Plant height as a simple predictor of the root to shoot ratio: Evidence from alpine grasslands on the Tibetan Plateau

Question: Since increases in altitude and grazing intensity generally result in decreases in height growth of alpine grass-lands, plant height may integrate effects of environmental stress and grazing disturbance and provide better assessments of the variation in root: shoot ( R: S) biomass ratio than other variables. However, it is unclear if there is a general relationship between plant height and R: S ratio across grassland ecosystems. Such knowledge would be helpful for root biomass estimation in grasslands. Location: An altitudinal transect in the Gonghe Basin ( 2880-4040 m a.s.l.), northeast Tibetan plateau. Methods: We measured standing biomass both above-ground and below-ground, maximum plant height (MPH) and soil variables across 43 plots. Results: Climatic variables explained the variations in MPH and R: S ratio of undegraded grasslands better than soil variables (46-50% vs < 19%), while those of degraded grasslands generally showed insignificant correlations with climatic and soil variables. There was a general relationship between R: S ratio and MPH ( negative, R-2 = 0.76, P < 0.001) across degraded and undegraded grasslands. The relationship was used to predict R: S ratio in 13 additional plots in steppe grasslands of Inner Mongolia, and good agreement of expected and observed values has been found ( R-2 = 0.87, P < 0.001). Conclusions: MPH, that is relatively easy to measure, can be used to predict R: S ratio at plot to regional scales. It is promising to develop a new method for large-scale estimation of root biomass in grasslands using MPH and shoot biomass avoiding tedious procedures of physical measuring of above and below-ground biomass.