Phytoliths in bamboos from eastern and north-eastern India: Implications in distinguishing different ecoclimatic conditions and in deciphering Late Holocene climate variability

To develop a phytolith (biogenic silica) reference and to understand the eco-climatic indicative values of some grass silica short cells (GSSCs) occurring in the bamboos (Bambusoideae grasses), one of the chief floral components of eastern and north-eastern parts of India, we studied 44 modern bambusoid grasses and 26 surface soils from different eco-climatic zones covering both the plains and mountainous regions. Of the diverse phytoliths retrieved from the bamboos, Saddle tall and Saddle collapsed were the most abundant types (except in Yushania maling) and these types were also common in surface soil phytolith assemblages of the eastern and north-eastern parts of India. To assess the environmental sensitivity of most consistent morphotypes, we categorized two commonly occurring GSSC morphotypes namely Saddle tall into three groups based on their length and Saddle collapsed into two groups based on their length to width ratio respectively. Pearson's correlation analysis, principal component analysis (PCA), and redundancy analysis (RDA) were used to understand if these morphotypes could distinguish different eco-climatic conditions. Variability of Saddle tall and Saddle collapsed types (both morphometric and abundance) in bamboos growing in these parts of India is a function of mean precipitation of the wettest quarter (MPWeQ) and mean temperature of the driest quarter (MTDQ). The present results served as a baseline for reevaluating the interpretations of a Late-Holocene fossil phytolith record from the eastern Himalaya further validating the potential of Saddle tall and Saddle collapsed types in reconstructing past climate variability in a wide geographical region.