Effects Of Phosphorus Fertilizer And Maize (Zea Mays L.)/Alfalfa (Medicago Sativa L.) Intercropping On Plant Root Morphology, Photosynthesis And Phosphorus Uptake In The Northeast Farming-pasture Zone, China

The agriculture sector is facing many issues regarding crop production,and fertilizer is the leading issue that directly or indirectly affects crop performance.On the other hand,the increasing world population rapidly results in less land for cultivation and more food demand.In this case,it is an important research topic about how to make more rational use of soil resources by changing cropping patterns,increase crop yield for the development of modern agriculture.Intercropping can improve plant nutrition and increase yield by strengthening a series of niche complementary/interspecific reciprocal processes,rationally utilizing natural resources such as light,water and nutrients,and reducing interspecific competition.Intercropping maintains soil fertility by increasing plant nutrient uptake and by exploiting the difference in soil space utilization between the two plants.In the agro-pastoral interlaced area of the Songnen Plain in Northeast China,Zea mays L.（maize）and Medicago sativa L.（alfalfa）are the main annual grain crops and perennial forage grown by local farmers,respectively.Plant intercropping has obvious advantages in increasing yield and economic income.Phosphorus（P）is regarded as the most important nutrient element that controls plant productivity,and their availability often limits the growth of terrestrial plants.Here we investigated the effects of fertilizer（P or without P）and cropping pattern i.e maize monoculture（MM）and/or intercropping of maize and purple alfalfa（IMA42,IMA23,IMA43）on maize belowground root network and photosynthetic characters by employing complete randomized block design with split plot arrangement.The present experiment was conducted at Jilin Songnen Grassland Ecosystem National Observation and Research Station（123°44′E 44°40′N）Songnen Grassland（typical agro-pastoral staggered area）.Seeds were hand sowed around the maize growing season（May）with or without pre-existing alfalfa strips at 26 cm inter-plant distance and 65 cm inter-row spacing.Phosphorus treatments received P as KH₂PO₄（potassium phosphate）an amount of 90 kg k ha^-1.At the end of the experiment,the plant was harvested and measured the root parameters.SPAD-502 Plus chlorophyll tester（KONICA MINOLTA Japan）,and PM2500 modulated fluorescence meter（WALZ,Germany）was used for photosynthetic parameters measurement.Gas exchange（photosynthesis rate,transpiration rate,and conductance to H₂O,leaf internal CO₂concentration）was measured using the LI-6400XT portable photosynthesis equipment（LI-COR,Inc.,Lincoln,NB,USA）.Phosphorus addition significantly increased root volume,root number,root length,dry root weight,root surface area,and photosynthetic rate.Maize yield in IMA43 and MM treatments was significantly higher than that in other treatments,and the lowest maize yield in the IMA23 treatment with P addition.Under the condition of P application,root volume of MM treatment was significantly higher than that of intercropping treatment,root volume of IMA43 treatment was significantly higher than that of IMA42 and IMA23treatments.And root volume of IMA23 treatment was significantly lower than that of other treatments with and without P application.Under the two P levels,the number of crown roots in the MM and IMA43 treatments was significantly higher than that in the other treatments,while the number of crown roots was the lowest in the IMA23 treatment.Under P application conditions,there was no significant difference in crown root length between MM and IMA43 treatments,but it was significantly higher than that in IMA42and IMA23 treatments.Under the condition of no P application,the length of crown and root in the MM treatment was significantly higher than that in the intercropping treatment.There was no significant difference in shoot root dry weight between MM and IMA43treatments at the two P levels,but it was significantly higher than IMA42 and IMA23.The photosynthetic rate and photosynthetically active radiation were the highest in the intercropping IMA43 treatment,followed by the MM treatment.Intercropping under P application increased transpiration rate,VPD and leaf temperature.The dynamic of soil water content（SWC）was changed over the period of study;the higher soil water content was recorded in June and the lower value in October.The SWC in P application and MM treatment was significantly higher than that in the intercropping treatment,and the water content of IMA43 was the highest in the intercropping treatment.The present study concluded that the P application increased the maize performances,it may also increase the photosynthetic activity in intercropping,thus resulting in higher production than monoculture.Cropping mode and P application have synergic effects on the chlorophyll content of maize,therefore,increase plant production.P availability is key factor for plant production,showing positive responses to P additions in both monoculture and intercropping systems.