Is there a pattern in growth of annual rings in roots of perennial forbs in relation to climate and climate extremes in grassland ecosystems?

Location

Semi-arid grassland in Duolun (42 degrees 27'N, 116 degrees 41'E, 1380 m a.s.l.), central Inner Mongolia, China.

Methods

Main roots of three perennial species, Potentilla anserina L., Cymbaria dahurica L. and Lespedeza daurica Schindl., were sampled. Cross-sections (10-15-mu m thick) were produced from the proximal end of sampled roots using a sledge microtome. Annual growth rings in the main roots were identified and measured by differentiating between earlywood and latewood in the secondary xylem. Relationships between annual growth rings and monthly mean temperature and total monthly precipitation were identified using correlation analysis. Differences in an annual ring width to the previous and following years were examined by calculating a distinctness score.

Results

The three perennial forbs showed clearly demarcated annual growth rings in all individuals and the same fluctuation patterns. Their ring widths were generally positively correlated with precipitation from April to October (except for August) and with temperature from February to June (except June for L. daurica), September to October, and the annual mean. Strong deviations of annual ring widths from their neighbour rings were observed in 1998 and 2000. The trend of absolute distinctness scores (D-m) increased significantly from 1988 to 2003, indicating an increase in the frequency of annual ring width variation.

Conclusions

Annual growth rings in the main roots of three perennial forb species can be used as an indicator of the influence of climate on below-ground grassland growth. The change in below-ground conditions and effects on the functioning of grassland should receive more attention in future studies.