| Straw mulching is a widespread farming technique in dryland around world. In China, straw mulching has been used in traditional agriculture long before. Recently, it has been developed quickly in northern China, and becoming an important part in the reduced-tillage and no-tillage system. Growth and development of plant is a systemic process of photosynthesis in leaves with water and nutrition uptake by root system. Soil temperature is one of the important ecological factors and its effects on plant growth and development are not only agriculture and forestry problems but also important theoretical problems. There have been so many contradictions in previous researches. Could straw mulching increase crop yield? Was soil temperature the main cause of yield-reduction of crop under straw mulching? And what was its functional mechanism? No any reasonable answers yet. A field experiment and two water culture experiments were conducted to study the effect of straw mulching on soil temperature and responses of wheat growth to temperature. The main results were obtained as follows:(1)According to the change characteristics of daily mean temperature, the six months from straw mulching to harvest of winter wheat could be divided into 4 stages: Before winter period and Early winter period (Nov.7~Jan.5)——soil temperature decreased quickly, Middle winter period (Jan.6~Jan.25)——soil temperature was the lowest within six months, Late winter period to Turning green stage (Jan.26~Mar.20)——soil temperature raised slowly, Jointing stage to Late stage of winter wheat (Mar.21~May 25)——soil temperature raised continuously. The average soil temperature of 24 hours in a day was significantly higher in mulched soil than no mulch soil. From the period of before winter to turning green stage, the difference of average soil temperature of 24 hours in a day between mulched and no mulch soil was smaller and smaller. The heating effect of straw mulching was significant more and more after turning green stage: temperature at the depth of 10 cm in mulched soil could increase by 2.52℃at the most, and 20 cm was 1.65℃at the most. Maximum of temperature difference at the soil depth of 10 cm between mulched and no mulch soil was at 9:00 to 17:00, and delayed 3~4 hours at the soil depth of 20 cm. The exact time varied with the growing period. Temperature at the soil depth of 10 cm raised from minimum to maximum within 6~9 hours, and there was no significant difference between mulched and no mulch soil. Daily amplitude of soil temperature (Daily Maximum-Daily Minimum) significantly decreased under straw mulching before jointing stage, so the temperature rising and cooling rates were significant lower than no mulch soil. From jointing to late stage of winter wheat, because daily amplitude of soil temperature in mulched soil was significantly higher than no mulch soil, the temperature rising and cooling rates were significantly higher than no mulch soil. The average temperature of 24 hours in a day at the soil depth of 20 cm was significantly higher than 10 cm before winter period to turning green stage, and straw mulching has no significant effect on it. From jointing to late stage of winter wheat, the average soil temperature of 24 hours in a day at the soil depth of 20 cm was lower than 10 cm, and the difference between them in mulched soil significantly higher than no mulch soil. Time of maximum and minimum temperature of mulched soil was in concordance with no mulch soil.(2)Compared with normal temperature treatment, low and high temperature treatments both affected growth and nutrition uptake of winter wheat to a certain degree before winter period to turning green stage. Low temperature had no significant effect on root length of winter wheat before winter period, but it reduced root length during winter period and turning green stage. High temperature increased root length before winter period and over winter period, but it was not favorable to the increase of root length during turning green stage. Compared with normal temperature, low temperature inhibited wheat growth, and the effect on shoot was greater than root before winter period. High temperature before winter period promoted root growth and went against dry matter accumulation in the shoot. During winter period, low temperature was not favorable to the growth of root and shoot. High temperature significantly increased root volume but had no significant effect on shoot growth during winter period. Low temperature significantly inhibited wheat growth during turning green stage, and the effect on root was a little greater than shoot. High temperature mainly affected root growth during turning green stage. Low temperature significantly inhibited nutrient uptake of winter wheat during 3 growing period, and high temperature was also not favorable to the nutrition uptake to a certain degree over winter period. But there was an increasing trend in above ground nutrition uptake at high temperature during turning green stage.(3)Over winter period, root length at 1/2 level of N (6 mmol·L-1) was higher than normal level (12 mmol·L-1) at normal temperature, and the difference between them was little at low temperature. At high temperature, root length at 6 mmol·L-1 was a little lower than 12 mmol·L-1. In this water culture experiment, N supply had no great effect on root and shoot growth of winter wheat. At 6 mmol·L-1, low temperature decreased root dry weight, root volume and shoot dry weight, and high temperature promoted root and shoot growth of winter wheat. N supply decreased had no significant effect on nutrition uptake of winter wheat at normal temperature. 6 mmol·L-1 or 12 mmol·L-1, low temperature significantly decreased nutrition uptake and high temperature significantly increased it. 6 mmol·L-1 or 12 mmol·L-1, high temperature significantly increased nitrate reductase activity (NRA). N supply decreased had no significant effect on CO2 concentration in cell clearance (Ci), transpiration rate (E) and stomatal conductance (Gs), and effects of it on photosynthesis rate (Pn) and water use efficiency at leaf level (WUEL) were related to root zone temperature. The effect at 6 mmol·L-1 on Pn had a given period of time at normal temperature. Pn at 6 mmol·L-1 was higher than 12 mmol·L-1 at low temperature and lower than 12 mmol·L-1 at high temperature. At normal and high temperature, there was no significant difference of WUEL between 6 and 12 mmol·L-1. WUEL at 6 mmol·L-1 was higher than 12 mmol·L-1 at low temperature.
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