| The global shortage of fresh water in the field of agricultural planting,irrational irrigation has caused the rapid deterioration of the agricultural ecological environment,which is not conducive to the sustainable development of agriculture.Temporary karst drought often occurs in the karst areas of Guizhou,China,and the agricultural ecological problems are particularly serious.The rapid detection of plant water demand information and the rational implementation of water-saving irrigation are the key to solve this problem.However,with the regulation of related enzymes in plants,the diagnosis of plant water demand information is somewhat inaccurate by using the traditional indicators such as leaf water potential or stomatal conductance.Therefore,the same family of plants with different carbonic anhydrase activities,Orychophragmus violaceus and Brassica napus L.,were used as materials in this paper.By adding the polyethylene glycol 6000?PEG?and NaHCO3,the karst arid environment was simulated and rehydration was set up.The relative water content,leaf capacitance,leaf tension,soluble sugar content,proline content,carbonic anhydrase activity,photosynthesis,leaf area and plant height of the leaves of the plants were determined.The leaf water variation was analyzed and a rapid detection method of plant water demand information was established.The results were shown as following:?1?Under the karst drought,the relative water content of O.violaceus and B.napus decreased in different degrees,the soluble sugar and proline content increased significantly,while the water potential of O.violaceus and B.napus had a significant decrease in the level of 20g·L-1PEG or 80g·L-1PEG,which is delayed by changes in osmotic adjustment substances and may be affected by water regulation of the related enzymes in plants such as carbonic anhydrase?CA?.The leaf tension?Td?can respond timely,and the water content of the blade decreases synchronously.Moreover,the leaf tension?Td?of O.violaceus and B.napus had a good correlation with leaf water potential??L?,osmotic adjustment substance,leaf relative water content and CA activity.Compared with water potential,Td can reflect the plant water status better.?2?Under the karst drought,the photosynthesis of O.violaceus was significantly inhibited at the treatment level of 20g·L-1PEG.The photosynthesis of B.napus is more sensitive to the karst drought and is inhibited.However,when the karst drought level is lower than 20g·L-1PEG,O.violaceus still has better photosynthesis recoverability.B.napus still has good recoverability when the karst drought level is lower than40g·L-1PEG.The water use efficiency of O.violaceus was not affected by karst drought.The water use efficiency of B.napus under 80g·L-1PEG level was more affected by water changes.At the same time,according to the results in?1?,the Td of O.violaceus has better recoverability when the karst drought level is lower than20g·L-1PEG,and the Td of B.napus has the karst drought level lower than 40g·L-1PEG.Better recoverability.In summary,the treatment level of 10g·L-1PEG was the physiological karst drought tolerance threshold of O.violaceus,and the treatment level of 40g·L-1PEG was the physiological karst drought tolerance threshold of B.napus.And there is a good nonlinear relationship between Td and net photosynthetic rate?Pn?.The higher Td value is always correlated with a higher value of Pn.?3?By establishing a leaf area and biomass estimation model,the online rapid measurement of biomass is achieved based on the determination of maximum leaf length,maximum leaf width and plant height.The leaf area and plant height of O.violaceus grew best when the karst drought level was 5g·L-1PEG,while that of B.napus grew best when it was 10g·L-1PEG.The dynamic growth law of dry weight biomass?DW?of O.violaceus and B.napus with time was analyzed by 4-parameter Logistic equation,and the growth rate of DW was calculated accordingly.Set a reasonable percentage reduction in biomass growth rate under karst drought stress to achieve product quality improvement,taking 30%or 50%as an example.By calculation,at the treatment level of 10g·L-1PEG,the rehydration time point of O.violaceus was day 3 or 2,and it was day 5 or day 4 at the level of 5g·L-1PEG treatment.Under the treatment level of 20g·L-1PEG,the rehydration time of B.napus was the second day,and it was the third day or the second day when the treatment level was 10g·L-1PEG.The Td corresponding to the above-mentioned rehydration time point is calculated according to the 4-parameter Logistic equation and the mathematical model between Td and DW.When Td was 1.38 or 0.93,O.violaceus under 10g·L-1PEG treatment level was rehydrated.When Td was 1.79 or 1.86,O.violaceus under 5g·L-1PEG treatment level was rehydrated.When the Td was 0.53,the B.napus at the treatment level of 20g·L-1PEG was rehydrated.When the Td was1.79 or 1.86,the B.napus at the treatment level of 10g·L-1PEG was rehydrated.O.violaceus at the treatment level of 5g·L-1PEG showed better long-term karst drought resistance than the treatment level of 10g·L-1PEG.Rewatering O.violaceus at a treatment level of 5g·L-1PEG can minimize the need for water and produce a corresponding minimum impact on DW,thereby increasing the economic benefits of water use.The B.napus under the treatment level of 10g·L-1PEG showed better long-term karst drought resistance than the treatment level of 20g·L-1PEG.Rehydration of B.napus with 10g·L-1PEG treatment level can improve the economic benefits of water use.According to the online non-destructive detection of biomass and its real-time analysis of the change law,the rehydration time node is calculated,and the 4 parameters logistic equation and the mathematical model between Td and DW are used to calculate the corresponding Td value.Based on the online monitoring of Td,water can be supplied when the Td reduced to the corresponding value,thereby realizing the rapid detection of plant variable irrigation time point. |
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