| Global climate change,despite rising temperatures,has also changed the global water cycle,leading to changes in precipitation patterns.At present,agricultural production in arid and semi-arid areas of China mainly depends on natural precipitation,which is greatly affected by climate change.Studies have shown that the climate in Northeast China has been warm and dry for nearly half a century.Exploring the competition mechanism between local crops and exotic weeds under different seasonal droughts,in this study,the crops of Glycine max in northeast China and the exotic weeds Amaranthus retroflexus were studied.Simulate four seasonal droughts(in the initial and medium growth stages(VE-R6),in the medium growth stage(R1-R6),in the medium and late growth stages(R1-R8)and in the initial,medium and late growth stages(VE-R8)),middle peak model in normal precipitation year was used as CK.The dynamics of growth,biomass accumulation and nutrient accumulation of two plants under s ole and mixed planted conditions were periodically determined to provide a theoretical basis for the scientific management of exotic weeds in the context of global changes.The results were explained as follows:The different seasonal droughts had significant effects on plant height and relative growth rate of G.max and A.retroflexus.Compared with the CK,different seasonal droughts decreased the plant height of the two plants,and the decrease of G.max plant height was greater than that of the A.retroflexus.Drought in the initial and medium growth stages significantly reduced the plant height of the two plants,while the drought in the medium and late growth stages had the weakest inhibitory effect on the G.max height.Compared with the two plants,the height of the A.retroflexus was significantly higher than that of the G.max(except for the beginning of June).The relative growth rate(RGR)of A.retroflexus in June was significantly higher than that of G.max.After July,it decreased rapidly and was lower than that of G.max.The RGR of G.max changed greatly under the treatment of seasonal drought than that of A.retroflexus,indicating that A.retroflexus could adapt to drought.The effects of different seasonal droughts on biomass accumulation and distribution of G.max and A.retroflexus were different.Compared with the two plants,the total biomass of A.retroflexus was significantly higher than that of G.max under different seasonal droughts.Compared with CK,different seasonal droughts reduced the total biomass of the two plants.G.max decreased the least in drought in the medium and late growth stages,and decreased most in drought in the initial andmedium growth stages,while A.retroflexus were not significantly different under different seasonal droughts.In terms of biomass distribution,the biomass distribution of G.max roots was significantly higher than that of A.retroflexus.The biomass distribution of stems and reproductive organs were significantly lower than that of A.retroflexus,and the biomass distribution of leaves was not significantly different from that of A.retroflexus.During drought in the medium growth stage and drought in the medium and late growth stages,G.max increased stems biomass distribution and reduce biomass distribution of reproductive organs,while A.retroflexus increased leaves biomass distribution during the drought in the medium growth stage.The different seasonal droughts had no significant effects on the biomass distribution of leaves of G.max and stems and reproductive organs of A.retroflexus.Different seasonal droughts also had different effects on the nutrient content of the two plant s.Compared with CK,G.max reduced the root N content during the drought in the medium growth stage and drought in the initial,medium and late growth stages,and increased stem N content during the drought in the initial and medium growth stages,reduced the leaf N content under different seasonal droughts,and the reproductive organs N content was not significantly different from CK.In the different seasonal droughts,A.retroflexus decreased the root N content and increased the stem N content.The content of N in leaves and reproductive organs of A.retroflexus decreased first and then increased.G.max increased leaf P content during the drought in the medium growth stage and drought in the medium and late growth stages,while A.retroflexus increased leaf P content during the drought in the initial and medium growth stages.G.max significantly reduced root and stem K content during the drought in the medium growth stage,and significantly increased the leaf and reproductive organs K content during the drought in the initial and medium growth stages,while A.retroflexus reduced the root and reproductive organs K content and increase the stem and leaf K content under different seasonal droughts.Different seasonal droughts reduced the accumulation of total N,P and K in two plants,of which the drought in the medium and late growth stages was the weakest.The accumulation of N in G.max was the lowest in the drought in the initial and medium growth stages,and the accumulation of P and K decreased in the drought in the initial and medium growth stages and the drought in the medium growth stage,while the accumulation of N,P and K in A.retroflexus was little change under different seasonal droughts(except for individual growth stages).The total accumulation of N,P and K in A.retroflexus was significantly higher than that of G.max.The interspecific competition inhibited plant height and biomass accumulation of G.max,and promoted plant height and biomass accumulation of A.retroflexus.Compared with sole planted species,the plant height and biomass of mixed planted G.max were significantly smaller than it.Mixed planted G.max distributed more biomass to roots and stems,and the distribution of biomass in the roots before the drought in the initial and medium growth stages and in the initial,medium and late growth stages increased more,the distribution of biomass in the stems before the drought in the medium growth stage and drought in the medium and late growth stages increased more,biomass distribution of leaves decreased first and then increased,biomass distribution of reproductive organs decreased,and drought treatment decreased most significantly duri ng the drought in the medium growth stage.However,there was no significant difference in biomass allocation between sole or mixed planted A.retroflexus,which indicated that the interspecific competition had a greater impact on the accumulation and distribution of G.max biomass.The interspecific also had different effects on different nutrient contents in various parts of G.max and A.retroflexus.Compared with the sole planted species,the root N content of the mixed planted G.max decreased,the stem and leaf N content decreased in the early stage,and the reproductive organ N content increased(except for the 2016 period),the root P content was significantly reduced,and the P content of stems,leaves and reproductive organs w ere not significantly different in 2016,and decreased in 2017,the root K content decreased in the early stage,and the content of K in stems,leaves and reproductive organs decreased.Compared with the sole planted species,the N content of the mixed planted A.retroflexus roots increased initially,and the difference was not significant at the later stage,the content of stem N decreased in the middle stage,and the content of leaf N decreased in the early stage,but there was no significant change in the N content of reproductive organs.There was no significant change in P content in roots,stems,leaves,and reproductive organs of mixed planted A.retroflexus,the content of K in roots,stems and leaves increased,and the K content in reproductive organs was not significant ly different in 2016,and increased in 2017.The interspecific competition significantly reduced the accumulation of N,P,and K in plants and various parts of G.max,and increased the accumulation of N,P,and K in plants and various parts of A.retroflexus.Summing up,the different seasonal droughts affected the growth,biomass and nutrient accumulation of G.max and A.retroflexus.The effects of different seasonal droughts on the biomass accumulation and nutrient accumulation of A.retroflexus were not significant,but the effects on G.max were significant.The drought in the initial and medium growth stages had the strongest inhibitory effects on G.max biomass accumulation and nutrient accumulation.In general,the A.retroflexus were weakly affected by drought,indicating that A.retroflexus had strong adaptability to drought.No matter what kind of seasonal drought conditions,plant height and biomass,and the relative growth rate and N,P,K accumulation of A.retroflexus were higher than that of G.max,indicating that the strong competitiveness of nutrients is likely to be an important mechanism for A.retroflexus successful invasion of G.max fields. |
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