Effect of climate on the growth of annual rings in the main roots of perennial forbs in an Inner Mongolian semi‐arid grassland,China

Question: 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°27′N, 116°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‐μm 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.     

Using tree rings to reconstruct changes in soil P availability – Results from forest fertilization trials

Hitherto, there are only few studies that have analysed the variation of P contents in individual tree rings to reconstruct fluctuations in soil P availability. Therefore, this pilot study aimed to assess the relationship between changes in P content in tree rings and known changes in soil P availability resulting from fertilization of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) in fertilization trials at two different sites. We compared P contents in single tree rings from fertilized and unfertilized plots formed before and after P fertilization and assessed (1) whether fertilization leads to an immediate increase in P uptake and higher P contents in tree rings formed after fertilization, and (2) whether P is translocated to older tree rings that were formed before fertilization.After application of 70 kg P ha⁻¹, a prompt and extended increase in relative wood P contents could be observed in both Norway spruce and Scots pine. However, only at the Norway Spruce site, this increase could be properly assigned to a P fertilization signal in heartwood rings formed after fertilization. In sapwood rings, however, P fertilization signals were masked by the inherent increase in P content from older towards younger sapwood rings, which was at least one order of magnitude higher than the increase from fertilization. We could not observe a P translocation into older tree rings, which existed as sapwood rings at the time of fertilization.This pilot study underlines the potential of dendrochemistry for reconstructing changes in soil P availability and improves the conceptual basis for further dendrochemical research, not only in fertilized but also in unfertilized forest ecosystems.