| Under the background of global warming,the change of decreasing water brings more challenges to the stable production of agriculture.The loess hilly region is a typical"rain-fed agriculture"mode,and the growth of crops is more vulnerable to the influence of precipitation changes.In this study,soybean,an important grain and oil crop in the loess hilly region,was taken as the research object.Seven different precipitation gradients were set up through the canopy:Natural precipitation(CK),20%precipitation increase(ZY20),40%precipitation increase(ZY40),60%precipitation increase(ZY60),20%precipitation decrease(JY20),40%precipitation decrease(JY40),60%precipitation decrease(JY60).By monitoring the characteristics of photosynthetic gas exchange and soil respiration in different periods of soybean growth season under different precipitation conditions,the change characteristics of soybean photosynthetic physiology and soil respiration in different growth periods were analyzed,and the response of soybean photosynthetic characteristics and soil respiration to precipitation change was explored in the loess hilly region.At the same time,combining with soybean biomass,growth rate,root-shoot ratio and yield components,the effects of precipitation change on soybean growth and yield were analyzed to explore the internal relationship between yield and photosynthetic rate,soil respiration rate and water use efficiency,so as to provide theoretical guidance for soybean high yield and income increase.The main conclusions of this study are as follows:(1)With the increase of precipitation,the growth rate of soybean firstly decreased and then increased,and reached the minimum value of 0.64 cm·d-1 at ZY20.Compared with CK,with the decrease of precipitation,the aboveground and underground biomass first decreased and then increased,while the root-shoot ratio first increased and then decreased.With the increase of precipitation,the aboveground and underground biomass first decreased and then increased and then decreased,while the root-shoot ratio first decreased and then increased under water increasing treatment.The maximum value of root-shoot ratio under reduced precipitation treatment appeared in JY40,and that under increased precipitation treatment appeared in ZY60.(2)Pod number per plant,grain number per plant and grain weight per plant showed the same changing trend under different precipitation gradiens,which first decreased,then increased and then decreased with the increase of precipitation.The minimum values all appeared in JY20,and the maximum values all appeared in ZY40.The general variation trend of hundred-grain weight was the same as that of the three,but its maximum value appeared in ZY20.Compared with CK,the yield elements in the gradient of decreasing water first decreased and then increased with the decrease of precipitation,while the yield elements in the gradient of increasing water first increased and then decreased with the increase of precipitation.(3)Compared with CK,Net photosynthetic Rate(Pn)at branching stage and flowering stage increased first and then decreased with the decrease of precipitation,and always increased with the increase of precipitation.In the pod setting stage,it first decreased and then increased with the increase of precipitation,and then decreased with the decrease of precipitation.In the bulging stage and mature stage,the variation trend with the decrease of precipitation was"increasing and decreasing",which increased first and then decreased with the increase of precipitation.Water Use Efficiency(WUE)of leaf increased firstly and then decreased with the increase and decrease of precipitation in each period.(4)There is a significant positive correlation between Stomatal conductance(GS)and leaf Transpiration Rate(Tr)at different periods(P<0.01),and the changing trend of GS and Tr is roughly the same at different periods.Compared with CK,in the branching stage,Tr showed a trend of"decreasing and decreasing"with the water decreasing and increasing,and Gs showed a trend of"decreasing and decreasing"with the water decreasing and increasing,and Gs first increased and then decreased with the water increasing.At the flowering stage,GS and Tr showed a trend of"increasing and decreasing"with the increase of water reduction,and a trend of decreasing first and then increasing with the increase of water increasing.In the pod setting stage,Gs and Tr showed a trend of"decreasing"with the increase of water reduction and water increase.At the granulation stage,Gs and Tr showed a trend of decreasing first and then increasing with increasing water and decreasing water.In the mature stage,Gs and Tr showed a trend of"increasing and decreasing"with the increase of water reduction,and they always decreased with the increase of water increase.(5)Compared with CK,the soil respiration rate increased first,then decreased and then increased with the decrease of precipitation in the branching stage,and decreased first and then increased with the increase of precipitation.At the flowering stage,the respiration rate decreased with the decrease of precipitation,and then decreased with the increase of precipitation.In the pod setting stage,the respiration rate firstly decreases,then increases and then decreases with the decrease of precipitation,and firstly decreases and then increases with the increase of precipitation.The respiratory rate increased firstly and then decreased with the decrease of precipitation and the increase of precipitation in the granulation stage.In the mature stage,the respiratory rate increased firstly,then decreased and then increased with the decrease of precipitation,and increased firstly and then decreased with the increase of precipitation.(6)There was no significant correlation between Pn,WUE and yield factors at different stages of soybean(P>0.05),but there was a significant negative correlation between Pn,WUE and root-shoot ratio at mature stage(r=-0.813,P<0.05;r=-0.761,P<0.05).There was no significant correlation between soil respiration rate and yield factors at each stage(P>0.05).Soil respiration rate at flowering stage was positively correlated with underground biomass(r=0.795,P<0.05),and soil respiration rate at grain bulging stage was negatively correlated with growth rate(r=-0.897,P<0.01).There was a significant negative correlation between soil respiration rate and root-shoot ratio at maturity stage(r=-0.764,P<0.05). |
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