Toward understanding the impact of nuisance algae bloom on the reduction of rice seedling emergence and establishment

Sara Ohadi,John Madsen,Kassim Al-Khatib,Guelta Laguerre

doi:10.1017/wsc.2021.69

Abstract

AbstractCalifornia rice (Oryza sativa L.) production has been recently challenged by the early-season nuisance algae blooms. The algal community in rice is a complex of green algae (Nostoc spongiforme Agardh ex Bornet) and cyanobacteria species that can develop a thick algal mat on the surface of the water and interfere with the emergence and establishment of rice seedlings. The objective of this research was to determine the impact of algal infestation level on rice seedling emergence. A mesocosm study was conducted in 57-L tubs. Three levels of algal infestation (low, medium, and high) were produced by adding fertilizer (N:P) into the tubs at 0:0, 75:35, and 150:70 kg−1 ha. Sixty rice seeds (‘M-206’) were soaked for 24 h and spread into tubs filled with water. Photosynthetic active radiation (PAR), chlorophyll a concentration as the quantitative measure of algae, number of emerged rice seedlings, and their dry biomass were studied during the experiment. Results showed that algal infestation can directly change the amount of light received into the water. Minimum, maximum, and mean percentage of PAR inside the water declined as the algal infestation level increased. As a consequence, rice seedling emergence dropped under the high algal pressure. At very high algal infestation (i.e., chlorophyll a concentration of above 500 µg ml−1), rice seedling emergence was reduced up to 90%. Furthermore, rice seedling emergence was delayed under algal infestation. When algal infestation was low, time to 50% rice seedling emergence (t50) ranged between 5 and 10 d, while at high algal infestation, t50 ranged between 12 and 20 d. Moreover, individual rice seedling biomass was reduced from 1 g to 0.01 g as algal infestation increased. The results from this study indicate that uncontrolled algae at the beginning of the rice-growing season could reduce rice seedling emergence, establishment, and rice stand. Given that algal infestation in fields has a patchy pattern, loss of rice stand in these patches could provide empty niches for other weeds to grow.

Highlights

Rice (Oryza sativa L.) is one of the main staple foods worldwide, grown on all continents except Antarctica (Prasad et al 2017). It is the staple food for nearly half of the world’s population, most of whom live in developing countries
In 2010, rice production contributed approximately $1.7 billion to California’s gross domestic product (GDP) (Richardson and Outlaw 2010). Rice growers flood their fields at the beginning of the growing season, and pre-germinated rice seed is broadcast by airplane
Because of the difficulties of obtaining a uniform algae-infested field, the experiment was conducted under semi-controlled outdoor conditions at the USDA-ARS Invasive Species and Pollinator Health Research Unit, Davis, from June to August 2019

Summary

Introduction

Rice (Oryza sativa L.) is one of the main staple foods worldwide, grown on all continents except Antarctica (Prasad et al 2017). It is the staple food for nearly half of the world’s population, most of whom live in developing countries. In 2010, rice production contributed approximately $1.7 billion to California’s gross domestic product (GDP) (Richardson and Outlaw 2010). Rice growers flood their fields at the beginning of the growing season, and pre-germinated rice seed is broadcast by airplane. A flood depth of 10 to 15 cm is maintained throughout the growing season

Objectives

Methods

Results