| In natural environments plant growth is limited by various resources. Suboptimal nitrogen and phosphorus availability are primary limitations to plant growth and production. To release nitrogen and phosphorus deficiency, large amount of nitrogen and phosphorus were applied in past decades, resulting in decreased nitrogen and phosphorus use efficiency, increased nitrogen and phosphorus losses and the risk of environmental pollution. In arid area, beside nutrient shortage, water deficiency is also a universal problem. Water conditions not only impacts plant growth, also affects the availability of soil mineral nutrients and subsequently affect plant uptake and nutrient-use efficiency. The development of plant roots is considerably variable and strongly influenced by environmental conditions. And the change of root architecture and physiology also impact nutrient and water acquisition. Therefore, in the present study, we collected data from farm and experiment site to study phosphorus requirement of high-yielding winter wheat.And conduted a long-term experiment to study the affects of long-term fertilizeation on soil phosphorus distribution and root growth. Then, we conducted greenhouse experiment to simulate phosphorus and water distribution in the field, and the impact on root morphologye and nutrient and water uptake. Finally, we conducted greenhouse and field experiment to study the influence of root architecture on nitrogen, phosphorus, and water uptake. The main results of this study were concluded as follows:(1) A database comprising 2157 measurements was developed from 2000 to 2013 using 45 on-farm and station trials to evaluate the relationship between P uptake and grain yield. A total of 224 data points were collected from optimal P treatment(P = Opt) samples to assess this relationship. Across all sites, the winter wheat(Triticum aestivum) yield ranged from 0.9 to 11.7 Mg ha-1 with an average of 4.8 Mg ha-1. P uptake requirement per Mg grain yield(Preq.) increased from 4.1 to 4.8 kg from no P supplied to P surplus treatment. Under P = Opt treatment, the average Preq was 4.5 kg, and declined with increasing grain yield, which was attributed to increasing harvest index and the diluting effect of declining grain P concentrations. The largest variation in shoot biomass and P accumulation under P = Opt treatment occurred from the stem elongation to anthesis growth stages, suggesting that, in addition to P supply, better crop management during the early part of the growth season is also important for achieving higher yields.(2) Results from 31-year long-term experiment indicated that compared with CK(control) and NK(apply N and K) treatments, soil Olsen-P, total-P, and Ca Cl2-P were accumulated in topsoil, and decreased with soil profile. Influenced by soil P content, root distribution in soil profile showed accumulation in topsoil, and decreased with depth. Wth P and manure application, root distribution in each soil profile were increased, but inhibite AM colonization. Shoot P concentration and shoot biomass were increased with P application, but we found that shoot biomass showed no difference between NPK and MNPK treatments, which indicates excessive P application could not keep increasing shoot growth.(3) Roots preferentially grow in the layer or compartment with both adequate water and P supply, subsequently stimulating SPU, PUE, and WUE, and enhancing shoot growth. Compared with the treatments in which both layers and compartments were supplied with adequate P and/or water, the growth of maize was maintained or minimally affected. SPU, PUE, and WUE were increased when both P and water were supplied in one layer or one compartment only. These findings show that normal plant growth with an adequate P uptake was achieved even if part of the roots were supplied with 2/3(soil column experiment) and 1/2(splitroot experiment) of the phosphorus and water supplied in the full-phosphorus and full-water treatment. Changes in root morphology under water stress conditions induced by the application of phosphorus and water in deeper soil layers or to a part of the roots may have substantial practical implications for agricultural production and environmental protection.(4) To cope with environmental stress, maize has evolved complex adaptive responses that include morphological and physiological modifications. A greenhouse experiment was conducted to investigate the effects of soil water on the response of maize agronomic and root traits to soil P supply. Our results showed that the growth of shoot dry weight(SDW), root morphology, arbuscular mycorrhiza(AM) colonization, and the expression of six Pi transporter genes to soil P supply were influenced by soil water condition. when soil P supply declined to 8.9 mg kg-1 in WS and 7.54 mg kg-1 in WW, root morphology, AM colonization, and the expression of Pi transporter genes were triggered, indicating compared with WW, root morphology, AM colonization, and the expression of Pi transporter genes were showed more sensitive to soil P supply under WS conditions. These, from morphology to molecular, proved that compared with WW, plant suffered more severe P-deficiency in WS and more P should be applied to ensure plant growth, which could provide useful information for optimizing P management under different water conditions.(5) Under low N conditions, maize(Zea mays) lines with few but long(FL) lateral roots would have greater axial root elongation, deeper rooting, and greater N acquisition than lines with many but short(MS) lateral roots. Maize recombinant inbred lines contrasting in lateral root number and length were grown with adequate and suboptimal N in greenhouse mesocosms and in the field in the USA and South Africa(SA). In low N mesocosms, FL lines had 67% less root respiration of lateral roots per unit axial root length than MS lines, as well as 38% greater length of crown root axes, 39% greater length of primary root axes, and 15% greater length of seminal root axes. In the field under low N, rooting depth(D95) of FL lines exceeded that of MS lines by 18% in the USA and 20% in SA. Under low N, FL lines had 147%, 43% and 52% more N content and 39%, 33%, and 34% higher photosynthesis than MS lines in mesocosms, in field in the USA, and in SA, respectively. Under low N, FL lines had 75%, 46%, and 41% more shoot biomass than MS lines in mesocosms and at anthesis in the field in the USA and SA, respectively. FL lines had 31.5% greater yield than MS lines in low N fields in the USA. Our results are consistent with the hypothesis that sparse but long lateral roots improve N capture from low N soils. The FL lateral root phenotype merits consideration as a selection target for greater crop N efficiency.(6) Reduced lateral root branching density will improve drought tolerance in maize(Zea mays) by reducing the metabolic costs of soil exploration, permitting greater axial root elongation, greater rooting depth, and thereby greater water acquisition from drying soil. Maize recombinant inbred lines with contrasting lateral root number and length(FL: few but long; MS: many but short) were grown under water stress in greenhouse mesocosms, in field rainout shelters, and in a second field environment with natural drought. Under water stress in mesocosms, lines with the FL phenotype had substantially less lateral root respiration per unit axial root length, deeper rooting, greater leaf relative water content, greater stomatal conductance, and 50% greater shoot biomass than lines with the MS phenotype. Under water stress in the two field sites, lines with the FL phenotype had deeper rooting, much lighter stem water δ18O signature signifying deeper water capture, 51 to 67% greater shoot biomass at flowering, and 144% greater yield than lines with the MS phenotype. These results entirely support the hypothesis that reduced lateral root branching density improves drought tolerance. The FL lateral root phenotype merits consideration as a selection target to improve the drought tolerance of maize and possibly other cereal crops. |
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