| The northeast region is an important corn production base in China and is highly susceptible to seasonal drought.Frequent spring droughts have become the most important ecological constraint to regional maize production.Fertilizer application is an important measure to meet the nutritional needs of high-yielding crops and to ensure increased yield and income,while appropriate fertilizer application helps to regulate root development and enhance plant resistance to ensure high and stable yields.Therefore,it is important to explore ways to optimize root growth and enhance drought tolerance of maize plants by adjusting fertilizer application to alleviate frequent drought stress and reduce the risk of yield reduction.In this study,we first quantitatively analyzed the combined effects of local fertilization on dry matter accumulation and root development by Meta-analysis,and integrated the effects of crop species on local fertilization as well as the effects of fertilizer type and cultivation environment on local fertilization in maize seedlings,and further guided the potting trials based on the results.A two-factor split-root test design with water and nitrogen was used in the pot experiment to clarify the effects of local nitrogen supply on the growth,root development,water and nitrogen uptake and utilization of maize plants under different drought stress conditions at the seedling stage,to elucidate the response mechanisms of maize seedling growth,root development and water and nitrogen utilization to drought stress under localized nitrogen supply conditions,and to provide a theoretical basis for high and stable yield and efficient water and nitrogen utilization of rainfed maize in the context of climate change.The main findings of this study are as follows:Meta-analysis results showed that the spatial heterogeneity of nutrient distribution could significantly promote crop dry matter accumulation and root development.Compared with other crops,maize had the best effect in total root length and specific root length,which increased by44.5%and 13.4%,respectively.Local application of N fertilizer significantly increased shoot dry matter,root dry matter,total root length,root:shoot ratio and specific root length by 11.0%,26.4%,79.6%,8.2%and 24.1%,respectively.Soil acidic conditions had a significant effect on total root dry matter and total root length of maize seedlings,which increasing by 23.1%and48.1%,respectively,while alkaline conditions had no significant effect on both total root dry matter and total root length.（2）The split-root pot experiments with different water and N levels were conducted in2021 and 2022.Five N supply patterns were designed:no N supply（N0/N0）,uniform low N supply（LN/LN）,localized low N supply（LN/N0）,uniform high N supply（HN/HN）and localized high N supply（HN/N0）.The N rates were 0.12 and 0.24 g N kg-1dry soil for LN and HN levels,respectively.Water management was initiated from 3-leaf stage and lasted for 3weeks,including three soil moisture contents:severe water-stress（35%of field capacity,W0）,moderate water-stress（55%of field capacity,W1）,and well-watered conditions（75%of field capacity,W2）.The results showed that drought stress significantly inhibited plant growth,dry matter accumulation,and nitrogen uptake in maize seedlings,but increased the root:shoot ratio.Compared with normal moisture conditions,moderate drought stress had relatively less effect on total root length,total root surface area,and total root volume.Drought stress reduced nitrogen recovery efficiency in maize,while moderate drought stress increased water use efficiency by an average of 11.9%.Nitrogen supply method also significantly affected plant growth,dry matter accumulation and nitrogen uptake and utilization in maize seedlings,and the two factors of water and nitrogen showed significant interactions.HN/HN had the most severe negative impact on maize seedling growth,where here root dry matter decreased more,thus significantly reducing the root:shoot ratio.HN/N0 had less effect on shoot dry matter,but significantly reduced root dry matter and root:shoot ratio.Compared to N0/N0,both LN/LN and LN/N0significantly increased total root length,total root surface area,and total root volume by promoting root proliferation on the side without nitrogen supply.Nitrogen uptake was higher in LN/LN and nitrogen recovery efficiency was higher in LN/LN under all moisture conditions.The differences in nitrogen uptake and nitrogen recovery efficiency among treatments increased significantly with the improvement of drought stress.Both plant water consumption and water use efficiency were higher for LN/LN and LN/N0,followed by HN/N0,while HN/HN was the lowest.There was a significant positive correlation between shoot dry matter,water use efficiency,nitrogen recovery efficiency and total root length at the seedling stage of maize under different water conditions and nitrogen supply methods.For the localized nitrogen supply method,the correlation between root length on the side without nitrogen supply and shoot dry matter,water use efficiency,and nitrogen recovery efficiency was higher.In conclusion,uniform or localized low nitrogen supply showed a promoting effect on maize seedling development,while uniform or localized high nitrogen supply showed an inhibiting effect,and the negative effect of uniform or localized high nitrogen supply was intensified by increasing the degree of drought stress.Compared with uniform nitrogen supply,the localized nitrogen supply at different nitrogen application levels significantly increased root dry matter and total root length by promoting root proliferation on the side without nitrogen supply,thus improving water use efficiency.Localized low nitrogen supply is recommended to enhance drought tolerance of seedling plants and improve water use efficiency.This study provides new ideas and technical approaches for optimal management of nitrogen fertilization in response to drought stress in maize seedlings. |
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