Differential growth, allocation and photosynthetic responses of Polygonum viviparum to simulated environmental change at a high Arctic polar semi-desert

Abstract

Growing season temperatures and precipitation, and soil nutrient status, were increased in situ at a polar semi-desert site in northwest Spitsbergen to simulate the possible impacts of climate change. During the second year of the experiment the responses of a perennial geophyte, Polygonum viviparum, were assessed both by biometric analyses of vegetative and reproductive structures and by measurements of instantaneous net photosynthesis (Pn). The objectives were (1) to determine whether P. viviparum demonstrates conservative or opportunistic responses to increased temperature, water supply and nutrient availability, (2) to assess whether vegetative and reproductive development show differential sensitivity, and thus whether allocation patterns are altered, and (3) to evaluate whether changes in rate of photosynthesis underlied any changes in growth and allocation. Biometric analyses revealed that P. viviparum responded dramatically to the addition of nutrients (N, P, and K, at rates of 5, 5 and 6.3 g m-2 yr'1, respectively), both in terms of increased vegetative development (leaf sizes and corm weights) and also asexual reproductive development (spike lengths, bulbil numbers and weights). The observa tion that annual structures (leaves, reproductive spikes and bulbils), as well as peren nating tissues (underground corms), responded strongly to nutrients suggests that this species exhibits opportunism when nutrient constraints are alleviated. By contrast, increasing the mean growing season air temperatures by 3.50C above the ambient values exerted no significant impact on vegetative parameters, but was associated with significant increases in reproductive development and thus in alloca tion to reproductive structures. Reproductive and vegetative development thus showed differential sensitivity to the abiotic environmental constraints examined here. Measurements of Pn on a 'unit leaf area' basis failed to indicate any significant treatment effects on P. viviparum at this site, although it is concluded that increased leaf growth in the nutrient amended plots maintained optimal photosynthetic rates. Water additions at the site, to simulate the impacts of increased summer precipitation, were not significant as main effects on any of the measured parameters of plant performance.