| More and more scholars and producers are paying attention to the suitable water,fertilizer supply and planting density as cultivation measures that can significantly increase crop yield.In this study,the experiment was conducted on tomato seedlings in a controlled environment.There were two levels of nitrogen application,i.e.sufficient nitrogen treatment(15 mmol/L)and nitrogen stress treatment(1 mmol/L);two levels of water application,i.e.sufficient water application(at level of 70~75% of sand saturation capacity)and stress water application(at level of 60~65% of sand saturation capacity);neighbor competition by setting 4 plants per pot(P4),root isolated competing 4 plants per pot(F4)and single plant per pot(P1);respectively.Through the system data monitoring and analysis,the effects of biotic and abiotic stress on hormones,photosynthetic characteristic,morphological development of root and above-ground part were analyzed.Based on the indoor experiment study and analysis,the conclusions are as follows:1.The presence of neighbor competition had a negative effect on roots growth at all water-nitrogen application rates.Even this inhibition increased along with this fierce competition intensity at water-nitrogen deficiency.So,a higher root shoot ratio appeared owing to more photosynthetic product distributing the root under the competing conditions.However,apart from the roots of competitors by board isolation could improve root development during competing conditions.2.The treatment with neighbor competing plants,increasing the water and nitrogen application could promote the seedlings development,photosynthetic area,and finally increased the accumulation of biomass finally.The results of experiment showed that nitrogen played a vital role in regulating plant growth as compared to water and competing factors.The existence of neighbor competition would increase the group absorbed nitrogen and reduce the soil nitrogen residue,thus significantly improving the group nitrogen utilization rate.Meanwhile,leaf water use efficiency of tomato seedlings of root isolated competing plants(F4)was higher than P1 and P4 treatments.3.Stomatal conductance,photosynthetic rate and transpiration rate showed a decline trend under a limited water and nitrogen application.The presence of neighbor competition could induce same results: a decline of photosynthesis and transpiration in group plants.It was helpful in improving the stomata exchanges materials with the outside environment while separating the roots of competitors.4.Leaf area increased because of the presence of neighbor competition.To some extent,ethylene production as a gas perception signal was promoted due to the neighbor competition.Moreover,roots isolation experiment treatment results confirmed that leaf canopy could detect neighbors by releasing ethylene and this detecting ability was not controlled by root competition.5.Accumulation of Abscisic acid(ABA),salicylic acid(SA)and jasmonic acid(JA)occurred when transformed from roots to ground and the controlling ability of signals enhanced.Grey relational analysis showed a higher correlation between photosynthetic index and ABA especially in shoot sap.ABA based stomatal modulation was confirmed.At the same time,shoot SA and root JA also showed a high correlation with net photosynthetic rate and stomatal conductance.6.Water and nitrogen stress was not conducive to the accumulation of plant root and above-ground JA,whereas competition between biological stress had a positive effect on the production of shoot JA.However,the content of shoot JA with isolation of roots in competing plants was the least compared with single plants and competing plants.Moreover,the change of SA concentration in root or shoot showed irregular trend,and SA seemed to be complicated in response to competition from biotic or water-nitrogen stress from abiotic stress.Thus,the change of SA content need to be further interpreted according to the plant growth conditions. |
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