| Abstract: These field experiments were carried out with Zhengmai 9023, a state-released strong-gluten wheat cultivar, as the material in the Scientific & Educational Park of Henan Agricultural University, Zhengzhou, Henan, China in growing seasons of 2008~2010. A randomized complete block design with 4 replications was employed with 2 levels of phosphorus and 3 levels of potassium fertilizers in 2008~2009, while in 2009~2010 a multi-site randomized block design with 4 replications was employed with 3 levels of irrigation and 3 levels of phosphorus fertilizers. From green-returning stage to late dough stage samples of nodal roots with special root hairs (SRH) were taken every 5 day to observe formation and growth, length and diameter, morphology and anatomical structures of SRH under different experimental conditions.The main results are as follows:(1) Difference in growth of SRH in conditions of different supply levels of phosphorus and potassium was made clear. Length of SRH-forming segments of nodal roots, occurring density, and length and diameter of SRH all increased with levels of phosphorus supply. Difference in occurring density, length, and diameter of SRH between treatments of high supply level of phosphorus and control was significant (P<0.05) from jointing to anthesis, respectively. With regards the order of effects of different supply levels of potassium on length of SRH-forming segments of nodal roots, occurring density, and length and diameter of SRH was just as K2>K3>K1. Difference in occurring density and length of SRH between K2 treatments and control was significant (P<0.05) from jointing to flag leaf expansion, respectively. Among different coupling treatments of phosphorus and potassium, the minimum length of SRH-forming segments of nodal roots, occurring density, and length and diameter of SRH was all found in P1K1 treatments. Difference in length of SRH-forming segments of nodal roots, occurring density, length, and diameter of SRH between P1K1 with either P2K2 or P2K3 treatments was extremely significant (P<0.01) from jointing to anthesis, respectively. The results indicated that in the conditions of these current field experiments increasing phosphorus application significantly improved growth of SRH. However, just a certain improving effects of increasing potassium application on growth of SRH were observed. Also, increasing potassium application could reduce influence of low level of phosphorus supply on SRH, but over application of potassium (K3 treatments in this study) couldn’t improve growth of SRH.(2) Coupling effects of irrigation and phosphorus application on growth of SRH were analysed. An extremely significant positive correlation was observed between soil relative moisture content and SRH number in the rain-fed treatments. Difference both in occurring density and length of SRH was extremely significant (P<0.01), respectively, between the rain-fed and waterlogging treatments. However, in waterlogging treatments an extremely significant negative correlation was observed between soil relative moisture content and number, occurring density, and length of SRH (P<0.01), respectively. Compared with that in optimal irrigation treatments, length of SRH from jointing to grain formation decreased in waterlogging treatments (P<0.01). The positive correlation between soil available phosphorus content and both number and occurring density of SRH became closer and closer with increased phosphorus supply. Both length and diameter of SRH increased with advance in plant developmental process (P<0.05). At anthesis, difference in length and diameter of SRH between P2 treatments and control was extremely significant (P<0.01), respectively. Length and diameter of SRH significantly increased with phosphorus supply at a fixed irrigation level or significantly decreased with soil moisture content at a fixed phosphorus level (P<0.05). The results indicated that both soil relative moisture content and phosphorus supply level all affected growth of SRH, and that there was an interaction found between and irrigation and phosphorus application. Increasing phosphorus supply in waterlogging treatments or reasonably controlling soil moisture content in low level of phosphorus supply treatments could all reduce influence either of waterlogging or low phosphorus supply on growth of SRH.(3) Coupling effects of irrigation and phosphorus application on growth rate of SRH were analysed. An S-shape curve was found in growing and developmental patterns of SRH: starting to occur at green-returning stage, presenting flourishing growth from flag leaf expansion to anthesis, and decaying after anthesis. Rate of change (ROC) of length of SRH-forming segments of nodal roots and occurring density of SRH, and growth rate of length and diameter of SRH during the observation time were all in an N-shaped curve. Occurring density, length and diameter of SRH in rain-fed treatments were larger that those in waterlogging treatments (P<0.05). Similarly, occurring density, length and diameter of SRH in treatments of high phosphorus supply were larger that those in treatments of low phosphorus supply (P<0.05). ROC of occurring density of SRH, and growth rate of length and diameter of SRH significantly increased with phosphorus supply at a fixed irrigation level or significantly decreased with soil moisture content at a fixed phosphorus level (P<0.01). The results indicated that there was a significant difference in growth rate of SRH when different levels of irrigation and phosphorus supply were applied.(4) Morphology and anatomical structure of SRH were studied in different coupling treatments of irrigation and phosphorus supply. Among all the coupling treatments of phosphorus and potassium supply, varied morphological characteristics of SRH were observed in P2K2 treatments: branching and protruding of SRH being a common phenomenon, and SRH cells being with thick walls and cytoplasm, and clear nuclei. However, in P1K1 treatments root epidermic cells were arranged loosely, SRHs were less, morphology of SRH was simple with incomplete cytomembrane and thin cytoplasm, and cell organelles were broken up and the cell died. Among all the coupling treatments of irrigation and phosphorus supply, SRH cells in the rain-fed treatment coupled with high phosphorus supply were full with complete structure, thickened cell wall, and distinct nuclei, vacuoles and mitochondria. But in waterlogging coupled with low phosphorus supply treatments, SRHs were twisted and deformed with thin cell wall, broken-up nuclei and disappeared plasma membrane and microbodies.(5) Relationships between RRH number and grain yield in different coupling treatments of irrigation and phosphorus application were made clear. Positive correlations were observed between SRH number in early SRH occurring period and grain yield at harvest. Among them, the correlation between SRH number and grain yield was significant (P<0.05) both at green-returning and jointing stage, and was extremely significant (P<0.01) flag leaf expansion stage. Correlation between diameter of SRH at jointing and grain yield was extremely significant (P<0.01). After flag leaf expansion, there were negative correlations between SRH number and grain yield. Among them, the negative correlation between either occurring density or length of SRH at dough stage and grain yield was extremely significant (P<0.01). The results indicated that growing condition of SRH in early growing period paved the way for an increase in grain yield.(6) Predication models for growth of SRH were set up. Relative growth traits of SRH and relative growing days were simulated by Curve Expert 1.38 software after growing and developmental traits of SRH and growing days were all normalized. The results showed that fitting effect of the rational equation was the best. Simulating models for relative length of SRH-forming segments of nodal roots, occurring density, and length and diameter of SRH were as follows: y﹦(0.0003+0.0944x)/(1-2.7398x+2.0050x~2) ( r2=0.9788**), y﹦(0.0029+0.0106x)/(1-2.9404x+2.6835x~2) ( r2=0.9678**), y﹦(0.0176+0.0144x)/(1-2.5245x+1.8362x~2) ( r2=0.9414**), y﹦(0.0056+0.1911x)/(1-2.4176x+1.7202x~2) ( r2=0.9690**). Integral of relative SRH growing model, y﹦(a+bx)/(1+cx+dx~2), was calculated (from 0 to 1) to obtain average datum of relative growth of SRH over the observation period. Multiplying the average datum of relative growth of SRH by the maximum datum of growth was the average datum of growth of SRH over the observation period. Simulating model for rate of change of relative growth rate of SRH, y’﹦(b-ac-2adx-bdx~2)/(1+cx+dx~2)2, was obtained by differentiating the model for relative growth characters of SRH, y﹦(a+bx)/(1+cx+dx~2). As a result, accurate growth rate of SRH at any growing stage during the observation period was available by the model to provide theoretical basis for regulating growth of SRH by reasonable irrigation-fertilizer application management. |
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