Phenology of Plant Production in the Northwestern Great Plains: Relationships with Carbon Isotope Discrimination, Net Ecosystem Productivity and Ecosystem Respiration

Abstract

This chapter represents a case study of seasonal and annual variation in above-ground biomass production in a northern temperate grassland during a 9 year period (1998–2006). I describe the relationship between variation in biomass production and the major environmental factor controlling this variation, precipitation inputs. Annual peak biomass production and leaf δ13C values were negatively correlated, and this relationship was consistent with lower biomass production being predominantly controlled by reduced water availability. Two patterns in the relationship between peak above-ground biomass and annual net ecosystem productivity (NEP) were observed. First, there was a strong linear relationship between biomass and NEP in 4 years when peak leaf area production was held significantly below the maximum by low water availability. Second, among 4 years with similar maximum LAI values, there was wide variation in NEP largely due to differences in the length of time leaf tissue was photosynthetically active. Water availability also had a significant effect on ecosystem respiration because it controlled grassland phenology. The product of plant biomass and soil water content was a good proxy for estimating ecosystem respiration because of relationships with both autotrophic and heterotrophic activities. Seasonal variation in grassland respiration was more strongly linked to carbon substrate availability and soil moisture than to shifts in temperature.