| Water and nutrients are major factors limiting crop production, but which is more important to crop yield is unsure. Lots of researches on water and fertilizer coupling in quantity and time had been made and many important results had been acquired, but research on water and fertilizer spatial coupling (in different soil layer) are relatively insufficient. So a cylindrical pot experiment was conducted with Eum-Orthic Anthrosols (Cinnamon soils) under rain-preventing condition to study the effects of spatial coupling of water, nitrogen and phosphorus on photosynthetic characteristics and yield of winter wheat, with the basis on the characteristic of surface layer drought and substrate wetness of loess plateau. The pot consisted of three layers with each layer of 30cm depth and a 2cm layer of coarse sand between soil layers for obstructing water and nutrients exchange. Before that, a study was made of the influence of water condition and temperature on soil nitrogen mineralization of different layers with aerobic incubation experiments. The main results are shown as follows:1. Nitrogen mineralization accumulation quantity of all soil layers gained with the increase in temperature and water content, but the mineralizable nitrogen in the layer of 0-30cm was much greater than those in other soil layers. The mineralizable nitrogen of the 0-30cm soil layer was the major part, accounting for 67.90% of the total, and the value of both 30-60cm and 60-90cm soil layers was 32.10%. Mineralization quantity of 0-30cm soil layer increased faster than another two soil layers. Every soil layer had different mineralization process under different water contents, that is to say, mineralization process of 0-30cm soil layer could be expressed with linear equation, and 30-60cm and 60-90cm soil layers with logarithm equation in incubation time. The relations of soil nitrogen mineralization rate (k) with water content (w) could be expressed by the linear equation, and the correlation coefficient was above 0.93. It was found that k of 0-30cm soil layer was most sensitive to temperature, and then of 30-60cm, and of 60-90cm the least. As a whole, nitrogen mineralization rate of deeper soil layer increased slowly with the temperature under the higher incubation temperature. These results suggested that temperature and water content had interactive effects on nitrogen mineralization quantity and rate. To 0-30cm, both temperature and water content had remarkable positive effect, but moisture is more evident under the higher incubation temperature. But to 30-60cm and 60-90cm, temperature exerted more evident effect. Temperature, moisture content and incubation time had also remarkable linear correlation (p< 0.0001). From the results, we found that mineralization process of 0-30cm soil layer was more sensitive to temperature and water content, which means that nitrogen mineralization process is determined by such factors as temperature, moisture and soil layer.2. The kinetic parameters of chlorophyll fluorescence of winter wheat were sensitive to water stress. The basic fluorescence(Fo) of wheat leaves increased under the water condition of 0-30cm soil-dry and 30-90cm soil-wet (D), while the maximal fluorescence(Fm), the variable fluorescence(Fv), the photochemical efficiency(Fv/Fm) and potential activites(Fv/Fo) of PSII decreased remarkably. Nitrogen and phosphorus nutrient could weaken the effect of water stress on fluorescence parameters; and the effect of NP treatments (mixing nitrogen and phosphorus) was better than P treatment (applying phosphorus). Comparing layer treatments with the same fertilizer, we found that the difference of fluorescence parameters with N applying in different layers was unapparent, that Fo with P applying layer of 0-90cm and 0-30cm were lowered than of 30-60cm and 60-90cm, but Fm, Fv, Fv/Fm and Fv/Fo was higher; that the difference of fluorescence parameters with NP applying in different layers was remarkable.3. SPAD and the net photosynthetic rate (Pn) of leaf and yield of wheat were inconsistently lower under the water condition of 0-30cm soil-dry and 30-90cm soil-wet (D) than of 0-90cm soil-wet (W). Under each water treatment, compared to fertilizer treatments at the same layer, it showed that SPAD, Pn and yield of NP treatments were maximal, followed by P treatment, then was N treatment (applying nitrogen). Compared to layer treatments with the same fertilizer, it was found that SPAD, Pn and yield with nitrogen applying layer of 0-90cm were maximal, but the results were ruleless when nitrogen was applied in layer of 0-30cm, 30-60cm and 60-90cm; that, under W condition, yield with phosphorus applying layer