increased by 10.6%to 23.33%.600 k g/hm2 of rice straw-returning can effectively improve the competition ability of wheat for light energy and nutrients under the associated conditions with gramineous weeds and wheat,thereby increasing wheat yield,which could play a certain role in prevention and control of Beckmannia syzigachne and Alopecurus japonicus Steud.3.Without the rice competition,wheat straw-returning can inhibit the growth of photosynthetic capacity and root system of Echinochloa crusgalli and Leptochloa chinensis(L.)Nees in the whole growth period of rice field.The photosynthetic parameters and root morphological parameters of Echinochloa crusgalli and Leptochloa chinensis was the most significantly declined at the tillering and mature period at the amount of wheat straw-returning as 400 kg/hm2,among which the net photosynthetic rates of Echinochloa crusgalli and Leptochloa chinensis was decreased significantly by 16.67%to 45.56%and 7.94%to 35.1%,respectively,while the photosynthetic performance index was decreased significantly by 18.97%to 25.56%and 45.77%to 53.39%,the total root length was decreased significantly by 9.15%to 18.74%and 12.22%to 45.26%,the total root surface area was decreased significantly by 13.27%to 40%and 25.08%to 48.46%,respectively,moreover,the total root volume was decreased significantly by 14.5%to 50.86%and 27.78%to 52.15%.Straw-returning would also affect the accumulation of N and P elements in Echinochloa crusgalli and the first full leaf expansion of Echinochloa crusgalli,among which the content of nitrogen and phosphorus in Echinochloa crusgalli was significantly different at the 400 kg/hm2 return rate,and significantly reduced at the tillering stage.10.81%and 26%,respectively,significantly increased by 4.05%and 21.97%during the maturity period;there is a similar trend in the change of elemental content in Leptochloa chinensis.The straw-returning was also reduced the accumulation of dry mass of Beckmannia syzigachne and Alopecurus japonicus Steud.At the amount of straw-returning as 400 kg/hm2,the dry weight of Echinochloa crusgalli and Leptochloa chinensis was dropped significantly by 15.49%and 17.90%,respectively.The above results indicate that the straw-returning of 400 kg/hm2 was more effective in inhibiting the growth and development of Echinochloa crusgalli and Leptochloa chinensis.4.Under the associated condition of gramineous weeds and rice,the effect of wheat straw-returning on the growth and development of Echinochloa crusgalli and Leptochloa chinensis was shown a similar influence trend without rice competition.At the same time,the straw-returning was promoted the growth and development of rice.At the amount of straw-returning as 400 kg/hm2 during the mature period,the net photosynthetic rate and photosynthetic performance index of the rice was increased significantly by 36.36%to 63.54%and 26.81%to 38.36%respectively;The total root length,the total surface area and volume of the roots was increased significantly by 21.43%to 28.9%,30.64%to 41.09%,and 20.83%to 27.97%,respectively.The straw-returning would also affect the accumulation of N and P elements in the first full expansion leaf of rice.The content of nitrogen and phosphorus in rice leaves was increased from the tillering stage and decreased to the mature stage,which was showing that the leaves obviously can promote the export effect of nitrogen and phosphorus.Thereinto,the content of nitrogen was increased by 3.14%to 10.32%during the tillering period,which was significantly decreased by 9.96%to 39.83%during the mature period,in addition,the content of phosphorus was increased by 0.4%to 13.82%during the tillering period,which was significantly decreased by 4.46%to 32.71%during the mature period.The dry weight of rice was increased significantly during the mature period by 10.54%to 25.96%,and the theoretical yield was increased by 14.63%to 29.94%.The amount of wheat straw-returning as 400 kg/hm2 can effectively improve the competitive ability of rice for light energy and nutrients under the associated conditions with gramineous weeds and rice,thereby rice yield could be increasing,which could prevent and control Echinochloa crusgalli and Leptochloa chinensis. |
