Fundamentals of rice crop science

Interactive effects of multiple global change factors on ecosystem processes are complex. It is relatively expensive to explore those interactions in manipulative experiments. We conducted a modeling analysis to identify potentially important interactions and to stimulate hypothesis formulation for experimental research. Four models were used to quantify interactive effects of climate warming (T), altered precipitation amounts [doubled (DP) and halved (HP)] and seasonality (SP, moving precipitation in July and August to January and February to create summer drought), and elevated [CO2 ]( C) on net primary production (NPP), heterotrophic respiration (Rh), net ecosystem production (NEP), transpiration, and runoff. We examined those responses in seven ecosystems, including forests, grasslands, and heathlands in different climate zones. The modeling analysis showed that none of the threeway interactions among T, C, and altered precipitation was substantial for either carbon or water processes, nor consistent among the seven ecosystems. However, two-way interactive effects on NPP, Rh, and NEP were generally positive (i.e. amplification of one factor’s effect by the other factor) between T and C or between T and DP. A negative interaction (i.e. depression of one factor’s effect by the other factor) occurred for simulated NPP between T and HP. The interactive effects on runoff were positive between T and HP. Four pairs of two-way interactive effects on plant transpiration were positive and two pairs negative. In addition, wet sites generally had smaller relative changes in NPP, Rh, runoff, and transpiration but larger absolute changes in NEP than dry sites in response to the treatments. The modeling results suggest new hypotheses to be tested in multifactor global change experiments. Likewise, more experimental evidence is needed for the further improvement of ecosystem models in order to adequately simulate complex interactive processes.

/pdf/modeled-interactive-effects-of-precipitation-temperature-and-1rc3p81o6j.pdf

Modeled interactive effects of precipitation, temperature, and [CO2] on ecosystem carbon and water dynamics in different climatic zones

The annual rate of rice yield increase in the world declined from 2.7 % in the 1980s to 1.1 % in the1990s. The continued world population increase requires resumption of the previous rate. The objectives of this paper are to review and assess rice production technologies for increased yield in the past and the current challenge on the basis of crop physiology and agronomy, and to discuss the way to increase irrigated rice yield to fulfil the expanding demand. Field experiments conducted in Kyoto, Japan and Yunnan, China showed that the best recent Chinese hybrid has a yield potential about 10 % higher than the best recent inbred cultivar in Japan. This result, and a review on recent challenges in breeding, suggested only moderate increases in the yield potential of rice genotypes in the coming decades. Contrary to the general understanding, the rapid rice yield increase in central Japan from the mid 1950s to mid 1970s was achieved mostly by improved crop and resource management. This, and the fact...

/pdf/can-yields-of-lowland-rice-resume-the-increases-that-they-t0kvdtakh0.pdf

Can Yields of Lowland Rice Resume the Increases that They Showed in the 1980s

Rice yield potential is closely related to crop growth rate during late reproductive period

http://www.clw.csiro.au/publications/waterforahealthycountry/2008/wfhc-MekongWaterResourcesAssessment.pdf

Mekong River Basin water resources assessment: impacts of climate change

The observed reaccumulation of non-structural carbohydrates (NSC) in culm and leaf sheath in the later half of the grain filling period, in spite of the existence of imperfectly filled rice spikelets, indicate that grain filling is determined not only by total availability of carbohydrates during the grain filling period but also by the sink ability for accumulating carbohydrates. The objectives of this study were to clarify which plant factors determine the sink ability of rice grain and their cultivar difference. Periodic measurements were made of crop dry weight and the amount of NSC during grain filling period of Milyang 23 and Nipponbare grown under various conditions. Filling percentage, defined as the ratio of rough brown rice yield to the product of spikelet density and weight of a fully ripened grain, was positively correlated with RGR in grain weight over the initial 10 days after full heading. This period corresponded to the reported period in which endosperm cell number is determined. A highly positive correlation was also obtained between the amount of NSC available per grain in thc initial 10 days of grain filling and the RGR of grain, indicating that the filling percentage of rice crop is determined by the availability of NSC in that period. Interestingly, Milyang 23 had a significantly higher filling percentage than Nipponbare under a given amount of NSC per grain in the initial 10 days of grain filling.

