Microtopography-induced ecohydrological effects alter plant community structure

Abstract

Microtopography affects radiation, reflection, and hydrological processes, thereby forming different microhabitats. This study aimed to determine how these processes influence the plot-scale ecosystem (~0.1–1000 m2). Soil was sampled at 0–10 cm and 10–25 cm on depressions, gentle and steep slopes, and gullies on an artificial hillslope. Moisture, temperature, ammonium, nitrate, and plant-available phosphorus (P) were measured. Plant species distributions were evaluated using quadrats and plant nitrogen (N) and P were quantified. Resource richness, evenness, and diversity were compared for all microtopographies. Seasonal dynamics of moisture, nitrate, and available phosphorus indicate that leaching processes shape resource heterogeneity at the plot-scale. Soil nutrient levels widely differed among microtopographies during the non-growing season, but these differences decreased during the growing season. Elevated soil nitrate (but not available P) increased plant nitrate and N:P ratios on steep slopes. Higher soil available P on steep slopes was associated with an increase in the relative abundance of legumes, and subsequently stimulated the accumulation of soil N. The hydrological pathway contributed towards shaping plant community structure by regulating soil resource distribution across microtopographies. In conclusion, this study demonstrated that slight differences in microtopography (e.g., gentle versus steep slopes) alter the soil environment and plant community; therefore, sampling and treatments should be implemented under similar microtopographic conditions to avoid heterogeneity, even at such small scales.