of 0-30cm was highest; under D condition, yield with phosphorus applying layer of 0-90cm were highest; both SPAD and Pn with phosphorus applying layer of 0-90cm were highest, followed by 0-30cm; that under W or D treatment, yield, SPAD and Pn with nitrogen and phosphorus applying layer of 0-90cm were highest, of 0-30cm, 30-60cm and 60-90cm presented downtrend.4. Compared with 0-90cm soil-wet (W), leaf area and plant height of heading stage decreased by 7.03% and 3.77% separately under the water condition of 0-30cm soil-dry and 30-90cm soil-wet (D). The above-ground biomass, root biomass and HI were inconsistently lower, but ratio of root to shoot (R/S) higher under the condition of D. Comparing fertilizer treatments at the same layer, it showed that the effective tillers were reduced by 2.6(n/pot) of P treatment than NP treatments; that the difference of the leaf area and plant height was not significant between P treatment and NP treatments; that leaf area, plant height and fertile tillers of N treatment and CK were markedly lower than P treatment and NP treatments. Under each water treatment, above-ground biomass of NP treatments was maximal, followed by P treatment, then was N treatment, but root biomass and R/S were maximal at the treatment of P, due to P deficiency and N enrichment in the soil. Comparing layer treatments with the same fertilizer, we found that leaf area, plant height and fertile tillers of P and NP applying layer of 0-90cm and 0-30cm were remarkably higher than of 30-60cm and 60-90cm; but the rule was not obvious at the treatment of N applying in different layer. Above-ground biomass and root biomass of N applying layer of 0-90cm was maximal, of 0-30cm was lowest. Above-ground biomass, root biomass and R/S of P applying layer of 0-90cm and 0-30cm were markedly higher than of 30-60cm and 60-90cm; and above-ground biomass and root biomass of NP applying layer of 0-90cm was maximal, followed by 0-30cm, 30-60cm and 60-90cm orderly. Because the soil was full of nitrogen, applying N in layer of 0-30cm was inhibitory to biomass, but of 0-90cm was stimulative, which was more obvious under the condition of D. The biomass of crop would be higher mixing nitrogen and phosphorus in layer of 0-30cm, regardless of the condition of D and W.5. Minirhizotrons is one of the new study methods, which has the merit of non-destructive and the fixed-point visual observation. The experiment dealt with the effects of spatial coupling of water, nitrogen and phosphorus on root character of different soil layers at different growth stages using minirhizotrons, and discussed the relation of root characteristics with water use efficiency (WUE). The root character indexes mainly included root length, root seeming area, root volume area, root number, root diameter and root biomass of winter wheat. The results showed that a majority of root diameters was between 0.0000mm and 0.5000mm and a little was beyond 0.5000mm. The diameters of root in 0-30cm soil layer were bigger than in other soil layers. And water and fertilizer had less effect on root diameter. There was a remarkable difference of different root character indexes between different water treatments. And compared with 0-90cm soil-wet (W), root length, root seeming area, root volume and root number increased by 18.9%, 25.3%, 29.8% and 8.0% separately under the water condition of 0-30cm soil-dry and 30-90cm soil-wet (D). The rule of root growth and distributing were different between different fertilizer treatments, although growth momentums of all wheat roots arrived at the zenith at the booming stage and started to decline at the filling stage. Root length, root seeming area, root volume and root number of N treatment and CK were less, but had faster growth rate all along. Root length, root seeming area, root volume and root number of P treatment and NP treatments were higher, but had lower growth rate after the jointing stage. Comparing layer treatments with the same fertilizer, we found that there was no significant difference of root character indexes between the treatment of N applying in different layer, that all root character indexes were significant higher at the treatment of P applying in 0-90cm than 0-30cm, 30-60cm and 60-90cm soil layer, that significantly higher at the treatment of NP applying in 0-90cm and 0-30cm than 30-60cm and 60-90cm soil layer. On the whole, root biomass of 0-30cm soil layer was highest, accounting for 67.2% of 0-90cm soil layer averagely. And those of 30-60cm and 60-90cm accounted for 17.4% and 15.4% separately. But root growth increased relatively at the fertilizer layer. Compared with W, WUE of wheat increased by 0.039mg/cm3 