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

Sanja Manitasevic-Jovanovic,Ana Vuleta,Branka Tucic

doi:10.2298/abs1402713j

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 sunexposed 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.

Highlights

The clonal habit in plants results from the production of genetically identical and physiologically semi-dependent units – ramets, which are physically connected by either overground or underground lateral stems (Hartnett and Bazzaz, 1983)
Numerous studies have documented that clonal integration influences leaf features such as lamina area (Liao et al, 2003; Chu et al, 2006), water potential (Alpert, 1999), as well as carbohydrate, nitrogen and chlorophyll content (Saarinen and Haansuu, 2000)
Since at the Deliblato Sands, during summer, naturally growing I. pumila plants are simultaneously exposed to high irradiance levels, elevated air temperature and soil water scarcity, we expect that these plants experience severe environmental stress (Manitašević et al, 2007; Vuleta et al, 2010)

Summary

INTRODUCTION

The clonal habit in plants results from the production of genetically identical and physiologically semi-dependent units – ramets, which are physically connected by either overground or underground lateral stems (Hartnett and Bazzaz, 1983). Since LWC is associated with leaf nitrogen content and leaf assimilatory capacity, it is commonly used as a predictor of plant performance (Wilson et al, 1999) This experiment was designed to elucidate the physiological consequences of physical integration between intraclonal ramets in a rhizomatous herb, Iris pumila L. We assumed the following: (i) if an Iris genet functions as a physiologically integrated system, the experimental disconnection of a group of ramets from the parental clone will impact metabolic processes within the detached clone part, and the phenotypic expression of leaf functional traits, SLA, LDMC and LWC; (ii) if shaded ramets acquire insufficient nutrition through a physical interconnection with their illuminated counterparts, they will exhibit better leaf performance relative to the disconnected ramets, experiencing similar light conditions

MATERIALS AND METHODS

Experimental setup

RESULTS AND DISCUSSION