Filling Percentage of Rice Spikelets as Affected by Availability of Non-Structural Carbohydrates at the Initial Phase of Grain Filling

To develop a rapid determination of nonstructural carbohydrate (NSC) in rice plant, the availability of gravimetric analysis was examined. A plant sample of 0.5 g in 30 mL of distilled water was heated on a hot plate. After the cooling, 20 mL of phosphate buffer (KH2PO4 ; 12.08 gL-1, Na2HPO4·12H2O ; 3.98 gL-1, NaN3. ; 0.025 gL-1) containing 1.5 mg of α-amylase and 0.5 mg of amyloglucosidase was added to it. The mixture was incubated at 40°C for 24 hours with continuous shaking, then filtrated through filter paper (Advantic Toyo, No. 5A), its dry weight being predetermined. The residue on the paper was washed out with distilled water, then dried and weighed. The nonreducing sugar in the filtrate was hydrolyzed in 15 mL of boiling 0.04M H2SO4. In the gravimetric analysis, the concentration of all water-soluble substrate (NSCWS) was determined from the difference between dry weights of sample and residue. In the calorimetric analysis, the concentration of reducing sugar equivalent to glucose (NSCGL) was determined by using the ρ-hydroxybenzotic acid hydrazine method. Although no significant relationship between NSCWS and NSCGL in leaf blade was noted, significantly high positive correlations (r2g0.912) were found between them in leaf sheath + culm and panicle, irrespective of cultivation conditions and growth stages. An analysis of errors associated with the determination of NSCWS and NSCGL revealed that the gravimetric method gave a higher accuracy than the calorimetric method did, even when NSCWS was converted into NSCGL by linear regression equations. Also, NSCWS was more effectively incorporated with the near infrared spectroscopic method to quickly determine NSC. These results indicate that the gravimetric analysis is useful for a proxy determination of NSC in rice leaf sheath + culm and panicle.

A Proxy Analysis of Nonstructural Carbohydrate in Rice Plant by Using the Gravimetric Method

In order to identify the key factors that arrest yield improvement in rice, we observed fifteen divergent cultivars in a field at Kyoto, Japan in 1995 and 2001 under various nitrogen (N) regimes. The contribution that sink size (spikelet number X single fully ripened grain mass), source size (total available carbohydrate), and source components, non-structural carbohydrate (pre-reserved) at full heading (NSCh) and dry matter production during grain filling (DMP) had to the variation in yield among cultivars was examined. The dry weight of rough brown rice (Y) ranged from 310 to 743 g m-2 throughout two years and under all N regimes examined. Although Y correlated with both sink and ource sizes, it tended to correlate more closely with source size than with sink size. In many cultivars, source size was smaller than sink size at all conditions examined except for the low nitrogen regime. The contribution of source components to Y was analyzed with the equation : Y = Cn NSCh + Cd DMP, where C„ and Cd...

Contribution of Sink and Source Sizes to Yield Variation among Rice Cultivars

Quantifying the toposequential distribution of environmental resources and its relationship with rice productivity.

The effects of elevated CO2 concentration and high temperatures on transpiration and gaseous diffusive resistances of rice canopy were investigated. Akihikari and IR36 cultivars were grown under two CO2 concentrations ( [CO2], 365 and 700 μL L-1) × three temperatures (29.8, 30.4 and 32.5°C on average over the experimental period), created by two Temperature Gradient Chambers. From 2 August (panicle initiation) to 22 August (booting), measurements were made of dry and wet bulb temperatures, canopy surface temperatures (Tc) and net radiation along with evapotranspiration (E) measurements by microlysimeters. Aerodynamic resistance (ra), obtained from the measured E and microclimate data, showed a fairly constant value (11.7 s m-1). Then, ra, Tc and microclimates data were substituted into energy budget equations to obtain E and canopy resistance (rc). In all plots, calculated E was in good agreement with measurement by lysimeters, and rc reached minimum values (rc, min) at solar radiation above 500 W m-2. Elevated [CO2] at the lowest temperature plot increased rc, min by 40-49% and Tc by 1.4-1.6°C and it reduced E by 14-16% of those under ambient CO2 conditions. With the rising growth temperature, these effects of elevated [CO2] drastically decreased. The observed rc, min responses to temperature and [CO2] seemed to have reflected a long-term acclimation of rice to these environments. These results indicate that anticipated global warming significantly reduces the advantageous effects of elevated [CO2] on plant water use.

Energy budget and transpiration characteristics of rice grown under elevated co2 and high temperature conditions as determined by remotely sensed canopy temperatures

Masao Ohnishi

Papers

Filling Percentage of Rice Spikelets as Affected by Availability of Non-Structural Carbohydrates at the Initial Phase of Grain Filling

A Proxy Analysis of Nonstructural Carbohydrate in Rice Plant by Using the Gravimetric Method

Contribution of Sink and Source Sizes to Yield Variation among Rice Cultivars

Quantifying the toposequential distribution of environmental resources and its relationship with rice productivity.

Energy budget and transpiration characteristics of rice grown under elevated co2 and high temperature conditions as determined by remotely sensed canopy temperatures