Belowground Consequences of Vegetation Change and Their Treatment in Models

Abstract

Abstract. The extent and consequences of global land-cover and land-use change are increasingly apparent. One consequence not so apparent is the altered structure of plants belowground. This paper examines such belowground changes, emphasizing the interaction of altered root distributions with other factors and their treatment in models. Shifts of woody and herbaceous vegetation with deforestation, afforestation, and woody plant encroachment typically alter the depth and distribution of plant roots, influencing soil nutrients, the water balance, and net primary productivity (NPP). For example, our analysis of global soil data sets shows that the major plant nutrients C, N, P, and K are more shallowly distributed than are Ca, Mg, and Na, but patterns for each element vary with the dominant vegetation type. After controlling for climate, soil C and N are distributed more deeply in arid shrublands than in arid grasslands, and subhumid forests have shallower nutrient distributions than do subhumid grasslands. Consequently, changes in vegetation may influence the distribution of soil carbon and nutrients over time (perhaps decades to centuries). Shifts in the water balance are typically much more rapid. Catchment studies indicate that the water yield decreases 25-40 mm for each 10% increase in tree cover, and increases in transpiration of water taken up by deep roots may account for as much as 50% of observed responses. Because models are increasingly important for predicting the consequences of vegetation change, we discuss the treatment of belowground processes and how different treatments affect model outputs. Whether models are parameterized by biome or plant life form (or neither), use single or multiple soil layers, or include N and water limitation will all affect predicted outcomes. Acknowledging and understanding such differences should help constrain predictions of vegetation change.

Effects of air-drying and freezing on phosphorus fractions in soils with different organic matter contents

“…These changes have important implications for soil phosphorus dynamics and the P exported downstream. In soils, more than half of the extractable P was found in the upper 30 cm in an analysis of global soil data sets averaged across climate zones and vegetation types (Jackson et al 2000). According to this analysis, P was more accumulated in the surface layer in soils and has the shallowest distribution of the major plant nutrients in soils.…”

Root dynamics and global change: seeking an ecosystem perspective

“…Ideally, those models are informed by the results of experiments and the best compilation of our understanding of processes and responses. Woodward & Osborne (2000) summarize how roots are currently considered in models used to address global change issues (see also Jackson et al, 2000). The range of approaches used for simulating root behavior in models has been fairly narrow, and modeling has not been as fruitful at providing new ideas to explore experimentally for belowground processes as for aboveground processes.…”

Mycorrhizal Interactions for Reforestation: Constraints to Dryland Agroforest in Brazil

“…Over the last centuries, land-cover change has been shocking and the rate of vegetation change has increased dramatically [89]. Authors reporting on this highlighted the increasingly important fact to include belowground processes into models parameterized by biome or plant life form (or neither) in order to understand predictions of vegetation change.…”

“…Despite reviews on mycorrhizal associations in agroforestry systems, focusing on the tropics [1,17,18,95], some specialized books such as those from Siddiqui and Pichtel [100] and Pagano [101] include related topics. The need to improve the treatment of belowground processes in models to understand the consequences of vegetation change and the novel combinations of climate and biota that will arise in the future was highlighted [89]. Further experiments including N fixation, fine root density correlation with nutrient and water uptake, soil profile characteristics, and soil macroporosity on the flow of water are also necessary [89].…”

“…The need to improve the treatment of belowground processes in models to understand the consequences of vegetation change and the novel combinations of climate and biota that will arise in the future was highlighted [89]. Further experiments including N fixation, fine root density correlation with nutrient and water uptake, soil profile characteristics, and soil macroporosity on the flow of water are also necessary [89].…”