| Intercropping has the advantages of improving both crop yield and resource utilization efficiency.However,most of the existing studies have been carried out under sufficient irrigation conditions,and less research has been conducted on the yield performance of intercropping under rainfed conditions.Competition recovery theory provides an important explanation for why intercropping increases yield,but research on the dynamics of interspecies competition and the mechanism of recovery growth remains insufficient.In this study,wheat/maize intercropping was examined through field experiments designed to explore the effects of wheat/maize intercropping systems on yield,and the influence of interspecific competition on the growth and physiological characteristics of intercropped wheat.The photosynthetic mechanism of recovery growth was analyzed to provide a theoretical basis for the development of the wheat/maize intercropping system in rainfed areas.The main research conclusions were as follows:(1)Wheat/maize intercropping showed an obvious yield advantage and land use advantage.Intercropped wheat yield was 9.3% and 14.8% greater than sole wheat yield under rainfed and irrigated treatments,respectively.Intercropped wheat yield at the first border row position was increased due to a significant increase in ear numbers,kernel numbers per ear,and thousand kernel weight.At the second border row position for rainfed intercropped wheat,only the ear numbers were increased compared with sole wheat.Under the irrigated treatment,both ear numbers and kernel numbers per ear were increased.Rainfed intercropped maize yield was less than sole maize yield,due to the border row disadvantage that resulted from a reduction in ear numbers and hundred kernel weight.Irrigated intercropped maize yield was greater than irrigated sole maize yield primarily because of the inner row advantage resulting from the increase in ear numbers and hundred kernel weight.(2)Interspecific competition increased dry matter accumulation and photosynthetic capacity of intercropped wheat.Intercropped wheat was more competitive than maize and exhibited stronger resource competitiveness.Dry matter accumulation of intercropped wheat was significantly higher than that of sole wheat.Interspecific competition intensity first increased and then decreased during the co-growth period,and the competition intensity was the highest during the wheat flowering period.Water deficit conditions increased the competitiveness of wheat relative to maize.Intercropping reduced the initial fluorescence(Fo)of the border row and inner row of intercropped wheat,and increased the maximum fluorescence(Fm),variable fluorescence(Fv),photosystem II(PSII)maximum photochemical efficiency(Fv/Fm),and potential PSII activity(Fv/Fo).Therefore,the photosynthetic rates of wheat at border row and inner row positions were significantly higher than those of sole wheat.The average photosynthetic rates during the growth period under the rainfed treatment increased by 29.8% and 18.1% at the border row and inner row positions,respectively,and the average rates under the irrigation treatment increased by 18.4% and 8.4%,respectively.(3)Irrigation promoted the growth and physiological recovery of intercropped maize after wheat harvest.The aboveground dry matter of irrigated intercropped maize at border row and inner row positions showed complete recovery growth,whereas rainfed conditions inhibited recovery growth at both positions.Intercropped maize dry matter at border row and inner row positions was 29.8% and 10.0% less,respectively,than sole maize dry matter.The root system of the intercropped maize under irrigation showed recovery and growth,and the recovery start time was earlier than the time when aboveground dry matter began to recover.In contrast,the root system did not recover under rainfed conditions.Physiological characteristics such as relative chlorophyll content(SPAD),net photosynthetic rate(Pn),and various fluorescence parameters(Fo,Fm,Fv,Fv/Fm,and Fv/Fo)of intercropped maize showed different degrees of recovery from that seen for sole maize.All of the parameters mentioned above for irrigated intercropped maize and for rainfed intercropped maize at the inner row position showed significant recovery.SPAD and Pn measurements for rainfed intercropped maize at the border row position showed a certain degree of recovery after wheat harvest,but the fluorescence parameters did not recover.The recovery of photosynthetic fluorescence provides a physiological basis for photosynthesis of crops.Drought damages the photosynthetic apparatus and limits maize recovery.In the recovery growth stage,transpiration efficiency(TE)of intercropped maize was much greater than that of sole maize,indicating that intercropped maize has great potential for efficient water use.(4)Intercropping canopy structure significantly changed over the wheat/maize growing season,affecting light energy distribution,radiation utilization efficiency,and hydrothermal characteristics.Plant height and leaf area index(LAI)of intercropped wheat during the cogrowth period were higher than those values observed for sole wheat.Plant height and LAI of the intercropped maize after wheat harvest were larger than those of the sole maize only under irrigation.The variation of photosynthetically active radiation intensity(PAR)at each row position in the intercropping system showed a single-peak curve,and the PAR values at different row positions were significantly different.The soil moisture content of the intercropped maize strip prior to maize planting was significantly higher than that of the intercropped wheat strip.During the wheat/maize co-growth period,the soil moisture content of the intercropped wheat strip in the 40–100 cm soil layer was lower than that of the intercropped maize strip.After wheat harvest,soil moisture in the wheat strip increased from the soil moisture values observed during the co-growth period.The daily variation of soil temperatures at 5 cm were quite obvious.The seasonal trends of soil temperature in the 5–25 cm soil layers under different treatments were similar.The soil temperature of each soil layer in the rainfed treatment was higher than the soil temperature in the irrigation treatment.The soil temperature in the 0–15 cm soil layer decreased with increasing soil depth,and the soil temperature in the 15–25 cm soil layer changed only slowly.Under rainfed and irrigation treatments,radiation utilization efficiency of intercropped wheat was greater than that of sole wheat under two water treatments.Radiation utilization efficiency of intercropped maize was greater than that of sole maize with irrigation.Average PAR interception rate of intercropped wheat during the co-growth period was more than 90%,while the PAR interception rate of intercropped maize was less than 2%.The PAR interception rate of intercropped maize during later growth stages increased significantly,and averaged 80%.Under both rainfed and irrigated treatments,radiation utilization efficiency of intercropped wheat was greater than that of sole wheat.Under the rainfed treatment,radiation utilization efficiency of intercropped maize was 16.3% less than observed for sole maize in 2015 and 23.4% less in 2016.Under the irrigated treatment,radiation utilization efficiency of intercropped maize was lower than that of sole maize before wheat harvest.Radiation utilization efficiency of intercropped maize after wheat harvest was higher than that of sole maize.There was no significant difference in radiation utilization efficiency between sole maize and intercropped maize under the irrigated treatment when considered over the entire growing season.The results of this study indicated that available moisture can change the intensity of interspecific competition,thereby affecting physiological processes such as crop root growth and photosynthetic fluorescence.The internal mechanism affecting efficient resource utilization in an intercropping system can be understood by analyzing the radiation utilization efficiency for each component in the intercropping system and transpiration efficiency of intercropped maize at the recovering growth stage.The structure of the intercropped canopy changed the field microclimate,water and thermal conditions,and the light distribution pattern,thereby improving the overall radiation utilization efficiency of the intercropping system.The comprehensive analysis of the dynamic growth recovery process from underground(root system)and aboveground(photosynthesis,fluorescence,dry matter,etc.)perspectives improved the theory and our understanding of recovery growth,and laid the foundation for optimizing the intercropping system.The yield and land use advantages of wheat/maize intercropping under rainfed conditions analyzed in this study provide a reference for future studies of applicable and successful planting patterns in fallow areas,and holds significant promise for the development of water-saving agriculture in semi-arid and semi-humid areas. |
PDF Full Text Request