Effect And Its Causes Of FACE On Growth And Development Of Three-line Indica Hybrid Rice (Oryza Sativa L.) Cultivar Shanyou 63

It is reported that Global atmospheric CO₂ concentration is increasing continually. And it is projected to reach levels of 450～550μmol·mol^-1 within year 2050. The enhancement of atmospheric CO₂ concentration commonly caused the climate change and affected the agriculture crops production. The effects of FACE on yield and yield components, biomass production and distribution, nutrient uptake and efficiency, roots of Japonica rice have been reported. This study was carried out in the platform for FACE study, located in Jiangdu (31°37'N,120°28'E), China, using three-line hybrid indica rice shanyou 63 as tested rice cultivar. The CO₂ concentration in FACE treatment was 570μmol·mol^-1, with 370μmol·mol^-1 as ambient (AMB). The main purpose of the experiment was to study the effects of elevated CO₂ concentration on three-line hybrid indica rice production. Results showed as follows:(1) Compared to ambient [CO₂], FACE increased plant height at maturity of Shanyou 63 by 6.7% on average, the effect reaching significant level (P < 0.01), however, no CO₂ effect was observed on the whole growth duration of Shanyou 63. On average, FACE increased the grain yield of Shanyou 63 significantly (P < 0.01), with an average increase of 34.8% across the three years (42.4%,27.3% and 31.2% in 2001, 2002 and 2003, respectively). The year effect and the interaction between [CO₂]×year were significant (P < 0.05 or P < 0.01) for grain yield; FACE increased yield components of Shanyou 63 significantly (P < 0.05 or P < 0.01), averaging 10.3%, 10.3%, 21.7%, 4.9% and 4.3% for panicle number per unit area, spikelet number per panicle, spikelet number per unit area, filled grain percentage and 1000-grain weight, respectively. N effect was not significant on yield and its components of Shanyou 63, while its interaction with [CO₂] was significant for panicle number, spikelet number and grain yield per unit area.(2) Across the two growing seasons, rice DM production under FACE was significantly enhanced by 39, 20, 32 and 41% during the growth periods from transplanting to tillering, tillering to jointing, jointing to heading and heading to grain maturity, respectively. As a result, the final total biomass at maturety was increased by 33% on average. In general, seasonal changes in crop response to FACE in both leaf area index (LAI) and net assimilation rate (NAR) followed a similar pattern to that of the DM production, with the degree of response much larger in LAI than NAR. Under FACE the leaves and spikes decreased significantly in proportion to the total above-ground DM over the season, while the stems showed an opposite trend. FACE significantly increased the content (%) and amount of soluble sugar and starch in stems and sheaths at heading and grain maturity. Huge differences existed between the three-line indica hybrid rice cultivar and japonica rice cultivar with respect to the responses of final DM accumulation at maturity, as well as mean LAI and NAR, and DM production during the different growth periods, while differences on dry matter distribution were small.(3) Compared with AMB, FACE significantly decreased N concentration in rice plant of Shanyou 63 over the season, FACE significantly increased nitrogen accumulation in rice plant, and the increasing rate at the middle growth stage was less than that at the early and late growth stage. FACE had no obvious effect on nitrogen allocation pattern of Shanyou 63 over the season. FACE treatment resulted in the significant increase in N use efficiency for biomass (NUEp) over the season and in N use efficiency for grain yield (NUEg) at grain maturity, but no CO₂ effect was observed on nitrogen harvest index (NHI). Nitrogen concentration and accumulation at different growth stages of Shanyou 63 increased with increasing N supply (P < 0.05 or 0.01), but NUEp and NUEg showed the opposite trends. Significant interactions between [CO₂]×year and N×year were observed for N concentration and accumulation. FACE decreased N concentration, increased N uptake, NUEp and NUEg at different growth stages of Shanyou 63, but no CO₂ effect was detected on N allocation(4) Compared with AMB, FACE significantly increased P concentration in rice plant of Shanyou 63 over the season, FACE significantly increased phosphorus accumulation in rice plant, and the increasing rate at the middle growth stage was less than that at the early and late growth stage. Before heading, FACE had no obvious effect on phosphorus allocation pattern of Shanyou 63, but after heading, it made the proportion of phosphorus allocation in leaves significant increased, the phosphorus allocation in spikes significant decreased. Under FACE treatment, P use efficiency for biomass (PUEp) over the season, P use efficiency for grain yield (PUEg) at grain maturity, and phosphorus harvest index (PHI) were significantly decreased. Phosphorus concentration and accumulation at majority growth stages of Shanyou 63 increased with increasing N supply (P < 0.05 or 0.01), but PUEp and PUEg showed the opposite trends. Significant interactions between [CO₂]×N and [CO₂]×year were observed for P concentration and accumulation. FACE increased P concentration and P uptake, decreased PUEp and PUEg at different growth stages of Shanyou 63.(5) FACE treatment increased the number of adventitious roots per hole, the length of adventitious roots per hole, the roots volume per hole, the dry weight of roots per hole significantly of Shanyou 63 at tillering, jointing and heading stages. the number of adventitious roots per hole and the roots volume per hole under FACE were significantly higher than those under AMB at heading stage, which was chiefly resulted from the larger increment of those root traits under FACE during effective-tillering and unproductive-tillering period. The length of adventitious roots per hole under FACE was significantly higher than that under AMB at heading stage, which was chiefly caused by the still larger increment of the length of adventitious roots per hole under FACE before heading. the dry weight of roots per hole under FACE was significantly higher than that under AMB at heading stage due to FACE substantially increased the dry weight of roots per hole during stem elongating and panicle bearing period. the length of per adventitious root under FACE was significantly higher than that under AMB at heading stage, which was chiefly resulted from the still larger increment of the length of per adventitious root under FACE before heading.(6) The total absorption area per unit dry weight of root, the active absorption area per unit dry weight of root and the amount ofα-NA per unit dry weight of root of shanyou63 under FACE were significantly higher than those under AMB at different growth stages. While FACE made larger increment of rice root, which resulted in no significant difference of root activity per hole between FACE and AMB at tillering and jointing stages, but FACE significantly increased root activity per hole at heading stage. Root activity per unit dry weight of root negatively correlated with the number of adventitious roots per plant, total length of adventitious roots per plant, roots volume and dry weight of root at jointing and heading stages. The larger the root productions, the lower the root activity per unit dry weight. For the most part,root activity per unit dry weight of root positively correlated with N content of rice plant, and negatively correlated with the content of soluble carbohydrates in stem and sheath and C/N ratio. The largeness of biomass accumulated, lower N content in rice plant and higher C/N ratio appear to be the primary causes of significant decrement of root activity per unit dry weight of root under FACE.