Does physiological integration among intraclonal ramets of Iris pumila enhance stress tolerance in heterogeneous environments?

Abstract

We tested the hypothesis that sharing essential resources through interconnected ramets increases stress tolerance of a clonal plant in patchy environments. A number of circle-shaped clones of Iris pumila naturally growing in a sun-exposed habitat were selected and cut into two equal halves with different integration status: one with intact and the other with disconnected rhizomes. One-half of each clone was then shaded with a neutral screen to provide 50\% of ambient irradiance, so that one-half of both clones consisted of connected and disconnected halves (referred to as ``clone quarters{''}). Leaves collected from each clone quarter were analyzed for malondialdehyde (MDA) content (a stress indicator) and the values of three functional traits, specific leaf area (SLA), leaf dry matter content (LDMC) and leaf water content (LWC). MDA content was greater in unshaded (more stressed) than in shaded (less stressed) leaves. All three morphological traits changed with light gradient, but only SLA was impacted by the ramet integration status. SLA and MDA tended to be inversely related in each clone quarter, indicating a (compensatory) mechanism utilized by I. pumila plants in coping with environmental stress. SLA and LDMC were highly negatively correlated in general, but less strongly in interconnected ramets compared to those with a disrupted connection. The results suggest that intraclonal physiological integration confers a fitness benefit to I. pumila plants in heterogeneous environments, likely by balancing two fundamental plant activities rapid biomass production and nutrient conservation.