Intra-seasonal variation and relationship among leaf traits of different forest herbs in a dry tropical environment

A range of leaf traits was measured for 17 herbaceous species fortnightly from July to September for two years in a dry tropical forest. These species belonged to four life forms: annual grasses, perennial grasses, annual forbs and perennial forbs. The objectives of this study were: (i) to assess the effect of herb types on leaf traits in tropical dry deciduous forest of the Vindhyan highlands; (ii) to measure the growing season variation in the traits, and (iii) to investigate the relationships between the leaf traits. Four sites, viz. Hathinala, Ranitalli, Bokrakhari and Neuriuadamar were selected in the region. At each site, five quadrats, each 1 m × 1 m in size, were sampled randomly for herbaceous plants at 15-day interval in the wet season from July to September during 2006 and 2007. At each site soil samples and leaf samples were collected and analysed. Specific leaf area (SLA), leaf nitrogen (N), leaf phosphorus (P), leaf chlorophyll content, stomatal conductance (Gs) and photosynthetic rate (Amass) were determined. The seasonal pattern in leaf traits, in general, was an early season peak in SLA, leaf nitrogen and leaf phosphorus, and a midseason peak in Gs and Amass. Annual forbs generally exhibited highest leaf trait values and the perennial grasses the lowest. Pearson correlation coefficients indicated significant positive relationship of SLA with all other leaf traits, between leaf N and leaf P and among chlorophyll, Gs and Amass. The decline in leaf nitrogen and leaf phosphorus during the growing season occurred due to the retranslocation of these elements from the leaves into the storage or reproductive organs. The peaks in Gs and Amass were associated with increase in soil moisture.