The Costs of Photorespiration to Food Production Now and in the Future

Photorespiration is essential for C3 plants but operates at the massive expense of fixed carbon dioxide and energy. Photorespiration is initiated when the initial enzyme of photosynthesis, ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco), reacts with oxygen instead of carbon dioxide and produces a toxic compound that is then recycled by photorespiration. Photorespiration can be modeled at the canopy and regional scales to determine its cost under current and future atmospheres. A regional-scale model reveals that photorespiration currently decreases US soybean and wheat yields by 36% and 20%, respectively, and a 5% decrease in the losses due to photorespiration would be worth approximately $500 million annually in the United States. Furthermore, photorespiration will continue to impact yield under future climates despite increases in carbon dioxide, with models suggesting a 12–55% improvement in gross photosynthesis in the absence of photorespiration, even under climate change scenarios predicting the largest increases in atmospheric carbon dioxide concentration. Although photorespiration is tied to other important metabolic functions, the benefit of improving its efficiency appears to outweigh any potential secondary disadvantages.This article is from Annual Review of Plant Biology 67 (2016): 107, doi: 10.1146/annurev-arplant-043015-111709. Posted with permission.</p

Evapotranspiration model comparison and an estimate of field scale Miscanthus canopy precipitation interception

The bioenergy crop Miscanthus x giganteus has a high water demand to quickly increase biomass with rapid canopy closure and effective rainfall interception, traits that are likely to impact on hydrology in land use change. Evapotranspiration (ET, the combination of plant and ground surface transpiration and evaporation) forms an important part of the water balance and few ET models have been tested with Miscanthus. Therefore this study uses field measurements to determine the most accurate ET model and to establish the interception of precipitation by the canopy (Ci). Daily ET estimates from 2012 to 2016 using the Hargreaves-Samani, Priestley-Taylor, Granger-Gray and Penman-Monteith (short grass) models were calculated using data from a weather station situated in a 6 ha Miscanthus crop. Results from these models were compared to data from on-site eddy covariance (EC) instrumentation to determine accuracy and calculate the crop coefficient (Kc) model parameter. Ci was measured from June 2016 to March 2017 using stem-flow and through-flow gauges within the crop and rain gauges outside the crop. The closest estimated ET to the EC data was the Penman-Monteith (short grass) model. The Kc values proposed are 0.63 for the early season (March and April), 0.85 for the main growing season (May to September), 1.57 for the late growing season (October and November), and 1.12 over the winter (December to February). These more accurate Kc values will enable better ET estimates with the use of the Penman-Monteith (short grass) model improving estimates of potential yields and hydrological impacts of land use change. Ci was 24 % and remained high during the autumn and winter thereby sustaining significant levels of canopy evaporation and suggesting benefits for winter flood mitigation.publishersversionPeer reviewe

Fluxes of CO2 above a sugarcane plantation in Brazil

Fluxes of CO2 were measured above a sugarcane plantation using the eddy-covariance method covering two growth cycles, representing the second and third re-growth (ratoons) harvested with stubble burning. The total net ecosystem exchange (NEE) in the first cycle (second ratoon, 393 days long) was −1964 ± 44 g C m−2; the gross ecosystem productivity (GEP) was 3612 ± 46 g C m−2 and the ecosystem respiration (RE) was 1648 ± 14 g C m−2. The NEE and GEP totals in the second cycle (third ratoon, 374 days long) decreased 51% and 25%, respectively and RE increased 7%. Accounting for the carbon emitted during biomass burning and the removal of stalks at harvest, net ecosystem carbon balance (NECB) totals were 102 ± 130 g C m−2 and 403 ± 84 g C m−2 in each cycle respectively. Thus the sugarcane agrosystem was approximately carbon neutral in the second ratoon. Yield in stalks fresh weight (SFW) attained the regional average (8.3 kg SFW m−2). Although it was a carbon source to the atmosphere, observed productivity (6.2 kg SFW m−2) of the third ratoon was 19% lower than the regional average due to the lower water availability observed during the initial 120 days of re-growth. However, the overall water use efficiency (WUE) achieved in the first cycle (4.3 g C kg−1 H2O) decreased only 5% in the second cycle