| In natural conditions, nutrients are heterogeneously distributed in soil. Plant roots can respond to local nutrients in order to effectively capture more nutrient resources through root morphological and physiological plasticity. Here, the related studies were conduced based on two different facets: meta-analysis and case study. Firstly, meta-analysis is performed with an extensive literature search and data collection to reveal the overall pattern (effect size and direction) and variation among plant functional group. Secondly, soil pot experiments were conducted in greenhouse to test root morphological responses to localized nutrient supply among different crop species with constrasting root traits; Five-year field experiments were conducted to examine the dynamic processes of the maize responses to localized nutrient supply over the whole growth stage. Key points of the results and progress were summarised as follows:1. The meta-analysis results showed that root:shoot ratio of plant increased or did not change under heterogeneous nutrient environments. Legume plants were generally less sensitive to the heterogeneous nutrient environments than non-legume herb and grass specie. There were significantly different effects of nutrient types on root and shoot growth, and the effect on root length density and root foraging precision increased with the decreasing level of nutrient transferability or increasing level of nutrient composition. Heterogeneous nutrient supply had a significant positive effect on the root:shoot ratio, which was also significant increase for wild species, except for domesticated species.2. The pot experimental results showed that localized supply of ammonium plus phosphorus induced maize and wheat root proliferation in the nutrient-rich zone. Localized supply of ammonium alone suppressed the whole root growth of chickpea and maize, whereas localized phosphorus plus ammonium induced the enhanced root proliferation. The localized root proliferation of chickpea in nutrient-rich zone did not increase the whole root length and root surface area. Faba bean had no significant responses to localized nutrient supply. The root morphological plasticity to localized nutrient supply could be highly modified by specific nutrients and plant species, with the greater plasticity in graminaceous than leguminous species.3. The field research showed that localized nutrient supply improved root proliferation and plant growth at seedling and jointing stages. The root length density and shoot biomass were465-667%and64-96%higher, respectively, in LNP, CF and OF than NP at seedling stage. However, despite rapid nutrient depletion, the whole-plant biomass did not differ between the LNP and NP treatments at ten-leaf stage. In contrast, the soil Nmin was kept at a high level (till62DAS) in the CF and OF treatments and the positive effect on plant growth was prolonged to flowering stage. The similar trend was also observed for root proliferation. The results indicated that localize nutrient supply elicits nutrient intensity-and duration-dependent improvement of maize root growth and nutrient uptake at vegetation stages.4. The further field research indicated that root proliferation in nutrient patches contributed more to maize growth and nutrient uptake at the early than late stages. Whether the root proliferation-based function could play a critical role for increased maize growth could highly depend on the timing of nutrient manipulation and management.5. Our results demonstrated that patterns of nutrient supply can modify the maize growth rate rather than the final biomass of individual plants; the effects of nutrient patch on plant reproductive output are highly dependent on competition intensity. How to optimize the timing and intensity of nutrient regulation and management is important to maximize root efficiency to improve crop productivity and nutrient use efficiency in intensive agriculture of China. |
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