A thirty percent increase in UV-B has no impact on photosynthesis in well-watered and droughted pea plants in the field

• Published in: Global change biology Vol. 5; no. 2; pp. 235 - 244
• Main Authors: Allen, D. J., Nogués, S., Morison, J. I. L., Greenslade, P. D., Mcleod, A. R., Baker, N. R.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-02-1999
• Subjects: biomass; drought; photosynthesis; Pisum sativum; ultraviolet-A; ultraviolet-B; United Kingdom of Great Britain
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1046/j.1365-2486.1999.00227.x

It has been suggested that field experiments which increase UV‐B irradiation by a fixed amount irrespective of ambient light conditions (‘square‐wave’), may overestimate the response of photosynthesis to UV‐B irradiation. In this study, pea (Pisum sativum L.) plants were grown in the field and subjected to a modulated 30% increase in ambient UK summer UV‐B radiation (weighted with an erythemal action spectrum) and a mild drought treatment. UV‐A and ambient UV control treatments were also studied. There were no significant effects of the UV‐B treatment on the in situ CO2 assimilation rate throughout the day or on the light‐saturated steady‐state photosynthesis. This was confirmed by an absence of UV‐B effects on the major components contributing to CO2 assimilation; photosystem II electron transport, ribulose 1,5‐bisphosphate regeneration, ribulose 1,5‐bisphosphate carboxylase/oxygenase carboxylation, and stomatal conductance. In addition to the absence of an effect on photosynthetic activities, UV‐B had no significant impact on plant biomass, leaf area or partitioning. UV‐B exposure increased leaf flavonoid content. The UV‐A treatment had no observable effect on photosynthesis or productivity. Mild drought resulted in reduced biomass, a change in partitioning away from shoots to roots whilst maintaining leaf area, but had no observable effect on photosynthetic competence. No UV‐B and drought treatment interactions were observed on photosynthesis or plant biomass. In conclusion, a 30% increase in UV‐B had no effects on photosynthetic performance or productivity in well‐watered or droughted pea plants in the field.