under the water condition of D. Fertilizer treatments could improve WUE, and WUE of 0-90cm fertilization was highest. Correlation analysis showed that WUE and root length, root seeming area, root volume and root number were remarkable positive correlation and correlation coefficient(r2) was 0.7992, 0.7719, 0.7243 and 0.7893(n=25), that WUE and root biomass were lower correlation and r2 was only 0.2974. It showed that root character indexes had more remarkable effect on WUE than root biomass.6. Nitrogen and phosphorus content of grain was highest, followed by root, then was leaf and rachis and hull (RH), and stem was lowest. Nitrogen and phosphorus uptake of grain was highest, followed by stem and leaf, then was RH, and root was lowest. Nitrogen content of grain and RH decreased by 0.90% and 2.40% separately under the water condition of 0-30cm soil-dry and 30-90cm soil-wet (D), and phosphorus content decreased by 4.34% and 12.99% separately. Compared with the water condition of 0-90cm soil-wet(W), nitrogen and phosphorus uptakes decreased under D, but distribution proportion changed little. Compared with CK, both nitrogen and phosphorus content of plant components of NP treatments increased. Nitrogen content of N treatment increased remarkably, but phosphorus content increased little. Nitrogen and phosphorus uptake increased with fertilizer treatments, but distribution proportion of grain decreased. Nitrogen and phosphorus uptake of different plant components lied mainly on biomass, not on nitrogen and phosphorus content. Root nitrogen and phosphorus uptake of 0-30cm soil layer were highest, and increased relatively at the fertilization layers. Nitrogen and phosphorus uptake of different plant components with fertilizer applying in the layer of 0-90cm was highest when only nitrogen applied. Nitrogen and phosphorus uptake of grain and root with fertilizer applying in the layer of 0-90cm was highest when only phosphorus or nitrogen and phosphorus applied.7. There was bigger difference between nitrogen utilization rate(NUR) and phosphorus utilization rate (PUR) of wheat of different treatments. NUR and PUR were in the range of 4.73%-41.19% and 4.11%-13.58% separately. Phosphorus agronomy efficiency (PAE) was higher than nitrogen agronomy efficiency (NAE). Compared with the water condition of 0-30cm soil-dry and 30-90cm soil-wet (D), NUR decreased by 4.87% under the water condition of 0-90cm soil-wet (W) when only nitrogen applied. But NUR increased by 6.38% when nitrogen and phosphorus mixed. There was no significant difference of PUR between W and D when only phosphorus applied, and remarkable difference when nitrogen and phosphorus mixed. PUR under W increased by 5.01% when nitrogen and phosphorus applied mixed. There was a difference of NUR and PUR between different fertilizer treatments. NUR of NP treatments was higher than N treatment under D, and NUR increased by 10.48%. But the difference of PUR between NP treatments and P treatment was only 0.58% under D. The difference of NUR and PUR was higher under W than D. NUR and PUR increased by 21.73% and 4.80% separately. It showed that better water condition of 0-30cm soil layer could improve NUR and PUR of NP treatments. NUR was highest whether nitrogen or nitrogen and phosphorus applying layer of 0-90cm under two water conditions. PUR was 8.55% when only phosphorus applying layer of 0-90cm, and it was higher than phosphorus applying in other layers. But PUR was highest when nitrogen and phosphorus applying at the same time in the layer of 0-30cm. NAE and PAE were higher under D than W when only nitrogen or phosphorus applied, but it was contrary when nitrogen and phosphorus mixed. NAE was highest when nitrogen or nitrogen and phosphorus applied in the layer of 0-90cm. PAE was highest when phosphorus applied in the layer of 0-90cm under D and nitrogen and phosphorus applied in the layer of 0-30cm under W.8. From the point of view of the effect of water and fertilizer spatial coupling on photosynthesis, chlorophyll fluorescence, root distribution, assimilation matter and nutrient distribution and nutrient efficiency, enough effective nitrogen and phosphorus supplying of 0-30cm and 0-90cm soil layer was very important to crop growth regardless of the condition of D and W. It was not only very important to increase yield and nutrient efficiency, but also advantageous to increase nitrogen and phosphorus content and transfer nutrient to grain. Practically, fertilizer should be applied in the layer of 0-30cm when mixed nitrogen and phosphorus, because NO3--N move easily in calcareous soil and phosphorus slow.
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