Cotton responses to ultraviolet-B radiation: experimentation and algorithm development

Abstract

The potential impact of an increase in solar ultraviolet-B (UV-B) radiation due to human activity on higher plants has been the subject of many studies. Little work has been carried out so far on cotton responses to enhanced UV-B radiation. The objective of this study was to determine whether or not the current and projected increases in UV-B levels affect cotton growth and development, and to quantify and develop UV-B radiation functional algorithms that can be used in simulation models. Two experiments were conducted during the summer of 2001 using sunlit plant growth chambers in a wide range of UV-B radiations under optimal growing conditions. Leaves exposed to UV-B radiation developed chlorotic and necrotic patches depending on the intensity and length of exposure. Along with changes in visible morphology, cotton canopy photosynthesis declined with increased UV-B radiation. The decline in canopy photosynthesis was partly due to loss of photosynthetic pigments and UV-B-induced decay of leaf-level photosynthetic efficiency (maximum photosynthesis) and capacity (quantum yield) as the leaves aged. The total leaf area was less due to smaller leaves and fewer leaves per plant. Less plant height was closely related to a shorter average internode length rather than a fewer mainstem nodes. The UV-B did not affect cotton major developmental events such as time taken to square, time to flower, and leaf addition rates on the mainstem. Lower biomass was closely related to both smaller leaf area and lower photosynthesis. The critical limit, defined as 90% of optimum or the control, for stem elongation was lower (8.7 kJ m −2 per day UV-B) than the critical limit for leaf expansion (11.2 kJ m −2 per day UV-B), indicating that stem elongation was more sensitive to UV-B than leaf expansion. The critical limits for canopy photosynthesis and total dry weight were 7 and 7.3 kJ m −2 per day, respectively. The identified UV-B-specific indices for stem and leaf growth and photosynthesis parameters may be incorporated into cotton simulation models such as GOSSYM to predict yields under present and future climatic conditions.

Preliminary results of a UV-B effect incorporated GOSSYM model

“…Data, which are being used in this study to develop functional algorithms on the effects of UV-B radiation, were obtained by Reddy et al (2003). For reader's convenience, we describe the methods and data collection concisely in this section.…”

“…Bolls and squares were counted at the end of the study in both the experiments. Canopy photosynthesis was measured using a mass balance approach as described by Reddy et al (2003).…”

“…The crop is sensitive to variations of weather factors, such as temperature, atmospheric CO 2 concentration, soil moisture, and UV-B radiation (Reddy et al, 1997a;Reddy et al, 2002;Zhao et al, 2005). Field and growth chamber experiments have revealed a variety of morphological, anatomical, growth, and physiological responses of cotton plant to enhanced UV-B radiation and its interactions with elevated CO 2 concentration and high air temperature Kakani et al, 2003a;Reddy et al, 2003;Zhao et al, 2003;Reddy et al, 2004;Zhao et al, 2004;Zhao et al, 2005). These include developments of chlorotic and necrotic patches on leaves, changes in plant structure and pigment, decreases in photosynthetic activity, and losses of yield, leaf area, and plant height.…”

Assessment of impact of solar UV components on growth and antioxidant enzyme activity in cotton plant

“…Supplemental UV-B reduces leaf area, plant height, photosynthesis and biomass in cotton Reddy et al 2003;Gao et al 2003). However there has been no data on the impact of ambient UV on the cotton plants.…”

Preliminary results of the coupled CWRF-GOSSYM system

“…Due to the great influences of surface albedo on surface energy budget and partitioning, which in turn change hydrological processes, and modify the absorption of photosynthetically active radiation (PAR), a new dynamic-statistical parameterization of snow-free land surface albedo has been developed, and implemented into the CWRF, using the Moderate Resolution Imaging Spectroradiometer (MODIS) products 10,12 . The solar ultraviolet-B (UV-B) radiation has increased due to human activity in recent years, and has impacts on cotton growth which includes reducing the canopy photosynthesis and cotton leaf area expansion and stem elongation 20 . The NCAR TUV solar radiation transfer model 14 has been recoded to follow the CWRF F90 standard and is being validated against the USDA UV-B network measurements.…”