LEAF AND CANOPY PHOTOSYNTHESIS MODELS FOR COCKSFOOT (DACTYLIS GLOMERATA L.) GROWN IN A SILVOPASTORAL SYSTEM

Transcription

1 LEAF AND CANOPY PHOTOSYNTHESIS MODELS FOR COCKSFOOT (DACTYLIS GLOMERATA L.) GROWN IN A SILVOPASTORAL SYSTEM A case study of plant physiology and agronomy by Pablo L. Peri PhD - Forestry engineer Unidad Academica Rio Gallegos (UARG) Universidad Nacional d~ la Patagonia Ausral (UNP A) Instituto Nacional de Tecnologia Agropecuaria (INT A) Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) EDITORIAL DUNKEN Buenos Aires 2005

2 CONTENTS Preface "' 15 PrOiogo List of abbreviations General Introduction Factors affecting pasture dry matter production and photosynthesis in silvopastoral systems Silvopastoral systems Effect of environmental and management factors on pasture dry matter production in silvopastoral systems Solar radiation and shade Temperature Water Nitrogen (N) Regrowth duration Modelling pasture growth based on canopy photosynthesis Leaf photosynthesis Effect of shade on maximum saturated leaf photosynthetic rate (Pmax) Continuous light regime Fluctuating light regime Effect of temperature on Pmax Effect of water on Pmax... 43

3 8 PABLO L. PERI Effect ofn on Pmax Effect ofleaf age and regrowth duration on Pmax Factors affecting the photosynthetic efficiency (a.) and the degree of curvature (9) of the light response curve Modelling leaf photosynthesis Factors affecting light interception Effect of shade on leaf area index (LAI) Effect of temperature on LAI Effect of water on LAI Effect of nitrogen on LAI Effect of regrowth duration on LAI Factors affecting canopy architecture Respiration..., Summary Dry matter production and canopy a1 chitecture of field grown cocks foot under different shade, nitrogen and water regimes Introduction... ; Description of the silvopastoral site Description of the experiments Experiment with four light regimes Grazing management Urine patches Exclosure experiment with different shade, water and N levels Physical environmental measurements,,,,,,,,,,,,,,,,,, TJ Air temperature and rainfall Soil moisture Soil moisture for the experiment with four light regimes Soil moisture for exclosure plots Light quantity Light quality Pasture dry matter (D M) production and growth rates... 81

4 LEAF AND CANOPY PHOTOSYNTHESIS MODELS Pasture DM production and growth rate for the four light regimes experiment Sheep urine N content and pasture production rate from urine patches Pasture DM production and growth rate from the exclosure experiment Effect ofn and irrigation on DM production Leaf area index (LAI) LAI for the experiment with four light regimes LAI from the exclosure experiment Canopy pasture height and tiller population Relationship between DM yield and LAI Mean canopy leaf angle and extinction coefficient Interactions between environmental factors and DM production Conclusions Modelling maximum net photosynthetic rate (Pmax) of field grown cocksfoot leaves under different nitrogen, water and temperature regimes Introduction Photosynthesis, herbage and environmental measurements Pmax and temperature Pmax and nitrogen content (N%) Relationship between nitrogen content and total chlorophyll concentration Pmax and water stress Relationship between pre-dawn leaf water potential ('l'lp) and soil volumetric water content (VWC) Stomatal conductance... : Empirical model for Pmax in cocksfoot Low nitrogen and high temperature effect on Pmax Modelling Pmax in cocksfoot- including the interaction Conclusions

5 10 PABLO L. PERI 5. Maximum net photosynthetic rate (Pmax) of field grown cocksfoot leaves under different regrowth duration Introduction Photosynthesis and herbage measurements Pmax and regrowth duration Impact of ageing effect and low light intensity at the apex on Pmax with regrowth duration Morphology changes related to ageing effect on leaf photosynthesis Shading within the canopy Direct factors affecting Pmax with regrowth duration Nitrogen content Chlorophyll content Stomatal conductance Maintenance respiration Modelling Pmax in cocksfoot- a modified version incorporating the regrowth duration function Interaction between regrowth duration and leafwater potential ('I' lp) on Pmax Stomatal conductance of the regrowth duration and leaf water potential (\}'lp) interaction Modelling Pmax in cocksfoot- including regrowth duration and the \}'lp interaction Use of the regrowth duration function into a canopy photosynthesis model and limitations Conclusions Maximum net photosynthetic rate (Pmax) of cocksfoot leaves under different field shade and environment conditions Introduction Experiment to evaluate the effect of time under shade on Pmax and gs

6 LEAF AND CANOPY PHOTOSYNTHESIS MODELS Response ofpmax to shade Effect of time under shade on stomatal conductance (gs) fuduction ofpmax after different times under severe shade Recovery of stomatal conductance (gs) after different times under severe shade Calculation of stomatal and non-stomatal limitations for Pmax under severe shade Hysteric response Validation ofpmax equations under different shade conditions Accuracy and practical implications of the fitted functions for shade duration and light intensity Effect of shade on Pmax interacting with temperature, water stress, N and regrowth duration Canopy and air temperature Multiplicative model Severe shade and leaf water potential ('I'lp) interaction effect on Pmax Severe shade and leaf water potential ('I'lp) interaction effect on gs Modelling Pmax in cocksfoot- including shade and 'I'lp interaction Conclusions Modelling photosynthetic efficiency and convexity of the light- response curve for field grown cocksfoot leaves under different environmental and regrowth duration conditions Introduction Photosynthesis measurements Photosynthetic efficiency (a) and temperature Photosynthetic efficiency (a) and nitrogen content (N%)

7 12 PABLO L. PERl 7.5 Photosynthetic efficiency (a) and water stress Photosynthetic efficiency (a) and regrowth duration Effect oftime in shade on photosynthetic efficiency (a) Degree of curvature (9) and temperature, N, water stress, regrowth duration and shade Empirical model for photosynthetic efficiency (a) in cocksfoot leaves Conclusions Simulation and validation of a canopy photosynthesis model for cocksfoot under different nitrogen, water, temperature, regrowth duration and shade regimes Introduction General description of the canopy photosynthesis model Light interception Canopy gross photosynthesis Canopy respiration and canopy net photosynthesis Simulations Simulation 1: Effect of temperature on net daily canopy photosynthesis (Pn) Simulation 2: Effect of foliage N content on Pn Simulation 3: Effect of water stress on Pn Simulation 4: Effect of regrowth duration on Pn Simulation 5: Effect oflight regime and light intensity on Pn Validation of the canopy photosynthesis model Conclusions General discussion Effect of environmental and management changes on DM production in the silvopastoral system Structural changes leading to DM changes Mechanistic changes leading to DM changes

8 LEAF AND CANOPY PHOTOSYNTHESIS MODELS Leaf photosynthesis models Pmax model a model and e What is shade-tolerance Advances in predicting leaf photosynthesis Canopy photosynthesis model Fluctuating versus continuous light regime Validation and use ofthe canopy photosynthesis model Dynamic features ofthe cocksfoot model Model improvements Conclusions References Appendix 1 - Cocksfoot canopy height and tiller population over time for four shade treatments Appendix 2 - Cocksfoot canopy height and tiller population over time for two levels oflight intensity, two levels ofirrigation and two levels ofnitrogen Appendix 3 - Mineral content in herbage cocksfoot pasture for different seasons Appendix 4 - List of publications related to this work