Trait differences between grass species along a climatic gradient in South and North America

Question: Are trait differences between grasses along a gradient related to climatic variables and/or photosynthetic pathway? Location: Temperate grassland areas of South and North America. Methods: In a common garden experiment, we cultivated C-3 and C-4 grasses from grasslands under different climatic conditions, and we measured a set of 12 plant traits related to size and resource capture and utilization. We described ( 1) interspecific plant trait differences along a climatic gradient defined by the precipitation and temperature at the location where each species is dominant and ( 2) the association between those plant trait differences and the photosynthetic pathway of the species. Results: Trait differences between grasses were related to the precipitation at the area where each species is dominant, and to the photosynthetic pathway of the species. Leaf length, leaf width, plant height, leaf area per tiller, specific leaf area, leaf delta C-13 ratio, and nitrogen resorption efficiency increased while leaf dry matter content and nitrogen concentration in senesced leaves decreased as precipitation increased. A proportion of these changes along the gradient was related to the photosynthetic pathway because dominant grass species in cold areas with low precipitation are mainly C-3 and those from warm and wet areas are C-4. Conclusions: A previous worldwide analysis showed that traits of graminoid species measured in situ changed slightly along climatic gradients (< 10% variance explained). In contrast, under a common environment we observed that ( 1) grass traits changed strongly along a climatic gradient (30-85% variance explained) and, ( 2) a proportion of those changes were related to the association between photosynthetic pathway of the species and precipitation.