The influence of the rhtx and rht2 alleles on the deposition and use of stem reserves in wheat

A field experiment was undertaken with a set of near-isogenic spring wheat lines (cv. Triple Dirk) to determine the influence of the Rht1 and Rht2 alleles on the deposition of carbon in the stem, and the subsequent use of these reserves during grain growth. The amount of dry matter stored and mobilized was estimated by the measurement of changes in masses of stem from frequent harvests. Deposition or absolute reserve was defined as the sum of the increments in mass in each segment of the large culm between the time that the segment ceased extending and the time that it reached maximum mass. The incorporation of the Rht1 and Rht2 alleles into a Triple Dirk background reduced the absolute amount of stored carbon in the stem by 35 and 39%, respectively. This was a consequence of the 21% reduction of stem height in Rht1 and Rht2 lines. Use or mobilization of reserve was defined as the sum of the decrements in mass in each segment of the large culm between maximum and maturity. The alleles did not confer an ability to mobilize more of the stored stem reserves in absolute terms, although the efficiency of use of stem reserves (i.e. use as a proportion of deposition) was higher in Rht1 than in rht or Rht2 . The possible contribution of stored carbon in the stem to final grain yield was estimated to be 22, 18 and 14% in the rht, Rht1 and Rht2 lines. In these estimates, the loss of mass was adjusted by 33% to allow for respiration. It was concluded that the larger stem reserves in rht wheats are of no real advantage under favourable environmental conditions, and may in fact be a disadvantage if the accumulation of that extra dry matter results in a reduction of sink size

Yield-SAFE: A parameter-sparse, process-based dynamic model for predicting resource capture, growth, and production in agroforestry systems.

1. Silvoarable agroforestry (SAF) is the cultivation of trees and arable crops on the same parcel of land. SAF may contribute to modern diversified land use objectives in Europe, such as enhanced biodiversity and productivity, reduced leaching of nitrogen, protection against flooding and erosion, and attractiveness of the landscape. Long-term yield predictions are needed to assess long-term economic profitability of SAF. 2. A model for growth, resource sharing and productivity in agroforestry systems was developed to act as a tool in forecasts of yield, economic optimization of farming enterprises and exploration of policy options for land use in Europe. The model is called Yield- SAFE; from “YIeld Estimator for Long term Design of Silvoarable AgroForestry in Europe”. The model was developed with as few equations and parameters as possible to allow model parameterization under constrained availability of data from long-term experiments. 3. The model consists of seven state equations expressing the temporal dynamics of: (1) tree biomass; (2) tree leaf area; (3) number of shoots per tree; (4) crop biomass; (5) crop leaf area index; (6) heat sum; and (7) soil water content. The main outputs of the model are the growth dynamics and final yields of trees and crops. Daily inputs are temperature, radiation and precipitation. Planting densities, initial biomasses of tree and crop species, and soil parameters must be specified. 4. A parameterization of Yield-SAFE is generated, using published yield tables for tree growth and output from the comprehensive crop simulation model STICS. Analysis of tree and crop growth data from two poplar agroforestry stands in the United Kingdom demonstrates the validity of the modelling concept and calibration philosophy of Yield-SAFE. A sensitivity analysis is presented to elucidate which biological parameters most influence short and long-term productivity and land equivalent ratio. 5. The conceptual model, elaborated in Yield-SAFE, in combination with the outlined procedure for model calibration, offers a valid tool for exploratory land use stu