Varied multi-season response of Aconitum heterophyllum Wall. to increased CO2 in the Indian Himalaya

Abstract

Plant responses to increasing atmospheric CO2 vary among species. The present study investigates the effects of elevated CO2 on an Indian alpine rhizomatous herb Aconitum heterophyllum using four open-top chambers. Thirty seedlings per chamber were observed for three growing seasons. Atmospheric CO2 was elevated to 650 ppm in two chambers during June to October when above-ground shoot systems were present. Shoot morphometric data were assessed at day 45, 90 and 120 of each season, while biomass and nutrient composition were assessed at completion. Flowering time, flower morphometric data and seed biomass were recorded, and seed germination tests conducted. Elevated CO2 resulted in greater plant height, individual leaf area, stem and leaf thickness during seasons 1 and 2, but in season 3 these shoot morphometric data were either lower or not significantly different. Shoot biomass production in the third season was lower but root biomass was not affected, resulting in a higher root mass fraction. Tissue nitrogen decreased and potassium increased. The soil pH and available nitrogen in 650 ppm CO2 decreased, while other soil nutrients increased. Plants in 650 ppm CO2 flowered 14 days earlier and produced smaller pods with smaller and lighter seeds. Vigor index and seedling biomass were lower, reducing seedling survival, though germination percentage was not affected. Reduced biomass accumulation in the third season could be due to reduced available nitrogen, or the first expression of a longer-term trend. More multi-season studies are required to predict the implications of climate change to this species.